U.S. patent application number 11/917718 was filed with the patent office on 2009-12-03 for transmission apparatus, transmission method, reception apparatus, and reception method.
This patent application is currently assigned to NTT DOCOMO, INC.. Invention is credited to Kenichi Higuchi, Yoshihisa Kishiyama, Mamoru Sawahashi.
Application Number | 20090296563 11/917718 |
Document ID | / |
Family ID | 37532307 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090296563 |
Kind Code |
A1 |
Kishiyama; Yoshihisa ; et
al. |
December 3, 2009 |
TRANSMISSION APPARATUS, TRANSMISSION METHOD, RECEPTION APPARATUS,
AND RECEPTION METHOD
Abstract
A disclosed transmission apparatus includes a multiplexing
portion that multiplexes a common pilot channel, a shared control
channel, and a shared data channel; a symbol generation portion
that performs an inverse Fourier transformation on the multiplexed
signal so as to generate a symbol; and a transmission portion that
transmits the generated symbol. The multiplexing portion
multiplexes the shared control channel including control
information necessary for demodulation of the shared data channel
including a payload and the common pilot channel to be used by
plural users in a frequency direction, and the shared data channel
in a time direction with respect to the common pilot channel and
the shared control channel. Even when the number of symbols
composing a transmission time interval (TTI) is reduced,
transmission efficiency of channels excluding the common pilot
channel can be maintained by reducing insertion intervals of the
common pilot channel accordingly.
Inventors: |
Kishiyama; Yoshihisa;
(Kanagawa, JP) ; Higuchi; Kenichi; (Kanagawa,
JP) ; Sawahashi; Mamoru; (Kanagawa, JP) |
Correspondence
Address: |
OSHA LIANG L.L.P.
TWO HOUSTON CENTER, 909 FANNIN, SUITE 3500
HOUSTON
TX
77010
US
|
Assignee: |
NTT DOCOMO, INC.
Tokyo
JP
|
Family ID: |
37532307 |
Appl. No.: |
11/917718 |
Filed: |
June 13, 2006 |
PCT Filed: |
June 13, 2006 |
PCT NO: |
PCT/JP2006/311878 |
371 Date: |
June 25, 2009 |
Current U.S.
Class: |
370/210 |
Current CPC
Class: |
H04L 5/0051 20130101;
H04J 13/00 20130101; H04J 13/004 20130101; H04L 5/0023 20130101;
H04L 5/0037 20130101; H04L 5/005 20130101 |
Class at
Publication: |
370/210 |
International
Class: |
H04J 11/00 20060101
H04J011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2005 |
JP |
2005-174400 |
Aug 23, 2005 |
JP |
2005-241905 |
Feb 8, 2006 |
JP |
2006-031752 |
Claims
1. A transmission apparatus comprising: a multiplexing portion that
multiplexes a common pilot channel, a shared control channel, and a
shared data channel; a symbol generation portion that performs an
inverse Fourier transformation on the multiplexed signal so as to
generate a symbol; and a transmission portion that transmits the
generated symbol; wherein the multiplexing portion multiplexes the
shared control channel including control information necessary for
demodulation of the shared data channel including a payload and the
common pilot channel to be used by plural users in either one of a
frequency direction and a time direction, or a combination thereof,
and multiplexes the shared data channel in either one of a
frequency direction and a time direction, or a combination thereof,
with respect to the common pilot channel and the shared control
channel.
2. The transmission apparatus of claim 1, wherein the multiplexing
portion multiplexes a dedicated pilot channel to be used by one or
more of specific users to demodulate the shared data channel in
either one of the frequency direction and the time direction, or a
combination thereof, with respect to the common pilot channel and
the shared control channel.
3. The transmission apparatus of claim 2, wherein the dedicated
pilot channel is time-multiplexed at a first point of time at
predetermined frequency intervals and also time-multiplexed at a
second point of time at the predetermined frequency intervals.
4. The transmission apparatus of claim 2, wherein the dedicated
pilot channel is transmitted to a communications party that moves
at high moving velocity but not to another communications party
that does not move at high moving velocity.
5. The transmission apparatus of claim 2, further comprising a
portion that adjusts transmission beam directionality to a specific
communications party, wherein the dedicated pilot channel is
inserted for the specific communications party.
6. The transmission apparatus of claim 2, further comprising plural
transmission antennas, wherein the common pilot channel is
transmitted from one or more of the plural transmission antennas
and the dedicated pilot channel is transmitted from any other one
or more of the plural transmission antennas.
7. The transmission apparatus of claim 2, wherein the common pilot
channel and the dedicated pilot channel are discontinuously mapped
in either one of the time direction and the frequency direction, or
a combination thereof.
8. The transmission apparatus of claim 1, wherein the common pilot
channel is transmitted with codes that are orthogonal between
either one of cells and sectors.
9. The transmission apparatus of claim 1, wherein the common pilot
channel is composed of either one of all and part of a CAZAC code
having a predetermined code length.
10. The transmission apparatus of claim 8, wherein when the shared
data channel is transmitted in a cell or sector, and transmission
power of the shared data channel is reduced below a predetermined
value in different cells or sectors.
11. The transmission apparatus of claim 8, wherein the common pilot
channel in a cell or sector is transmitted at either one of a
different time and a different frequency, or a combination thereof,
from the common pilot channel to be transmitted in a different cell
or sector.
12. The transmission apparatus of claim 11, wherein when the common
pilot channel is transmitted in a cell or sector, transmission
power of the shared data channel is reduced below a predetermined
value in a different cell or sector.
13. A transmission method comprising steps of: multiplexing a
common pilot channel to be used by plural users and a shared
control channel including control information necessary for
demodulation of a shared data channel including a payload in either
one of a frequency direction and a time direction, or a combination
thereof, and the shared data channel in either one of the frequency
direction and the time direction, or a combination thereof, with
respect to the common pilot channel and the shared control channel;
performing an inverse Fourier transform on the multiplexed signal
so as to generate a symbol; and transmitting the generated
symbol
14. A reception apparatus comprising: a reception portion that
receives a symbol transmitted from a transmitter; a transformation
portion that performs a Fourier transformation on the received
symbol; and a separation portion that separates a common pilot
channel, a shared control channel and a shared data channel from
the transformed signal; wherein the separation portion separates
the common pilot channel to be used by plural users and the shared
control channel including control information necessary for
demodulation of the shared data channel in either one of a
frequency direction and a time direction, or a combination thereof,
and separates the shared data channel including a payload in either
one of the frequency direction and the time direction, or a
combination thereof, with respect to the common pilot channel and
the shared control channel.
15. A reception method comprising steps of: receiving a symbol
transmitted from a transmitter; performing a Fourier transformation
on the received signal; and separating a common pilot channel to be
used by plural users and a shared control channel including control
information necessary for demodulation of a shared data channel
including a payload in either one of a frequency direction and a
time direction, or combination thereof, and the shared data channel
in either one of the frequency direction and the time direction, or
a combination thereof, with respect to the common pilot channel and
the shared control channel.
16. A transmission apparatus comprising: a generation portion that
generates a common pilot channel to be used by plural mobile
stations; a multiplexing portion that multiplexes two or more
channels to be transmitted; and a first multiplication portion that
multiplies the common pilot channel by a spreading code sequence
common to plural sectors and an orthogonal code sequence different
in different sectors.
17. The transmission apparatus of claim 16, wherein the first
multiplication portion multiplies other channels excluding the
pilot channel by the spreading code sequence common to plural
sectors and the orthogonal code sequence different in different
sectors.
18. The transmission apparatus of claim 17, further comprising: a
derivation portion that derives another spreading code sequence
from the spreading code sequence common to the plural sectors in
accordance with a predetermined rule; and a second multiplication
portion that multiplies other channels excluding the pilot channel
by the derived spreading code sequence.
19. The transmission apparatus of claim 18, wherein the first
multiplication portion multiplies the common pilot channel and the
shared control channel by the spreading code sequence common to the
plural sectors and the orthogonal code sequence different in
different sectors; and wherein the second multiplication portion
multiplies the shared data channel by the derived spreading code
sequence.
20. The transmission apparatus of claim 9, wherein when the shared
data channel is transmitted in a cell or sector, and transmission
power of the shared data channel is reduced below a predetermined
value in different cells or sectors.
21. The transmission apparatus of claim 9, wherein the common pilot
channel in a cell or sector is transmitted at either one of a
different time and a different frequency, or a combination thereof,
from the common pilot channel to be transmitted in a different cell
or sector.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to a mobile
communications field of technology, and specifically to a
transmission apparatus, a transmission method, a reception
apparatus, and a reception method for use in an Orthogonal
Frequency Division Multiplexing (OFDM) method mobile communications
system.
