U.S. patent application number 11/493821 was filed with the patent office on 2007-04-12 for wireless data communication system, wireless data communication method and communication apparatus.
Invention is credited to Shigenori Hayase, Tomoaki Ishifuji, Shinji Murai.
Application Number | 20070081450 11/493821 |
Document ID | / |
Family ID | 37910990 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070081450 |
Kind Code |
A1 |
Hayase; Shigenori ; et
al. |
April 12, 2007 |
WIRELESS DATA COMMUNICATION SYSTEM, WIRELESS DATA COMMUNICATION
METHOD AND COMMUNICATION APPARATUS
Abstract
A wireless communication system has no limitation in the number
of AP antennas and UT antennas, and determines the
parallel-communication data units to be a maximum value of MIMO
communication, such that it provides a MIMO-SDMA wireless data
communication system having superior transmission characteristics.
The MIMO-SDMA wireless data communication system includes a single
AP (Access Point) and U UTs (User Terminals) communicating with the
AP using the same frequency signal at the same time. The UT
includes the SDMA reception (Rx) processor, and synthesizes Rx
signals of antennas, such that it controls the number of Rx data
units. By the control of the number of Rx data units, the
communication system controls the number of parallel-communication
data units to be equal to a maximum value capable of being
implemented by the MIMO-SDMA wireless data communication. The AP
informs the UTs of a coefficient matrix required for the SDMA Rx
process, prior to transmitting actual data.
Inventors: |
Hayase; Shigenori; (Kodaira,
JP) ; Murai; Shinji; (Hachioji, JP) ;
Ishifuji; Tomoaki; (Tokyo, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
37910990 |
Appl. No.: |
11/493821 |
Filed: |
July 27, 2006 |
Current U.S.
Class: |
370/210 |
Current CPC
Class: |
H04B 7/0617
20130101 |
Class at
Publication: |
370/210 |
International
Class: |
H04J 11/00 20060101
H04J011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 12, 2005 |
JP |
2005-297624 |
Claims
1. A wireless data communication system comprising: a single
transmitter; and a plurality of receivers for communicating with
the single transmitter using the same frequency signal at the same
time, wherein the transmitter includes: a plurality of transmission
(Tx) antennas; and a Space Division Multiple Access (SDMA)
transmission (Tx) processor for multiplying each of signals
transmitted to the receivers by a complex coefficient, distributing
the multiplied result to the Tx antennas, adding the signals
distributed to the same Tx antennas, and transmitting the added
result to each Tx antenna, wherein each of the receivers includes:
at least one reception (Rx) antenna; and an SDMA reception (Rx)
processor for multiplying signals received via the Rx antennas by a
complex coefficient, adding the multiplied result to the received
signals, and creating specific signals equal to or less than the
number of Rx antennas, and wherein an SDMA-control signal process
of the SDMA Tx processor, transmission characteristics of space
propagation signals, an SDMA-control signal process of the SDMA Rx
processor are synthesized with each other, such that signals
transmitted to the remaining receivers other than a desired
receiver are suppressed.
2. The wireless data communication system according to claim 1,
wherein the SDMA Rx processor calculates a Singular Value
Decomposition (SVD) H=U.SIGMA.V.sup.H (where superscript H is a
conjugate transpose) of a signal transfer matrix (H) between the
transmitter and the remaining receivers, and determines the complex
coefficient using the calculated SVD, such that the complex
coefficient acts as a complex coefficient for use in the SDMA Rx
processor by a column vector of a synthetic matrix U.sup.H.
3. The wireless data communication system according to claim 2,
wherein the transmitter, if the number of the transmitter's
antennas is higher than the number of the receivers' antennas,
simultaneously parallel-transmits different data units, the number
of which is equal to the number of the transmitter's antennas.
4. The wireless data communication system according to claim 3,
wherein the number of parallel-transmission data units applied to
the receivers is changed according to requests of the
receivers.
5. A wireless data communication method for use in a wireless data
communication system, which includes: a single transmitter; and a
plurality of receivers for communicating with the single
transmitter using the same frequency signal at the same time,
wherein the transmitter includes: a plurality of transmission (Tx)
antennas; and a Space Division Multiple Access (SDMA) transmission
(Tx) processor for multiplying each of signals transmitted to the
receivers by a complex coefficient, distributing the multiplied
result to the Tx antennas, adding the signals distributed to the
same Tx antennas, and transmitting the added result to each Tx
antenna, and wherein each of the receivers includes: at least one
reception (Rx) antenna: and an SDMA reception (Rx) processor for
multiplying signals received via the Rx antennas by a complex
coefficient, adding the multiplied result to the received signals,
and creating specific signals equal to or less than the number of
Rx antennas, the wireless data communication method comprising the
steps of: estimating a transfer matrix of signals between the
transmitter and the receivers by a training signal transmitted from
either the transmitter or the receivers; determining, by the
transmitter, the number of parallel transmission data units
simultaneously applied to the receivers, and the complex
coefficient of the SDMA Rx processor; determining, by the
transmitter, the complex coefficient of the SDMA Tx processor;
transmitting, by the transmitter, the complex coefficient of the
SDMA Rx processor to the receivers, and informing the receivers of
the complex coefficient of the SDMA Rx processor; outputting, by
the transmitter, transmission (Tx) signals processed by the SDMA Tx
processor; and controlling, by the receivers, signals received in
Rx antennas to be signal-processed by the SDMA Rx processor,
wherein the communication between the transmitter and the receivers
is established.
