U.S. patent application number 12/556092 was filed with the patent office on 2009-12-31 for wireless communication system and transmission device.
This patent application is currently assigned to Fujitsu Limited. Invention is credited to Akira Ito, Masahiko Shimizu.
Application Number | 20090325514 12/556092 |
Document ID | / |
Family ID | 36177734 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090325514 |
Kind Code |
A1 |
Shimizu; Masahiko ; et
al. |
December 31, 2009 |
WIRELESS COMMUNICATION SYSTEM AND TRANSMISSION DEVICE
Abstract
The present invention relates to a wireless communication system
to properly switch over a transmission method of radio signals
corresponding to a configuration of a receiver. The wireless
communication system according to the present invention includes a
transmitting device having a plurality of antennas and capable of
transmitting radio signals different from each other from these
antennas, and a receiving device having at least one antenna and
receiving the radio signals transmitted from the transmitting
device. The receiving device comprises an information transmitting
unit transmitting, to the transmitting device, configuration
information about a configuration of the receiving device, and the
transmitting device includes a transmitting unit transmitting the
radio signals by a transmission method corresponding to the
configuration information received from the receiving device.
Inventors: |
Shimizu; Masahiko;
(Kawasaki, JP) ; Ito; Akira; (Kawasaki,
JP) |
Correspondence
Address: |
HANIFY & KING PROFESSIONAL CORPORATION
1055 Thomas Jefferson Street, NW, Suite 400
WASHINGTON
DC
20007
US
|
Assignee: |
Fujitsu Limited
Kawasaki
JP
|
Family ID: |
36177734 |
Appl. No.: |
12/556092 |
Filed: |
September 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11128285 |
May 13, 2005 |
|
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|
12556092 |
|
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Current U.S.
Class: |
455/101 |
Current CPC
Class: |
H04B 7/0626 20130101;
H04B 7/0628 20130101; H04B 7/0452 20130101 |
Class at
Publication: |
455/101 |
International
Class: |
H04B 7/02 20060101
H04B007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2005 |
JP |
JP2005-006352 |
Claims
1. A wireless communication system including a transmitting
apparatus that includes a plurality of antennas and can transmit
different radio signals from the respective antennas, and a
receiving apparatus that includes at least one antenna and receives
the radio signals transmitted from the transmitting apparatus, the
receiving apparatus comprising: an information notification unit to
expressly notify the transmitting apparatus of information on the
number of antennas of the receiving apparatus or information on the
number of multiplexed signals concurrently-processable by the
receiving apparatus, the transmitting apparatus comprising: a
transforming unit to transform transmitting signals based on the
information on the number of antennas or the information on the
number of multiplexed signals which are received from the receiving
apparatus; and a transmission unit to transmit radio signals
corresponding to the transformed transmitting signals.
2. A wireless communication system including a transmitting
apparatus that includes a plurality of antennas and can transmit
different radio signals from the respective antennas, and a
receiving apparatus that includes at least one antenna and receives
the radio signals transmitted from the transmitting apparatus, the
receiving apparatus comprising: an information transmission unit to
transmit, to the transmitting apparatus, configuration information
on configuration of the receiving apparatus, the configuration
information including information on the number of antennas of the
receiving apparatus or information on the number of multiplexed
signals concurrently-processable by the receiving apparatus, the
transmitting apparatus comprising: a detection unit to detect the
information on the number of antennas or the information on the
number of multiplexed signals from the configuration information
received from the receiving apparatus; a transforming unit to
transform transmitting signals based on the detected information on
the number of antennas or the detected information on the number of
multiplexed signals; and a transmission unit to transmit radio
signals corresponding to the transformed transmitting signals.
3. A wireless communication system including a transmitting
apparatus that includes a plurality of antennas and can transmit
different radio signals from the respective antennas, and a
receiving apparatus that includes at least one antenna and receives
the radio signals transmitted from the transmitting apparatus, the
receiving apparatus comprising: an extraction unit to extract, from
received radio signals, transmission characteristic information
including transmission path information corresponding to an
environment where the received radio signals have been transmitted;
and an information transmission unit to transmit, to the
transmitting apparatus, configuration information on configuration
of the receiving apparatus and the extracted transmission
characteristic information, the configuration information including
information on the number of antennas of the receiving apparatus or
information on the number of multiplexed signals
concurrently-processable by the receiving apparatus, the
transmitting apparatus comprising: a detection unit to detect the
information on the number of antennas or the information on the
number of multiplexed signals from the configuration information
received from the receiving apparatus, and detect the transmission
path information from the transmission characteristic information
received from the receiving apparatus; a transforming unit to
transform transmitting signals based on the detected information on
the number of antennas or the detected information on the number of
multiplexed signals and based on the detected transmission path
information; and a transmission unit to transmit radio signals
corresponding to the transformed transmitting signals.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/128,285, filed on May 13, 2005, now
pending, the entire disclosures of which are incorporated by
reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Present Invention
[0003] The invention relates to a wireless communication system
including a transmitting device having a plurality of antennas and
capable of transmitting different radio signals from the respective
antennas, and to the transmitting device.
[0004] 2. Description of the Related Art
[0005] MIMO (Multi Input and Multi Output) communication system is
given as a communication system capable of improving a transmission
rate (transmission capacity) as a total by transmitting different
pieces of data by use of same frequency band (and further the same
spread code) from a plurality of antennas in parallel. The MIMO
communication system is that plural pieces of data are transmitted
from a plurality of transmitting antennas in parallel, and the
signals synthesized while passing through a variety of
communication paths are received by a plurality of receiving
antennas. FIG. 7 is a diagram showing an outline of the MIMO
communication system. FIG. 7 shows, in the MIMO communication
system configured by i-pieces of transmitting antennas 500 and
j-pieces of receiving antennas 510, how plural pieces of data
(x.sub.1-x.sub.i) are transmitted to the receiving antennas 510
from the transmitting antennas 500, and the respective antennas
obtain signals y.sub.1-y.sub.j synthesized with these pieces of
data (x.sub.1-x.sub.i).
