U.S. patent application number 12/303696 was filed with the patent office on 2010-06-24 for data generation apparatus, data generation method, base station, mobile station, synchronication detection method, sector identification method, information detection method and mobile communication system.
Invention is credited to Shoichi Shitara.
Application Number | 20100157940 12/303696 |
Document ID | / |
Family ID | 38831864 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100157940 |
Kind Code |
A1 |
Shitara; Shoichi |
June 24, 2010 |
DATA GENERATION APPARATUS, DATA GENERATION METHOD, BASE STATION,
MOBILE STATION, SYNCHRONICATION DETECTION METHOD, SECTOR
IDENTIFICATION METHOD, INFORMATION DETECTION METHOD AND MOBILE
COMMUNICATION SYSTEM
Abstract
[Problems] To reduce a cell search process including sector
identification without increasing a load on a
transmission/reception device. [Means for Solving Problems] A
synchronization channel (SCH) contained in a down link of a
multi-carrier mobile communication system is multiplied by a sector
unique code and a cell unique code (step S1). The multiplication
result is allocated to a sub-carrier on the frequency axis (step
S2) and subjected to a spread process and an IFFT process (steps
S3, S4). Furthermore, GI is inserted and D/A conversion are
performed (steps S5, S6). A multi-carrier is transmitted from a
directivity antenna of each sector (step S7). A reception side
identifies the SCH position by the self-correlation method or the
mutual correlation method and performs the FFT. After this, the
reception side simultaneously performs identification of a sector
by detecting a sector unique code and acquisition of cell unique
information by demodulating a cell unique code.
Inventors: |
Shitara; Shoichi; ( Chiba,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
38831864 |
Appl. No.: |
12/303696 |
Filed: |
June 18, 2007 |
PCT Filed: |
June 18, 2007 |
PCT NO: |
PCT/JP2007/062243 |
371 Date: |
December 5, 2008 |
Current U.S.
Class: |
370/331 ;
370/329; 375/260 |
Current CPC
Class: |
H04W 28/06 20130101;
H04L 5/0053 20130101; H04W 64/00 20130101; H04J 11/0076 20130101;
H04L 5/0023 20130101; H04L 27/2655 20130101; H04L 5/005 20130101;
H04J 11/0073 20130101; H04J 11/0079 20130101; H04L 27/2675
20130101; H04W 48/08 20130101; H04J 11/0069 20130101; H04L 27/2613
20130101; H04W 88/08 20130101; H04W 8/005 20130101 |
Class at
Publication: |
370/331 ;
370/329; 375/260 |
International
Class: |
H04W 36/00 20090101
H04W036/00; H04W 4/00 20090101 H04W004/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2006 |
JP |
2006-168168 |
Aug 3, 2006 |
JP |
2006-212658 |
Claims
1-33. (canceled)
34. A data structure of a synchronization channel (SCH) in a mobile
communication system adopting a multicarrier communication scheme
in which a cell is divided into a plurality of sectors, a base
station controlling over the cell transmits a downlink signal to a
mobile station in the cell by multicarrier communication, the
downlink signal contains a synchronization channel (SCH), and the
synchronization channel (SCH) is capable of being used in a cell
search including sector identification, wherein a sector common
code common in the plurality of sectors in the same cell is
multiplied by sector specific codes varying with the sectors in the
same cell, thereby enabling a cell search including sector
identification using the synchronization channel (SCH) to be
executed.
35. The data structure of a synchronization channel (SCH) according
to claim 34, wherein each of the sector specific codes has m (m is
a natural number of "2" or more) code elements as a group, and is
configured by repeatedly assigning the code elements of the group
to subcarriers on the frequency axis, and the sector specific codes
corresponding to respective sectors are orthogonal to one
another.
36. The data structure of a synchronization channel (SCH) according
to claim 34, wherein a cell specific code is further multiplied, in
addition to the sector common code and the sector specific
codes.
37. The data structure of a synchronization channel (SCH) according
to claim 36, wherein the cell specific code is a code indicating
information specific to a cell that a mobile station acquires in
the cell search.
38. A base station controlling over a cell containing a plurality
of sectors, wherein the base station has a transmitting section for
transmitting a signal including data of different synchronization
channels to the sectors.
39. A base station controlling over a cell containing a plurality
of sectors, wherein the base station has a transmitting section for
transmitting a signal generated by using a sector specific code
corresponding to a sector identification number to identify each of
the sectors.
Description
TECHNICAL FIELD
[0001] The present invention relates to mobile communication of the
E-UTRA (Evolved-UTRA) standard adopting a multicarrier
communication scheme, and more particularly to a data generation
apparatus, data generation method, base station, mobile station,
synchronization detection method, sector identification method,
information detection method and mobile communication system for
generating data of a synchronization channel (SCH) included in a
downlink (transmission) signal.
BACKGROUND ART
[0002] In recent years, the third generation mobile communication
(3G) including W-CDMA systems has been in widespread use on a
worldwide basis. Currently, the fourth generation mobile
communication (4G) has further been considered to implement
communication rates of 100 Mb/s to 1 Gb/s on downlink. However, it
is not easy to completely shift from 3G to 4G. Therefore, attention
is directed toward E-UTRA (Evolved-UTRA) for increasing the rate in
communication using a frequency band of 3G while introducing new
techniques of 4G. Active proposals have been made also in 3GPP (3rd
Generation Partnership Project).
[0003] In the mobile communication system, a mobile station needs
to identify a cell and a section to which the mobile station
intends to connect for initial synchronization establishment or
handover. In other words, it is necessary to detect a base station
targeted for communication and an antenna of the base station. In
the third generation mobile communication, the so-called 3-step
cell search method is adopted to perform a fast cell search. In
addition, the concept of "cell search" includes "sector
search".
[0004] The 3-step cell search in the third generation mobile
communication generally uses a Synchronization Channel (SCH) and a
Common Pilot Channel (CPICH). First, the reception timing of the
SCH is detected (first step), and next, identification of the frame
timing and a scramble code group is performed by correlation
detection with the SCH code (second step). Then, a scramble code is
identified by correlation detection using the CPICH (third
step).
[0005] In the E-UTRA that is the next generation mobile
communication standard, OFDM (Orthogonal Frequency Division
Multiplexing) is used as a modulation scheme, and regarding the
cell search, techniques following the philosophy of the
above-mentioned 3-step cell search are proposed (for example, see
Patent Document 1, Patent Document 2, Non-patent Document 1 and
Non-patent Document 2).
[0006] Patent Document 1 discloses techniques for
frequency-multiplexing a second synchronization code (S-SCH signal)
for scramble code group identification on a plurality of
subcarriers in the 3-step cell search in the multicarrier
communication system adopting OFDM.
[0007] Patent Document 2 discloses techniques for multiplexing a
cell identification code on a Common Pilot Channel (CPICH) in the
3-step cell search in the multicarrier communication system
adopting OFDM.
[0008] Moreover, Non-patent Document 1 proposes standardization of
a one-cell reuse communication system adopting OFDM. Further, a
draft of standardization has been proposed in consideration of a
base station provided for each sector concurrently performing
communications with a plurality of mobile stations in the cell. In
this technique, the Common Pilot Channel (CPICH) is doubly
multiplied by a spreading code specific to a cell and a spreading
code specific to a sector. Accordingly, a mobile station performs
despreading and correlation detection using each spreading code
replica, and is thereby capable of identifying the cell (and the
sector).
[0009] Further, Non-patent Document 2 discloses techniques for
identifying a cell (and a sector) by a 3-step cell search similar
to techniques of the third generation in the multicarrier
communication system adopting OFDM. In the techniques, as in the
techniques disclosed in Non-patent Document 1, a cell is divided
into three sectors, and the same Synchronization Channel code (SCH
code) is used among the sectors. With respect to transmission of
the SCH code, time synchronization is acquired among the sectors,
and transmission of the SCH for each sector is performed at the
same time. Then, identification of a cell and a sector i.e.
selection of a cell and a sector providing the maximum reception
power is made by correlation detection with replicas of spreading
codes using a pilot channel in the third step.
[0010] Thus, also in the E-UTRA that is the next generation
communication standard, proposals are made to adopt the techniques
following the 3-step cell search of 3G using the SCH and CPICH.
Particularly, with respect to sector identification, as disclosed
in Non-patent Documents 1 and 2, the Common Pilot Channel is
multiplied by a spreading code specific to a sector, and a sector
providing the maximum reception power is detected by despreading
and correlation detection processing in the third step.
Patent Document 1: Japanese Laid-Open Patent Publication No.
2003-179522
Patent Document 2: Japanese Laid-Open Patent Publication No.
2005-198232
Non-patent Document 1: 3GPP "TR 25.814, "Physical Layer Aspects for
Evolved UTRA (Release 7) v.0.3.1''2005/10/18
Non-patent Document 2: 3CPP "R1-060042, "SCH Structure and Cell
Search Method in E-UTRA Downlink"2006/1/25
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0011] As described above, also in the E-UTRA that is the next
generation communication standard, proposals are made to adopt the
techniques following the 3-step cell search of 3G using the SCH and
CPICH. In this case, sector identification is made by despreading
and correlation detection processing using the CPICH (Common Pilot
Channel) in the third step. In other words, in the current
techniques, it is not possible to identify a sector and a cell
without undergoing the 3-step processing. Accordingly, the 3-step
cell search has limitations in reducing the process required for
the processing for identifying a cell and a sector.
[0012] Further, in the third step, in addition to despreading and
correlation detection processing for cell identification using the
CPICH, it is further required to perform the similar processing for
sector identification. In other words, in the final step of the
3-step cell search, a cell ID is detected by despreading using
replica codes, while needing to determine which sector in the same
cell provides high signal intensity. Therefore, as a result, it is
necessary to perform correlation detection using replica signals
corresponding (the number of cell IDs contained in a cell ID group)
multiplied by (the number of sector IDs). Hence, the time required
for correlation detection in the third step increases in proportion
to the number of sectors contained in a single cell.
[0013] Furthermore, to compare between correlation values
corresponding to the replica signals, required is memory having the
capacity for storing correlation calculation results by the replica
signals. In other words, the memory is required that stores
correlation calculation results corresponding to (the number of
cell IDs contained in a cell ID group multiplied by the number of
sector IDs), resulting in increases in memory capacity.
[0014] Still furthermore, as disclosed in above-mentioned
Non-patent Document 2, the same SCH data is concurrently
transmitted for each sector in the same cell. Therefore, a mobile
station near a boundary of sectors has a possibility that a
frequency band with the reception power decreased occurs by mutual
interference of signals from a plurality of sectors or fading
caused by propagation environment. In this case, the probability
for cell and sector identification may decrease.
[0015] The present invention is carried out in view of such
circumstances, and it is an object of the invention to decrease the
time required for cell search processing including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel. It is another
object to actualize a cell search including sector identification
more easily with high accuracy while improving resistance to
interference or anti-fading characteristics of the cell search
processing including sector identification without increasing loads
on a transmission/reception apparatus.
Means for Solving the Problem
[0016] (1) To attain the above-mentioned objects, the present
invention takes the following measures. In other words, a data
generation apparatus of the invention is a data generation
apparatus that generates data of a synchronization channel
transmitted from a base station controlling over a cell containing
a plurality of sectors, and is characterized by generating data of
synchronization channels for each of the sectors using sector
specific codes corresponding to sector identification numbers for
identifying the sectors.
[0017] According to this constitution, by multiplying a sector
common code by a sector specific code, it is possible to perform
sector identification using the synchronization channel without
using a pilot channel.
[0018] (2) Further, in the data generation apparatus of the
invention, it is a feature that the sector specific codes are
orthogonal to one another.
[0019] According to this constitution, it is possible to perform
sector identification or synchronization detection with high
accuracy.
[0020] (3) Furthermore, in the data generation apparatus of the
invention, it is a feature that the sector specific codes are
common among adjacent cells.
[0021] According to this constitution, it is possible to perform
sector identification or synchronization detection with
efficiency.
[0022] (4) Still furthermore, the data generation apparatus of the
invention is characterized by generating data of pilot channels for
each of the sectors using orthogonal codes corresponding to the
sector identification numbers.
[0023] According to this constitution, it is possible to decrease
the time required for the cell search process including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel, and further to
actualize a faster cell search including sector identification with
high accuracy while improving resistance to interference or
anti-fading characteristics of the cell search processing including
sector identification without increasing loads on a
transmission/reception apparatus.
[0024] (5) Moreover, a data generation method of the invention is a
data generation method for generating data of synchronization
channels transmitted from a base station controlling over a cell
containing a plurality of sectors, and is characterized by
generating data of synchronization channels for each of the sectors
using sector specific codes corresponding to sector identification
numbers for identifying the sectors.
[0025] According to this constitution, by multiplying a sector
common code by a sector specific code, it is possible to perform
sector identification using the synchronization channel without
using a pilot channel.
[0026] (6) Further, the data generation method of the invention is
characterized by generating data of pilot channels for each of the
sectors using orthogonal codes corresponding to the sector
identification numbers.
[0027] According to this constitution, it is possible to decrease
the time required for the cell search process including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel, and further to
actualize a faster cell search including sector identification with
high accuracy while improving resistance to interference or
anti-fading characteristics of the cell search processing including
sector identification without increasing loads on a
transmission/reception apparatus.
[0028] (7) Further, a base station of the invention is a base
station that controls over a cell containing a plurality of
sectors, and is characterized by having a storing section that
stores data of synchronization channels for each of the sectors
using sector specific codes corresponding to sector identification
numbers for identifying the sectors, and a transmitting section
that transmits the data of synchronization channels corresponding
to the sectors to the sectors, respectively.
[0029] According to this constitution, by multiplying a sector
common code by a sector specific code, it is possible to perform
sector identification using the synchronization channel without
using a pilot channel.
[0030] (8) Furthermore, a base station of the invention is a base
station that controls over a cell containing a plurality of
sectors, and is characterized by having a synchronization data
generating section that generates data of synchronization channels
for each of the sectors using sector specific codes corresponding
to sector identification numbers for identifying the sectors, and a
transmitting section that transmits the data of synchronization
channels corresponding to the sectors to the sectors,
respectively.
[0031] According to this constitution, by multiplying a sector
common code by a sector specific code, it is possible to perform
sector identification using the synchronization channel without
using a pilot channel.
[0032] (9) Still furthermore, in the base station of the invention,
it is a feature that the synchronization channel data generating
section generates data of pilot channels for each of the sectors
using orthogonal codes corresponding to the sector identification
numbers, and that the transmitting section transmits the data of
pilot channels corresponding to the sectors to the sectors,
respectively.
[0033] According to this constitution, it is possible to decrease
the time required for the cell search process including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel, and further to
actualize a faster cell search including sector identification with
high accuracy while improving resistance to interference or
anti-fading characteristics of the cell search processing including
sector identification without increasing loads on a
transmission/reception apparatus.
[0034] (10) Moreover, a mobile station of the invention is a mobile
station that communicates with a base station controlling over a
cell containing a plurality of sectors, and is characterized by
receiving a signal including synchronization channels derived from
sector specific codes corresponding to sector identification
numbers for identifying the sectors from the base station.
[0035] According to this constitution, by multiplying a sector
common code by a sector specific code, it is possible to perform
sector identification using the synchronization channel without
using a pilot channel.
[0036] (11) Further, the mobile station of the invention is
characterized by performing sector identification based on the
synchronization channels.
[0037] According to this constitution, it is possible to perform
sector identification with high accuracy.
[0038] (12) Furthermore, the mobile station of the invention is
characterized by performing synchronization detection based on the
synchronization channels.
[0039] According to this constitution, it is possible to perform
synchronization detection with high accuracy.
[0040] (13) Still furthermore, in the mobile station of the
invention, it is a feature that the sector specific codes are
orthogonal to one another.
[0041] According to this constitution, it is possible to perform
sector identification or synchronization detect ion with high
accuracy.
[0042] (14) Moreover, in the mobile station of the invention, it is
a feature that the sector specific codes are common among adjacent
cells.
[0043] According to this constitution, it is possible to perform
sector identification or synchronization detect ion with
efficiency.
[0044] (15) Further, the mobile station of the invention is
characterized by performing synchronization detection by
calculating correlation using the signal and the sector specific
codes.
[0045] According to this constitution, it is possible to complete a
cell search by timing detection of the SCH (first step) on the time
axis by an auto-correlation method using periodicity of the SCH or
cross-correlation method using time waveforms of replica codes of
the sector specific codes, and identification of a sector ID and
cell ID (second step) based on information on the frequency axis.
Accordingly, it is possible to reduce the search process as
compared with the conventional 3-step cell search.
[0046] (16) Furthermore, the mobile station of the invention is
characterized by having a synchronization channel signal processing
section, where the synchronization channel signal processing
section performs the synchronization detection by calculating
correlation between the signal and each of replicas corresponding
to the sector specific codes.
[0047] According to this constitution, it is possible to detect
correlation using replicas of the sector specific codes.
[0048] (17) Still furthermore, the mobile station of the invention
is characterized by performing the sector identification by
calculating correlation using the signal and the sector specific
codes.
[0049] According to this constitution, it is possible to perform
sector identification with high accuracy.
[0050] (18) Moreover, in the mobile station of the invention, it is
a feature that the synchronization channel signal processing
section performs the sector identification by calculating
correlation between the signal and each of replicas corresponding
to the sector specific codes.
[0051] According to this constitution, it is possible to detect
correlation using replicas of the sector specific codes.
[0052] (19) Further, the mobile station of the invention is
characterized by beforehand storing a plurality of replicas
corresponding to the plurality of sectors.
[0053] According to this constitution, it is possible to detect
correlation using replicas of the sector specific codes.
[0054] (20) Furthermore, in the mobile station of the invention, it
is a feature that the synchronization channel signal processing
section calculates correlation between each of the plurality of
replicas and the signal in parallel with one another.
[0055] According to this constitution, it is possible to
efficiently perform correction detection.
[0056] (21) Still furthermore, in the mobile station of the
invention, it is a feature that the synchronization channel signal
processing section specifies the sector specific code with a
maximum correlation value, and thereby performs the sector
identification.
[0057] According to this constitution, it is possible to perform
sector identification with high accuracy.
[0058] (22) Moreover, in the mobile station of the invention, it is
a feature that the synchronization channel signal processing
section transforms the signal into a signal in the frequency domain
to calculate correlation with the sector specific code, and thereby
performs the sector identification.
[0059] According to this constitution, it is possible to perform
sector identification with high accuracy.
[0060] (23) Further, the mobile station of the invention is
characterized by further having a sector specific code storing
section that stores a plurality of sector specific codes
corresponding to the plurality of sectors.
[0061] According to this constitution, it is possible to perform
sector identification or synchronization detection efficiently and
promptly, and it is made easy to increase the number of sector
specific codes in accordance with an increase in the number of
sectors.
[0062] (24) Furthermore, in the mobile station of the invention, it
is a feature that the synchronization channel signal processing
section calculates correlation between each of the plurality of
sector specific codes and the signal in the frequency domain in
parallel with one another.
[0063] According to this constitution, it is possible to
efficiently perform sector identification or correlation detection
with high accuracy.
[0064] (25) Still furthermore, in the mobile station of the
invention, it is a feature that the synchronization channel signal
processing section detects information included in a pilot channel
using an orthogonal code of the pilot channel corresponding to a
sector obtained by sector identification using the synchronization
channels.
[0065] According to this constitution, it is possible to decrease
the time required for the cell search process including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel, and further to
actualize a faster cell search including sector identification with
high accuracy while improving resistance to interference or
anti-fading characteristics of the cell search processing including
sector identification without increasing loads on a
transmission/reception apparatus.
[0066] (26) Moreover, a synchronization detection method of the
invention is a synchronization detect ion method used in a mobile
station in receiving a signal which is transmitted from a base
station controlling over a cell containing a plurality of sectors,
and which includes synchronization channels generated using sector
specific codes corresponding to sector identification numbers for
identifying the sectors, and is characterized in that
synchronization detection is performed by calculating correlation
using the signal and the sector specific codes.
[0067] According to this constitution, it is possible to complete a
cell search by timing detection of the SCH (first step) on the time
axis by an auto-correlation method using periodicity of the SCH or
cross-correlation method using time waveforms of replica codes of
the sector specific codes, and identification of a sector ID and
cell ID (second step) based on information on the frequency axis.
Accordingly, it is possible to reduce the search process as
compared with the conventional 3-step cell search.
[0068] (27) Further, a sector identification method of the
invention is a sector identification method used in a mobile
station in receiving a signal which is transmitted from a base
station controlling over a cell containing a plurality of sectors,
and which includes synchronization channels generated using sector
specific codes corresponding to sector identification number for
identifying the sectors, and is characterized in that sector
identification is performed by calculating correlation using the
signal and the sector specific codes.
[0069] According to this constitution, it is possible to perform
sector identification with high accuracy.
[0070] (28) Furthermore, the sector identification method of the
invention is characterized in that synchronization detection is
performed by calculating correlation using the signal and the
sector specific codes.
