U.S. patent application number 13/787436 was filed with the patent office on 2013-08-08 for radio communication system, radio communication method, base station device, and terminal device.
This patent application is currently assigned to PANASONIC CORPORATION. The applicant listed for this patent is Panasonic Corporation. Invention is credited to Takaaki Kishigami, Yoichi Nakagawa.
Application Number | 20130201944 13/787436 |
Document ID | / |
Family ID | 35428659 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130201944 |
Kind Code |
A1 |
Kishigami; Takaaki ; et
al. |
August 8, 2013 |
RADIO COMMUNICATION SYSTEM, RADIO COMMUNICATION METHOD, BASE
STATION DEVICE, AND TERMINAL DEVICE
Abstract
A base station apparatus performs a radio communication with a
terminal apparatus using a spatial division multiplex access method
in a downlink. The base station apparatus includes a simultaneous
connection information generation section that generates a
simultaneous connection information data sequence, which includes a
pilot sequence number concerning a number of a pilot signal
assigned to another terminal apparatus. The base station apparatus
also includes a multiplexing section that multiplexes a signal of
the generated simultaneous connection information data sequence
with a dedicated data signal which indicates data to be transmitted
to the terminal apparatus. The base station apparatus further
includes a transmission section that transmits, to the terminal
apparatus, the multiplexed signal which includes the simultaneous
connection information data sequence, and transmits, to the
terminal apparatus, a unique pilot signal which is different from
the aforementioned pilot signal assigned to the another terminal
apparatus.
Inventors: |
Kishigami; Takaaki; (Tokyo,
JP) ; Nakagawa; Yoichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Corporation; |
Osaka |
|
JP |
|
|
Assignee: |
PANASONIC CORPORATION
Osaka
JP
|
Family ID: |
35428659 |
Appl. No.: |
13/787436 |
Filed: |
March 6, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11568571 |
Nov 2, 2006 |
8416748 |
|
|
PCT/JP2005/007524 |
Apr 20, 2005 |
|
|
|
13787436 |
|
|
|
|
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04B 7/0634 20130101;
H04B 7/0639 20130101; H04B 7/0665 20130101; H04B 7/0632 20130101;
H04B 7/0452 20130101; H04W 16/28 20130101; H04B 7/0854
20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 16/28 20060101
H04W016/28 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2004 |
JP |
2004-150137 |
Mar 28, 2005 |
JP |
2005-092544 |
Claims
1. A base station apparatus that performs a radio communication
with a terminal apparatus using a spatial division multiplex access
method in a downlink, the base station apparatus comprising: a
simultaneous connection information generation section that
generates a simultaneous connection information data sequence, the
simultaneous connection information data sequence including a pilot
sequence number concerning a number of a pilot signal assigned to
another terminal apparatus; a multiplexing section that multiplexes
a signal of the generated simultaneous connection information data
sequence with a dedicated data signal which indicates data to be
transmitted to the terminal apparatus; and a transmission section
that transmits, to the terminal apparatus, the multiplexed signal
which includes the simultaneous connection information data
sequence, and transmits, to the terminal apparatus, a unique pilot
signal which is different from said pilot signal assigned to said
another terminal apparatus.
2. The base station apparatus according to claim 1, wherein the
unique pilot signal includes a pilot signal used for calculation of
an interference component.
3. The base station apparatus according to claim 1, wherein the
unique pilot signal includes a pilot signal used for channel
estimation.
4. The base station apparatus according to claim 1, wherein the
simultaneous connection information data sequence includes
information concerning a modulation scheme.
5. The base station apparatus according to claim 1, wherein the
simultaneous connection information data sequence includes
information concerning a data signal assigned to said another
terminal apparatus, and the data signal assigned to said another
terminal apparatus is a data signal with which the dedicated data
signal is multiplexed.
6. A terminal apparatus that performs a radio communication with a
base station apparatus using a spatial division multiplex access
method in a downlink, the terminal apparatus comprising: a
simultaneous connection information reception section that
receives, from the base station apparatus, a multiplexed signal
which includes a simultaneous connection information data sequence,
and receives, from the base station apparatus, a unique pilot
signal which is different from a pilot signal assigned to another
terminal apparatus, wherein the simultaneous connection information
data sequence includes a pilot sequence number concerning a number
of said pilot signal assigned to said another terminal
apparatus.
7. The terminal apparatus according to claim 6, wherein the unique
pilot signal includes a pilot signal used for calculation of an
interference component.
8. The terminal apparatus according to claim 6, further comprising:
a channel estimation section that performs channel estimation using
a pilot signal assigned to the terminal apparatus which is included
in the unique pilot signal.
9. The terminal apparatus according to claim 6, wherein the
simultaneous connection information data sequence includes
information concerning a modulation scheme.
10. The terminal apparatus according to claim 6, wherein the
simultaneous connection information data sequence includes
information concerning a data signal assigned to said another
terminal apparatus, and the data signal assigned to said another
terminal apparatus is a data signal with which a dedicated data
signal for the terminal apparatus is multiplexed.
11. A method to be executed in a base station apparatus for
performing a radio communication with a terminal apparatus using a
spatial division multiplex access method in a downlink, the method
comprising: generating a simultaneous connection information data
sequence, the simultaneous connection information data sequence
including a pilot sequence number concerning a number of a pilot
signal assigned to another terminal apparatus; multiplexing a
signal of the generated simultaneous connection information data
sequence with a dedicated data signal which indicates data to be
transmitted to the terminal apparatus; transmitting, to the
terminal apparatus, the multiplexed signal which includes the
simultaneous connection information data sequence; and
transmitting, to the terminal apparatus, a unique pilot signal
which is different from said pilot signal assigned to said another
terminal apparatus.
12. A method to be executed in a terminal apparatus for performing
a radio communication with a base station apparatus using a spatial
division multiplex access method in a downlink, the method
comprising: receiving, from the base station apparatus, a
multiplexed signal which includes a simultaneous connection
information data sequence; and receiving, from the base station
apparatus, a unique pilot signal which is different from a pilot
signal assigned to another terminal apparatus, wherein the
simultaneous connection information data sequence includes a pilot
sequence number concerning a number of said pilot signal assigned
to said another terminal apparatus.
13. A radio communication system in which a base station apparatus
performs a radio communication with a terminal apparatus using a
spatial division multiplex access method in a downlink, wherein the
base station apparatus comprises: a simultaneous connection
information generation section that generates a simultaneous
connection information data sequence, the simultaneous connection
information data sequence including a pilot sequence number
concerning a number of a pilot signal assigned to another terminal
apparatus; a multiplexing section that multiplexes a signal of the
generated simultaneous connection information data sequence with a
dedicated data signal which indicates data to be transmitted to the
terminal apparatus; and a transmission section that transmits, to
the terminal apparatus, the multiplexed signal which includes the
simultaneous connection information data sequence, and transmits,
to the terminal apparatus, a unique pilot signal which is different
from said pilot signal assigned to said another terminal apparatus,
and wherein the terminal apparatus comprises: a simultaneous
connection information reception section that receives, from the
base station apparatus, the multiplexed signal which includes the
simultaneous connection information data sequence, and the unique
pilot signal.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] This invention relates to a wireless communication system, a
wireless communication method, a base station apparatus, and a
terminal for conducting wireless communications using space
division multiple access.
[0003] 2. Description of the Related Art
[0004] In recent years, there have been growing demands for a large
capacity and speeding up of wireless communications, and research
on methods of improving the effective utilization factor of finite
frequency resources have flourished. As one of the methods,
attention is focused on a technique of using a spatial domain. An
adaptive array antenna (adaptive antenna) is known as one of
spatial domain use technologies. With the adaptive array antenna, a
weighted coefficient by which a reception signal is multiplied is
used to adjust the amplitude and the phase, whereby a signal coming
from any desired direction is strongly received and the
interference wave direction is suppressed. Accordingly, identical
inter channel interference can be decreased and the communication
capacity of a wireless communication system can be improved.
[0005] Known as other spatial domain use technologies are space
division multiple access (SDMA) of transmitting different data
series to different terminals and space division multiplexing (SDM)
of transmitting different data series to the same terminal using
physical channel at the identical time, at the same frequency, and
of the same code using spatial orthogonality in a propagation line.
If the spatial correlation coefficient between terminals is smaller
than a predetermined value, the SDMA technology can be used for
improving the throughput and the number of simultaneously
accommodated users of a wireless communication system (refer to
non-patent document 1).
[0006] On the other hand, in the SDM technology, a transmitter and
a receiver are provided each with a plurality of antenna elements
and SDM transmission is realized in a propagation environment
wherein the reception signal correlation between antennas is low
(refer to non-patent document 2). In this case, the transmitter
transmits different data series using physical channel at the
identical time, at the same frequency, and of the same code for
each antenna element from the attached antennas. The receiver
separates and receives the different data series from the reception
signal through the attached antennas. Thus, a plurality of space
division multiplex channels are used, whereby speeding up can be
accomplished without using a multilevel modulation. To execute SDM
transmission, in an environment wherein a large number of
scatterers exist between the transmitter and the receiver under a
sufficient S/N (signal-to-noise ratio) condition, if the number of
antennas of the transmitter and that of the receiver are the same,
the channel capacity can be expanded in proportion to the number of
the antennas.
[0007] Multiuser MIMO (Multiple Input Multiple Output) technology
is known as a technology provided by fusing the SDMA technology and
the SDM technology (refer to non-patent document 3). The multiuser
MIMO technology makes possible space division multiplexing
transmission and space division multiple access based on
directivity under a condition that the channel matrix of a terminal
connected at the same time by way of space division multiplexing is
already known in the transmitter. The channel matrix is represented
as a channel vector in a terminal including only a single antenna,
but is handled as a general channel matrix.
[0008] Non-patent document 1: T. Ohgane et al, "A study on a
channel allocation scheme with an adaptive array in SDMA," IEEE
47th VTC, vol. 2, 1997, p. 725-729
[0009] Non-patent document 2: G. J. Foschini, "Layered space-time
architecture for wireless communication in a fading environment
when using multi-element antennas," Bell Labs Tech. J, Autumn 1996,
p. 41-59
[0010] Non-patent document 3: Q. Spencer et al, "Zero-Forcing
Methods for Downlink Spatial Multiplexing in Multiuser MIMO
channels," IEEE Trans SP, Vol. 52, No. 2, 2004, p. 461-471
DISCLOSURE OF THE INVENTION
Problems that the Invention is to Solved
[0011] However, the wireless communication system using the space
division multiple access (SDMA) in the related art described above
involves the following problems: In the SDMA technology, to
decrease interference between transmission signals to the connected
terminals, the transmitting party needs to form transmission beams
to spatially separate the terminals and thus the feedback amount of
the channel estimation value from the receiver must be decreased in
an FDD (Frequency Division Duplex) line. On the other hand, in a
TDD (Time Division Duplex) line, it is not necessary to feed back
the channel estimation value from the relativity of a propagation
line under a sufficiently close condition in time, but a
calibration circuit for correcting the deviation between branches
of reception and transmission, usually contained in a plurality of
array elements and a high-frequency circuit stage becomes
necessary. To transmit under a condition that different
terminal-to-terminal transmission beams are orthogonal to each
other, the transmission beams are formed with priority given to the
orthogonal condition and thus the array gain is impaired; this is a
problem.