[0006] Note that when the transmission signal from each antenna is
designated by a transmission vector x, the receipt signal received
by each antenna is designated by a receipt vector y, a state of a
radio path is expressed as a channel matrix H, and a noise vector
is designated by n, there is established a relationship such as
y=Hx+n.
[0007] In the MIMO communications as shown in FIG. 7, a
receiving-side device receiving the signals transmitted from the
plurality of antennas and then synthesized, utilizes a method
called MLD (Maximum Likelihood Detection) defined as a maximum
likelihood decoding method in order to acquire an excellent radio
characteristic. By this method, the receiving-side device detects a
necessary piece of data by separating the synthesized signals. The
MLD is a method of detecting a data pattern by judging, with
respect to combinations of all the transmission data patterns that
can be transmitted by the transmitting side, if transmitted in such
a manner, how much a possibly-acquired receipt signal gets
approximate to the actual receipt signal (a degree of maximum
likelihood) (see FIG. 8). In the MLD, however, in the case of
transmitting the signals from, for example, four pieces of
transmitting antennas by 16 QAM (Quadrature Amplitude Modulation)
defined as a digital modulation method of transmitting 4-bit data
with one symbol, there is a necessity of obtaining the likelihood
of data patterns numbered as tremendously as 65536 (=16.sup.4). In
this case, it follows that the receiving-side device detects the
data pattern exhibiting the maximum likelihood from within this
tremendous number of data patterns. Thus, the MIMO communication
system requires an enormous throughput for the data detection.
[0008] A method for solving this problem involves employing
Pre-Rake, etc. shown in FIG. 9(B) in the transmitting-side device.
The method typified by Pre-Rake is a method for reducing the
receiving-side processes by the signal processing on the
transmitting side. For instance, FIG. 9 shows wireless
communications based on normal CDMA (Code Division Multiple Access)
(FIG. 9(A)) and CDMA-based wireless communications using Pre-Rake
(FIG. 9(B)). In the normal CDMA-based wireless communications shown
in FIG. 9(A), the receiving side detects the data by the signal
processing (channel compensation) based on the transmission path
information. On the other hand, in the case of employing Pre-Rake
shown in FIG. 9(B), the signal processing is previously executed
based on the transmission path information of the signal before
transmitting the signals.
[0009] In the Pre-Rake method, for example, in the case of a
transmission environment (an environment where a path 1 and a path
2 shown in FIG. 10(A) exit) as shown in FIG. 10(A), though normally
the receiving side makes channel compensation corresponding to the
transmission environment, the transmitting side executes a channel
compensation process equivalent to that on the receiving side.
[0010] For instance, a weighting synthesis (Rake creating) unit as
shown in FIG. 10(B) multiplies the transmission signal by a
weighting coefficient of each transmission environment. With this
operation, the receiving-side signal processing can be reduced.
[0011] A technology disclosed in the document ("Examinations about
Configuration of Transmitter/Receiver of MTMT Array System Using
Weight Batchwise Control at Base Station", written by Hoshida,
B-5-54, General Meeting of Electronic Information Communication
Institution in 2002) is proposed as a method of increasing a
channel capacity by executing this type of signal processing
employing the transmission path information on the transmitting
side in the MIMO communication system.
[0012] That is, in the MIMO communication system, there are
proposed a method of using an MLD receiver requiring an enormous
throughput for acquiring an excellent radio characteristic and a
method of employing a simple receiver requiring merely a low
throughput by executing the signal processing that previously takes
account of the transmission path on the transmitting side.
[0013] A base station performing the MIMO communications, however,
has a case of desiring to separately use the MLD receiver and the
simple receiver. In this case, there is none of a method of making
the above methods coexistent with each other.
SUMMARY OF THE INVENTION
[0014] It is an object of the present invention to provide a
wireless communication system capable of properly switching over a
transmission method of a radio signal corresponding to a
configuration of a receiver.
[0015] The present invention adopts the following configurations in
order to solve the above-mentioned problems. Namely, the present
invention is about a wireless communication system comprising a
transmitting device having a plurality of antennas and capable of
transmitting radio signals different from each other from the
plurality of antennas, and a receiving device having at least one
of antennas and receiving the radio signals transmitted from the
transmitting device. In the present invention, the receiving device
includes an information transmitting unit transmitting, to the
transmitting device, configuration information about a
configuration of the receiving device, and the transmitting device
includes a transmitting unit transmitting the radio signals by a
transmission method corresponding to the configuration information
received from the receiving device.
[0016] In the present invention, the transmitting device is
notified of the configuration information of the receiving device,
and the transmitting device transmits the radio signals by a
transmission method based on the notified configuration
information.
[0017] Therefore, according to the present invention, the
transmission method executed by the transmitting device can be
changed corresponding to the configuration of the receiving
device.
[0018] Further, in the present invention, the configuration
information contains a piece of number-of-antenna information held
by the receiving device, and the transmitting unit determines the
transmission method on the basis of the number-of antenna
information contained in the configuration information.
[0019] Hence, according to the present invention, the transmission
method executed by the transmitting device can be changed
corresponding to the number-of-antenna information of the receiving
device.
[0020] Moreover, in the present invention, the receiving device
further includes an extraction unit extracting, from the received
radio signals, transmission characteristic information containing
transmission path information corresponding to an environment where
the radio signals are transmitted, the information transmitting
unit transmits the configuration information and the transmission
characteristic information, the transmitting device further
includes a detection unit detecting the transmission path
information from the transmission characteristic information
received from the receiving device, and a transforming unit
transforming the transmission signals on the basis of the detected
transmission path information and the number-of-antenna information
contained in the configuration information, and the transmitting
unit transmits the radio signals corresponding to the transformed
transmission signals.