[0071] According to this constitution, it is possible to complete a
cell search by timing detection of the SCH (first step) on the time
axis by an auto-correlation method using periodicity of the SCH or
cross-correlation method using time waveforms of replica codes of
the sector specific codes, and identification of a sector ID and
cell ID (second step) based on information on the frequency axis.
Accordingly, it is possible to reduce the search process as
compared with the conventional 3-step cell search.
[0072] (29) Moreover, an information detection method of the
invention is an information detection method for detecting
information included in a pilot channel in a mobile station
receiving a signal which is transmitted from a base station
controlling over a cell containing a plurality of sectors, and
which includes synchronization channels generated using sector
specific codes corresponding to sector identification numbers for
identifying the sectors and pilot channels generated using
orthogonal codes corresponding to the sector identification
numbers, and is characterized in that the information included in a
pilot channel is detected using an orthogonal code of the pilot
channel corresponding to a sector obtained by sector identification
using the synchronization channels.
[0073] According to this constitution, it is possible to decrease
the time required for the cell search process including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel, and further to
actualize a faster cell search including sector identification with
high accuracy while improving resistance to interference or
anti-fading characteristics of the cell search processing including
sector identification without increasing loads on a
transmission/reception apparatus.
[0074] (30) Further, a mobile station of the invention is
characterized by having a receiving section that receives a signal
from a base station controlling over a cell containing a plurality
of sectors, and a sector identifying section that identifies a
sector where the signal is transmitted using the received signal,
where based on identification of the sector by the sector
identifying section, the sector providing good reception
characteristics is specified to perform handover, and the receiving
section receives data of a synchronization channel for each sector
using a sector specific code corresponding to a sector
identification number for identifying the sector.
[0075] According to this constitution, it is possible to perform
fast handover with high accuracy.
[0076] (31) Moreover, a mobile communication system of the
invention is comprised of a base station which controls over a cell
containing a plurality of sectors, and which transmits, to each
sector, data of a synchronization channel for each sector using a
sector specific code corresponding to a sector identification
number for identifying the sector, and a mobile station that
receives the data from the base station.
[0077] According to this constitution, by multiplying a sector
common code by a sector specific code, it is possible to perform
sector identification using the synchronization channel without
using a pilot channel.
[0078] (32) Further, the mobile communication system of the
invention is characterized in that a communication method between
the base station and the mobile station is a multicarrier
communication method.
[0079] According to this constitution, fast transmission with large
capacity is made possible on downlink. Further, it is possible to
contribute to practical application of communication methods
conforming to the E-UTRA.
[0080] (33) Furthermore, the mobile communication system of the
invention is characterized in that OFDM is applied to the
multicarrier communication method.
[0081] According to this constitution, fast transmission with large
capacity is made possible on downlink. Further, it is possible to
contribute to practical application of communication methods
conforming to the E-UTRA.
ADVANTAGEOUS EFFECT OF THE INVENTION
[0082] According to the invention, by a sector common code being
multiplied by a sector specific code, it is possible to identify a
sector only by despreading and correlation detection using the SCH
without using a pilot channel. Accordingly, with respect to sector
identification, the need is eliminated for despreading and
correlation detection processing using a pilot channel, and it is
possible to reduce the capacity of memory to be used in correlation
calculation using the pilot channel.
[0083] Further, since the SCH is multiplied by the sector specific
code, it is possible to eliminate interference between sectors even
in a boundary of the sectors. Furthermore, it is possible to obtain
the effect of enhancing anti-fading characteristics by randomizing
effect produced by code multiplication. It is easy to increase the
number of sector specific codes (orthogonal codes) assigned for
each sector according to an increase in the number of sectors, and
to respond to the sector configuration flexibly.
[0084] Moreover, when the number of subcarriers of the SCH is
adequate (to multiply by the cell specific code of the SCH), it is
also possible to directly identify a cell ID only by the SCH. In
this case, the cell search processing including sector
identification is completed by 2-step processing using only the SCH
(2-step cell search), and the search time can be reduced as
compared with the conventional 3-step cell search.
[0085] Further, by devising structures, contents and arrangements
on the frequency axis of a cell specific code and sector specific
code to multiply, it is possible to prevent the sector specific
code and cell specific code from imposing an adverse effect on each
other, and to suppress a decrease in information transmission
accuracy. Furthermore, each information can be demodulated
independently (i.e. in parallel processing). By this means, it is
possible to reduce the processing time of a cell search including a
sector search.
[0086] In other words, a 2m-chip code is generated by combining two
orthogonal m-chip codes, the m-chip code is used for sector
identification, the other m-chip code is used for identification of
cell specific information, and further, the cell specific
information is transmitted as phase difference information between
subcarriers (that are more preferably adjoined on the frequency
axis) multiplied by a sector specific code element of the same
value. It is thereby possible to efficiently transmit the sector
specific information and cell specific information, while the
receiving side can divide and extract both of the information with
efficiency.
[0087] Further, in the cell search method of the invention, it is
possible to complete the cell search by timing detection of the SCH
(first step) on the time axis by an auto-correlation method using
periodicity of the SCH or cross-correlation method using time
waveforms of replica codes of the sector specific codes, and
identification of a sector ID and cell ID (second step) based on
information on the frequency axis. Accordingly, it is possible to
reduce the search process as compared with the conventional 3-step
cell search. Further, correlation detection using a pilot channel
is required only in demodulating a data channel while being not
required in a cell search, and it is thereby possible to achieve
reductions (such as a reduction in memory capacity and the like) in
loads of hardware used for correlation calculation of the pilot
channel. Furthermore, since the sector specific code is multiplexed
on the SCH, with respect to sector identification, it is possible
to obtain effects of having resistance to interference between
sectors and fading. However, when the number of subcarriers is not
adequate, the cell ID cannot be identified directly only by the
SCH, and there may be a case that cell ID group information is only
detected. In this case, the cell ID can be identified by
implementing despreading and correlation detection using a pilot
channel as processing of the third step.
[0088] Moreover, according to the multicarrier
transmission/reception apparatus of the invention, fast
transmission with large capacity is allowed on downlink.
[0089] Thus, according to the invention, it is possible to decrease
the time required for the cell search process including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel, and further to
actualize a faster cell search including sector identification with
high accuracy while improving resistance to interference or
anti-fading characteristics of the cell search processing including
sector identification without increasing loads on a
transmission/reception apparatus.
[0090] Further, the invention includes various variations (specific
examples, modifications and applications), and the variations
contribute to practical application of communication schemes
complying with the E-UTRA (Evolved-UTRA).
[0091] For example, in the processing (detection processing of SCH
timing) of the first step in the cell search, as well as the
auto-correlation method, it is possible to adopt a
cross-correlation method with a particular time waveform focused,
and in this case, it is possible to obtain the effect of enabling
the configuration of a correlator to be simplified. Further, by
unifying all the codes of subcarriers as a phase reference on the
frequency axis to, for example, "1", it is possible to eliminate
limitations that six subcarriers should be a group in despreading
using the sector specific code. Furthermore, when a mobile station
knows all kinds of sector specific codes transmitted from the base
station, nearest sector detection can be performed by detection
using cross-correlation by time waveforms prior to FFT without
despreading. Moreover, when the number of sectors increases, it is
possible to adopt a "sector group specific code" as the "sector
specific code".
BRIEF DESCRIPTION OF DRAWINGS
[0092] FIG. 1 is a flowchart showing an example of main procedures
of multicarrier transmission processing according to the
invention;
[0093] FIG. 2 is a flowchart showing an example of main procedures
of multicarrier reception processing according to the
invention;
[0094] FIG. 3 is a diagram showing a basic concept of orthogonal
code generation;
[0095] FIG. 4 is a diagram to explain an arrangement of code
elements constituting three orthogonal codes (code 1, code 2 and
code 3) and principles in demodulating only code 2;
[0096] FIG. 5 is a diagram to explain a method of multiplexing cell
specific information (sector ID, broadcast channel bandwidth,
antenna arrangement, GI length and the like) on SCH;
[0097] FIGS. 6A to 6D are diagrams to explain a code format to
multiplex sector specific information and cell specific information
on SCH to transmit;
[0098] FIG. 7 is a diagram showing subcarrier indexes (subcarrier
numbers) on the frequency axis;
[0099] FIG. 8A is a diagram showing an assignment of a sector
common code on the frequency axis; FIG. 8B is a diagram showing
structures of three sector specific codes; FIG. 8C is a diagram
showing the basic concept of generation of the sector specific
code;
[0100] FIG. 9 is a diagram showing a structure of a code sequence
to transmit the cell specific information on the frequency
axis;
[0101] FIG. 10 is a block diagram showing a configuration example
of a physical layer and MAC (Media Access Control) sub-layer in a
base station (multicarrier transmission apparatus) of the mobile
communication system;
[0102] FIG. 11 is a block diagram illustrating a specific
configuration of a transmission circuit section as shown in FIG.
10;
[0103] FIG. 12 is a block diagram showing an example of a
configuration of a multicarrier receiver according to the
invention;
[0104] FIG. 13 is a block diagram showing a configuration example
of a circuit having functions of timing detection and frequency
error detection;
[0105] FIG. 14 is a diagram showing the specific content of
despreading processing for sector identification;
[0106] FIG. 15 is a diagram to explain demodulation processing of
the cell specific information;
[0107] FIG. 16 is a diagram showing subcarriers, assigned the SCH,
arranged on the frequency axis (i.e. structure of the SCH on the
frequency axis);
[0108] FIG. 17A is a diagram illustrating an arrangement on the
frequency axis of the sector common code to be multiplied by the
SCH in Embodiment 3; FIG. 17B is a diagram showing three sector
specific codes in Embodiment 3;
[0109] FIG. 18 is a diagram illustrating an arrangement of the cell
specific code in Embodiment 3
[0110] FIG. 19 is a diagram illustrating a frame structure in
Embodiment 3;
[0111] FIG. 20 is a diagram illustrating a specific content example
of correlation calculation processing using the sector specific
code;
[0112] FIG. 21 is a diagram illustrating a demodulation method of
the cell specific information in Embodiment 3;
[0113] FIG. 22 is a diagram illustrating a downlink frame structure
in the multicarrier communication system used in the invention;
[0114] FIG. 23 is a diagram showing an example of configurations of
a cell and a sector;
[0115] FIG. 24 is a diagram showing an example of an arrangement
position of SCH (synchronization channel) in a frame;
[0116] FIG. 25 is a diagram showing a structure example of SCH;
[0117] FIG. 26 is a block diagram illustrating a configuration of a
receiver for detecting a repeated waveform of SCH to acquire time
synchronization;
[0118] FIG. 27 is a diagram showing an example of the
synchronization channel (SCH) assigned to subcarriers on the
frequency axis;
[0119] FIG. 28 is a diagram showing an example of a structure of a
resource block in the OFDM communication scheme under review in the
3GPP;
[0120] FIG. 29A is a diagram showing an assignment of a sector
common code on the frequency axis; FIG. 29B is a diagram showing
structures of three sector specific codes; FIG. 29C is a diagram
showing the basic concept of generation of the sector specific
code, and shows vectors on the complex phase plane;
[0121] FIG. 30 is a diagram illustrating a structure on the
frequency axis of a code sequence to transmit the cell specific
information;
[0122] FIG. 31 is a block diagram illustrating a configuration of a
receiver for detecting a time position of SCH by a replica signal
to acquire time synchronization;
[0123] FIG. 32 is a diagram illustrating 76 subcarriers used in
Embodiment 5 for each function;
[0124] FIG. 33 is a diagram showing the relationship between a
subcarrier (cell specific information detection SCH subcarrier)
multiplied by the cell specific information and another subcarrier
that is paired with the subcarrier and that is a subcarrier
(cross-correlation detection SCH subcarrier) as a phase
reference;
[0125] FIG. 34A is a diagram showing an assignment of a sector
common code on the frequency axis in Embodiment 5; FIG. 34B is a
diagram showing structures of three sector specific codes in
Embodiment 5; FIG. 34C is a diagram showing the basic concept of
generation of the sector specific code, and shows vectors on the
complex phase plane in Embodiment 5;
[0126] FIGS. 35A to 35D are diagrams to explain that a waveform in
the time domain formed by a plurality of combined SCH subcarriers
in a SCH-symbol period is of repetition of a reference waveform
(or, waveform of the inverted reference waveform) in a one-symbol
period in Embodiment 5; and
[0127] FIG. 36 is a diagram illustrating a structure on the
frequency axis of a code sequence to transmit the cell specific
information in Embodiment 5.
DESCRIPTION OF SYMBOLS
[0128] 10 MAC section [0129] 12 SCH data generating section [0130]
14 Transmission data output section [0131] 16 Transmission circuit
control section [0132] 20 (20a.about.20b) Physical layer section
[0133] 22 (22a.about.22c) Reception circuit section [0134] 24
(24a.about.24c) Transmission circuit section [0135] 26
(26a.about.26C) Analog circuit section [0136] 28 (28a.about.28C)
Antenna section [0137] 210 Despreading section for sector specific
code identification [0138] 220 Sector power determining section
[0139] 230 SCH data (including the cell specific information)
demodulation section [0140] 400 Shift register [0141] 402 Adder
[0142] 404 Multiplier [0143] CL1.about.CL3 Cell [0144]
SC1.about.SC3 Sector
BEST MODE FOR CARRYING OUT THE INVENTION
[0145] Described first are basic techniques and fundamental concept
of multicarrier communication used in the invention.
[0146] (Basic Matters of Multicarrier Communication)
[0147] In the following descriptions, OFDM is used as a digital
modulation scheme. In the OFDM communication system,
standardization proceeds in consideration of the fact that a base
station controlling a cell, for example, as three communication
control areas (sectors) performs communications concurrently with a
plurality of mobile stations in the cell. In the OFDM communication
system, a radio communication frame (hereinafter, referred to as a
"frame") is divided into small units (hereinafter, this divided
unit is referred to as a "resource block") so that a plurality of
mobile stations can use, each resource block is allocated to a
mobile station with good communication environment, and thus, it is
intended to enhance the communication rate.
[0148] Further, a frame is transmitted at the same timing in each
sector controlled by a single base station. In other words, frame
transmission is synchronized. Furthermore, the same frequency band
is used. Therefore, near the cell boundary and the sector boundary,
signals used in the adjacent cell or adjacent sector interfere with
a desired reception signal, resulting in a decrease in
communication rate (throughput). In the scheme of above-mentioned
Non-patent Document 1, the sector specific code (meaning three code
sequences specific to sectors in the following example) is
multiplied by a pilot subcarrier that is a subcarrier for
propagation path estimation assigned to the same subcarrier among
the sectors. Then, the system designed is made such that
interference by a signal from an adjacent sector is cancelled by de
spreading M (M is an integer of "2" or more) pilot subcarriers
determined by a code sequence, so as to enable propagation path
estimation with higher accuracy to be performed.
[0149] Meanwhile, with respect to interference with an adjacent
cell, such a design is made that an interfering signal caused by a
signal used in the adjacent cell is randomized by multiplying a
pilot channel and data channel by a spreading code specific to the
cell. In other words, the pilot channel is doubly multiplied by the
sector specific orthogonal code and cell specific spreading
code.
[0150] (Description of Frame)
[0151] FIG. 22 is a diagram illustrating a downlink frame structure
in the multicarrier communication system used in the invention. The
frame structure is the same as a typical frame structure used in an
OFDMA communication scheme. In other words, in the frame structure,
a certain time interval (frame interval) is divided into a
plurality of units, and the frequency region is also divided into
certain bandwidths comprised of a plurality of subcarriers. A
single area of thus divided areas is referred to as a resource
block in this description of the invention. Generally, a unit
divided from a frame in the time region may be referred to as a
sub-frame, while a unit divided in the frequency region may be
referred to a sub-channel. In FIG. 22, a frame is comprised of six
sub-channels, F1 to F6, in the frequency-axis direction, and ten
sub-frames, SF1 to SF10, in the time axis direction. However, the
number of block divisions and block size are not limited thereto.
Further, each mobile station shares these blocks. Particularly, to
enhance communication characteristics (throughput), each block
undergoes scheduling to a mobile station with good propagation path
environment. Further, when a plurality of mobile stations performs
communication with small data amounts, a single resource block can
further be divided to be shared.
[0152] (Cell Search)
[0153] Each mobile station selects a base station providing good
reception characteristics from among a plurality of base stations
in starting communication, and after connecting to the base
station, starts wireless communication. Good reception
characteristics mean high reception power of a received signal.
Such an operation in starting wireless communication is generally
designated as a cell search. The cell search includes selection of
a base station providing good communication characteristics,
acquisition of cell specific information including information of a
base station ID and the like, frame synchronization and symbol
synchronization, and the like. In addition, symbol synchronization
means an FFT window synchronization, or window synchronization.
[0154] FIG. 23 is a diagram showing an example of configurations of
a cell and a sector. As shown in the figure, each of base stations
(BS1 to BS3) is located in the center of one of cells (CL1 to CL3),
respectively. Further, each of cells (CL1 to CL3) is divided into
three sectors (SC1 to SC3). A plurality of mobile stations (UE1 and
the like) exists in each cell, and each mobile station selects a
base station providing the most excellent reception quality to
perform wireless communication. For example, when the base stations
(BS1 to BS3) as shown in FIG. 23 perform downlink wireless
communication with the same transmit power, a mobile station UE1
connects to BS1 providing the smallest propagation loss to perform
communication. Thus, it is necessary to make the cell search to
thus detect a plurality of base stations, and select a base station
with the most excellent communication quality from among the base
stations to connect. Further, in Non-patent Document 1 as described
previously, it is required to acquire information of a code
specific to the cell in the cell search to multiply a data channel
by the code specific to the cell.
[0155] (3-Step Cell Search)
[0156] As described above, the cell search method is proposed which
is designated as the 3-step cell search method having steps. In the
first step, symbol synchronization, frequency offset, detection of
1/N frame timing is performed using time correlation detection of
the SCH. The detection of 1/N frame timing is detection performed
when N SCHs are multiplexed in the time domain. Details will be
described later.
[0157] FIG. 24 is a diagram showing an example of an arrangement
position of the synchronization channel (SCH) in a frame. As shown
in the figure, the SCH is arranged in an end symbol in the fifth
sub-frame (SF5) and the tenth sub-frame (SF10). As described
previously, in the first step, synchronization is acquired in a
half period of the frame interval by detecting temporal positions
of two SCHs within the frame. By configuring the SCH using a
particular subcarrier, a characteristic waveform is formed in the
time-axis region. In the first step, time synchronization is
acquired using the waveform characteristic.
[0158] In the second step, by correlation detection in the
frequency region, data forming the SCH is demodulated, and the cell
specific information is acquired (such as, for example, a cell ID
or cell group ID, cell structure, the number of antennas of a base
station, broadcast information notifying bandwidth and the
like).
[0159] In the third step, the cell ID is identified by correlation
between a pilot channel multiplied by a spreading code specific to
the base station corresponding to the cell ID and a replica signal
of the pilot channel generated in the mobile station.
[0160] FIG. 25 is a diagram showing a structure example of the SCH.
In FIG. 25, the vertical axis represents the frequency axis, and
the horizontal axis represents the time axis. In the figure, each
small rectangle represents a subcarrier forming the SCH, and
constitutes a channel with a one-symbol length. Thus, the SCH is
comprised of a plurality of subcarriers, even-numbered subcarriers
from the low-frequency side and a subcarrier (DC subcarrier) with
the center frequency are made null subcarriers, and signals for the
SCH are assigned to odd-numbered subcarriers except the
center-frequency subcarrier. In addition, the null subcarrier is a
subcarrier with zero power to which a signal is not assigned.
[0161] Hereinafter, a subcarrier of the SCH assigned data is
referred to as a "SCH subcarrier". By configuring in this way, a
symbol assigned the SCH has a waveform in the time domain such that
the same signal with a 1/2 symbol length is repeated twice. One or
more symbols with such a channel structure are arranged in
predetermined positions of a frame, and by detecting the repeated
waveform with a receiver, time synchronization is acquired.
[0162] FIG. 26 is a block diagram illustrating a configuration of a
receiver for detecting the repeated waveform of the SCH to acquire
time synchronization. As shown in the figure, the receiver has a
delay section 91 for delaying a received signal 90, complex
conjugate calculating section 92, multiplying section 93, averaging
section 94, and peak detecting section 95. A synchronization timing
signal 96 is output from the peak detecting section 95.
[0163] In this receiver, a received signal is multiplied by a
complex conjugate of a signal which is received previously and
delayed by 1/2 effective symbol. As are suit, by using the fact
that the correlation value is high when matching with SCH timing of
the configuration as described previously, synchronization timing
is detected. As shown in FIG. 24, in the case of the system that
the SCH is arranged in a position obtained by dividing a frame by N
at the same time intervals (N=2 in FIG. 24), the multiplied signal
is averaged over a 1/N frame interval, a peak position is detected,
and it is thereby possible to acquire synchronization and symbol
synchronization with accuracy in a 1/N frame. In addition, the
number of SCHs in a frame and positions thereof are known to the
mobile station.