[0012] It is therefore an object of the invention to provide a
wireless communication system, a wireless communication method, a
base station apparatus, and a terminal capable of removing a
transmission signal to a different terminal space division
multiplexed, an interference signal, in a terminal when wireless
communications are conducted using space division multiple
access.
Means for Solving the Problems
[0013] The base station apparatus of the invention is a base
station apparatus for conducting space division multiple access
with a terminal in a downlink, the base station apparatus including
space division multiplexing information notification means for
sending space division multiplexing information concerning a
different terminal as well as the terminal to the terminal; and
dedicated data transmission means for executing dedicated data
transmission using a transmission weight corresponding to each of
the terminals based on the space division multiplexing information
after the space division multiplexing information is sent.
[0014] Accordingly, when wireless communications are conducted
using space division multiple access, the space division
multiplexing information concerning not only the terminal, but also
a different terminal space division multiplexed at the space
division multiple access time is sent, whereby the transmission
signal to the different terminal space division multiplexed, an
interference signal, can be removed in the terminal. Accordingly,
interference between the transmission beams from the base station
apparatus to the different terminals is allowed, so that the
flexibility of transmission beam formation is increased and it is
made possible to improve the reception quality and the system
capacity.
[0015] As one form of the invention, the above-described base
station apparatus includes transmission weight generation means for
generating the transmission weight used for the dedicated data
transmission to the space division multiplexing terminal, wherein
the space division multiplexing information includes information of
the generated transmission weight.
[0016] As one form of the invention, in the above-described base
station apparatus, one selected from among known transmission
weight candidates is adopted as the transmission weight, and the
space division multiplexing information includes information of the
identification number of the selected transmission weight.
[0017] As one form of the invention, in the above-described base
station apparatus, the space division multiplexing information
includes information of transmission power to the terminal.
[0018] As one form of the invention, in the above-described base
station apparatus, the space division multiplexing information
includes information concerning the transmission format used for
the dedicated data transmission to the terminal.
[0019] As one form of the invention, in the above-described base
station apparatus, the space division multiplexing information
includes information concerning at least one of modulation level
and coding rate used for the dedicated data transmission to the
terminal.
[0020] As one form of the invention, in the above-described base
station apparatus, the space division multiplexing information
includes information of a user dedicated pilot signal series
transmitted to the terminal.
[0021] The invention of the terminal is a terminal for conducting
space division multiple access with a base station apparatus in a
downlink, the terminal including space division multiplexing
information reception means for receiving space division
multiplexing information concerning a different terminal space
division multiplexed together with the terminal, sent from the base
station apparatus; interference cancel means for decreasing the
transmission signal component to the different terminal space
division multiplexed based on the received space division
multiplexing information; and dedicated data reception means for
receiving a dedicated data signal addressed to the terminal,
transmitted from the base station apparatus through the
interference cancel means.
[0022] Accordingly, when wireless communications are conducted
using space division multiple access, the space division
multiplexing information concerning not only the terminal, but also
a different terminal space division multiplexed at the space
division multiple access time is received, whereby the transmission
signal to the different terminal space division multiplexed, an
interference signal, can be removed in the terminal. Accordingly,
interference between the transmission beams from the base station
apparatus to the different terminals is allowed, so that the
flexibility of transmission beam formation is increased and it is
made possible to improve the reception quality and the system
capacity.
[0023] As one form of the invention, in the above-described
terminal, if the terminal has a plurality of antennas, the
interference cancel means generates a reception weight according to
minimum square error criterion and the dedicated data reception
means receives the signal provided by weighting the dedicated data
signal addressed to the terminal by the reception weight based on
maximum likelihood estimation.
[0024] Accordingly, if the terminal has a plurality of antennas, it
is made possible to remove interference of the transmission signals
from the base station apparatus to the different terminals based on
the reception weight.
[0025] As one form of the invention, in the above-described
terminal, the interference cancel means generates a candidate of
transmission signal replica including an interference signal to the
different terminal space division multiplexed and the dedicated
data reception means receives the dedicated data signal addressed
to the terminal based on maximum likelihood estimation using the
generated candidate of transmission signal replica.
[0026] Accordingly, it is made possible to remove interference of
the transmission signals from the base station apparatus to the
different terminals based on the candidate of transmission signal
replica including the interference signal to the different
terminal.
[0027] As one form of the invention, in the above-described
terminal, the space division multiplexing information includes
information of a transmission weight used for dedicated data
transmission to the terminal space division multiplexed, generated
by the base station apparatus.
[0028] As one form of the invention, in the above-described
terminal, the space division multiplexing information includes
information of the identification number of the transmission weight
selected from among known transmission weight candidates by the
base station apparatus.
[0029] As one form of the invention, in the above-described
terminal, the space division multiplexing information includes
information of transmission power to the terminal.
[0030] As one form of the invention, in the above-described
terminal, the space division multiplexing information includes
information concerning the transmission format used for the
dedicated data transmission to the terminal.
[0031] As one form of the invention, in the above-described
terminal, the space division multiplexing information includes
information concerning at least one of modulation level and coding
rate used for the dedicated data transmission to the terminal.
[0032] As one form of the invention, in the above-described
terminal, the space division multiplexing information includes
information of a user dedicated pilot signal series transmitted to
the terminal.
[0033] The wireless communication system of the invention is a
wireless communication system for conducting space division
multiple access in a downlink from a base station apparatus to a
terminal, wherein the base station apparatus includes space
division multiplexing information notification means for sending
space division multiplexing information concerning a different
terminal as well as the terminal to the terminal; and dedicated
data transmission means for executing dedicated data transmission
using a transmission weight corresponding to each of the terminals
based on the space division multiplexing information after the
space division multiplexing information is sent, and wherein the
terminal includes space division multiplexing information reception
means for receiving space division multiplexing information
concerning a different terminal space division multiplexed together
with the terminal, sent from the base station apparatus;
interference cancel means for decreasing the transmission signal
component to the different terminal space division multiplexed
based on the received space division multiplexing information; and
dedicated data reception means for receiving a dedicated data
signal addressed to the terminal, transmitted from the base station
apparatus through the interference cancel means.
[0034] Accordingly, when wireless communications are conducted
using space division multiple access, the space division
multiplexing information concerning not only the terminal, but also
a different terminal space division multiplexed at the space
division multiple access time is sent, whereby the transmission
signal to the different terminal space division multiplexed, an
interference signal, can be removed in the terminal. Accordingly,
interference between the transmission beams from the base station
apparatus to the different terminals is allowed, so that the
flexibility of transmission beam formation is increased and it is
made possible to improve the reception quality and the system
capacity.
[0035] The wireless communication method of the invention is a
wireless communication method for conducting space division
multiple access in a downlink from a base station apparatus to a
terminal, the wireless communication method including in the base
station apparatus, a space division multiplexing information
notification step of sending space division multiplexing
information concerning a different terminal as well as the terminal
to the terminal; and a dedicated data transmission step of
executing dedicated data transmission using a transmission weight
corresponding to each of the terminals based on the space division
multiplexing information after the space division multiplexing
information is sent, and in the terminal, a space division
multiplexing information reception step of receiving space division
multiplexing information concerning a different terminal space
division multiplexed together with the terminal, sent from the base
station apparatus; an interference cancel step of decreasing the
transmission signal component to the different terminal space
division multiplexed based on the received space division
multiplexing information; and a dedicated data reception step of
receiving a dedicated data signal addressed to the terminal,
transmitted from the base station apparatus through the
interference cancel step.
[0036] Accordingly, when wireless communications are conducted
using space division multiple access, the space division
multiplexing information concerning not only the terminal, but also
a different terminal space division multiplexed at the space
division multiple access time is sent, whereby the transmission
signal to the different terminal space division multiplexed, an
interference signal, can be removed in the terminal. Accordingly,
interference between the transmission beams from the base station
apparatus to the different terminals is allowed, so that the
flexibility of transmission beam formation is increased and it is
made possible to improve the reception quality and the system
capacity.
[0037] The wireless communication method of the invention is a
wireless communication method for conducting space division
multiple access in a downlink from a base station apparatus to a
terminal, the wireless communication method including in the base
station apparatus, a space division multiplexing information
notification step of sending space division multiplexing
information concerning a different terminal as well as the terminal
to the terminal; and a dedicated data transmission step of
executing dedicated data transmission using a transmission weight
corresponding to each of the terminals based on the space division
multiplexing information after the space division multiplexing
information is sent.
[0038] The wireless communication method of the invention is a
wireless communication method for conducting space division
multiple access in a downlink from a base station apparatus to a
terminal, the wireless communication method including in the
terminal, a space division multiplexing information reception step
of receiving space division multiplexing information concerning a
different terminal space division multiplexed together with the
terminal, sent from the base station apparatus; an interference
cancel step of decreasing the transmission signal component to the
different terminal space division multiplexed based on the received
space division multiplexing information; and a dedicated data
reception step of receiving a dedicated data signal addressed to
the terminal, transmitted from the base station apparatus through
the interference cancel step.
[0039] As one form of the invention, in any of the above-described
wireless communication methods, the space division multiplexing
information includes information of a transmission weight used for
dedicated data transmission to the terminal space division
multiplexed, generated by the base station apparatus.
[0040] As one form of the invention, in any of the above-described
wireless communication methods, the space division multiplexing
information includes information of the identification number of
the transmission weight selected from among known transmission
weight candidates by the base station apparatus.
[0041] As one form of the invention, in any of the above-described
wireless communication methods, the space division multiplexing
information includes information of transmission power to the
terminal.
[0042] As one form of the invention, in any of the above-described
wireless communication methods, the space division multiplexing
information includes information concerning the transmission format
used for the dedicated data transmission to the terminal.
[0043] As one form of the invention, in any of the above-described
wireless communication methods, the space division multiplexing
information includes information concerning at least one of
modulation level and coding rate used for the dedicated data
transmission to the terminal.
[0044] As one form of the invention, in any of the above-described
wireless communication methods, the space division multiplexing
information includes information of a user dedicated pilot signal
series transmitted to the terminal.
[0045] As one form of the invention, any of the above-described
wireless communication methods includes, before the space division
multiplexing information notification step, the steps of previously
detecting the propagation channel state in the downlink and
previously sending a notification of the transmission weight in the
downlink for the terminal based on the propagation channel state by
the terminal.
[0046] As one form of the invention, any of the above-described
wireless communication methods includes, before the space division
multiplexing information notification step, the steps of previously
detecting the propagation channel state in the downlink, selecting
the transmission weight in the downlink for the terminal from among
weight candidates based on the propagation channel state, and
previously sending a notification of the selected transmission
weight to the base station apparatus by the terminal.
[0047] As one form of the invention, in the above-described
wireless communication method, the step of selecting the
transmission weight includes a step of selecting a predetermined
number of transmission weight candidates with the maximum inner
product with the right singular vector corresponding to singular
values in a descending order of the singular values which is
obtained by decomposing the channel matrix obtained as a result of
detection of the propagation channel state.