[0021] In the present invention, the receiving device notifies the
transmitting device of the transmission characteristic information
and the configuration information of the receiving device. Then,
the transmitting device detects the transmission path information
from the notified transmission characteristic information. Further,
the transmitting device transforms the transmission signals based
on the detected transmission path information and the
number-of-antenna information of the receiving device so that the
receiving device can receive only the radio signals corresponding
to the number-of-antenna information, and transmits the transformed
signals.
[0022] Therefore, according to the present invention, it is
possible to determine the transmission method corresponding to the
number-of-antenna information of the receiving device having none
of a high-level demodulating function by taking account of both of
the number-of-antenna information of the receiving device and the
transmission path information.
[0023] Note the present invention may be a program for actualizing
any one of the functions described above. Moreover, the present
invention may also be a readable-by-computer storage medium stored
with such a program.
[0024] According to the present invention, it is feasible to
actualize the wireless communication system capable of properly
switching over the transmission method corresponding to the
configuration of the receiver.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a diagram showing an architecture of a MIMO
communication system in an embodiment;
[0026] FIG. 2 is a diagram showing a principle of the MIMO
communication system in the embodiment;
[0027] FIG. 3 is a diagram showing a functional configuration of
the MIMO communication system in the embodiment;
[0028] FIG. 4 is a diagram showing an example of executing
weighting of a transmission data symbol and controlling a
transmission rate in accordance with transmission path
information;
[0029] FIGS. 5A and 5B are diagram showing a modified example in a
case where a transmission side can not know the transmission path
information;
[0030] FIGS. 6A and 6B are diagram showing a modified example 2 in
a case where a transmission side can not know the transmission path
information;
[0031] FIG. 7 is a diagram showing an outline of the MIMO
communication system;
[0032] FIG. 8 is a diagram showing an outline of MLD;
[0033] FIGS. 9A and 9B are diagram showing an outline of a Pre-Rake
method; and
[0034] FIGS. 10A and 10B are diagram showing an outline of
weighting synthesis by the Pre-Rake method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] An embodiment of a MIMO communication system according to
the present invention will hereinafter be described with reference
to the drawings. A configuration in the embodiment is an
exemplification, and the present invention is not limited to the
configuration in the embodiment.
[0036] .Device Configuration.
[0037] FIG. 1 is a diagram showing an outline of a hardware (H/W)
architecture in the embodiment of the MIMO communication system
according to the present invention. The outline of the H/W
architecture in the embodiment of the present invention will be
explained with reference to FIG. 1.
[0038] The MIMO communication system in the embodiment is comprised
of, by way of an example, a transmitter 11 and a plurality of
receivers 21, 22, and 23. For instance, the transmitter 11 has four
pieces of antenna elements 10, the receiver 21 has one antenna
element 200, the receiver 22 has one antenna element 201, and the
receiver 23 has two antenna elements 203, respectively.
[0039] Signals transmitted from the antenna elements 10 of the
transmitter 11 are received by the respective antenna elements 201,
202 and 203, and data (carried on the signals) are detected by the
respective receivers 21, 22, 23. Further, pieces of transmission
characteristic information of the signals received by the
respective antennas are individually specified by signal processing
of the receivers 21, 22 and 23 ((2) shown in FIG. 1). Then, the
transmission characteristic information and information about the
configuration of the receiver ((1) shown in FIG. 1) are transmitted
to the transmitter 11 by use of, e.g., dedicated antennas
(unillustrated). As a matter of course, the illustrated antennas
can be also employed. The transmission characteristic information
is characteristic information of a transmission path along which
the signal is transmitted from each of the transmission antennas 10
to each of the receiving antennas 200, 201, 202 and 203. The
configuration information of the receiver can contain at least one
item among items such as the number of receivers, the number of
antenna elements possessed by each receiver, a demodulation method
of each receiver, and performance (a processing speed, a degree of
signal processability) of the receiver.
[0040] The transmitter 11 receiving the configuration information
of the receiver and the transmission characteristic information,
after effecting signal processing upon the signals on the basis of
these items of information, transmits these signals to the
receivers 21, 22 and 23. Note that for an easy understanding of the
description in the embodiment, only unidirectional wireless
communications are illustrated in separation into the transmitter
and the receivers, however, each device may have both of the
receiving function and the transmitting function, whereby
bidirectional communications may be performed.
[0041] Further, the MIMO communication system in the embodiment
exemplifies the receivers 21, 22 and 23 having the number of
antennas as shown in FIGS. 1 and 2, however, this is nothing but
the exemplification, and there may be a single receiver having four
pieces of antennas and may also be two receivers each having two
pieces of antennas. Namely, the MIMO communication system in the
embodiment limits neither the configuration of the receiver nor the
configuration of the transmitter.
[0042] .Principle of System.
[0043] Next, the principle of the MIMO communication system having
the H/W architecture described above in the embodiment will be
explained with reference to FIG. 2. FIG. 2 is a diagram showing the
principle of the MIMO communication system in the embodiment.
[0044] In the MIMO communication system in the embodiment, the
transmitting side previously executes the signal processing
corresponding to, e.g., the number of antennas held by the
receiver. The transmitter 11 performs the signal processing on the
signals so that the symbol data series of which the number is equal
to or smaller than the number corresponding to the number of
receiving antennas possessed by the respective receivers 21, 22 and
23 reach the respective receivers, and transmits the signals. To be
specific, the transmitter 11 performs the signal processing based
on the transmission characteristic information on the signals so
that one symbol data series directed to the receivers 21, 22 each
having one antenna reaches each of the receivers 21, 22, and
transmits the signals. Further, the transmitter 11 performs the
signal processing on the signals so that two or less symbol data
series (which are the data for two antennas) directed to the
receiver 23 having two antennas reach the respective antennas as
the symbol data of the receiver 23 itself, and transmits the
signals. For instance, the signal processing may also be performed
so that first and second symbol data series reach both of first and
second antennas, and so that the first symbol data series reach the
first antenna and the second symbol data series reach the second
antenna.
[0045] Herein, the principle of the signal processing by the
transmitter 11 will be explained.