BACKGROUND ART
[0002] A future mobile communications system that mainly carries
out image or data communications requires capabilities far beyond
the capability of the conventional mobile communications system
(for example, an IMT-2000-based system). To this end, higher
capacity, higher speed, broader band or the like have to be
realized.
[0003] In a broadband mobile communications system, frequency
selective fading caused by a multi-path transmission environment
tends to be problematic, which makes an OFDM (Orthogonal Frequency
Division Multiplexing) method be considered promising as a method
of the next generation communications system. In the OFDM method,
guard intervals are added to active symbols including information
to be transmitted so as to produce symbols, which are in turn
transmitted one by one at predetermined transmission time intervals
(TTIs). Here, plural TTIs compose one frame. In addition, the guard
interval is generated using part of information included in the
active symbol. The guard interval may be called a cyclic prefix
(CP) in some cases. FIG. 1 shows a relationship among the frame,
the TTI, and the symbol. Since a receiver receives signals with
various transmission delays, inter-symbol interference is caused.
However, in the OFDM method, such inter-symbol interference can be
sufficiently suppressed as long as the transmission delays fall
within a time length of the guard interval.
[0004] During a time period of one TTI, various channels are
transmitted. The channels may include a common pilot channel, a
shared control channel, and a shared data channel. The common pilot
channel is used by plural users to demodulate the shared control
channel. Specifically, the common pilot channel is used for channel
estimation, synchronous detection, reception signal quality
measurement, or the like. The shared control channel is used to
demodulate the shared data channel including payload (or traffic
information channel). Regarding conventional signal formats
including the pilot channel, see non-patent document 1, for
example.
[0005] [Non-patent document 1] Keiji Tachikawa, "W-CDMA mobile
communications method", MARUZEN Co., Ltd., pp. 100-101.
SUMMARY OF INVENTION
Problem to be Solved by the Invention
[0006] By the way, the TTI is used to define various units in
information transmission. For example, the TTI determines a
transmission unit of a packet, an update unit of data-modulating
and channel-coding in Modulation and Coding Scheme (MCS), a unit of
error correction coding, a retransmission unit of Automatic Repeat
reQuest (ARQ), a packet scheduling unit, or the like. Under such
circumstances, the TTI length and thus the frame length should be
maintained constant. However, the number of symbols included in the
TTI may be optionally changed depending on application or
system.
[0007] The common pilot channel is allocated to one or more symbols
in the TTI, and a control channel or a data channel is allocated to
other symbols in the same TTI in various conventional transmission
methods. When it is assumed that one symbol is occupied by the
common pilot channel while the TTI is composed of ten symbols, the
common pilot channel occupies 10% of the TTI ( 1/10) . On the other
hand, when it is assumed that one symbol is occupied by the common
pilot channel while the TTI is composed of five symbols, the common
pilot occupies as much as 20% of the TTI (1/5). Therefore,
reduction of the number of the symbols included in the TTI leads to
a problem of reduced transmission efficiency of the data channel.
Such a problem becomes significant especially when the number of
the symbols in the TTI is reduced.
[0008] The present invention has been made to address the above
problem, and is directed to a transmission apparatus, a
transmission method, a reception apparatus, and a reception method
in which the data channel transmission efficiency can be maintained
or improved even when the number of the symbols included in the TTI
is reduced.
Means for Solving the Problem
[0009] An embodiment according to the present invention provides a
transmission apparatus that includes a multiplexing portion that
multiplexes a common pilot channel, a shared control channel, and a
shared data channel; a symbol generation portion that performs an
inverse Fourier transformation on the multiplexed signal so as to
generate a symbol; and a transmission portion that transmits the
generated symbol. In this embodiment, the multiplexing portion
multiplexes in a frequency direction the shared control channel
including control information necessary for demodulation of the
shared data channel including a payload and the common pilot
channel to be used by plural users, and also multiplexes the shared
data channel in a time direction with respect to both the common
pilot channel and the shared control channel. Even when the number
of symbols composing the transmission time interval (TTI) is
reduced, transmission efficiency of channels excluding the common
pilot channel can be maintained by reducing insertion intervals of
the common pilot channel accordingly.
Advantage of the Invention
[0010] According to the present invention, the data channel
transmission efficiency can be maintained or improved even when the
number of the symbols included in the TTI is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a relationship among a frame, a transmission
time interval (TTI), and a symbol;
[0012] FIG. 2 is a block diagram of a transmitter according to an
example of the present invention;
[0013] FIG. 3 is a block diagram of a receiver according to an
example of the present invention;
[0014] FIG. 4 shows an example of a channel configuration according
to an example of the present invention;
[0015] FIG. 5 shows various channel configurations;
[0016] FIG. 6 shows various channel configurations including
dedicated pilot channels;
[0017] FIG. 7 shows a relationship among an insertion interval, a
symbol length, and a maximum delay time;
[0018] FIG. 8 is a diagram of a transmitter according to an example
of the present invention;
[0019] FIG. 9 shows an example of a channel configuration according
to the present invention;
[0020] FIG. 10 is a block diagram of a transmitter according to an
example of the present invention;
[0021] FIG. 11 shows a sector beam and a directional beam;
[0022] FIG. 12 shows an example of a channel configuration
according to an example of the present invention;
[0023] FIG. 13 shows a MIMO multiplexing method according to an
example of the present invention;
[0024] FIG. 14 shows an example of a channel configuration
according to an example of the present invention;
[0025] FIG. 15 shows various channel configurations of common pilot
channels;
[0026] FIG. 16 shows a channel configuration of dedicated/common
pilot channels;
[0027] FIG. 17 schematically shows the pilot channels to be
transmitted by a multi-beam;
[0028] FIG. 18 schematically shows the pilot channels to be
transmitted by an adaptive directional beam;
[0029] FIG. 19 shows an example of channel allocation of the
dedicated/common pilot channels in accordance with a TDM
method;
[0030] FIG. 20A shows a relationship between throughput and an
average reception E.sub.s/N.sub.0 when the number N.sub.stg of
staggered mapping is changed;
[0031] FIG. 20B shows an example of channel mapping when the number
N.sub.stg of the staggered mapping is 0, 1, and 2;
[0032] FIG. 21A schematically shows mobile communications using
pilot sequences orthogonal with each other between sectors;
[0033] FIG. 21B shows a pilot channel generation portion for use in
a transmitter according to an example of the present invention;
[0034] FIG. 22 shows a specific example of orthogonal pilot
sequences;
[0035] FIG. 23 shows a specific example of orthogonal pilot
sequences;
[0036] FIG. 24 shows a relationship between a scramble code and an
orthogonal code;
[0037] FIG. 25 shows a first example in which the common pilot
channel and other channels are multiplied by the scramble code and
the orthogonal code;
[0038] FIG. 26 shows a second example in which the common pilot
channel and other channels are multiplied by the scramble code and
the orthogonal code;
[0039] FIG. 27 shows an example of a combination of the examples
shown in FIGS. 25 and 26;
[0040] FIG. 28 shows the pilot channel and data channel of a
desired signal and a non-desired signal;
[0041] FIG. 29 shows inter-sector orthogonal sequences for MIMO
pilot channels;
[0042] FIG. 30 is an explanatory view of CAZAC codes; and
[0043] FIG. 31 shows the pilot channel and the data channel of a
desired signal and a non-desired signal.