[0164] FIG. 27 is a diagram showing an example of the SCH assigned
to subcarriers on the frequency axis. FIG. 27 shows a scheme for
calculating a phase difference P between adjacent SCH subcarriers,
and thereby acquiring the information of the SCH. The information
by the phase difference P between SCH subcarriers indicates a cell
ID group, information indicating a position of the SCH among a
plurality of SCHs in a frame, cell structure, and the number of
antennas of the base station (second step). A pilot symbol replica
signal is generated corresponding to each cell ID included in the
cell ID group thus detected. Then, it is possible to detect the
cell ID by calculating correlation with a pilot symbol arranged in
a sub-frame.
[0165] FIG. 28 is a diagram showing an example of a structure of a
resource block in the OFDM communication scheme under review in the
3GPP. FIG. 28 shows a typical resource block when the SCH is
included. In the figure, as well as SCHs, provided are a pilot
channel and data channel (including a control information channel).
The pilot symbol is multiplied by a cell specific spreading code to
randomize interference, and an orthogonal code to orthogonalize
pilot symbols between sectors in the same cell. A pilot channel
arranged in a first symbol of a frame is used for channel
estimation in each sector. However, near the boundary of sectors,
in a position enabling reception of a transmission signal from a
different sector in the same cell, a transmission signal from an
adjacent sector in the same symbol acts as an interfering signal,
and channel estimation accuracy deteriorates. Therefore, used in
such an environment are characteristics of an orthogonal code
orthogonalized among sectors and multiplied by the pilot symbol. In
other words, a propagation path estimation method is applied in
which a subcarrier of a pilot channel is multiplied by a complex
conjugate of an orthogonal code used in a desired sector and
undergoes despreading, thereby canceling an interfering signal from
the adjacent sector.
[0166] In the conventional cell search method, when a cell ID is
detected using replica signals, it is required to determine a
sector in the same cell that provides high signal intensity while
detecting the cell ID. Therefore, it is necessary to perform
correlation detection with replica signals corresponding to (the
number of cell IDs) included in the cell ID group multiplied by
(the number of sector IDs). In other words, in the first and second
steps, it is not possible to determine reception power of a
transmission signal from each sector using the SCHs concurrently
transmitted from sectors in the same cell. Therefore, the
processing amount required for correlation detection in the 3-step
cell search increases in proportion to the number of sectors
included in a cell.
[0167] When a storing section for storing results corresponding to
a plurality of replica signals is provided to compare correlation
values corresponding to the replica signals, it is required to
prepare the number of storing sections corresponding to (the number
of cell IDs) included in the cell ID group multiplied by (the
number of sector IDs). Further, since each sector in the same cell
transmits the same SCH data concurrently, depending on conditions
of propagation paths of signals from a plurality of sectors, there
is a possibility of generating consecutive subcarriers with
remarkably small amplitude in the frequency region by fading, and
decreasing the cell ID identification probability.
[0168] Therefore, the present invention provides a synchronization
channel (SCH) with sector and cell identification functions. By
this means, the invention intends to actualize a cell search
without recourse to correlation detection using a pilot channel and
overcome the above-mentioned inconvenience. Embodiments of the
invention will be described below with reference to accompanying
drawings.
Embodiment 1
[0169] Embodiment 1 describes a cell search method according to the
invention. FIG. 1 is a flowchart showing an example of main
procedures of multicarrier transmission processing according to the
invention. As shown in the figure, a base station in a multicarrier
mobile communication system adopting an OFDM communication scheme
multiplies three kinds of code to generate a synchronization
channel (SCH) included on downlink. In other words, the base
station multiplies a "sector common code common in the same cell"
by a "sector specific code (orthogonal code varying with sectors in
the same cell)", and a "cell specific code (code varying with cells
to transmit cell specific information)" (step S1). The sector
common code may be a common code in a plurality of cells.
[0170] Next, by assignment (mapping) in the time/frequency plane,
the SCH and pilot channel are assigned to subcarriers of a resource
block (step S2). Then, multiplication of spreading code and IFFT
processing is executed (steps S3 and S4). Performed next is
insertion of a GI (Guard Interval, also referred to as CP (Cyclic
Prefix)), and D/A conversion processing (steps S5 and S6). Finally,
frequency conversion is performed, and a multicarrier signal is
transmitted from a directional antenna of each sector (step
S7).
[0171] FIG. 2 is a flowchart showing an example of main procedures
of multi carrier reception processing according to the invention. A
mobile station receives the multicarrier signal from the base
station, and executes frequency conversion and A/D conversion (step
S10). In addition, the mobile station includes a cellular telephone
device, PDA terminal, and portable personal computer.
[0172] Next, by the auto-correlation method focusing on a repeated
waveform of the SCH periodically arranged, the mobile station
detects SCH positions, and establishes SCH symbol synchronization
(step S2). This step S2 corresponds to the first step (step a) of
the cell search. Next, the mobile station removes the GI (step
S12), and performs serial/parallel transform and FFT (Fast Fourier
Transform processing) (step S13).
[0173] Thereafter, the sector identification processing and cell
identification processing is performed at the same time (the second
step (step b) of the cell search). In other words, by despreading
using the sector specific code, the mobile station detects a sector
specific code providing maximum reception power, and identifies an
optimal sector (antenna of the base station with which the mobile
station should communicate) (step S14). Further, in parallel with
the processing, the mobile station demodulates the cell specific
code (further, correlation detection with the cell specific code
when necessary) to acquire the cell specific information (cell ID
and the like) (step S15).
[0174] When the number of subcarriers is adequate, identification
of the cell and sector is completed by this 2-step cell search.
However, when subcarriers lack in number, in step S15, the cell ID
cannot be identified directly, and the cell ID group is only
identified. In this case, the mobile station executes
identification of the cell ID by correlation detection using a
pilot channel (step S16). This case is the 3-step cell search (step
c).
[0175] Described next is generation of sector specific codes (codes
orthogonalized for each sector). Herein, the case is descried where
the number of sectors is "3", and three mutually orthogonal codes
are generated.
[0176] FIG. 3 is a diagram showing a basic concept of orthogonal
code generation. As shown in the figure, three vectors are set on
the complex phase plane. The complex phase plane is the IQ plane
where the I axis corresponds to the real axis, and the Q axis
corresponds to the imaginary axis. On the complex phase plane are
set three vectors, P1, P2 and P3, with the amplitude of "1" forming
an angle of 120.degree. with respect to one another. Vector
addition of three vectors cancels the imaginary-axis components of
vectors P2 and P3. Further, the result (=-1) of addition of
real-axis components of vectors P2 and P3 and vector P1 (=+1)
cancel each other out, and the result of vector addition is "0".
Three orthogonal codes are generated by using three vectors having
such a relationship.
[0177] FIG. 4 is a diagram to explain an arrangement of code
elements constituting three orthogonal codes (code 1, code 2 and
code 3) and principles in demodulating only code 2. In the figure,
the horizontal axis represents the time axis, and the vertical axis
represents the frequency axis. As shown in FIG. 4, it is assumed
that (code 1)=(P1, P1, P1), (code 2)=(P1, P2, P3), and that (code
3)=(P1, P3, P2). Each code is formed using any one of three vectors
of FIG. 3 as a code element. Codes 2 and 3 use the same code
elements, but are different in arrangement on the frequency
axis.
[0178] Herein, for example, a case is assumed that only code 2 is
demodulated. In this case, each of code elements P1, P2 and P3 of
code 2 is multiplied by a respective complex conjugate. By this
means, the phase rotates, and the imaginary-axis components are
canceled. When each multiplication result is added, since three
real-axis components (=1 each) are added, the correlation detection
result is "3". The same complex conjugate is similarly multiplied
by code 1 and code 3 to add. As a result, with respect to any
codes, the phase of each code element rotates, and eventually,
vectors P1, P2 and P3 do not disappear, and remain. Therefore,
adding the vectors provides an addition result of "0" (see FIG. 3).
It is thus possible to extract only code 2. The aforementioned
description is the same as in the case of extracting only code 1 or
code 3. Thus, codes 1 to 3 in FIG. 4 are orthogonal to one another
with three code elements (three chips) as a group.
[0179] In addition, in the invention, the number of sectors is not
limited to "3". There is a case that the number of sectors is "4"
or more. Also in this case, by using the above-mentioned
philosophy, it is possible to generate orthogonal codes in response
to the number of sectors with ease. In other words, the number of
orthogonal vectors in FIG. 3 is increased, and the vectors are
arranged on the frequency axis using the technique of FIG. 4. By
this means, it is possible to generate the higher number of codes.
That is, as the number of code elements of a group arranged on the
frequency axis increases, it is possible to generate the higher
number of orthogonal codes. Accordingly, it is possible to flexibly
cope with the case that the number of sectors increases.
[0180] It is described next how to multiplex the cell specific
information on the SCH. The cell specific information includes a
cell ID, broadcast channel bandwidth, antenna arrangement, GI
length and the like.
[0181] FIG. 5 is a diagram to explain a method of multiplexing the
cell specific information on the SCH. In FIG. 5, the horizontal
axis represents the time axis, and the vertical axis represents the
frequency axis. In FIG. 5, a subcarrier as a phase reference is
assigned code A. Then, a subcarrier adjacent to the subcarrier as a
reference phase is assigned code (C1, C2, C3 . . . ) indicating a
phase difference from the subcarrier. The cell specific code to
transmit the cell specific information is formed using code "A" as
a phase reference and the code (C1, C2, C3 . . . ) indicating the
phase difference. In other words, the cell specific information is
not an absolute phase of a subcarrier, but is transmitted as
information indicating a relative phase difference between a pair
of subcarriers. In FIG. 5, K1, K2, K3 . . . enclosed by dotted
lines indicate a pair of subcarriers.
[0182] Described next are characteristics of a code format to
concurrently transmit the sector specific information and cell
specific information using the SCH. As shown in FIG. 4, when three
sectors are distinguished from one another, it is enough to prepare
mutually orthogonal codes of 3-chip cycle. However, when the cell
specific information is also transmitted at the same time, it is
not possible to support such transmission by codes with the simple
structure as shown in FIG. 4. Particularly, in the case of using
relative phase difference information between subcarriers as shown
in FIG. 5, it is difficult to transmit the cell specific
information with the code of the structure as shown in FIG. 4.
[0183] In other words, both of the sector specific information and
cell specific information is transmitted in phase modulation of
subcarriers, and one information should not have an adverse effect
on the other information. In addition to the aforementioned
respect, the receiving side needs to be able to demodulate both of
the information at the same time to make a cell search fast.
Therefore, used are two orthogonal 3-chip (three code elements)
groups as shown in FIG. 4. The elements are combined on the
frequency axis to map, and codes are formed using six chips (six
code elements) as a group (i.e. the six chips are a generation
unit).
[0184] FIGS. 6A to 6D are diagrams to explain a code format to
multiplex the sector specific information and the cell specific
information on the SCH to transmit. In FIG. 6A, two orthogonal
3-chip (three code elements) groups as shown in FIG. 4 are used,
and combined on the frequency axis to arrange. Then, FIG. 6A shows
an example of an arrangement of chips in the case of using these
six chips (six code elements) as a group to form a code. Herein,
these six chips are used as a structure unit.
[0185] FIG. 6A shows a manner that three chips (=P1, P2, P3) and
other three chips (=P1, P2, P3) are arranged such that code
elements of the same value are adjacent to each other on the
frequency axis, and thus, the groups are alternated and arranged.
By this means, a 6-chip code (=P1, P1, P2, P2, P3, P3) is generated
as shown in FIG. 6B. Three chips of the 6-chip code are used as a
sector specific code, and the other three chips are used to
multiply the cell specific information.
[0186] In other words, as shown in FIG. 6C, three odd-numbered
chips (=P1, P2, P3) are used for correlation detection (sector
identification) by the technique as shown in FIG. 4. Meanwhile,
three even-numbered chips (=P1, P2, P3) are multiplied respectively
by codes (C1 to C3) indicating relative phase difference
information as the cell specific information. As shown in FIG. 5,
the "relative phase difference information" is "information of a
phase difference between subcarriers multiplied by the cell
specific code of the same value". In FIG. 60, each subcarrier
assigned one of three odd-numbered chips (=P1, P2, P3) is a phase
reference subcarrier.
[0187] For example, two subcarriers are paired that are assigned a
sector specific code with the same value of (P1, P1), P1 on the
high-frequency side is multiplied by C1 indicating a phase
difference, and the C1 is used as a code to convey the cell
specific information. Similarly, two subcarriers are paired that
are assigned a sector specific code with the same value of (P2,
P2), P2 on the high-frequency side is multiplied by C2 indicating a
phase difference, and the C2 is used as a code to convey the cell
specific information. In addition, in FIG. 6C, codes C1, C2 and C3
indicating the phase difference information are circled by dotted
lines. Cn=(C0, C1, C2 . . . ) is the cell specific code.
[0188] In the above-mentioned descriptions, for the sake of
convenience, the order is described in which the "sector specific
code" is assigned to a subcarrier, and then, the "cell specific
code" is further assigned. However, such a case may occur actually
that assignment (multiplication) of the "cell specific code" is
performed prior to assignment (multiplication) of the "sector
specific code". The same result is obtained when either
multiplication is performed first. In other words, the sector
common code (S.sub.0), cell specific code, and sector specific code
are multiplied by the SCH triply as a result. Therefore, it is not
an essential problem performing multiplication of the cell specific
code, or multiplication of the sector specific code earlier. In
addition, the above-mentioned "sector common code (S.sub.0)" is a
common code in a plurality of sectors in the same cell, and is
sometimes referred to as simply a "sector common code" in this
description.
[0189] In the case of the code structure as shown in FIG. 6C, since
subcarriers assigned the sector specific code of the same value are
adjacent to each other and arranged on the frequency axis, the
probability is high that both of the subcarriers arrive at the
receiving side through equivalent propagation paths. Therefore,
there is an advantage capable of neglecting a phase rotation by the
difference in the transfer function of the propagation path.
Accordingly, the receiving side is capable of detecting only a
phase difference between adjacent subcarriers caused by the cell
specific code with accuracy. It is thereby possible to demodulate
the cell specific information.
[0190] In addition, the structure of the sector specific code is
not limited to the structure as shown in FIG. 6B. For example, as
shown in FIG. 6D, three sector chips (P1, P2, P3) are simply
aligned on the frequency axis in a two-stage manner. With respect
to transmission of the cell specific information, for example, two
subcarriers assigned the sector specific code with the same value
of (P1, P1) are paired, P1 on the high-frequency side is multiplied
by C1 indicating a phase difference, the C1 is made the cell
specific information, and in this respect, the transmission is the
same as that in the case of FIG. 6C.
[0191] Thus, in the invention, the synchronization channel (SCH) is
multiplied by the sector specific code orthogonalized for each
sector. In other words, SCHs that are not orthogonal on sectors are
orthogonalized. Then, sector identification is allowed by reception
power measurement using the SCH, and even in the boundary of
sectors, good frequency characteristics enable sector
identification with high quality. Further, it is possible to
identify also a cell ID by multiplying the SCH by the cell specific
code to concurrently transmit.
[0192] Accordingly, it is possible to actualize a new 2-step cell
search method, substituting for the conventional 3-step cell search
method using both the SCH and CPICH. It is thereby possible to
reduce the processing process of a cell search including sector
identification. Further, devising is required in code structure to
multiply by the SCH to achieve both of identification of sector and
identification cell, and in the invention, orthogonal codes having
a plurality of chips as a unit are paired and used. In other words,
one of codes having the same value is further multiplied by a code
indicating a relative phase difference, and the cell specific
information is transmitted by the relative phase difference. By
this means, the code is simplified and made compact, while it is
possible to transmit the identification information of both of the
sector and cell.
[0193] As a result, any particular loads are not imposed on the
multicarrier transmission/reception apparatus. Further, the
multicarrier reception apparatus is capable of implementing
identification of the sector ID and demodulation of the cell
specific information at the same time, and performing the efficient
cell search.
Embodiment 2
[0194] This Embodiment describes a data structure of the SCH and a
cell search method including sector identification, using the case
where the SCH is arranged at the end of a sub-frame, as an
example.
[0195] A cellular system is a mobile communication system comprised
of a plurality of cells, and a cellular system used in this
Embodiment is a one-cell reuse communication system in which each
cell uses the same frequency band, and an OFDMA communication
scheme is used as a communication scheme. As shown in FIG. 23, in
this communication system, a cell is divided into three
communication areas (sectors), and a base station located in the
center of the cell performs wireless communication with mobile
stations positioned in a plurality of sectors. The same frequency
band is used in each sector, a pilot channel is multiplied by an
orthogonal code specific to the sector, and by using despreading,
accurate propagation path estimation can be made even near the
sector boundary.
[0196] A downlink communication scheme is the same OFDM
communication scheme as in the foregoing. Structures of a
communication frame and resource block have the same formats as
those shown in FIGS. 22 and 28. Further, this Embodiment adopts a
structure where the SCH is arranged at the end of a time period
obtained by dividing a frame into Ss (Ss is a submultiple of the
number Sf (natural number) of sub-frames). By this means, the SCH
is arranged periodically on the time axis. In the Embodiment as
shown in FIG. 24, Sf is "10", and Ss is "2".
[0197] With respect to a pilot channel, this Embodiment uses a Code
Division Multiplex (CDM) scheme that is a scheme for multiplexing
on the same subcarrier of the same symbol among sectors. However,
the invention is applicable to schemes, such as a Frequency
Division Multiplex (FDM) scheme for multiplexing on different
subcarriers of the same symbol, a Time Division Multiplex (TDM) for
multiplexing on the same subcarriers of different symbols and the
like, where pilot channels of sectors are mutually orthogonal.
[0198] In this Embodiment, a base station transmits a signal
multiplied by a code sequence corresponding to an orthogonal code
to multiply by a pilot channel in CDM, as the SCH transmitted from
each sector. By this means, in determining reception power of a
signal from the base station, a mobile station is capable of
achieving good frequency characteristics even in the sector
boundary, by spreading effect of the code. Together therewith, it
is possible to determine reception power for each sector. In
addition, the code sequence corresponding to an orthogonal code to
multiply by a pilot channel does not need to always be the same as
a code sequence multiplied by the pilot channel.
[0199] Described first is a specific structure of a physical
channel (hereinafter, referred to as a "SCH") for a mobile station
to acquire synchronization of time and frequency of a transmission
signal transmitted from a base station in the mobile communication
scheme in this Embodiment.
[0200] FIG. 7 is a diagram showing subcarrier indexes (subcarrier
numbers) on the frequency axis. As shown in the figure, a
subcarrier number on the lowest frequency side (lowermost end) is
"1", and a subcarrier number in the center frequency is "n+1". In
the following descriptions, these subcarrier indexes are used as
appropriate.
[0201] FIGS. 8A to 8C are diagrams to explain a data structure of
the SCH concurrently transmitted from three sectors in the same
cell. FIG. 8A is a diagram showing an assignment of a sector common
code on the frequency axis, FIG. 8B is a diagram showing structures
of three sector specific codes, and FIG. 8C is a diagram showing
the basic concept of generation of the sector specific code, and
shows vectors on the complex phase plane.
[0202] A frame of a signal transmitted from a base station is
comprised of a plurality of symbols. FIG. 8 shows the diagrams with
SCH data of a plurality of symbols focused. In FIG. 8, the vertical
axis represents the frequency axis, while the horizontal axis
represents the time axis. With respect to each subcarrier, as in
the case shown in FIG. 4, null subcarriers are even-numbered
subcarriers (subcarrier indexes 2, 4, 6 . . . , 2n) from the
low-frequency side and the center-frequency subcarrier. Then
odd-numbered subcarriers (subcarrier indexes 1, 3, 5 . . . , 2n+1)
except the center-frequency subcarrier are used as subcarriers for
data assignment.
[0203] The signal as shown in FIG. 8A indicates a sector common
code. Each SCH subcarrier is assigned S.sub.0. S.sub.0 is an
arbitrary value expressed by A*exp(j.omega.). A represents the
amplitude, j represents an imaginary unit, and .omega. represents a
phase. In addition, in this description, the explanation is made
with the amplitude A being "1". The sector common code S.sub.0 is
common in all the sectors within each cell, and can be used to
randomize signals among cells.
[0204] The sector specific code will be described below. FIG. 8B
shows the case where the sector specific codes are used in three
sectors. The codes are specific to respective sectors in the same
cell, and codes 1 to 3 support three sectors in this Embodiment. It
is assumed that the mobile station and base station beforehand know
about correspondence between the codes and sector IDs in the same
cell. In code sequences to be multiplied by SCH subcarriers as the
sector specific code, phase differences from odd-numbered SCH
subcarriers (subcarrier indexes 1, 5, 9 . . . ) from the
low-frequency side to even-numbered subcarriers (subcarrier indexes
3, 7, 11, . . . ) are 0.degree., 0.degree. and 0.degree. in each
sector. Phase differences from even-numbered SCH subcarriers to
odd-numbered subcarriers are 0.degree., 120.degree. or 240.degree.
in each sector.