[0046] To start with, the signal sent from the transmitter 11 is
influenced by a transmission environment of the respective channels
between the transmitter 11 and the respective receivers 21, 22, 23.
Further, in the MIMO communication system, plural items of data are
transmitted from the plurality of transmitting antennas, and hence
the signals sent therefrom pass through a variety of communication
paths and are received by the respective receiving antennas in the
form of being synthesized with the signals sent from other
antennas. Therefore, in the case of transforming the channel
transmission environment into numerical values, this can be
expressed by a matrix corresponding to the number of antennas held
by the transmitter and the number of antennas held by the
receiver.
[0047] Specifically, in the MIMO communication system in the
embodiment, when h.sub.ij represents transmission characteristics
of transmission paths from four pieces of transmitting antennas i
to four pieces of receiving antennas j, whereby the channel
transmission environment can be expressed by a matrix H (which will
hereinafter be called a transmission path matrix H) in a formula
(1.1).
[0048] Then, when the transmission signal and the receipt signal
are expressed in vector, a transmission signal vector x and a
receipt signal vector y can be expressed by a formula (1.2).
H = ( h 11 h 12 h 13 h 14 h 21 h 22 h 23 h 24 h 31 h 32 h 33 h 34 h
41 h 42 h 43 h 44 ) ( 1.1 ) y = Hx + n ( 1.2 ) ##EQU00001##
[0049] where n is a noise vector of each of the receiving
antennas.
[0050] The signal vectors of the signals received by the receivers
21, 22 and 23 are expressed by the formula (1.2), and hence the
transmitter 11 executes the following process in order for the
symbol data series of which the number corresponds to the number of
antennas of the receiving antennas held by the receivers 21, 22 and
23 to reach the respective receivers. Namely, the transmitter 11
executes the process of multiplying the transmission symbol data by
a 4-row/4-column matrix G (which will hereinafter be called a
change-of-variable matrix G) that satisfies the following formula
(1.3).
F = ( f 11 0 0 0 0 f 22 0 0 0 0 f 33 f 34 0 0 f 43 f 44 ) = ( h 11
h 12 h 13 h 14 h 21 h 22 h 23 h 24 h 31 h 32 h 33 h 34 h 41 h 42 h
43 h 44 ) G ( 1.3 ) ##EQU00002##
[0051] With the transmission of the signals subjected this change
of variable, it follows that the receivers 21 and 22 each having
the single receiving antenna receive one self-addressed data
series, and the receiver 23 having the two antennas receive the two
data series in parallel. Herein, f is an appropriate complex
number. Namely, let x.sub.0 be a pre-transformation symbol data
vector, and the receiving data vector y can be expressed by a
calculation formula as by the formula (1.4).
y = Hx = HGx 0 = Fx 0 = ( f 11 0 0 0 0 f 22 0 0 0 0 f 33 f 34 0 0 f
43 f 44 ) x 0 ( 1.4 ) ##EQU00003##
[0052] As can be understood also from the formula (1.4), with the
multiplication by the change-of-variable matrix G, the transmitter
21 may simply consider only the signals influenced by only the
element f.sub.11, i.e., the signals that are transmitted from the
transmitting antenna 1 and should be received by the receiver 11
without taking account of the synthesis of the signals transmitted
from other antennas. That is, the influence of the signals
transmitted from other antennas can be already restrained at a
stage of receiving the signals by the self-antenna.
[0053] This is the same with the receiver 22. The receiver 23, as
the influence of the transmission signals from other antennas were
already restrained at the stage of receiving the signals by the
self-antenna, may simply consider the signals influenced by
elements f.sub.33, f.sub.34, f.sub.43, and f.sub.44, i.e., the
signals received by the two antennas possessed by the receiver
23.
[0054] .Functional Configuration.
[0055] Next, functions of the respective devices in the MIMO
communication system in the embodiment will be described with
reference to FIG. 3. FIG. 3 is a diagram showing a functional
configuration of the MIMO communication system in the embodiment.
The functional units shown in FIG. 3 actualize the principle of the
system described earlier. FIG. 23 shows the transmitter 11 and the
receiver 23 illustrated in FIG. 1. The receivers 21, 22
unillustrated in FIG. 3 have the same configuration as that of the
receiver 23 except that each of the receivers 21, 22 has a single
piece of antenna and has none of high-level demodulating function
(which is a signal separating function exemplified as below).
[0056] To begin with, the functional configuration of the
transmitter 11 will be explained as follows. The transmitter 11 is
constructed of a variable changing unit 111 (corresponding to a
transmission unit and a transformation unit according to the
present invention), a signal separating unit 112, a transmission
processing unit 113, antenna elements 10, an antenna element 100, a
receipt processing unit 114 and a transmission characteristic
information/receiver configuration information detecting unit 115
(corresponding to a detection unit according to the present
invention).
[0057] ..Variable Changing Unit 111..
[0058] The variable changing unit 111 obtains (updates), based on
transmission characteristic information and receiver configuration
information inputted from the transmission characteristic
information/receiver configuration information detecting unit 115,
the change-of-variable matrix G that satisfies the formula (1.3). A
method by which the variable changing unit 111 obtains the
change-of-variable matrix G will be explained in depth in an item
of <Operational Example>.
[0059] The variable changing unit 111, when a data transmission
request is given, multiplies the transmission symbol data by this
change-of-variable matrix G, and outputs the transmission symbol
data after being multiplied to the signal separating unit 112.
[0060] ..Signal Separating Unit 112..
[0061] The signal separating unit 112 separates the
serially-arranged symbol data signals inputted from the variable
changing unit 111 in parallel for every antenna to which the data
signal is transmitted, and outputs the data signal to the
transmission processing unit 113 for sending from each of the
antenna elements 10. The signal separating unit 112, when
separating the signals, by a use of the symbol data signal inputted
from the variable changing unit 111, determines the antenna to
which the symbol data signal should be transmitted. This
transmitting antenna is determined based on the transmission signal
transformed by the variable changing unit 111.
[0062] ..Transmission Processing Unit 113..
