U.S. patent application number 13/349963 was filed with the patent office on 2012-05-03 for radio communication system, radio communication method, and radio communication device.
This patent application is currently assigned to Panasonic Corporation. Invention is credited to Takaaki KISHIGAMI, Yoichi Nakagawa.
Application Number | 20120106519 13/349963 |
Document ID | / |
Family ID | 32473702 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120106519 |
Kind Code |
A1 |
KISHIGAMI; Takaaki ; et
al. |
May 3, 2012 |
RADIO COMMUNICATION SYSTEM, RADIO COMMUNICATION METHOD, AND RADIO
COMMUNICATION DEVICE
Abstract
In the environment of a communication area including a
SDM-compatible mobile station for space division multiplex
transmission and a SDM-uncompatible mobile station not compatible
with space division multiplex transmission, a base station having a
plurality of antennas and capable of adaptively changing
directivity performs allocation of a mobile station which
simultaneously performs space division multiplex transmission (SDM)
and space division multiplex access (SDMA) by using a predetermined
space division multiplex transmission evaluation criterion and a
space division multi access evaluation criterion. By using this
radio communication method, it is possible to use the spatial
degree of freedom at its maximum and provide a radio communication
system having an improved communication capacity.
Inventors: |
KISHIGAMI; Takaaki; (Ota-ku,
JP) ; Nakagawa; Yoichi; (Ota-ku, JP) |
Assignee: |
Panasonic Corporation
Osaka
JP
|
Family ID: |
32473702 |
Appl. No.: |
13/349963 |
Filed: |
January 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10524803 |
Feb 16, 2005 |
8098616 |
|
|
PCT/JP03/15605 |
Dec 5, 2003 |
|
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13349963 |
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Current U.S.
Class: |
370/336 ;
370/329 |
Current CPC
Class: |
H04B 7/0408
20130101 |
Class at
Publication: |
370/336 ;
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04; H04J 3/16 20060101 H04J003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2002 |
JP |
2002-354103 |
Dec 1, 2003 |
JP |
2003-401269 |
Claims
1. A base station apparatus comprising: a beam forming section for
forming a first transmission beam by use of a single maximum ratio
synthetic directional transmission beam in a single space division
multiplex channel in order to send a first transmission data
sequence to a SDM uncompatible mobile station, and forming a
plurality of other directional transmission beams in a plurality of
other space division multiplex channels in order to send a second
transmission data sequence to an SDM compatible mobile station such
that the directional beams are orthogonal to each other, the SDM
compatible mobile station being a terminal allocated for SDM
communication in a communication area of the base station, and an
antenna for simultaneously transmitting the directional
transmission beams to the SDM uncompatible and SDM compatible
mobile stations at the same frequency.
2. The base station according to claim 1, wherein the second
transmission data sequence includes a plurality of third
transmission data sequence by performing a weighting process and
the plurality of third transmission data sequence have
orthogonality.
3. A method, for a downlink multi-user multiple input multiple
output (MIMO) scheme for enabling a base station to allocate
resources to communicate data to a plurality of mobile users,
wherein a mobile user of the plurality of mobile users existing
within a communication area has N receiving antennas, the method
comprising: obtaining, by the base station, a feedback information
from the plurality of mobile users, the feedback information
including: an information about a channel state information between
the base station and each of the plurality of mobile users, and a
received quality information, determining multiple mobile users to
simultaneously transmit data to according to certain criteria;
deciding, adaptively, a number of space-division multiplex channels
for transmitting to each of the mobile users according to the
feedback information; generating a number of space streams by using
serial to parallel mapping according to the decisions, for
allocating resources in space dimension to the plurality of users,
wherein a maximum number of the allocated resources are limited by
a number of transmitting antennas of the base station; determining
weight vectors according to the feedback information; and applying
the weight vectors to the space streams and communicating data to
each of the plurality of mobile users simultaneously with the N
transmitting antennas.
4. The method according to claim 3, wherein the generating step
applies a sum of a unitary matrix.
5. The method according to claim 3, wherein the number of antennas
is 1 for a space-division-multiplex uncompatible mobile user, and
the number of antennas is greater than 1 for a
space-division-multiplex compatible mobile user.
6. The method according to claim 3, wherein the base station forms
a closed feedback loop with each of the plurality of mobile
users.
7. The method according to claim 3, wherein when time division
duplex is used in the obtaining step, and the information about the
channel state is derived from corresponding reciprocal uplink
channels from each of the mobile users to the base station.
8. The method of claim 3, wherein in the determining step, weight
vectors for the mobile users are determined based on the channel
information, and the weight vectors of the mobile users are
determined based on weight vectors of other mobile users.
9. A radio communication system comprising: a
space-division-multiplex compatible mobile station compatible with
space division multiplex transmission; a space-division-multiplex
uncompatible mobile station uncompatible with space division
multiplex transmission; and a base station apparatus including: a
partial-space orthogonalizing means for making a weighting process,
for enhancing orthogonality over a propagation path for the space
division multiplex transmission, on a transmission data sequence to
be sent by space division multiplex to the space-division-multiplex
compatible mobile station allocated for space division multiplex
transmission within a communication area, and a beam forming
section for forming a transmission beam to the
space-division-multiplex compatible mobile station and the
space-division-multiple-access mobile station, responsive to a
transmission data sequence to the space-division-multiple-access
mobile station allocated for space division multiple access within
a communication area and to an output of the partial-space
orthogonalizing means, the transmission beam being to reduce an
interference with another mobile station to access simultaneously,
and a plurality of antennas for transmitting the transmission
beam.
10. The radio communication system according to claim 9, wherein
forming the transmission beam for reducing an interference by the
beam forming section of the base station apparatus is to form the
transmission beam from the transmission data sequence to the
allocated space-division-multiple-access mobile station and an
output of the partial-space orthogonalizing means in a manner being
orthogonal to a channel estimation matrix on another mobile station
for providing simultaneous access.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/524,803, filed on Feb. 16, 2005, which is a
National Phase Application of PCT International Application No.
PCT/JP2003/015605, which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a radio communication
system using space division multiple access and space division
multiplex, and more particularly to a radio communication system,
radio communication method and apparatus for same, adapted to
determine the applicability of and apply both simultaneously or any
one of space division multiple access and space division multiplex
transmission in accordance with propagation environment, traffic
status and the like where there are coexisting mobile stations
compatible with space division multiplex transmission and mobile
stations uncompatible therewith, within a communication area.
BACKGROUND ART
[0003] Recently, there is an increasing demand toward the increase
in the capacity and speed of radio communication. Studies are
vigorous as to the methods for improving the effective utilization
ratio of definite frequency resources, as one method of which
attentions are drawn to the technique to make use of space domains.
The space-domain utilization techniques includes, as one, an
adaptive array antenna (adaptive antenna) wherein, by adjusting the
amplitude and phase by means of a weighting coefficient for
multiplication on a received signal (hereinafter, referred to as
"weight"), reception is intense for the signals arriving in a
desired direction, thus enabling suppression in directions of
interference waves. This can improve the communication capacity for
the system.
[0004] Meanwhile, there are other arts utilizing space domains,
i.e. 1) space division multiple access technique for transmission
to different mobile stations (hereinafter, referred to as "SDMA"
wherein SDMA is an abbreviation of space division multiple access)
and 2) space division multiplex technique for transmission to the
same mobile station (hereinafter, referred to as "SDM" wherein SDM
is an abbreviation of space division multiplex), of different data
sequences by use of the physical channels same in time, frequency
and sign through utilization of a spatial orthogonality over the
propagation path. The SDMA technique is disclosed of information in
JP-A-2002-261670 and in Document T. Ohgane et al, "A study on a
channel allocation scheme with an adaptive array in SDMA," (IEEE
47th VTC, Page(s): 725-729 vol. 2 1997). Where the spatial
correlation coefficient between mobile stations is lower than a
predetermined value, SDMA is available thus making it possible to
improve the throughput of a radio communication system and the
number of simultaneous active users.
[0005] Meanwhile, the SDM technique is disclosed of information in
JP-T-2001-505723 and in Document G. J. Foschini, "Layered
space-time architecture for wireless communication in a fading
environment when using multi-element antennas," (Bell Labs Tech. J,
pp. 41-59, Autumn 1996), wherein the transmitter and the receiver
both has a plurality of antenna elements thus realizing SDM
transmission under the propagation environment low in received
signal correlation between the antennas. In this case, different
data sequences are sent from a plurality of antennas provided on
the transmitter by use of physical channels same in time, frequency
and sign on an antenna-element-by-antenna-element basis. At the
receiver, demultiplex-reception is made based on different data
sequence from the received signal at a plurality of antennas
provided on the receiver. This allows to achieve speed increase by
use of a plurality of space division multiplex channels instead of
using multi-level modulation. In implementing SDM transmission,
communication capacity can be increased in proportion to the number
of antennas on condition that the transmitter and the receiver have
the equal number of antennas, in an environment that a multiplicity
of scatterers exist between the transmitter and the receiver under
satisfactory S/N (signal-to-noise ratio) conditions.
[0006] However, in the conventional SDM art, the maximum number of
space division multiplex ones undergoes restriction at the end of
transmitter and receiver which is less in the number of antennas.
Consequently, where there is a deviation in the number of
transmission and receive antennas, space division multiplex is
possibly not utilized efficiently under certain propagation
environments. Particularly, because antenna elements can be set up
greater in the number at the base station end than at the mobile
station, there arises a case to cause a room for the degree of
spatial freedom in transmission of from the base station to the
mobile station. Meanwhile, in order to make the mobile station
compatible with SDM, there is a need for a plurality of antennas, a
plurality of transmission or reception systems and a signal
processing section for demultiplexing a space-division-multiplexed
signal, thus raising cost. For this reason, it can be considered
that the mobile stations not compatible with SDM coexist within the
communication area, thus requiring a method for space division
multiple access under coexistence of mobile stations compatible
with space division multiplex and mobile stations uncompatible
therewith. Meanwhile, SDMA, when to implement, usually employs
space division based on directive beams. In case SDM is done
furthermore, beam-to-beam spatial correlation is increased
resulting in a propagation condition not suited for SDM in general
cases.