[0048] As one form of the invention, any of the above-described
wireless communication methods includes the steps of, before the
space division multiplexing information notification step,
previously detecting the propagation channel state in the downlink
and sending reception quality information to the base station
apparatus based on the propagation channel state by the terminal,
and assigning the terminal to conduct space division multiple
access in the down link based on the transmission weight and the
reception quality information.
[0049] As one form of the invention, in the above-described
wireless communication method, the step of assigning the terminal
to conduct space division multiple access in the down link is a
step of selecting the terminal with the best reception quality and
assigning the selected terminal as the terminal to conduct space
division multiple access if there are a plurality of
transmission-possible terminals using a transmission weight whose
correlation with a transmission weight for the terminal
preferentially assigned is lower than a predetermined value.
[0050] According to the invention, there can be provided the
wireless communication system, the wireless communication method,
the base station apparatus, and the terminal capable of removing a
transmission signal to a different terminal space division
multiplexed, an interference signal, in a terminal when wireless
communications are conducted using space division multiple access.
Consequently, when the base station apparatus transmits a
directional beam, it is made possible to form a transmission beam
to allow interference between different terminals, so that the
spatial flexibility in the transmission array antenna can be used
to improve the communication quality; the transmission array gain
can be improved, etc., and the system capacity of the downlink can
be improved.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0051] FIG. 1 is a diagram to show the schematic configuration of a
wireless communication system in a first embodiment.
[0052] FIG. 2 is a diagram to show the configurations of a base
station apparatus and terminals in the first embodiment.
[0053] FIG. 3 is a chart to show a communication processing
procedure between the base station apparatus and the mth
terminal.
[0054] FIGS. 4A-4C are drawings to show the frame structure of each
transmission signal from the base station apparatus containing an
antenna dedicated pilot signal.
[0055] FIG. 5 is a characteristic drawing to show directivity
generated according to a base station transmission weight
table.
[0056] FIG. 6 is a drawing of a table previously listing
information concerning the array configuration in the base station
apparatus 1.
[0057] FIG. 7 is a flowchart to show a transmission weight
candidate selection processing procedure.
[0058] FIG. 8 is a flowchart to show a terminal assignment
processing procedure.
[0059] FIGS. 9A-9B are drawings to show frame structures for using
space division multiplexing transmission of SDMA or SDM.
[0060] FIG. 10 is a chart to show a processing procedure of a base
station apparatus and different mth terminal in a second
embodiment.
[0061] FIG. 11 is a chart to show a processing procedure of a base
station apparatus and different mth terminal in a third
embodiment.
DESCRIPTION OF REFERENCE NUMERALS
[0062] 1 Base station apparatus
[0063] 2 SDM compatible terminal
[0064] 3 SDM incompatible terminal
[0065] 4 Transmission beam
[0066] 5 Communication area
[0067] 23 Terminal assignment means
[0068] 24 Dedicated data transmission means
[0069] 25 Space division multiplexing information notification
means
[0070] 42 Reception quality detection means
[0071] 43 Channel state estimation means
[0072] 44 Transmission weight selection means
[0073] 45 Control information generation means
[0074] 49 Spatial demultiplexing means
[0075] 50, 60 Data extraction means
DETAILED DESCRIPTION
First Embodiment
[0076] FIG. 1 is a diagram to show the schematic configuration of a
wireless communication system according to a first embodiment of
the invention. The embodiment shows communication processing using
space division multiple access (SDMA) when transmission from a base
station apparatus to a terminal (which will be hereinafter referred
to as downlink) is performed. The wireless communication system is
made up of a base station apparatus 1 and a plurality of terminals
2a, 2b, 3a, 3b, and 3c existing in a communication area 5 of the
base station apparatus 1. The base station apparatus 1 has a
plurality of antenna elements 1a to 1d and can change array antenna
directivity adaptively. The base station apparatus 1 makes space
division multiple access to an appropriate combination of the
terminals 2a, 2b, 3a, 3b, and 3c existing in the communication area
5 from the antenna elements 1a to 1d and emits a plurality of
transmission beams 4a, 4b, 4c, 4d (which will be hereinafter
collectively called transmission beam 4), for example. The
terminals 2a and 2b (which will be hereinafter collectively called
terminal 2) are a plurality of SDM (Space Division Multiplexing)
compatible terminals compatible with space division multiplexing
transmission for spatially multiplexing a plurality of transmission
signal series for the same terminal. The terminals 3a, 3b, and 3c
(which will be hereinafter collectively called terminal 3) are a
plurality of SDM incompatible terminals incompatible with SDM
transmission.
[0077] The number of the SDM compatible terminals and that of the
SDM incompatible terminals are not limited to them. The number of
the transmission beams changes adaptively in response to the
communication environment and an example of the number of the
transmission beams is shown in FIG. 1. Here, the terminal numbered
with the SDM compatible terminals 2 and the SDM incompatible
terminals 3 mixed is represented as terminal MS.sub.m. "m" is a
natural number equal to or less than the number of terminals
N.sub.ms existing in the communication area 5.
[0078] The wireless communication system enables space division
multiple access to the terminals under circumstances where the SDM
incompatible terminals 3 and the SDM compatible terminals 2 that
can conduct communications are mixed in the communication area 5.
The base station apparatus 1 determines whether or not both or
either of SDM transmission and SDMA transmission is possible in the
terminals made up of a large number of SDM compatible terminals 2
and SDM incompatible terminals 3 and forms a plurality of
transmission beams 4 from the antenna elements of the base station
apparatus 1, thereby realizing the SDM, SDMA transmission
determined to be possible.
[0079] FIG. 2 is a diagram to show the configurations of the base
station apparatus 1, the SDM compatible terminal 2 and the SDM
incompatible terminal 3. In FIG. 2, the base station apparatus 1
has the following configuration. It has a plurality of base station
antennas 20 for receiving and transmitting a high frequency signal,
a reception section 21 for performing demodulation and decoding
processing of the reception signal from the base station antennas
20, control information extraction means 22 for extracting control
information sent from the terminal MS.sub.m from the decoded data,
and terminal assignment means 23 for assigning the terminal to
communicate based on output from the control information extraction
means 22. The terminal assignment means 23 outputs connection
information by way of space division multiplexing of the assigned
terminal MS.sub.k to dedicated data transmission means 24 and space
division multiplexing information notification means 25 where k=1
to s.
[0080] The dedicated data transmission means 24 multiplies
transmission data series 26-1 to 26-2 generated based on a
predetermined transmission format for the dedicated data to be
transmitted to the terminal MS.sub.k assigned by the terminal
assignment means 23 by a transmission weight in corresponding beam
formation sections 27-1 to 27-s and then outputs. The space
division multiplexing information notification means 25 has space
division multiplexing information data series generation means 28
for generating data series to send the space division multiplexing
information of the assigned terminal and multiplexing means 29 for
multiplexing the generated space division multiplexing information
data series into signal from the dedicated data transmission means
24. Transmission sections 30-1 to 30-Nt convert a baseband signal
from the multiplexing means 29 into a high frequency signal of a
carrier frequency band and output the high frequency signal through
the base station antennas 20. FIG. 2 shows the configuration for
executing SDMA transmission to two terminals #1 and #2 (s=2) by way
of example. The multiplexing means 29 multiplexes the space
division multiplexing information data series into dedicated data
series using time division multiplexing, frequency division
multiplexing, code division multiplexing, etc.
[0081] On the other hand, the SDM compatible terminal 2-m has
reception antennas 40-1 to 40-Ns(m) for receiving a high frequency
signal from the base station apparatus 1, reception sections 41-1
to 41-Ns(m) for converting the received high frequency signal into
a baseband signal, reception quality detection means 42 for
detecting the reception quality based on the received baseband
signal or high frequency signal, channel state estimation means 43
for estimating a channel matrix as the channel state, and
transmission weight selection means 44 for selecting an appropriate
transmission weight based on the channel matrix. It also has
control information generation means 45 for generating a data
series in a predetermined format to be sent as control information
to the transmission party and dedicated data generation section 46
for generating a dedicated data series for transmission based on a
predetermined transmission format for the dedicated data to be
transmitted to the base station apparatus 1. It also has a
transmission section 47 for converting the output of control
information generation means 45 of baseband signal and the output
of the dedicated data generation section 46 into a high frequency
signal of a carrier frequency band, a transmission antenna 48 for
outputting the high frequency signal, spatial demultiplexing means
49 for demultiplexing and receiving any desired signal from the
signal spatially multiplexed and transmitted to the home terminal
or a different terminal based on the output of the channel state
estimation means 43, and data extraction means 50 for extracting
transmission data from the output signal from the spatial
demultiplexing means 49. Incidentally, m is to uniquely number each
SDM compatible terminal in the communication area 5 and represents
a natural number equal to or less than a predetermined value. The
reception antenna 40 and the transmission antenna 48 are handled as
separate components, but may share the same antenna. A plurality of
transmission antennas and a plurality of transmission sections may
be provided for executing directional transmission.
[0082] Next, the configuration of the SDM incompatible terminal 3
is the same as that of the SDM compatible terminal 2 except that
the spatial demultiplexing means 49 is not included and that data
extraction means 60 operates in a different manner from the data
extraction means 50 and therefore the configuration will not be
discussed again. A reception antenna 40 and a transmission antenna
48 are handled as separate components, but may share the same
antenna. Likewise, for the reception antenna 40 and a reception
section 41, FIG. 2 shows the configuration of only one channel, but
a plurality of channels may be provided for performing diversity
reception for selecting or combining reception signals based on
channel state estimation means 43.
[0083] FIG. 3 is a chart to show a communication processing
procedure between the base station apparatus 1 and the mth terminal
MS.sub.m. FIG. 3 shows the operation after frame synchronization
and symbol synchronization are established between the base station
apparatus and the terminal, and does not show the synchronization
establishing operation.
[0084] The base station apparatus 1 includes the N.sub.t base
station antennas 20 and the transmission sections 30-1 to 30-Nt and
first transmits a known signal series made up of a predetermined
number of symbols N.sub.p (which will be hereinafter referred to as
antenna dedicated pilot signal AP.sub.k(t)) from each of the
transmission sections (step S1). Here, k is the number of the
antenna and the transmission section in the base station apparatus
1 and k=1, 2, . . . , N.sub.t where t=1, . . . , N.sub.p. If the
number of the antennas N.sub.t of the base station apparatus 1 is
sufficiently large or if the number of spatial multiplex to execute
SDM is limited to a value smaller than the number of the antennas
N.sub.t of the base station apparatus 1, all N.sub.t transmission
sections need not be used and only some of the transmission
sections may be used to transmit antenna dedicated pilot
signals.
[0085] FIG. 4 is a drawing to show the frame structure of each
transmission signal from the base station apparatus 1 containing an
antenna dedicated pilot signal. The transmission signal in the
frame is made up of an antenna dedicated pilot signal 30, user
control information 31, and a dedicated data series 32. The user
control information 31 stores user identification information of
the destination of the dedicated data series 32 following the user
control information and control information of the modulation
scheme, the coding rate, etc., required for demodulating the
dedicated data series 32.