6. A communication apparatus composed of a plurality of
communication units to communicate with a single transmitter using
the same frequency signal at the same time, the communication
apparatus comprising: at least one reception (Rx) antenna; and a
Space Division Multiple Access (SDMA) reception (Rx) processor for
multiplying signals received via the Rx antennas by a complex
coefficient, adding the multiplied result to the received signals,
and creating specific signals equal to or less than the number of
Rx antennas, wherein an SDMA-control signal process of the
transmitter, transmission characteristics of space propagation
signals, and an SDMA-control signal process of the SDMA Rx
processor are synthesized with each other, such that signals
transmitted to the remaining communication units other than a
desired communication unit are suppressed.
7. The communication apparatus according to claim 6, further
comprising: a plurality of transmission (Tx) antennas; and a Space
Division Multiple Access (SDMA) transmission (Tx) processor for
multiplying each of signals transmitted to the communication units
(i.e., receivers) by a complex coefficient, distributing the
multiplied result to the Tx antennas, adding the signals
distributed to the same Tx antennas, and transmitting the added
result to each Tx antenna.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese
application JP 2005-297624 filed on Oct. 12, 2005, the content of
which is hereby incorporated by reference into this
application.
FIELD OF THE INVENTION
[0002] The present invention relates to a wireless data
communication technique, and more particularly to a wireless data
communication system based on a Space Division Multiple Access
(SDMA) scheme, a wireless data communication method based on the
SDMA scheme, and effective techniques associated with the system
and method.
BACKGROUND OF THE INVENTION
[0003] A plurality of conventional wireless data communication
technologies are as follows.
[0004] For example, many developers have conducted intensive
research into a MIMO (Multiple-Input Multiple-Output) technique for
increasing spectral efficiency (i.e., an amount of communication
information for each unit time and each unit frequency) in a
wireless communication field.
[0005] For example, there is almost no doubt that the IEEE 802.11
standard for WLAN (Wireless LAN) standardization adopts the MIMO
technology in a task group (n).
[0006] Also, many developers are conducting research into a method
for applying the MIMO technology to the fourth-generation mobile
communication system to increase a transmission rate (also called a
transfer rate).
[0007] The above-mentioned MIMO technology begins to extend/apply
to the SDMA technology. The SDMA technology allows a single AP
(Access Point) to simultaneously communicate with a plurality of
UTs (User Terminals) using the same frequency signal.
[0008] Representative examples of the above-mentioned MIMO-SDMA
technology are United States Patent Publication No. 2004-0252632A1,
and a Japanese reference document entitled "Method for calculating
MIMO/SDMA downlink weight using Rx antenna selection" published in
The Institute of Electronics, Information and Communication
Engineers Book B-5-230, filed by Nishimura Tosihiko, Takatori
Yasusi, Ogane Takeo, Ogawa Yasutaka, and Osa Keizo.
SUMMARY OF THE INVENTION
[0009] The above-mentioned conventional wireless data communication
technologies have the following characteristics.
[0010] Firstly, the principles of the above-mentioned conventional
MIMO-SDMA technology will hereinafter be described in detail.
[0011] FIG. 1 is a block diagram illustrating the principles of the
conventional MIMO-SDMA technology. Referring to FIG. 1, APs (Access
Points) are located at the left side, and UTs (User Terminals) are
located at the right side.
[0012] In this example of FIG. 1, a single AP communicates with U
UTs (i.e., U number of UTs) using the MIMO-SDMA technology, such
that data is transmitted from the AP to the UTs.
[0013] Transmission data (TxData) (1 to u) transmitted to each UT
is processed by a MIMO transmission processor (MIMO TxProcess) 101
(101-1 to 101-u). Thereafter, data is distributed to a transmission
(Tx) antenna 103 composed of M Tx antennas (103-1 to 103-M) by a
SDMA transmission processor (SDMA TxProcess) 102. Output data of
the Tx antenna 103 propagates through space.
[0014] The UT-i (i=1 to u) receives the output data of the Tx
antenna 103 via Ni reception (Rx) antennas 104 (104-1-1 to
104-1-N.sub.1, 104-u-1 to 104-u-N.sub.u). The MIMO reception (Rx)
processor (MIMO RxProcess) 105 (105-1-1 to 105-u) recovers data,
such that it acquires Rx data (RxData) (1 to u).
[0015] The signal transmission characteristic of space propagation
between the Tx antenna 103 and the Rx antenna (104-i) of the UT-i
may be denoted by the following transfer matrix H.sub.i as denoted
by Equation 1: y.sub.i=H.sub.ix [Equation 1]
[0016] where, x is a transmission (Tx) signal vector x=(x(1),x(2),
. . . ,x(M)).sup.T, x(1) to x(M) are complex amplitudes of wave
signals generated from the M transmission antennas 103, y.sub.i is
a reception (Rx) signal vector y.sub.i=(y.sub.i(1), . . .
,y.sub.i(N.sub.i)).sup.T, and y.sub.i(1) to y.sub.i(N.sub.i) are
complex amplitudes of wave signals received in the N.sub.i Rx
antennas 104-i.