DISCLOSURE OF THE INVENTION
[0007] A radio communication system of the present invention is
characterized to implement space division multiplex transmission
and space division multiple access by use of a predetermined space
division multiplex transmission evaluation criterion and
space-division-multiple-access evaluation criterion in an
environment that there are coexisting a base station having a
plurality of antennas and capable of adaptively changing the
directionality, space-division-multiplex compatible mobile stations
that are compatible with space division multiplex transmission and
space-division-multiplex uncompatible mobile stations that are
uncompatible with space division multiplex transmission, within a
communication area.
[0008] Meanwhile, a radio communication system of the invention
comprises: a space-division-multiplex compatible mobile station
compatible with space division multiplex transmission; a
space-division-multiplex uncompatible mobile station uncompatible
with space division multiplex transmission; and a base station
including partial-space orthogonalizing means for making a
weighting process, for enhancing orthogonality over a propagation
path for the space division multiplex transmission, on a
transmission data sequence to be sent by space division multiplex
to the space-division-multiplex compatible mobile station allocated
for space division multiplex transmission within a communication
area, a beam forming section for forming a transmission beam to the
space-division-multiplex compatible mobile station and the
space-division-multiple-access mobile station, responsive to a
transmission data sequence to the space-division-multiple-access
mobile station allocated for space division multiple access within
a communication area and to an output of the partial-space
orthogonizing means, the transmission beam being to reduce an
interference with another mobile station to access simultaneously,
and a plurality of antennas for transmitting the transmission
beam.
[0009] Meanwhile, forming the transmission beam for reducing an
interference by the beam forming section of the base station
apparatus in the radio communication system of the invention is to
form the transmission beam from the transmission data sequence to
the allocated space-division-multiple-access mobile station and an
output of the partial-space orthogonalizing means in a manner being
orthogonal to a channel estimation matrix on another mobile station
to access simultaneously.
[0010] This allows for implementing space division multiplex
transmission and space division multiple access at the same time
and for selecting a mobile station with which multiplexing is
available with use of a space domain, hence having a function to
efficiently make use of space division multiplex.
[0011] A radio communication method of the invention comprises: a
step for allowing a base station apparatus to calculate a space
division multiplex transmission evaluation criterion and
space-division-multiple-access evaluation criterion, on a basis of
a channel estimation matrix and received quality for a
space-division-multiplex compatible mobile station and
space-division-multiplex uncompatible mobile station; a step for
allowing the base station apparatus to allocate the
space-division-multiplex compatible mobile station to space
division multiplex transmission by the space division multiplex
transmission evaluation criterion and make a weighting process for
an enhancement of orthogonality over a propagation path for the
space division multiplex transmission, on a transmission data
sequence to be sent by space division multiplex to the allocated
space-division-multiplex compatible mobile station; and a step for
allowing the base station apparatus to assign the
space-division-multiplex compatible mobile station and
space-division-multiplex uncompatible mobile station to space
division multiple access by the space-division-multiple-access
evaluation criterion, and form a transmission beam to the
space-division-multiplex compatible mobile station and
space-division-multiple-access mobile station responsive to a
transmission data sequence to the allocated
space-division-multiple-access mobile station and the transmission
data sequence weighting-processed and to be sent by space division
multiplex, the transmission beam being to reduce an interference
with another mobile station to access simultaneously, thus sending
same from the base-station antenna.
[0012] Meanwhile, a radio communication method according to the
invention further comprises a step for allowing the base station
apparatus to send known signals on each of antennas provided in a
number of N, a step for allowing the space-division-multiplex
compatible mobile station and space-division-multiplex uncompatible
mobile station to measure, on each of antennas provided in a total
number of M, a channel estimation matrix constituted by channel
estimation values in a number of N.times.M by use of a received
result of the known signals in a number of N, and further to
measure a received quality, and a step for allowing the
space-division-multiplex compatible mobile station and
space-division-multiplex uncompatible mobile station to send the
channel estimation matrix and received quality to the base-station
apparatus through a communication line, wherein, forming the
transmission beam for reducing an interference by the base station
apparatus is to form the transmission beam from a transmission data
sequence to the space-division-multiple-access mobile station
allocated and a transmission data sequence weight-processed and to
be sent by space division multiplex, in a manner being orthogonal
to a channel estimation matrix on another mobile station to access
simultaneously.
[0013] This enables to decide the applicability of space division
multiplex transmission and space division multiple access,
depending upon a channel estimation value and received quality
information.
[0014] Meanwhile, a radio communication method according to the
invention is characterized in that the known signal is to be sent
by time division multiplex on an antenna-by-antenna basis by use of
different code sequences from base-station antennas in the number
of N, thus having a function to measure at the base station a
channel estimation value on each of the base-station antennas.
[0015] Meanwhile, a radio communication method according to the
invention is characterized in that the known signal is sent by code
division multiplex on an antenna-by-antenna basis by use of
different code sequences from base-station antennas in the number
of N, thus having a function to measure at the base station a
channel estimation value on each of the base-station antennas.
[0016] Meanwhile, a radio communication method according to the
invention is characterized in that the known signal is to be sent
by a combination of time division multiplex and code division
multiplex on an antenna-by-antenna basis by use of different code
sequences from base-station antennas in the number of N, thus
having a function to measure at the base station a channel
estimation value on each of the base-station antennas.
[0017] Meanwhile, a radio communication method of the invention
comprises: a step for allowing the space-division-multiplex
compatible mobile station and space-division-multiplex uncompatible
mobile station to send known signals to a base station at each of
antennas provided thereon in a total number of M; a step for
allowing the base station to receive at each of a plurality N of
base-station antennas and measure a channel estimation matrix
constituted by channel estimation values in a number of N.times.M
depending upon the known signal, and further to measure a received
quality; a step for allowing the base station to calculate a space
division multiplex transmission estimating criterion and
space-division-multiple-access estimating criterion depending upon
the channel estimation matrix and the received quality; a step for
allowing the base station apparatus to allocate the
space-division-multiplex compatible mobile station to space
division multiplex transmission by the space division multiplex
transmission evaluation criterion and make a weighting process for
an enhancement of orthogonality, over a propagation path for the
space division multiplex transmission, on a transmission data
sequence to be sent by space division multiplex to the allocated
space-division-multiplex compatible mobile station; and a step for
allowing the base station to allocate the space-division-multiplex
compatible mobile station and space-division-multiplex uncompatible
mobile station to space division multiple access by the
space-division-multiple-access evaluation criterion, and form a
transmission beam to the space-division-multiplex compatible mobile
station and space-division-multiple-access mobile station
responsive to a transmission data sequence to the allocated
space-division-multiple-access mobile station and the transmission
data sequence weighting-processed and to be sent by space division
multiplex, the transmission beam being to reduce an interference
with another mobile station to access simultaneously, thus
transmitting the transmission beam from the base-station antenna.
This enables the decision for applicability of space division
multiplex transmission and space division multiple access,
depending upon a channel estimation value and received quality
information.
[0018] Meanwhile, forming the transmission beam for reducing an
interference by the base station in a radio communication method
according to the invention is to form the transmission beam from a
transmission data sequence to the allocated
space-division-multiple-access mobile station and a transmission
data sequence weight-processed and to be sent by space division
multiplex, in a manner being orthogonal to a channel estimation
matrix on another mobile station to access simultaneously.
[0019] Meanwhile, a radio communication method according to the
invention is characterized in that the received quality uses any of
received-signal-power-to-noise-power ratio,
received-signal-power-to-interference-power ratio and received
power. This provides a function to grasp a received quality of in
the mobile station.
[0020] Meanwhile, a radio communication method according to the
invention is characterized in that the received quality uses
received-signal-power-to-noise-power ratio, and any one of moving
speed of the mobile station and fading frequency estimation value,
thus enabling to decide the applicability of space division
multiplex transmission and space division multiple access in
accordance with a roaming status of the mobile station.
[0021] Meanwhile, a radio communication method according to the
invention is characterized in that the step of calculating a space
division multiplex transmission estimating criterion comprises a
step of selecting a space-division-multiplex compatible mobile
station satisfying a predetermined received quality, and a step of
deciding a space division multiplex transmission count depending
upon a space correlation coefficient of between channel estimation
values in a number of N obtained between different antennas on the
space-division-multiplex compatible mobile station of among
selected ones of the space-division-multiplex compatible mobile
stations, thus enabling to decide the applicability of space
division multiplex transmission and space division multiple access
in accordance with a propagation environment of the mobile
station.
[0022] Meanwhile, a radio communication method according to the
invention is characterized in that the base station embeds
previously a known signal in a data sequence to be sent on a
transmission beam to the space-division-multiplex compatible mobile
station or the space-division-multiplex uncompatible mobile station
that is space-division-multiple accessed, and the
space-division-multiplex compatible mobile station
space-division-multiple accessed calculates a channel estimation
value depending upon the known signal and makes
demultiplex-receiving of a signal sent by space division multiplex
depending upon the channel estimation value, thus having a function
to demultiplex-receive at the mobile station a plurality
space-division-multiplex-transmission signals
space-division-multiplex-transmitted.
[0023] Meanwhile, a radio communication method according to the
invention is characterized in that the step of calculating a
space-division-multiple-access evaluation criterion comprises a
step of allocating the mobile station, with priority, by
predetermined scheduling means, a step of selecting a
space-division-multiplex compatible mobile station or
space-division-multiplex uncompatible mobile station satisfying a
predetermined received quality from the others than the mobile
station allocated with priority, and a step of selecting a mobile
station having an antenna minimal in a space correlation
coefficient to a channel estimation matrix obtained at an antenna
of the mobile station allocated with priority from among selected
ones of the space-division-multiplex compatible mobile stations or
space-division-multiplex uncompatible mobile stations, thus having
a function to select a mobile station with which space division
multiple access is available with a predetermined communication
quality.
[0024] Meanwhile, a radio communication method according to the
invention is characterized in that the transmission beam for space
division multiple access or space division multiplex transmission
is placed under power control into a predetermined communication
quality. This provides a function to enable communication at
between the base station and the mobile station with a
predetermined communication quality.
