U.S. patent number RE44,092 [Application Number 12/949,425] was granted by the patent office on 2013-03-19 for apparatus and method for adaptively modulating signal by using layered time-space detector used in mimo system.
This patent grant is currently assigned to Electronics and Telecommunications Research Institute. The grantee listed for this patent is Jae-Young Ahn, Jihoon Choi, Taehyun Jeon, Inhyoung Kim, Young-Doo Kim, Yong-Hoon Lee, Heejung Yu. Invention is credited to Jae-Young Ahn, Jihoon Choi, Taehyun Jeon, Inhyoung Kim, Young-Doo Kim, Yong-Hoon Lee, Heejung Yu.
United States Patent |
RE44,092 |
Kim , et al. |
March 19, 2013 |
Apparatus and method for adaptively modulating signal by using
layered time-space detector used in MIMO system
Abstract
An apparatus for adaptively modulating/demodulating signals in a
multi-input multi-output (MIMO) system having a layered time-space
architecture detector and a method thereof is disclosed. The
apparatus includes: a bit and power allocation information
calculator for deciding an equivalent channel gain in a reverse
order of Vertical-Bell laboratories Space Time (V-BLAST) based on
MIMO channel information feedbacked from a receiver and determining
the number of bits and transmission power to be transmitted to each
transmitting antenna by using the equivalent channel gain; and
adaptive modulation means for modulating signal of each layer with
corresponding modulation method based on the determined number of
bits and transmitting power, controlling the transmitting power and
transmitting the adaptively modulated signal through each
transmitting antenna. The present invention can improve performance
without increase of implementation complexity and easily expand to
MIMO-OFDM system by adaptively modulating and demodulating signals
in reverse order of conventional V-BLAST detection method.
Inventors: |
Kim; Young-Doo (Seoul,
KR), Kim; Inhyoung (Yongin-si, KR), Yu;
Heejung (Daejeon, KR), Choi; Jihoon (Seoul,
KR), Jeon; Taehyun (Sungnam, KR), Ahn;
Jae-Young (Daejon, KR), Lee; Yong-Hoon (Daejeon,
KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Young-Doo
Kim; Inhyoung
Yu; Heejung
Choi; Jihoon
Jeon; Taehyun
Ahn; Jae-Young
Lee; Yong-Hoon |
Seoul
Yongin-si
Daejeon
Seoul
Sungnam
Daejon
Daejeon |
N/A
N/A
N/A
N/A
N/A
N/A
N/A |
KR
KR
KR
KR
KR
KR
KR |
|
|
Assignee: |
Electronics and Telecommunications
Research Institute (Daejon, KR)
|
Family
ID: |
32464618 |
Appl.
No.: |
12/949,425 |
Filed: |
November 18, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
10737398 |
Dec 16, 2003 |
7453947 |
Nov 18, 2008 |
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Foreign Application Priority Data
|
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Dec 26, 2002 [KR] |
|
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10-2002-0084478 |
|
Current U.S.
Class: |
375/267 |
Current CPC
Class: |
H04L
5/006 (20130101); H04L 5/0046 (20130101); H04B
7/0697 (20130101); H04B 7/0417 (20130101); H04L
1/0003 (20130101); H04B 7/0626 (20130101); H04W
52/42 (20130101); H04L 5/0028 (20130101); H04L
1/0656 (20130101); H04B 7/0891 (20130101); H04L
5/0023 (20130101); H04L 5/0007 (20130101) |
Current International
Class: |
H04B
7/02 (20060101) |
Field of
Search: |
;375/267,130,347,299
;455/101,132 ;348/607 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
GG. Raleigh et al.; "Spatio-Temporal Coding For Wireless
Communications"; 0-7803-3336-5/96 IEEE (pp. 1809-1814). cited by
applicant .
Cheong Yui Wong et al.; "Multiuser OFDM With Adaptive Subcarrier,
Bit and Power Allocation"; IEEE Journal on Selected Areas in Comm.,
vol. 17, No. 10, Oct. 1999; pp. 1747-1758. cited by applicant .
Ka-Wai Ng, et al.; "A Simplified Bit Allocation . . . Fading
Channels"; 0-7803-7400-2/2/02 IEEE (pp. 411-415). cited by
applicant .
Ka-Wai Ng, et al.; "Iterative Bit & Power . . . Fading
Channel"; 0-7803-7376-6/02/02 IEEE (pp. 271-275). cited by
applicant .
P.W. Wolniansky, et al.; "V-Blast: An Architecture . . . Wireless
Channel"; 0-7803-4900-8/98 IEEE (pp. 295-300). cited by
applicant.
|
Primary Examiner: Tran; Khai
Attorney, Agent or Firm: NSIP Law
Claims
What is claimed is:
1. An apparatus for adaptively modulating signal in a MIMO system
having a layered space-time architecture based detector, the
apparatus comprising: a bit and power allocation information
calculator for deciding an equivalent channel gain in a reverse
order of Vertical-Bell laboratories Space Time (V-BLAST) based on
MIMO channel information feedbacked from a receiver and determining
the number of bits and transmission power to be transmitted to each
transmitting antenna by using the equivalent channel gain; and
adaptive modulation mean for modulating signal of each layer with
corresponding modulation method based on the determined number of
bits, controlling the transmitting power and transmitting the
adaptively modulated signal through each transmitting antenna.
2. The apparatus as recited in claim 1, wherein the transmitter
detects and modulates signals in a reverse order of a V-BLAST.