[0063] The transmission processing units 113 output, to the antenna
elements 10, high-frequency signals obtained by performing a
modulation process upon the transmission signals inputted from the
signal separating unit 112. Simultaneously, the transmission
processing units 113 transmit a plurality of different known
signals (which will hereinafter be referred to as transmission
characteristic estimation signals) having signal patterns
orthogonal to each other in order to make the receiver 23 estimate
a transmission path characteristic. Note that the transmission
processing units 113 in the embodiment are configured in the form
of being divided for every antenna element 10 and may also be made
to operate in the form of being organized into one unit.
[0064] ..Antenna Element 10..
[0065] The antenna element 10 is an antenna for transmitting the
high-frequency signals outputted from the transmission processing
units 113 to the receiver 23. Though explained later on, the
antenna element 10 can be constructed as a transmitting/receiving
dual-purpose antenna by use of a duplexer, etc.
[0066] ..Antenna Element 100..
[0067] The antenna element 100 is an antenna for receiving the
high-frequency signals transmitted from an antenna element 200 of
the receiver 23. The high-frequency signals received by the antenna
element 100 are outputted to the receipt processing unit 114.
[0068] ..Receipt Processing Unit 114..
[0069] The receipt processing unit 114 acquires the receipt signals
by effecting an amplifying process upon the high-frequency signals
inputted from the antenna element 100. The receipt processing unit
114 outputs the receipt signals to the transmission characteristic
information/receiver configuration information detecting unit
115.
[0070] ..Transmission Characteristic Information/Receiver
Configuration Information Detecting Unit 115..
[0071] The transmission characteristic information/receiver
configuration information detecting unit 115 detects data of the
transmission characteristic information and data of the receiver
configuration information from the inputted receipt signals
(receipt signals received from each of the receivers). The detected
transmission characteristic information and the detected receiver
configuration information are outputted to the variable changing
unit 111. Note that the transmission characteristic information and
the receiver configuration information are detected and generated
by the receiver 23. Incidentally, the receiver configuration
information may be acquired from a upper device side. For example,
the receiver configuration information is stored in an HLR (Home
Location Register), and is downloaded as the necessity may arise.
On this occasion, the respective terminal configurations may be
distinguished from each other by use of terminal IDs, etc.
[0072] Next, the functional configuration of the receiver 23 will
be explained as below. The receiver 23 is constructed of an antenna
element 203, a receipt processing unit 231, a transmission
characteristic estimating unit 232 (corresponding to an extraction
unit according to the present invention), a signal separating/data
detecting unit 233, a transmission characteristic
information/receiver configuration information generating unit 234,
a transmission processing unit 235 (corresponding to an information
transmitting unit according to the present invention), and an
antenna element 200.
[0073] ..Antenna Element 203..
[0074] The antenna element 203 is an antenna for receiving the
signals transmitted from the antenna elements 10 of the transmitter
11. The high-frequency signals received by the antenna element 203
are outputted to the receipt processing unit 231. As will be
explained later on, the antenna element 203 may be constructed as a
transmitting/receiving dual-purpose antenna as in the case of the
antenna 100.
[0075] ..Receipt Processing Unit 231..
[0076] The receipt processing unit 231 acquires the receipt signals
by executing the amplifying process, etc. upon the high-frequency
signals inputted from the antenna element 203. The receipt signals
are outputted to the signal separating/data detecting unit 233 and
to the transmission characteristic estimating unit 232.
[0077] ..Transmission Characteristic Estimating Unit 232..
[0078] The transmission characteristic estimating unit 232 obtains
a transmission path matrix H of the transmission paths between the
antenna elements 10 and the antenna elements 203 by use of the
known signals, etc. from the inputted receipt signals, and
estimates transmission characteristic information expressed by a
transmission characteristic matrix F (=HG) in a form multiplied by
a change-of-variable matrix G by which the variable changing unit
111 of the transmitter 11 multiplies the transmission signals. In
the embodiment, the transmission characteristic matrix F is a
matrix expressed by the formula (1.4), and it follows that the
change-of-variable matrix G can be updated with this estimated
value, corresponding to, even when the transmission path changes,
this change. Further, the transmission characteristic information
is matrix elements f.sub.33, f.sub.34, f.sub.43, and f.sub.44 of
the transmission characteristic matrix F shown in the formula (1.4)
in the transmission characteristic estimating unit 232 of the
receiver 23. Note that the matrix elements f.sub.11 and f.sub.22 of
the transmission characteristic matrix F shown in the formula (1.4)
are estimated in the unillustrated receivers 21 and 22.
[0079] Then, the transmission characteristic estimating unit 232
outputs the transmission characteristic information to the signal
separating/data detecting unit 233. This transmission path matrix
H, the transmission path becoming different corresponding to each
antenna element on the receiving side, as a matter of course,
changes for every antenna element receiving the signal.
Accordingly, the transmission characteristic estimating unit 232 is
prepared for every antenna element 203 and estimates the
transmission characteristic information from the signals received
by each antenna. An in-depth description of how the transmission
characteristic estimating unit 232 estimates the transmission
characteristic information, will be given in the item of
<Operational Example>.
[0080] ..Signal Separating/Data Detecting Unit 233..
[0081] The signal separating/data detecting unit 233 separates the
receipt signals (which will hereinafter be called a signal
separating function) based on the MIMO method by employing the
transmission characteristic information (the matrix elements
f.sub.33, f.sub.34, f.sub.43, and f.sub.44 shown in the formula
(1.4)) inputted from the transmission characteristic estimating
unit 232, and detects the receiving data. Note that the detection
of the receiving data may involve employing MLD, etc.
[0082] Further, the unillustrated receivers 21 and 22 may not have
the signal separating function with the signal processing performed
by the transmitter 11 as the transmitting side so that each of the
receivers receives only the signals that should be received by the
self-receiver.
[0083] ..Transmission Characteristic Information/Receiver
Configuration Information Generating Unit 234..