[0025] Meanwhile, a radio communication method according to the
invention is characterized in that power control is made to set a
communication quality of from the base station apparatus to the
space-division-multiplex uncompatible mobile station higher than a
communication quality of from the base station apparatus to the
space-division-multiplex compatible mobile station. This provides a
function to enhance, with priority, the received quality at the
space-division-multiplex uncompatible mobile station low in
interference suppression performance, and thereby to compensate for
it.
[0026] Meanwhile, a radio communication method according to the
invention is characterized in that the
space-division-multiple-access evaluation criterion is to give
priority to a multiple access of between the
space-division-multiplex uncompatible mobile stations in the case
that call loss is greater than a predetermined value. This can
increase the number of mobile stations with which simultaneous
connections are available by giving priority to space division
multiple access, thus having a function to suppress call loss.
[0027] A base station apparatus of the invention comprises: a
partial-space orthogonalizing means for making a weighting process,
for enhancing orthogonality over a propagation path for the space
division multiplex transmission, on a transmission data sequence to
be sent by space division multiplex to the space-division-multiplex
compatible mobile station allocated for space division multiplex
transmission within a communication area; a beam forming section
for forming a transmission beam to the mobile station responsive to
a transmission data sequence to the space-division-multiple-access
mobile station allocated for space division multiple access within
a communication area and an output of the partial-space
orthogonizing means, the transmission beam to the mobile station
being to reduce an interference with another mobile station to
access simultaneously; and a plurality of antennas for transmitting
the transmission beam.
[0028] Meanwhile, a base station apparatus according to the
invention is characterized in that forming the transmission beam
for reducing an interference by the beam forming section is to form
the transmission beam from the transmission data sequence to the
allocated space-division-multiple-access mobile station and the
output of the partial-space orthogonizing means, in a manner being
orthogonal to a channel estimation matrix on another mobile station
to access simultaneously. This provides a function to form a
transmission beam to which space division multiplex transmission
and space division multiple access are to be applied
simultaneously.
[0029] Meanwhile, in the weighting process in the beam forming
section of the base station apparatus of the invention, in a case
that the space-division-multiplex compatible mobile station and the
space-division-multiplex uncompatible mobile station are allocated
for space division multiple access at a same time, the beam forming
section makes, for the space-division-multiplex uncompatible mobile
station, a maximum ratio synthetic beam as a transmission beam to
the space-division-multiplex uncompatible mobile station and, for
the space-division-multiplex compatible mobile station, a
transmission beam as a beam for reducing an interference with
another of the space-division-multiplex uncompatible mobile station
and space-division-multiplex compatible mobile station to access
simultaneously, whereby transmission is made possible that the
received quality at the space division multiplex compatible mobile
station not having a spatial interference suppression ability is
enhanced with priority rather than the space-division multiplex
mobile station.
[0030] Meanwhile, forming the transmission beam for reducing an
interference by the beam forming section of the base station
apparatus of the invention is to form the transmission beam
orthogonal to a channel estimation matrix on another of the
space-division-multiplex uncompatible mobile station and
space-division-multiplex compatible mobile station to access
simultaneously.
[0031] Meanwhile, a base station apparatus according to the
invention further comprises space-time coding means for making a
space-time coding process on a transmission data sequence to the
space-division-multiplex compatible mobile station, the
transmission data sequence space-time coded being outputted to the
partial-space orthogonizing means. This can improve the received
quality due to addition of the error correction ability added with
a transmission diversity effect despite transmission rate
lowers.
[0032] Meanwhile, a base station apparatus according to the
invention further comprises a deciding section for allocating the
space-division-multiple-access mobile station and the
space-division-multiplex mobile station by use of a predetermined
space division multiplex transmission evaluation criterion and
space-division-multiple-access evaluation criterion. This enables
to decide the applicability of space division multiplex
transmission and space division multiple access.
[0033] Meanwhile, a base station apparatus according to the
invention is characterized in that the space division multiplex
transmission evaluation criterion and the
space-division-multiple-access evaluation criterion are to be
calculated depending upon a channel estimation value and received
quality received from the mobile station of within the
communication area. This enables to decide the applicability of
space division multiplex transmission and space division multiple
access, depending upon a channel estimation value and received
quality information.
[0034] Meanwhile, a base station apparatus according to the
invention is characterized in that, in a case that the
space-division-multiple-access mobile stations include a
space-division-multiplex compatible mobile station and a
space-division-multiplex uncompatible mobile station, a
transmission beam to the space-division-multiplex uncompatible
mobile station is formed by use of a
complex-conjugate-transposition of a channel estimation matrix on
the space-division-multiplex uncompatible mobile station, and a
transmission beam to the space-division-multiplex compatible mobile
station is formed in a manner being orthogonal to a channel
estimation matrix on another space-division-multiple-access mobile
stations to access simultaneously. This enables the
space-division-multiplex uncompatible mobile station to gain a
received signal that a plurality of transmission signals from a
plurality of antennas of the base station are synthesized in
maximal ratio.
[0035] As described above, according to the present invention,
there is provided a radio communication system allowed for space
division multiplex transmission to particular mobile stations as
well as space division multiple access to other mobile stations in
a radio communication system having a base station having a
plurality of antennas, thus efficiently utilizing the spatial
freedom at the base station and improving the communication
capacity over the radio communication system.
[0036] Meanwhile, by providing a control method for adaptively
changing the space division multiplex method (SDM, SDMA) depending
upon a traffic status, etc. of within a communication area,
communication capacity is improved for the radio communication
system through the effective utilization of SDM- or SDMA-based
space division multiplex technique and user diversity effect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a figure showing an arrangement of a radio
communication system in embodiment 1 of the present invention.
[0038] FIG. 2 is a figure showing a configuration of a base station
and mobile station in embodiment 1 of the invention.
[0039] FIG. 3A is a flowchart showing a mobile-station allocation
process procedure at the base station in embodiment 1 of the
invention.
[0040] FIG. 3B is a flowchart showing a allocation process
procedure at the mobile station end in embodiment 1 of the
invention.
[0041] FIG. 4A is a figure showing a frame structure in time
division transmission of an antenna-based pilot signal in
embodiment 1 of the invention.
[0042] FIG. 4B is a figure showing a frame structure in code
division transmission of an antenna-based pilot signal in
embodiment 1 of the invention.
[0043] FIG. 4C is a figure showing a frame structure in time/code
division transmission of an antenna-based pilot signal in
embodiment 1 of the invention.
[0044] FIG. 5A is a figure showing a frame structure in time
division transmission of a space-division-multiplex-channel-based
pilot signal in embodiment 1 of the invention.
[0045] FIG. 5B is a figure showing a frame structure in code
division transmission of a space-division-multiplex-channel-based
pilot signal in embodiment 1 of the invention.
[0046] FIG. 6 is a figure showing a configuration of a base station
in embodiment 2 of the invention.
[0047] FIG. 7 is a figure showing a configuration of a base station
and mobile station in embodiment 3 of the invention.
[0048] FIG. 8 is a figure showing another configuration of a base
station in embodiment 3 of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0049] Now an embodiment of the present invention will be explained
with the use of FIGS. 1 to 8.
Embodiment 1
[0050] FIG. 1 is a figure showing the outline of a radio
communication system according to embodiment 1 of the invention.
Explained hereunder is a method of communication using a space
division multiplex in a transmission of from a base station to a
mobile station (hereinafter, referred to as "downlink").
[0051] In FIG. 1, a base station 1 has a plurality of antenna
elements to adaptively vary the directivity of the antennas.
SDM-compatible mobile stations 2-1-2 are a plurality of mobile
stations compatible with space division multiplex while
SDM-uncompatible mobile stations 3-1-3 are a plurality of mobile
stations uncompatible with SDM transmission. Transmission beams
4-1-4 are a plurality of beams of from the base station 1 to the
mobile stations to communicate. A communication area 5 is an area
in which the base station 1 is allowed to communicate with the
SDM-compatible mobile stations 2 and the SDM-uncompatible mobile
stations 3. Incidentally, this is not limitative in respect of the
number of SDM-compatible mobile stations 2 and the number of
SDM-uncompatible mobile stations 3.
[0052] When there are a plurality of communicatable SDM-compatible
mobile stations 2 and SDM-uncompatible mobile stations 3 coexisting
within the communication area 5, the radio communication system of
the invention is allowed to make any one of or both simultaneously
of a space division multiple access to between different mobile
stations and a space division multiplex to the same one of the
mobile stations. Thus, space division multiplex is made feasible
with efficiency. Note that the SDM-compatible mobile stations 2, or
including SDM-uncompatible mobile stations 3, are hereinafter
expressed as mobile stations MS.sub.m with numbering. Incidentally,
m takes a natural number equal to or smaller than the number of
mobile stations N.sub.ms within the communication area 5. The base
station 1 is to decide, from a multiplicity of SDM-compatible
mobile stations 2 and SDM-uncompatible mobile stations 3, whether
both simultaneously of or any one of SDM and SDMA are available,
thus forming a plurality of transmission beams 4 at the base
station antenna. This allows the base station 1 to realize space
division multiplex and space division multiple access as decided
available.
[0053] FIG. 2 shows a detailed configuration of the base
station
[0054] BS and mobile station MS in the radio communication system
of the present embodiment. Incidentally, FIG. 2 shows the case to
send an individual-user transmission data sequence 211 to the
SDM-compatible mobile station MS.sub.1 by use of two space division
multiplex channels (SCH1, SCH2) as well as an individual-user
transmission data sequence 212 to the SDM-uncompatible mobile
station MS.sub.2 by use of one space division multiplex channel
(SCH3). However, this is not limitative.
[0055] In the base station BS in FIG. 2, space-division multiplex
transmission evaluation criterion calculating means 201 is to
calculate an evaluation criterion for deciding whether suited for
space division multiplex transmission.
Space-division-multiple-access evaluation criterion calculating
means 202 is to calculate an evaluation criterion for deciding
whether suited for space division multiple access. By use of those
evaluation criterion values, deciding means 203 is to decide an
allocation of mobile stations to which SDM or SDMA is to be made.