3. The apparatus as recited in claim 1, wherein the receiver
transmits identical adaptive modulation information with the
modulation method and transmitting power instead of feedbacking the
MIMO channel information.
4. The apparatus as recited in claim 1, wherein the bit and power
allocation information calculation mean determines an equivalent
channel gain in the reverse order of V-BLAST and calculates the
number of bit information and corresponding transmitting power at
each layer by using the equivalent channel gain in a greedy
algorithm instead of using channel gain.
5. An apparatus for adaptively demodulating signal in a MIMQ system
having a layered space-time architecture based detector, the
apparatus comprising: MIMO channel estimation means for estimating
MIMO channel from a signal received through each receiving antenna;
a bit and power allocation information calculator for determining
an equivalent channel gain in reverse order of Vertical-Bell
laboratories Space Time (V-BLAST) based on MIMO channel information
from the MIMO channel estimation means and determining the number
of bits to be transmitted from each transmitting antenna by using
the equivalent channel gain; and adaptive demodulation means for
demodulating signal of each layer with corresponding modulation
method based on the determined number of bits and the MIMO channel
information.
6. An apparatus for adaptively modulating and demodulating signals
in MIMO system using multiple antennas at transmitter and
receivers, the apparatus comprising: an adaptive modulation means
for adaptively modulating signals in order to transmit the
modulated signal after determining an equivalent channel gain in a
reverse order of a vertical-bell laboratories space time and
determining the number of bits and transmitting power based on the
determined equivalent channel gain; and adaptive demodulation means
for detecting and adaptively demodulating received signals in
reverse order of V-BLAST.
7. The apparatus as recited in claim 6, wherein the adaptive
demodulation means feedbacks the MIMO channel information to the
modulation means or transmits identical adaptive modulation
information including the modulation method and transmitting power
instead of the MIMO channel information.
8. The apparatus as recited in claim 7, wherein the apparatus has
(the number of subcarriers).times.(the number of transmission
antennas) of equivalent channel gains and determines the number of
bits and transmitting power to be transmitted through each
transmission antennas in a MIMO-OFDM system having a layered
space-time architecture detector.
9. The apparatus as recited in claim 6, wherein the apparatus
independently detects and demodulates signals per each subcarrier
by determining the number of bits and transmitting power to be
transmitted through each transmitting antenna per each subcarrier
in a MIMO OFDM system having a layered space-time architecture
detector.
10. A method for adaptive modulating signals in a MIMO system using
multiple antennas in a receiver and transmitter, the method
comprising the steps of: a) determining equivalent channel gain in
a reverse order of V-BLAST at transmitter based on information
feedbacked from the receivers; and b) adaptively modulating signals
by determining the number of bits and corresponding transmitting
power to be transmitted through each layer by using the equivalent
channel gain in a greedy algorithm instead of using subcarrier.
11. The method as recited in claim 10, wherein the transmitter
detects and modulates signals in a reverse order of a V-BLAST.
12. The method as recited in claim 11, wherein the step a) includes
the steps of: a-1) initializing an antenna index set; a-2) nulling
layers in an order of layer having a smallest equivalent channel
gain and modifying the antenna index set or a channel matrix based
on a result of nulling layers; a-3) repeatedly performing the step
a-2) as many as the number of antennas; and a-4) deciding the
equivalent channel gain of each antenna layer based on a result of
the step a-3).
13. The method as recited in the claim 12, wherein the step a-2)
includes the steps of: a-2-1) computing an pseudo-inverse matrix of
channel matrix; a-2-2) computing square root of norm of nulling
vector for deciding a nulling layer; a-2-3) selecting a layer
having a biggest norm of nulling vectors among layers of computing
results from the step a-2-2); and a-2-4) nulling the selected layer
and eliminating the selected layer from the antenna index set.
14. The method as recited in claim 10, the step a) includes the
steps of: a-a) initializing an antenna index set; a-b) nulling
layers in an order of layer having a smallest equivalent channel
gain and modifying the antenna index set or a channel matrix based
on a result of nulling layers; a-c) reputedly performing the step
a-b) as many as the number of antennas; a-d) deciding the
equivalent channel gain of each antenna layer based on a result of
the step a-c); and a-e) deciding the equivalent channel gain by
reputedly performing the step a), the step b), the step a-a) and
the step a-c).
15. The method as recited in the claim 14, the number of bit
transmitting to each antenna and a transmitting power are decided
by performing a greedy algorithm based on the decided equivalent
channel gain computed from the step a-e) in the step b).
16. The method as recited in claim 10, wherein the step a), in a
case there are preset data bits of the system and data bits
allocated to each subcarrier are identical, includes the steps of:
a-I) initializing an antenna index set according to a subcarrier;
a-II) nulling layers in an order of layer having a smallest
equivalent channel gain and modifying the antenna index set or a
channel matrix based on a result of nulling layers for the
subcarrier; a-III) repeatedly performing the step a-II) as many as
the number of antennas for the subcarrier; and a-IV) deciding the
equivalent channel gain of each antenna layer based on a result of
the step a-III).
17. The method as recited in claim 16, wherein the step a-II)
includes the steps of: a-II-1) performing a greedy algorithm from
the equivalent channel gain decided to one of the subcarrier in the
step of a-IV) and deciding the number of bits transmitting through
an antenna according to the one of carrier waves and transmitting
power; and a-II-2) deciding identical number of bits and
transmitting power which are decided in the step a-II-1) for all
other sub carrier waves.