[0205] Each code is a code with the amplitude of "1". Further,
since these code sequences are of 6-chip reuse (one period is six
chips), the number n of SCH subcarriers is an integral multiple of
"6". With attention drawn to one reuse part (six chips) of these
three code sequences, when a complex conjugate of an arbitrary code
sequence is multiplied by each code sequence and consecutive three
chips are added every four chips, the sum is "0" in the case of
multiplying code sequences except the selected arbitrary code
sequence, while being "3" in the case of multiplying the arbitrary
code sequence.
[0206] For example, the case is considered of (exp(j0.pi.),
exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.)) of
code 1, (exp(j0.pi.), exp(j0.pi.), exp(j2.pi./3), exp(j2.pi./3),
exp(j4.pi./3), exp(j4.pi./3)) of code 2, and (exp(j0.pi.),
exp(j0.pi.), exp(j4.pi./3), exp(j4.pi./3), exp(j2.pi./3),
exp(j2.pi./3)) of code 3. When code 2 is selected as an arbitrary
code, a complex conjugate of code 2 is (exp(j0.pi.), exp(j0.pi.),
exp(-j2.pi./3), exp(-j2.pi./3), exp(-j4.pi./3), exp(-j4.pi./3)).
Codes obtained by multiplying codes 1 to 3 by the complex conjugate
of code 2 are respectively (exp(j0.pi.), exp(j0.pi.),
exp(-j2.pi./3), exp(-j2.pi./3), exp(-j4.pi./3), exp(-j4.pi./3)),
(exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.),
exp(j0.pi.)), and (exp(j0.pi.), exp(j0.pi.), exp(j2.pi./3),
exp(j2.pi./3), exp(-j2.pi./3), exp(-j2.pi./3)). Further, when
odd-numbered chips and even-numbered chips are subjected to vector
addition, the results are (0,0), (3,3) and (0,0). Thus, the code
sequences have characteristics that the sum of the codes except
code 2 selected as an arbitrary code is "0". This means that in
concurrently transmitting the SCH of the same data multiplied by an
orthogonal code (FIG. 8B) corresponding to each sector from each
sector in the same cell, a mobile station receiving the SCH
performs despreading of the SCH every three predetermined chips,
and is thereby capable of separating a signal from an arbitrary
sector from an interfering signal from an adjacent sector.
[0207] Described next is a code sequence to transmit the cell
specific information. FIG. 9 is a diagram showing a structure of a
code sequence to transmit the cell specific information on the
frequency axis. Since the code sequence as shown in FIG. 9 is a
code sequence to transmit the cell specific information, different
code sequences are used between cells, while the same code sequence
is used among sectors in the same cell. The cell specific
information is a cell ID or information of a specific spreading
code used in the cell, information of the number of antennas of the
base station and system bandwidth, and the like. The cell specific
information includes information required for a mobile station to
first connect to the base station.
[0208] However, the spreading code information is an extremely high
number of codes depending on the code length constituting the
information, and there is a case that codes as shown in FIG. 9 lack
in the information amount to notify. In such a case, it is possible
to group some cells (spreading codes), and generate a code sequence
by the same information in the cells belonging to the group. In
this case, since the spreading code specific to the cell is not
completely identified from the information of the SCH, an ultimate
cell specific spreading code is identified using a pilot channel
multiplied by the spreading code.
[0209] The code sequence of FIG. 9 is formed using six chips as a
group from the low-frequency side. In the six chips, odd-numbered
SCH subcarriers (subcarrier indexes 1, 5, 9) are assigned the same
code. Further, even-numbered SCH subcarriers (subcarrier indexes 3,
7, 11) are assigned a code obtained by multiplying the code
assigned to the odd-numbered subcarriers by the cell specific code.
The codes assigned to odd-numbered subcarriers are the same among
six chips, but do not need to be the same as those used in other
six chips. Each chip forming a code sequence has the amplitude of
"1". Further, as the code length, when the number of SCH
subcarriers is n, a code sequence with the code length of n/2 is
required to form the even-numbered subcarriers. Since the code
length is dependent on the number of SCH subcarriers, generally, it
is possible to generate the high number of code sequences with good
correlation characteristics when the number of SCH subcarriers is
sufficiently high. Therefore, instead of the code sequence
indicating a cell ID group as described previously, it is made
possible to form using a code sequence containing information
directly indicating the cell ID.
[0210] Three kinds of code sequences as shown above are code
sequences constituting the SCH, and the SCH multiplied by these
code sequences is transmitted from a transmitter of each sector. A
configuration of a base station will be described below.
[0211] FIG. 10 is a block diagram showing a configuration example
of a physical layer and MAC (Media Access Control) sub-layer in a
base station (multicarrier transmission apparatus) of the mobile
communication system. As shown in figure, the base station has a
MAC section 10 that performs mapping of a logical channel and
physical channel, scheduling processing, and control of the
physical layer section, and outputs data input from a higher layer
to the physical layer section, while outputting data input from the
physical layer section to the higher layer, and physical layer
sections 20a to 20c that perform transformation of transmission
data input from the MAC section 10 to a radio transmission signal,
and transformation of a radio reception signal received in an
antenna section to transmission data based on control information
from the MAC section.
[0212] The MAC section 10 has a transmission circuit control
section 16 that controls transmission circuit sections based on
allocation information of each resource block of a frame notified
from the higher layer, a transmission data output section 14 that
inputs data of physical channels such as a data channel of each
resource block, pilot channel and the like to the transmission
circuit sections in accordance with timing subjected to scheduling,
and a SCH data generating section 12 that generates or stores cell
specific data to assign to the SCH.
[0213] In this Embodiment, the SCH is a channel for a mobile
station to synchronize temporally with a frame and symbol
transmitted from the base station to acquire the cell specific
information. Therefore, when the SCH data is not variable, the MAC
section 10 does not need to always generate data for each
transmission, and the data is stored in the MAC section 10 or each
physical layer section (20a to 20c) corresponding to the sector,
assigned to a symbol in accordance with the SCH transmission
timing, and is capable of being transmitted on a regular basis. In
this Embodiment, the SCH data generating section 12 in the MAC
section 10 generates the SCH data, and the physical layer section
(20a to 20c) of each sector can be provided with this function to
execute.
[0214] The SCH data is input to the physical layer sections (20a to
20c) from the MAC section 10 together with the data of other data
channels. The SCH data and data of the data channel is input to the
physical layer sections (20a to 20c) together with allocation
control information of each resource block notified from the
transmission circuit control section 16 of the MAC section 10, and
the data is allocated to each resource according to the allocation
information of the resource block.
[0215] Each of the physical layer sections (20a to 20c) has a
transmission circuit section (24a to 24c) which performs modulation
and multiplication of the sector specific code on the data channel,
pilot channel and SCH input from the MAC section 10 to multiplex on
the resource block, and inputs the resultant to an analog circuit
section (26a to 26c), a reception circuit section (22a to 22c) that
demodulates an output from the analog circuit section (26a to 26c)
to input to the MAC section 10, the analog circuit section (26a to
26c) that converts a transmission signal input from the
transmission circuit section (24a to 24c) into a radio-frequency
signal, while converting a reception signal received in an antenna
section (28a to 28c) into a frequency-band signal capable of being
processed in the reception circuit (22a to 22c), and an antenna
section 28 (having directional antennas 28a to 28c corresponding to
the sectors) that transmits a transmission signal input from the
analog circuit section (26a to 26c) to radio space, while receiving
a signal in the radio space, respectively.
[0216] Described next is a specific internal configuration of the
transmission circuit section (24a to 24c). FIG. 11 is a block
diagram illustrating a specific configuration of the transmission
circuit section as shown in FIG. 10. The transmission circuit
section 24 (reference numerals 24a to 24c in FIG. 10) performs
coding and modulation on the data channel and pilot channel input
from the MAC section 10, while modulating the SCH data as described
previously to multiply the sector specific code, and multiplexes
the SCH, data channel, and pilot channel on a resource block to
transmit in an assigning section, based on a control signal from
the MAC section.
[0217] "SCH data" in FIG. 11 indicates code data obtained by
multiplying the sector common code (see FIG. 8A) by the cell
specific code (see FIG. 9). Then, the code data is multiplied by
the sector specific code (see FIG. 8B) in the physical layer
section of each sector and transmitted.
[0218] The transmission circuit section 24 (24a to 24c) as shown in
FIG. 11 has a signal processing section 50 (50a to 50c) that
performs signal processing of transmission data on the data channel
input from the MAC section 10 for each resource block, and a SCH
data processing section 60 that performs modulation and
multiplication of the sector specific code on the SCH data also
input from the MAC section 10. Further, the section 24 has a pilot
channel data processing section 70 that performs modulation and
multiplication of a sector specific orthogonal code on the pilot
channel data also input from the MAC section 10, and an assigning
section 81 that assigns an output signal from the signal processing
section 50 (50a to 50c), an output signal from the SCH data
processing section 60, and an output signal from the pilot channel
data processing section 70 to each subcarrier of a resource
block.
[0219] The section 24 further has a spreading code multiplying
section 82 that multiplies a spreading code using a spreading code
generated in a spreading code generating section 83, an IFFT
section (Inverse Fast Fourier Transform) section 84 that transforms
a data signal sequence in the frequency domain subjected to
spreading processing into a time waveform, a P/S transform section
85 that performs parallel/serial transform on an output from the
IFFT section 84, a GI inserting section 86 that inserts a GI into
an output signal of the P/S transform section 85, and a D/A
conversion section 87 that converts an output signal of the GI
inserting section 86 from a digital signal to an analog signal.
Both of the assigning section 81 and spreading code multiplying
section 82 perform the processing based on control information from
the MAC section 10. The assigning section 81 assigns each physical
channel to a desired subcarrier. The spreading code multiplying
section 82 multiplies physical channels except the SCH by spreading
codes.
[0220] The signal processing section 50 (50a to 50c) is comprised
of an error correcting coding section 51 that performs error
correcting coding on transmission data, an S/P transform section 52
that performs parallel/serial transform on an output of the error
correcting coding section, and a modulation section 53 that
performs modulation processing such as BPSK, QPSK, 16QAM and the
like on an output of the S/P transform section.
[0221] Further, the SCH data processing section 60 is comprised of
a SCH modulation section 61 that performs modulation processing on
SCH data input from the MAC section 10, a multiplying section 62
that multiplies an output of the SCH modulation section by a sector
specific code, and a sector specific code generating section 63
that generates (or stores) the sector specific code.
[0222] Furthermore, the pilot channel data processing section 70 is
comprised of a pilot data modulation section 71 that performs
modulation processing on pilot data input from the MAC section 10,
a multiplying section 72 that multiplies an output of the pilot
data modulation section 71 by a sector specific code, and a code
generating section 73 that generates (or stores) the sector
specific code.
[0223] An output of the signal processing section 50 (50a to 50c)
is assigned to an appropriate signal in the assigning section 81
for assigning to an appropriate subcarrier based on control
information notified from the transmission circuit control section
(reference numeral 16 in FIG. 10) of the MAC section 10, and output
to the IFFT section 84.
[0224] In addition, when code 1 as shown in FIG. 8B is used as a
sector specific code, since all the codes are "1", it is possible
to omit the multiplying sections (62, 72) and code generating
sections (63, 73). Further, when the SCH data is a fixed value as
described previously, the MAC section 10 does not need to always
output the SCH data for each SCH transmission. Therefore,
substituting for the SCH data processing section 60, a SCH data
storing section or the like may be provided to store the SCH data.
By this means, it is possible to read the SCH data from the SCH
storing section whenever transmitting the SCH to multiplex the data
channel and pilot channel in the assigning section 81.
[0225] An output of the D/A conversion section 87 is transmitted to
the atmosphere as a radio signal from the antenna section 28
(directional antennas 28a to 28c in FIG. 10) through the analog
circuit section (reference numerals 26a to 26c in FIG. 10) that
performs frequency conversion to a radio frequency.
[0226] As described above, the transmitter of the base station that
controls a plurality of sectors multiplies the same SCH data by
respective sector specific codes to concurrently transmit from
antennas corresponding to the sectors. By this means, it is
possible to receive the SCH with high quality frequency
characteristics. As well as such reception, it is possible to
select an optimal cell at the time of receiving the SCH, and also
select a sector providing good reception.
[0227] Described next is a multicarrier receiver. FIG. 12 is a
block diagram illustrating a configuration of a multicarrier
receiver according to the invention. The multicarrier receiver
corresponds to a cellular telephone terminal, PDA terminal,
portable personal computer, and the like. As shown in the figure,
the multicarrier receiver has an antenna section 100, analog
reception circuit section 101, A/D conversion section 102, timing
detecting section 103, GI removing section 104, S/P
(Serial/Parallel) transform section 105, FFT section 106, spreading
code multiplying section 107, subcarrier compensation section 108,
demodulation section 109, error correcting decoding section 110,
spreading code generating section 111, and SCH signal processing
section 200. The SCH signal processing section 200 has a
despreading section 210 for sector identification, a sector power
determining section 220, and a SCH data demodulation section 230
that demodulates cell specific information.
[0228] The multicarrier receiver (hereinafter, simply referred to
as a "receiver" as appropriate) basically executes a cell search
including sector identification according to the flowchart as shown
in FIG. 2. First, the receiver detects SCH timing from a reception
signal for temporal synchronization with a signal transmitted from
the base station and compensation for a shift of the frequency. In
other words, the antenna section 100 receives a radio signal
transmitted from the base station, and the analog reception circuit
section 101 converts the received radio signal from the radio
frequency band to a baseband frequency band. Then, the A/D
(Analog/Digital) conversion section 102 converts the analog signal
with the converted baseband frequency band into a digital
signal.
[0229] Next, to acquire symbol synchronization, the timing
detecting section 103 performs detect ion processing of the SCH
from reception data that is converted into digital data in the A/D
conversion section 102. Described herein is a circuit configuration
of the timing detecting section 103.
[0230] FIG. 13 is a block diagram showing a configuration example
of the timing detecting section 103. The timing detecting section
103 has functions of timing detection and frequency error
detection. As shown in FIG. 13, the timing detecting section 103
has a delay section 301, complex conjugate calculating section 302,
multiplier 303, averaging section 304, peak detecting section 305,
and arctangent calculating section 307 as a frequency error
detecting section.
[0231] As can be seen from the configuration, the timing detecting
section 103 multiplies a complex conjugate of a signal obtained by
delaying the received signal by 1/2 effective symbol by reception
data, and thus, is a circuit that detects a peak when the same
waveform of 1/2 effective symbol is repeated. In other words, the
peak is detected at the timing of the SCH data using odd-numbered
subcarriers (subcarrier indexes 1, 3, 5, . . . , 2n+1) from the
low-frequency side as described previously. A plurality of peaks is
detected by signals from a plurality of cells, and generally, the
mobile station determines the timing with the highest peak of an
absolute value or real part of the correlation value to be timing
of the SCH transmitted from the nearest cell, and starts the
operation of connecting to the base station.
[0232] In the case of the frame structure as shown in FIG. 24, it
is possible to acquire synchronization at a time interval a half
the frame that is an interval at which the SCH is arranged. By
concurrently acquiring synchronization with a SCH symbol, the
mobile station acquires symbol synchronization. Further, by fixing
a position of a SCH symbol in a sub-frame, it is possible to
concurrently acquire synchronization at a sub-frame interval.
[0233] In FIG. 12, after the timing detecting section 103 acquires
synchronization in a symbol period, the GI removing section 104
removes a GI portion added to the front of an effective symbol from
each symbol in accordance with the symbol period The symbol with
the GI removed therefrom is transformed in the S/P
(Serial/Parallel) transform section 105 from a serial signal to a
parallel signal, and subjected to FFT processing in the FFT section
106.
[0234] The data of the SCH symbol portion is input to the SCH
signal processing section 200 for processing the SCH data from the
FFT section 106. Further, the pilot channel and data channel
including the control information to the mobile station are input
to the spreading code multiplying section 107 from the FFT section
106. When a mobile station first connects to a base station, the
mobile station does not have the cell specific information and
sector specific information, and the processing in the SCH signal
processing section 200 is given a priority and performed. In the
SCH signal processing section 200, the data of the SCH symbol is
concurrently input to three multiplying sections 212 corresponding
to the number of sectors in this Embodiment and the SCH data
demodulation section 230 from the FFT section 106.
[0235] Based on the control information from the MAC section (not
shown), the multiplying section 212 performs multiplication of the
sector specific code (FIG. 8B) generated or stored in the sector
specific code generating section 211. Each multiplying section 212
calculates a complex conjugate of the sector specific code input
from the sector specific code generating section 211, and
multiplies the odd-numbered subcarriers (subcarrier indexes 1, 5,
9, . . . ) of the SCH symbol input from the FFT section 106 by a
code of the complex conjugate so as to correspond to subcarriers
multiplied by the sector specific code when the base station
transmits. Further, the data multiplied by the complex conjugate is
input to an adding section 214 and subjected to in-phase addition.
In other words, data of three subcarriers multiplied by the complex
conjugate is added among six subcarriers that is the repeated cycle
of the sector specific code. The aspect of this processing is shown
by processing 1 and processing 2 in FIG. 14.
[0236] FIG. 14 is a diagram showing the specific content of the
despreading processing for sector identification. In FIG. 14, px is
the sector specific code as shown in FIG. 8B, and x represents an
index of the sector. Further, f represents a propagation path, and
is fixed in a band of nine subcarriers that is a subcarrier
interval for performing despreading.
[0237] Further, the sector power determining section 220 receives
the root mean square of data that is one-third of the data
subjected to despreading in FIG. 12. The root-mean-square data from
each sector is used as a criterion of reception power determination
in the sector power determining section 220.
[0238] The sector power determining section 220 compares data
indicating the addition result input from the adding section 214
corresponding to each of three sectors with one another. Then, the
section 220 determines a sector providing the highest reception
power i.e. a sector providing the most excellent reception
environment to connect. The sector detection result is notified to
the MAC section by a control signal.
[0239] Meanwhile, the SCH symbol data (that is the data obtained by
multiplying the sector common code by the cell specific
information) input to the SCH data demodulation section 230 from
the FFT section 106 in FIG. 12 is demodulated by a demodulation
method as shown in FIG. 15.
[0240] FIG. 15 is a diagram to explain demodulation processing of
the cell specific information. The processing in FIG. 15 is such
processing that in a pair of subcarriers, the subcarrier on the
high-frequency side is multiplied by a complex conjugate of the
cell specific code assigned to the subcarrier on the low-frequency
side, and that the relative phase difference information (i.e. cell
specific information) is thereby demodulated.
[0241] The SCH data demodulation section 230 in FIG. 12 multiplies
a complex conjugate of the data of an odd-numbered SCH subcarrier
(subcarrier indexes 1, 5, 9 . . . ) of the SCH symbol from the
low-frequency side by the data of the even-numbered SCH subcarrier
(subcarrier indexes 3, 7, 11 . . . ) on the high-frequency
side.
[0242] As shown in FIG. 15, an ideal value of the multiplication
result is formed of the propagation path f between each sector and
the mobile station and the cell specific code c. c is a complex
number with the amplitude of "1" and readily obtained by deriving
the phase. Herein, x of fxy represents a sector ID (that
corresponds to a sector identification number, and also referred to
as a sector index), and y is assumed to be an index in the
frequency domain in the propagation paths of two subcarriers to
multiply by each other. Further, the propagation paths of two
subcarriers to multiply are assumed to be the same.
[0243] In demodulating the cell specific information, the SCH data
demodulation section 230 generates replicas of candidate codes (Cn)
having the possibility of being used in the base station for
notification of the cell specific information from code sequences
of the cell specific information. Then, it is possible to determine
and acquire the cell specific information also by calculating
cross-correlation with the result actually calculated by the method
as described previously. It is actually desired to make a
determination by such cross-correlation processing.
[0244] In this Embodiment, the SCH symbol is provided in two
positions in a frame, and synchronization is acquired by a period
half the frame in symbol synchronization by delay correlation. To
acquire synchronization in a frame period, the information
indicated by the cell specific code c described previously includes
information indicating any one of the SCHs in the frame. Further,
information may be assigned to a symbol whose temporal position is
fixed from the SCH.
[0245] Further, as described previously, since the spreading code
information has the extremely high number of codes depending on the
code length forming the information, there is a case that the
information amount lacks to notify the cell specific information.
In other words, depending on the number of subcarriers used in the
SCH, such a case is considered that the information amount is not
enough to notify the cell specific information, and that
information indicating a group obtained by grouping cells is
notified, instead of the information indicating a spreading code
specific to the cell. In this case, it is necessary to make the
following detection on all conceivable spreading codes of the
grouped cells.
[0246] In other words, the mobile station uses the pilot channel
for cell spreading code detection, and generates a replica signal
by multiplying the pilot channel by codes (cell specific code and
orthogonal code) multiplied by the pilot channel. The mobile
station calculates cross-correlation between the generated replica
signal and an actual received signal on spreading code candidates
for all the cells in the cell group as described previously. After
finishing all the correlation detection, the mobile station
determines a spreading code candidate showing the highest
correlation value as a spreading code used in the nearest base
station. This is a typical method. However, in this Embodiment, by
using only the orthogonal code of the sector determined in sector
determination as described previously, it is possible to reduce the
cross-correlation detection processing.