Meanwhile, weight generating means 204 is to generate a weight for
forming a directivity suited for a propagation path, depending upon
an output of the deciding means 203. Space-division-multiple-access
control means 205 is to make an output control of a transmission
data sequence for a desired mobile station, depending upon an
output of the deciding means 203. Here, output control is to be
effected, as an example, on the transmission data sequence 211 to
the mobile station MS.sub.1 and on the transmission data sequence
212 to a mobile station MS.sub.2. Space-division-multiplex
transmission control means 16 is to make a control for space
division multiplex transmission to a desired mobile station,
depending upon an output of the deciding means 203. Here, control
is effected, as an example, for space division multiplex on the
transmission data sequence 211 to the SDM-compatible mobile station
MS.sub.1. Meanwhile, space-division-multiplex transmission control
means 206 is made by series-parallel converting means 209 for
generating, as to one transmission data sequence, a plurality of
transmission data sequence commensurate with space division
multiplex count, and partial space orthogonalizing means 210 for
sending, by spatially orthogonalizing, the transmission data
sequence series-parallel-converted (showing a case with two space
division multiplex channels (SCH1, SCH2) in the figure).
[0056] Meanwhile, beam forming section 207 is to multiply
transmission weights W.sub.1-W.sub.3 respectively on the space
division multiplex channels SCH1-SCH3. A base-station antenna 208
is made up by a plurality Nt (Nt>1) of antenna elements.
Incidentally, the transmission weight W.sub.j is constituted by a
column vector having elements (complex number values) in the number
of antenna elements Nt.
[0057] Now explanation is made on the configuration of the
SDM-compatible mobile station MS.sub.1.
[0058] A plurality Ns.sup.(1) of antennas 221 are provided on the
mobile station MS.sub.1 to receive a radio-frequency signal sent
from the base station BS. A receiver section 222 is to convert the
radio-frequency signal into a base-band signal. Space division
demultiplex means 223 is to demultiplex-receive a space division
multiplex signal out of the base-band signal. Data mixing means 224
is to mix together the signals demultiplex-received, and restore
them into the former data sequence transmitted. A received data
sequence 225 is to be outputted from the data mixing means 224.
[0059] Now explanation is made on the SDM-uncompatible mobile
station MS2.
[0060] A mobile station antenna 231 is provided on the mobile
station MS.sub.2 to receive a radio-frequency signal sent from the
base station BS. A receiver section 232 is to output an MS.sub.2
received data sequence 233 out of the radio-frequency signal.
[0061] Now explanation is made on the communicating operation of
between the base station 1 and the mobile stations MS.sub.m in the
present embodiment. FIG. 3 is a flowchart showing a process
procedure for communication allocation to the base station 1 and
mobile stations MS.sub.m. After establishing a frame
synchronization and symbol synchronization, the base station 1
having antenna elements and transmission systems in the number of
Nt first sends, from the respective transmissing systems, a known
signal sequence (hereinafter, referred to as "antenna-based pilot
signals APk(t)") comprising a predetermined symbol number Np (step
S301). Note that k is a transmission-system number wherein k=1, 2,
. . . , Nt. Meanwhile, t=1, . . . , Np. Incidentally, where the
base station 1 has a sufficiently great number of antenna elements
Nt or where the SDM space division multiplex count is limited
smaller than the number of antenna elements Nt at the base station
1, there is no need to use all the transmission systems in the
number of Nt. Part of them may be used to send antenna-based pilot
signals.
[0062] Here, FIGS. 4A-C are figures showing the transmission timing
of antenna-based pilot signals (frame structure). FIG. 4A
illustrates time division transmission by a deviation in
transmission timing of a known signal sequence A (401) as
antenna-based pilot signals, on an antenna-by-antenna basis.
Incidentally, there is shown that the antenna-based pilot signals
use the same pattern or mutually-orthogonal code sequence based on
PN signals, etc. FIG. 4B illustrates code division multiplex
transmission at different antennas by use of a known code sequence
B.sub.k (402) orthogonal one to another. FIG. 4C illustrates a
scheme in combination of time division transmission and code
division transmission. Namely, for a certain combination of
antennas, time division slots at the same time are shared to send
respective antenna-based pilot signals A1 (403), A2 (404) by code
division multiplex with the use of code sequences orthogonal one to
another. This can reduce the overhead in time division transmission
where the number of antennas is great at the base station 1.
Meanwhile, it is possible to moderate the reduction in
orthogonality over a propagation path during code division
multiplex.
[0063] Meanwhile, the mobile station MS.sub.m existing within the
communication area 5 demultiplex-receives the antenna-based pilot
signal AP.sub.k(t) sent on an antenna-by-antenna basis of the base
station, and calculates a channel estimation value (step S321).
Furthermore, it measures a quality of reception (step S322).
[0064] Now explanation is made on the operation at the steps S321
and S322. The m-th mobile station MS.sub.m existing within the
communication area 5 has antennas in the number of Ns(m) and
reception systems in the number of Ns(m), thus enabling
SDM-reception at space division multiplex channels in the number of
maximally Ns(m). Note that m is a natural number equal to or
smaller than the number of mobile stations N.sub.ms present within
the communication area 5. Here, Ns(m)=1 is given for the
SDM-uncompatible mobile station 3 while Ns(m)>1 is for the
SDM-compatible mobile station 2. The mobile station MS.sub.m makes
a correlation operation on r.sub.j,k.sup.(m)(t) (j=1, . . . ,
Ns(m)) as a result of reception of a k-th antenna-based pilot
signal AP.sub.k(t) at the j-th antenna and reception system with
AP.sub.k(t) generated in the mobile station MS.sub.m, and
calculates a propagation-path channel estimation value h.sup.m(j,
k) as shown in (Equation 1). Incidentally, * is an operator for
complex conjugate. Incidentally, the correlation operation may be
by saving a received result of antenna-based pilot signals
AP.sub.k(t) in a plurality of number of times and making an
averaging process over those. In such a case, in case the mobile
station is at a sufficiently low speed of movement, the effect of
noise can be reduced to possibly enhance the quality of channel
estimation. Finally, the channel estimation values on the m-th
mobile station MS.sub.m are to be calculated totally in the number
of (the number of antenna-based pilot signals Nt).times.(the number
of mobile-station antennas Ns(m)).
h m ( j , k ) = i = 1 Np AP k * ( t ) r j , k ( m ) ( t ) ( 1 )
##EQU00001##
[0065] Subsequently, a received quality P.sup.m(j, k) is calculated
for each antenna-based pilot signal and on each mobile-station
antenna. For received quality, it is possible to apply received
signal power, SIR (signal power to interference power ratio), SNR
(signal power to noise power ratio), etc. In the below is shown an
example using SNR. In the case to estimate an SNR by use of an
antenna-based pilot signal AP.sub.k(t), signal power is taken as
S.sup.m(j, k)=|h.sup.m(j, k)|.sup.2/Np. Received quality Pm(j, k),
i.e. SNR (=S.sup.m(j, k)/N.sup.m(j, k)) can be evaluated by use of
the noise power N.sup.m(j, k) shown in (Equation 2).
N m ( j , k ) = 1 Np t = 1 Np r j , k ( m ) ( t ) - S m ( j , k ) 2
( 2 ) ##EQU00002##
[0066] The above corresponds to the operation at steps S321 and
S322.
[0067] Then, the mobile station MS.sub.m feeds the calculated
channel estimation value h.sup.m(j, k) and received quality
P.sup.m(j, k) back to the base station 1 through a communication
channel (step S323). Incidentally, as for received quality, it is
possible to feed an average of Ps(m) shown in (Equation 3) taken
over the number of base-station antennas Nt and the number of
mobile-station antennas Ns(m) back to the base station 1 through
the communication channel in order to diminish the feedback
information, instead of feeding back all of (the number of
antenna-based pilot signals Nt).times.(the number of mobile station
antennas Ns(m)). The below explains a scheme to convey Ps(m) as a
received quality. Incidentally, although average value is
calculated here over the received qualities Pm(j, k) as shown in
(Equation 3), median or maximum value may be employed. In order to
further diminish the amount of feedback information, the base
station and the mobile station may share a table whose channel
estimation values h.sup.m(j, k) and received qualities P.sup.m(j,
k) are quantized at a predetermined interval, to thereby exchange
its table number.
P s ( m ) = 1 N t N s ( m ) k = 1 Nt j = 1 Ns ( m ) P m ( j , k ) (
3 ) ##EQU00003##
[0068] Meanwhile, in the base station 1, it is checked whether or
not the space-division-multiplex-transmission evaluation criterion
calculating means 201 and space-division-multiple-access evaluation
criterion calculating means 202 received feedback information about
a channel estimation value h.sup.m(j, k) and received quality
information Ps(m) 213 (step S302). When received, the deciding
means 203 decides a preferentially-allocated mobile station
depending upon an output result calculated from them (step S303).
The scheduling method for preferentially allocating a mobile
station includes a maximum CIR method, a proportional fairness
method and the like that are packet scheduling based on SIR, which
are disclosed of information in Document A. Jalali et al, "Data
Throughput of CDMA-HDR a High Efficiency-High Data Rate Personal
Communication Wireless System," IEEE VTC2000-Spring, pp. 1854-1858.
It is assumed here that the A-th mobile station MS.sub.A is
preferentially allocated to commence mobile-station-based
(user-based) communication.
[0069] Then, the deciding means 203 of the base station 1 decides
whether or not SDM transmission is available with the
preferentially-allocated mobile station MS.sub.A depending upon an
evaluation value calculated by the
space-division-multiplex-transmission evaluation criterion
calculating means 201 (step S304). In case it is an
SDM-uncompatible mobile station 3, the deciding means 203 searches
for a mobile station to which SDMA is available (step S306).
[0070] Meanwhile, in case it is an SDMA-compatible mobile station
2, an SDM-compatible process is made (step S305) by using the fed
back propagation-path channel estimation value h.sup.A(j, k).
Subsequently, searched for is a mobile station with which SDMA is
available (step S306). Note that k=1, . . . , Nt while j=1, . . . ,
Ns(A). It is assumed that space-division-multiplex channels are
used in the number of Nc as a result of decision. Note that it is a
natural number satisfying 1.ltoreq.Nc<Ns(A). Here, in the
SDM-compatible process, the channel estimation values h.sup.A(j, k)
concerning the mobile station MS.sub.A can be expressed as a matrix
as in (Equation 4), to calculate singular values .lamda.j in the
number of Ns(A) obtainable by singular value resolution of H(A)
whereby the number of space division multiplex channels can be
decided due to the number of the singular values exceeding a
predetermined value. Here, j=1, . . . , Ns(A). Meanwhile,
calculation can be made, as another method, for correlation
coefficients at between row vectors in the number of (Ns(A)-1) of
H(A) (hereinafter, spatial correlation coefficients), to take a
number assuming equal to or smaller than a predetermined value as
the number of space division multiplex channels.