[0086] FIGS. 4A, B, and C show different transmission formats of
the antenna dedicated pilot signal 30. In FIG. 4A, the transmission
timing of the antenna dedicated pilot signal 30 is shifted for each
antenna for transmission in a time division manner. Code series
orthogonal to each other according to the same pattern, pseudo
random code, etc., are used for the antenna dedicated pilot signal
30. In FIG. 4B, transmission is executed in a code division
multiplexing manner using code series orthogonal to each other from
different antennas.
[0087] A system using time division transmission and code division
transmission in combination can also be applied. That is, in the
antenna combination in FIG. 4C, the time division slot at the
identical time is shared and the antenna dedicated pilot signals 30
(A1 and A2 in the figure) are transmitted in the code division
multiplexing manner using code series orthogonal to each other.
Accordingly, the overhead of time division transmission when the
number of antennas is large in the base station apparatus 1 can be
decreased and a decrease in the orthogonality in the propagation
line at the code division multiplexing time can be relieved.
[0088] The terminal MS.sub.m existing in the communication area 5
calculates the channel estimation value of the antenna dedicated
pilot signal AP.sub.k(t) transmitted for each base station antenna
in the channel state estimation means 43 using the signals received
at the reception antennas 40 and the reception sections 41-1 to
41-N.sub.s (step S2 in FIG. 3). Calculation of the channel
estimation value is shown. The mth terminal MS.sub.m existing in
the communication area 5 has N(m) antennas and N(m) reception
channels and can execute SDM reception using a maximum of N(m)
space division multiplex channels.
[0089] Here, "m" is a natural number equal to or less than the
number of terminals N.sub.ms existing in the communication area 5.
The mth SDM incompatible terminal 3 becomes N.sub.s(m)=1, and the
first SDM compatible terminal 2 becomes N.sub.s(1)>1. For the
kth antenna dedicated pilot signal AP.sub.k(t), correlation
operation between the reception result at the jth antenna and
reception channel in the mth terminal MS.sub.m, r.sub.j,
k.sup.(m)(t) (where j=1, . . . , N(m)), and a replica of
AP.sub.k(t) generated in the terminal MS.sub.m is performed as
shown in expression (1), whereby the channel estimation value
h.sup.m(j, k) of the propagation line is calculated. In the
expression, * is an operator for executing a complex conjugate.
[ Expression 1 ] h m ( j , k ) = 1 N p t = 1 N p AP k * ( t ) r j ,
k ( m ) ( t ) ( 1 ) ##EQU00001##
[0090] The obtained channel estimation value h.sup.m(j, k) is
represented as a channel matrix with j rows and k columns of
elements as shown in expression (2). Here, in the mth SDM
incompatible terminal 3, it is represented as N.sub.s(m)=1, in
which case channel matrix H(m) becomes a row vector.
[ Expression 2 ] H ( m ) = [ h m ( 1 , 1 ) h m ( 1 , 2 ) h m ( 1 ,
N t ) h m ( 2 , 1 ) h m ( 2 , 2 ) h m ( 2 , N t ) h m ( N s ( m ) ,
1 ) h m ( N s ( m ) , 2 ) h m ( N s ( m ) , N t ) ] ( 2 )
##EQU00002##
[0091] Two or more reception results of the antenna dedicated pilot
signal AP.sub.k(t) may be saved and averaging processing may be
performed. In this case, if the move speed of the terminal is
sufficiently small, the effect of noise can be decreased and it is
made possible to enhance the channel estimation quality. Finally,
as many channel estimation values based on the mth terminal
MS.sub.m as (the number of antenna dedicated pilot signals
N.sub.t).times.(the number of antennas N.sub.s(m) of the terminal
MS.sub.m) are calculated in total.
[0092] The transmission weight selection means 44 selects a maximum
of N.sub.s(m) transmission beams 4 from among transmission beam
candidates in each terminal MS.sub.m using the calculated channel
estimation values (step S3 in FIG. 3). To select the transmission
beam from among the transmission beam candidates, the base station
apparatus 1 and the terminal MS.sub.m previously share
predetermined transmission weight candidates W.sub.n from the base
station apparatus as a base station transmission weight table,
where n is a natural number equal to or less than a predetermined
number N.sub.b. The base station transmission weight table is a
list of transmission weights in the base station apparatus 1
covering the communication area 5 in a predetermined angle range
with a predetermined spatial resolution. The number of elements of
the table is the number of elements of the number of base station
transmission array elements N.sub.t.times.the number of
transmission weight candidates N.sub.b.
[0093] FIG. 5 is a characteristic drawing of a graph indicating
directivity generated according to the base station transmission
weight table. FIG. 5 shows directivity when the base station
apparatus has an eight-element equal spacing linear array with 0.5
wavelength spacing assuming that array elements in the base station
apparatus 1 are omni-directional. In this case, the directivity is
made up of transmission weight candidates for covering the
communication area 5 (120.degree. sector) every spatial resolution
10.degree.. In addition to the method for the base station
apparatus 1 and the terminal MS.sub.m to previously share the base
station transmission weight table, a method may be adopted wherein
the base station apparatus 1 previously reports the number of
elements, the antenna element spacing, arrangement (linear or
circular), the angle range of the communication area 5 [.theta.s,
.theta.e], and angle resolution .DELTA..theta. to each terminal
MS.sub.m and the base station transmission weight table is
generated in each terminal MS.sub.m.
[0094] For example, if the array has equally spaced elements (where
the number of elements is N.sub.t and the element spacing is d), a
base station transmission weight table with transmission weight
W.sub.n as shown in expression (3) as element can be created.
[ Expression 3 ] w n = [ 1 exp { j 2 .pi. d 1 sin { .theta. s - ( n
- 1 ) .DELTA. .theta. } / .lamda. } exp { j 2 .pi. d ( N - 1 ) sin
{ .theta. s - ( n - 1 ) .DELTA. .theta. } / .lamda. } ] ( 3 )
##EQU00003##
[0095] where n is a natural number equal to or less than the value
resulting from dropping the fractional portion of
{1+(.theta.e-.theta.s)/.DELTA..theta.}. The information to generate
the base station transmission weight table need not frequently be
updated and may be updated at the same time, for example, when a
new position is registered in the communication area 5 with a move
of the terminal MS.sub.m, etc. Accordingly, it becomes necessary
for the base station apparatus 1 to send information to the mobile
station apparatus, but the configuration of the base station
apparatus 1 can be made flexible.
[0096] A method of previously listing information concerning the
representative configuration of the array antenna in the base
station apparatus 1 and reporting the list number may be adopted.
FIG. 6 is a drawing of a table previously listing information
concerning the array configuration in the base station apparatus 1.
Information of the number of elements, the element arrangement, the
element spacing, the angle range in the communication area 5, and
the angle resolution indicating the main beam spacing of the
transmission beam 4 is listed under the list numbers. Such a list
is introduced, whereby the amount of information sent from the base
station apparatus 1 to each terminal MS.sub.m can be decreased.
[0097] As another method, a method of sharing a list for giving
predetermined phase rotation to each array element regardless of
the array configuration may be adopted. As another method, a method
of calculating an average phase difference between the channel
estimation values and reporting the value or reporting the
quantization value based on a predetermined value may be adopted.
Accordingly, an equal gain in-phase synthetic beam can be obtained
in a sight propagation environment. Although it is assumed that the
base station apparatus 1 and the terminal MS.sub.m previously share
predetermined transmission weight candidates W.sub.n from the base
station apparatus as a base station transmission weight table, the
terminal MS.sub.m may send information of the optimum transmission
beam 4 to the base station apparatus. In this case, the amount of
the information to be sent increases, but it is made possible to
optimize the communication quality.
[0098] Transmission beam candidates are selected as follows (step
S3 in FIG. 3): To select the transmission beam candidates, the
operation differs depending on whether the number of the reception
channels N.sub.s(m) in the mth terminal MS.sub.m is value 1 or
value 2 or more. Transmission beam candidate selection methods are
shown.
[0099] (.alpha.) When N.sub.s(m)=1
[0100] In this case, a transmission weight with reception power
reaching the maximum is selected from among the transmission weight
candidates W.sub.n in the base station transmission weight table.
That is, the maximum transmission weight T.sub.1(m) satisfying
expression (4) is selected. Here, n is a natural number equal to or
less than a predetermined number N.sub.b.
[ Expression 4 ] T n ( m ) = arg { w n | max n ( H ( m ) w n 2 ) }
( 4 ) ##EQU00004##
[0101] (.beta.) When N.sub.s(m).gtoreq.2
[0102] FIG. 7 is a flowchart to show the transmission weight
candidate selection processing procedure. In this case, first,
channel matrix H (m) obtained in the terminal MS.sub.m is
decomposed into singular values as shown in expression (5) (step
S40).
[Expression 5]
H(m)=U.sub.mD.sub.mV.sub.m.sup.H (5)
[0103] where H is an operator indicating complex conjugate
transposition, and D.sub.m is a matrix with N.sub.s(m) rows and
N.sub.t columns and the singular values are arranged in principal
diagonal components as shown in expression (6).
[ Expression 6 ] D m = [ .lamda. 1 ( m ) 0 0 .lamda. 2 ( m ) ] ( 6
) ##EQU00005##
[0104] An initial value 0 is assigned to a counter n (step S41) and
the counter n is incremented by one (step S42). Then, whether or
not n=1 or whether or not n.gtoreq.2 and the singular value is a
predetermined value .mu. or more is determined (step S43). In this
case, n=1 and therefore the determination at step S43 is YES and
the column vector of the right singular value matrix corresponding
to the largest singular value is selected (step S44). Further, the
transmission weight candidate W.sub.n with the maximum correlation
with the column vector v.sub.l of the right singular value matrix
V.sub.m corresponding to the maximum singular value of the channel
matrix is selected as the first transmission beam T.sub.1 (step
S45). Here, k is a natural number equal to or less than a
predetermined number N.sub.b.
[ Expression 7 ] T n ( m ) = arg { w k | max k ( w k H v n ) } ( 7
) ##EQU00006##
[0105] Whether or not n matches N.sub.s(m) is determined (step
S46). If a match is not found, the process returns to step S42 and
the counter n is incremented by one and again the transmission
weight candidate selection processing is performed. On the other
hand, if a match is found at step S46, the transmission weight
candidate selection processing is terminated.
[0106] In the second or later loop, namely, when n.gtoreq.2,
whether or not the singular value is equal to or greater than a
predetermined value .mu. is determined at step S43. If the singular
value is less than the predetermined value .mu., it is assumed that
an effective space division multiplex channel is not obtained in
the propagation environment, and the transmission weight candidate
selection processing is terminated. On the other hand, if the
singular value is equal to or greater than the predetermined value
.mu., at step S44, the column vector v.sub.n in the right singular
value matrix V.sub.m corresponding to the nth largest singular
value is selected and the transmission weight candidate W.sub.n
with the maximum inner product with the selected right singular
vector v.sub.n is selected as the nth transmission beam T.sub.n
from among the transmission weight candidates W.sub.k as shown in
expression (7). The predetermined value .mu. can be determined
based on the technique of Waterfilling with information disclosed
in Document: I. Telatar, "Capacity of multi-antenna Gaussian
Channels," European Trans. Tel., 10 (6), 1999, p. 585-595, for
example.