LIST OF REFERENCE SYMBOLS
[0044] 202-1 through 202-K: data channel processing portion [0045]
210: spreading and channel coding portion [0046] 212: interleaving
portion [0047] 214: data demodulation portion [0048] 216:
time/frequency mapping portion [0049] 204: common pilot
multiplexing portion [0050] 206: Inverse Fast Fourier
Transformation (IFFT) portion [0051] 208: guard interval insertion
portion [0052] 302: guard interval removal portion [0053] 304: Fast
Fourier Transformation portion [0054] 308: channel estimation
portion [0055] 310: dedicated pilot separation portion [0056] 312:
time/frequency data extraction portion [0057] 314: data
demodulation portion [0058] 316: deinterleaving portion [0059] 318:
despreading and channel decoding potion [0060] 72: dedicated pilot
channel control portion [0061] 74: dedicated pilot multiplexing
portion [0062] 102: dedicated pilot multiplexing portion [0063]
104: antenna weight control portion [0064] 106: weight setting
portion [0065] 2102: pilot sequence providing portion [0066] 2104:
scramble code portion [0067] 2106: orthogonal code portion [0068]
2108, 2110: multiplication portion [0069] 2502, 2504: providing
portion [0070] 2506: scramble code portion [0071] 2508: orthogonal
code portion [0072] 2510, 2512, 2514: multiplication portion [0073]
2602: scramble code portion [0074] 2604: multiplication portion
BEST MODE FOR CARRYING OUT THE INVENTION
[0075] According to one aspect of the present invention, a common
pilot channel and a shared data channel are time-multiplexed, and a
common control channel and a data channel are also
time-multiplexed. Since the common pilot channel is allocated not
to an entire frequency band but to part of the frequency band or
part of sub-carriers, other channels excluding the common pilot
channel are allocated to other sub-carriers in the symbol. By
adjusting an insertion position of the common pilot channel in a
frequency direction, the ratio of the common pilot channel in
relation to the symbol can also be adjusted. Therefore, even when
the number of symbols composing the TTI is reduced (and a time
period of one symbol becomes longer), transmission efficiencies of
other channels excluding the common pilot channel can be maintained
by reducing the number (frequency) of the inserted common pilot
channels accordingly.
[0076] According to another aspect of the present invention, a
dedicated pilot channel to be used by one or more specific users to
demodulate the shared data channel and a combination of the common
pilot channel and the shared control channel are multiplexed in a
time direction. By estimating channels using the dedicated pilot
channel in addition to the common pilot channel, channel estimation
accuracy or the like will be improved.
[0077] The dedicated pilot channel is time-multiplexed at a first
point of time at constant frequency intervals and also
time-multiplexed at a second time at the constant frequency
intervals. By dispersing the pilot channels in the time and the
frequency direction, a diversity effect of the pilot channel can be
improved while transmission efficiency of channels excluding the
pilot channel is improved.
[0078] The dedicated pilot channel is transmitted to a
communications party that moves at a higher moving velocity but not
necessarily transmitted to a communications party that does not
move at a higher moving velocity. By transmitting the dedicated
pilot channel to only a user whose channel fluctuation is
considered to be large in the time direction, unnecessary
transmission of the dedicated transmission channel can be
avoided.
[0079] A beam directionality adjuster that adjusts directionality
of the transmission beam toward a specific communications party may
be provided in a transmission apparatus. The dedicated pilot
channel may be inserted for a specific communications party. When
the directional beam is used, channel qualities are different from
beam to beam. By utilizing the dedicated pilot channel directed
toward the specific communications party in addition to the common
pilot channel, channel estimation accuracy is improved.
[0080] When the MIMO multiplexing method is used, the pilot channel
may be transmitted from one or more transmission antennas and the
dedicated pilot channel may be transmitted from another one or more
transmission antennas, which allows for appropriate MIMO
multiplexing transmission depending on the class of a reception
apparatus (specifically, the number of reception antennas).
[0081] According to another aspect of the present invention, there
is provided a reception apparatus having a reception portion that
receives a symbol transmitted from a transmitter, a transformation
portion that performs the Fourier transformation on the received
symbol, and a separation portion that separates a common pilot
channel, a shared control channel, and a shared data channel from
the transformed signal. The separation portion frequency-separates
the common pilot channel used by plural users to demodulate the
shared control channel and the shared control channel used to
demodulate the shared data channel, and time-separates the shared
data channel including a payload and a combination of the common
pilot channel and the shared control channel.
[0082] In a transmission apparatus according to another aspect of
the present invention, the common pilot channel is multiplied by a
spreading code sequence (scramble code) common to plural sectors
and an orthogonal code sequence which is different from sector to
sector, and the resultant signal is transmitted to a communications
party (typically, a mobile station). Since one sector is
distinguished from the other sectors by not the scramble code but
the orthogonal code, distinguishing sectors is easily and highly
accurately carried out, thereby improving quality of the pilot
channel.
[0083] Other channels excluding the common pilot channel may be
multiplied by the spreading code sequence (scramble code) common to
plural sectors and the orthogonal code sequence which is different
from sector to sector.
[0084] From a spreading code sequence common to plural sectors,
another spreading code is derived in accordance with a
predetermined rule, and the derived spreading code may multiply
other channels excluding the pilot channel. With this, while
different scramble codes are used for the pilot channel and other
channels, those scramble codes can be readily detected by using the
deriving rule.
[0085] The pilot channel and the shared control channel may be
multiplied by the spreading code sequence (scramble code) common to
plural sectors and the orthogonal code sequence which is different
from sector to sector, and the shared data channel may be
multiplied by another spreading code. With this, scramble codes can
be used accordingly from the viewpoint of, for example, a change in
a spreading factor.
[0086] In the following examples, although the present invention is
described in the context of a system employing the OFDM method in
downlink, other systems employing, for example, a multi-carrier
method may be used.
EXAMPLE 1
[0087] FIG. 2 shows a part of a transmitter according to a first
example of the present invention. Although this transmitter is
typically provided in a radio base station of a mobile
communications system as described in this example, the transmitter
may be provided in other apparatuses. The transmitter has plural
data channel processing portions 202-1 to 101-K, the number of
which is K, a common pilot multiplexing portion 204, an IFFT
portion 206, and a guard interval insertion portion 208. Since the
K data channel processing portions 202-1 to 202-K have identical
functions and configurations, a first data channel processing
portion 202-1 represents the others in the following explanation.
The data channel processing portion 202-1 has a spreading and
channel coding portion 210, an interleaving portion 212, a data
modulation portion 214, and a time and frequency mapping portion
216.
[0088] The data channel processing portion 202-1 processes a data
channel for a first user. While one data channel processing portion
carries out a process for one user for simplicity of explanation,
plural data channel processing portions may be used for one
user.
[0089] The spreading and channel coding portion 210 performs
channel coding on the data channel to be transmitted, thereby
enhancing error correction capability. It should be noted that code
spreading is not performed in this particular example because the
OFDM method is employed. However, when an OFCDM (Orthogonal
Frequency and Code Division Multiplexing) method is employed in
other examples, the spreading and channel coding portion 210
conducts both the channel coding and the code spreading on the data
channel to be transmitted. The channel coding may be turbo
coding.
[0090] The interleaving portion 212 changes the order of symbols of
the channel-coded signal in a time direction and/or a frequency
direction in accordance with a predetermined rule known by the
transmitter and its corresponding receiver.
[0091] The data modulation portion 214 maps the signal to be
transmitted in a signal constellation in accordance with an
appropriate modulation method. As the modulation method, various
modulation methods such as QPSK, 16QAM, 64QAM or the like may be
employed. When Adaptive Modulation and Coding Scheme (AMCS) is
employed, the modulation method and a channel coding rate are
assigned on a case-by-case basis.
[0092] The time and frequency mapping portion 216 determines how
the data channels to be transmitted are mapped in the time and/or
the frequency direction.
[0093] The common pilot multiplexing portion 204 multiplexes the
common pilot channels, the shared control channels, and the data
channels, and outputs the multiplexed channels. The multiplexing
may be made in the time direction, in the frequency direction, or
in both the time and the frequency directions.
[0094] The IFFT portion 206 performs the Inverse Fast Fourier
Transformation on the signal to be transmitted, or the modulation
according to the OFDM method, which forms an active symbol
portion.
[0095] The guard interval insertion portion 208 extracts a part of
the active symbol and adds the extracted part to a top or end of
the active symbol, thereby forming a transmission symbol
(transmission signal).
[0096] The data channel processing portions 202-1 through 202-K
process the data channels to be transmitted to the corresponding
users. In the data channel processing portions 202-1 to 202-K, the
data channels are channel-coded, interleaved, data-modulated, and
mapped in the time/frequency directions. The mapped data channels
are output from the corresponding data channel processing portions
202-1 to 202-K and input to the common pilot multiplexing portion
204, in which the data channels are multiplexed with the common
pilot channels and the shared control channels. The multiplexed
signal undergoes the Inverse Fast Fourier Transformation, and a
guard interval is added to the transformed signal (the active
symbol portion), thereby forming the transmission symbol. The
transmission symbol is transmitted via a radio portion (not
shown).
[0097] FIG. 3 shows a part of a receiver according to this example
of the present invention. While this receiver is provided in a
mobile station (for example, user equipment of a user #1) of the
mobile communications system as shown in this example, the receiver
may be provided in other apparatuses. The receiver has a guard
interval removal portion 302, an FFT portion 304, a common pilot
separation portion 306, a channel estimation portion 308, a
dedicated pilot separation portion 310, a time and frequency data
extraction portion 312, a data demodulation portion 314, a
deinterleaving portion 316, and a despreading and channel decoding
portion 318.