H ( A ) = [ h A ( 1 , 1 ) h A ( 1 , 2 ) h A ( 1 , N t ) h A ( 2 , 1
) h A ( 2 , 2 ) h A ( 2 , N t ) h A ( N s ( A ) , 1 ) h A ( N s ( A
) , 2 ) h A ( N s ( A ) , N t ) ] ( 4 ) ##EQU00004##
[0071] Meanwhile, searching for an SDMA-available mobile station
SDMA (step S306) is based on a channel estimation value or received
quality information fed back to the base station 1. At first, by
using the received quality information Ps(m) except for the
received quality information Ps(A) about the A-th mobile station
MS.sub.A, a mobile station having a quality exceeding a
predetermined level is selected in the first stage. As
predetermined level setting, setting may be as Ps(m)>Ps(A)+C
using a predetermined margin value C (where m represents a mobile
station number within the communication area 5, except for A).
[0072] In this case, selection is possible for a mobile station
higher in received quality than the A-th mobile station MS.sub.A.
In the case of effecting a transmission power control to the base
station 1, the transmission power from the base station 1 can be
set lower than the A-th mobile station MS.sub.A, thus enabling to
reduce the interference with the mobile station MS.sub.A.
[0073] Then, calculated is a spatial correlation coefficient SC(m,
A) between the channel estimation value h.sup.A(j, k) on the
already allocated mobile station MS.sub.A and the channel
estimation value h.sup.m(j, k) among the mobile stations selected
in the first stage, by use of (Equation 5) or (Equation 6). Here, *
represents a complex conjugate. Here, m represents a number of the
mobile station selected in the first stage.
SC ( m , A ) = 1 N s ( m ) N s ( A ) N t j A = 1 Ns ( A ) j m = 1
Ns ( m ) k = 1 Nt [ h m ( j m , k ) ] * h A ( j A , k ) h m ( j m ,
k ) h A ( j A , k ) ( 5 ) SC ( m , A ) = max j A .di-elect cons. Ns
( A ) , j m .di-elect cons. Ns ( m ) 1 N t k = 1 Nt [ h m ( j m , k
) ] * h A ( j A , k ) h m ( j m , k ) h A ( j A , k ) ( 6 )
##EQU00005##
[0074] For all the subjects of mobile stations MS.sub.m selected in
the first stage, spatial correlation coefficient operation is made
in the space-division-multiple-access evaluation criterion
calculating means 202 according to (Equation 5) or (Equation 6), to
decide whether or not the mobile station MS.sub.m lowest in spatial
coefficient SC(m, A) relative to the A-th mobile station MS.sub.A
is below a predetermined spatial correlation coefficient (step
S307). When below, it is selected as a
space-division-multiple-access mobile station (assumably taken as a
B-th mobile station) and furthermore it is determined whether the
space-division-multiple-access mobile station is an SDM-compatible
mobile station 2 or not (step S308). In case it is an
SDM-uncompatible mobile station 3, search is made again for a
mobile station MS.sub.m SDMA is available (step S306). In case it
is an SDM-compatible mobile station 2, SDM-compatible process is
made using the similar method to the step S305 by use of a channel
estimation value h.sup.B(j, k) over a propagation path feedback has
been made (step S309). Note that k=1, . . . , Nt while j=1, . . . ,
Ns(B). It is assumed that space division multiplex channels in the
number of Nc.sup.(B) are assumably used as a result of decision.
However, it is a natural number satisfying
1<Nc.sup.(B)<Ns.sup.(B). After the decision, search is made
again for a mobile station MS.sub.m SDMA is available (step
S306).
[0075] Incidentally, when searching for a mobile station MS.sub.m
SDMA is available in the case a plurality of mobile stations
MS.sub.m have been allocated in the step S306, MSC(m) shown in
(Equation 7) is used in place of SC(m, A). MSC(m) provides the
maximum SC(m, k) for the already allocated mobiles stations A, B,
C, . . . . However, k provides a number of the already allocated
mobile station MS.sub.A, MS.sub.B, MS.sub.C, . . . .
MSC ( m ) = max k = A , B , C , SC ( m , k ) ( 7 ) ##EQU00006##
[0076] Then, in the case of a determination at step S307 that there
are no mobile stations MS.sub.m SDMA is available, a communication
start notification including a notification (notifying the number
of space division multiplex ones) as to whether to carry out an
SDM, to the allocated predetermined mobile station MS.sub.m without
effecting space division multiple accesses furthermore (step
S310).
[0077] Then, the base station starts an individual-user channel
transmission to the mobile station MS.sub.m (step S311). Meanwhile,
a predetermined mobile station MS.sub.m, when receiving the
communication start notification from the base station 1, makes a
process for individual-user channel reception (step S324) and
starts to receive the signals thereafter sent through the
individual user channel (step S325). Incidentally, the transmission
power to the mobile stations MS.sub.m allocated for SDMA are placed
under transmission power control to obtain a predetermined received
quality.
[0078] Incidentally, in the case of carrying out an SDMA at between
the SDM-compatible mobile station 2 and the SDM-uncompatible mobile
station 3, the SDM-uncompatible mobile station 3 cannot be
suppressed against interference in the space domain. Consequently,
by setting a target received quality higher to the SDM-uncompatible
mobile station 3 than the SDM-compatible mobile station 2, received
quality in SDMA can be assured.
[0079] As in the above, even where there are SDM-compatible mobile
stations 2 and SDM-uncompatible mobile stations 3 within the
communication area 5, the mobile station MSm feeds a channel
estimation value and received quality information back to the base
station 1 by use of an antenna-based pilot signal whereby the base
station 1 is allowed to select a mobile station MS.sub.m where
multiplexing is available using a space domain combined with both
simultaneously or any one of SDA and SDMA, thus enabling to
efficiently utilize space division multiplex.
[0080] Now explanation is made on the directivity control operation
at the mobile station MS and base station BS after completing the
communication allocation process.
[0081] The transmission data sequence is assumably S.sub.k.sup.n(t)
(where t represents a time) which is on the k-th space division
multiplex channel to the n-th mobile station MS.sub.n. Here, n is a
natural number equal to or smaller than the number of mobile
stations Nd to which space division multiple access is to be made
while k is a natural number equal to or smaller than the number of
space division multiplex ones Nc.sup.(n) to the n-th mobile station
MS.sub.n. Meanwhile, 1.ltoreq.Nc.sup.(n)<Ns.sup.(1). The channel
estimation value is assumed h.sup.n(p, m) which is received at the
p-th antenna of the n-th mobile station MS.sub.n. The channel
estimation value h.sup.n(p, m) is for the antenna-based pilot
signal AP.sub.m(t) of from the m-th base-station antenna fed back
from the mobile station MS.sub.n to the base station BS.
Incidentally, m is a natural number equal to or smaller than the
number of base-station antennas Nt while p is a natural number
equal to or smaller than the number of antennas Ns.sup.(n) on the
n-th mobile station MS.sub.n. Here, the channel estimation matrix
H.sup.n for the n-th mobile station MS.sub.n is defined as in
(Equation 8).
H n = [ h n ( 1 , 1 ) h n ( 1 , 2 ) h n ( 1 , N t ) h n ( 2 , 1 ) h
n ( 2 , 2 ) h n ( 2 , N t ) h n ( N s ( n ) , 1 ) h n ( N s ( n ) ,
2 ) h n ( N s ( n ) , N t ) ] ( 8 ) ##EQU00007##
[0082] In FIG. 2, the weight generating means 204 generates a
transmission weight by use of the channel estimation matrix H.sup.n
shown in (Equation 8). Here, the transmission weight vector Wj for
the j-th space division multiplex channel is to form a beam not to
cause interference with the other user n, SDMA is to be made, than
j-th one. n is a natural number equal to or smaller than the total
number Nd of the mobile stations, SDMA is to be made, except for
j-th one. Meanwhile, in the case that allocation is only to the
n-th mobile station MSn wherein SDMA is not to be made, when the
number of space division multiplex ones at that mobile station is
Nc.sup.(n), antennas in the number of Nc.sup.(n) are selected out
of the base-station antennas 208, thereby effecting
transmission.
H.sup.nW.sub.j=0,(j.noteq.n) (9)
[0083] Incidentally, (Equation 9) uses an orthogonal condition
under which transmission signals are free from interference between
the mobile stations. Besides, usable is a weight generating method
based on minimum mean square error (MMSE) as shown in (Equation
10). Here, y.sub.nj is a signal component of the transmission
signal to the j-th mobile station MS.sub.j to be received by the
n-th mobile station MS.sub.n.
W j = arg min W y nj - H n W 2 , ( j .noteq. n ) ( 10 )
##EQU00008##
[0084] The beam forming section 207 duplicates the transmission
data sequence SCH.sup.(j) of j-th space division multiplex channel
by the number of the base-station antennas (Nt) by the use of
transmission weight vectors W.sub.j=[W.sub.j1, W.sub.j2, . . . ,
W.sub.jNt].sup.T (where j is a natural number equal to or smaller
than the total number Tc of the space division multiplex channels,
and T represents a vector transposition) in the number equal to the
total number of the space division multiplex channels Tc for use in
SDM and SDMA, and multiplies thereon the elements of the
transmission weight vectors, thus sending it at the base-station
antenna 208.
[0085] As in the above, by generating transmission weights W.sub.j
satisfying (Equation 9), reception is at a channel estimation value
C.sub.A to be expressed as in (Equation 11) provided that W.sub.j
is the transmission weight directed to the A-th mobile station
MS.sub.A having the number of space division multiplex channels of
Nc.sup.(A)=1. Meanwhile, where W.sub.j, W.sub.j+1 and W.sub.j+Nc
(B)-1 are the transmission weights directed to the B-th mobile
station MS.sub.B having the number of space division multiplex
channels of Nc.sup.(B)>1, reception is at a channel estimation
matrix C.sub.B in a degree of (Ns.sup.(B).times.Nc.sup.(B)) to be
expressed as (Equation 12).