18. A method for adaptively demodulating in a multi input and multi
output system, the method comprising the steps of: a) estimating a
channel from a signal received at each receiving antenna; b)
deciding an equivalent channel gain in a reverse order of a
vertical-bell laboratories space time (V-BLAST) based on the
channel information; and c) detecting and adaptively demodulating
by deciding the number of bits based on the equivalent channel
gain.
19. A computer readable recoding medium storing instruction for
executing a method for adaptive modulation, the method comprising
the steps of: a) at a transmitter, deciding an equivalent channel
gain in a reverse order of V-BLAST based on a feedback information
from a receiver; and b) at the transmitter, deciding the number of
bit transmitting through each layer (transmitting antenna) and
transmitting power based on the equivalent channel gain computed at
the step a).
20. A computer readable recoding medium storing instructions for
executing a method for adaptively demodulating signals, the method
comprising the steps of: a) estimating a channel from a signal
received from each receiving antenna; b) deciding an equivalent
channel gain in a reverse order of V-BLAST based on the channel
information; and c) detecting and adaptively demodulating by
deciding the number bits transmitted from the each transmitting
antenna based on the equivalent channel gain.
.Iadd.21. An apparatus for adaptively modulating signal in a MIMO
system, the apparatus comprising: a bit and power allocation
information calculator configured to determine an equivalent
channel gain for each trasmitting antenna in a reverse order of a
Vertical-Bell Laboratories Space Time (V-BLAST) and determine the
number of bits and transmission power for each transmitting antenna
by using the equivalent channel gain; and an adaptive modulator
configured to modulate a signal to be transmitted through each
transmitting antenna based on the determined number of bits and
transmit the modulated signal through each transmitting antenna at
the determined transmission power..Iaddend.
.Iadd.22. The apparatus as recited in claim 21, wherein the bit and
power allocation information calculator configured to determine the
equivalent channel gain based on MIMO channel information
feedbacked from a receiver..Iaddend.
.Iadd.23. An apparatus for adaptively demodulating signal in a MIMO
system, the apparatus comprising: a MIMO channel estimator
configured to estimate a MIMO channel from a signal received
through each receiving antenna; a bit and power allocation
information calculator configured to determine an equivalent
channel gain for each receiving antenna in reverse order of a
Vertical-Bell Laboratories Space Time (V-BLAST) and determine the
number of bits for each receiving antenna by using the equivalent
channel gain; and an adaptive demodulator configured to demodulate
the signal of each layer based on the determined number of
bits..Iaddend.
.Iadd.24. The apparatus as recited in claim 23, wherein the bit and
power allocation information calculator configured to determine the
equivalent channel gain based on MIMO channel information from each
transmitting antenna..Iaddend.
.Iadd.25. A system for adaptively modulating and demodulating
signals in MIMO system, the system comprising: an adaptive
modulator configured to modulate signals to be transmitted through
each transmitting antenna after determining an equivalent channel
gain in a reverse order of a Vertical- Bell Laboratories Space Time
(V-BLAST) and determine the number of bits based on the determined
equivalent channel gain; and an adaptive demodulator configured to
detect and demodulate received signals in reverse order of
V-BLAST..Iaddend.
.Iadd.26. A method for adaptively modulating signals in a MIMO
system, the method comprising the steps of: determining an
equivalent channel gain for each transmitting antenna in a reverse
order of a Vertical-Bell Laboratories Space Time (V-BLAST); and
adaptively modulating signals by determining the number of bits to
be transmitted through each transmitting antenna based on the
equivalent channel gain in a greedy algorithm..Iaddend.
.Iadd.27. The method as recited in claim 26, wherein the equivalent
channel gain is determined based on MIMO channel information
feedbacked from a receiver..Iaddend.
.Iadd.28. The method as recited in claim 26, wherein the step of
determining the equivalent channel gain comprises steps of:
initializing an antenna index set; nulling layers in an order of
layer having a smallest equivalent channel gain and modifying the
antenna index set or a channel matrix based on a result of nulling
layers; and deciding the equivalent channel gain of each antenna
layer based on a result of nulling..Iaddend.
.Iadd.29. The method as recited in the claim 28, wherein the step
of nulling comprises steps of: computing an pseudo-inverse matrix
of channel matrix; computing square root of norm of nulling vector
for deciding a nulling layer; selecting a layer having a biggest
norm of nulling vectors among layers of computing results from the
step of computing square root of norm of nulling vector for
deciding a nulling laye; and nulling the selected layer and
eliminating the selected layer from the antenna index
set..Iaddend.
.Iadd.30. A method for adaptively demodulating in a MIMO system,
the method comprising the steps of: estimating a channel from a
signal received through each receiving antenna; determining an
equivalent channel gain for each receiving antenna in a reverse
order of a Vertical-Bell Laboratories Space Time (V-BLAST); and
adaptively demodulating the received signals by deciding the number
of bits based on the equivalent channel gain..Iaddend.
.Iadd.31. The method as recited in claim 30, wherein the equivalent
channel gain is determined based on MIMO channel
information..Iaddend.
.Iadd.32. A computer readable recoding medium storing instruction
for executing a method for adaptive modulation, the method
comprising the steps of: determining an equivalent channel gain for
each transmitting antenna in a reverse order of V-BLAST; and
determining a number of bit to be transmitted through each
transmitted antenna based on the equivalent channel
gain..Iaddend.