[0084] The transmission characteristic information/receiver
configuration information generating unit 234 generates the
receiver configuration information of the self-device (e.g., stores
the configuration information on an unillustrated memory, reads the
information therefrom and generates the information), and also
generates the transmission data to be transmitted together with the
transmission characteristic information estimated by the
transmission characteristic estimating unit 232 to the transmitter
11. In the embodiment, it is assumed that the receiver
configuration information contains information about the number of
antennas held by the receiver 23 (this is the same with other
receivers).
[0085] ..Transmission Processing Unit 235..
[0086] The transmission processing unit 235 performs the modulation
process upon the transmission signals in order to transmit, to the
transmitter 11, the transmission data containing the transmission
characteristic information and the receiver configuration
information inputted from the transmission characteristic
information/receiver configuration information generating unit 234
by a use of signaling etc., and outputs the high-frequency signals
to the antenna element 200. Simultaneously, the transmission
processing unit 235 transmits the transmission characteristic
estimation signals with their signal patterns orthogonal to each
other to make the transmitter 11 estimate the transmission path
characteristic.
[0087] Note that the known signals for the transmission
characteristic estimation may be transmitted in the form of being
distinguished from the actual transmission data by employing a
timewise separating method with respect to the data, a spread-code
based separating method utilizing CDMA, a sub-carrier frequency
based separating method utilizing OFDM (orthogonal Frequency
Division Multiplexing) and a combined method of these separating
methods.
[0088] ..Antenna Element 200..
[0089] The antenna element 200 is an antenna for transmitting, to
the transmitter 11, the high-frequency signals outputted from the
transmission processing unit 235.
[0090] .Receiver Configuration Information.
[0091] Next, the receiver configuration information of which each
of the receivers 21-23 notifies the transmitter 11, will be
explained as follows.
[0092] An example of employing the number of antennas for every
receiver is given as the receiver configuration information in the
embodiment. The receiver configuration information can be also
categorized as below by way of other example. Further, it is also
possible to categorize in a way that combines the following
categorizations.
[0093] .Categorization 1. Categorization corresponding to the
number of antennas held by the receiver.
[0094] .Categorization 2. Categorization corresponding to the
demodulation method held by the receiver. The demodulation method
connoted herein can exemplify the aforementioned signal separating
function. There is considered a case, wherein the receiver is
categorized as a receiver capable of demodulating received signals
into which radio signals transmitted from the transmitter are
synthesized with radio signals transmitted from other antenna
possessed by this transmitter, or a receiver capable of
demodulating only the signals received in the form of being
separated so as not to be synthesized with the radio signals
transmitted from other antenna, or a receiver capable of
demodulating by sue of signals that are partially separated and
received by other receiving antenna. An operation of the
transmitter 11 in this case will be explained in detail in an item
of <<Generation of Change-of-Variable Matrix G Suited to
Configuration of Receiver>>.
[0095] .Categorization 3. Categorization corresponding to a data
identifying method held by the receiver. For instance, there is
considered a case of categorization depending on whether MLD or
MMSE (Minimum Mean Square Error).
Operational Example
Estimation of Transmission Characteristic Information by
Transmission Characteristic Estimating Unit 232
[0096] The transmission characteristic estimating unit 232
estimates the transmission characteristic information from the
received signals. This transmission characteristic information is
estimated by the following method as elements of the transmission
characteristic matrix F expressed by the formula (1.4) and
comprising of the transmission path matrix H reflecting the
transmission path environment and the change-of-variable matrix G
multiplied by the transmitter 11.
[0097] The transmission characteristic estimating unit 232
estimates the transmission characteristic information by use of the
transmission characteristic estimation signals as the known signals
given from the transmitter 11. To be specific, the transmission
characteristic estimating unit 232 estimates the matrix elements
f.sub.33, f.sub.34, f.sub.43, and f.sub.44 shown in the formula
(1.4).
[0098] The transmission characteristic estimation signals involve
using data patterns (1, 1, 1, 1), (1, -1, 1, -1) (1, 1, -1, -1) and
(1, -1, -1, 1) defined as the known signals with their signal
patterns orthogonal to each other. Note that each data pattern is
transmitted from each of the transmitting antennas. Then,
preferably, the known signals orthogonal to each other are
transmitted from the respective receiving antennas of the receiver
and also received by the transmitting antenna of the transmitter in
order for the transmitter to estimate the transmission path (H)
between each of the receiving antennas of each receiver and the
transmitting antenna of the transmitter.
[0099] From the left element in the brackets, there are shown the
first symbol data, the second symbol data, the third symbol data
and the fourth symbol data. In the receiver 23 receiving the
transmission characteristic estimation signals, the data received
by one of the two receiving antennas are expressed such as
y.sub.1,1 and y.sub.1,2 in the formula (2.1) and the formula (2.2).
The symbol y.sub.1,1 represents the first symbol receipt data, and
the symbol y.sub.1,2 represents the second symbol receipt data.
With this operation, the transmission characteristic estimating
unit 232 of the receiver 23 estimates f.sub.33 by adding the two
symbols and estimates f.sub.34 by subtracting the symbols. Note
that the estimations of f.sub.33 and f.sub.34 employ only the first
symbol data and the second symbol data, however, as a matter of
course, the third symbol data and the fourth symbol data may also
be used.
[0100] The data y.sub.2,1 and y.sub.2,2 received by the other
receiving antenna are subjected to the same processing, thereby
estimating f.sub.43 and f.sub.44.
y.sub.1,1=f.sub.33+f.sub.34 (2.1)
y.sub.1,2=f.sub.33-f.sub.34 (2.2)
y.sub.2,1=f.sub.43+f.sub.44 (2.3)
y.sub.2,2=f.sub.43-f.sub.44 (2.4)
[0101] Note that the known signals for the transmission
characteristic estimation may be transmitted in the form of being
distinguished from the actual transmission data by employing the
timewise separating method with respect to the data, the
spread-code based separating method utilizing CDMA (Code Division
Multiple Access), the sub-carrier frequency based separating method
utilizing OFDM (Orthogonal Frequency Division Multiplexing) and the
combined method of these separating methods.