[0098] The guard interval removal portion 302 removes the guard
interval from the transmitted symbol and thus extracts the active
symbol portion.
[0099] The FFT portion 304 performs the Fast Fourier Transformation
on the signal, or demodulation according to the OFDM method.
[0100] The common pilot separation portion 306 separates every
sub-carrier demodulated in accordance with the OFDM method so as to
obtain the common pilot channels, the shared control channels, and
other channels.
[0101] The channel estimation portion 308 performs channel
estimation using the separated common pilot channels and outputs to
the data demodulation portion 314 or the like a control signal for
channel compensation. Such control signal is also used for the
channel compensation for the shared control channels, though not
shown for simplicity of illustration.
[0102] The dedicated pilot separation portion 310 is not used in
this example but used to separate the dedicated pilot channels from
the other channels in a below-described example. The dedicated
pilot channels are given to the channel estimation portion 308 and
used in order to enhance the channel estimation accuracy.
[0103] The time and frequency data extraction portion 312 extracts
the data channels in accordance with the mapping rule determined by
the transmitter and outputs the extracted data channels.
[0104] The data demodulation portion 314 performs channel
compensation and then demodulation on the data channels. The
modulation method is in accordance with the modulation method
performed in the transmitter.
[0105] The deinterleaving portion 316 changes the order of the
symbol of the data channels in accordance with the interleaving
performed in the transmitter.
[0106] The despreading and channel coding portion 318 performs
channel decoding on the received data channels. Since the OFDM
method is employed, code despreading is not performed in this
example. However, when the OFCDM method is employed in other
examples, the despreading and channel decoding portion 318 conducts
both the code despreading and the channel decoding on the received
data channels.
[0107] A signal received by an antenna (not shown) passes through a
radio portion (not shown), is converted into a base band signal,
and undergoes the guard interval removal and the Inverse Fast
Fourier Transformation. From the transformed signal is separated
the common pilot channels, which are used in the channel
estimation. Additionally, the shared control channels and the data
channels are separated from the transformed signal and then
demodulated. The demodulated data channels are deinterleaved and
channel-decoded, and thus the data that have been transmitted from
the transmitter are restored.
[0108] FIG. 4 shows how various channels are multiplexed in this
example. As an example, 20 TTIs are included in a 10 ms frame,
which means one TTI is 0.5 ms. One TTI is composed of 7 symbols
arranged along the time direction (N.sub.D=7).
[0109] In the illustrated example, the common pilot channels, the
shared control channels, the dedicated pilot channels, and the data
channels are multiplexed. The dedicated pilot channels are
described in a second example and beyond. The common pilot channels
and the shared control channels are frequency-multiplexed in one
symbol. Specifically, the common pilot channels are inserted at
certain frequency intervals into a leading symbol of the TTI. On
the other hand, the shared data channels are transmitted by a
second symbol and beyond in the same TTI. Namely, the common pilot
channels and the shared data channels are time-multiplexed, and the
shared control channels and the data channels are also
time-multiplexed. Since the common pilot channels are allocated not
to the entire frequency band in the TTI but to a part of the
frequency band or a part of the sub-carriers, other channels
excluding the common pilot channels can be allocated to the other
sub-carriers. By adjusting insertion intervals of the common pilot
channels in the frequency direction, the ratio of the common pilot
channels in relation to the TTI can be adjusted. For example, when
the number of the symbols in the TTI is reduced (and a time period
per symbol becomes longer accordingly), channel transmission
efficiency of the channels excluding the common pilot channels can
be maintained by accordingly reducing insertion frequencies of the
common pilot channels.
[0110] FIG. 5 shows various examples of channel configurations in
which the common pilot channels and the shared control channels are
multiplexed. It should be noted that the channel configurations are
not limited to the illustrated examples but are realized into yet
another configuration. A channel configuration 1 shown in FIG. 5 is
the same as the channel configuration shown in FIG. 4. As stated,
the common pilot channels are used for the channel estimation to
demodulate the shared control channels. In the channel
configuration 1, since the common pilot channels and the shared
control channels are frequency-multiplexed, there are no common
pilot channels for the sub-carrier that contains the shared control
channels and therefore a channel estimation value cannot be
directly obtained for the shared control channels in the channel
configuration 1. Therefore, the channel estimation value for the
shared control channel has to be obtained by interpolating the
channel estimation values for the sub-carriers that contain the
common pilot channels. The interpolation may be a linear
interpolation. By the way, bi-directional arrows in FIG. 5 indicate
that the interpolation is carried out in the marked section. In
this particular example, since all the common pilot channels and
the shared control channels are allocated to the leading symbol,
demodulation of the shared data channels can be carried out
quickly. In addition, since the common pilot channels and the
shared control channels are distributed widely in the frequency
direction, a frequency diversity effect can be improved and
resilience to frequency selective fading can be enhanced.
[0111] In a channel configuration 2, the common pilot channels and
the shared control channels are time-multiplexed. In this
configuration, no interpolation is necessary in contrast to the
channel configuration 1. In addition, the common pilot channels and
the shared control channels are distributed widely in the frequency
direction, thereby enhancing resilience to the frequency selective
fading.
[0112] In a channel configuration 3, the shared control channels
are inserted after a part of the common pilot channels but not
after the other common pilot channels. The common pilot channels
and the shared control channels multiplexed in the time direction
allow for power ratio adjustment during transmission. In this
configuration, since the shared control channels are inserted so as
to substantially cover the TTI in the time direction, the channel
estimation throughout the entire TTI is necessary. In this case, if
only the common pilot channels in the leading symbol are used for
the channel estimation, the channel estimation accuracy for the end
symbol is not sufficiently assured. The situation becomes worse
especially when the receiver is moving at a higher moving velocity
since channel fluctuation in the time direction tends to be rather
large in this case. Therefore, the channel estimation value
obtained from the leading symbol in the TTI and the channel
estimation value obtained from the end symbol in the TTI are used
(for example, linearly interpolated) so as to preferably perform
the channel estimation.
[0113] In a channel configuration 4, the shared control channels
are multiplexed by frequency hopping in the time and the frequency
directions. Since the common pilot channels and the shared control
channels are distributed widely in the frequency direction, the
resilience to the frequency selective fading can be enhanced. In
addition, since the common pilot channels and the shared control
channels are distributed also in the time direction, the power
ratio can be adjusted during transmission.
EXAMPLE 2
[0114] In a second example of the present invention, the dedicated
pilot channels are used in addition to the common pilot channels.
These channels are the same in that these channels are used for the
channel estimation or the like. However, these channels are
different in that the dedicated pilot channels are used only for a
particular mobile station while the common pilot channels are used
for all the mobile stations. Therefore, while only one kind of
signal may be prepared as a signal indicating the common channel,
plural kinds of signals have to be prepared as signals indicating
the dedicated pilot channels, the number of which is larger than
the number of the mobile phones. The dedicated pilot channels are
used when the mobile phones move at higher moving velocity, when a
directional beam is used in downlink, and when the mobile stations
have the predetermined number of reception antennas, or the like,
the details of which are explained below.
[0115] FIG. 6 shows various channel configurations including the
dedicated pilot channels. The channel configurations are not
limited to the illustrated configurations but may be realized in
any other configuration. In a channel configuration 1 of FIG. 6,
the dedicated pilot channels are inserted in a second symbol at
predetermined intervals. In a channel configuration 2 of FIG. 6,
the dedicated pilot channels are inserted in a frequency hopping
pattern both in the time and the frequency directions. In a channel
configuration 3 of FIG. 3, the dedicated pilot channels are
time-multiplexed after a part of the common pilot channels but not
after the other common pilot channels. In a channel configuration 4
of FIG. 6, the dedicated pilot channels and the shared data
channels are code-multiplexed.
[0116] Regarding the common pilot channels and the dedicated pilot
channels, when the channel estimation is carried out in the time
domain, insertion intervals .DELTA..sub.p of the pilot channels are
required to satisfy the sampling theorem. Specifically, the
insertion intervals .DELTA..sub.p are set so as to satisfy the
following relationship:
.DELTA..sub.p<T.sub.s/d.sub.max
where T.sub.s represents a time period of the active symbol portion
(a symbol time period obtained after the guard interval removal)
and d.sub.max represents the maximum value of path propagation
delay, the relationship of which is illustrated in FIG. 7. For
example, when T.sub.s and d.sub.max are equal to 80 .mu.s and 20
.mu.s, respectively, the insertion intervals have to be 4 or
below.