[0107] Next, the reception quality detection means 42 predicts and
estimates the reception quality in each terminal MS.sub.m for
transmission with the selected transmission beam 4 (step S4 in FIG.
3). As the reception quality, reception signal power, SIR (signal
power to interference power ratio), SNR (signal power to noise
power ratio), etc., can be applied. Here, the case where the SNR is
used is shown. To evaluate the SNR using the antenna dedicated
pilot signal AP.sub.k(t), L.sub.n(m) is calculated as the SNR when
the nth transmission beam 4 in the terminal MS.sub.m as shown in
expression (8).
[ Expression 8 ] L n ( m ) = .lamda. n ( m ) [ T n H v n ] N ( m )
( 8 ) ##EQU00007##
[0108] where N(m) denotes noise power, which is calculated using
expression (9).
[ Expression 9 ] N ( m ) = 1 Ns ( m ) NtNp j = 1 Ns ( m ) k = 1 Nt
i = 1 N p AP k * ( t ) r j , k ( m ) ( t ) - h m ( j , k ) 2 ( 9 )
##EQU00008##
[0109] To calculate the SIR, for example, if maximum ratio
synthetic beam is formed and is received in the terminal MS.sub.m
to receive the transmission beam, the reception signal power to the
signal transmitted by the transmission beam excluding that
transmission beam is considered as the interference component.
[0110] Next, the control information generation means 45 generates
control information based on output of the transmission weight
selection means 44 and output of the reception quality detection
means 42. The dedicated data generation section 46 outputs a signal
provided by performing predetermined transmission line coding and
modulation for the data signal unique to the terminal The
transmission section 47 converts the baseband signal of the
transmission data series in a predetermined frame format formed
based on output of the control information generation means 45 and
output of the dedicated data generation section 46 into a high
frequency signal subjected to band limitation processing and
amplification processing and transmits the high frequency signal
from the transmission antenna 48.
[0111] Thus, each terminal MS.sub.m sends a notification about
N.sub.b(m) transmission beams T.sub.n(m)(where n=1 to N.sub.b(m))
provided by each terminal MS.sub.m and the reception quality to the
base station apparatus 1 (step S5A in FIG. 3). In this case, as the
control information in the control information generation means 45,
the transmission beam notification uses the number in the base
station transmission weight table shared between the base station
apparatus 1 and the terminal MS.sub.m. Accordingly, information of
only the transmission beam number needs to be transmitted and thus
the information amount in making the transmission beam notification
can be reduced. As for the reception quality, a reception quality
table subjected to appropriate quantization can also be shared
between the base station apparatus 1 and the terminal MS.sub.m for
making a reception quality notification using the number in the
reception quality table. Accordingly, it is made possible to reduce
to the information amount of only a predetermined number of
quantization bits.
[0112] As another notification method about the reception quality,
a multilevel modulation coding rate table associating the
multilevel modulation count and the coding rate with each other
based on the measured reception quality can also be shared between
the base station apparatus 1 and the terminal MS.sub.m for making a
reception quality notification using the number in the multilevel
modulation coding rate table. Accordingly, the information amount
in making the reception quality notification can be reduced.
[0113] On the other hand, the base station apparatus 1 receives the
high frequency signal transmitted from the terminal MS.sub.m at the
base station antenna 20 and performs frequency conversion
processing of the high frequency signal in the reception section 21
to generate a baseband signal. The control information extraction
means 22 extracts the control information sent from the terminal
MS.sub.m from the received baseband signal.
[0114] The terminal assignment means 23 assigns the terminal
MS.sub.m to communicate considering the transmission beam
notification from each terminal MS.sub.m (step S5 in FIG. 3). FIG.
8 is a flowchart to show the assignment processing procedure of the
terminal MS.sub.m. First, the terminal MS.sub.m to be assigned
preferentially using a predetermined scheduling algorithm based on
QoS information of the data to be transmitted (allowable delay,
requirement rate, etc.,) and transmission quality information (step
S50). Here, Maximum CIR method, Proportional fairness method, and
the like of high-speed packet schedulers based on reception SIR are
proposed as the scheduling algorithm. For example, information is
disclosed in Document: A. Jalali, R. Padovani and R. Pankaj, "Data
Throughput of CDMA-HDR a High Efficiency-High Data Rate Personal
Communication Wireless System," IEEE VTC2000-Spring, May 2000, p.
1854-1858.
[0115] The transmission beam 4 is assigned using the transmission
beam T.sub.n(m) making the transmission beam notification by the
terminal MS.sub.m (step S51) where n is a natural number equal to
or less than N.sub.s(m) at most. If a plurality of transmission
beams 4 are sent, namely, if N.sub.s(m)>1, different data
streams are spatially multiple-transmitted (SDM).
[0116] Whether or not there is a terminal MS.sub.m making
transmission beam notification with low correlation with the
transmission beam 4 of the assigned terminal MS.sub.m is determined
(step S52). That is, mutual interference amount I (m, l) between
the terminal MS.sub.m to be newly assigned and the already assigned
transmission beam is calculated based on the already assigned
transmission beam T.sub.n(m) and the first terminal MS.sub.m as
shown in expression (10), and whether or not the mutual
interference amount I (m, l) is equal to or less than a
predetermined value is determined.
[ Expression 10 ] I ( m , l ) = k = 1 Ns ( l ) n = 1 Na P nk ( m ,
l ) T n ( m ) H T k ( l ) 2 ( 10 ) ##EQU00009##
[0117] where P.sub.nk(m, l) is the ratio between the transmission
power using the transmission beam T.sub.n(m) and the transmission
power using a transmission beam T.sub.k(l), and N.sub.a represents
the total number of the already assigned transmission beams 4.
Here, the ratio when the smaller transmission power is the
denominator is calculated to estimate the mutual interference
amount.
[0118] If the mutual interference amount I (m, l) is equal to or
less than the predetermined value, the corresponding terminal is
adopted as an assignment candidate terminal (step S53). If two or
more assignment candidate terminals exist, the terminal MS.sub.m
with the maximum reception quality is assigned. After the
assignment operation terminates, the process returns to step S52
and similar processing is repeated for determining the terminal
MS.sub.m to be connected by way of space division multiplexing.
When it is not determined at step S52 that there is a terminal
MS.sub.m making transmission beam notification with low
correlation, the processing is terminated.
[0119] As another method, when SDMA is executed, the upper limit
number of terminals connected at the same time by way of space
division multiplexing may be previously fixed. Accordingly, the
throughput of the wireless communication system is degraded, but
the computation amount when a search is made for the terminals
MS.sub.m that can be connected at the same time by way of space
division multiplexing and a delay to connection can be decreased.
Since the term T.sub.n(m).sup.HT.sub.k(l) in expression (10) exists
only in a known predetermined combination, a method of previously
creating a computation result table and selecting the terminal
MS.sub.m sending the transmission beam 4 being equal to or less
than a predetermined value of the mutual interference amount I (m,
l) multiplied by the transmission power ratio P.sub.nk(m, l) can be
applied. Accordingly, the computation amount when a search is made
for the terminals MS.sub.m that can be connected at the same time
by way of space division multiplexing and a delay to connection can
be decreased.
[0120] After the terminals MS.sub.m to be connected by way of space
division multiplexing are determined, the space division
multiplexing information notification means 25 notifies the
terminals MS.sub.m that dedicated data transmission is to be
started, and to execute SDMA, sends information concerning the
transmission beam 4 used in a different terminal connected at the
same time by way of space division multiplexing and information
concerning signal power used in the different terminal normalized
in the terminal MS.sub.m (step S5A in FIG. 3). Thus, the space
division multiplexing information data series generation means 28
generates control information in a predetermined format, and the
multiplexing means 29 multiplexes the output data of the dedicated
data transmission means 24. The transmission section 30 performs
frequency conversion, band limitation processing, and amplification
processing for the baseband signal output by the multiplexing means
29 to generate a high frequency signal, and transmits the high
frequency signal through the base station antenna 20. The
multiplexing means 29 multiplexes space division multiplexing
information data series using time division multiplexing, frequency
division multiplexing, code division multiplexing, etc.
[0121] The dedicated data transmission means 24 performs
predetermined transmission line coding, modulation, and interleave
for transmission data to one or more assigned predetermined
terminals to generate transmission data series 26. The beam
formation sections 27 multiply the transmission data series 26 by
the transmission weight forming the transmission beam 4 previously
sent, and output. If a plurality of transmission beams 4 are
assigned to one terminal MS.sub.m, different data streams are
spatially multiple-transmitted (SDM). As another method, time space
coding may be performed for the data streams and transmission may
be executed using different beams. In this case, the data rate
decreases, but the communication quality can be improved by the
space diversity effect or the coding gain.
[0122] FIG. 9 is a drawing to show frame structures for using space
division multiplexing transmission of SDMA or SDM. A frame is made
up of a pilot signal 30, user control information 31, and dedicated
data series 32 to each terminal MS.sub.m. Two types of frame
structures of the frame structure not to transmit directivity for
the user control information 31 (see FIG. 9B) and the frame
structure to transmit directivity for the user control information
31 (see FIG. 9B) can be applied to the user control information 31.
The dedicated data series 32 is transmitted using different
transmission directivity assigned. A different user interference
cancel weight to separate and receive the dedicated data signal for
each terminal MS.sub.m transmitted in a downlink from the base
station apparatus 1 (step S7 in FIG. 3) in each terminal MS.sub.m
is calculated based on the information (step S6 in FIG. 3), and
reception processing of dedicated data different for each terminal
MS.sub.m is performed (step S8 in FIG. 3).
[0123] The dedicated data reception processing of the SDM
compatible terminal 2-m is performed as follows: First, a high
frequency signal from the base station apparatus 1 is received at
the reception antenna 40. The reception section 41 converts the
received high frequency signal into a baseband signal. The channel
state estimation means 43 estimates a channel matrix as the channel
state. The spatial demultiplexing means 49 separates and receives
any desired signal from the signal spatially multiplexed and
transmitted to the home terminal or a different terminal based on
the output of the channel state estimation means 43. The data
extraction means 50 extracts transmission data from the output
signal of the spatial demultiplexing means 49 and further performs
demodulation processing, deinterleave processing, and transmission
line error correction coding processing to restore the transmission
data. The dedicated data reception processing of the SDM
incompatible terminal 3 is the same as that of the SDM terminal 2
except that the data extraction means 60 operates in a different
manner from the data extraction means 50.
[0124] Next, the reception operation of the terminal MS.sub.m will
be discussed in detail separately in the case where the number of
the reception channels is two or more and the case where the number
of the reception channels is one.
[0125] (.alpha.) When the number of the reception channels in the
terminal MS.sub.m is two or more (operation of the spatial
demultiplexing means 49 of the SDM compatible terminal 2)
[0126] In this case, a signal y.sub.m(t) received by the terminal
MS.sub.m is represented as shown in expression (11) where t denotes
the time, y.sub.m(t) is a column vector having as many elements as
the number of the reception channels N.sub.s(m), x.sub.m(t) is a
column vector having N.sub.s(m) elements and representing
transmission data to the terminal MS.sub.m, z.sub.jl(t) is a column
vector representing transmission data to a terminal MS.sub.j except
the terminal MS.sub.m and having N.sub.s(j) elements, and P.sub.jl
represents signal power normalized by transmission power of the
terminal MS.sub.m reported from the base station apparatus 1 and
transmitted using a transmission beam T.sub.1(j) in the different
terminal MS.sub.j. In expression (11), the second term represents
the interference component with the terminal MS.sub.m. Therefore,
if the weight to minimize the interference, namely, maximize the
SINR is calculated according to MMSE (minimum square error
criterion) criterion, interference cancel weight G(m) shown in
expression (12) is obtained, where Z.sub.i is represented by
expression (13).