[0247] Desirable as a code sequence of the cell specific code c is
a code excellent in cross-correlation characteristics with codes
indicating information of other cells. More specifically, desired
are Walsh-Hadamard code sequences, Generalized Chirp Like (GCL)
sequence codes and the like.
[0248] The SCH data demodulated as described above is sent to the
MAC section. The MAC section performs reception according to the
information, and is capable of connecting to the base station. In
general, the following configuration is required to receive a data
channel transmitted from the base station. In addition, it is
possible to use reception circuitry as well as the following
circuitry.
[0249] In FIG. 12, the data channel and pilot channel subjected to
the FFT processing in the FFT section 106 are being spread by the
spreading code specific to the cell included in the cell specific
information. Therefore, the spreading code multiplying section 107
multiplies a complex conjugate of the spreading code specific to
the cell. The spreading code specific to the cell is output from
the spreading code generating section 111. The spreading code
generating section 111 selects a spreading code of a desired cell
from a plurality of spreading codes by a control signal from the
higher layer.
[0250] Further, the spreading code generating section 111 also
selects an orthogonal code specific to the sector at the same time
to input to the spreading code multiplying section 107. The input
orthogonal code is multiplied by the pilot channel in the spreading
code multiplying section 107. The data multiplied by the code is
subjected to subcarrier compensation in the subcarrier compensation
section 108 using the pilot channel as a reference signal, and
input to the demodulation section 109. The demodulation section 109
demodulates the data channel, and further, the error correcting
decoding section 110 performs error correcting decoding.
Embodiment 3
[0251] Embodiment 3 of the invention will be described below. In
Embodiment 2 shown above, the SCH is inserted for each frame (FIG.
24), and therefore, a null subcarrier is set every two subcarriers
(FIG. 25).
[0252] In this Embodiment, as shown in FIG. 16, subcarriers except
a subcarrier (DC subcarrier) in the center of the band are SCH
subcarriers. Further, as an arrangement of SCH symbols in a frame
shown in FIG. 19, the same SCH symbols are arranged in two
consecutive symbols in a specific temporal position in the frame.
FIG. 19 is a diagram illustrating a frame structure in Embodiment
3.
[0253] In other words, in this Embodiment, as compared with
Embodiment 2 shown above, the number of SCH subcarriers is twice,
and the code length usable in the cell specific information is
increased. Accordingly, it is possible to transmit and receive a
SCH signal with a larger information amount.
[0254] FIG. 16 is a diagram showing subcarriers assigned the SCH.
In this Embodiment, the SCH is configured on the frequency axis as
shown in FIG. 16. In other words, FIG. 16 shows the diagram with
attention drawn to SCH data of a plurality of symbols constituting
a frame of a signal transmitted from the based station, and the
vertical axis represents the frequency axis, while the horizontal
axis represents the time axis. With respect to each subcarrier, as
shown in FIG. 16, subcarriers except the center subcarrier (DC
subcarrier) are used as subcarriers to assign the SCH data.
[0255] The following descriptions are made assuming that the number
of subcarriers (SCH subcarriers) constituting the SCH is 2n. FIGS.
17A and 17B are diagrams illustrating a data structure of the SCH
in Embodiment 3. FIG. 17A is a diagram showing an arrangement on
the frequency axis of the sector common code to be multiplied by
the SCH, and FIG. 17B is a diagram showing three sector specific
codes.
[0256] FIG. 17A shows a sector common code. Each SCH subcarrier
(subcarrier indexes 1, 2, 3, . . . ) is assigned S.sub.0. S.sub.0
is an arbitrary value expressed by A*exp(j.omega.). Herein, A
represents the amplitude, j represents an imaginary unit, and
.omega. represents a phase. Sector common code S.sub.0 is common in
all the sectors (three sectors in this Embodiment) within each
cell. As in Embodiment 2 described previously, using S.sub.0 known
to the mobile station enables S.sub.0 to be used in decoding the
cell specific code multiplied by the SCH.
[0257] FIG. 17B shows an example related to the case that the
sector specific codes are used in three sectors in Embodiment 3.
The codes are specific to respective sectors in the same cell, and
codes 1 to 3 support three sectors in Embodiment 3. It is assumed
that the mobile station and base station beforehand know about
correspondence between the codes and sector IDs in the same cell.
In code sequences to be multiplied by SCH subcarriers as the sector
specific code, phase differences from odd-numbered SCH subcarriers
(subcarrier indexes 1, 3, 5 . . . ) from the low-frequency side to
even-numbered subcarriers (subcarrier indexes 2, 4, 6, . . . ) are
0.degree., 0.degree. and 0.degree. in each sector. Phase
differences from even-numbered SCH subcarriers to odd-numbered
subcarriers are 0.degree., 120.degree. or 240.degree. in each
sector. Each code is a code with the amplitude of "1". Further,
since these code sequences are of 6-chip reuse (one period is six
chips), the number 2n of SCH subcarriers is an integral multiple of
"6".
[0258] With attention drawn to one reuse part (six chips) of these
three code sequences, when a complex conjugate of an arbitrary code
sequence is multiplied by each code sequence and consecutive three
chips are added every four chips, the sum is "0" in the case of
multiplying code sequences except the selected arbitrary code
sequence, while being "3" in the case of multiplying the arbitrary
code sequence.
[0259] For example, the case is considered of (exp(j0.pi.),
exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.)) of
code 1, (exp(j0.pi.), exp(j0.pi.), exp(j2.pi./3), exp(j2.pi./3),
exp(j4.pi./3), exp(j4.pi./3)) of code 2, and (exp(j0.pi.),
exp(j0.pi.), exp(j4.pi./3), exp(j4.pi./3), exp(j2.pi./3),
exp(j2.pi./3)) of code 3. When code 2 is selected as an arbitrary
code, a complex conjugate of code 2 is (exp(j0.pi.), exp(j0.pi.),
exp(-j2.pi./3), exp(-j2.pi./3), exp(-j4.pi./3), exp(-j4.pi./3)).
Codes obtained by multiplying codes 1 to 3 by the complex conjugate
of code 2 are respectively (exp(j0.pi.), exp(j0.pi.),
exp(-j2.pi./3), exp(-j2.pi./3), exp(-j4.pi./3), exp(-j4.pi./3)),
(exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.), exp(j0.pi.),
exp(j0.pi.)), and (exp(j0.pi.), exp(j0.pi.), exp(j2.pi./3),
exp(j2.pi./3), exp(-j2.pi./3), exp(-j2.pi./3)).
[0260] Further, when odd-numbered chips and even-numbered chips are
subjected to vector addition, the results are (0,0), (3,3) and
(0,0). Thus, the code sequences have characteristics that the sum
of the codes except code 2 selected as an arbitrary code is "0".
This means that in concurrently transmitting the SCH of the same
data multiplied by an orthogonal code (FIG. 17B) corresponding to
each sector from each sector in the same cell, a mobile station
receiving the SCH performs despreading of the SCH every three
predetermined chips, and is thereby capable of separating a signal
from an arbitrary sector from an interfering signal from an
adjacent sector.
[0261] FIG. 18 is a diagram illustrating an arrangement of the cell
specific code in Embodiment 3. Since the code sequence as shown in
FIG. 18 is a code sequence to transmit the cell specific
information, a different code sequence is used in each cell, while
the same code sequence is used among sectors in the same cell. The
cell specific information is information of a specific spreading
code used in the cell, information of the number of antennas of the
base station and system bandwidth, and the like, and includes
information required for a mobile station to first connect to the
base station.
[0262] However, the spreading code information is an extremely high
number of codes depending on the code length, and there is a case
that the code as shown in FIG. 18 lacks in the information amount.
In such a case, it is possible to group some cells, and generate a
code sequence by the same information in the cells belonging to the
group. In this case, since the spreading code specific to the cell
is not completely identified from the information of the SCH, an
ultimate cell specific spreading code is identified using a pilot
channel multiplied by the spreading code.
[0263] The code sequence as shown in FIG. 18 is formed using six
chips as a group from the low-frequency side. In the six chips,
odd-numbered SCH subcarriers are assigned the same code, while
even-numbered SCH subcarriers are assigned a code obtained by
multiplying the code assigned to the odd-numbered subcarriers by
the cell specific code. The codes assigned to odd-numbered
subcarriers are the same among six chips, but do not need to be the
same as those used in other six chips. Each chip forming a code
sequence has the amplitude of "1". Further, as the code length,
when the number of SCH subcarriers is 2n, a code sequence with the
code length of n is required to form the even-numbered subcarriers.
[0207] Since the code length is dependent on the number of SCH
subcarriers, generally, it is possible to generate the high number
of code sequences with good correlation characteristics when the
number of SCH subcarriers is sufficiently high. Therefore, as
described previously, instead of the code sequence indicating a
cell ID group, it is made possible to form a code sequence
containing information directly indicating the cell ID.
[0264] The same code is as signed to two consecutive symbols as the
code to multiply the subcarriers constituting the SCH as descried
above. Three kinds of code sequences as described above are code
sequences constituting the SCH in Embodiment 3, and the SCH
multiplied by the code sequence is transmitted from a transmitter
of each sector.
[0265] A transmission method of the SCH and a configuration of a
transmitter in this Embodiment are the same as in Embodiment 2
shown above, and descriptions thereof are omitted. The different
respects from Embodiment 2 are the code (see FIGS. 17 and 18)
generated in the sector specific code generating section 63 in the
SCH data generating section 60 and the SCH data input from the MAC
section 10. Further, in this Embodiment, the same SCH symbol is
transmitted in two consecutive symbols (see FIG. 19). FIG. 19 is a
diagram illustrating an arrangement of the SCH in a frame period. A
receiver configuration and a reception method in this Embodiment
are basically the same as in the Embodiment shown above. In
addition, the timing detecting section 103 (FIG. 13) in Embodiment
2 delays a received signal by 1/2 effective symbol period to
multiply by the signal, and detects a position of the SCH symbol,
but in this Embodiment, a received symbol is delayed by one symbol
to multiply the signal, and a symbol of the SCH is thereby
detected.
[0266] Procedures of a cell search will be described below. A
mobile station receives a radio signal transmitted from the base
station in the antenna section 100 as in Embodiment 2. The analog
reception circuit section 101 converts the received radio signal
from the radio frequency band to a baseband frequency band. The A/D
(Analog/Digital) conversion section 102 converts the signal with
the converted baseband frequency band from the analog signal into a
digital signal.
[0267] Next, the timing detecting section 103 performs the SCH
detection processing to acquire symbol synchronization based on
reception data that is converted into digital data in the A/D
conversion section 102. Then, the timing detecting section 103
multiplies a complex conjugate of a signal obtained by delaying the
received signal by one symbol by reception data, and thereby,
detects the peak when the waveform of the same symbol is repeated.
In other words, the peak is detected at the timing of receiving two
symbols of the same SCH symbol as described previously. A plurality
of peaks is detected by signals from a plurality of cells, and
generally, the mobile station determines the timing with the
highest peak of the correlation value to be timing of the SCH
transmitted from the nearest cell, and starts the operation of
connecting to the base station.
[0268] In this Embodiment, since the SCH of two symbols are
arranged at the end of a frame, by detecting a correlation peak of
the SCH signal by the method as described previously, it is
possible to acquire frame synchronization. By concurrently
acquiring synchronization with a SCH symbol, the mobile station
acquires symbol synchronization. Then, after finishing acquisition
of synchronization in a symbol period, the GI removing section 104
removes a GI portion added to the front of an effective symbol from
each symbol in accordance with the symbol period The symbol with
the GI removed therefrom is transformed in the S/P
(Serial/Parallel) transform section 105 from a serial signal to a
parallel signal, and subjected to FFT processing in the FFT section
106.
[0269] The data of the SCH symbol portion is input to the SCH
signal processing section 200 for processing the SCH data from the
FFT section 106. Further, the pilot channel and data channel
including the control information to the mobile station are input
to the spreading code multiplying section 107 from the FFT section
106. When a mobile station first connects to a base station, the
mobile station does not have the cell specific information and
sector specific information, and the processing in the SCH signal
processing section 200 is given a priority and performed. In the
SCH signal processing section 200, the data of the SCH symbol is
input to three multiplying sections 212 corresponding to the number
of sectors in this Embodiment and the SCH data demodulation section
230 from the FFT section 106. The multiplying section 212 receives
the sector specific code generated or stored in the sector specific
code generating section 211 based on the control information from
the MAC section (not shown).
[0270] Each multiplying section 212 calculates a complex conjugate
of the sector specific code input from the sector specific code
generating section 211, and multiplies each of the odd-numbered
subcarriers (subcarrier indexes 1, 3, 5, . . . ) of the SCH signal
input from the FFT section 106 by a code of the complex conjugate
so as to correspond to a subcarrier multiplied by the sector
specific code when the base station transmits. This processing is
shown by processing 1 in FIG. 20. FIG. 20 is a diagram illustrating
a specific content example of the correlation calculation
processing using the sector specific code. The data multiplied by
the complex conjugate is input to the despreading section 210 and
subjected to despreading processing. The despreading processing is
performed by adding data of three subcarriers multiplied by the
complex conjugate among six subcarriers that are the repeated cycle
of the sector specific code (see processing 2 in FIG. 20).
[0271] Further, the sector power determining section 220 receives
the root mean square of data that is one-third of the data
subjected to the despreading processing. The root-mean-square data
from each sector is used as a criterion of reception power
determination in the sector power determining section 220. In FIG.
20, px is the sector specific code as shown in FIG. 17B, and x
represents an index of the sector. Further, f represents a
propagation path, and is fixed in a band of five subcarriers that
is a subcarrier interval for performing despreading.
[0272] The sector power determining section 220 receives the values
from the de spreading sections 210 corresponding to three sectors
to compare with one another. Then, the section 220 determines a
sector providing the highest reception power i.e. a sector
providing the most excellent reception environment to connect. The
determination is notified to the MAC section as a control
signal.
[0273] Meanwhile, the SCH symbol data input to the SCH data
demodulation section 230 from the FFT section 106 is demodulated by
a demodulation method as shown in FIG. 21. FIG. 21 is a diagram
illustrating a demodulation method of the cell specific information
in Embodiment 3. The SCH data demodulation section 230 multiplies a
complex conjugate of data of an odd-numbered SCH subcarrier
(subcarrier indexes 1, 3, 5 . . . ) of the SCH symbol from the
low-frequency side by data of the even-numbered SCH subcarrier
(subcarrier indexes 2, 4, 6 . . . ) on the high-frequency side.
[0274] As shown in FIG. 21, an ideal value of the multiplication
result is formed of the propagation path f between each sector and
the mobile station and the cell specific code c. c is a complex
number with the amplitude of "1" and readily obtained by deriving
the phase. Herein, x of fxy represents a sector ID, and y is
assumed to be an index in the frequency domain in the propagation
paths of two subcarriers to multiply by each other. Further, the
propagation paths of two subcarriers to multiply are assumed to be
the same.
[0275] In demodulating the cell specific information, the SCH data
demodulation section generates replicas of candidates having the
possibility of being used in the base station for notification of
the cell specific information from code sequences of the cell
specific information as described below, and it is possible to
determine and acquire the cell specific information also by
calculating cross-correlation with the result actually calculated
by the method as described previously. Further, in Embodiment 3,
since the same SCH symbol is transmitted in two consecutive
symbols, by performing the above-mentioned demodulation
successively in a two-symbol period, it is possible to perform
demodulation with higher reliability.
[0276] The SCH data demodulated as described above is sent to the
MAC section. The MAC section performs reception according to the
information, and is capable of connecting to the base station. In
Embodiment 3, the SCH is arranged in last two symbols of a frame
period. By this means, when the SCH is arranged on the time axis
with periodicity, while the same SCH symbol is transmitted in two
consecutive symbols, since the information amount increases, the
receiving side is capable of performing demodulation with higher
reliability. Further, since it is possible to transmit the SCH
using subcarriers of the entire frequency band, when different
information is transmitted for each symbol, it is possible to
increase the code length usable in transmission of the sector
specific information (relative phase difference information), and
to transmit a larger amount of cell specific information.
Embodiment 4
[0277] Embodiment 4 of the invention will be described below. This
Embodiment descries an example of performing timing detection of
the SCH in the first step in a cell search by a cross-correlation
method using the time waveform of a replica of the sector specific
code.
[0278] In Embodiments 2 and 3 shown above, in the first step of the
3-step cell search as described previously, symbol synchronization,
frequency offset, and 1/N frame timing is detected using time
correlation detection of the SCH. In this Embodiment, timing
detection of the SCI in the first step in the 3-step cell search as
described previously is performed by cross-correlation processing
between a reception signal and a replica signal generated in a
mobile station. To enable such detection, it is necessary to devise
a data structure of the SCH.
[0279] The SCH position detection method in the first step shown in
this Embodiment can be actualized by using the frame structure and
arrangement of the SCH as shown in Embodiment 2 or 3 without
modification. The second or third step can be implemented also as
in the Embodiment shown above.
[0280] In addition, also in the case of adopting a data structure
of the SCH as in this Embodiment, the respect that the SCH is
periodically arranged in a frame period is the same as in the
Embodiments shown above. Accordingly, it is also possible to
execute SCH position detection (i.e. establishment of symbol
synchronization by auto-correlation using the repeated waveform)
using the auto-correlation method as in Embodiments 2 and 3. In
addition, in detection of a SCH position using cross-correlation, a
shaper correlation peak is obtained, and it is possible to detect
the SCH position with higher accuracy.
[0281] The SCH timing detection method in the first step in this
Embodiment is a detection method applying a detection method
designated as the cross-correlation detection (or replica
detection) method. As described above, as compared with the
auto-correlation detection method using consecutive SCH waveforms
as shown in Embodiments 2 and 3, it is possible to detect a
detection pea k sharply. In other words, as compared with
Embodiments 2 and 3 shown above, this Embodiment is capable of
using a different method in the first step of the 3-step cell
search. Accordingly, it is possible to detect the SCH timing with
higher accuracy.
[0282] In this Embodiment, as in Embodiment 2, an OFDM
communication scheme is used as a downlink communication scheme.
Further, structures of a communication frame and resource block are
assumed to have the same formats as shown in FIGS. 22 and 28.
First, with respect to a synchronization physical channel (SCH)
that is a feature in this Embodiment, the specific structure will
be described.
[0283] As in Embodiment 2, FIGS. 29A to 29C are diagrams to explain
a data structure of the SCH concurrently transmitted from three
sectors in the same cell. FIG. 29A is a diagram showing an
assignment of a sector common code on the frequency axis, FIG. 29B
is a diagram showing structures of three sector specific codes, and
FIG. 29C is a diagram showing the basic concept of generation of
the sector specific code, and shows vectors on the complex phase
plane. The basic structure is the same as in Embodiment 2, but part
of structural code differs to enable the cross-correlation
detection method to be applied to the first step of the 3-step cell
search.
[0284] A signal as shown in FIG. 29A indicates a sector common code
constituting the SCH. SCH subcarriers are assigned S.sub.01 to
S.sub.0n/6 every six chips. S.sub.0 is an arbitrary value expressed
by A*exp(j.omega.). Herein, A represents the amplitude (in
addition, in the invention, the explanation is made with the
amplitude A being "1"), j represents an imaginary unit, and .omega.
represents a phase.
[0285] One of features of this Embodiment is that the sector common
code is a common code in all the cells, as distinct from
Embodiments 2 and 3. In other words, the sector common code is also
the cell common code. Another feature is that among cell specific
codes, a code element as a phase reference is also common in all
the cells. By this means, it is possible to perform correlation
detection using replicas of the sector specific codes.
[0286] In other words, the SCH is configured by multiplying three
kinds of codes (sector common code, sector specific code and cell
specific code). Herein, the sector common code is made common in
cells, and among the cell specific codes, a code element as a phase
reference is also made common in the cells. With respect to a
subcarrier multiplied by the code element as a phase reference,
multiplied codes are the (sector common code common in all the
cells), (sector specific code) and (cell specific code common in
all the cells), and substantially, the (codes common in all the
cells) are multiplied by the (sector specific code). In other
words, with respect to the subcarrier multiplied by the code
element as a phase reference, three kinds of codes are multiplied,
and among the codes, two codes are common in all the cells.
Accordingly, a different code is only the sector specific code.
This means enabling correlation detection using replicas of the
sector specific codes.
[0287] Therefore, the receiver side prepares a time waveform of a
replica code of the sector specific code corresponding to each
sector, multiplies a reception signal prior to FFT by the time
waveform of the replica signal to detect a correlation peak, and is
thereby capable of detecting the SCH timing in the reception signal
with high accuracy. Accordingly, it is made possible to perform
subsequent sector identification and cell identification
efficiently. In addition, even when such a specialized SCH
structure is adopted, the SCH is periodically arranged in a frame
period, which is not different, and it is also possible to perform
position detection by the auto-correlation method (i.e. the method
of detecting correlation between a signal delayed from a reception
signal by a predetermined period and an original reception
signal).