EXAMPLE 3
[0117] FIG. 8 shows a part of transmitter according to a third
example of the present invention. In FIG. 8, like numerals are
given to the elements that have been already explained in reference
to FIG. 2. As shown, the data channel processing portion 202-1
additionally has a dedicated pilot channel control portion 72 and a
dedicated pilot channel multiplexing portion 74. These elements are
provided in the other data channel processing portions 202-2 to
202-K. The dedicated pilot channel control portion 72 determines,
in accordance with mobility of a mobile station concerned, whether
the dedicated pilot channels are inserted into a signal to be
transmitted to the mobile station. The mobility may be measured,
for example, through the maximum Doppler frequency. When the
measured mobility exceeds a predetermined level, the dedicated
pilot channels may be inserted. The dedicated pilot multiplexing
portion 74 inserts or does not insert the dedicated pilot channels
to the signal to be transmitted to the user in accordance with
instruction from the dedicated pilot channel control portion 72,
and outputs the signal with or without the dedicated pilot channels
to the common pilot multiplexing portion 204.
[0118] For example, the mobile station shown in FIG. 3 notifies the
radio base station of any indication that can be used by the radio
base station to determine whether the mobile station is moving at a
higher speed. Such indication may be, but not limited to, the
maximum Doppler frequency. When it is determined by the dedicated
pilot channel control portion 72 that the mobile station is moving
at a higher moving velocity, the dedicated pilot channels are
multiplexed with the signal in the dedicated pilot multiplexing
portion 74. When it is determined to the contrary, the dedicated
pilot channels are not multiplexed. In this example, the dedicated
pilot channels are inserted to the signal to be transmitted to the
fast-moving mobile station, whereas the dedicated pilot channels
are not inserted to the signal to be transmitted to the slowly
moving or stationary mobile station. The dedicated pilot channels
in addition to the common pilot channels are used in the
fast-moving mobile station, thereby enhancing the channel
estimation accuracy.
[0119] FIG. 9 shows an example of a channel configuration when the
frequency band is divided into plural frequency blocks. One
frequency block includes plural sub-carriers. Such a frequency
block may be called a chunk, a frequency chunk, or a resource
block. A user can use one chunk or more in accordance with
transmission contents (data size or the like) In the illustrated
example, a frequency chunk 1 is used by a fast-moving user and the
shared data channels and the dedicated pilot channels are
multiplexed in the chunk 1. In addition, anther frequency chunk 2
is used by a user who is not moving fast, and the dedicated pilot
channels are not multiplexed in the chunk 2. In the case of the
fast-moving mobile station, since the channel estimation value may
change largely from time to time, both the common pilot channels
and the dedicated pilot channels are used, thereby obtaining the
highly accurate channel estimation value. On the other hand, in the
case of the stationary or slowly moving mobile station, the channel
estimation value is not expected to change largely from time to
time. Transmitting the common pilot channels and the dedicated
pilot channels to such a user may result in impaired data
transmission efficiency since the unnecessary pilot channels are
transmitted. However, the dedicated pilot channel estimation
portion 72 detects the mobility of the mobile station and
determines whether the dedicated pilot channels are required in
accordance with the detected mobility in this example, thereby
preventing wasteful transmission of the dedicated pilot
channels.
EXAMPLE 4
[0120] FIG. 10 shows a part of transmitter according to a fourth
example of the present invention. In FIG. 10, like numerals are
given to the elements that have been already explained in reference
to FIG. 2. In this example, plural antennas are used for signal
transmission. Therefore, the data channel processing portion 202-1
is provided additionally with a dedicated pilot multiplexing
portion 102, an antenna weight control portion 104, and a weight
setting portion. Moreover, each of the plural antennas is provided
with elements such as the common pilot multiplexing portion 204,
the IFFT portion 206 and the guard interval insertion portion 208,
or the like. The dedicated pilot multiplexing portion 102
multiplexes the dedicated pilot channels in the signal to be
transmitted. The antenna weight control portion 104 adjusts a
weight for each of the plural antennas. Adjusting appropriately the
weight realizes a beam pattern that has directionality in a
specific direction or no directivity. The weight setting portion
106 sets the weight for each transmission antenna in accordance
with a control signal from the antenna weight control portion 104.
The weight is typically expressed by an amount of phase rotation to
which amplitude may be added.
[0121] By the way, the common pilot channels and the shared control
channels need to be provided to all the users, whereas the
dedicated pilot channels need to be provided to a specific user.
Therefore, the common pilot channels and the shared control
channels are transmitted by a sector beam that covers an entire
sector and the dedicated pilot channels are transmitted by a
directional beam having directionality toward the user. FIG. 11
shows schematically the sector beam and the directional beams. In
FIG. 11, the sector beam covering the entire sector having a wide
directional angle of 120 degree is shown by a solid line, whereas
the directional beams having a narrower directivity toward a user 1
and a user 2, respectively are shown by dotted lines.
[0122] FIG. 12 shows an example of a channel configuration when the
frequency band is divided into plural frequency blocks or chunks.
One user can use one chunk or more in accordance with transmission
contents (data size or the like) In the illustrated example, a
frequency chunk 1 is used by the user 1 and a frequency chunk 2 is
used by the user 2. Since each user can use the dedicated pilot
channels transmitted by the directional beam, in addition to the
common pilot channels transmitted throughout the sector, the
channel estimation regarding the direction of the directional beam
is carried out with high accuracy.
EXAMPLE 5
[0123] In the Example 4, the plural transmission antennas are used
to form one directional beam. On the other hand, in a Multi-Input
Multi-Output (MIMO) method, while plural antennas are independently
used so as to concurrently transmit different signals from the
corresponding antennas at the same frequency, the signals are
received by plural reception antennas and separated using an
appropriate signal separation algorithm. Independent use of the
plural transmission antennas can produce plural transmission routes
(channels), thereby enhancing a data transmission rate up to a
level corresponding to a factor of the number of the transmission
antennas. Since the transmission routes are formed by the
corresponding antennas, the pilot channels are transmitted from the
corresponding antennas and the channel estimation is carried out
for the corresponding antennas. In addition, the transmissions need
to be carried out in accordance with the least number of the
antennas when the number N.sub.TX of the transmission antennas and
the number N.sub.RX of the reception antennas are different. For
example, when a radio base station transmits signals from four
antennas, a transmission rate that has been expected from the use
of the four antennas cannot be realized if a mobile station has
only two reception antennas, leading to throughput that can be
realized by only the two of the four transmission antennas. In
other words, if the mobile station has only two antennas, use of
the four antennas in the radio base station cannot contribute to an
improvement of the data transmission efficiency. From this point of
view, a way of transmission from the radio base station is changed
in accordance with the number of the reception antennas provided in
the mobile station in the fifth example of the present
invention.
[0124] It is assumed for simplicity of explanation that the mobile
station has two or four antennas and the radio base station has
four antennas, although this example is applicable to the mobile
station and the radio base station having any appropriate number of
antennas. In this example, the common pilot channels and the shared
control channels are received by any type of mobile station and the
dedicated pilot channels are received by the mobile station having
the four antennas.
[0125] FIG. 13 schematically shows the MIMO method according to
this example of the present invention. As shown, the common pilot
channels (and the shared control channels) are transmitted from a
first antenna and a second antenna of a transmitter (radio base
station). The common pilot channels are used by all mobile
stations. In addition, the dedicated pilot channels are transmitted
from a third antenna and a fourth antenna. The dedicated pilot
channels are used only by a receiver (mobile station) having the
four antennas.
[0126] FIG. 14 shows an example of a channel configuration when the
frequency band is divided into plural frequency blocks or chunks.
One user can use one chunk or more in accordance with transmission
contents (data size or the like) In the illustrated example, a
frequency chunk 1 is used by a user 2 and a frequency chunk 2 is
used by a user 1. The common pilot channels and the shared control
channels in the leading slot of the TTI are transmitted from the
first and the second transmission antennas. A second symbol and
beyond in the frequency chunk 2 are used to transmit the shared
data channels to the user 1 having only the two antennas. The
second symbol and beyond in the frequency chunk 1 are used to
transmit the dedicated pilot channels from the third and the fourth
antennas to the user 2 having the four antennas. With this,
throughput can be improved for the user 1 and the user 2.
[0127] FIG. 15 shows several multiplexing methods about the common
pilot channels. However, various multiplexing methods rather than
the shown methods are applicable to this example of the present
invention. In a method 1, the common pilot channels are multiplexed
only in the frequency direction, which corresponds to the
multiplexing method shown in FIG. 14. In a method 2, the common
pilot channels are multiplexed in the time and the frequency
directions. In a method 3, the common pilot channels are
multiplexed only in the time direction.