.Iadd.33. The computer readable recoding medium as recited in claim
32, wherein the equivalent channel gain is determined based on on
MIMO channel information feedbacked from a receiver..Iaddend.
.Iadd.34. A computer readable recoding medium storing instructions
for executing a method for adaptively demodulating signals, the
method comprising the steps of: estimating a channel from a signal
received through each receiving antenna; determining an equivalent
channel gain for each receiving antenna in a reverse order of
V-BLAST; and adaptively demodulating the receiving signals by
deciding number of bits based on the equivalent channel
gain..Iaddend.
.Iadd.35. The computer readable recoding medium as recited in claim
34, wherein the equivalent channel gain based on MIMO channel
information from each transmitting antenna..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to an apparatus for
modulating/demodulating signal by using a layered time-space
architecture detector in a multi-input multi-output (MIMO) system
and a method thereof; and, more particularly, to the apparatus for
modulating/demodulating signal by using a layered time-space
architecture detector in a multi-input multi-output (MIMO) system
in order to increase a system performance by deciding an equivalent
channel gain, deciding the number of bits for transmitting through
each antenna and deciding a transmission power by using the a
greedy algorithm based on the decided equivalent channel gain.
DESCRIPTION OF RELATED ARTS
Generally, a multi-input multi-output (MIMO) system is a wireless
communication system obtaining high frequency efficiency by
transmitting each different data through a plurality of
transmission antennas in an identical bandwidth. There have been
several detection methods for MIMO systems, such as a Diagonal Bell
Laboratories Space Time (D-BLAST) system proposed in an article by
G. J. Foschini, entitled "Layered Space-Time Architecture for
Wireless Communication in a Fading Environment When using
Multi-Element Antennas," Bell Labs Technical Journal, fall, pp.
41.about.59, 1999 and a Vertical-Bell Laboratories Space Time
(V-BLAST) system introduced in an article by P. W. Wolniansky
et.al., entitled "V-Blast: An Architecture for Realizing Very High
Data Rates Over the Rich-Scattering Wireless Channel." Proc.
International Symposium Signals, Systems and Electronics,
September, 1998.
The V-BLAST system is a modified scheme of the D-BLAST system.
Operations of detection in the V-BLAST system are explained in more
detail hereinafter. At first, a symbol corresponding to a layer
having the largest equivalent channel gain is detected based on a
MIMO channel matrix and new channel matrix is built by nulling a
channel corresponding to the currently detected layer after
canceling the effect of the detected symbol in the channel matrix
H. And the above mentioned steps are repeated until all symbols are
detected. As a result of these operations, a layer having largest
equivalent channel gain is detected for the first time. When the
next symbol is detected, the effect of the first symbol is
eliminated because it is considered as interference and then the
next symbol is detected. Therefore, a diversity gain can be
obtained when the next symbol is detected and a performance is
increased.
In a meantime, a structure of V-BLAST system is in U.S. Pat. No.
6,317,466 B1 issued to G. J. Foschini, entitled "Wireless
Communications System Having a Space-Time Architecture Employing
Multi-Element antenna at both the Transmitter and Receiver" and
also an adaptive modulation method is disclosed. But in the above
mentioned patent by G. J. Foschini, a method for minimizing
transmission power and changing modulation method commonly used for
all antennas.
Furthermore, a greedy algorithm for allocating power and the number
of bits in multicarrier systems is introduced in an article by C.
Y. Wong, entitled "Multi-user OFDM with adaptive sub-carrier, bit
and power allocation", IEEE Journal on Selected Areas in
Communication, Vol. 17, pp. 1747.about.1758, October, 1999. The
greedy algorithm is used for calculating a power and the number of
bits of each subcarrier in order to transmit all information bits
with the minimum transmission power while satisfying desired bit
error rate under conditions such as single user orthogonal
frequency division multiplexing (OFDM) is used, a frequency domain
channel response corresponding to each subcarrier is known at the
transmitter, the number of bits for transmitting at one OFDM symbol
is predetermined and there is a desired bit error rate.
There are two methods implementing the MIMO-OFDM system with the
adaptive modulation method. A first method is introduced in an
article by Ka-Wai Ng. et. al., entitled "A simplified bit
allocation for V-BLAST based OFDM MIMO system in frequency
selective fading channels" IEEE international conference on
communication, pp. 411.about.415, 2002. A second method is
disclosed in an article by Ka-wai Ng et. al., entitled "Iterative
bit & power allocation for V-BLAST based OFDM MIMO system in
frequency selective fading channel", Proc. Wireless Communications
and Networking Conference, 2002, pp. 271.about.275.
The first method calculates the equivalent channel gain based on an
ordering method of the V-BLAST and decides the number of bits
according to the greedy algorithm based on the calculated
equivalent channel. It is also disclosed that a method of selecting
a subcarrier and transmitting antenna in order to reduce the amount
of information transmitted to the transmitter. The above mentioned
approaches using the V-BLAST ordering method may obtain nearly same
performance for all layers when fixed modulation method is used.
However, the performance is degraded in a case of an adaptive
modulation is used.
The second method allocates a predetermined number of bits to all
possible combinations of decision order for the optimal solution
and selects the optimal order with minimum total transmission
power. However, by reducing the number of combinations to be
considered for finding the optimal solution, the performance is
degraded.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an
apparatus for adaptively modulating/demodulating signal by using a
layered time-space architecture detector in a multi-input
multi-output (MIMO) system for improving a system performance by
deciding an equivalent channel gain, deciding the number of bits
for transmitting through each antenna and a transmission power by
using a greedy algorithm based on the decided equivalent channel
gain.