[0017] In the SDMA technology, signals are simultaneously
transmitted from the AP to a plurality of UTs, such that the Rx
antennas 104 may unexpectedly receive desired signals and undesired
signals at the same time, resulting in the occurrence of mixed Rx
signals composed of the desired and undesired signals.
[0018] In order to solve the above-mentioned problem, the
above-mentioned United States Patent Publication No. 2004-0252632A1
allows the SDMA Tx processor (SDMA TxProcess) 102 to distribute
desired signals to the Tx antennas 103, and controls a plurality of
wave signals generated from the Tx antennas 103 to interfere with
the Rx antennas 104 operation, such that it can remove unnecessary
signals from the signals received in the Rx antennas 104.
[0019] For example, the Tx data (i) from the AP to the UT-i will
hereinafter be described. The Tx data (i) is unnecessary for UTs
other than the UT-i, such that it is preferable that no signal
arrives at the Rx antennas 104 of the UTs other than the UT-i.
[0020] For this purpose, there is a need to calculate a specific
value (x) for acquiring y.sub.j=0 in association with all j values
(where j=any one of values other than "i").
[0021] In this case, y.sub.<i> and H.sub.<i> can be
represented by the following Equation 2: y < i > = ( y 1 M y
u ) .rarw. y i .times. .times. deleted , H < i > = ( H 1 M H
u ) .rarw. H i .times. .times. deleted [ Equation .times. .times. 2
] ##EQU1##
[0022] Under the above-mentioned situation, a necessary condition
can be represented by the following Equation 3:
y.sub.<i>=H.sub.<i>x=0 [Equation 3]
[0023] where, x is a kernel of H.sub.<i> in a linear algebra,
and is acquired by L(i) unit vectors orthogonal to each other. In
this case, the number L(i) of the unit vectors can be represented
by the following Equation 4: L .function. ( i ) = M - j = 1 j
.noteq. i u .times. N j [ Equation .times. .times. 4 ] ##EQU2##
[0024] The unit vectors are hereinafter referred to as SDMA control
vectors, and are denoted by A.sub.i, 1, . . . , A.sub.i, L(i).
[0025] Therefore, if the Tx data (s) is distributed to the Tx
antennas 103 according to a predetermined Equation "x=sA", the
signal is not applied to the Rx antennas 104 other than the UT-i.
There are a plurality of SDMA control vectors, such that it is
possible to perform parallel transmission of L(i) data.
[0026] The above-mentioned process is applied to Tx data toward all
the UTs. If the values of signals allocated to individual Tx
antennas 103 are added, and the added signals are outputted, the
SDMA communication can be made available.
[0027] FIG. 2 is a detailed block diagram illustrating the SDMA
transmission processor (SDMA TxProcess) 102.
[0028] Referring to FIG. 2, a multiplier 106 multiplies Tx data by
the SDMA control vector, such that it distributes the multiplied Tx
data to M Tx antennas 103. The signal distributed to the same Tx
antenna is added by an adder 107, such that the added signal is
generated from the Tx antennas 103.
[0029] Under the above situation, if the SDMA control matrix is
defined by Ai=(A.sub.i, 1, . . . , A.sub.i, L(i)), a transfer
matrix of the Tx data (i) from an input terminal of the SDMA
transmission processor (SDMA TxProcess) 102 to the Rx antenna 104-i
is represented by H.sub.iA.sub.i. Based on the transfer matrix
"H.sub.iA.sub.i", it is possible to control the MIMO Tx process and
the MIMO Rx process between a single AP and a single UT, such that
the SDMA communication from the single AP to the u number of UTs
can be made available. The above-mentioned scheme is hereinafter
referred to as a "null-steering" scheme.
[0030] However, the above-mentioned null-steering scheme can be
made available under the condition of the following Equation 5: L
.function. ( i ) = M - j = 1 j .noteq. i u .times. N j > 0
.times. .A-inverted. i [ Equation .times. .times. 5 ] ##EQU3##
[0031] For example, if the number of AP antennas is 2 (M=2), the
number of UTs is 2 (u=2), and the number of antennas is 2
(N.sub.1=2 and N.sub.2=2), the above-mentioned Equation 5 is not
satisfied, such that it is impossible to apply the null-steering
scheme to the above-mentioned Equation 5.
[0032] Then, the number of data units capable of being transmitted
in parallel to the UT-i will hereinafter be described. The number
of data units capable of being transmitted to the UT-i is L(i),
such that the sum of the Li data units can be calculated by the
following Equation 6: i = 1 u .times. L .function. ( i ) = u
.times. .times. M - ( u - 1 ) .times. j = 1 u .times. N j [
Equation .times. .times. 6 ] ##EQU4##
[0033] In the meantime, provided that the MIMO-SDMA wireless data
communication system is defined by MIMO communication between the
AP having M antennas and the UT having .SIGMA.N.sub.i antennas, it
can be recognized that the maximum number of data units capable of
being transmitted in parallel is min (M, .SIGMA.N.sub.i). Under
this situation, the following Equation 7 can be assumed as follows:
M < j = 1 u .times. N j [ Equation .times. .times. 7 ]
##EQU5##
[0034] In this case, the maximum number of data units capable of
being transmitted in parallel is M.