EXAMPLE 6
[0128] Downlink pilot channels can be divided into the common pilot
channels and the dedicated pilot channels. The common pilot
channels may be transmitted by the sector beam or a multi-beam due
to a fixed antenna weight (a fixed beam pattern) using plural
antennas. When the multi-beam is used, the entire sector is covered
by a predetermined number of directional beams.
(Pilot Channel)
[0129] The common pilot channels may be used to identify a sector
to which a user concerned belongs out of plural sectors in the same
cell. All the sectors in the same cell use cell-specific scramble
codes. The common pilot channels may be used for cell-search or
handover, or for measurement of reference level in adjacent
cells/sectors. In addition, the common pilot channels may be used
for quality measurement to obtain channel quality information (CQI)
for the purpose of scheduling in accordance with instantaneous
channel quality. The CQI may be used, for example, in an adaptive
link control. The common pilot channels may be used for channel
estimation of a physical channel transmitted by the sector beam or
the multi-beam.
[0130] The dedicated pilot channels may be transmitted by the
sector beam or the multi-beam, or by an adaptive beam (adaptive
directional beam) produced adaptively for each user. The adaptive
directional beam and the directional beam included in the
multi-beam are the same in that the beams have a strong antenna
gain in a particular direction. However, the directional beam is
produced at a fixed weight whereas the weight of the adaptive
directional beam is changed in accordance with a position of the
mobile station. Namely, the directional beam is a fixed directional
beam and the adaptive directional beam is a variable directional
beam whose directionality is variable. The dedicated pilot channels
are used (though not always used) in accordance with transmission
channel quality that is dependent on the user or an environment.
The dedicated pilot channels may be transmitted by the adaptive
beam produced adaptively for each user. The dedicated pilot
channels may be used to assist the channel estimation of the
physical channel transmitted by the sector beam or the multi-beam,
although the common pilot channels are basically used for the
channel estimation. The dedicated pilot channels may be used for
the channel estimation of the physical channel transmitted by the
adaptive beam. The dedicated pilot channels may be used for the CQI
measurement of the physical channel transmitted by the adaptive
beam.
[0131] FIG. 16 shows an example of a channel configuration of the
common pilot channels and the dedicated pilot channels. In the
illustrated example, the common pilot channels are mapped in
sub-carriers at predetermined frequency intervals in one symbol (or
one time slot). On the other hand, the dedicated pilot channels are
mapped in other sub-carriers at predetermined frequency intervals
in another symbol or more. By the way, the common pilot channels
may be mapped in one symbol or more.
(Beam)
[0132] The common pilot channels may be transmitted by the sector
beam and used for demodulation of the physical channel, namely for
the channel estimation and reception synchronization. In addition,
the common pilot channels may be transmitted from a MIMO-based
transmitter. Moreover, the dedicated pilot channels may be
additionally used in accordance with the user or the environment so
as to improve the channel estimation accuracy. When a specific
chunk used for the shared data channels is used only by one or a
few users, the dedicated pilot channels may be additionally used in
accordance with the transmission environment of the user (a moving
velocity, a delay spread, a received Signal-to-Interference plus
Noise power Ratio (SINR), or the like), thereby further improving
the channel estimation accuracy. In a multicast/broadcast channel,
the dedicated pilot channels are additionally used taking account
of a user in the worst transmission environment in the cell
concerned, thereby improving the channel estimation accuracy. On
the other hand, the reference level measurement for the cell-search
or the handover and the CQI measurement for the scheduling, the
adaptive link control, or the like are carried out principally
using the common pilot channels may be carried out supplementarily
using the dedicated pilot channels.
[0133] The common pilot channels may be used for demodulation of
the physical channel transmitted by the multi-beam, namely for the
channel estimation and reception synchronization. In addition, as
is the case with the sector beam, the dedicated pilot channels may
be additionally used in accordance with the user or the
environment, thereby improving the channel estimation accuracy. On
the other hand, the reference level measurement for the cell-search
or the handover and the CQI measurement for the scheduling, the
adaptive link control, or the like are carried out principally
using the common pilot channels and may be carried out
supplementarily using the dedicated pilot channels. When there are
a large number of multi-beams in the same cell, pilot sequences to
be used for identifying a beam to which a particular user belongs
may be re-used in the same cell, thereby reducing the number of the
pilot sequences to be used.
[0134] FIG. 17 schematically shows the pilot channels transmitted
by the multi-beam. In the illustrated example, five directional
beams (fixed beam patterns) are used. A pilot sequence is re-used
by two directional beams that are directed in largely different
directions among the five beams.
[0135] Since the adaptive (directional) beam forms adaptively
transmission beams for the corresponding users, the dedicated pilot
channels are used for the channel estimation. In addition, the
common pilot channels may be used in addition to the dedicated
pilot channels in order to improve the channel estimation accuracy
when there is a higher channel correlation between the multi-beam
transmission and the adaptive beam transmission. On the other hand,
the reference level measurement for the cell-search or the handover
and the CQI measurement for the scheduling, the adaptive link
control, or the like are carried out principally using the common
pilot channels transmitted by the sector beam and the
multi-beam.
[0136] FIG. 18 shows the pilot channels transmitted by the adaptive
directional beam.
(Pilot Channel Configuration)
[0137] The common pilot channels and the dedicated pilot channels
may be multiplexed periodically in every TTI. Depending on the user
and the environment, the dedicated channels are used so as to
improve the channel estimation accuracy. When one chunk is used
exclusively by one or several user(s) regarding the shared data
channels under situations of, for example, high mobility, a large
delay spread, or an extremely low SINR, the dedicated pilot
channels are allocated in addition to the common pilot channels,
thereby enabling accurate channel estimation. In the
multicast/broadcast channel, the dedicated pilot channels are used
in addition to the common pilot channels, thereby improving user
quality of the user which has had the worst quality. Additional
user-dependent dedicated pilot channel information in the shared
data channels is provided by a control signaling channel.
Therefore, by using more pilot symbols in lower delay conditions,
high quality demodulation of the shared data channels can be
realized. In the multicast/broadcast channel, additional
environment-dependent dedicated pilot channel information is
provided by the control signaling channel based on the user quality
in the worst environment. By using more pilot symbols in lower
delay conditions, a high quality multicast/broadcast channel is
provided.
[0138] The pilot channels may be mapped at higher density taking
more account of the frequency domain rather than the time domain.
More pilot channels may be allocated in the frequency domain rather
than in the time domain. Namely, the pilot channel density may be
higher in the frequency domain than in the time domain. Although
channel fluctuations in the time domain might be less significant
when the TTI length is relatively short, it is expected that the
channel fluctuations in the frequency domain become significant due
to time dispersiveness in the frequency selective multi-path
fading. Therefore, it is more advantageous to densely map the pilot
channels than to divide the pilot channels into sub-carriers for
allocation according to a TDM method.
[0139] TDM-based and/or FDM-based multiplexing may be employed by
carrying out staggered mapping from the top of the TTI. In the
staggered mapping, channels are mapped at predetermined intervals
in one time slot, whereas the channels are mapped at the
predetermined intervals in different frequencies in other time
slots, as shown in FIG. 16. The common pilot channels and the
dedicated pilot channels may be mapped in each TTI in accordance
with the staggered mapping. The common pilot channels may be mapped
highly preferentially before the dedicated channels. When the pilot
channels are mapped at the top of each TTI, at least the following
advantages are exerted. When the control signaling channels are
mapped at the top of each TTI along with the common/dedicated pilot
channels, the control signaling channels are reliably demodulated
by accurate channel estimation even under a situation where channel
quality fluctuation takes place due to various delay spreads and
Doppler frequencies. When the control signaling channels are mapped
at the top of each TTI and no traffic data are transmitted by a
chunk (namely when only control signaling bits are transmitted), it
is advantageous that user equipment (UE) performs efficient cyclic
reception.
[0140] FIG. 19 shows an example of allocation of the common and the
dedicated pilot channels.