In accordance with an aspect of the present invention, there is
provided an apparatus for adaptively modulating signal in a MIMO
system having a layered space-time architecture based detector, the
apparatus including: a bit and power allocation information
calculator for deciding an equivalent channel gain-in a reverse
order of Vertical-Bell laboratories Space Time (V-BLAST) based on
MIMO channel information feedbacked from a receiver and determining
the number of bits and transmission power to be transmitted from
each transmitting antenna by using the equivalent channel gain; and
adaptive modulation means for modulating signal of each layer with
corresponding modulation method based on the determined number of
bits and transmitting power.
In accordance with an aspect of the present invention, there is
provided an apparatus for adaptively demodulating signal in a MIMO
system having a layered space-time architecture based detector, the
apparatus including: MIMO channel estimation unit for estimating
MIMO channel from a signal received through each receiving antenna;
a bit and power allocation information calculator for determining
an equivalent channel gain in reverse order of Vertical-Bell
laboratories Space Time V-BLAST based on MIMO channel information
from the MIMO channel estimation unit and determining the number of
bits corresponding to each transmitting antenna by using the
equivalent channel gain.
In accordance with an aspect of the present invention, there is
provided apparatus for adaptively modulating and demodulating
signals in MIMO system using multiple antennas at transmitter and
receiver, the apparatus including: an adaptive modulation unit for
adaptively modulating signals in order to transmit the modulated
signal after determining an equivalent channel gain in a reverse
order of a vertical-bell laboratories space time and determining
the number of bits and transmitting power based on the determined
equivalent channel gain; and adaptive demodulation unit for
detecting and adaptively demodulating received signals through each
receiving antenna in reverse order of V-BLAST.
In accordance with an aspect of the present invention, there is
provided a method for adaptively modulating signals in a MIMO
system using multiple antennas in a receiver and transmitter, the
method, including the steps of: a) determining equivalent channel
gain in a reverse order of V-BLAST at transmitter based on channel
information feed backed from the receivers; and b) adaptively
modulating signals by determining the number of bits and
corresponding transmitting power to be transmitted through each
layer (antenna) by using the equivalent channel gain in a greedy
algorithm.
In accordance with an aspect of the present invention, there is
provided a method for adaptively demodulating in MIMO systems, the
method including the steps of: a) estimating a channel from a
signal received at each receiving antenna; b) deciding an
equivalent channel gain in a reverse order of a vertical-bell
laboratories space time (V-BLAST) based on the channel information;
and c) detecting and adaptively demodulating the received signal
using the adaptive modulation information for each layer.
In accordance with an aspect of the present invention, there is
provided a computer readable recoding medium storing instructions
for executing a method for an adaptive modulation, the method
including the steps of: a) at a transmitter, deciding an equivalent
channel gain in a reverse order of V-BLAST based on a feedback
information from a receiver; and b) at the transmitter, deciding
the number of bit transmitting through each layer (transmitting
antenna) and transmitting power based on the equivalent channel
gain computed at the step a).
In accordance with an aspect of the present invention, there is
provided a computer readable recoding medium storing instructions
for executing a method for an adaptive demodulation, the method
including the steps of: a) estimating a channel from a signal
received from each receiving antenna; b) deciding an equivalent
channel gain in a reverse order of V-BLAST based on the channel
information; and c) detecting and adaptively demodulating by
deciding the number bits for each layer.
BRIEF DESCRIPTION OF THE DRAWING(S)
The above and other objects and features of the present invention
will become apparent from the following description of the
preferred embodiments given in conjunction with the accompanying
drawings, in which:
FIG. 1 is a diagram for illustrating a MIMO wireless communication
system having a layered space-time architecture detector in
accordance with a preferred embodiment of the present
invention;
FIG. 2 is a view showing changing of equivalent channel gain
according to the detection order in layered space-time architecture
in accordance with the present invention;
FIG. 3 is a flowchart for explaining a method for determining the
equivalent channel gain in a reverse order of the V-BLAST detection
method;
FIG. 4 is a flowchart for explaining steps for determining the
number of bits for transmitting of each transmitting antenna and
corresponding transmitting power by using a equivalent channel gain
according to greedy algorithm in accordance with a preferred
embodiment;
FIG. 5 is a diagram showing an apparatus for adaptively
modulating/demodulating signal in the MIMO wireless communication
system having layered space-time architecture in accordance with a
preferred embodiment of the present invention;
FIG. 6 is a graph showing a performance of a method for adaptively
modulating/demodulating signals in a MIMO wireless communication
system having V-BLAST type detector in accordance with a preferred
embodiment of the present invention;
FIG. 7 is a diagram showing an apparatus for adaptively
modulating/demodulating signals in MIMO OFDM wireless communication
system having V-BLAST type detector in accordance with a preferred
embodiment of the present invention; and
FIG. 8 is a graph showing a result of a simulation of a method for
adaptively modulating/demodulating signal in MIMO OFDM wireless
system having V-BLAST type detector in accordance with a preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Other objects and aspects of the invention will become apparent
from the following description of the embodiments with reference to
the accompanying drawings, which is set forth hereinafter.
For helping to understand the present invention, a greedy algorithm
used in an adaptive modulation/demodulation method in accordance
with the present invention is explained at first.