[0035] In the meantime, in order to compare the M data units with
the number of parallel-communication data units of the
null-steering scheme, the M data units are subtracted from the
number of parallel-communication data units of the null-steering
scheme shown in the above Equation 6, such that the following
Equation 8 can be acquired as follows: i = 1 u .times. L .function.
( i ) - M = ( u - 1 ) .times. ( M - j = 1 u .times. N j ) < 0 i
= 1 u .times. L .function. ( i ) < M [ Equation .times. .times.
8 ] ##EQU6##
[0036] Therefore, it can be recognized that the number of
parallel-communication data units of the null-steering scheme is
less than the maximum value.
[0037] In other words, if the above Equation 7 is established
although the above-mentioned null-steering scheme is made available
by the completion of the above Equation 5 (i.e., if the number of
AP antennas is less than the total number of UTs), it is impossible
to maximally acquire the MIMO performance.
[0038] A representative method for acquiring the maximum number of
the parallel-communication data units when the above-mentioned
Equation 7 is established regardless of the situation of the
above-mentioned Equation 5 has been disclosed in the
above-mentioned Japanese reference document.
[0039] The above-mentioned problem occurs when many UT antennas are
used. Therefore, if all the UT antennas are not used, and the
antenna for use in the UT to establish Equation (M=.SIGMA.N.sub.i),
the null-steering scheme capable of providing the maximum number of
parallel-communication data units can be made available. The
above-mentioned operation is hereinafter referred to as an
"antenna-selection null-steering" scheme.
[0040] However, the above-mentioned antenna-selection null-steering
(also called "null-steering with antenna selection") scheme does
not use a few antennas from among all UT antennas. As a result,
although data is received in the above-mentioned unused antennas,
the received data is unavoidably discarded, and power consumption
encountered when the signal is received in the unused antennas is
unnecessarily wasted.
[0041] Therefore, the present invention has been made in view of
the above problems, and it is an object of the invention to provide
a wireless data communication technique for implementing MIMO-SDMA
communication even if the above Equation 5 is not satisfied, and
effectively employing signals received in all Rx antennas under the
situation of the above Equation 7, thereby improving a performance
of the MIMO-SDMA communication.
[0042] Additional advantages, objects, and features of the
invention will be set forth in part in the description which
follows and in part will become apparent to those having ordinary
skill in the art upon examination of the following or may be
learned from practice of the invention. The objectives and other
advantages of the invention may be realized and attained by the
structure particularly pointed out in the written description and
claims hereof as well as the appended drawings.
[0043] In accordance with an aspect of the present invention, the
above and other objects can be accomplished by the provision of a
MIMO-SDMA wireless data communication system comprising: a single
AP acting as a transmitter and U UTs acting as receivers
communicating with the single AP using the same frequency signal at
the same time.
[0044] The AP includes a Tx antennas, and the i-th UT (i=1 to u)
has N.sub.i Rx antennas. The AP includes an SDMA Tx processor. The
UT includes an SDMA Rx processor, and the present invention is
characterized in that the UT conducts the SDMA Rx process.
[0045] In the above-mentioned configuration, the signal process of
the SDMA Tx processor, transmission characteristics of space
propagation signals, the signal process of the SDMA Rx processor
are synthesized with each other, such that signals transmitted to
the remaining receivers other than a desired receiver are
suppressed.
[0046] In other words, if the condition of Equation 5 is not
provided, the SDMA Rx processor of the UT synthesizes signals
received in Rx antennas, controls the number of synthesized signals
to be less than the number of Rx antennas, such that the number of
Rx antennas seems to be less than the actual number of the same.
Therefore, the MIMO-SDMA communication based on the null-steering
scheme is implemented.
[0047] In accordance with another aspect of the present invention,
there is provided a wireless data communication method comprising
the steps of: estimating a transfer matrix of signals between the
AP and the UTs by a training signal transmitted from either the AP
or the UTs; determining, by the AP, the number of parallel
transmission data units simultaneously applied to the UTs, and the
complex coefficient of the SDMA Rx processor; determining, by the
AP, the complex coefficient of the SDMA Tx processor; transmitting,
by the AP, the complex coefficient of the SDMA Rx processor to the
UTs, and informing the UTs of the complex coefficient of the SDMA
Rx processor; outputting, by the AP, transmission (Tx) signals
processed by the SDMA Tx processor; and controlling, by the UTs,
signals received in Rx antennas to be signal-processed by the SDMA
Rx processor, whereby the communication between the AP and the UTs
is established.
[0048] The present invention is characterized in that a
communication apparatus includes an SDMA Rx processor in each UT
operated in the above-mentioned wireless data communication
system.
[0049] The above-mentioned system and method have the following
effects.
[0050] The present invention has no limitation in the number of AP
antennas and UT antennas, and determines the parallel-communication
data units to be a maximum value of MIMO communication, such that
it provides a MIMO-SDMA wireless data communication system having
superior transmission characteristics.