[0141] FIG. 20A shows simulation results obtained in accordance
with an example of the present invention, in which a relationship
between energy per symbol per noise power spectral density
(E.sub.s/N.sub.0) and throughput. Three kinds of plots in FIG. 20A
correspond to simulation results obtained by three numbers
(N.sub.stg=0, 1, 2) of time slots to be subjected to the staggered
mapping of the pilot symbols, respectively. Channel configurations
corresponding to N.sub.stg=0, 1, 2, are shown in FIG. 20B,
respectively. A curve with open circles in FIG. 20A shows the
relationship at N.sub.stg=0; a curve with hatched circles shows the
relationship at N.sub.stg=1; and a curve with closed circles shows
the relationship at N.sub.stg=2. A moving velocity at which a
mobile station moves is assumed to be 120 km/h in these
simulations. In FIG. 20A, as the time slot number N.sub.stg to be
subjected to the pilot symbol mapping. is increased, the throughput
is further improved, which indicates effectiveness of the staggered
mapping. This is thought to be because of an improved traceability
of the channel estimation in the time domain.
[0142] In the mapping method of the common pilot channels and the
dedicated pilot channels, the pilot symbols may be discontinuously
allocated in the frequency domain and the time domain. For example,
discontinuous mapping along the frequency domain of the OFDM
symbols may be employed. When the pilot symbols are allocated in a
discontinuously dispersive manner in the frequency domain and the
time domain, the following advantage is exerted. First, since the
sub-carriers that are allocated to the pilot symbols in the
frequency domain are thinned, a reduction in data transmission
efficiency, which is caused by inserting the pilot symbols, can be
prevented while the channel estimation accuracy is kept comparable
with the channel estimation accuracy realized when the sub-carriers
are not thinned. Allocation amount in the time domain is reduced.
Transmission power of the common pilot channels needs to be changed
depending on a target cell radius in an actual cellular method.
Therefore, the pilot symbols are thinned in the frequency domain,
namely the pilot symbols and other channels are multiplexed and
transmitted in the same OFDM symbols, thereby maintaining overall
transmission power and flexibly changing the transmission power of
the common pilot channels.
EXAMPLE 7
[0143] In an example 7 of the present invention, there is described
a method utilizing orthogonal code sequences in sectors of the same
cell site. This method can be employed not only between plural
sectors, which are included in a cell, but also between cells. In
conventional W-CDMA, scrambling is performed using different
spreading codes for different sectors; a received signal is
scrambled by the corresponding scramble codes so as to produce the
pilot channels; and the channel estimation or the like is
performed. Since the scramble codes which are different in each
sector are determined at random, the pilot channels are interfered
with due to inter-code interference from the symbols whose
sub-carrier and sub-frame are the same in the sector (inter-sector
interference). As a result, it becomes relatively difficult to
perform highly accurate channel estimation and cell search, or it
takes more time even if the channel estimation and the cell search
can be performed. This results in a disadvantage especially when
the mobile station requires a fast hand-over or moves frequently
across sector boundaries. In regard to this point, it seems
possible to improve signal quality to some extent under a
multi-path transmission environment by employing the OFDM method in
data channel downlink and eliminating the need for multiplying the
data channels by the scramble code. However, since the pilot
channels are multiplied by the scramble codes that are different
for each sector in order to distinguish the sectors, reception
qualities of the pilot channels are not substantively improved,
which makes still difficult the highly accurate channel estimation
or the like. The seventh example has been contemplated in view of
such a disadvantage and directed to an improvement of reception
qualities of the pilot channels in OFDM method downlink.
[0144] According to this example, sector-specific orthogonal
sequences are used in the pilot channels in addition to
cell-specific orthogonal code sequences. With this, the pilot
channels are prevented from being interfered from adjacent sectors
in the same cell. Since such inter-sector interference is
prevented, the channel estimation accuracy can be improved.
Improvement of the channel estimation accuracy is advantageous in
concurrent transmissions related to a fast sector selection and
soft-combining.
[0145] FIG. 21A schematically shows use of a pilot sequence
orthogonal between sectors (or beams) according to this example. A
terminal that is to perform handover at a sector edge can perform
the channel estimation concurrently based on the pilot signals from
two base stations, thereby enabling high accuracy and high speed
channel estimation. For example, a user #1 existing at an edge or
end of a sector (namely, a user that is to perform the fast sector
selection or the soft-combining) distinguishes the sectors by
despreading the orthogonal sequences so as to enable accurate
channel estimation. A user #2 that is not to perform the fast
sector selection or soft-combining can use each pilot symbol (or,
takes account of the cell-specific and/or the sector-specific
orthogonal code) so as to perform the channel estimation.
[0146] FIG. 21B shows a pilot channel generation portion used in a
transmitter according to this example of the present invention. The
transmitter is typically a radio base station. The pilot channel
generation portion includes a pilot sequence portion 2102 that
provides a pilot channel sequence, a scramble code portion 2104
that provides a scramble code, an orthogonal code portion 2106 that
provides different spreading symbols (orthogonal codes) for
different sectors, a multiplication portion 2108 that multiplies
the scramble codes by the orthogonal codes, and a multiplication
portion 2110 that multiplies the pilot sequence by an output from
the multiplication portion 2108. The pilot sequence has been known
by the radio base station and the mobile station. The scramble code
is a random sequence to be commonly used by plural sectors. The
orthogonal codes are determined for each sector so as to be
orthogonal with one another.
[0147] FIG. 22 shows a specific example of the orthogonal codes
multiplied on the pilot sequence. As shown, codes indicated by (1,
1, 1, 1, 1, 1, 1, 1, . . . ) are mapped at intervals of one
sub-carrier in a sector #1; codes indicated by (1, -1, 1, -1, 1,
-1, 1, -1, . . . ) are mapped at intervals of one sub-carrier in a
sector #2; and codes indicated by (1, -1, -1, 1, 1, -1, -1, 1, . .
. ) are mapped at intervals of one sub-carrier in a sector #3.
These codes are orthogonal with one another.
[0148] FIG. 23 shows another specific example of the orthogonal
codes multiplied on the pilot sequence. As shown, codes indicated
by (1, 1, 1, 1, 1, 1, 1, 1, . . . ) are mapped at intervals of one
sub-carrier in the sector #1; codes are mapped at intervals of one
sub-carrier in the sector #2; and codes indicated by (1,
e.sup.-j2/3n, e.sup.j2/3n, 1, e.sup.-j2/3n, e.sup.-j2/3n, 1,
e.sup.-j2/3n, . . . ) are mapped at intervals of one sub-carrier in
the sector #3. Such codes can be orthogonal with one another.
[0149] FIG. 24 shows a correspondence relationship between the
scramble codes and the orthogonal codes. In the illustrated
example, 40 sub-carriers are assumed in an available channel band
and various types of data are associated with the corresponding
sub-carriers so as to perform transmission according to the OFDM
method. It goes without saying that the illustrated numerals are
just examples. The channel band may be the entire band available to
the system focused on, or one chunk. In the illustrated example,
the scramble code is expressed by 40 data sequences and mapped to
the corresponding sub-carriers. In the drawing, numerals 1 through
40 related to the scramble code express the codes that compose the
scramble code. The scramble code in a second line in FIG. 1 is
shifted by one individual code from the scramble code in a first
line, since the scramble code is transmitted so that the
correspondence relationship is shifted by one individual code in
the frequency axis direction, although the two scramble codes used
are the same. With this, a signal in the frequency axis direction
can be averaged out.
[0150] In the specific example described in reference to FIG. 22,
the scramble codes are multiplied by the orthogonal codes of (1, 1,
1, 1, . . . ) and the resultant codes are multiplied by the pilot
sequence in the sector #1; the scramble codes are multiplied by the
orthogonal codes of (1, -1, -1, 1, . . . ) and the resultant codes
are multiplied by the pilot sequence in the sector #2; and the
scramble codes are multiplied by the orthogonal codes of (1, 1, -1,
-1, . . . ) and the resultant codes are multiplied by the pilot
sequence in the sector #3. In the specific example described in
reference to FIG. 23, the scramble codes are multiplied by the
orthogonal codes of (1, 1, 1, 1, . . . ) and the resultant codes
are multiplied by the pilot sequence in the sector #1; the scramble
codes are multiplied by the orthogonal codes of (1, e.sup.j2/3n,
e.sup.-j2/3n, . . . ) and the resultant codes are multiplied by the
pilot sequence in the sector #2; and the scramble codes are
multiplied by the orthogonal codes of (1, e.sup.-j2/3n,
e.sup.j2/3n, . . . ) and the resultant codes are multiplied by the
pilot sequence in the sector #3.