[0086] In case the partial-space orthogonizing means 210 has
transmission weights W.sub.j, W.sub.j+1 and W.sub.j+Nc(B)-1
directed to the B-th mobile station MS.sub.B having the number of
space division multiplex channels of Nc.sup.(B)>1 where to make
an SDM-transmission to the B-th mobile station MS.sub.B, reception
is at a channel estimation matrix C.sub.B in a degree of
(Ns.sup.(B).times.Nc.sup.(B)) to be expressed as (Equation 12).
Meanwhile, it previously singular-value-resolves C.sub.B as shown
in (Equation 13), to select the number Nc.sup.(B) of singular
values in the greater order of singular values obtained. By using
right singular-valued matrix Vs=[V.sub.1, V.sub.2, . . . ,
V.sub.Nc(B)] constituted by the right singular value vectors
corresponding to those singular values .lamda..sub.k, the right
singular-valued matrix Vs is multiplied from left on the space
division multiplex channel data sequence S(t)=[S.sub.1.sup.B(t)
S.sub.2.sup.B(t) . . . S.sub.Nc(B).sup.B(t)].sup.T as shown in
(Equation 14), thereby calculating a signal sequence S.sub.2(t).
Here, k=1-Nc.sup.(B). The beam forming section 207 multiplies the
transmission weights W.sub.j, W.sub.j+1 and W.sub.j+Nc(B)-1
respectively on the elements of S.sub.2(t) in the number of
Nc.sup.(B). Here, in (Equation 13), U is a unitary matrix
constituted by the left singular value vectors of the channel
estimation matrix C.sub.B, V is a unitary matrix constituted by the
right singular value vectors of the channel estimation matrix
C.sub.B, and Q is a diagonal matrix having diagonal components as
singular values.
[0087] Incidentally, the receiver section 222 can be configured by
omitting the partial-space orthogonizing means 210. In such a case,
Vs in (Equation 14) is given an Nc-degree unit matrix.
H A W j = C A ( 11 ) H A [ W j W j + 1 W j + Nc ( n ) - 1 ] = C B (
12 ) C B = U .LAMBDA. V H = U [ Q 0 0 0 ] V H ( 13 ) S 2 ( t ) = V
s S ( t ) ( 14 ) ##EQU00009##
[0088] The above is the operational explanation as to the base
station 1.
[0089] Then, in order for the SDM-compatible mobile station MSn to
demultiplex-receive the space division multiplex channels in the
number of Nc.sup.(n) and in order for the SDM-uncompatible mobile
station MS.sub.n to make a reception with synchronous detection,
transmission is made by embedding a known signal sequence
(hereinafter, space-division-multiplex-channel-based pilot signals)
CP.sub.k(t) in each space division multiplex channel. Here, k is a
natural number equal to or smaller than the total number of space
division multiplex channels Tc. However, where the transmission
signal is differentially coded and delayed detection is applied,
there is no need to send such a
space-division-multiplex-channel-based pilot signal.
[0090] FIGS. 5A and 5B shows a transmission method (frame
structure) of a space-division-multiplex-channel-based pilot signal
CP.sub.k(t). FIG. 5A shows a method to send a
space-division-multiplex-channel-based pilot signal sequence
A.sub.k (501) by time division with a deviation of transmission
timing. The antenna-based pilot signals use the same pattern, or
mutually-orthogonal code sequences based on PN (pseudo random
signals) signals, etc. FIG. 5B shows a method of sending by code
division multiplex at different space division multiplex channels
by the use of space-division-multiplex-channel-based pilot signal
sequences B.sub.k (502) as mutually-orthogonal code sequences.
[0091] Meanwhile, it is possible to use a method that time division
transmission and code division transmission are combined together
as explained in FIG. 4C.
[0092] Now explanation is made on the reception operation at the
mobile station MS, as for the n-th SDM-compatible mobile station
MS.sub.n.
[0093] At first, the mobile-station antennas 221 in the number of
Ns.sup.(n) receive a space-division-multiplexed radio-frequency
signal.
[0094] The receiver section 222 in the number of Ns.sup.(n) output
complex base-band signals r.sub.j.sup.(n)(t) in the number of
Ns.sup.(n) comprising I and Q signals by orthogonal detection after
frequency conversion, for the received radio-frequency signals in
the number of Ns.sup.(n) respectively. (Note that j is a natural
number equal to or smaller than Ns.sup.(n)) Then, the space
division demultiplex means 223 demultiplexes the space division
multiplex channels in the number of Nc.sup.(n) to the
SDM-compatible mobile station MS.sub.n.
[0095] In the method of demultiplexing the space division multiplex
channel, it is possible to apply such techniques as 1) a method of
utilizing an inverse matrix to a channel estimation matrix
(zero-forcing technique), 2) maximum likelihood estimation (joint
estimation), 3) V-BLAST and so on. In the below, explanation is on
the operation using the method 1).
[0096] At first, by using the
space-division-multiplex-channel-based pilot signal CP.sub.k(t)
individually embedded in the space-division multiplex channel,
channel estimation values h.sup.n(j, k) are calculated on each
space-division multiplex channel as shown in (Equation 15). Here, k
is a natural number equal to or smaller than the number of space
division multiplex channels Nc.sup.(n) to be sent to the
SDM-compatible mobile stations MS.sub.n. Incidentally, * is a
complex conjugate operator and wherein the
space-division-multiplex-channel-based pilot signal CP.sub.k(t)
assumably has the number of symbols N.sub.q. For each space
division multiplex channel obtained, a channel estimation matrix
H.sup.n shown in (Equation 16) is generated having constituent
elements of channel estimation values h.sup.n(j, k). By multiplying
the general inverse matrix (H.sup.n).sup.-1 of the same on a
reception signal vector R=[r.sub.1.sup.(n)(t), r.sub.2.sup.(n)(t),
. . . , r.sub.NS(n).sup.(n)(t)].sup.T, the respective space
division multiplex channels are demultiplex-received. Incidentally,
concerning the number of space division multiplex ones and the kind
of the space-division-multiplex-channel-based pilot signal to the
mobile station MS.sub.n, notification is previously made from the
base station BS to the mobile station MS.sub.n by way of the
control channel, etc.
h n ( j , k ) = t = 1 Nq CP k * ( t ) r j ( n ) ( t ) ( 15 ) H n =
[ h n ( 1 , 1 ) h n ( 1 , 2 ) h n ( 1 , N c ( n ) ) h n ( 2 , 1 ) h
n ( 2 , 2 ) h n ( 2 , N c ( n ) ) h n ( N s ( n ) , 1 ) h n ( N s (
n ) , 2 ) h n ( N s ( n ) , N c ( n ) ) ] ( 16 ) ##EQU00010##
[0097] Incidentally, there is a method as another method for space
division demultiplex that, when the partial space orthogonalizing
means 210 is used in SDM transmission to the B-th mobile station
MS.sub.B, singular values are selected Nc in the greater order of
those obtained in singular value resolution of C.sub.B as shown in
(Equation 13). By using a right singular-valued matrix Us=[U.sub.1,
U.sub.2, . . . , U.sub.Nc(B)] constituted by left singular-value
vector corresponding to those singular values, whose
complex-conjugate-interposed matrix (Us)H is multiplied from left
on the reception signal vector R=[r.sub.1.sup.(B)(t),
r.sub.2.sup.(B)(t), . . . , r.sub.Ns(B).sup.(B)(t)].sup.T. With
this method, the respective space division multiplex channels can
be demultiplex-received. In this case, the right singular-valued
matrix Us is previously notified to the mobile station MS.sub.B via
the communication line. In the case of using this method, there is
a merit of no need of sending a
space-division-multiplex-channel-based pilot signal because
propagation channel variation is simultaneously compensated for.
Incidentally, as for the number of space division multiplex ones
and the kind of the space-division-multiplexed-channel-based pilot
signal to the mobile station MS.sub.n, notification is previously
made from the base station BS to the mobile station MS.sub.n by way
of the control channel, etc.
[0098] Now explanation is made on the reception operation in the
SDM-uncompatible mobile station MS.sub.1.
[0099] The receiver section 222 suitably frequency-converts the
radio-frequency signal received at the antenna and makes a
reception operation by use of delayed detection, semi-synchronous
detection or synchronous detection. The received signal is
code-decided and decoded by a not-shown decoder, to restore the
user-transmitted data. Incidentally, the SDM-uncompatible mobile
station MS.sub.1 is expected to increase in the same interference
wave component because of its space division multiple access. In
order to remove interference, by mounting a multi-path interference
canceler described in the document, etc. disclosed in Electronic
Information Society technical Report RCS2000-134 (2000) by Higuchi
et al., the same interference component can be removed. The
post-removal received signal is code-decided and decoded by the
decoder section, to restore the user-transmitted data thereby
obtaining high-quality reception performance.
[0100] As discussed above, in the present embodiment, the base
station BS makes an allocation of the mobile stations for
transmission through a combination of SDM and SDMA while the mobile
station implements a transmission-directivity control method and an
in-mobile-station space division demultiplex receiving method. This
allows the base station to make a space division multiple access to
another mobile station in accordance with a propagation
environment, together with space division multiplex transmission to
a particular mobile station. This makes it possible to efficiently
utilize the spatial freedom at the base station, to effectively
make use of the space division multiplex technique and
user-diversity effect based on SDM or SDMA, and to improve the
communication capacity of a radio communication system.
[0101] Incidentally, the present embodiment can be applied
similarly to a radio communication system of a multi-carrier
transmission scheme. In this case, there is available 1) a method
of making a similar operation to embodiment 1 by use of one of a
plurality of sub-carriers (e.g. a sub-carriers at around a center
frequency, etc.) and forming one transmission beam common to the
sub-carriers, and 2) a method of making a similar operation to
embodiment 1, i.e. channel estimation value calculation and
received quality estimation on a sub-carrier-by-sub-carrier basis,
to feed those pieces of information back to the base station 1
thereby allocating mobile stations MS.sub.m for effecting SDM and
SDMA depending upon a calculated spatial correlation coefficient.