[ Expression 11 ] y m ( t ) = H ( m ) [ T 1 ( m ) T Ns ( m ) ] x m
( t ) + H ( m ) j = 1 Nu [ P j 1 T 1 P jNs ( l ) T Ns ( l ) ( j ) ]
z jl ( t ) ( 11 ) [ Expression 12 ] G ( m ) = [ Z i Z i H + .sigma.
2 I ] - 1 ( H ( m ) [ T 1 ( m ) T Ns ( m ) ( m ) ] ) ( 12 ) [
Expression 13 ] Z 1 = j - 1 Nu H ( k ) [ P j 1 T 1 ( j ) P jNs ( 1
) T Ns ( 1 ) ( j ) ] ( 13 ) ##EQU00010##
[0127] Therefore, the reception signal y.sub.m(t) is multiplied by
the obtained interference cancel weight G(m) as shown in expression
(14) for decreasing the interference component and then the signal
is detected by maximum likelihood estimation based on information
of signal constellation s.sub.k transmitted for separating and
receiving spatially multiple-transmitted signal s.sub.m(t) as shown
in expression (15).
[ Expression 14 ] d m ( t ) = G H ( m ) y m ( t ) ( 14 ) [
Expression 15 ] s m ( t ) = arg { s k min S k .di-elect cons. c M L
d m ( t ) - G H H ( m ) [ T 1 ( m ) T Ns ( m ) ( m ) ] s , k 2 } (
15 ) ##EQU00011##
[0128] (.beta.) When the number of the reception channels in the
terminal MS.sub.m is one (operation of the data extraction means 60
of the SDM incompatible terminal 3)
[0129] In this case, interference cancel using spatial flexibility
cannot be executed in the terminal MS.sub.m and therefore the data
extraction means 60 first detects the maximum interference
component in the second term indicating the interference component
in expression (16). That is, as shown in expression (17), if the
inner product of the transmission beam 4 to different terminal
MS.sub.m and the transmission beam 4 to the home terminal
multiplied by the transmission power ratio becomes the maximum, it
becomes the maximum interference component and therefore the
maximum likelihood estimation method considering the signal
constellation becoming the interference component is executed. This
means that the signal is detected by maximum likelihood estimation
as shown in expression (18). Deinterleave processing and
transmission line error correction coding processing are performed
for the detected output signal to restore the transmission
data.
[ Expression 16 ] ( J , L ) = arg { j , l | max j , l ( P jl T 1 H
( m ) T 1 ( j ) ) } ( 16 ) [ Expression 17 ] y m ( t ) = H ( m ) T
1 ( m ) x m ( t ) + H ( m ) j - 1 P j 1 T 1 ( j ) P jNs ( 1 ) T Ns
( l ) ( j ) z jl ( t ) .apprxeq. H ( m ) T 1 ( m ) x m ( t ) + H (
m ) P JL T L ( J ) z JL ( t ) ( 17 ) [ Expression 18 ] s m ( t ) =
arg min s k .di-elect cons. C M L y m ( t ) - { H ( m ) T 1 ( m ) x
m ( t ) + H ( m ) P JL T L ( J ) z JL ( t ) } 2 ( 18 )
##EQU00012##
[0130] As another method, the base station apparatus 1 may send the
result found in expression (16). Accordingly, the advantage that
the computation amount of the terminal MS.sub.m can be decreased
can be provided. As another method, the terminal 3 may perform
detection processing including an interference signal based on
maximum likelihood estimation according to expression (18) only if
the reception SINR of the terminal exceeds a predetermined
value.
[0131] According to the operation, in the embodiment, when the
transmission beam 4 required at the SDMA time is determined, the
need for feeding back the channel estimation value or the
transmission weight itself is eliminated and the information amount
can be decreased and consequently the transmission efficiency can
be enhanced. Since the transmission beam 4 is determined through
feedback, a calibration circuit for removing the effect of the
deviation caused by the hardware between array series becomes
unnecessary in the base station apparatus 1 and the configuration
of the base station apparatus 1 can be simplified and can be
reduced in cost. If identical channel interference exists at the
SDMA time, the terminal MS.sub.m performs the operation for
decreasing the interference, so that the transmission beam 4 can be
selected without impairing the array gain.
[0132] The embodiment can be applied regardless of connection
oriented or packet data exchange transmission. In the embodiment,
transmission power control may be added so that the reception
quality in the spatial multiplexing terminal MS.sub.m becomes
constant. This can be accomplished by measuring the index of SIR,
etc., for example, as the reception quality in the terminal
MS.sub.m, sending the index to the base station apparatus 1, and
controlling the transmission power from the base station apparatus
1 based on the index.
[0133] In the first embodiment, the transmission beam 4 with the
maximum correlation is selected using expression (4) or (7) at the
operation time of transmission weight candidate selection; however,
as another method, a notification of the transmission beam 4 with
the minimum correlation as shown in expression (19) or (20) may be
sent to the base station apparatus 1. Accordingly, the base station
apparatus 1 can eliminate the need for the operation to determine
whether or not the terminal MS.sub.m making transmission beam
notification with low correlation exists based on expression (10).
That is, the terminal MS.sub.m selecting the transmission beam 4
with the minimum correlation sent by the terminal MS.sub.m assigned
preferentially based on the specific scheduling algorithm as the
transmission beam 4 is adopted as an assignment candidate, whereby
search using expression (10) can be made unnecessary.
[ Expression 19 ] G n ( m ) = arg { w n | min k ( H ( m ) w n 2 ) }
( 19 ) [ Expression 20 ] G n ( m ) = arg { w k min k ( w k H v n )
} ( 20 ) ##EQU00013##
[0134] In the procedure in FIG. 3, if the same terminal MS.sub.m is
assigned again in a sufficiently short time period from assignment
of transmission terminal, it is assumed that a move of the terminal
MS.sub.m is sufficiently gentle and variation in the propagation
environment is small and a procedure of skipping steps S1 to S4 and
using the previous transmission beam request and reception quality
notification result at step S4A may be applied. In this case, the
procedure can be implemented by providing temporary storage means
in the base station apparatus 1. Accordingly, as steps S1 to S4 are
skipped, the time other than the dedicated data transmission time
can be shortened and consequently the dedicated data transmission
efficiency can be improved.
Second Embodiment
[0135] FIG. 10 is a chart to show a processing procedure of a base
station apparatus 1 and different mth terminal MS.sub.m in a second
embodiment. The processing in the second embodiment is processing
wherein a part of the processing procedure shown in FIG. 3 in the
first embodiment described above is changed and therefore steps
identical with those in the first embodiment are denoted by the
same step numbers in the second embodiment and only different
processing from that in the first embodiment will be discussed. The
configurations of the base station apparatus 1 and terminals 2 and
3 are the same as those in the first embodiment and therefore will
not be discussed again. In the description to follow, the operation
after frame synchronization and symbol synchronization are
established between the base station apparatus 1 and the terminal
is shown, and the synchronization establishing operation is not
shown.
[0136] First, the base station apparatus 1 includes N.sub.t base
station antennas 20 and transmission sections 30-1 to 30-Nt and
transmits a known signal series made up of a predetermined number
of symbols N.sub.p (which will be hereinafter referred to as beam
dedicated pilot signal BP.sub.k(t)) from each of the transmission
sections using a predetermined number N.sub.d of different
transmission beams W.sub.k (step S90). Here, k is the transmission
beam number in the base station apparatus 1 and k=1, 2, . . . ,
N.sub.d where t=1, . . . , N.sub.p.
[0137] The beam dedicated pilot signal BP.sub.k(t) is transmitted
according to a similar frame structure to that of the antenna
dedicated pilot signal 30 shown in the FIG. 4. This means that the
frame structure is a frame structure wherein the antenna dedicated
pilot signal 30 in the FIG. 4 is replaced with the beam dedicated
pilot signal. The antenna dedicated pilot signal 30 and the beam
dedicated pilot signal differ in that the antenna dedicated pilot
signal 30 is transmitted separately from each antenna element and
in the beam dedicated pilot signal, a different dedicated pilot
signal is transmitted for each beam. A transmission beam 4 is
provided by multiplying an antenna almost equal in directivity by a
transmission weight; it can also be provided by using a plurality
of antennas having different directivity. Here, the former method
will be discussed using the transmission beam 4, but the embodiment
can also be applied to the latter method in a similar manner.
[0138] The terminal MS.sub.m existing in a communication area 5
executes channel estimation for each beam, of the beam dedicated
pilot signal BP.sub.k(t) transmitted for each base station antenna
in channel state estimation means 43 using the signals received at
reception antennas 40 and reception sections 41-1 to 41-N.sub.s
(step S91). The mth terminal MS.sub.m existing in the communication
area 5 includes N.sub.s(m) antennas and N.sub.s(m) reception
channels and can execute SDM reception of a maximum of N(m) space
division multiplex channels. Here, m is a natural number equal to
or less than the number of terminals N.sub.ms existing in the
communication area 5.
[0139] The mth SDM incompatible terminal 3 becomes N.sub.s(m)=1,
and the first SDM compatible terminal 2 becomes N.sub.s(l)>1.
For the kth beam dedicated pilot signal BP.sub.k(t), correlation
operation between the reception result at the jth antenna and
reception channel in the mth terminal MS.sub.m, r.sub.j,
k.sup.(m)(t) (where j=1, . . . , N(m)), and a replica of the beam
dedicated pilot signal BP.sub.k(t) generated in the terminal
MS.sub.m is performed, whereby the channel estimation value
h.sup.m(j, k) of the propagation line is calculated as shown in
expression (21)
[ Expression 21 ] h m ( j , k ) = 1 N p t - 1 N p BP k * ( t ) r j
, k ( m ) ( t ) ( 21 ) ##EQU00014##
[0140] where * is a complex conjugate operator. The obtained
channel estimation value h.sup.m(j, k) is represented as a channel
matrix with j rows and k columns of elements as shown in expression
(22). Here, in the SDM incompatible terminal 3, N.sub.s(m)=1 and
therefore channel matrix H(m) in this case becomes a row
vector.
[ Expression 22 ] H ( m ) = [ h m ( 1 , 1 ) h m ( 1 , 2 ) h m ( 1 ,
N d ) h m ( 2 , 1 ) h m ( 2 , 2 ) h m ( 2 , N d ) h m ( N s ( m ) ,
1 ) h m ( N s ( m ) , 2 ) h m ( N s ( m ) , 2 ) ] ( 22 )
##EQU00015##
[0141] Two or more reception results of the beam dedicated pilot
signal BP.sub.k(t) may be saved and averaging processing may be
performed. In this case, if the move speed of the terminal is
sufficiently small, the effect of noise can be decreased and it is
made possible to enhance the channel estimation quality. Finally,
as many channel estimation values based on the mth terminal
MS.sub.m as (the number of beam dedicated pilot signals
N.sub.d).times.(the number of antennas N.sub.s(m) of the terminal
MS.sub.m) are calculated in total.