[0102] ..Generation of Change-of-Variable Matrix G by Variable
Changing Unit 111..
[0103] The transmission path environment momentarily changes, and
hence, unless the change-of-variable matrix G is used in response
to changing in the transmission path environment, the
communications exhibiting a high-level wireless characteristic can
not be performed. Such being the case, the way of how the variable
changing unit 111 obtains the change-of-variable matrix G
reflecting the latest transmission path environment, will be next
described as below.
[0104] At first, the variable changing unit 111 obtains the latest
transmission path matrix H by making use of the transmission
characteristic information to be transmitted to the transmitter 11
from each of the receivers 21, 22, 23. Namely, the transmission
characteristic information (f.sub.11, f.sub.22, f.sub.33, f.sub.34,
f.sub.43, and f.sub.44) transmitted from the respective receivers
21, 22, 23 consists of the change-of-variable matrix G by that the
variable changing unit 111 multiplies the transmission data last
time and the transmission path matrix H reflecting the transmission
path environment at that time (F=HG), and therefore the variable
changing unit 111 acquires the transmission path matrix H by
employing the change-of-variable matrix G used last time, which
corresponds to this transmission characteristic matrix F. Then, the
variable changing unit 111 obtains a new change-of-variable matrix
G by use of the latest transmission characteristic information F
received and the formula (1.3) from the obtained transmission path
matrix H.
[0105] Further, on the occasion of getting the feedback about the
transmission characteristic information and the receiver
configuration information to the transmitter from the receiver,
when the transmission processing unit 235 utilizes TDD (Time
Division Duplex), the different and orthogonal known signals (the
transmission characteristic estimation signals) may be transmitted
from the respective receivers. With this operation, the variable
changing unit 111 estimates the transmission path matrix H by
employing the transmission characteristic estimation signals,
thereby acquiring the change-of-variable matrix G. Namely, as the
proper transmission characteristic information F (e.g., as shown in
FIG. 3, other elements excluding a part of the elements (which is
set to, e.g., 1) are set to 0), the change-of-variable matrix G is
obtained by using the formula (1.3) and can be employed for
converting the transmission signal.
[0106] Note that the first setting of the change-of-variable matrix
G, in the case of adopting, e.g., the TDD method employing the same
frequency and so on, can be done by the transmitter estimating the
transmission path between each receiving antenna of each receiver
and the transmitting antenna of the transmitter.
[0107] In short, the orthogonal known signals are transmitted from
the respective receiving antennas of the receiver and received by
the transmitting antenna of the transmitter, thereby estimating the
transmission path matrix H. If the TDD method is adopted,
bidirectional paths can be deemed as the same transmission paths,
and hence there are obtained the estimated transmission path matrix
H and the change-of-variable matrix G as the proper transmission
characteristic information F (e.g., as shown in FIG. 3, other
elements excluding a part of the elements (which is set to, e.g.,
1) are set to 0), and these matrixes can be employed for the
conversion of the transmission signals. On this occasion, as a
matter of course, it is desirable that the receiver configuration
information be also employed.
[0108] ..Generation of Change-of-Variable Matrix G Suited to
Configuration of Receiver..
[0109] As described above, the receiver configuration information
(for example, the number of antennas) is fed back to the
transmitter 11, whereby the variable changing unit 111 of the
transmitter 11 obtains the change-of-variable matrix G
corresponding to the receiver configuration information.
[0110] Given hereunder is an example of the operation of the
variable changing unit 111 of the transmitter 11 that obtains the
change-of-variable matrix G in accordance with, herein, the
demodulation method of the receiver in the receiver configuration
information (Categorization 2) described above. To be specific, the
operation of the transmitter in the case of differing from the
configuration of the receiver in the MIMO communication system in
the embodiment shown in FIGS. 1 and 2, will be described as
below.
[0111] .First Configuration.
[0112] In the MIMO communication system in the embodiment, the
receiver 23 holding the two antennas has the configuration that the
signal separating/data detecting unit 233 has the signal separating
function. The first configuration, which will be described herein,
is a case of being constructed of the receiver capable of
demodulating only the signals received in the form of being
separated so as not to be synthesized with the radio signals
transmitted from other antennas.
[0113] In this case, the transmission characteristic
information/receiver configuration information generating unit 234
of the receiver 23 organizes the receiver configuration information
so as to contain a piece of category information showing that the
receiver has the demodulation method as described above. Then, the
variable changing unit 111 obtains, based on the category
information, a change-of-variable matrix G that will be given as
follows. Subsequently, the variable changing unit 111 multiplies
the transmission data by this change-of-variable matrix G and
transmits the data, and each receiver may detect the data per
antenna.
[0114] The transmitter configuring the MIMO communication system
according to the present invention can correspond to the case where
such a simple receiver exists.
F = HG = [ f 11 0 0 0 0 f 22 0 0 0 0 f 33 0 0 0 0 f 44 ] ( 1.5 )
##EQU00004##
[0115] .Second Configuration.
[0116] A second configuration is a case in which there is one
single receiver holding four pieces of antennas, and the receiver
has the following demodulation method. The receiver in the second
configuration enables simple modulation in the way that the
receiver provides predetermined order per antenna, the data are
detected with respect to the signals received by the antennas in
this order, and a result of the data detection in the earlier order
is utilized on the occasion of the data detection.
[0117] In this case, the transmission characteristic
information/receiver configuration information generating unit 234
of the receiver 23 organizes the receiver configuration information
so as to contain a piece of information showing that the
demodulation method described above is adopted. Then, the variable
changing unit 111 obtains, based on this information, the
change-of-variable matrix G shown in the formula (1.6).
Subsequently, the variable changing unit 111 multiplies the
transmission data by this change-of-variable matrix G, and
transmits the data, whereby the receiver can demodulate the data
received from the antennas in the predetermined order.