[0051] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory and are intended to provide
further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0053] FIG. 1 is a block diagram illustrating the principles of a
conventional MIMO-SDMA technology;
[0054] FIG. 2 is a detailed block diagram illustrating an SDMA
transmission processor (SDMA TxProcess);
[0055] FIG. 3 is a block diagram illustrating a wireless data
communication system according to a first preferred embodiment of
the present invention;
[0056] FIG. 4 is a graph illustrating the comparison result between
a conventional scheme and the inventive scheme in association with
characteristics of a SNR (Signal-to-Noise Ratio) to transmission
capacity;
[0057] FIG. 5 is a flow chart illustrating a communication sequence
of a wireless data communication system according to a second
preferred embodiment of the present invention;
[0058] FIG. 6 is a flow chart illustrating a communication sequence
of a wireless data communication system according to a third
preferred embodiment of the present invention;
[0059] FIG. 7 is a block diagram illustrating a transceiving unit
acting as a wireless data communication system according to a
fourth preferred embodiment of the present invention; and
[0060] FIG. 8 is a conceptual diagram illustrating a preferred
application for use in a wireless data communication system
according to a fifth preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0061] Now, preferred embodiments of the present invention will be
described in detail with reference to the annexed drawings. In the
drawings, the same or similar elements are denoted by the same
reference numerals even though they are depicted in different
drawings. In the following description, a detailed description of
known functions and configurations incorporated herein will be
omitted when it may make the subject matter of the present
invention rather unclear.
First Preferred Embodiment
[0062] FIG. 3 is a block diagram illustrating a wireless data
communication system according to a first preferred embodiment of
the present invention. The wireless data communication system of
FIG. 3 is provided to explain the MIMO-SDMA communication according
to the present invention, such that the simplified configurations
of actual AP and UT are shown in FIG. 3.
[0063] Referring to FIG. 3, the wireless data communication system
includes the AP and the UT.
[0064] The AP includes a MIMO transmission processor (MIMO
TxProcess) 101 (101-1 to 101-u), an SDMA transmission processor
(SDMA TxProcess) 102, and a Tx antenna 103 composed of M Tx
antennas (103-1 to 103-M), in association with Tx data (TxData) (1
to u).
[0065] The UT includes an Rx antenna 104 (104-1-1 to 104-1-N.sub.i,
. . . , 104-u-1 to 104-u-N.sub.u), an SDMA Rx processor (SDMA
RxProcess) 108 (108-1 to 109-u), and the MIMO Rx processor 105
(105-1 to 105-u), in association with Rx data (RxData) (1 to
u).
[0066] In FIG. 3, the same or similar elements are denoted by the
same reference numerals as FIG. 1 even though they are depicted in
different drawings, such that their detailed description will
herein be omitted for the convenience of description, and only new
elements depicted in FIG. 3 will hereinafter be described in
detail.
[0067] Specifically, the wireless data communication system
according to the first preferred embodiment of the present
invention includes a single AP (i.e., transmitter) and a plurality
of UTs (i.e., receivers), and controls the single AP to communicate
with the UTs using the same frequency wave signals at the same
time.
[0068] The AP includes a plurality of Tx antennas 103 and an SDMA
Tx processor (SDMA TxProcess) 102, etc. The SDMA Tx processor (SDMA
TxProcess) 102 multiplies each of signals transmitted to the UTs by
a complex coefficient, distributes the multiplied result to the Tx
antennas 103, adds the signals distributed to the same Tx antennas
103, and transmits the added result to each Tx antenna 103.
[0069] The UT includes at least one Rx antenna 104 and an SDMA Rx
processor (SDMA RxProcess) 108. The SDMA Rx processor (SDMA
RxProcess) 108 multiplies signals received via the Rx antennas 104
by a complex coefficient, and adds the multiplied result to the
received signals, such that it creates signals, the number of which
is equal to or less than the number of Rx antennas 104.
[0070] In this configuration of FIG. 3, the signal process of the
SDMA TxProcess 102, transmission characteristics of space
propagation signals, and the signal process of the SDMA RxProcess
108 are mixed or synthesized with each other, such that signals
transmitted to UTs other than a desired UT are suppressed.
[0071] As can be seen from FIG. 3, the AP is located at the left
side, and the UT is located at the right side. A single Ap
communicates with u UTs according to the MIMO-SDMA scheme, such
that data is transmitted from the AP to the u UTs.
[0072] Tx data (1 to u) transmitted to each UT is processed by: the
MIMO Tx processor (MIMO TxProcess) 101. Thereafter, data is
distributed to the Tx antenna 103 composed of M Tx antennas by the
SDMA Tx processor (SDMA TxProcess) 102. Output data of the Tx
antenna 103 propagates through space.
[0073] The UT-i (i=1 to u) receives the output data of the Tx
antenna 103 via Ni Rx antennas 104, such that the SDMA Rx processor
(SDMA RxProcess) 108 synthesizes the received signals. The MIMO Rx
processor (MIMO RxProcess) 105 recovers data, such that it acquires
Rx data (1 to u).
[0074] The signal transmission characteristic of space propagation
between the Tx antenna 103 and the Rx antenna (104-i) of the UT-i
may be denoted by the transfer matrix H.sub.i denoted by the
above-mentioned Equation 1.
[0075] In the first preferred embodiment of the present invention,
if the condition of the above-mentioned Equation 7 is not provided,
the SDMA Rx processor (SDMA RxProcess) 108 performs no process, and
the wireless data communication based on the MIMO-SDMA scheme is
executed by a general null-steering scheme.