[0288] A specific example will be described below with reference to
drawings. The sector specific code is described first. FIG. 29B
shows an example of the sector specific codes (herein, the number
of sectors is "3"). Herein, the same codes as shown in Embodiment 2
are used.
[0289] Described next is a code sequence to transmit the cell
specific information. FIG. 30 is a diagram illustrating a structure
on the frequency axis of a code sequence to transmit the cell
specific information. In this Embodiment, the cell specific
information is transmitted using the code sequence as shown in FIG.
30, and as distinct from Embodiments 2 and 3, the information is
formed of a code sequence different between cells, and another code
sequence common in cells. More specifically, c.sub.ik (k is a
natural number from 1 to n/6, n is the number of SCH subcarriers)
as shown in FIG. 30 is the "code common in cells" and c.sub.l (l is
a natural number from 1 to n/2) is the "code specific to the
cell".
[0290] The code sequence of FIG. 30 is configured sequentially
using six chips as a group from the low-frequency side. In six
chips, odd-numbered SCH subcarriers (subcarrier indexes 1, 5, 9)
are assigned the "code common in cells". Even-numbered SCH
subcarriers (subcarrier indexes 3, 7, 11) are assigned a code
obtained by multiplying the code assigned to the odd-numbered
subcarriers by the cell specific code (i.e. a code having phase
difference information with respect to a phase reference code). The
codes assigned to odd-numbered subcarriers are the same among six
chips, but do not need to be the same as those used in other six
chips.
[0291] Three kinds of code sequences as shown above are code
sequences constituting the SCH, and the SCH is configured by
multiplying these code sequences. Then, a transmitter of each
sector transmits a multicarrier signal containing the SCH.
[0292] A transmission method of the SCH and a configuration of a
transmitter in this Embodiment are the same as in Embodiment 2
shown above, and descriptions thereof are omitted. The different
respect is a code generated in the sector specific code generating
section 63 in the SCH data processing section 60 (see FIGS. 29 and
30).
[0293] A receiver configuration and a reception method in this
Embodiment are basically the same as in the Embodiment shown above
except the first step. The timing detecting section 103 (FIG. 13)
in Embodiment 2 shown above delays a received signal by 1/2
effective symbol period to multiply by the signal, and detects a
position of the SCH symbol. In this Embodiment, a SCH symbol is
detected by calculating a cross-correlation value between a
received signal and a replica signal of the SCH symbol generated or
stored in a mobile station. Procedures of a cell search will be
described below.
[0294] A mobile station receives a radio signal transmitted from
the base station in the antenna section 100 as in Embodiment 2. The
analog reception circuit section 101 converts the received radio
signal from the radio frequency band to a baseband frequency band.
The A/D (Analog/Digital) conversion section 102 converts the signal
with the converted baseband frequency band from the analog signal
into a digital signal. Next, the timing detecting section 103
performs the SCH detection processing to acquire symbol
synchronization, based on reception data that is converted into
digital data in the A/D conversion section 102.
[0295] FIG. 31 is a block diagram illustrating a configuration
(including a correlator) of a symbol synchronization circuit in
this Embodiment. The symbol synchronization circuit in FIG. 31 has
an m-stage shift register 400, adder 402, and multiplier 404. In
the symbol synchronization circuit in FIG. 31, a reception signal
is input to the m-stage shift register 400. A signal output from
the shift register 400 is multiplied by a complex conjugate of a
replica signal (r.sub.m: m is a natural number) generated by the
mobile station or beforehand stored in the mobile station.
[0296] The replica signal is derived from a value of multiplication
by three codes constituting the SCH subcarrier as described
previously, and data on the odd-numbered SCH subcarrier (index
numbers 1, 5, 9 . . . ) is used. Since the reception signal is data
in the time-axis direction, a signal in the time-axis direction is
calculated as the replica signal from the data using the
above-mentioned SCH subcarrier.
[0297] The data of the odd-numbered SCH subcarrier is used for
generation of such a replica signal. As described above, the
odd-numbered SCH subcarrier is multiplied by the sector common code
S.sub.0 (see FIG. 29A) common in all the cells and a code (code as
a phase reference) indicating part of the cell specific information
common in all the cells as shown in FIG. 30. In other words, in the
odd-numbered SCH subcarriers, the sector specific code as shown in
FIG. 29B is only different between cells. Accordingly, in this
Embodiment, three replica signals are generated corresponding to
the number of sector specific codes, a reception signal and
cross-correlation values are monitored, and it is thereby possible
to detect a SCH time position.
[0298] In addition, as in Embodiments 2 and 3, a plurality of peaks
is detected by signals from a plurality of cells, and generally,
the mobile station determines the timing with the highest peak of
the correlation value to be timing of the SCH transmitted from the
nearest cell, and starts the operation of connecting to the base
station.
[0299] As described above, in the first step of the cell search in
this Embodiment, symbol synchronization is achieved using
cross-correlation values of a reception signal and replica signals.
The second step and third step in the cell search method in this
Embodiment are the same as in Embodiment 2 shown above, and
descriptions thereof are omitted.
Embodiment 5
[0300] Embodiment 5 of the invention will be described below.
Following items 1 to 5 are described in this Embodiment.
[0301] [1. Embodying of the First Step in a Cell Search]
[0302] Described herein is a specific variation of the technique
for performing detection of SCH timing in the first step of a cell
search by the cross-correlation method using time waveforms of
replica signals of sector specific codes. This is a modification of
Embodiment 4. In other words, in the Embodiment shown above, the
total number of subcarriers (except the DC subcarrier) is based on
multiples of "6", but this Embodiment specifically defines the
number of subcarriers as "75" (except the DC subcarrier). With
respect to a subcarrier multiplied by a code element as a phase
reference, this Embodiment is the same as Embodiment 4 in the
respects that the subcarrier is substantially multiplied by (the
code common in all the cells) and (the sector specific code), and
that the timing of the SCH is detected by the cross-correlation
method using the subcarrier. However, this Embodiment includes
subcarriers (subcarriers multiplied by a dummy code) that do not
contribute to detection of the cell specific information. This
Embodiment is the same as Embodiment in the respect that as well as
the method using cross-correlation, the auto-correlation method can
be used.
[0303] [2. Formation of a Characteristic Time Waveform By Symmetric
Arrangement of Subcarriers as a Phase Reference]
[0304] Subcarriers multiplied by code elements as a phase reference
are arranged symmetrically on the low-frequency side and the
high-frequency side with respect to the center frequency. The
subcarriers multiplied by code elements as a phase reference are
SCH subcarriers used in detection of SCH timing by the
cross-correlation method, and may be referred to as
"cross-correlation detection SCH subcarriers" in the following
description. Embodiment 4 is an embodiment for performing an
assignment with respect to the low-frequency side, and does not
need to meet the conditions of this Embodiment providing a
symmetric arrangement with respect to the center frequency.
[0305] The cross-correlation detection SCH subcarriers are
symmetrically arranged with respect to the center frequency at
predetermined intervals. As a time waveform of a signal on which
the subcarriers are mixed, in a one-symbol period (in which the SCH
is arranged), for example, by using the second, sixth, tenth,
subcarriers from the center, a waveform with the same amplitude and
inverted polarity such as "B", "-B", "B", "-B", (B has the
arbitrary signal amplitude: reference waveform) is repeated on a
one-fourth (1/4) symbol basis, and thus, the time waveform is
formed with specific periodicity. Further, by using the fourth,
eighth, twelfth, . . . subcarriers from the center, a time waveform
such as "D", "D", "D", "D", (D has the arbitrary signal amplitude:
reference waveform) is formed on a one-fourth symbol basis.
Accordingly, the replica time waveform prepared on the receiver
side for cross-correlation detection is also a time waveform
varying as "B", "-B", "B", "-B", or "D", "D", "D", "D", on a
one-fourth symbol basis. In other words, it is only essential
enabling detection of a characteristic signal waveform on a
one-fourth symbol basis. Accordingly, it is possible to simplify
the configuration of a correlator.
[0306] [3. Sector Identification in the Second Step in the Cell
Search]
[0307] Herein, despreading using the sector specific code is
executed, and it is intended to enhance the flexibility of the
operation for detecting a sector showing the maximum correlation
value. Codes multiplied by a subcarrier (cross-correlation detect
ion subcarrier) multiplied by the code element as a phase reference
are the (sector common code common in all the cells), (sector
specific code) and (cell specific code common in all the cells),
and this respect is the same as in Embodiment 4. However, in this
Embodiment, in all the subcarriers as a phase reference among all
the subcarriers, both of the sector common code (reference code)
common in all the cells and the cell specific code common in all
the cells are made "1". In Embodiment 4, new codes are used every
six subcarriers as the cell specific code (C.sub.i1, C.sub.i2 . . .
C.sub.in/6 in FIG. 30). In other words, first six subcarriers are
of C.sub.i1, and next six subcarriers are of C.sub.i2. In this
case, to perform despreading for sector identification, it is
required to perform despreading every six subcarriers sequentially.
In this respect, the flexibility of sector identification is
limited. However, when C.sub.i1, C.sub.i2 . . . C.sub.in/6 are made
all "1" as described above, all of the cell specific codes
multiplied by subcarriers as a phase reference among all the
subcarriers are "1". Accordingly, the subcarrier is multiplied by
"1 (sector common code common in all the cells)".times."1 (cell
specific code common in all the cells)".times."sector specific code
(P1, P2 or P3): see FIG. 29B). Eventually, the code multiplied by
each subcarrier as a phase reference is the sector specific code
(P1, P2 or P3). By this means, the need is eliminated for
performing despreading of six subcarriers as a group, and it is
only essential selecting any one of subcarriers from among all the
subcarriers to specify the sector specific code (P1, P2 or P3), and
executing despreading using this code. Accordingly, for sector
identification, such a limitation is eliminated that despreading is
performed every six subcarriers. As a result, the flexibility of
sector identification processing is enhanced.
[0308] [4. Consideration of Performing Sector Identification Using
Cross-Correlation of Time Waveforms Prior to FFT Instead of
Correlation Value Peak Determination By Despreading Subsequent to
FFT Processing]
[0309] In adopting the code structure of above-mentioned (3),
without performing despreading using orthogonal codes (P1, P2, P3)
after FFT, it is possible to identify a nearest sector before the
FFT processing using the cross-correlation method by replica time
waveforms described in (1) as mentioned above. In other words,
before the FFT processing, a cross-correlation peak is detected
using replica time waveforms (time waveform formed by one of codes
1, 2 and 3 in FIG. 34) of the sector specific codes, the code (one
of codes 1, 2 and 3 in FIG. 34) providing the maximum peak is
specified, and it is thereby possible to identify the nearest
sector. Particularly, in the case of acquiring timing
synchronization of the SCH by the replica correlation method in the
first step of a cell search, it is possible to perform sector
identification by comparing the correlation values calculated in
timing synchronization acquisition between different sector
specific codes, and it is thereby not necessary to perform the
operation of sector identification again after the acquisition. In
addition, to apply the cross-correlation method using the replica
time waveforms, it is a condition that mobile stations know various
sector specific codes transmitted from the base station. As the
sector identification method, it can be determined as appropriate
using the technique for detecting correlation by despreading using
orthogonal codes, or using the technique for detecting
cross-correlation using replica time waveforms, in consideration of
required detection accuracy, restrictions on circuitry, or the
like.
[0310] [5. Clarification of that the Sector Specific Code Includes
a Sector Group Specific Code as Well as a Code to Directly Identify
the Sector]
[0311] When the number of sectors is exceedingly high, groups with
the higher number of subcarriers are required to reserve orthogonal
codes, and the case is assumed that the number of subcarriers
lacks. In such a case, the concept of "sector group" is introduced
by grouping a plurality of sectors to identify the sector group by
the sector specific code. In other words, the "sector specific
code" as described above does not need to be always a code for
directly identifying the sector, and may be a code indicating a
sector group with some sectors. This concept is common and applied
to all the Embodiments shown above. Each of these respects will
specifically be described.
[0312] In Embodiments 1 to 4 shown above, the explanations are made
based on that the total number of subcarriers (including the center
DC subcarrier) is 2n+1, but this Embodiment describes about the
specific case that the total number of subcarriers as "76"
(including the center DC subcarrier). In this Embodiment, since 75
subcarriers except the DC subcarrier are used, the number of
subcarriers is different between the low-frequency side and
high-frequency side in the band with respect to the DC subcarrier
as a center. In addition, also in this Embodiment, since the cell
specific information is notified using a phase difference of
subcarriers constituting the SCH, the number of subcarriers
essentially used is 2n+1 (n=37 in this Embodiment) including the DC
subcarrier.
[0313] In this Embodiment, as in Embodiment 4, timing detection of
the SCH in the first step of the 3-step cell search is performed by
cross-correlation processing between a reception signal and replica
signals generated in a mobile station. Further, by arranging
subcarriers as targets to perform the cross-correlation processing
using the replica signals in specific positions, the characteristic
time waveform is made. To actualize the aforementioned respects, it
is necessary to devise the data structure of the SCH and subcarrier
arrangement.
[0314] The SCH position detection method of the first step shown in
this Embodiment can be implemented using the frame structure and
arrangement of the SCH shown in Embodiment 4 without modification.
It is also possible to perform the second step or third step as in
the Embodiment shown above.
[0315] According to the data structure of the SCH shown in this
Embodiment, as in Embodiment 4, the SCH is actualized that
indicates a periodical waveform (repeated waveform) in a symbol
required for the auto-correlation detection method. At the same
time, it is possible to achieve the SCH enabling application of the
detection method using the cross-correlation detection method using
replica signals. It is known that the auto-correlation detection
method can be implemented generally by a circuit configuration
simpler than that in the cross-correlation detection method, while
a peak of the correlation value is detected more gently than in the
cross-correlation detection method. It is known that the
cross-correlation detection method enables more accurate time
synchronization since a peak of the correlation value can be
sharply detected, while the circuit configuration and processing is
made complicated. Therefore, in part of wireless LAN communication
schemes, in time synchronization, rough time synchronization is
acquired by the auto-correlation detection method, and in a time
interval limited to some extent, accurate time synchronization is
acquired by the cross-correlation detection method. Also in this
Embodiment, the similar technique can be used.
[0316] As the SCH timing detection method in the first step in this
Embodiment, as described above, two detection methods can be
applied. The auto-correlation detection method is the method of
using a repeated waveform in the time domain of a SCH symbol
determined by positions in the frequency domain of subcarriers used
in the SCH, and therefore, does not have any differences from the
method specifically shown in Embodiment 2 or 3. Accordingly,
described below is the cross-correlation detection method using
replica signals that is a feature of this Embodiment. The
cross-correlation detection method uses a characteristic signal
waveform formed by an arrangement of subcarriers.
[0317] This Embodiment uses an OFDM communication scheme in the
downlink communication scheme as in Embodiment 2. Further,
structures of a communication frame and resource block are assumed
to have the same formats as shown in FIGS. 22 and 28. First, with
respect to a synchronization physical channel (SCH) that is a
feature of the invention, the specific structure will be
described.
[0318] FIG. 32 is a diagram illustrating 76 subcarriers used in
this Embodiment for each function. As shown in the figure, the
center DC subcarrier and odd-numbered subcarriers from the center
are made null subcarriers, and the other subcarriers are used as
SCH subcarriers. Among the SCH subcarriers, odd-numbered
subcarriers from the center are used as subcarriers for use in
cross-correlation detection i.e. subcarriers (cross-correlation
detection SCH subcarriers) as a phase reference in detecting the
cell specific information. Further, even-numbered SCH subcarriers
from the center are used as subcarriers (referred to as cell
specific information detection subcarriers as appropriate in the
following description) multiplied by the cell specific
information.
[0319] Herein, the odd-numbered SCH subcarriers from the center are
second, sixth, tenth, fourteenth . . . subcarriers from the center
as a whole. In addition, the center is assumed to be the zeroth.
Further, the even-numbered SCH subcarriers from the center are
fourth, eighth, twelfth . . . subcarriers from the center as a
whole.
[0320] As described above, the cross-correlation detection SCH
subcarriers are symmetrically arranged on the low-frequency side
and the high-frequency side with respect to the center frequency.
Further, the cross-correlation detection SCH subcarriers are
arranged with three subcarriers between adjacent SCH subcarriers
such as second, sixth, tenth . . . subcarriers when the center
frequency is the zeroth. This Embodiment differs from Embodiment 4
in the respect that the center frequency is a reference. In FIG.
32, the number of arranged cross-correlation detection SCH
subcarriers is different between the high-frequency side and
low-frequency side with respect to the center frequency. In other
words, ten subcarriers (1) to (10) are arranged on the
high-frequency side, while nine subcarriers (11) to (19) are
arranged on the low-frequency side. In addition, this Embodiment is
the same as Embodiment 4 in the respect that the cross-correlation
detection SCH subcarrier (subcarrier that is a phase reference) and
the cell specific information detection SCH subcarrier are paired
and used. Using a pair of subcarriers as a unit, in the case of
FIG. 32, one cross-correlation detection SCH subcarrier (subcarrier
that is a phase reference: subcarrier (10) in FIG. 32) is left on
the high-frequency side, and this subcarrier (10) is assigned a
dummy code (with "1" in this Embodiment).
[0321] FIG. 33 is a diagram showing the relationship between a
subcarrier (cell specific information detection SCH subcarrier)
multiplied by the cell specific information and another subcarrier
that is paired with the subcarrier and that is a subcarrier
(cross-correlation detection SCH subcarrier) as a phase reference.
In the case of 76 subcarriers in this Embodiment, 37 subcarriers
can be used as SCH subcarriers. Accordingly, it is possible to set
information P1(x) (where x=1.about.18) with the code length of "18"
as a relative value of the subcarrier (cross-correlation detection
subcarrier) as a phase reference as described previously and the
cell specific information detection subcarrier. In addition, in
this Embodiment for assigning information as a pair, a single
subcarrier is not used in code assignment. In other words, code 019
in FIG. 33 is a dummy code ("1" in this Embodiment).
[0322] As in Embodiment 4, FIGS. 34A to 34C are diagrams to explain
a data structure of the SCH concurrently transmitted from three
sectors in the same cell. FIG. 34A is a diagram showing an
assignment of the sector common code on the frequency axis, and
FIG. 34B is a diagram showing structures of three sector specific
codes. Then, FIG. 34C is a diagram showing the basic concept of
generation of the sector specific code, and shows vectors on the
complex phase plane.
[0323] The basic structure is the same as in Embodiment 4, but as
described previously, differs from Embodiment 4 in the positional
relation between a subcarrier for use in cross-correlation
detection and a subcarrier to multiply by the cell specific
information as described previously. As shown in FIG. 32, as SCH
subcarriers, even-numbered subcarriers on the higher and lower
frequency sides than the center DC subcarrier are used.
[0324] FIGS. 35A to D are diagrams to explain that a waveform in
the time domain formed by a plurality of combined SCH subcarriers
in a SCH-symbol period is of repetition of a reference waveform
(or, waveform of the inverted reference waveform) in a one-symbol
period by devising the arrangement of cross-correlation detection
SCH subcarriers on the frequency axis and the number of SCH symbols
on the time axis.
[0325] In this Embodiment (including the Embodiment shown above), a
SCH subcarrier is arranged periodically at frequency intervals of
every two subcarriers on the frequency axis (for example, see FIG.
25). When thus periodically arranged SCH subcarriers in a
one-symbol period are combined, as shown in FIG. 35A, a time
waveform (waveform in the time domain prior to FFT) is obtained
such that a reference waveform (assumed as A) is repeated on a half
(1/2) symbol basis in a one-effective symbol period (period
obtained by subtracting a period of inserted GI from a one-symbol
period). Accordingly, as described in the Embodiment shown above,
the time waveform is delayed by 1/2 effective symbol to calculate
correlation with an original time waveform, and the correlation
peak is thereby obtained. Accordingly, it is possible to detect a
SCH position (the processing of the first step in a cell search by
the auto-correlation method).
[0326] In addition, as shown in FIG. 19, in the case where the SCH
is arranged in last two symbols in a one-frame period, as shown in
FIG. 35C, the same time waveform (assumed as C) is repeated in a
two-adjacent effective symbol period. Accordingly, the time
waveform is delayed by one symbol to calculate correlation with an
original time waveform, and the correlation peak is thereby
obtained. Accordingly, it is possible to detect a SCH position (the
processing of the first step in a cell search by the
auto-correlation method).
[0327] Meanwhile, in Embodiment 5, further, the cross-correlation
detection SCHs are arranged symmetrically on the low-frequency side
and the high-frequency side with respect to the center frequency.
In other words, second, sixth, tenth, fourteenth . . . subcarriers
(every fourth subcarrier starting with the second subcarrier) from
the DC subcarrier as the center are used as described previously.