[0118] Namely, in this example, the signal received by the
receiving antenna corresponding to the first row in the following
matrix or a transmission signal x.sub.1 is obtained. Next, a
transmission signal x.sub.2 is obtained by use of a signal received
by the receiving antenna corresponding to the second row in the
following matrix and the transmission signal x.sub.1, sequentially,
and results that are thus acquired in the order from the top are
utilized at the receiving time, thereby making it possible to
easily regenerate the transmission signals.
[0119] Note that the respective elements such as f.sub.11, etc. can
be estimated by use of the known signals, and it follows that
unknown transmission signals are easily obtained while giving a
degree of freedom to some extent to the elements of the matrix
F.
F = HG = [ f 11 0 0 0 f 21 f 22 0 0 f 31 f 32 f 33 0 f 41 f 42 f 43
f 44 ] ( 1.6 ) ##EQU00005##
[0120] .Third Configuration.
[0121] A third configuration is a case of the receiver capable of
demodulating the signals obtained by synthesizing the radio signals
transmitted from the transmitter with the radio signals transmitted
from other antenna possessed by this transmitter and received.
[0122] Even in the case of this receiver having the highest-level
data detecting function, the variable changing unit 111 obtains the
change-of-variable matrix G shown in the formula (1.7) by which a
transmission capacity can be maximized without any restraint
condition. Namely, the variable changing unit 111 sets the elements
fixed to "0" less than a half, ideally, to zero (0).
F = HG = [ f 11 f 12 f 13 f 14 f 21 f 22 f 23 f 24 f 31 f 32 f 33 f
34 f 41 f 42 f 43 f 44 ] ( 1.7 ) ##EQU00006##
Modified Example 1
[0123] In the MIMO communication system in the embodiment, the
transmitter executes the signal processing based on the
configuration of the receiver, however, the transmission path
matrix H as the transmission path information is employed on the
occasion of effecting the signal processing.
[0124] Namely, the transmitter side knows the transmission path
information, and hence the signal processing may be executed to
perform the high-speed data transmission on the transmission path
exhibiting a high quality of the transmission path, and to perform
the low-speed data transmission on the low-quality transmission
path (which corresponds to a transmission rate control unit
according to the present invention).
[0125] With this contrivance, the high-speed data transmission can
be performed as a whole of the system.
Modified Example 2
[0126] Further, the higher-speed data transmission may additionally
be conducted on the high-quality transmission path by increasing
the electric power for transmission, and the lower-speed data
transmission may be effected on the low-quality transmission path
by decreasing the electric power for transmission. With this
contrivance, the higher-speed data transmission can be done as a
total system because of getting approximate to the power control
based on Water Filling Principal. In this case, for example, when
constructed of the simple receiver as in the aforementioned (first
configuration), the transmitter may execute processing as
below.
[0127] The transmitter at first effects weighting in a way that
multiplies the change-of-variable matrix G given in the formula
(1.8) with respect to the transmission path matrix H by a weighting
coefficient w.sub.i so that an electric power weight P.sub.i with
respect to a diagonal section a.sub.i of the matrix A shown in the
formula (1.9) meets the formula (1.10). Herein, H represents
Conjugate Transpose, max (x, y) indicates that the larger of x and
y is selected, and .lamda. and .sigma.2 are constants determined
from average transmission power and noise power. The transmitter
multiplies the weighted signal by the change-of-variable matrix G
in the same way as in the embodiment, and transmits this
signal.
G = H - 1 ( 1.8 ) A = G H G ( 1.9 ) P i = max ( 0 , .lamda. a i -
.sigma. 2 ) ( 1.10 ) w i = P i ( 1.11 ) C i .varies. log ( 1 + w i
2 .sigma. 2 ) ( 1.12 ) ##EQU00007##
[0128] The transmitter may further effect rate matching upon each
symbol data series so as to gain a transmission rate proportional
to C.sub.i shown in the formula (1.12), and may thus transmit the
symbol data series.
[0129] FIG. 4 is a diagram showing an example of the transmitter
that executes power weighting corresponding to the transmission
path information and transmission rate control. The transmitter
shown in FIG. 4 puts a weight w.sub.1-w.sub.4 on the transmission
signal controlled to have a transmission rate of a transmission
rate C.sub.1-C.sub.4 for every transmitting antenna.
[0130] With this contrivance, the high-speed data transmission can
be done as the total system.
Modified Example 3
[0131] The system described so far has the configuration in which
the transmission side can know the transmission path information
and may also take a configuration in which the transmission side
can not know the transmission path information. In this case also,
it is possible to adopt the transmission method corresponding to
the receiver by notifying the transmission side of the receiver
configuration information.
[0132] FIGS. 5(A) and 5(B) show the MIMO communication system in
the case of a configuration in which the transmitter can not know
the transmission path information. In FIG. 5(A), the transmitter is
notified of the number of antennas held by the receiver and thereby
transmits the signals from one arbitrary transmitting antenna to
the receiver having the single antenna. Similarly, in FIG. 5(B),
the signals are transmitted from the two transmitting antennas to
the receiver having the two antennas.
[0133] Moreover, there are categorized, according to not the number
of antennas but a type of receiver, into a case of being a MLD
receiver and a case of being an MMSE (Minimum Mean Square Error)
receiver, and the transmitter may control the transmission rate.
FIG. 6(A) shows the case of having the MLD receiver, and FIG. 6(B)
shows the example of having the MMSE receiver. The transmitter in
this case controls the transmission rate to perform the high-speed
data transmission to the MLD receiver exhibiting a high wireless
characteristic and to perform the low-speed data transmission to
the MMSE receiver inferior in characteristic to the MLD
receiver.
[0134] With this contrivance, even in the case where the
transmitter has such a configuration as to be unrecognizable of the
transmission path information, it is possible to conduct the
transmission corresponding to the configuration of the
receiver.
[0135] <Others>
[0136] The disclosures of Japanese patent application
No.JP2005-006352, filed on Jan. 13, 2005 including the
specification, drawings and abstract are incorporated herein by
reference.
* * * * *