[0151] FIG. 25 shows an example in which the common pilot channels
and other channels are multiplied by the scramble code and the
orthogonal code. In FIG. 25, there are illustrated a providing
portion 2502 that provides a sequence for the common pilot
channels, a providing portion 2504 that provides a sequence for
other channels, a scramble code portion 2506 that provides the
scramble code, an orthogonal code portion 2508 that provides
different sectors with different spreading code sequences
(orthogonal codes), a multiplication portion 2510 that multiplies
the scramble code and the orthogonal code, another multiplication
portion 2512 that multiplies the data sequence for the other
channels by an output from the multiplication portion 2510, a yet
another multiplication portion 2514 that multiplies the pilot
sequence by an output from the multiplication portion 2512. As
stated above, the scramble code is commonly determined for the
plural cells, and the orthogonal codes are determined so as to be
different (orthogonal) for different cells. In the illustrated
example, the common pilot channels and other channels are
multiplied by the same scramble code and the same orthogonal
code.
[0152] FIG. 26 shows another example in which the common pilot
channels and other channels are multiplied by the scramble code and
the orthogonal code. Like numerals are given to elements and
components that have already been described in reference to FIG. 25
and repetitive explanations are omitted. In FIG. 26, there are
additionally illustrated a second scramble code portion 2602 and a
multiplication portion 2604 that multiplies a second scramble code
by the orthogonal code. The (first) scramble code portion 2506
outputs the (first) scramble code to be commonly used by the plural
sectors. In accordance with a predetermined rule instructed by the
first scramble code portion 2506, the second scramble code portion
2602 outputs a second scramble code to the multiplication portion
2604. The output from the multiplication portion 2604 is multiplied
by the data sequence for other channels (excluding the common pilot
channels). Therefore, other channels are multiplied by the second
scramble code and the orthogonal code, whereas the common pilot
channels are multiplied by the first scramble code and the
orthogonal code. With this, the common pilot channels are
distinguished from other channels by their spreading codes. In this
example, since the second scramble code may be derived from the
first scramble code, the transmitter can easily search for any
channel as far as the derivation rule is known.
[0153] FIG. 27 shows a combination of the specific examples shown
in FIGS. 25 and 26. Without being limited to the illustrated
combination, any combination of channels may be employed as an
example of the present invention. The illustrated combination is
advantageous in that the shared data channels whose spreading
factor may change can be easily distinguished from channels whose
spreading factor is kept at a constant level.
[0154] In addition to the above-mentioned suppression of
interference in the pilot channels, transmission power of the
shared data channels may be adjusted.
[0155] FIGS. 28 (A), (B), (C) show signals received by a certain
user. FIG. 28 (A) shows a signal (desired signal) to be received by
a certain user from a cell or a sector to which the user is
connected. In the drawing, the pilot channel is illustrated higher
than the data channel since the pilot channel is transmitted and
received with higher electric power than the data channel. FIG. 28
(B) shows a signal (non-desired signal) that is not the desired
signal for the user. The non-desired signal indicates a signal from
a cell (or a sector) to which the user is not connected, and is an
interference signal to the desired signal. In this example, the
interference to the pilot channel is suppressed because different
orthogonal codes are used for the pilot channels of the desired
signal and the pilot channels of the non-desired signal. FIG. 28(C)
schematically shows that the transmission power for transmitting
the data channel from the radio base station (transmission power
for the non-desired signal) is reduced, or the transmission is
halted, so that the interference between the desired signal and the
non-desired signal is reduced by adjusting transmission timing or
downlink frequency bands between the radio base stations or the
sectors. More specifically, the transmission power for the
non-desired signal is limited to less than a predetermined value.
With this, interference between data channels, which may be a
concern in the example of FIG. 28 (B), can be suppressed. Or, the
user may perform soft-combining by concurrently transmitting
identical data channels instead of reducing the transmission power
for the non-desired signal (to zero, if necessary).
EXAMPLE 8
[0156] In an eighth example, there is described an orthogonal pilot
mapping for MIMO transmission. Orthogonal multiplexed pilot
channels may be used in an antenna gain technique such as MIMO
multiplexed transmission, MIMO diversity transmission, and adaptive
array antenna transmission. Only as an example, the pilot channels
are transmitted according to the MIMO transmission from all the
antennas in the transmitter. This is because the pilot channels are
required to measure a CQI value for all the signal transmissions.
All overheads of the common pilot symbols are the same regardless
of the number of transmission antennas, because corresponding areas
in cell coverage for the data channels are assured by using the
MIMO transmission. In the MIMO transmission, the channel estimation
is improved by further using the dedicated pilot channels (in the
case of four branch MIMO transmission, the number of the pilot
symbols per antenna becomes one-fourth of the number of the pilot
symbols in single antenna transmission). Adaptive partial pilot
symbol mapping for the MIMO transmission may be employed, namely
the pilot symbols from a sector beam transmission mode may be
thinned in accordance with an application scenario such as the
delay spread and the moving velocity.
[0157] FIG. 29 shows orthogonal sequences for the MIMO pilot
channels between sectors in the case of a four antenna transmitter.
The dedicated pilot channels are used to complement the channel
estimation. In the drawing, #1, #2, #3, and #4 correspond to a
first, a second, a third, and a fourth antenna.
EXAMPLE 9
[0158] In Examples 7 and 8, the inter-cell or inter-sector
interference for the pilot channels is suppressed by multiplying
the pilot channels by the orthogonal codes. While such orthogonal
codes are preferably used from the viewpoint of further suppression
of the interference, use of the orthogonal codes is not necessary
from the viewpoint of distinguishing cells and/or sectors but
non-orthogonal codes may be used. However, when the non-orthogonal
code expressed by a general random sequence is used, quality
degradation of the pilot channels caused by the inter-code
interference described at the beginning of Example 7 may be a
concern. On the other hand, there are some types of non-orthogonal
codes that are less problematic in terms of the inter-code
interference (correlation) compared with the non-orthogonal codes
expressed by the random sequence. Such a high-correlativity code
(for example, a code that allows the inter-code interference to be
on average within one-tenth of the code length) may be used to
distinguish the cells and/or the sectors. As an example of such a
code, there is a CAZAC code, which is briefly described in the
following.
[0159] As shown in FIG. 30, it is assumed that a code length of one
CAZAC code A is L. For simplicity of explanation, this code length
L is assumed to correspond to a time period of L samples, although
this assumption is not necessary to the present invention. A series
of .DELTA. samples (shown by hatching in the drawing) including the
end sample (L-th sample) of the CAZAC code A are shifted to the top
of the CAZAC code A and thus another CAZAC code B is generated, as
shown in the bottom of FIG. 30. In this case, the CAZAC codes A, B
are orthogonal with each other regarding .DELTA.=1 through L-1.
Namely, a first CAZAC code is orthogonal with a second CAZAC code
generated by cyclically shifting the first CAZAC code. Therefore,
when one CAZAC code having a code length of L is prepared, a group
of L codes that are orthogonal with one another can be
theoretically prepares. In addition, one CAZAC code A is not
orthogonal with another CAZAC code B that is not derived from the
CAZAC code A. However, even in this case, the inter-code
interference between these CAZAC codes A, B is not significant
compared with the inter-code interference between different random
sequences. Moreover, the inter-code interference between a code
sequence composed of part of one CAZAC code A and a code sequence
composed of another part of the CAZAC code A or B is less
significant compared with the inter-code interference between
different random sequences. For a detailed explanation about the
CAZAC code, see "Polyphase codes with good periodic correlation
properties", D. C. Chu, IEEE Trans. Inform. Theory, vol. IT-18, pp.
531-532, July 1972; and "On allocation of uplink sub-channels in
EUTRA SC-FDMA", 3GPP, R1-050822, Texas Instruments.
EXAMPLE 10
[0160] In Examples 7, 8, and 9, the pilot channels of the desired
signal and the non-desired signal are concurrently transmitted. In
a tenth example, the pilot channels of the desired signal and the
non-desired signal are transmitted from a radio base station either
at different times or in different frequencies, or both, as shown
in FIG. 31. With this, the inter-cell or the inter-sector
interference regarding the pilot channels can be suppressed. In
addition, when transmitting the data channels of the desired signal
is prohibited during which time the pilot channels of the
non-desired signal are being transmitted, the interference between
the desired signal and the non-desired signal can be further
suppressed.
[0161] While preferred examples according to the present invention
have been described in the foregoing, the present invention is not
limited to the described examples but may be modified or altered in
various ways within the scope of the present invention. In
addition, although the present invention has been described in
individual examples for simplicity of explanation, the present
invention is not necessarily practiced as each example but one or
more of the examples may be combined.
[0162] This international patent application is based on Japanese
Priority Applications No. 2005-174400, 2005-241905, and
2006-031752, filed on Jun. 14, 2005, Aug. 23, 2005, and Feb. 8,
2006, respectively with the Japanese Patent Office, the entire
contents of which are hereby incorporated by reference.
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