[0076] If the condition of the above-mentioned Equation 7 is
provided, the number (N.sub.i) of Rx antennas is replaced with the
number of parallel Rx data units of each UT, such that the number
of parallel Rx data units is established to satisfy a predetermined
condition denoted by M=.SIGMA.N.sub.i. In this case, it should be
noted that the number of parallel Rx data units cannot be higher
than the number of original antennas of each UT.
[0077] Under the above-mentioned situation, the number of parallel
Rx data units of each UT can be freely determined. For example, a
large number of parallel Rx data units can be assigned to the UT
requiring a high throughput.
[0078] Then, a synthetic coefficient matrix (B.sub.i) acquired when
the Rx signals (y.sub.i=(y.sub.i(1), . . . ,
y.sub.i(N.sub.i)).sup.T of the Rx antennas 104 are synthesized by
the SDMA Rx processor (SDMA RxProcess) 108 is determined. A
Singular Value Decomposition (SVD) of the transfer matrix H.sub.i
loaded on Tx data (i) toward the UT-i can be represented by the
following Equation 9: H.sub.i=U.sub.i.SIGMA..sub.iV.sub.i.sup.H
[Equation 9]
[0079] where superscript H is indicative of a conjugate transpose,
U.sub.i.sup.H is indicative of a synthetic matrix in association
with the MIMO Rx process, such that a column vector is denoted by a
synthetic coefficient corresponding to a unique mode.
[0080] The higher the singular value of the unique mode, the higher
the gain and diversity effects, such that the column vectors, the
number of which is equal to the number of parallel Rx data units of
the UT-i, are sequentially removed from a first column vector of
the synthetic matrix U.sub.i.sup.H.
[0081] Therefore, B.sub.i is a matrix acquired when predetermined
data units corresponding to the number of parallel Rx data units
are deducted from an upper part of the synthetic matrix
U.sub.i.sup.H. As a result, a transfer matrix between the Tx
antennas 103 of the AP and output terminals of the SDMA Rx
processor (SDMA RxProcess) can be represented by B.sub.iH.sub.i. If
the null-steering scheme is executed by considering the transfer
matrix B.sub.iH.sub.i to be a new transfer matrix H.sub.i, the SDMA
can be implemented such that the number of parallel Tx data units
is equal to the maximum number of parallel data units of the
MIMO.
[0082] In order to describe the above-mentioned effects in detail,
an exemplary case in which the number of AP antennas is 4, the
number of UTs is 2, and the number of antennas of each UT is 3 is
shown in FIG. 4 illustrating the comparison result of
characteristics between an SNR and transmission capacity.
[0083] FIG. 4 is a graph illustrating the comparison result between
a conventional scheme and the inventive scheme in association with
characteristics of a SNR (Signal-to-Noise Ratio) to transmission
capacity.
[0084] The above-mentioned situation of FIG. 4 satisfies the
above-mentioned Equation 5, such that the null-steering scheme is
made available. However, the above-mentioned situation of FIG. 4
corresponds to the condition of the above-mentioned Equation 7,
such that the number of parallel Tx data units does not reach the
maximum value of a MIMO performance (i.e., a MIMO throughput).
[0085] As can be seen from FIG. 4, a horizontal axis of the graph
is indicative of an SNR configured in the form of dB units, and a
vertical axis of the graph is indicative of transmission (Tx)
capacity calculated by the Shannon's Capacity Theorem.
[0086] In FIG. 4, (a) is capacity of a TDMA (Time Division Multiple
Access) alternately communicating with two UTs using a time
division method, (b) is capacity of the null-steering case, (c) is
capacity of the antenna-selection null-steering case (depicted by
"Null-steering with antenna selection" in FIG. 4), and (d) is
capacity of the present invention.
[0087] The above-mentioned antenna-selection null-steering case and
the present invention assume that the number of parallel Tx data
units of each UT (UT-1 or UT-2) is set to "2".
[0088] The MIMO performance is not maximally elicited in the
null-steering case, such that the capacity does not reach the TDMA
capacity.
[0089] Conventionally, if the SNR value is high in the
antenna-selection null-steering scheme, capacity of the
antenna-selection null-steering scheme is higher than that of the
TDMA scheme. Otherwise, if the SNR value is low in the
antenna-selection null-steering scheme, capacity of the
antenna-selection null-steering scheme is less than that of the
TDMA scheme.
[0090] However, compared with the above-mentioned conventional
scheme, the inventive scheme according to the present invention can
acquire capacity higher than those of other schemes, irrespective
of SNR values. In this way, it can be recognized that the inventive
scheme according to the present invention acquires transmission
characteristics superior to those of the conventional scheme, such
that it is superior to the conventional scheme.
[0091] As described above, according to the above-mentioned
preferred embodiment of the present invention, the MIMO-SDMA scheme
is implemented even when the condition of Equation 5 is not
satisfied.
[0092] Although the condition of Equation 7 is provided, the
present invention can effectively use signals received in all Rx
antennas, resulting in an increased MIMO-SDMA throughput.
[0093] Therefore, the limitation of the number of AP antennas or UT
antennas is removed, and the number of parallel-communication data
units is set to the maximum value of the MIMO communication, such
that MIMO-SDMA wireless data communication system having superior
transmission characteristics can be provided.
Second Preferred Embodiment
[0094] FIG. 5 is a flow chart illustrating a communication sequence
of a wireless data communication system according to a second
preferred embodiment of the present invention.