[0142] In each terminal MS.sub.m, transmission weight selection
means 44 selects a maximum of N.sub.s(m) transmission beams 4 from
among transmission beam candidates using the calculated channel
estimation values (step S92). As the transmission beam candidates,
the base station apparatus 1 and the terminal MS.sub.m previously
share predetermined transmission weight candidates W.sub.k from the
base station as a base station transmission weight table according
to a similar method to that in the first embodiment, where n is a
natural number equal to or less than a predetermined number
N.sub.b.
[0143] Although it is assumed that the base station apparatus 1 and
the terminal MS.sub.m previously share predetermined transmission
weight candidates W.sub.n from the base station apparatus as a base
station transmission weight table, the terminal MS.sub.m may send
information of the optimum transmission beam 4 to the base station
apparatus. In this case, the amount of the information to be sent
increases, but it is made possible to optimize the communication
quality.
[0144] To select the transmission beam candidates at step S92, the
operation differs depending on whether the number of the reception
channels N.sub.s(m) in the mth terminal MS.sub.m is value 1 or 2 or
more. Transmission beam candidate selection methods are shown.
[0145] (.alpha.) When N.sub.s(m)=1
[0146] In this case, a transmission weight with reception power,
SNR, SIR, or SINR in the mth terminal MS.sub.m reaching the maximum
is selected from among the transmission weight candidates W.sub.k
in the base station transmission weight table. To use the SNR as
the selection index, transmission weight T.sub.1(m)=W.sub.k0 having
k=k.sub.0 the maximum so as to satisfy expression (23), for
example, is selected. Here, k is a natural number equal to or less
than a predetermined number N.sub.d. N.sub.k(m) indicates reception
noise power in the kth transmission weight candidate W.sub.k and is
calculated according to expression (24).
[ Expression 23 ] k 0 = arg { k | max k = 1 , , nd [ h m ( l , k )
2 N k ( m ) ] 2 } ( 23 ) [ Expression 24 ] N k ( m ) = 1 N p t - 1
N p BP k * ( t ) r j , k ( m ) ( t ) - h m ( l , k ) 2 ( 24 )
##EQU00016##
[0147] (.beta.) When Ns(m).gtoreq.2
[0148] In this case, a transmission weight with reception power,
SNR, SIR, or SINR in the mth terminal MS.sub.m reaching the maximum
is selected from among the transmission weight candidates W.sub.k
in the base station transmission weight table. To use the SNR
obtained according to the transmission beam for performing maximum
ratio combining in the mth terminal MS.sub.m as the selection
index, evaluation function f.sub.m(W.sub.k) satisfying expression
(25), for example, is used. High-order N.sub.s(m) transmission
weights T.sub.n(m) of evaluation values exceeding a predetermined
value according to the evaluation function f.sub.m(W.sub.k) are
selected. Here, n is a natural number equal to or less than a
predetermined number N.sub.s.
[ Expression 25 ] f m ( W k ) = j = 1 Ns ( m ) h m ( j , k ) 2 ( 25
) ##EQU00017##
[0149] Next, in each terminal MS.sub.m, reception quality detection
means 42 predicts and estimates the reception quality for
transmission with the selected transmission beam 4 (step S93). As
the reception quality, the SNR obtained according to the
transmission beam for performing maximum ratio combining that can
be given according to expression (25) may be used. Alternatively,
dispersion of interference noise power obtained according to the
transmission beam for performing maximum ratio combining is
estimated, whereby the SIR or the SINR may be applied.
[0150] Next, control information generation means 45 generates
control information based on output of the transmission weight
selection means 44 and output of the reception quality detection
means 42. Dedicated data generation section 46 outputs a signal
provided by performing predetermined transmission line coding and
modulation for the data signal unique to the terminal. Transmission
section 47 converts the baseband signal of the transmission data
series in a predetermined frame format formed based on output of
the control information generation means 45 and output of the
dedicated data generation section 46 into a high frequency signal
subjected to band limitation processing and amplification
processing and transmits the high frequency signal from a
transmission antenna 48.
[0151] Thus, each terminal MS.sub.m sends a notification about
N.sub.b(m) transmission beams T.sub.n(m) (where n=1 to N.sub.b(m))
provided by each terminal MS.sub.m and the reception quality to the
base station apparatus 1 (step S94). In this case, as the control
information in the control information generation means 45, the
transmission beam notification uses the number in the base station
transmission weight table shared between the base station apparatus
1 and the terminal MS.sub.m. Accordingly, information of only the
transmission beam number needs to be transmitted and thus the
information amount in making the transmission beam notification can
be reduced.
[0152] As for the reception quality, a reception quality table
subjected to appropriate quantization can also be shared between
the base station apparatus 1 and the terminal MS.sub.m for making a
reception quality notification using the number in the reception
quality table. Accordingly, the information amount can be reduced
to the information amount of only a predetermined number of
quantization bits.
[0153] As another notification method about the reception quality,
a multilevel modulation coding rate table associating the
multilevel modulation count and the coding rate with each other
based on the measured reception quality can also be shared between
the base station apparatus 1 and the terminal MS.sub.m for making a
reception quality notification using the number in the multilevel
modulation coding rate table. Accordingly, the information amount
in making the reception quality notification can be reduced.
[0154] The base station apparatus 1 receives the high frequency
signal transmitted from the terminal MS.sub.m at the base station
antenna 20 and performs frequency conversion processing of the high
frequency signal in a reception section 21 to generate a baseband
signal. Control information extraction means 22 extracts the
control information sent from the terminal MS.sub.m from the
received baseband signal.
[0155] Terminal assignment means 23 assigns the terminal MS.sub.m
to communicate considering the transmission beam notification from
each terminal MS.sub.m (step S95). The assignment processing of the
terminal MS.sub.m is similar to that in the first embodiment
described above.
[0156] After the terminals MS.sub.m to be connected are determined,
the space division multiplexing information notification means 25
notifies the terminals MS.sub.m that dedicated data transmission is
to be started, and to execute SDMA, sends information concerning
the transmission beam 4 used in a different terminal MS.sub.m
connected at the same time by way of space division multiplexing
and information concerning signal power use in the different
terminal MS.sub.m normalized in the terminal MS.sub.m (step S96).
Thus, space division multiplexing information data series
generation means 28 generates control information in a
predetermined format, and multiplexing means 29 multiplexes the
output data of dedicated data transmission means 24. The
transmission section 30 performs frequency conversion, band
limitation processing, and amplification processing for the
baseband signal output by the multiplexing means 29 to generate a
high frequency signal, and transmits the high frequency signal
through the base station antenna 20. The multiplexing means 29
multiplexes space division multiplexing information data series
using time division multiplexing, frequency division multiplexing,
code division multiplexing, etc.
[0157] The dedicated data transmission means 24 performs
predetermined transmission line coding, modulation, and interleave
for transmission data to one or more assigned predetermined
terminals to generate transmission data series 26. Beam formation
sections 27 multiply the transmission data series 26 by the
transmission weight forming the transmission beam 4 previously
sent, and output. If a plurality of transmission beams 4 are
assigned to one terminal MS.sub.m, different data streams are
spatially multiple-transmitted (SDM). As another method, time space
coding may be performed for the data streams and transmission may
be executed using different beams. In this case, the data rate
decreases, but the communication quality can be improved by the
space diversity effect or the coding gain.
[0158] As shown in the first embodiment described above, FIG. 9
shows the frame structures for using space division multiplexing
transmission of SDMA or SDM. The frame is made up of a pilot signal
30, user control information 31, and dedicated data series 32 to
each terminal MS.sub.m. Two types of frame structures of the frame
structure not to transmit directivity for the user control
information 31 (see FIG. 9A) and the frame structure to transmit
directivity for the user control information 31 (see FIG. 9B) can
be applied to the user control information 31. The dedicated data
series 32 is transmitted using different transmission directivity
assigned.
[0159] A different user interference cancel weight to separate and
receive the dedicated data signal for each terminal MS.sub.m
transmitted in a downlink from the base station apparatus 1 in each
terminal MS.sub.m is calculated based on the information (step S97)
and when beam transmission of dedicated data is performed (step
S98), reception processing of dedicated data different for each
mobile terminal MS.sub.m is performed (step S99)
[0160] The dedicated data reception processing of the SDM
compatible terminal 2-m is performed as follows: First, a high
frequency signal from the base station apparatus 1 is received at
the reception antenna 40. The reception section 41 converts the
received high frequency signal into a baseband signal. The channel
state estimation means 43 estimates a channel matrix as the channel
state. Spatial demultiplexing means 49 separates and receives any
desired signal from the signal spatially multiplexed and
transmitted to the home terminal or a different terminal based on
the output of the channel state estimation means 43. Data
extraction means 50 extracts transmission data from the output
signal of the spatial demultiplexing means 49 and further performs
demodulation processing, deinterleave processing, and transmission
line error correction coding processing to restore the transmission
data. The dedicated data reception processing of the SDM
incompatible terminal 3 is the same as that of the SDM terminal 2
except that data extraction means 60 operates in a different manner
from the data extraction means 50.
[0161] Next, the reception operation of the terminal MS.sub.m will
be discussed in detail separately in the case where the number of
the reception channels is two or more and the case where the number
of the reception channels is one.
[0162] (.alpha.) When the number of the reception channels in the
terminal MS.sub.m is two or more (operation of the spatial
demultiplexing means 49 of the SDM compatible terminal 2)
[0163] In this case, a signal y.sub.m(t) received by the terminal
MS.sub.m is represented as shown in expression (26) where t denotes
the time, y.sub.m(t) is a column vector having as many elements as
the number of the reception channels N.sub.s(m), x.sub.m (t) is a
column vector having N.sub.s(m) elements and representing
transmission data to the terminal MS.sub.m, z.sub.jl(t) is a column
vector representing transmission data to a terminal MS.sub.j except
the terminal MS.sub.m and having N.sub.s(j) elements, P.sub.jl
represents signal power normalized by transmission power of the
terminal MS.sub.m reported from the base station apparatus 1 and
transmitted using a transmission beam T.sub.1(j) in the different
terminal MS.sub.j, and h.sub.m(T.sub.n(m)) denotes a channel
response vector at the transmission time with the selected
transmission weight T.sub.n(m) in the channel matrix shown in
expression (22) and indicates a row vector at the time of the
transmission beam corresponding to T.sub.n(m) in channel matrix
H.
[0164] In expression (26), the second term indicates the
interference component with the terminal MS.sub.m. Therefore, if
the weight to minimize the interference, namely, maximize the SINR
is calculated according to MMSE (minimum square error criterion)
criterion, interference cancel weight G(m) in expression (27) is
obtained, where Z.sub.i is represented by expression (28).