For explaining the greedy algorithm, an orthogonal frequency
division multiplexing method is used as an example.
At first, the transmission power of the n.sup.th subcarrier of,
P.sub.n, is given as:
.function..times. ##EQU00001##
In the Eq. 1, h.sub.n is a channel gain of the n.sup.th subcarrier,
C.sub.n is the number of bit for transmitting with the subcarrier,
and f(C.sub.n) is a is a transmission power for transmitting c bits
with desired bit error rate (BER).
In a meantime, if an entire bits for transmitting one of OFDM
symbol is R, a bit allocation method for minimizing a sum of
transmission power of entire subcarrier can be expressed as:
.di-elect cons..times..times..times..times..function..times.
##EQU00002## subject to
.times. ##EQU00003##
In the Eq. 2, Nc is the number of total subcarriers, D represents a
set of information bits per subcarrier determined by
modulation/demodulation methods. For example, if a QPSK, 16-QAM,
64-QAM and so on can be selected for the modulation/demodulation
methods, then D={0, 2, 4, 6, 8, . . . }. In here, 0 means that no
information is sent in the corresponding subcarrier.
The Eq. 2 can be solved by the greedy algorithm through following
steps. step 1: For all subcarriers, we define c.sub.n=0,
.DELTA..times..function..DELTA. ##EQU00004## step 2: following
equations 3, 4 and 5 are repeatedly operated until the
condition
.times. ##EQU00005## is satified.
.times..times..times..DELTA..times..DELTA..times..function..DELTA..functi-
on..times. ##EQU00006##
In the Eqs. 4 and 5, .DELTA..beta. is the difference of elements of
set D e.g., D={0, 2, 4, 6, . . . }. Therefore, .DELTA..beta.=2.
step 3: after completing step 2, each C.sub.n is determined and
P.sub.n is calculated by using eq. 1.
Finally, the number of bits allocated to each subcarrier, C.sub.n,
and the transmission power, P.sub.n, is determined.
In the V-BLAST detection method, data transmitted from a plurality
of transmitting antenna is detected as one by one and the detected
symbols are cancelled for reducing interference to other signals.
The next symbol is detected after canceling the channel effect
corresponding to the previously detected symbol. Therefore, the
equivalent channel gain is varied according to an order of nulling.
The present invention provides a method for achieving performance
gain by adaptively modulating the signal with an equivalent channel
gain obtained by the reverse order of conventional V-BLAST
detection order. Hereinafter, the V-BLAST detection method is
explained at first.
FIG. 1 is diagram for illustrating a MIMQ wireless communication
system having a layered space-time architecture detector in
accordance with a preferred embodiment of the present
invention.
Referring to FIG. 1, in the MIMO wireless communication system
having a detector of V-BLAST structure, a signal vector transmitted
from each transmission antenna 13-1, 13-2, . . . , 13-M is defined
as x=[x.sub.0, x.sub.1, . . . , x.sub.M-1].sup.T and a signal
vector received to each receiving antenna 15-1, 15-2, . . . 15-N is
defined as y=[y.sub.0, y.sub.1, . . . , y.sub.N-1].sup.T. M and N
is the number of transmitting/receiving antennas and it is
satisfied with a condition, N.gtoreq.M. The received signal vector
is expressed as: y=Hx+v Eq. 6 In the Eq. 6, H is N.times.M channel
matrix, the element of the n.sup.th row and, a m.sup.th column,
h.sub.n,m, is a flat fading channel gain between m.sup.th
transmitting antenna and n.sup.th receiving antenna. In a meantime,
v is a N.times.1 white noise vector with zero mean and its
covariance matrix is E[vv.sup.H]=.sigma..sup.2I. I is N.times.N
unit matrix.
For detection of the transmitting signal vector x from the
receiving signal vector y, the V-BLAST detection method is used. A
nulling vector for k.sup.th layer (k.sup.th transmission antenna
signal) is defined as:
.function..delta..noteq..times. ##EQU00007## In the Eq. 7,
(H).sub.t is 1.sup.th column of matrix H and W.sub.k.sup.T is a
k.sup.th column of a pseudo-inverse matrix H.sup.+. A detection
order is determined by considering a value of w.sub.k. In the
conventional V-BLAST detection, a column of the matrix having
smallest value of .parallel.w.sub.k.parallel. is detected at first.
In a meantime, Z.sub.k is a decision statistic of k.sup.th layer
and it is expressed as: Z.sub.k=x.sub.k+w.sub.k.sup.Tv Eq. 8
In the Eq. 8, k={1, 2, . . . , M}. After determining the signal by
considering the decision statistic Z.sub.k, an interference of the
previous detected signal is cancelled and the channel matrix H is
updated. That is, new channel matrix H is generated by setting
k.sup.th column of prior matrix H as `0`. New received signal
vector y' is determined as: y'=y-(H).sub.kx.sub.k Eq. 9
In the Eq. 9, x.sub.k is a result of decision of Z.sub.k. The Eqs.
6 to 9 are repeatedly executed for calculating a nulling vector by
using new channel matrix H' and receiving signal vector y' until
all signals are detected. The above mentioned steps are detection
steps of conventional V-BLAST. Order of detection is determined
according to the magnitude of norm of nulling vector.
If the eq. 7 is used for calculating a signal-to-noise ratio of the
decision statistics, .rho..sub.k, which is calculated as:
.rho..times..sigma..times..times. ##EQU00008##
In the, Eq. 10, E{ } is an expectation function and
.parallel.w.sub.k.parallel..sup.2 is the equivalent channel gain.