Incidentally, during calculating a spatial correlation coefficient,
a spatial correlation coefficient is calculated on each sub-carrier
similarly to embodiment 1, to allocate mobile stations MS.sub.m by
taking, as the final spatial correlation coefficient, a
representative value such as an average or median thereof, a
maximum value and a minimum value. Meanwhile, by a
transmission-beam forming method for forming a transmission beam on
each sub-carrier, the present embodiment can be applied
similarly.
[0102] Incidentally, in the present embodiment it is possible to
change adaptively the allocation process of mobile stations
MS.sub.m in accordance with the traffic status of SDM or SDMA.
Where a number of mobile stations MS.sub.m exist within the
communication area 5 and call loss occurs more frequently than a
predetermined level, the process to omit the SDM-compatible process
(step S305, S309) in FIG. 3 can give priority to the mobile-station
allocation that SDMA is available rather than SDM. This can obtain
an effect that can increase the number of mobile stations that
communications are possible at the same time.
[0103] Meanwhile, the allocation process of mobile stations
MS.sub.m can be adaptively changed in accordance with the magnitude
of communication area 5 (or cell radius). In this case, in the case
that generally the base-station antenna has a height greater than
the surrounding buildings as in the macro-cell, there is a
comparative increase in the percentage of the region where the
sight in transmission and reception can be secured within the
communicating area 5. Hence, it becomes under the environment of
communications suited for SDMA rather than SDM. For this reason,
priority is given to the mobile-station allocation for SDMA rather
than that for SDM by the process to omit the SDM-compatible process
(step S305, S309) in FIG. 3.
[0104] Incidentally, although this embodiment explained the
communication method using space division multiplex in the
transmission of from the base station 1 to the mobile station
MS.sub.m (downlink), it can be similarly applied to the
transmission of from the mobile station MS.sub.m to the base
station 1 (uplink). In this case, antenna-based pilot signals are
sent to the base station 1 by time or code division based on each
antenna provided on the mobile station MS.sub.m so that a channel
estimation value and received quality can be calculated on each
antenna-based pilot signal in the base station 1. This allows SDM
or SDMA allocation to the mobile stations MS.sub.m by the similar
operation to the explanation with FIG. 3, without using the
feedback information from the mobile stations MS.sub.m.
[0105] Incidentally, in the present embodiment, the channel
estimation value and received quality information in the
transmission of from the base station 1 to the mobile station
MS.sub.m (downlink) is fed back to the base station 1 through the
communication line. Because the radio communication system using
TDD (time division duplex) uses the same frequency as transmission
medium, antenna-based pilot signals are sent by time or code
division to the base station 1 on each of the antennas provided on
the mobile stations MS.sub.m. In the base station 1, channel
estimation values and received qualities are calculated on the
respective antenna-based pilot signals. This allows SDM or SDMA
allocation to the mobile stations MS.sub.m by the similar operation
to the communication allocation process explained with FIG. 3,
without using the feedback information from the mobile stations
MS.sub.m. Meanwhile, the present embodiment can be applied
similarly to a TDD uplink.
[0106] Incidentally, the evaluation values related to the mobility
of mobile-stations MS.sub.m, such as estimated roaming velocity of
the mobile station MS.sub.m and Doppler-frequency estimation value,
may be combined as received quality information, besides the
received quality such as SNR explained in the present embodiment.
In this case, although delay occurs due to received quality
information feedback or SDMA or SDMA allocation process, operation
is made available by adding the step S306 in FIG. 3 with a decision
operation that SDMA or SDM allocation process is not made to the
mobility stations higher than a predetermined mobility.
Embodiment 2
[0107] FIG. 6 is a diagram showing a configuration of a base
station apparatus according to embodiment 2 of the invention. This
embodiment explained a spatial-channel forming method for
communication, with priority, with the SDM-uncompatible mobile
station, in a radio communication system where SDM-compatible
mobile stations and SDM-uncompatible mobile stations coexist within
the area.
[0108] The base station BS shown in FIG. 6 is different in
configuration in that there are provided
SDM-uncompatible-mobile-station weight generating means 601 and
SDM-compatible-mobile-station weight generating means in place of
the weight generating means 204 in FIG. 2 used in embodiment 1,
thereby being different in the method to generate a transmission
beam. Explanation is made below mainly on the different part from
embodiment 2, to omit the explanation as to the part similar to
embodiment 1. Incidentally, the explanation is on a directivity
control method in the mobile station MS and base station BS of
after communication allocation process to the mobile stations MS by
use of space division multiplex in the downlink.
[0109] The transmission data sequence is assumed S.sub.k.sup.n(t)
(where t represents a time) which is for the k-th space division
multiplex channel to the n-th mobile station MS.sub.n. Here, n is a
natural number equal to or smaller than the number of mobile
stations Nd to which space division multiple access is to be made
while k is a natural number equal to or smaller than the number of
space division multiplex ones Nc.sup.(n) to the mobile stations
MS.sub.n. Meanwhile, 1.ltoreq.Nc.sup.(n)<Ns.sup.(1). The channel
estimation value is assumed h.sup.n(p, m) which is in the case of
reception at the p-th antenna on the n-th mobile station MS.sub.n.
This channel estimation value h.sup.n(p, m) is for the
antenna-based pilot signal AP.sub.m(t) of from the base-station
antenna 208 fed back from the mobile station MS.sub.n to the base
station BS. Incidentally, m is a natural number equal to or smaller
than the number of base station antennas Nt while p is a natural
number equal to or smaller than the number of antennas Ns.sup.(n)
at the n-th mobile station MS.sub.11. Here, the channel estimation
matrix H.sup.n for the n-th mobile station Ms.sub.n is defined as
in (Equation 8).
[0110] SDM-uncompatible-mobile station weight generating means 601
generates a transmission weight vector Ws=(H.sup.(s)).sup.H for the
s-th SDM-uncompatible mobile station MS.sub.s and outputs it to
SDM-compatible mobile station weight generating means 602. Note
that .sup.H represents complex conjugate transposition. Due to the
transmission weight vector Ws, the s-th SDM-uncompatible mobile
station MS.sub.s obtains a received signal that combined in the
maximal ratio are a plurality of transmission signals from a
plurality of antennas of the base station BS.
[0111] The SDM-compatible-mobile station weight generating means
602 generates a beam that the transmission weight vector Wj for the
j-th space division multiplex channel to the SDM-compatible mobile
station MSj does not cause interference with the other users n,
SDMA is to be made, than the j-th one, as in (Equation 9). n is a
natural number equal to or smaller than the total number of mobile
stations Nd to which SDMA is to be made. Due to this, in the case
the transmission weight is W.sub.j which is directed to the A-th
mobile station MS.sub.A having the number of space division
multiplex channels of NC.sup.(A)=1, reception is at a channel
estimation value C.sub.A to be expressed as (Equation 10).
Meanwhile, where the transmission weight is W.sub.j, W.sub.j+1,
W.sub.j+Nc(B)-1 which is directed to the B-th mobile station
MS.sub.B having the number of space division multiplex channels of
NC.sup.(B)>1, reception is at a channel estimation value C.sub.B
in the degree of (Ns.sup.(B).times.Nc.sup.(B)) to be expressed as
(Equation 12). Here, in case the partial-space orthogonizing means
210 has transmission weights W.sub.j, W.sub.j+1 and W.sub.j+Nc(B)-1
directed to the B-th mobile station MS.sub.B having the number of
space division multiplex channels of NC.sup.(B)>1 where to make
an SDM-transmission to the mobile station MS.sub.B, reception is at
a channel estimation value C.sub.B in the degree of
(Ns.sup.(B).times.Nc.sup.(B)) to be expressed as (Equation 12).
C.sub.B is previously resolved into singular values as shown in
(Equation 13), to select the number Nc.sup.(B) of singular values
in the greater order of those obtained. By use of a right
singular-valued matrix Vs=[V.sub.1, V.sub.2, . . . , V.sub.Nc(B)]
constituted by right singular values corresponding to those
singular values .lamda..sub.k, the right singular-valued matrix Vs
is multiplied from left on the data sequence S(t)=[S.sub.1.sup.B(t)
S.sub.2.sup.B(t) . . . S.sub.Nc(B).sup.B(t)].sup.T of space
division multiplex channel as shown in (Equation 14), to calculate
a signal sequence S.sub.2(t). Here, k=1-Nc.sup.(B).
[0112] Then, the beam forming section 207 multiples the
transmission weights W.sub.j, W.sub.j+1 and W.sub.j+Nc(B)-1
respectively on the elements of S.sub.2(t) in the number of
Nc.sup.(B). Here, in (Equation 13), U is a unitary matrix
constituted by the left singular value vectors of the channel
estimation matrix C.sub.B, Visa unitary matrix constituted by the
right singular value vectors of the channel estimation matrix
C.sub.B, and Q is a diagonal matrix having diagonal components as
singular values. Incidentally, the partial-space orthogonizing
means 210 can be structurally omitted, in which case Vs in
(Equation 14) is given as Nc-degree unit matrix.
[0113] The operation in the mobile station MS.sub.n is similar to
embodiment 1.
[0114] As discussed above, explanation was made on the radio
communication system using a method of forming a beam to
SDM-uncompatible mobile stations different from embodiment 1, as to
the case of transmission through a combination of SDM and SDMA at
the base station BS. Due to the present embodiment, the base
station uses, for the SDM-uncompatible mobile stations, a
transmission beam from which can be obtained a received signal
combined in the maximum ratio of a plurality of transmission
signals of from a plurality of antennas. This enables SDMA in the
state the received quality to the SDM-uncompatible mobile stations
is sectured at a certain level. Meanwhile, although there is an
increasing interference with the SDM-compatible mobile stations,
the SDM-compatible mobile station can remove the interference by
use of a space domain due to a plurality of antennas provided
thereon, thus being higher in immunity to interference than the
SDM-uncompatible mobile station. Due to this, the radio
communication system can put the decrease of throughput to a small
range.
[0115] Incidentally, the present embodiment can be applied
similarly to a multi-carrier-schemed radio communication system. In
this case, there is available 1) a method of making a similar
operation to embodiment 1 by use of one of a plurality of
sub-carriers (e.g. a sub-carrier at around a center frequency,
etc.) and forming one transmission beam common to the sub-carriers,
and 2) a transmission beam forming method of making a similar
operation to embodiment 1 by use of a part or all of a plurality of
sub-carriers and forming transmission beams on a
sub-carrier-by-sub-carrier basis based on channel estimation values
for the antenna-based pilot signals of the respective
sub-carriers.
Embodiment 3
[0116] FIG. 7 is a diagram showing a configuration of a base
station apparatus according to embodiment 3 of the invention. This
embodiment is different from embodiment 1 in that space division
multiplex transmission control means 701 has space-time coding
means 702 for making a space-time-coding at between the channels
for space division multiplex transmission.
[0117] Explanation is made mainly on the part of the space division
multiplex control means 701 different from embodiment 1. Meanwhile,
the explanation is made, using FIG. 7, on a directivity control
method in the mobile station MS and base station BS of after
communication allocation process to the mobile stations MS by use
of space division multiplex in the downlink, similarly to
embodiment 1.
[0118] The transmission data sequence is assumed S.sub.k.sup.n(t)
(where t represents a time) which is on the k-th space division
multiplex channel to the n-th mobile station MS.sub.n. Here, n is a
natural number equal to or smaller than the number of mobile
stations Nd to which space division multiple access is to be made
while k is a natural number equal to or smaller than the number of
space division multiplex ones Nc.sup.(n) to the mobile stations
MS.sub.n. Meanwhile, 1.ltoreq.Nc.sup.(n)<Ns.sup.(1). The channel
estimation value is assumed h.sup.n(p, m) which is in the case of
reception at the p-th antenna on the n-th mobile station MS.sub.n.
This channel estimation value h.sup.n(p, m) is for the
antenna-based pilot signal AP.sub.m(t) of from the base-station
antenna 208 fed back from the mobile station MS.sub.n to the base
station BS. Incidentally, m is a natural number equal to or smaller
than the number of base station antennas Nt while p is a natural
number equal to or smaller than the number of antennas Ns.sup.(n)
at the n-th mobile station MS.sub.n. Here, the channel estimation
matrix H.sup.n for the n-th mobile station Ms.sub.n is defined as
in (Equation 8).
[0119] The space-time coding means 702 outputs a
space-division-multiplex-channel data sequence
S(t)=[S.sub.1.sup.B(t) S.sub.2.sup.B(t) . . .
S.sub.Nc(B).sup.B(t)].sup.T which space-time coding process is made
on a transmission data sequence 211 to mobile station MS1, to which
space division multiplex is to be made, of after being processed by
a not shown predetermined error-correction coding process,
interleave process and symbol-mapping process onto a
modulation-phase plane. Concerning space-time coding and a decoding
method thereof, there are information-disclosed of the techniques
including STBC (Space-Time Block Coding), STTC (Space-Time Trellis
Coding) and ST Turbo TC (Space-Time Turbo Trellis Codes), in B.
Vucetic, J. Yuan, "Space-Time Coding", J. Wiley & Sons Ltd
(2003), which is omitted to explain here. By making a space-time
coding, transmission rate lowers. However, reception-quality
improvement effect can be obtained due to diversity effect.
[0120] In the case the partial-space orthogoniizing means 210 has
transmission weights W.sub.j, W.sub.j+1 and W.sub.j+Nc(B)-1
directed to the B-th mobile station MS.sub.B having the number of
space division multiplex channels of Nc.sup.(B)>1 where to make
an SDM-transmission to the B-th mobile stations MS.sub.B, reception
is at a channel estimation matrix C.sub.B in a degree of
(Ns.sup.(B).times.Nc.sup.(B)) to be expressed as (Equation 12). It
previously singular-value-resolves C.sub.B as shown in (Equation
13), to select the number Nc.sup.(B) of singular values in the
greater order of those obtained. By using right singular-valued
matrix Vs=[V.sub.1, V.sub.2, . . . , V.sub.Nc(B)] constituted by
the right singular value vectors corresponding to those singular
values .lamda..sub.k, the right singular-valued matrix Vs is
multiplied from left on the space-division-multiplex-channel data
sequence S(t)=[S.sub.1.sup.B(t) S.sub.2.sup.B(t) . . .
S.sub.Nc(B).sup.B(t)].sup.T as shown in (Equation 14), thereby
calculating a signal sequence S.sub.2(t). Here, k=1-Nc.sup.(B).
[0121] Incidentally, the partial-space orthogonizing means 210 can
be structurally omitted, in which case Vs in (Equation 14) is given
as Nc-degree unit matrix. Accordingly, in this case, the
configuration is of the space division multiplex transmission
control means 801 as shown in FIG. 8.
[0122] Then, the beam forming section 207 multiples the
transmission weights W.sub.j, W.sub.j+1 and W.sub.j+Nc(B)-1
obtained by the similar operation to embodiment 1 in the weight
generating means 204, on the elements of S.sub.2(t) in the number
of Nc.sup.(B). Here, in (Equation 13), U is a unitary matrix
constituted by the left singular value vectors of the channel
estimation matrix C.sub.B, V is a unitary matrix constituted by the
right singular value vectors of the channel estimation matrix
C.sub.B, and Q is a diagonal matrix having diagonal components as
singular values.
[0123] Meanwhile, in order for the SDM-compatible mobile station
MSn to demultiplex-receive the space division multiplex channels in
the number of Nc.sup.(n) and in order for the SDM-uncompatible
mobile station MSn to make a reception with synchronous detection,
transmission is made by embedding a known signal sequence
(hereinafter, space-division-multiplexed-channel-based pilot
signals) CP.sub.k(t) in each space division multiplex channel.
Here, k is a natural number equal to or smaller than the total
number Tc of space division multiplex channels. Note that, where
the transmission signal is differentially coded and delayed
detection is applied, there is no need of sending such a
space-division-multiplex-channel-based pilot signal. Incidentally,
how to send a space-division-multiplexed-channel-based pilot signal
CP.sub.k(t) (frame structure) is the same as the explanation in
embodiment 1 using FIG. 5.
[0124] Now explanation is made on the reception operation at the
mobile station MS.
[0125] At first, the n-th SDM-compatible mobile station MSn
receives a space-division-multiplexed radio-frequency signal at
mobile-station antennas 221 in the number of Ns.sup.(n). The
receiver sections 222 in the number of Ns.sup.(n) output the number
Ns.sup.(n) of complex base-band signals r.sub.j.sup.(n)(t)
comprising I and Q signals due to post-frequency-conversion
orthogonal detection, in response to the respective radio-frequency
signals in the number of Ns.sup.(n) received. (Note that j is a
natural number equal to or smaller than Ns.sup.(n).)
[0126] Then, space division demultiplex means 721 demultiplexes the
space-division multiplex channels in the number of Nc.sup.(n) to
the SDM-compatible mobile stations MS.sub.n. The space division
demultiplex means 721 calculates a channel estimation value
h.sup.n(j, k) on each space division multiplex channel as shown in
(Equation 15) by use of a space-division-multiplex-channel-based
pilot signal CPk(t) embedded individually in the space-division
multiplex channel. Furthermore, the transmission signal is decoded
by use of a decode method corresponding to the space-time coding
method used in the space-time coding means 702, thereby outputting
a reception data sequence 722. Here, k is a natural number equal to
or smaller than the number of space-division multiplex channels
Nc.sup.(n) for transmission to the SDM-compatible mobile stations
MS.sub.n. Incidentally, * is a complex conjugate operator and the
number of symbols in the space-division-multiplex-channel-based
pilot signal CP.sub.k(t) is assumed Nq.
[0127] Incidentally, the following is included as another method of
space division demultiplex. Namely, when the partial space
orthogonalizing means 210 is used in SDM transmission to the B-th
mobile station MS.sub.B, singular values are selected Nc in the
greater order of those obtained in singular value resolution of
C.sub.B as shown in (Equation 13). By using a right singular-valued
matrix Us=[U.sub.1, U.sub.2, . . . , U.sub.Nc(B)] constituted by
left singular-value vector corresponding to those singular values,
whose complex-conjugate-interposed matrix (Us).sup.H is multiplied
from left on the received signal vector R=[r.sub.1.sup.(B)(t),
r.sub.2.sup.(B)(t), . . . , r.sub.Ns(B).sup.(B)(t)].sup.T. With
this method, a signal can be demultiplex-received through the
respective space-division multiplex channels. In this case, the
right singular-valued matrix Us is previously notified to the
mobile station MS.sub.B via the communication line. Incidentally,
as for the number of space division multiplex ones and the kind of
the space-division-multiplexed-channel-based pilot signal,
notification is previously made from the base station BS to the
mobile station MS.sub.n by way of the control channel, etc.
[0128] The operation to the SDM-uncompatible mobile station
MS.sub.1 is similar to embodiment 1.
[0129] As described above, the present embodiment is lower in
transmission rate to the SDM-compatible mobile stations but can
obtain a received quality improvement due to an addition of an
error correction ability added with a transmission diversity effect
in addition to the effect of embodiment 1, because of making a
space-time coding during spatially multiplex transmission to
SDM-compatible mobile stations thereby sending the same one of data
by space division multiplex. This can obtain a transmission-power
reduction effect where effecting transmission-power control in a
manner to obtain a required received quality. Besides, where
transmission power is constant, there can obtain an effect to
increase the communication area where a required received quality
is to be obtained.
[0130] In the present embodiment, the coding way and rate at the
space-time coding means can be changed in accordance with
propagation environment. This can improve the throughput in
compliance with a versatility of propagation environments.
[0131] Although the present embodiment showed the example of making
a space-time coding during spatially multiplex transmission to the
SDM-compatible mobile stations in the downlink, similar application
is available in the uplink. In this case, space-time coding is
applied in the SDM-compatible mobile station to the space division
multiplex transmission signal while decode process is applied in
the base station in compliance with the space-time coding.
INDUSTRIAL APPLICABILITY
[0132] As described above, the present invention is useful for a
radio communication system that mobile stations compatible with
spatially multiplex transmission and mobile stations uncompatible
therewith coexist within a communication area, and suited in
effectively utilizing the spatial freedom within the base station
and improving the communication capacity of the radio communication
system.
* * * * *