By this means, a characteristic time waveform is formed which has a
configuration where a signal is repeated in a half (1/2) period of
an effective symbol and further, in a half (1/2) of the period i.e.
in a one-fourth (1/4) period of the whole as a unit, a time wave
form with the polarity of the amplitude inverted is repeated. More
specifically, as shown in FIG. 35B, the time waveform such that B,
-B, B, -B is repeated is formed. This phenomenon is caused by
symmetry in the time domain regarding the frequency relationship
between mutually orthogonal subcarriers in the OFDM communication
scheme. In this case, it is possible to specify a SCH position by
detecting the characteristic periodicity on a one-fourth (1/4)
effective symbol basis. By using this characteristic, it is
possible to produce a correlator used in cross-correlation
detection with a simpler configuration. In other words, by the
correlator with a simple configuration, it is possible to detect
the SCH timing with high accuracy.
[0328] Further, by using fourth, eighth, twelfth, sixteenth . . .
cross-correlation detection SCH subcarriers (every fourth
subcarrier starting with the fourth subcarrier) from the DC
subcarrier as the center, it is also possible to form a
characteristic time waveform such that a signal is repeated in a
one-fourth (1/4) period of an effective symbol. More specifically,
as shown in FIG. 35D, the time waveform that D, D, D, D is repeated
is formed.
[0329] The most simplified subcarrier structure with the cell
specific code common in all cells made all "1" will specifically be
described below. This subcarrier structure is advantageous in
practical use.
[0330] A signal shown in FIG. 34A indicates the sector common code
constituting the SCH. In Embodiment 4, as shown in FIG. 29A, SCH
subcarriers are respectively assigned S.sub.01 to S.sub.0n/6 every
six chips. In this Embodiment, all the SCH subcarriers are assigned
S.sub.0. Herein, S.sub.0 is an arbitrary value expressed by
A*exp(j.omega.), where A represents the amplitude (in addition, in
this Embodiment, the explanation is made with the amplitude being
"1"), j represents an imaginary unit, and .omega. represents a
phase. All the SCH subcarriers are multiplied by S.sub.0, while
codes of subcarriers as a phase reference are uniquely made "1"
(described later). By this means, the need is eliminated for always
performing power calculation for sector identification using a
group of six subcarriers as a unit. In other words, using code 2 of
FIG. 34B as an example, it is possible to select each of codes
"P1", "P2" and "P3" from any one of SCH subcarriers on the
frequency axis to perform the power calculation processing. In
addition, since there is the condition that subcarriers used in the
power calculation processing can be regarded as having the same
propagation path, the accuracy decreases when selecting subcarriers
apart from each other on the frequency axis, and it is desirable to
use adjacent subcarriers.
[0331] In this Embodiment, as in Embodiment 4, the sector common
code is a code common in all the cells. Further, among the cell
specific codes, a code element as a phase reference is also common
in all the cells.
[0332] The SCH is configured by multiplying three kinds of codes
(sector common code, sector specific code and cell specific code).
Herein, the sector common code is made common in cells, and among
the cell specific codes, a code element as a phase reference is
also made common in the cells. As a result, with respect to a
subcarrier multiplied by the code element as a phase reference,
multiplied codes are the (sector common code common in all the
cells), (sector specific code) and (cell specific code common in
all the cells), and substantially, the (codes common in all the
cells) are multiplied by the (sector specific code). In other
words, with respect to the subcarrier multiplied by the code
element as a phase reference, three kinds of codes are multiplied,
and among the codes, two codes are common in all the cells.
Accordingly, a different code is only the sector specific code.
This means that correlation detection using replicas of the sector
specific codes can be performed with ease.
[0333] Therefore, the reception apparatus side prepares a time
waveform of a replica code of the sector specific code
corresponding to each sector, multiplies a reception signal (signal
prior to FFT) by the time waveform of the replica signal to detect
a correlation peak, and is thereby capable of detecting the SCH
timing in the reception signal with high accuracy. Accordingly, it
is made possible to perform subsequent sector identification and
cell identification with higher efficiency.
[0334] Further, in this Embodiment, by arranging subcarrier
positions for use in cross-correlation detection in particular
positions, the same signal wave form is repeated at 1/2 effective
symbol length intervals as shown in FIG. 35B. Furthermore, a signal
waveform is formed such that the sign is inverted at 1/4 effective
symbol length intervals. By this means, it is possible to adopt a
configuration of a simplified correlator using the
characteristics.
[0335] However, even when such a specialized SCH structure is
adopted, the repeated signal waveform is formed in a SCH-symbol
interval, which is not different, and it is also possible to
perform position detection by the auto-correlation method. The
auto-correlation method is a method of detecting correlation
between a signal delayed from a reception signal by a predetermined
period and an original reception signal.
[0336] An example will specifically be described below with
reference to drawings. The sector specific code is described first.
FIG. 34B shows an example of the sector specific codes (herein, the
number of sectors is "3"). Herein, the same codes as shown in
Embodiment 4 are used.
[0337] Described next is a code sequence to transmit the cell
specific information. FIG. 36 is a diagram illustrating a structure
on the frequency axis of a code sequence to transmit the cell
specific information. In this Embodiment, the cell specific
information is transmitted using the code sequence as shown in FIG.
36. cl as shown in FIG. 36 (1 is a natural number from 1 to 18) is
the "code specific to the cell", and notifies a mobile station of
the cell specific information. cl is a code sequence with the
amplitude of "1".
[0338] The code sequence of Embodiment 4 as shown in FIG. 30 is
configured sequentially using six chips as a group from the
low-frequency side. The code sequence of this Embodiment as shown
in FIG. 36 is of a specialized form that code sequence cik of FIG.
30 is all "1". By this means, the limitation as described
previously is eliminated that a group of adjacent six subcarriers
on the frequency axis is necessarily selected in calculating the
sector power, and the flexibility of the sector identification
processing is enhanced.
[0339] Three kinds of code sequences as shown above are code
sequences constituting the SCH, and the SCH is configured by
multiplying these code sequences. Then, a transmitter of each
sector transmits a multicarrier signal containing the SCH.
[0340] A transmission method of the SCH and a configuration of a
transmitter in this Embodiment are the same as in Embodiment 2
shown above, and descriptions thereof are omitted. The different
respect is a code (see FIGS. 35 and 36) generated in the sector
specific code generating section 63 in the SCH data processing
section 60.
[0341] A receiver configuration and a reception method in this
Embodiment are basically the same as in Embodiment shown above, and
descriptions thereof are omitted. Further, in adopting the code
structure as shown in FIG. 36, without performing de spreading
using orthogonal codes (P1, P2, P3) after FFT, it is possible to
identify a nearest sector before the FFT processing using the
cross-correlation method by replica time waveform described as in
the processing of the first step in the cell search.
[0342] In other words, before the FFT processing, a
cross-correlation peak is detected using replica time waveforms
(time waveform formed by one of codes 1, 2 and 3 in FIG. 34) of the
sector specific codes, the code (one of codes 1, 2 and 3 in FIG.
34) providing the maximum peak is specified, and it is thereby
possible to identify the nearest sector.
[0343] Particularly, when SCH time synchronization is acquired by
the cross-correlation method in the first step of the cell search,
it is possible to identify a sector using the result without
modification. In other words, SCH time synchronization is acquired
by the position of correlation value in the time domain by
cross-correlation detection, and the amplitude enables
determination of a sector providing high reception power.
[0344] As the sector identification method, it can be determined as
appropriate using the technique for detecting correlation by de
spreading using orthogonal codes, or using the technique for
detecting cross-correlation using replica time waveforms, in
consideration of required detection accuracy, restrictions on
circuitry, or the like.
[0345] Further, when the number of sectors is exceedingly high,
groups with the higher number of subcarriers are required to
reserve orthogonal codes, and the case is assumed that the number
of subcarriers lacks. In such a case, the concept of "sector group"
is introduced by grouping a plurality of sectors to identify the
sector group by the sector specific code. In other words, the
"sector specific code" as described above does not need to be
always a code for directly identifying the sector, and may be a
code indicating a sector group with some sectors. This concept is
common and applied to all the Embodiments shown above.
[0346] As described above, according to the invention, by a sector
common code being multiplied by a sector specific code, it is
possible to identify a sector only by despreading and correlation
detection using the SCH without using a pilot channel. Accordingly,
with respect to sector identification, the need is eliminated for
de spreading and correlation detection processing using a pilot
channel, and it is possible to reduce the capacity of memory to be
used in correlation calculation using the pilot channel.
[0347] Further, since the SCH is multiplied by the sector specific
code, it is possible to eliminate interference between sectors even
in a boundary of sectors. Furthermore, it is possible to obtain the
effect of enhancing anti-fading characteristics by randomizing
effect. It is easy to increase the number of sector specific codes
(orthogonal codes) assigned for each sector corresponding to an
increase in the number of sectors, and to respond to the sector
configuration flexibly.
[0348] Moreover, when it is possible to reserve the adequate number
of subcarriers in multiplying the SCH by the cell specific code,
only the SCH enables a cell ID to be identified directly. In this
case, the cell search processing including sector identification is
completed by 2-step processing using only the SCH (2-step cell
search), and the search process can be reduced as compared with the
conventional 3-step cell search.
[0349] Further, by devising structures, contents and arrangement on
the frequency axis of a cell specific code and sector specific code
to multiply, it is possible to prevent the sector specific code and
cell specific code from imposing an adverse effect on each other,
and to suppress a decrease in information transmission accuracy.
Furthermore, each of the information can be demodulated
independently (i.e. in parallel processing), and it is thereby
possible to reduce the processing time of cell search including
sector search.
[0350] In other words, a 2m-chip code is generated by combining two
orthogonal m-chip codes, the m-chip code is used for sector
identification, and the other m-chip code is used for
identification of cell specific information. The cell specific
information is transmitted as phase difference information between
subcarriers (that are more preferably adjoined on the frequency
axis) multiplied by a sector specific code element of the same
value, and it is thereby possible to efficiently transmit the
sector specific information and cell specific information with
efficiency, while the receiving side can divide and extract both
information with efficiency.
[0351] Further, in the cell search method of the invention, it is
possible to complete the cell search by timing detection of the SCH
(first step) on the time axis by an auto-correlation method using
the periodicity of the SCH or cross-correlation method using time
wave forms of replica codes of the sector specific codes, and
identification of frame timing and identification of a sector ID
and cell ID (second step) based on information on the frequency
axis. Accordingly, it is possible to reduce the search process as
compared with the conventional 3-step cell search.
[0352] Further, despreading and correlation detection using a pilot
channel is required only in demodulating a data channel while being
not required in a cell search, and it is thereby possible to
achieve reductions (such as a reduction in memory capacity and the
like) in loads of hardware used for correlation calculation of the
pilot channel. Furthermore, since the sector specific code is
multiplexed on the SCH, with respect to sector identification, it
is possible to obtain effects of having resistance to interference
between sectors and fading. However, when the number of subcarriers
is not adequate, the cell ID cannot be identified directly only by
the SCH, and there may be a case that cell ID group information is
only detected. In this case, the cell ID can be identified by
implementing despreading and correlation detection using a pilot
channel as processing of the third step.
[0353] Moreover, according to the multicarrier
transmission/reception apparatus of the invention, fast
transmission with large capacity is allowed on downlink.
[0354] Thus, according to the invention, it is possible to decrease
the process required for cell search processing including sector
identification, while reducing the capacity of memory for storing
correlation detection results using a pilot channel. It is further
possible to actualize a faster cell search including sector
identification with high accuracy while improving resistance to
interference or anti-fading characteristics of the cell search
processing including sector identification without increasing loads
on a transmission/reception apparatus.
[0355] Further, the invention includes various variations (specific
examples, modifications and applications), and the variations
contribute to practical application of communication schemes
conforming to the E-UTRA (Evolved-UTRA). For example, in the
processing (detection processing of SCH timing) of the first step
in the cell search, as well as the auto-correlation method, it is
possible to adopt a cross-correlation method with a particular time
waveform noted. In this case, it is possible to obtain the effect
of enabling the configuration of a correlator to be simplified.
Further, by unifying all the codes of subcarriers as a phase
reference on the frequency axis to, for example, "1", it is
possible to eliminate limitations that six subcarriers should be a
group in despreading using the sector specific code. Furthermore,
when a mobile station knows each kind of sector specific code
transmitted from the base station, nearest sector detection can be
performed by detection using cross-correlation by time waveform
prior to FFT without despreading. Moreover, when the number of
sectors increases, it is possible to adopt a "sector group specific
code" as the "sector specific code".
[0356] Furthermore, the invention is capable of being configured as
a data structure of a synchronization channel (SCH). In other
words, a data structure of the invention is a data structure of a
synchronization channel (SCH) in a mobile communication system
adopting a multicarrier communication scheme in which a cell is
divided into a plurality of cells, a base station controlling over
the cell transmits downlink signals to mobile stations in the cell
by multi carrier communication, and the downlink signal includes a
synchronization channel (SCH) capable of being used in a cell
search including sector identification, where a sector common code
common in a plurality of sectors in the same cell is multiplied by
a sector specific code varying with each sector in the same cell,
and it is thereby made possible to execute a cell search including
sector identification using the synchronization channel (SCH).
[0357] Anew structure including the sector specific code is adopted
as a data structure of the synchronization channel (SCH:
hereinafter, simply referred to as "SCH" as appropriate) included
on downlink of the multicarrier mobile communication scheme. In
other words, the sector common code is multiplied by the sector
specific code, and it is intended to identify a sector only by
despreading and correlation detection using the synchronization
channel (SCH) without using a pilot channel. That is, the invention
is to vary the SCH conventionally used to be common (i.e.
non-orthogonal with respect to sectors) in sectors in a single cell
to an orthogonal channel specific for each sector, and enables
direct sector identification using the SCH. Accordingly, with
respect to sector identification, the need is eliminated for
despreading and correlation detection processing using a pilot
channel, and it is possible to reduce the capacity of memory to be
used in correlation calculation using the pilot channel. Further,
since the SCH is multiplied by the sector specific code, it is
possible to eliminate interference between sectors even in a
boundary of sectors. Furthermore, it is possible to obtain the
effect of enhancing anti-fading characteristics by randomizing
effect. Moreover, when the information to multiplex on the SCH can
be increased, it is brought into view to directly identify a cell
ID only by the SCH, and in this case, it is possible to achieve the
cell search processing including sector identification by 2-step
processing (2-step cell search) using only the SCH.
[0358] Further, in a data structure of the synchronization channel
(SCH) of the invention, the sector specific code is configured by
making m (m is a natural number of "2" or more) code elements a
group, and assigning a group of code elements repeatedly to
subcarriers on the frequency axis, while sector specific codes
corresponding to the sectors are orthogonal to one another.
[0359] The respect is clarified that the sector specific code is
repeatedly assigned to subcarriers on the frequency axis on a unit
of a group of m code elements, and that the m code elements are
orthogonal for each sector. In addition, the term of "code element"
is used for the sake of convenience to distinguish between "code as
a higher concept" meaning a "code sequence" and each code (code as
a lower concept") that is a structural element of the code
sequence, and for example, corresponds to a "chip" that is a unit
of despreading. Further, by assigning code elements to subcarriers
on the frequency axis, for example, the phase of the subcarrier
varies, and it is thereby possible to transmit the sector specific
information. Herein, as an example, assuming that m=3, code M1
corresponding to sector 1 is repeatedly assigned from the
low-frequency side to the high-frequency side in a three-code
element period such as M1=(m1, m2, m3, m1, m2, m3, . . . ) on the
frequency axis on a unit of code elements (m1, m2, m3). Code M2 of
sector 2 is also repeatedly assigned from the low-frequency side to
the high-frequency side in a three-code element period such as
M2=(m4, m5, m6, m4, m5, m6, . . . ). Then, (m1, m2, m3) and (m4,
m5, m6) that are respectively structural units of code M1 and M2
are mutually orthogonal.
[0360] For example, when a complex conjugate of each of m1, m2 and
m3 is multiplied (despread) by codes M1 and M2, a high correlation
value is shown on code M1, while a correlation value of code M2 is
"0", and it is possible to distinguish between both codes to
extract. Described below is an example of the fundamental
philosophy to generate orthogonal codes. On the complex phase plane
(that is the IQ plane where the I axis corresponds to the real
axis, and the Q axis corresponds to the imaginary axis), for
example, three vectors (P1, P2, P3) with the amplitude of "1"
arranged to form an angle of 120.degree. with respect to one
another are set. The three vectors have the relationship that
vector addition thereof results in "0", and using the vectors, it
is possible to generate orthogonal codes (in the case of m=3) with
ease. For example, code M1=(P1, P1, P1), code M2=(P1, P2, P3), and
code 3=(P1, P3, P2) are mutually orthogonal. For example, when each
complex conjugate of code elements (P1, P2, P3) of code M2 is
multiplied by each of codes M1, M2 and M3 each) and the code
elements are added, the correlation value of code M2 is "3", while
in the case of M1 and M3, the relationship of vectors P1, P2 and P3
is eventually kept without change as a relative relationship
between code elements. Accordingly, the addition results in "0". In
the aforementioned example, three vectors having the orthogonal
relationship are used, and by increasing the number of vectors (for
example, using four vectors forming an angle of 90 degrees), it is
possible to further increase the number of code elements. By this
means, it is possible to increase the number of codes (the
above-mentioned example allows generation of three codes, M1, M2
and M3, and the number of code is "3") having the orthogonal
relationship. Accordingly, when the number of sectors contained in
a single cell increases, by using the above-mentioned philosophy,
it is possible to generate orthogonal codes corresponding to the
number of sectors with ease.
[0361] Further, the data structure of the synchronization channel
(SCH) of the invention is formed by multiplying the sector common
code, the sector specific code, and further, a cell specific code
("code indicating the cell specific information" or there is the
case of being referred to as a "a code including a cell specific
cell ID (or information indicating a cell ID group common in some
cells").
[0362] By multiplying the SCH also by the cell specific code, when
predetermined conditions are met, it is possible to directly
identify a cell ID only by the SCH, as well as sector
identification by the SCH. In this case, the cell search processing
including sector identification is completed by 2-step processing
using only the SCH (2-step cell search), and it is possible to
reduce the search process as compared with the conventional 3-step
cell search.
[0363] Further, in the data structure of the synchronization
channel (SCH) of the invention, the cell specific code is a code
indicating the cell specific information for a mobile station to
acquire in a cell search. It is clarified that the cell specific
code indicates the cell specific information (cell ID or the
like).
[0364] Furthermore, in the data structure of the synchronization
channel (SCH) of the invention, the sector common code is assigned
to subcarriers on the frequency axis, the sector specific code is
assigned to the subcarriers assigned the sector common code, and
each of code elements constituting the cell specific code indicates
information of a relative phase difference between a pair of
subcarriers among the subcarriers assigned the sector common code.
Accordingly, in the subcarriers assigned the sector common code on
the frequency axis, one of a paired subcarrier is multiplied by the
code element that is a phase reference, and the other subcarrier is
multiplied by the code element indicating the relative phase
difference.
[0365] It is clarified that the cell specific information (cell ID,
antenna arrangement, BCH (Broadcast Channel) bandwidth, GI (Guard
Interval, also referred to as CP: Cyclic Prefix) length and the
like) is transmitted by information of a relative phase difference
between two subcarriers arranged on the frequency axis. In other
words, such a scheme is adopted that the cell specific code
indicates a relative phase of a paired subcarrier without
indicating an absolute phase of each subcarrier, it is thereby made
ease generating the cell specific code, and for example, by using
GCL codes, Walsh-Hadamard codes and like to correspond to the cell
specific information, it is possible to notify a mobile station of
the information. When the number of subcarriers is enough, all the
information required for cell identification can be transmitted by
the SCH.
[0366] Further, in the data structure of the synchronization
channel (SCH) of the invention, the sector common code and each of
code elements that are the phase references constituting the cell
specific code are common codes in all the cells.
[0367] Thus, the data structure of the SCH is devised to enable the
signal processing (signal processing to detect a position of the
SCH in a reception signal) in the first step of a cell search to be
implemented by a cross-correlation method using replicas of sector
specific codes. Since the SCH is arranged periodically in a
one-frame period, the position can be detected by the
"auto-correlation method" using the periodicity, and using the
"cross-correlation method" using replica codes actualizes a shaper
correlation peak, and enables the SCH position to be detected with
higher accuracy. The SCH is configured by multiplying three kinds
of codes (sector common code, sector specific code and cell
specific code). Herein, the sector common code is made common in
all the cells, and among cell specific codes, a code element as a
phase reference is also made common in all the cells. Codes
multiplied by a subcarrier multiplied by the code element as a
phase reference are the (sector common code common in all the
cells), (sector specific code) and (cell specific code common in
all the cells), and substantially, the (codes common in all the
cells) are multiplied by the (sector specific code). In other
words, with respect to the subcarrier multiplied by the code
element as a phase reference, three kinds of codes are multiplied,
and among the codes, two codes are common in all the cells.
Accordingly, a different code is only the sector specific code.
This means enabling correlation detection using replicas of the
sector specific codes. Therefore, the reception apparatus side
prepares a time waveform of a replica code of the sector specific
code corresponding to each sector, multiplies a reception signal
(signal prior to FFT) by the time waveform of the replica signal to
detect a correlation peak, and is thereby capable of detecting the
position of the SCH in the reception signal with high accuracy.