Therefore, a state of channel is better as
.parallel..sub.k.parallel. is getting smaller. The V-BLAST method
for MIMO system using a fixed modulation/demodulation method
detects a layer of best channel state at first and then detects a
layer of worse channel state after eliminating interference of
signals, which have already been detected in order to enhance
performance of all layers.
However, the adaptive modulation/demodulation method detects a
layer of best channel state later and information of a layer of
worse channel is not transmitted or less amount of information is
transmitted in order to enhance the performance. Therefore, the
detection order must to be reversed for enhancing the performance
in accordance with the present invention.
FIG. 5 is a diagram showing an adaptive modulation/demodulation,
and in the MIMO wireless communication system with V-BLAST type in
accordance with a preferred embodiment of the present
invention.
Referring to FIG. 5, a MIMO system having V-BLAST detector includes
an adaptive modulation unit 52 and an adaptive demodulation unit 57
for modulating/demodulating signals with using different
demodulation/modulation method and controlling transmission power
of the signal. The demodulation unit 57 includes a V-BLAST type
detection unit.
Operations of the adaptive modulation/demodulation units 52 and 57
are explained in detail as followings.
A transmitting data 51 is data transmitted from a transmitter. If
necessary, this date would be scrambled, channel coded, and
interleaved. The adaptive modulation unit receives the channel
information and controls transmitting power by modulating the data
with different modulation methods according to each layer by using
bit and power allocation information.
When adaptively modulated signals are transmitted through M
transmitting antennas 53-1 to 53-M, a bit and power allocation
information calculator 54 determines the number of bits and
transmitting power to be transmitted to each transmitting antennas
53-1 to 53-M by using MIMO channel information feedbacked from a
receivers and the greedy algorithm.
Through the above mentioned operations, signals transmitted from
the M transmitting antennas 53-1 to 53-M are transmitted to N
receiving antennas 56-1 to 56-N through frequency non-selective
fading MIMO channel. And the adaptive demodulation unit 57
demodulates the received signals by using channel estimation result
from a MIMO channel estimator 58 and a bit allocate information
from the bit allocation information calculator 59 in reverse order
of V-BLAST. Finally, the demodulated signal is outputted.
FIG. 2 is a view showing changing of equivalent channel gain
according to an order of nulling in a layered space-time
architecture in accordance with the present invention.
Referring to FIG. 2, although identical channel matrix is used, the
equivalent channel gain is changed according to an order of
detection such as an order of V-BLAST, a random order and a reverse
order of V-BLAST. Thus, in case of detection according to the order
of V-BLAST, a deviation of the equivalent channel gain is small and
the sum of equivalent channel gain is small. And in case of
detecting according to the reverse order of V-BLAST, the deviation
and sum of the equivalent channel gain become larger.
A method for determining the equivalent channel gain in a reverse
order of the V-BLAST detection method in accordance with a
preferred embodiment of the present invention is explained in
detail.
FIG. 3 is a flowchart for explaining the method for determining the
equivalent channel gain in a reverse order of the V-BLAST detection
method.
Referring to FIG. 3, at step 31, an antenna index set is defined
(S={1, 2, . . . , M}) because of determining an order of detection
for determining the equivalent channel gain. An pseudo-inverse
Matrix of channel matrix H.sup.+ is calculated at step 32. At step
33, all nulling vectors w.sub.k.sup.T, k.epsilon.S, are calculated
based on the Eq. 7 for calculating transmitting signal vector
x.
After the step 33, square root of a norm of nulling vector is
calculated for determining a layer for nulling and k.sup.th layer
having the largest value is selected at step 34. A column of the
channel matrix corresponding to the selected k.sup.th layer is
transformed to 0 vector and a value k is eliminated from the set S
at step 35. The above mentioned steps are repeated M times with
newly transformed set S and channel matrix H.
As mentioned above, an order of the selected layers becomes a
detection order and an inverse of square root norm of the nulling
vector for the selected layer becomes the equivalent channel gain.
Furthermore, the number of bits transmitted at each layer
(transmitting antenna) and corresponding transmitting power is
calculated by using the calculated equivalent channel gain instead
of subcarrier channel gain .parallel.h.sub.n.parallel..sup.12 in
greedy algorithm.
FIG. 4 is a flowchart for explaining steps for determining the
number of bits for transmitting of each transmitting antenna and
corresponding transmitting power by using a equivalent channel gain
according to greedy algorithm in accordance with a preferred
embodiment of the present invention.
Referring to FIG. 4, at step 41, the number of bits transmitted at
each layer (each transmitting antenna) is initialized as `0`.
.DELTA..beta. is defined based on the Eq. 2 and a transmitting
power is calculated for obtaining an additional bit value of
.DELTA..beta. with desired bit error rate at each layer by using
the equivalent channel gain of each layer. Among the calculated
layers, a layer requiring the least transmitting power is selected
and the value of .DELTA..beta. is putted to the selected layer. The
above mentioned steps are repeatedly performed until allocated
total bit number is assigned. After determining the number of bits
transmitted through each layer, a transmitting power of each layer
is calculated based on the Eq. 1.
FIG. 6 is a graph showing a performance of an adaptive
modulation/demodulation method of a MIMO wireless communication
system with V-BLAST type detector in accordance with a preferred
embodiment of the present invention. The graph shows result of
simulation for comparing performance of a conventional
modulation/demodulation method and the modulation/demodulation
method in accordance with the present invention.