[ Expression 26 ] y m ( t ) = [ h m ( T 1 ( m ) ) h m ( T Ns ( m )
( m ) ) ] x m ( t ) + j = 1 Nu [ P j 1 h m ( T 1 ( j ) ) P jNs ( l
) h m ( T Ns ( l ) ( j ) ) ] z jl ( t ) ( 26 ) [ Expression 27 ] G
( m ) = [ Z i Z i H + .sigma. 2 I ] - 1 ( h m ( T 1 ( m ) ) h m ( T
Ns ( m ) ( m ) ) ) ( 27 ) [ Expression 28 ] Z i = j - 1 Nu [ P j 1
h m ( T 1 ( j ) ) P jNs ( l ) h m ( T Ns ( l ) ( j ) ) ] ( 28 )
##EQU00018##
[0165] Therefore, the reception signal y.sub.m(t) is multiplied by
the obtained interference cancel weight G(m) as shown in expression
(14) for decreasing the interference component and then the signal
is detected by maximum likelihood estimation based on information
of signal constellation s.sub.k transmitted for separating and
receiving spatially multiple-transmitted signal s.sub.m(t) as shown
in expression (15).
[0166] (.beta.) When the number of the reception channels in the
terminal MS.sub.m is one (operation of the data extraction means 60
of the SDM incompatible terminal 3)
[0167] In this case, interference cancel using spatial flexibility
cannot be executed in the terminal MS.sub.m and therefore the data
extraction means 60 first detects the maximum interference
component in the second term indicating the interference component
in expression (26). That is, as shown in expression (29), if the
inner product of the transmission beam 4 to different terminal
MS.sub.m and the transmission beam 4 to the home terminal MS.sub.m
multiplied by the transmission power ratio becomes the maximum, it
becomes the maximum interference component and therefore the
maximum likelihood estimation method considering the signal
constellation becoming the interference component is executed. That
is, the signal is detected by maximum likelihood estimation as
shown in expression (30). Deinterleave processing and transmission
line error correction coding processing are performed for the
detected output signal to restore the transmission data.
[0168] As another method, the base station apparatus 1 may send the
result found according to expression (29). Accordingly, the
advantage that the computation amount of the terminal MS.sub.m can
be decreased can be provided. As another method, the terminal 3 may
perform detection processing including an interference signal based
on maximum likelihood estimation according to expression (30) only
if the reception SINR exceeds a predetermined value in the terminal
3 . . . times.
[ Expression 29 ] ( J , L ) = arg max j , l { P jl T 1 H ( m ) T 1
( j ) } ( 29 ) [ Expression 30 ] y m ( t ) = h m ( T 1 ( m ) ) x m
( t ) + j = 1 Nu [ P j 1 T 1 ( j ) P jNs ( l ) h m ( T Ns ( l ) ( j
) ) ] z jl ( t ) .apprxeq. h m T 1 ( m ) x m ( t ) + P JL h m ( T L
( J ) z JL ( t ) ) ( 30 ) [ Expression 31 ] s m ( t ) = arg min s k
C M L y m ( t ) - { h m ( T 1 ( m ) ) x m ( t ) + P JL h m ( T L (
J ) ) z JL ( t ) } 2 ( 31 ) ##EQU00019##
[0169] Thus, in the second embodiment, if the beam dedicated pilot
signal is transmitted for each of the different transmission beams,
when the transmission beam 4 required at the SDMA time is
determined, the need for feeding back the channel estimation value
or the transmission weight itself is also eliminated and the
information amount can also be decreased. Since the transmission
beam 4 is determined through feedback, a calibration circuit for
removing the effect of the deviation caused by the hardware between
array series made up of a plurality of base station antennas 20
becomes unnecessary in the base station apparatus 1 and the
configuration of the base station apparatus 1 can be simplified and
can be reduced in cost. If identical channel interference exists at
the SDMA time, the terminal MS.sub.m performs the operation for
decreasing the interference, so that the transmission beam 4 can be
selected without impairing the array gain.
[0170] The second embodiment can be applied regardless of
connection oriented or packet data exchange transmission. In the
second embodiment, transmission power control may be added so that
the reception quality in the spatial multiplexing terminal MS.sub.m
becomes constant. This can be accomplished by measuring the index
of SIR, etc., for example, as the reception quality in the terminal
MS.sub.m, sending the index to the base station apparatus 1, and
controlling the transmission power from the base station apparatus
1 based on the index.
[0171] In the second embodiment, the transmission beam 4 with the
maximum correlation is selected using expression (23) or (25) at
the operation time of transmission weight candidate selection;
however, as another method, a notification of the transmission beam
4 with the minimum correlation as shown in expression (32) or (33)
may be sent to the base station apparatus 1. Accordingly, the base
station apparatus 1 can eliminate the need for the operation to
determine whether or not the terminal MS.sub.m making transmission
beam notification with low correlation exists based on expression
(11). That is, the terminal MS.sub.m selecting the transmission
beam 4 with the minimum correlation sent by the terminal MS.sub.m
assigned preferentially based on the specific scheduling algorithm
as the transmission beam 4 is adopted as an assignment candidate,
whereby search using expression (10) can be made unnecessary.
[ Expression 32 ] G n ( m ) = arg { w k | min k = 1 , , Nd [ h m (
1 , k ) 2 N k ( m ) ] } ( 32 ) [ Expression 33 ] G n ( m ) = arg {
w k | min k = 1 , , Nd f m ( W k ) } ( 33 ) ##EQU00020##
[0172] In the procedure in FIG. 10, if the same terminal MS.sub.m
is assigned again in a sufficiently short time period from
assignment of transmission terminal, it is assumed that a move of
the terminal MS.sub.m is sufficiently gentle and variation in the
propagation environment is small and a procedure of skipping steps
S90 to S94 and using the previous transmission beam request and
reception quality notification result at step 94 may be applied. In
this case, the procedure can be implemented by providing temporary
storage means in the base station apparatus 1. Accordingly, as
steps S90 to S94 are skipped, the time other than the dedicated
data transmission time can be shortened and consequently the
dedicated data transmission efficiency can be improved.
Third Embodiment
[0173] FIG. 11 is a chart to show a processing procedure of a base
station apparatus 1 and different mth terminal MS.sub.m in a third
embodiment. The processing in the third embodiment is processing
wherein a part of the processing procedure shown in FIG. 10 in the
second embodiment described above is changed and therefore steps
identical with those in the second embodiment are denoted by the
same step numbers in the third embodiment and only different
processing from that in the second embodiment will be discussed.
The processing in the third processing differs from that in the
second embodiment mainly in two points. As one different point,
although the channel estimation value for each beam is calculated
at step S91 in the second embodiment, reception power is easily
estimated as the reception quality for each transmission beam in
the mth terminal MS.sub.m (step S91A) and N.sub.s(m) transmission
beams 4 giving high-order transmission power are requested (step
S92).
[0174] As another different point, after the terminal MS.sub.m to
which data is to be transmitted is assigned (step S95), in space
division multiplexing different user transmission weight
notification at the time of dedicated data transmission
notification, signal power ratio notification, and space division
multiplexing different user transmission weight notification, a
notification of the series number of the discrete pilot signal
addressed to a different user is sent at the beam transmission time
of the user dedicated pilot signal transmitted from a pilot series
signal different for each user (for each terminal) (step S96A).
[0175] Based on the sent information, in the terminal MS, channel
estimation of the home user and different user is executed for the
beam transmission signal of the user dedicated pilot signal
transmitted from the base station (step S95A), whereby a channel
estimation vector according to the transmission beam 4 addressed to
the home user space division multiplexed corresponding to the first
term in expression (26) and a channel estimation vector addressed
to different user corresponding to the second term in expression
(26), h.sub.m(T.sub.n(m)) are calculated (step S97A). After this, a
different user interference cancel weight is calculated (step S97)
and when beam transmission of dedicated data is performed in the
base station apparatus 1 (step S98), reception of dedicated data in
the terminal MS.sub.m is executed (step S99). The processing is
similar to that in the first embodiment.
[0176] Thus, in the third embodiment, reception power is easily
estimated as the reception quality for each transmission beam in
the mth terminal MS.sub.m and N.sub.s(m) transmission beams 4
giving high-order transmission power are requested, whereby the
computation amount in the terminal MS.sub.m can be decreased. Since
the need for calculating precise phase information is eliminated,
the series length of the pilot signal for each beam transmitted at
step S90 can be shortened.
[0177] In the procedure in FIG. 11, if the same terminal MS.sub.m
is assigned again in a sufficiently short time period from
assignment of transmission terminal, it is assumed that a move of
the terminal MS.sub.m is sufficiently gentle and variation in the
propagation environment is small and a procedure of skipping steps
S90 to S94 and using the previous transmission beam request and
reception quality notification result at step S94 may be applied.
In this case, the procedure can be implemented by providing
temporary storage means in the base station apparatus 1.
Accordingly, as steps S90 to S94 are skipped, the time other than
the dedicated data transmission time can be shortened and
consequently the dedicated data transmission efficiency can be
improved.
[0178] As described above, according to the embodiment, when
wireless communications based on SDMA are conducted, the base
station apparatus sends transmission information concerning other
space division multiplexed users to each space division multiplexed
terminal, whereby it is made possible to remove the different user
interference signal in the terminal. Consequently, when the base
station apparatus transmits a directional beam, it is made possible
to form a transmission beam to allow interference between different
terminals, so that the spatial flexibility in the transmission
array antenna can be used to improve the communication quality.
Therefore, the transmission array gain can be improved and the
system capacity of the downlink can be improved. The transmission
beam from the base station apparatus is a predetermined multibeam
and the terminal and the base station apparatus share the base
station transmission weight table, whereby control of transmission
directivity through feedback information with the feedback
information amount reduced can be performed and the calibration
circuit in the base station apparatus can be made unnecessary.
Therefore, the configuration of the base station apparatus can be
simplified and the base station apparatus at low cost can be
provided. If the space division multiplexed terminal encounters a
terminal capable of space division multiplexing (SDM), a plurality
of transmission beam weights are assigned in response to the
propagation environment, whereby it is made possible to execute
SDMA while executing SDM. Therefore, in the wireless communication
system of the embodiment, the flexibility of transmission beam
formation is increased and it is made possible to improve the
reception quality and the system capacity. At this time, the
feedback amount in the wireless communication system can be
reduced, the calibration circuit can be made unnecessary, and the
SDMA technology can be applied without impairing the array
gain.
[0179] While the invention has been described in detail with
reference to the specific embodiments, it will be obvious to those
skilled in the art that various changes and modifications can be
made without departing from the spirit and the scope of the
invention.
[0180] The present application is based on Japanese Patent
Application (No. 2004-150137) filed on May 20, 2004 and Japanese
Patent Application (No. 2005-092544) filed on Mar. 28, 2005, which
are incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0181] The invention has the advantage that when wireless
communications are conducted using space division multiple access,
the terminal can remove the transmission signal to a space division
multiplexed different terminal, an interference signal, and
consequently interference between the transmission beams to the
different terminals is allowed, whereby beam formation contributing
to improvement of the communication quality of the array gain,
etc., is made possible and improvement of the system capacity is
made possible; the invention is useful for a wireless communication
system, a wireless communication method, a base station apparatus,
a terminal, and the like for conducting wireless communications
using space division multiple access.
* * * * *