Accordingly, it is made possible to perform subsequent sector
identification and cell identification with more efficiency. In
addition, even when the SCH structure as described above is
adopted, the SCH is periodically arranged in a one-frame period,
which is not different, and it is also possible to perform position
detection by the auto-correlation method (i.e. the method of
detecting correlation between a signal delayed from a reception
signal by a predetermined period and an original reception
signal).
[0368] Further, in the data structure of the synchronization
channel (SCH) of the invention, the sector specific code is
configured by making 2m (m is a natural number of "2" or more) code
elements a group, and assigning a group of code elements repeatedly
to subcarriers on the frequency axis, while 2m code elements are
configured by preparing two groups of code elements orthogonal for
each sector as described in claim 2 or 3, and assigning each group
to subcarriers to be adjacent on the frequency axis, and among the
2m code elements that is a structure unit of the sector specific
code, each of half m code elements is multiplied by a code element
constituting the cell specific code, having the same value as that
of the code element, indicating a relative phase difference from
respective one of the other half m code elements.
[0369] When the SCH is used only for sector identification, as
described above, it is enough arranging an orthogonal code having m
code elements as a structure unit repeatedly on the frequency axis,
but to further transmit the cell specific information, the
conditions become severer. In other words, in order to multiplex
both of the sector specific information and cell specific
information on the SCH to transmit, it is the condition that the
sector specific information and cell specific information do not
have an adverse effect on each other, and it is important to enable
each information to be restored independently (i.e. by parallel
processing) to reduce the processing time. To meet these
conditions, herein, two groups are prepared where the group has m
code elements that is a structure unit of an orthogonal code for
sector identification, and combined in a two-stage manner on the
frequency axis, and 2m code elements are made a new unit structure
and arranged repeatedly on the frequency axis. M code elements are
used to identify the sector. Remaining m code elements are used to
multiply the cell specific code. Since the cell specific code
indicates a relative phase difference between a pair of subcarriers
as described previously, each of the remaining m code elements is
multiplied by a code indicating a phase difference from respective
one (i.e. respective code element of the sector specific code) of
the other m code elements with the same value. For example, such a
case is considered that an orthogonal code for sector
identification comprised of code elements (m1, m2, m3) is combined
in a two-stage manner on the frequency axis, and arranged as a unit
repeatedly from the low-frequency side to the high-frequency side
to form a code. For example, code M1 is assumed that M1=(m1, m2,
m3, "m1", "m2", "m3" . . . ). " " is added to distinguish between
code elements with the same value. Then, "m1" is multiplied by a
code "c1" indicating a phase difference from m1 having the same
value on the lower frequency side, and "m2" and "m3" are also
multiplied by code "c2" and "c3" each indicating a phase difference
from m1 or m3 on the lower frequency side, respectively.
[0370] By this means, sector and cell identification code M1 is
M1=(m1, m2, m3, m1c1, m2c2, m3c3 . . . ). As described above, since
(m1, m2, m3) is orthogonal among sectors, it is possible to
distinguish the sector specific code to extract by multiplication
of the complex conjugate and correlation detection. Further, for
example, for "m1c1", by multiplying the complex conjugate of m1
(code multiplied by a subcarrier as a phase reference), m1 is
cancelled, and it is possible extract "c1" having the cell specific
information. c2 and c3 can be extracted in the same way. Thus,
basically, by detecting a phase difference of another subcarrier
from a subcarrier as a phase reference, it is possible to
demodulate the cell specific code (Cn) (in addition, to enhance
demodulation accuracy, it is desirable to calculate
cross-correlation with cell specific code Cn as a candidate.) It is
possible to execute sector identification by despreading and
correlation detection using the sector specific code (m1, m2, m3)
and demodulation processing of the cell specific information Cn
(c1, c2, c3) by multiplying the complex conjugate independently of
(in parallel with) each other. Further, with respect to
transmission of the cell specific information, for example, two
subcarriers multiplied by the same value "m1" are paired, one is a
phase reference subcarrier, the other subcarrier is assigned the
cell specific code Cn, and it is possible to provide a relative
phase difference from the phase reference subcarrier. Therefore,
without receiving interference by the sector specific code, it is
possible to transmit only the cell specific information as the
relative phase difference information between subcarriers.
Accordingly, the cell specific information can be transmitted
efficiently.
[0371] Further, in the data structure of the synchronization
channel (SCH) of the invention, the sector specific code is
configured by making 2m (m is a natural number of "2" or more) code
elements a group, and assigning a group of code elements repeatedly
to subcarriers on the frequency axis, while 2m code elements are
configured by preparing two groups of m code elements orthogonal
for each sector of the invention, and assigning code elements of
each group to subcarriers alternately so that code elements with
the same value in each code are arranged to be adjacent on the
frequency axis, and among the 2m code elements that is a structure
unit of the sector specific code, one of the code elements with the
same value assigned to the adjacent subcarriers on the frequency
axis is multiplied by a code element constituting the cell specific
code indicating a relative phase difference from the other code
element as a phase reference.
[0372] In the aforementioned example, two groups of m code elements
(orthogonal code for sector identification: for example (m1, m2,
m3)) are prepared, and simply stacked and arranged on the frequency
axis. In the invention, an arrangement is made in a mixed form so
that the same code elements of each group are adjacent to each
other on the frequency axis. For example, code M1 is assumed that
code M1=(m1, m1, m2, m2, m3, m3). Then, one of code elements with
the same value is multiplied by the cell specific code indicating a
relative phase difference. Accordingly, sector and cell
identification code M1 is M1=(m1, m1c1, m2, m2c2, m3, m3c3 . . . ).
Then, sector identification is performed using odd-numbered code
elements (m1, m2, m3), each of even-numbered code elements (m1c1,
m2c2, m3c3) is multiplied by a complex conjugate of m1, m2 or m3
multiplied by the adjacent subcarrier as a phase reference, and it
is possible to demodulate the cell specific code (c1, c2, c3 . . .
). It is an excellent respect of the invention that code elements
with the same value are arranged to be adjacent to each other (i.e.
arranged as a pair on the frequency axis such as "m1, m1", "m2,
m2", "m3, m3") in a sector specific code element sequence prior to
being multiplied by the cell specific code Cn. Since codes with the
same value are arranged on the proximal frequency axis, it is
possible to regard transfer functions of propagation paths of
subcarriers assigned the codes as being equivalent (in other words,
when the transfer function of the propagation path of each
subcarrier differs by positions of subcarriers being apart from
each other on the frequency axis, the phase rotates by this effect,
the rotation results in an error in transmitting the cell specific
information using a relative phase difference between two
subcarriers, and there is a case that demodulation accuracy of the
cell specific information degrades.) In the invention, since two
subcarriers are adjacent and arranged on the frequency axis, the
probability is high that propagation conditions of the subcarriers
are estimated at the same, and it is thus possible to transmit the
cell specific information (i.e. phase difference between two
subcarriers) with high accuracy.
[0373] Further, in the data structure of the synchronization
channel (SCH) of the invention, Sf (Sf is a natural number)
sub-frames are arranged over a one-frame period in the time-axis
direction, while a plurality of sub-channels is arranged over the
entire band in the frequency-axis direction, a frame in
multicarrier communication is thereby configured, the
synchronization channel (SCH) is arranged in each last one symbol
in a time period obtained by dividing the one-frame period into Ss
(Ss is a submultiple of Sf) portions, and the synchronization
channel (SCH) is periodically arranged at intervals of the
predetermined number of subcarriers on the frequency axis.
Accordingly, the time waveform formed by subcarriers for use in
sector identification being combined is a time waveform having the
periodicity that a predetermined waveform is repeated in a
one-symbol period, and by using the periodicity of the time
waveform, it is possible to detect the SCH position by the
auto-correlation method.
[0374] The SCH is assigned to the last (one) symbol in a time
period obtained by dividing a one-frame period into the
predetermined number of portions, and among subcarriers assigned
the SCH, subcarriers for use in sector identification are arranged
at predetermined intervals with periodicity on the frequency axis.
According to this arrangement, due to the frequency relationship
between orthogonal subcarriers in the OFDM communication scheme
i.e. the symmetry in the time domain, as the time waveform formed
by the subcarriers being combined, such a waveform is obtained that
has the periodicity such that a predetermined waveform is repeated
in a one-symbol period (for example, such a wave form that assuming
a predetermined waveform as A, A is repeated on a half (1/2) symbol
basis). Using the periodicity of the time waveform, it is possible
to detect the SCH position by the auto-correlation method or
cross-correlation method.
[0375] Further, in the data structure of the synchronization
channel (SCH) of the invention, a plurality of sub-frames are
arranged over a one-frame period in the time-axis direction, while
a plurality of sub-channels is arranged over the entire band in the
frequency-axis direction, a frame in multicarrier communication is
thereby configured, and the synchronization channel (SCH) is
arranged in predetermined two symbols in the one-frame period.
Accordingly, the time waveform formed by subcarriers for use in
sector identification being combined is a time waveform having the
periodicity that the same waveform is repeated in a one-symbol
period, and by using the periodicity of the time waveform, it is
possible to detect the SCH position by the auto-correlation
method.
[0376] The SCH is assigned to two symbols, and among subcarriers
assigned the SCH, subcarriers for use in sector identification are
arranged at predetermined intervals with periodicity on the
frequency axis. In the case of the invention, since the SCH is
assigned over two symbols, as a result, the same time waveform
appears for each symbol (for example, such a waveform that assuming
a waveform in a one-symbol period as C, C is repeated on a
one-symbol period basis in a two-symbol period.) Using thus
periodicity of the time waveform on a one-symbol period basis, it
is possible to detect the SCH position by the auto-correlation
method. Further, since the SCH can be transmitted using subcarriers
over the entire frequency band, when different information is
transmitted for each symbol, it is possible to increase a code
length usable in transmitting the cell specific information
(relative phase difference information), and to transmit a larger
amount of cell specific information.
[0377] Further, a cell search method of the invention is a cell
search method for receiving a multicarrier signal from a
multicarrier transmission apparatus, and using a synchronization
channel (SCH) of the invention including the cell and sector
identification information to identify a sector and a cell, and is
performed by the first step of detecting a synchronization channel
(SCH) position in a reception signal by an auto-correlation method
or cross-correlation method, and the second step of detecting a
sector specific code providing the maximum reception power to
identify a sector by de spreading processing with a sector specific
code of the synchronization channel (SCH) arranged on the frequency
axis, concurrently detecting a phase difference between a
subcarrier as a phase reference and another subcarrier, associated
with the subcarrier, multiplied by a code element of a cell
specific code among subcarriers assigned the synchronization
channel (SCH), thereby demodulating the cell specific code, further
performing correlation detection processing with a cell specific
code desired to detect when necessary, and thereby detecting the
cell specific code.
[0378] As described above, by multiplexing the information to
identify a sector and a cell on the downlink SCH in multicarrier
communication, when predetermined conditions are met (in other
words, when the sufficient number of subcarriers is used, and all
the required cell specific information can be transmitted by a
relative phase difference between a pair of subcarriers), it is
possible to complete a cell search including sector identification
only using the SCH. In other words, it is possible to complete the
cell search by detection of SCH timing (first step) on the time
axis by an auto-correlation method using the periodicity of the SCH
or cross-correlation method using replica codes of the sector
specific codes, and identification of frame timing and
identification of a sector ID and cell ID (second step) based on
the information on the frequency axis. Accordingly, it is possible
to reduce the search process as compared with the conventional
3-step cell search. Further, in this case, despreading and
correlation detection using a pilot channel is required only in
demodulating a data channel while being not required in a cell
search, and it is thereby possible to achieve reductions (such as a
reduction in memory capacity and the like) in loads of hardware
used for correlation calculation of the pilot channel. Furthermore,
since the sector specific code is multiplexed on the SCH, with
respect to sector identification, it is possible to obtain effects
of having resistance to interference between sectors and fading.
However, when the number of subcarriers is not adequate, the cell
ID cannot be identified directly only by the SCH, and there may be
a case that cell ID group information is only detected. In this
case, the cell ID is identified by implementing despreading and
correlation detection using a pilot channel as processing of the
third step.
[0379] Further, a multicarrier transmission apparatus of the
invention has assigning means for assigning a synchronization
channel (SCH) having the structure of the invention onto the
frequency axis in a frame period, and transmitting means having
directional antennas provided for each of a plurality of sectors
for transmitting a multicarrier signal with the synchronization
channel (SCH) assigned onto the frequency axis.
[0380] According to this configuration, it is possible to transmit
a multicarrier signal with the sector specific information and cell
specific information assigned on the frequency axis from the
antennas for each sector.
[0381] Further, a multicarrier reception apparatus of the invention
is a multicarrier reception apparatus for receiving a multicarrier
signal transmitted from the multicarrier transmission apparatus of
the invention, and using a synchronization channel (SCH) multiplied
by a sector specific code included in the reception signal to
identify a sector and a cell, and has timing detecting means for
detecting a synchronization channel (SCH) position in a reception
signal using the fact that the synchronization channel (SCH) is
arranged periodically on the time axis, and sector identifying
means for detecting a sector specific code providing the maximum
reception power by despreading processing with the sector specific
code multiplied by the synchronization channel (SCH) arranged on
the frequency axis.
[0382] It is thereby possible to receive a multicarrier signal and
implement the sector identification processing (sector search) by
the SCH.
[0383] Further, a multicarrier reception apparatus of the invention
is a multicarrier reception apparatus for receiving a multicarrier
signal transmitted from the multicarrier transmission apparatus,
and using a synchronization channel (SCH) adopting a code common in
cells included in the reception signal to identify a sector, and
has timing detecting means for detecting a synchronization channel
(SCH) position in a reception signal by a cross-correction method
using a time waveform of a replica signal of the sector specific
code multiplied by a subcarrier assigned a code element that is a
phase reference among code elements constituting the cell specific
code, and sector identifying means for detecting a sector specific
code providing the maximum reception power by despreading
processing with the sector specific code of the synchronization
channel (SCH) arranged on the frequency axis.
[0384] In the multicarrier reception apparatus of the invention, in
the first step of detecting a position of the SCH included in a
reception signal, applied is the method (cross-correlation method)
for multiplying the reception signal by a time waveform of a
replica signal of the sector specific code to obtain correlation.
It is thereby possible toe detect the SCH timing with high
accuracy.
[0385] Furthermore, the multicarrier reception apparatus of the
invention further has cell identifying means for detecting,
concurrently with the detection processing of the sector specific
code in the sector identifying means, a phase difference between a
subcarrier as a phase reference and another subcarrier, associated
with the subcarrier, multiplied by a code element of a cell
specific code among subcarriers assigned the synchronization
channel (SCH), thereby demodulating the cell specific code, further
performing correlation detection processing with a cell specific
code desired to detect when necessary, thereby detecting the cell
specific code, and detecting a cell ID or cell ID group
information.
[0386] It is thereby possible to receive a multicarrier signal and
implement a cell search including sector identification by the SCH.
When the number of subcarriers is adequate, it is possible to
identify a sector ID and cell ID only by the SCH.
[0387] Moreover, the multicarrier reception apparatus of the
invention further has means for implementing despreading and
correlation detection processing using a pilot channel, and
detecting a cell ID to complete the cell identification processing
when the information specified by the cell identifying means is
cell ID group information.
[0388] By this means, when the number of subcarriers is not
sufficient, and only the cell ID group is identified by the SCH, a
cell ID is subsequently identified by despreading and correlation
detect ion of the pilot channel, and the cell search can be
completed.
[0389] Further, in the data structure of the synchronization
channel (SCH) of the invention, subcarriers (i.e. subcarriers for
use in sector identification) multiplied by code elements as a
phase reference constituting the cell specific code are arranged
symmetrically on the low-frequency side and high-frequency side
with respect to the center frequency at intervals of the
predetermined number of subcarriers, the time waveform formed by
the subcarriers for use in sector identification being combined is
thereby a time waveform having the periodicity that a reference
waveform, or an inverted waveform of the reference waveform is
repeated on a 1/M (M is a natural number of "2" or more) symbol
basis in a one-symbol period, and by using the periodicity of the
time waveform, it is possible to detect the synchronization channel
(SCH) position by the auto-correlation method.
[0390] Furthermore, by devising the arrangement on the frequency
axis of subcarriers for use in sector identification, it is
possible to obtain a characteristic time waveform on a 1/N (N is a
natural number of "4" or more) symbol basis, and by using the
characteristic periodicity of the time waveform, it is possible to
perform correlation determination with high accuracy more
efficiently. Since simplified correlation detection can be
performed with the periodicity on a 1/N basis noted, it is possible
to simplify the configuration of a correlator (also referred to as
a matched filter).
[0391] Moreover, in the data structure of the synchronization
channel (SCH) of the invention, subcarriers for use in sector
identification are arranged symmetrically on the low-frequency side
and high-frequency side with respect to the center frequency at
positions apart from one another by three subcarriers i.e. at the
second, sixth, tenth, fourteenth and similarly subsequent positions
with the center frequency assumed to be the zeroth, and the time
waveform formed by the subcarriers for use in sector identification
being combined is thereby a time waveform having the periodicity
that a reference waveform, and an inverted waveform of the
reference waveform are alternately repeated on a 1/4 symbol basis
in a one-symbol period.
[0392] Assuming the reference waveform as B, the time waveform is
obtained, such as B, -B, B, -B, having the periodicity that the
reference waveform and the inverted wave form of the reference wave
form are alternately repeated on a 1/4 symbol basis in a one-symbol
period. In this case, it is only required to detect the specific
periodicity of the time waveform repeated on a 1/4 symbol basis,
and the configuration of a correlator can be simplified.
[0393] Further, in the data structure of the synchronization
channel (SCH) of the invention, subcarriers for use in sector
identification are arranged symmetrically on the low-frequency side
and high-frequency side with respect to the center frequency at
positions apart from one another by three subcarriers i.e. at the
fourth, eighth, twelfth, sixteenth and similarly subsequent
positions with the center frequency assumed to be the zeroth, and
the time waveform formed by the subcarriers for use in sector
identification being combined is thereby a time waveform having the
periodicity that the same reference waveform is repeated on a 1/4
symbol basis in a one-symbol period.
[0394] Assuming the reference waveform as D, the time waveform is
obtained, such as D, D, D, D, having the periodicity that the same
reference waveform is repeated on a 1/4 symbol basis in a
one-symbol period. Also in this case, it is possible to simplify
the configuration of a correlator.
[0395] Furthermore, in the data structure of the synchronization
channel (SCH) of the invention, the sector common code and each of
code elements that are the phase references constituting the cell
specific code are common codes in all the cells, code elements of
the sector common code are common in subcarriers on the frequency
axis to be assigned the synchronization channel (SCH), the code
elements that are the phase references constituting the cell
specific code are also common in the subcarriers as a phase
reference, and such a condition is thereby eliminated that
subcarriers to obtain a code element targeted for despreading are
limited to a group of adjacent subcarriers in detecting a sector
specific code providing the maximum reception power by the
despreading processing with the sector specific code to identify a
sector.
[0396] In the case of performing the processing (SCH position
detection processing) in the first step in a cell search by
cross-correlation detection, it is intended to adopt the most
simplified code structure by providing subcarriers on the frequency
axis with commonality of (i.e. all the same) a sector common code
common in all the cells and code elements to be multiplied by
subcarriers as a phase reference among the sector specific codes
common in all the cells. It is thereby possible to select some
subcarriers from among all the subcarriers to specify the sector
specific code. Accordingly, such a condition is eliminated that
subcarriers to obtain a code element targeted for despreading are
limited to a pair of adjacent subcarriers.
[0397] Further, a cell search method of the invention includes the
first step of detecting a synchronization channel (SCH) position in
a reception signal by an auto-correlation method or
cross-correlation method, and the second step of using that a time
waveform formed by a combination of subcarriers as a phase
reference assigned code elements of the sector specific code has a
characteristic waveform corresponding to the assigned code
elements, thereby detecting a correlation value by the
cross-correlation method, identifying a sector providing the
highest correlation value as the nearest sector, concurrently
detecting a phase difference between a subcarrier as the phase
reference and another subcarrier, associated with the subcarrier,
multiplied by a code element of the cell specific code in
subcarriers assigned the synchronization channel (SCH), thereby
demodulating the cell specific code, further performing correlation
detection processing with a cell specific code desired to detect
when necessary, and thereby detecting the cell specific code.
[0398] It is clarified in the cell search method that sector
identification can be performed by not only correlation value peak
determination by despreading subsequent to FFT processing, but also
cross-correlation in time waveform prior to FFT. In other words,
before the FFT processing, a cross-correlation peak is detected
using replica time waveforms of the sector specific codes, the code
providing the maximum peak is specified, and it is thereby possible
to identify the nearest sector. To apply the cross-correlation
method using the replica time waveforms, it is a condition that
mobile stations know various sector specific codes transmitted from
the base station. In addition, as the sector identification method,
it can be determined as appropriate using the technique for
detecting correlation by despreading using orthogonal codes, or
using the technique for detecting cross-correlation using replica
time waveforms, in consideration of required detection accuracy,
restrictions on circuitry, or the like.
* * * * *