In the simulation, the number of transmitting and receiving
antennas is 4 and a channel of each transmitting and receiving
antenna is a complex Gaussian random variable with zero mean. For
preventing to limit performance by influence of specific channel
matrix, more than 1000 statistic channels are generated. The number
of information bits for transmitting in a predetermined time is set
to 8 and QPSK and 16-QAM are used for modulation method. Thus,
D={0, 2, 4} and therefore, .DELTA..beta. is 2.
In the simulation, a system performance of a conventional
modulation/demodulation method implemented by using greed algorithm
with singular value decomposition (SVD), which is known as the
optimal solution in the adaptive modulation MIMO system is used for
a lower bound for comparison. The conventional
modulation/demodulation method is introduced by G. G Raleigh et.
al., in "spatio-temporal coding for wireless communication" at
Proc. IEEE Globecom, November, 1996, pp. 1809-1814 and it has too
complicated structure. Thus, it is impossible to be implemented to
real system.
Referring to the FIG. 6, SVD is a result of the conventional
modulation/demodulation method, BLAST is a result of using V-BLAST
detection order introduced by Ka-wai Ng and BLAST(random order) is
a result of using random detection order. BLAST(reverse) is a
result of using reverse order of the V-BLAST detection order.
As shown in FIG. 6, the present invention has 0.7 bB performance
gain and 1 dB performance loss in comparison with Ka-wai Ng's
method and the conventional modulation/demodulation method proposed
by Raleigh.
FIG. 7 is a diagram showing an adaptive modulation/demodulation
apparatus of MIMO OFDM wireless communication system with V-BLAST
type detector in accordance with a preferred embodiment of the
present invention.
Referring to FIG. 7, an adaptive modulation MIMO system of the
present invention can be expanded to the MIMO OFDM system. It is
because a channel matrix H of the MIMO system can be replaced with
a channel matrix in each subcarrier of MIMO-OFDM system. There are
two methods implemented to the MIMO OFDM system.
A first method is a method for implementing adaptive modulation
method to all layers M and all subcarriers N.sub.c. At first, an
equivalent channel gain is independently calculated according to a
layer of each transmitting antenna and subcarrier. The equivalent
channel gain is calculated according to the method in FIG. 4 as
much as the number of layers of the transmitting antenna times the
number of subcarriers. Finally, N.sub.c.times.R number of
information bits and transmitting power is allocated according to
the greedy algorithm introduced in FIG. 4 by using the obtained
N.sub.c.times.R number of equivalent channel gains.
Therefore, when total data rate is determined in the MIMO-OFDM
transmitter, the number of information bits and corresponding
transmitting power can be determined by using the equivalent
channel gain obtained by the greedy algorithm in FIG. 4 for
allocating data bits to total antennas and subcarriers. Inhere, a
value of M in FIG. 4 is a value of N becomes N.sub.c.times.M.
However, the first method is very complicated to be implemented in
real system because of large number of comparison and equivalent
channel gain calculation in the greedy algorithm.
A second method is a method for adaptively modulating signal per
each subcarrier, independently. That is, if total data rate is
predetermined in MIMO-OFDM system and the identical data bits are
allocated to each sub carrier wave, the data bits must be allocated
by obtaining the equivalent channel gain of each subcarrier. In
this case, the number of the equivalent channel gain is M per each
subcarrier. The data bits are allocated by using the greedy
algorithm in FIG. 4 in M layers. Thus, Nc times of greedy algorithm
are performed and the repetition number is decreased. The second
method can be simply implemented comparing to the first method but
its performance is decreased compared with the first method.
The bit and power allocation information calculator 73 allocates
the data bits by using the channel matrix H of each subcarrier
delivered by the MIMO channel estimation unit 82 and the
transmission power is also allocated to each transmitting antennas
76-1 to 76-M by using the equivalent channel gain of each
subcarrier.
The adaptive modulation unit based on V-BLAST type detector
performs modulation operations using bits and power allocated to
each transmitting antenna 76-1 to 76-M per each subcarrier.
For demodulating a received signal at the MIMO OFDM system, bits
and transmitting power is known. Therefore, in the MIMO channel
estimator 82 at a receiver, a channel matrix H of each subcarrier
is estimated and performs operations for obtaining bits and power
information using the greedy algorithm. The V-BLAST detection and
adaptive demodulation unit 81 demodulates a signal using bit
allocation information.
FIG. 8 is a graph showing a result of a simulation of an adaptive
modulation/demodulation method of MIMO OFDM wireless system with
V-BLAST type detector in accordance with a preferred embodiment of
the present invention.
Referring to FIG. 8, the simulation is progressed by using 4
transmitting and receiving antennas, 64 subcarriers and 16 cyclic
prefixes are used for OFDM modulation. An exponentially decaying
quasi-static fading channel having 8 taps is used.
The method as mentioned above can be implemented as a program and
can be stored in a computer readable recording medium such as
CD-ROM, RAM, ROM, Floppy disk. Hard disk and optical magnetic
disk.
The present invention can improve performance above 0.7.about.1.4dB
performance gain comparing to conventional modulation method with
random and V-BLAST detection orders without increase of
implementation complexity.
While the present invention has been described with respect to
certain preferred embodiments, it will be apparent to those skilled
in the art that various changes and modifications may be made
without departing from the scope of the invention as defined in the
following claims.
* * * * *