[0095] It should be noted that the wireless data communication
system of the second preferred embodiment is the same as in FIG. 1
of the above-mentioned first preferred embodiment. However,
although only two UTs are depicted in FIG. 5 for the convenience of
description, it should be noted that the concept of FIG. 5 is
applicable to not only two UTs but also other UTs irrespective of
the number of UTs.
[0096] The wireless data communication system according to the
second preferred embodiment of the present invention is based on
the MIMO technology, such that there is a need to recognize a
transfer matrix H.sub.i(i=1,2) of wave signals. Therefore, training
data for observing the transfer matrix is transmitted from the AP
to each UT at step S1. The training data is pre-determined, such
that each UT can calculate the transfer matrix (H.sub.i) using the
received training data at steps S2a, S2b, S3a, and S3b.
[0097] Then, the transfer matrix (H.sub.i) calculated by each UT is
fed back to the AP at steps S4a and S4b. The AP receives the
fed-back transfer matrix (H.sub.i) at steps S5a to S5b, and
calculates SDMA Tx/Rx (transmission/reception) coefficient matrices
(A, B) and MIMO Tx/Rx coefficient matrices (U, V) at step S6. The
calculated Rx coefficient matrices (B.sub.i, U.sub.i) are
transmitted to each UT at steps S7a to S7b. Each UT receives the Rx
coefficient matrices (B.sub.i, U.sub.i) at steps S8a to S8b.
[0098] Then, the AP processes the MIMO Tx coefficient and the SDMA
Tx coefficient using the Tx coefficient matrix (B, U), and outputs
the processed result at step S9. Each UT performs processing using
the received Rx coefficient matrix (B.sub.i, U.sub.i), resulting in
the implementation of data recovery.
[0099] In this case, the above-mentioned second preferred
embodiment of the present invention must transmit the SDMA Rx
coefficient matrix to the UT, differently from the conventional
art. The UT can estimate the MIMO Rx coefficient matrix on the
basis of a periodically-transmitted training signal, such that
there is no need for the AP to inform the UT of the MIMO Rx
coefficient matrix.
[0100] As described above, according to the above-mentioned second
preferred embodiment of the present invention, the SDMA Rx
coefficient matrix is transmitted to each UT, such that the same
effect as the first preferred embodiment is acquired.
Third Preferred Embodiment
[0101] FIG. 6 is a flow chart illustrating a communication sequence
of a wireless data communication system according to a third
preferred embodiment of the present invention. Although most parts
of FIG. 6 are equal to those of FIG. 5, it should be noted that a
method for calculating the transfer matrix (H.sub.i) in FIG. 6 is
different from that of FIG. 5.
[0102] Generally, the signal transmission characteristics from the
AP to one UT are equal to the signal transmission characteristics
from the UT to the AP. Therefore, although the signal is
transmitted from the AP to the UT, the Tx/Rx coefficient matrices
can be calculated by the signal transmission characteristics from
the UT to the AP, such that there is no problem in calculating the
Tx/Rx coefficient matrices.
[0103] Therefore, training data is transmitted from each UT at
steps S11a to S11b, as shown in FIG. 6. The AP receives the
training data at steps S12a to S12b, and calculates the transfer
matrix (H.sub.i) using the received training data at steps S13a to
S13b.
[0104] The SDMA Rx coefficient matrix must be transmitted to the
UTs as shown in FIG. 6, differently from the conventional art.
[0105] As described above, according to the third preferred
embodiment of the present invention, the Tx/Rx coefficient matrices
are calculated by the transfer matrix of signals from the UTs to
the AP, the SDMA Rx coefficient matrix is transmitted to the UTs,
such that the same effect as the first preferred embodiment is
acquired.
Fourth Preferred Embodiment
[0106] FIG. 7 is a block diagram illustrating a transceiving unit
acting as a wireless data communication system according to a
fourth preferred embodiment of the present invention.
[0107] Referring to FIG. 7, in association with Tx data (TxData) (1
to u), the transceiving unit acting as the wireless data
communication system according to the fourth preferred embodiment
of the present invention includes at least one MIMO Tx processor
(MIMO TxProcess) 101 (101-1 to 101-u), an SDMA Tx processor (SDMA
TxProcess) 102, at least one OFDM (Orthogonal Frequency Division
Multiplex) transmission converter 109 (109-1 to 109-M), and at
least one transmission RF unit 110 (110-1 to 110-M).
[0108] In association with Rx data (1 to u), the above-mentioned
transceiving unit includes at least one reception RF unit 112
(112-1 to 112-M), at least one OFDM reception converter 113 (113-1
to 113-M), an SDMA Rx processor (SDMA RxProcess) 108, and at least
one MIMO Rx processor (MIMO RxProcess) 105 (105-1 to 105-u).
[0109] Furthermore, for both the transmission and the reception of
signals, the above-mentioned transceiving unit further includes at
least one transceiving antenna 111 (111-1 to 111-M) and at least
one switch 114 (114-1 to 114-M).
[0110] In FIG. 7, the same or similar elements are denoted by the
same reference numerals as FIG. 3 even though they are depicted in
different drawings, such that their detailed description will
herein be omitted for the convenience of description, and only new
elements depicted in FIG. 3 will hereinafter be described in
detail.
[0111] Tx data is processed by the MIMO Tx processor (MIMO
TxProcess) 101 and the SDMA Tx processor (SDMA TxProcess) 102, and
the processed result is transmitted to the OFDM transmission
converter 109. The OFDM transmission converter 109 converts the
received signals arranged in a frequency axis into other signals
arranged in a time axis.
[0112] The above-mentioned fourth preferred embodiment of the
present invention is not limited to the OFDM communication scheme,
and can also be applied to other communication schemes as
necessary. Typically, the MIMO technology combined with the OFDM
communication scheme is -being widely used because the MIMO
technology is very suitable for the OFDM communication scheme, such
that only the OFDM processor is depicted in FIG. 7 for illustrative
purposes.
[0113] Then, the signal is received in the transmission RF unit
110, and the transmission RF unit 110 performs frequency-up
conversion, power-amplification, and filtering process on the
received signal, such that the resultant signal of the transmission
RF unit 110 is generated from the transceiving antenna 111 via the
switch 114.
[0114] In this case, the antenna 111 is designed for both the
transmission and the reception of signals, such that the switch 114
is switched to the transmission or reception mode by the antenna
111.
[0115] A signal received in the transceiving antenna 111 is applied
to the reception RF unit 112 via the switch 114. The reception RF
unit 112 performs frequency-down conversion, power-amplification,
and filtering process on the received signal.
[0116] The OFDM reception converter 113 converts signals arranged
in a time axis into other signals arranged in a frequency axis.
Thereafter, the output signals of the OFDM reception converter 113
is processed by the SDMA Rx processor (SDMA RxProcess) 108 and the
MIMO Rx processor (MIMO RxProcess) 105, resulting in the
implementation of data recovery.
[0117] The above-mentioned fourth preferred embodiment of the
present invention requires the SDMA Rx processor (SDMA RxProcess)
108 in the processing system of Rx signal, differently from the
conventional art.
[0118] As described above, the transceiving unit acting as the
wireless data communication system according to the above-mentioned
fourth preferred embodiment of the present invention includes the
SDMA Rx processor (SDMA RxProcess) 108 in the Rx-signal processing
system, such that it acquires the same effect as the first
preferred embodiment.
Fifth Preferred Embodiment
[0119] FIG. 8 is a conceptual diagram illustrating a preferred
application for use in a wireless data communication system
according to a fifth preferred embodiment of the present
invention.
[0120] The present invention is preferable for a wireless data
communication system between Personal Computers, and is also
preferable for a household multimedia data communication
system.
[0121] The system according to the above-mentioned fifth preferred
embodiment includes a media server 201 as shown in FIG. 8, such
that the media server 201 accumulates all the multimedia data. The
system according to the fifth preferred embodiment transmits
multimedia data to individual UTs upon receiving requests from the
UTs (e.g., a first display 202, a second display 203, and a music
player 204, etc.)
[0122] The above-mentioned application of FIG. 8 can easily
consider that data requests are simultaneously generated from
different sections or rooms.
[0123] For example, a request for movie data (i.e., a movie-data
request) may occur to view the movie data on the display 202 of a
bedroom, and at the same time a request for pre-recorded TV program
data may occur to view the TV program data on the other display 203
of a living room. Also, under the same situation as the
aforementioned, a request of music data may also be generated from
the music player of a child's room.
[0124] In this case, a method for simultaneously transmitting data
to individual UTs according to the SDMA communication scheme is
superior to a method for sequentially transmitting data to
individual UTs according to the TDMA communication scheme, because
the former method can implement a higher throughput than that of
the latter method.
[0125] Also, the system according to the fifth preferred embodiment
of the present invention can control each UT to freely change the
number of parallel-transmission data units, such that it can
firstly assign the number of parallel-transmission data units to a
specific UT conducting higher-importance communication.
[0126] As described above, although the system according to the
fifth preferred embodiment of the present invention is applied to
the household multimedia data communication system, the system can
acquire the same effect as the first preferred embodiment.
[0127] As apparent from the above description, the present
invention provides a wireless data communication system based on a
Space Division Multiple Access (SDMA), a wireless data
communication method based on the SDMA, and effective techniques
associated with the system and method.
[0128] The present invention is applicable to all the wireless data
communication systems. Particularly, the present invention is
preferably applied to an OFDM-based wireless data communication
system.
[0129] The OFDM technology is being widely applied to the wireless
LAN, and the IEEE 802.11n standard will certainly adopt the MIMO
technology in the future, such that the MIMO-SDMA communication
scheme of the present invention is very suitable for the wireless
LAN and the IEEE 802.11n standard.
[0130] The above-mentioned SDMA communication scheme acquires the
best throughput when the AP simultaneously communicates with a
plurality of UTs.
[0131] For example, provided that the media server is located at
home, and users of several rooms desire to access the media server
to view desired moving images, the media server can simultaneously
provide the users with their desired data using the SDMA
communication scheme. In this way, if the simultaneous
communication function is required for the above-mentioned
situation, the wireless data communication system according to the
present invention can easily implement the simultaneous
communication function according to the MIMO-SDMA communication
scheme.
[0132] As described above, the present invention has no limitation
in the number of AP antennas and UT antennas, and determines the
parallel-communication data units to be a maximum value of MIMO
communication, such that it provides a MIMO-SDMA wireless data
communication system having superior transmission
characteristics.
[0133] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *