U.S. patent number RE44,959 [Application Number 10/702,053] was granted by the patent office on 2014-06-24 for method and wireless systems using multiple antennas and adaptive control for maximizing a communication parameter.
This patent grant is currently assigned to Intel Corporation. The grantee listed for this patent is David J. Gesbert, Arogyaswami J. Paulraj, Peroor K. Sebastian, Jose Tellado. Invention is credited to David J. Gesbert, Arogyaswami J. Paulraj, Peroor K. Sebastian, Jose Tellado.
United States Patent |
RE44,959 |
Paulraj , et al. |
June 24, 2014 |
Method and wireless systems using multiple antennas and adaptive
control for maximizing a communication parameter
Abstract
A method of maximizing a communication parameter, such as data
capacity, signal quality or throughput of a channel between a
transmit unit with M transmit antennas and a receive unit with N
receive antennas and a communication system such as a wireless
network (including networks with multiple access techniques such as
TDMA, FDMA, CDMA, OFDMA) employing the method. The data is first
processed to produce parallel spatial-multiplexed streams SM.sub.i,
where i=1 . . . k, which are converted or mapped to transmit
signals TS.sub.p, where p=1 . . . M, assigned for transmission from
the M transmit antennas. Corresponding receive signals RS.sub.j,
where j=1 . . . N, are received by the N receive antennas of the
receiver and used to assess a quality parameter, such as a
statistical signal parameter including SINR, SNR, power level,
level crossing rate, level crossing duration of the signal of a
predetermined threshold and reception threshold, or a parameter of
the data, such as BER or packet error rate. The quality parameter
is used to adaptively adjust k as well as other parameters such as
coding and mapping to transmit antennas such that the communication
parameter of the channel is maximized.
Inventors: |
Paulraj; Arogyaswami J.
(Stanford, CA), Sebastian; Peroor K. (Mountain View, CA),
Gesbert; David J. (Nice, FR), Tellado; Jose
(Sunnyvale, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Paulraj; Arogyaswami J.
Sebastian; Peroor K.
Gesbert; David J.
Tellado; Jose |
Stanford
Mountain View
Nice
Sunnyvale |
CA
CA
N/A
CA |
US
US
FR
US |
|
|
Assignee: |
Intel Corporation (Santa Clara,
CA)
|
Family
ID: |
23843684 |
Appl.
No.: |
10/702,053 |
Filed: |
November 5, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09464372 |
Dec 15, 1999 |
6351499 |
Feb 26, 2002 |
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Current U.S.
Class: |
375/267; 375/347;
375/299; 375/346; 370/334; 375/285; 455/101 |
Current CPC
Class: |
H01Q
3/2605 (20130101); H04L 1/0009 (20130101); H04L
1/0003 (20130101); H04B 7/0669 (20130101); H01Q
1/246 (20130101); H04B 7/0697 (20130101); H04L
1/0618 (20130101); H04B 7/0857 (20130101); H04L
1/06 (20130101); H04B 7/0891 (20130101); H04L
1/0606 (20130101); H04B 7/0673 (20130101); H04L
1/0026 (20130101) |
Current International
Class: |
H04B
7/02 (20060101); H04L 1/02 (20060101) |
Field of
Search: |
;375/267,285,299,346,347
;370/334 ;455/101 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0951091 |
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Oct 1999 |
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EP |
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WO98/09381 |
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Mar 1998 |
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WO |
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WO98/09385 |
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Mar 1998 |
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WO |
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Other References
Paulraj, A., Taxonomy of space-time processing for wireless
networks, IEE Proc--Radar Sonar Navig., vol. 145, No. 1, Feb. 1998.
cited by applicant.
|
Primary Examiner: Wang; Ted
Attorney, Agent or Firm: Cool Patent, P.C.
Claims
What is claimed is:
1. A method of maximizing a communication parameter of a channel
between a transmit unit having a number M of transmit antennas and
a receive unit having a number N of receive antennas, said method
comprising the following steps: a) processing .[.said.]. data to
produce parallel spatial-multiplexed streams SM.sub.i, where i=1 .
. . k; b) mapping said spatial-multiplexed streams SM.sub.i to
transmit signals TS.sub.p, where p=1 . . . M, for transmission from
said M transmit antennas to said receiver via said channel, wherein
the mapping comprises processing each of said spatial-multiplexed
streams SM.sub.i by a coding unit to produce coded streams
CS.sub.h, where h=1 . . . k'; c) receiving receive signals
RS.sub.j, where j=1 . . . N by said N receive antennas; d)
assessing a quality parameter of said receive signals RS.sub.j; e)
using said quality parameter to adjust k to maximize said
communication parameter of said channel; and f) using said quality
parameter in said transmit unit to adjust k'.
2. The method of claim 1, wherein said quality parameter is
utilized in said transmit unit to adjust the coding of said coding
unit.
3. The method of claim 1, wherein said coding unit is selected from
the group consisting of space-time coders, space-frequency coders,
adaptive modulation rate coders.
4. The method of claim 3, wherein said space-time coders and said
space-frequency coders use different coding and modulation
rates.
5. The method of claim 1, further comprising the step of receive
processing said receive signals RS.sub.j to reproduce said
spatial-multiplexed streams SM.sub.i.
6. The method of claim 5, wherein said quality parameter is
obtained from said receive processed spatial-multiplexed streams
SM.sub.i.
7. The method of claim 6, wherein said quality parameter is derived
by a statistical unit.
8. The method of claim 6, wherein said quality parameter is
selected from the group consisting of signal-to-interference noise
ratio, signal-to-noise ratio, power level, level crossing rate,
level crossing duration.
9. The method of claim 1, further comprising the steps of
processing said receive signals RS.sub.j to reconstitute said data
and obtaining said quality parameter from said data.
10. The method of claim 9, wherein said quality parameter is
selected from the group consisting of bit-error-rate and packet
error-rate.
11. The method of claim 1, wherein said mapping step further
comprises a transmit processing step by a transmit processing block
and said quality parameter is used for adjusting the transmit
processing of said transmit processing block.
12. The method of claim 1, wherein said quality parameter is fed
back to said transmit unit.
13. The method of claim 1, wherein said step of processing said
data comprises a technique selected from the group consisting of
adaptive modulation, adaptive coding, Space-Time coding, and
Space-Frequency coding.
14. The method of claim 1, wherein said transmit signals TS.sub.p
are formatted in accordance with at least one multiple access
technique selected from the group consisting of TDMA, FDMA, CDMA,
OFDMA.
15. The method of claim 1, wherein said communication parameter is
selected from the group consisting of data capacity, signal quality
and throughput.
16. The method of claim 1, wherein said receive unit and said
transmit unit belong to a cellular communication system.
17. The method of claim 16, used in the downlink of said cellular
communication system.
18. The method of claim 16, used in the uplink of said cellular
communication system.
19. A communication system with an adaptively maximized
communication parameter of a channel in which data is transmitted
between a transmit unit having a number M of transmit antennas and
a receive unit having a number N of receive antennas, said transmit
unit comprising: a) processing means for processing said data to
produce parallel spatial-multiplexed streams SM.sub.i, where i=1 .
. . k; b) antenna mapping means for converting said
spatial-multiplexed streams SM.sub.i to transmit signals TS.sub.p,
where p=1 . . . M, and transmitting said transmit signals TS.sub.p
from said M transmit antennas via said channel; said receive unit
receiving receive signals RS.sub.j, where j=1 . . . N, and said
communication system comprising: a) means for assessing a quality
parameter of said receive signals RS.sub.j; b) means for adjusting
k based on said quality parameter to maximize said communication
parameter of said channel; and c) an adaptive controller in
communication with said processing means and said antenna mapping
means, said adaptive controller adjusting said processing means and
said antenna mapping means based on said quality parameter.
20. The communication system of claim 19, wherein said means for
assessing said quality parameter comprises a statistical unit.
21. The communication system of claim 19, wherein said means for
assessing said quality parameter is located in said receive
unit.
22. The communication system of claim 19, wherein said means for
assessing said quality parameter is located in said transmit
unit.
23. The communication system of claim 19, further comprising a
coding unit in said transmit unit for processing said
spatial-multiplexed streams SM.sub.i to produce coded streams
CS.sub.h, where h=1 . . . k'.
24. The communication system of claim 23, wherein said means for
adjusting k further comprises a mechanism for adjusting k'.
25. The communication system of claim 23, wherein said coding unit
is selected from the group consisting of space-time coders,
space-frequency coders, adaptive modulation rate coders.
26. The communication system of claim 23, further comprising a
database of codes and antenna mapping parameters in communication
with said coding unit and said antenna mapping means.
27. The communication system of claim 23, further comprising an
adaptive controller in communication with said processing means,
said coding unit and said antenna mapping means, said adaptive
controller adjusting said processing means, said coding unit and
said antenna mapping means based on said quality parameter.
28. The communication system of claim 19, wherein said means for
adjusting k is located in said transmit unit.
29. The communication system of claim 19, said communication system
operating in accordance with at least one multiple access technique
selected from the group consisting of TDMA, FDMA, CDMA, OFDMA.
30. The communication system of claim 19, wherein said
communication system is a cellular communication system.
31. The communication system of claim 19 employing multi-carrier
modulation.
.Iadd.32. A method of improving a communication parameter of a
wireless communication channel between a transmit unit having a
number M of transmit antennas and a receive unit having a number N
of receive antennas, said method comprising: processing data to
produce parallel spatial-multiplexed streams; mapping said
spatial-multiplexed streams to transmit signal(s) for transmission
from one or more of said M transmit antennas to the receiver via
the wireless communication channel, wherein the mapping comprises
processing at least a subset of the spatial multiplexed streams to
produce a plurality of coded streams; and receiving an indication
from a receiver denoting one or more quality parameters associated
with the wireless communication channel; and modifying one or more
of the number of parallel spatial-multiplexed streams and the
mapping of said spatial multiplexed streams to transmit signals
based, at least in part, on the received indication; wherein the
quality parameter is utilized in the transmit unit to adjust one or
more coding parameters employed by a coding unit in generating the
plurality of coded streams..Iaddend.
.Iadd.33. A method according to claim 32, wherein the transmit
signals are formatted in accordance with at least one multiple
access technique selected from a group consisting of TDMA, FDMA,
CDMA, and OFDM..Iaddend.
.Iadd.34. A method according to claim 32, wherein the indication is
received from a remote receiver..Iaddend.
.Iadd.35. A method according to claim 32, wherein the indication is
received from a receiver co-located with the transmit
unit..Iaddend.
.Iadd.36. A method of improving a communication parameter of a
wireless communication channel between a transmit unit having a
number M of transmit antennas and a receive unit having a number N
of receive antennas, said method comprising: processing data to
produce parallel spatial-multiplexed streams; mapping said
spatial-multiplexed streams to transmit signal(s) for transmission
from one or more of said M transmit antennas to the receiver via
the wireless communication channel, wherein the mapping comprises
processing at least a subset of the spatial multiplexed streams to
produce a plurality of coded streams; and receiving an indication
from a receiver denoting one or more quality parameters associated
with the wireless communication channel; and modifying one or more
of the number of parallel spatial-multiplexed streams and the
mapping of said spatial multiplexed streams to transmit signals
based, at least in part, on the received indication, wherein a
coding unit is selected from a group consisting of space-time
coders, space-frequency coders, adaptive modulation rate
coders..Iaddend.
.Iadd.37. A method of improving a communication parameter of a
wireless communication channel between a transmit unit having a
number M of transmit antennas and a receive unit having a number N
of receive antennas, said method comprising: processing data to
produce parallel spatial-multiplexed streams; mapping said
spatial-multiplexed streams to transmit signal(s) for transmission
from one or more of said M transmit antennas to the receiver via
the wireless communication channel, wherein the mapping comprises
processing at least a subset of the spatial multiplexed streams to
produce a plurality of coded streams; and receiving an indication
from a receiver denoting one or more quality parameters associated
with the wireless communication channel, wherein the indication
denotes one or more of a bit-error rate (BER), packet error rate
(PER), signal to noise ratio (SNR), signal to interference and
noise ratio (SINR), and a received signal strength indication
(RSSI) measured at the receiver of the communication channel; and
modifying one or more of the number of parallel spatial-multiplexed
streams and the mapping of said spatial multiplexed streams to
transmit signals based, at least in part, on the received
indication..Iaddend.
.Iadd.38. A method of improving a communication parameter of a
wireless communication channel between a transmit unit having a
number M of transmit antennas and a receive unit having a number N
of receive antennas, said method comprising: processing data to
produce parallel spatial-multiplexed streams; mapping said
spatial-multiplexed streams to transmit signal(s) for transmission
from one or more of said M transmit antennas to the receiver via
the wireless communication channel, wherein the mapping comprises
processing at least a subset of the spatial multiplexed streams to
produce a plurality of coded streams; and receiving an indication
from a receiver denoting one or more quality parameters associated
with the wireless communication channel; and modifying one or more
of the number of parallel spatial-multiplexed streams and the
mapping of said spatial multiplexed streams to transmit signals
based, at least in part, on the received indication, wherein the
coding of the spatial-multiplexed streams comprises a technique
selected from a group consisting of adaptive modulation, adaptive
coding, space-time coding, and space-frequency coding..Iaddend.
.Iadd.39. A transmitter comprising: a mapping unit, to selectively
process a plurality (k) of spatial-multiplexed streams to produce a
plurality (k') of coded spatial-multiplexed streams, and to map at
least a subset of the plurality (k') of coded spatial-multiplexed
streams to a plurality of (M) of transmit antennae for transmission
to a remote receiver via a wireless communication channel; and a
control unit, coupled to the mapping unit, to control one or more
aspects of one or more of the selective processing
spatial-multiplexed streams and the mapping of the coded
spatial-multiplexed streams based, at least in part, on an
indication of a quality parameter associated with the wireless
communication channel; wherein the quality parameter is utilized in
the transmitter to adjust one or more coding parameters employed by
a coding unit in generating the plurality of coded
streams..Iaddend.
.Iadd.40. A transmitter according to claim 39, the mapping unit
comprising: a coding unit, to receive the plurality (k) of
spatial-multiplexed streams and to generate the plurality (k') of
coded spatial-multiplexed streams..Iaddend.
.Iadd.41. A transmitter according to claim 40, wherein the coding
unit comprises a number (k) of space-time coders..Iaddend.
.Iadd.42. A transmitter according to claim 40, wherein the coding
unit comprises a number (k) of space-frequency coders..Iaddend.
.Iadd.43. A transmitter according to claim 40, the mapping unit
further comprising: a transmit processing unit, to receive the
plurality (k') of coded spatial-multiplexed streams to select ones
of at least a subset of a plurality (M) of transmit
antennae..Iaddend.
.Iadd.44. A transmitter according to claim 39, wherein the
indication of the quality parameter is received from a remote
receiver..Iaddend.
.Iadd.45. A transmitter according to claim 39, wherein the
indication of the quality parameter associated with the wireless
communication channel is received from a co-located receive
unit..Iaddend.
.Iadd.46. A transceiver comprising: a plurality of dipole antennae;
and a transmitter according to claim 40, coupled with at least a
subset of the plurality of dipole antennae through which a wireless
communication channel may be established with a remote receiver,
wherein the transmitter adaptively modifies one or more of a number
of spatial-multiplexed streams, the coding applied to the
spatial-multiplexed streams, and/or the mapping of the coded
spatial-multiplexed streams to the plurality of dipole
antennae..Iaddend.
.Iadd.47. A transmitter comprising: a mapping unit comprising a
coding unit, to receive a plurality (k) of spatial-multiplexed
streams and to generate a plurality (k') of coded
spatial-multiplexed streams, to selectively process a plurality (k)
of spatial-multiplexed streams to produce a plurality (k') of coded
spatial-multiplexed streams, and to map at least a subset of the
plurality (k') of coded spatial-multiplexed streams to a plurality
of (M) of transmit antennae for transmission to a remote receiver
via a wireless communication channel, the coding unit comprising a
number (k) of space time coders and at least a subset of the k
space-time coders applies one of a number of space-time codes to an
associated subset of the received k spatial-multiplexed streams
based, at least in part, on a control signal generated by a control
unit in view of the received indication; and a control unit,
coupled to the mapping unit, to control one or more aspects of one
or more of the selective processing spatial-multiplexed streams and
the mapping of the coded spatial-multiplexed streams based, at
least in part, on an indication of a quality parameter associated
with the wireless communication channel..Iaddend.
.Iadd.48. A transmitter comprising: a mapping unit comprising a
coding unit, to receive a plurality (k) of spatial-multiplexed
streams and to generate a plurality (k') of coded
spatial-multiplexed streams, to selectively process a plurality (k)
of spatial-multiplexed streams to produce a plurality (k') of coded
spatial-multiplexed streams, and to map at least a subset of the
plurality (k') of coded spatial-multiplexed streams to a plurality
of (M) of transmit antennae for transmission to a remote receiver
via a wireless communication channel, the coding unit comprising a
number (k) of space time coders and at least a subset of the k
space-time coders applies one of a number of space-time codes to an
associated subset of the received k spatial-multiplexed streams
based, at least in part, on a control signal generated by a control
unit in view of the received indication and the space-time code
selected is designed to improve the quality parameter associated
with the wireless communication channel; and the control unit,
coupled to the mapping unit, to control one or more aspects of one
or more of the selective processing spatial-multiplexed streams and
the mapping of the coded spatial-multiplexed streams based, at
least in part, on an indication of a quality parameter associated
with the wireless communication channel..Iaddend.
.Iadd.49. A transmitter comprising: a mapping unit comprising a
coding unit and a transmit processing unit, the coding unit to
receive the plurality (k) of spatial-multiplexed streams and to
generate the plurality (k') of coded spatial-multiplexed streams,
to selectively process a plurality (k) of spatial-multiplexed
streams to produce a plurality (k') of coded spatial-multiplexed
streams, and to map at least a subset of the plurality (k') of
coded spatial-multiplexed streams to a plurality of (M) of transmit
antennae for transmission to a remote receiver via a wireless
communication channel and the transmit processing unit to receive
the plurality (k') of coded spatial-multiplexed streams to select
one of at least a subset of a plurality (M) of transmit antennae
and applies a select one of a number of k M.times.M space-time
filtering matrix set G(z) to the received k' coded
spatial-multiplexed streams; and a control unit, coupled to the
mapping unit, to control one or more aspects of one or more of the
selective processing spatial-multiplexed streams and the mapping of
the coded spatial-multiplexed streams based, at least in part, on
an indication of a quality parameter associated with the wireless
communication channel..Iaddend.
.Iadd.50. A transmitter comprising: a mapping unit comprising a
coding unit and a transmit processing unit, the coding unit to
receive the plurality (k) of spatial-multiplexed streams and to
generate the plurality (k') of coded spatial-multiplexed streams,
to selectively process a plurality (k) of spatial-multiplexed
streams to produce a plurality (k') of coded spatial-multiplexed
streams, and to map at least a subset of the plurality (k') of
coded spatial-multiplexed streams to a plurality of (M) of transmit
antennae for transmission to a remote receiver via a wireless
communication channel and the transmit processing unit to receive
the plurality (k') of coded spatial-multiplexed streams to select
one of at least a subset of a plurality (M) of transmit antennae
and applies a select one of a number of k M.times.M spacetime
filtering matrix set G(z) to the received k' coded
spatial-multiplexed streams; and a control unit, coupled to the
mapping unit, to control one or more aspects of one or more of the
selective processing spatial-multiplexed streams and the mapping of
the coded spatial-multiplexed streams based, at least in part, on
an indication of a quality parameter associated with the wireless
communication channel, the selection of the space-time filtering
matrix set is made in response to control input from the control
unit based, at least in part, on the received
indication..Iaddend.
.Iadd.51. A transmitter comprising: a mapping unit comprising a
coding unit and a transmit processing unit, the coding unit to
receive the plurality (k) of spatial-multiplexed streams and to
generate the plurality (k') of coded spatial-multiplexed streams,
to selectively process a plurality (k) of spatial-multiplexed
streams to produce a plurality (k') of coded spatial-multiplexed
streams, and to map at least a subset of the plurality (k') of
coded spatial-multiplexed streams to a plurality of (M) of transmit
antennae for transmission to a remote receiver via a wireless
communication channel and the transmit processing unit to receive
the plurality (k') of coded spatial-multiplexed streams to select
one of at least a subset of a plurality (M) of transmit antennae
and; and a control unit, coupled to the mapping unit, to control
one or more aspects of one or more of the selective processing
spatial-multiplexed streams and the mapping of the coded
spatial-multiplexed streams based, at least in part, on an
indication of a quality parameter associated with the wireless
communication channel, the transmit processing unit applies a
select one of a number of k M.times.M space-frequency filtering
matrix set to the received k' coded spatial-multiplexed streams in
response to control input from the control unit based, at least in
part, on the received indication..Iaddend.
.Iadd.52. A wireless communication device comprising: a plurality
of dipole antennae, wherein the wireless communication device
establishes a wireless communication channel with one or more
remote wireless communication devices through at least a subset of
such antennae; and a transmit unit, coupled with at least a subset
of the dipole antennae, to selectively process a plurality (k) of
spatial-multiplexed streams to produce a plurality (k') of coded
spatial-multiplexed streams, and to map at least a subset of the
plurality (k') of coded spatial-multiplexed streams to a plurality
of (M) of the antennae for transmission to the remote receiver via
the wireless communication channel, and to control one or more
aspects of one or more of the selective processing
spatial-multiplexed streams and the mapping of the coded
spatial-multiplexed streams based, at least in part, on a received
indication of a quality parameter associated with the wireless
communication channel; wherein the quality parameter is utilized in
the transmit unit to adjust one or more coding parameters employed
by a coding unit in generating the plurality of coded
streams..Iaddend.
.Iadd.53. A wireless communication device according to claim 52,
further comprising: a receive unit, coupled with the transmit unit,
to provide the indication of a quality parameter associated with
the wireless communication channel..Iaddend.
.Iadd.54. A wireless communication device according to claim 52,
wherein the indication of the quality parameter associated with the
wireless communication channel is received from a remote receive
unit..Iaddend.
.Iadd.55. A wireless communication device according to claim 54,
wherein the remote receive unit is an intended target of the
wireless communication channel..Iaddend.
.Iadd.56. A wireless communication device comprising: a plurality
of dipole antennae, wherein the wireless communication device
establishes a wireless communication channel with one or more
remote wireless communication devices through at least a subset of
such antennae; a transmit unit, coupled with at least a subset of
the dipole antennae, to selectively process a plurality (k) of
spatial-multiplexed streams to produce a plurality (k') of coded
spatial-multiplexed streams, and to map at least a subset of the
plurality (k') of coded spatial-multiplexed streams to a plurality
of (M) of the antennae for transmission to the remote receiver via
the wireless communication channel, and to control one or more
aspects of one or more of the selective processing
spatial-multiplexed streams and the mapping of the coded
spatial-multiplexed streams based, at least in part, on a received
indication of a quality parameter associated with the wireless
communication channel; a receive unit, coupled with the transmit
unit, to provide the indication of a quality parameter associated
with the wireless communication channel, the quality parameter
represents one or more of a received signal strength indication
(RSSI), a crossing level, a signal to noise ratio (SNR), a signal
to interference and noise ratio (SINR), a bit error rate (BER), and
a packet error rate (PER)..Iaddend.
.Iadd.57. A wireless communication device comprising: a plurality
of dipole antennae, wherein the wireless communication device
establishes a wireless communication channel with one or more
remote wireless communication devices through at least a subset of
such antennae; and a transmit unit, coupled with at least a subset
of the dipole antennae, to selectively process a plurality (k) of
spatial-multiplexed streams to produce a plurality (k') of coded
spatial-multiplexed streams, and to map at least a subset of the
plurality (k') of coded spatial-multiplexed streams to a plurality
of (M) of the antennae for transmission to the remote receiver via
the wireless communication channel, and to control one or more
aspects of one or more of the selective processing
spatial-multiplexed streams and the mapping of the coded
spatial-multiplexed streams based, at least in part, on a received
indication of a quality parameter associated with the wireless
communication channel, the indication of the quality parameter
associated with the wireless communication channel is received from
a remote receive unit and represents one or more of a received
signal strength indication (RSSI), a crossing level, a signal to
noise ratio (SNR), a signal to interference and noise ratio (SINR),
a bit error rate (BER), and a packet error rate (PER)..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates generally to wireless communication
systems and methods of using transmit and receive units with
multiple antennas to adapt the transmissions to channel conditions
and maximize a communication parameter.
BACKGROUND OF THE INVENTION
Wireless communication systems serving stationary and mobile
wireless subscribers are rapidly gaining popularity. Numerous
system layouts and communications protocols have been developed to
provide coverage in such wireless communication systems.
The wireless communications channels between the transmit and
receive devices are inherently variable and thus their quality
fluctuates. Hence, their quality parameters also vary in time.
Under good conditions wireless channels exhibit good communication
parameters, e.g., high signal-to-noise ratio, large data capacity
and/or throughput. At these times significant amounts of data can
be transmitted via the channel reliably. However, as the channel
changes in time, the communication parameters also change. Under
altered conditions former data rates, coding techniques and data
formats may no longer be feasible. For example, when the channel
performance is degraded the transmitted data may experience
excessive corruption yielding unacceptable communication
parameters. For instance, transmitted data can exhibit excessive
bit-error rates or packet error rates. The degradation of the
channel can be due to a multitude of factors such as general noise
in the channel, multi-path fading, loss of line-of-sight path,
excessive Co-Channel Interference (CCI) and other factors.
By reducing CCI the carrier-to-interference (C/I) ratio can be
improved and the spectral efficiency increased. Specifically,
improved C/I ratio yields higher per link bit rates, enables more
aggressive frequency re-use structures and increases the coverage
of the system.
It is also known in the communication art that transmit units and
receive units equipped with antenna arrays, rather than single
antennas, can improve receiver performance. Antenna arrays can both
reduce multipath fading of the desired signal and suppress
interfering signals or CCI. Such arrays can consequently increase
both the range and capacity of wireless systems. This is true for
wireless cellular telephone and other mobile systems as well as
Fixed Wireless Access (FWA) systems.
In mobile systems, a variety of factors cause signal degradation
and corruption. These include interference from other cellular
users within or near a given cell. Another source of signal
degradation is multipath fading, in which the received amplitude
and phase of a signal varies over time. The fading rate can reach
as much as 200 Hz for a mobile user traveling at 60 mph at PCS
frequencies of about 1.9 GHz. In such environments, the problem is
to cleanly extract the signal of the user being tracked from the
collection of received noise, CCI, and desired signal portions
summed at the antennas of the array.
In FWA systems, e.g., where the receiver remains stationary, signal
fading rate is less than in mobile systems. In this case, the
channel coherence time or the time during which the channel
estimate remains stable is longer since the receiver does not move.
Still, over time, channel coherence will be lost in FWA systems as
well.
Antenna arrays enable the system designer to increase the total
received signal power, which makes the extraction of the desired
signal easier. Signal recovery techniques using adaptive antenna
arrays are described in detail, e.g., in the handbook of Theodore
S. Rappaport, Smart Antennas, Adaptive Arrays, Algorithms, &
Wireless Position Location; and Paulraj, A. J et al., "Space-Time
Processing for Wireless Communications", IEEE Signal Processing
Magazine, Nov. 1997, pp. 49-83.
Prior art wireless systems have employed adaptive modulation of the
transmitted signals with the use of feedback from the receiver as
well as adaptive coding and receiver feedback to adapt data
transmission to changing channel conditions. However, effective
maximization of channel capacity with multiple transmit and receive
antennas is not possible only with adaptive modulation and/or
coding.
U.S. Pat. No. 5,592,490 to Barratt et al., U.S. Pat. No. 5,828,658
to Ottersten et al., and U.S. Pat. No. 5,642,353 Roy III, teach
about spectrally efficient high capacity wireless communication
systems using multiple antennas at the transmitter; here a Base
Transceiver Station (BTS) for Space Division Multiple Access
(SDMA). In these systems the users or receive units have to be
sufficiently separated in space and the BTS uses its transmit
antennas to form a beam directed towards each receive unit. The
transmitter needs to know the channel state information such as
"spatial signatures" prior to transmission in order to form the
beams correctly. In this case spatial multiplexing means that data
streams are transmitted simultaneously to multiple users who are
sufficiently spatially separated.
The disadvantage of the beam-forming method taught by Barratt et
al., Ottersten et al., and Roy III is that the users have to be
spatially well separated and that their spatial signatures have to
be known. Also, the channel information has to be available to the
transmit unit ahead of time and the varying channel conditions are
not effectively taken into account. Finally, the beams formed
transmit only one stream of data to each user and thus do not take
full advantage of times when a particular channel may exhibit very
good communication parameters and have a higher data capacity for
transmitting more data or better signal-to-noise ratio enabling
transmission of data formatted with a less robust coding
scheme.
U.S. Pat. No. 5,687,194 to Paneth et al. describes a Time Division
Multiple Access (TDMA) communication system using multiple antennas
for diversity. The proposed system exploits the concept of adaptive
transmit power and modulation. The power and modulation levels are
selected according to a signal quality indicator fed back to the
transmitter.
Addressing the same problems as Paneth et al., U.S. Pat. No.
5,914,946 to Avidor et al. teaches a system with adaptive antenna
beams. The beams are adjusted dynamically as the channel changes.
Specifically, the beams are adjusted as a function of a received
signal indicator in order to maximize signal quality and reduce the
system interference.
The last two patents certainly go far in the direction of
adaptively changing multiple antenna systems to optimize
performance with varying channel conditions. However, further
improvements are desirable. In particular, it would be desirable to
develop a system where both the transmit unit and receive unit take
full advantage of multiple antennas to not only adaptively change
the modulation and/or coding but also use a suitable diversity
scheme, and spatial multiplexing order all at the same time. These
adaptive changes would help to ensure that the communication
parameters of the channel remain maximized while the channel
varies. Furthermore, it would be an advance in the art to develop a
communications system which could take advantage of multiple
antennas at the transmit and receive unit to adapt to changing
channel conditions and maximize any of a number of desirable
communication parameters such as data capacity, signal-to-noise
ratio and throughput. This would permit the system to continuously
adapt to the type of data being transmitted via the channel.
OBJECTS AND ADVANTAGES OF THE INVENTION
Accordingly, it is a primary object of the present invention to
provide a method to maximize a communication parameter in a channel
between a wireless transmit unit and receive unit, both using
multiple antennas. Specifically, the method should permit the
system to continuously optimize data capacity, signal-to-noise
ratio, signal quality, throughput and other desirable parameters
while the channel varies.
It is a further object of the invention to provide a method which
takes full advantage of multiple antennas at the transmit unit and
receive unit to optimize a communication parameter of the channel
using a quality parameter derived from the received signals.
Yet another object of the invention is to provide a method as
indicated above in any wireless communication system using any
combination of multiple access techniques such as TDMA, FDMA, CDMA,
and OFDMA.
It is also an object of the invention to provide a wireless
communication system taking advantage of adaptive coding, spatial
multiplexing, and antenna diversity to continuously maxmize the
desired communication parameters under varying channel
conditions.
The above objects and advantages, as well as numerous other
improvements attained by the method and apparatus of the invention
are pointed out below.
SUMMARY
The objects and advantages of the invention are achieved by a
method of maximizing a communication parameter, such as data
capacity, signal quality or throughput of a channel between a
transmit unit with M transmit antennas and a receive unit with N
receive antennas. The data is first processed to produce parallel
spatial-multiplexed streams SM.sub.i, where i=1 . . . k. Then, the
spatial-multiplexed streams SM.sub.i are converted or mapped to
transmit signals TS.sub.p, where p=1 . . . M, assigned for
transmission from the M transmit antennas.
The transmitted signals propagate through the channel and are
received in the form of receive signals RS.sub.j, where j=1 . . .
N, by the N receive antennas of the receiver. The receive signals
RS.sub.j are used to assess a quality parameter. The quality
parameter is used to adaptively adjust k such that the
communication parameter of the channel is maximized.
In a preferred embodiment, each of the spatial-multiplexed streams
SM.sub.i is processed by a coding unit to produce coded streams
CS.sub.h, where h=1 . . . k'. The quality parameter is utilized in
the transmitter to adjust the coding, e.g., by changing k', used by
the coding unit. The coding unit can be a space-time coder, a
space-frequency coder, an adaptive modulation rate coder or other
suitable coding device. The space-time and space-frequency coders
can use different coding and modulation rates.
At the receiver the receive signals RS.sub.j are receive processed
to reproduce the spatial-multiplexed streams SM.sub.i. The quality
parameter can be obtained from the receive processed streams
SM.sub.i. This can be accomplished by a statistical unit which
examines streams SM.sub.i. In this case the quality parameter can
be signal-to-interference ratio, signal-to-noise ratio, power
level, level crossing rate, level crossing duration of the signal
of a predetermined threshold and reception threshold. Alternatively
or in addition the quality parameter can be obtained from
reconstituted data. In this case the quality parameter can be the
bit-error-rate (BER) or packet error rate.
The mapping step at the transmitter preferably also includes a
transmit processing step implemented by a transmit processing
block. The quality parameter is then preferably also used for
adjusting the processing of the transmit processing block.
Although the quality parameter is typically evaluated at the
receiver and fed back or sent to the transmitter in any suitable
way, e.g., over a reciprocal channel as used in Time Division
Duplexed (TDD) systems, the analysis of the receive signals to
derive the quality parameter can be performed by the transmitter.
This can be advantageous, e.g., when the receiver does not have
sufficient computational resources to derive the quality
parameter.
The step of processing the data at the transmitter can be performed
by using any suitable coding technique. For example, Space-Time
coding or Space-Frequency coding can be used. Meanwhile, the
transmit signals TS.sub.p are formatted in accordance to at least
one multiple access technique such as TDMA, FDMA, CDMA, OFDMA.
The method of the invention can be used between any transmit and
receive units including portable and stationary devices. In one
embodiment, the method is employed in a wireless network such as a
cellular communication system. In this case the method can be used
to improve the communication parameter in both downlink and uplink
communications.
The method of the invention can be used in existing systems having
multiple receive and transmit antennas. The method also permits
other useful methods to be employed concurrently. In particular, it
is advantageous to use the techniques of the invention together
with interference canceling.
A communication system employing the method of the invention
achieves adaptive maximization of the communication parameter
between its transmit and receive units. The transmit unit has a
processing device for processing the data to produce the parallel
spatial-multiplexed streams SM.sub.i and an antenna mapping device
for converting streams SM.sub.i to transmit signals TS.sub.p and
mapping them to the M transmit antennas. The communication system
is equipped with a unit for assessing the quality parameter of
received signals RS.sub.j. In addition, the communication system
has a device for adaptively adjusting k based on the quality
parameter to maximize the communication parameter. This device can
be located in the transmit unit.
The unit for assessing the quality parameter is a statistical unit
and is preferably located in the receive unit. Of course, the
statistical unit can be located in the transmit unit, as may be
advantageous when the receive unit has insufficient resources or
power to support the statistical unit.
The communication system also has a coding unit for processing
streams SM.sub.i to produce coded streams CS.sub.h (h=1 . . . k').
The device for adjusting k then also has a mechanism for adjusting
k'. The coding unit can be a space-time coder, space-frequency
coder or an adaptive modulation and coding rate coder. Preferably,
a database of codes and transmit processing parameters is connected
to the coding unit and the antenna mapping device.
An adaptive controller is connected to the processing device, the
coding unit and the antenna mapping device. The adaptive controller
adjusts these based on the quality parameter. Alternatively, the
adaptive controller is connected just to the processing device and
the antenna mapping device and adjusts them based on the quality
parameter.
The communication system can employ any one or more of the
available multiple access techniques such as TDMA, FDMA, CDMA,
OFDMA. This can be done in a wireless system, e.g., a cellular
communication system.
A detailed description of the invention and the preferred and
alternative embodiments is presented below in reference to the
attached drawing figures.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a simplified diagram illustrating a communication system
in which the method of the invention is applied.
FIG. 2 is a simplified block diagram illustrating the transmit and
receive units according to the invention.
FIG. 3 is a block diagram of an exemplary transmit unit in
accordance with the invention.
FIG. 4 is a block diagram of an exemplary receive unit in
accordance with the invention.
FIG. 5A is a block diagram illustrating the operation of the
statistical units for deriving the quality parameter.
FIG. 5B is a block diagram illustrating the operation of
alternative data analysis blocks for deriving a quality parameter
from reconstituted data.
FIG. 6 is a block diagram of a portion of another embodiment of
transmit unit in accordance with the invention.
FIG. 7 is a block diagram of a portion of a receive unit for
receiving receive signals RS.sub.j from the transmit unit of FIG.
6.
FIG. 8 illustrates performance curves for S-T code selection in
accordance with the invention.
DETAILED DESCRIPTION
The method and wireless systems of the invention will be best
understood after first considering the high-level diagrams of FIGS.
1 and 2. FIG. 1 illustrates a portion of a wireless communication
system 10, e.g., a cellular wireless system. For explanation
purposes, the downlink communication will be considered where a
transmit unit 12 is a Base Transceiver Station (BTS) and a receive
unit 14 is a mobile or stationary wireless user device. Exemplary
user devices include mobile receive units 14A, 14B, 14C which are
portable telephones and car phones and stationary receive unit 14D,
which can be a wireless modem unit used at a residence or any other
fixed wireless unit. Of course, the same method can be used in
uplink communication from wireless units 14 to BTS 12.
BTS 12 has an antenna array 16 consisting of a number of transmit
antennas 18A, 18B, . . . , 18M. Receive units 14 are equipped with
antenna arrays 20 of N receive antennas (for details see FIGS. 2,
4). BTS 12 sends transmit signals TS to all receive units 14 via
channels 22A and 22B. For simplicity, only channels 22A, 22B
between BTS 12 and receive units 14A, 14B are indicated, although
BTS 12 transmits TS signals to all units shown. In this particular
case receive units 14A, 14B are both located within one cell 24.
However, under suitable channel conditions BTS 12 can transmit TS
signals to units outside cell 24, as is known in the art.
The time variation of channels 22A, 22B causes transmitted TS
signals to experience fluctuating levels of attenuation,
interference, multi-path fading and other deleterious effects.
Therefore, communication parameters of channels 22A, 22B such as
data capacity, signal quality or throughput undergo temporal
changes. Thus, channels 22A, 22B can not at all times support
efficient propagation of high data rate signals RS or signals which
are not formatted with a robust coding algorithm. Antenna array 16
at BTS 12 can be used for spatial multiplexing, transmit diversity,
beam-forming to reduce interference, increase array gain and
achieve other advantageous effects. Antenna arrays 20 at receive
units 14 can be used for spatial multiplexing, interference
canceling, receive diversity, increased array gain and other
advantageous effects. All of these methods improve the capacity of
channels 22A, 22B. The method of the invention finds an optimum
combination of these techniques chosen adaptively with changing
conditions of channels 22A, 22B. In other words, the method of the
invention implements an adaptive and optimal selection of order of
spatial multiplexing, order of diversity as well as rate of coding
and bit-loading over transmit antenna array 16 to antenna array
20.
Specifically, the method of the invention addresses these varying
channel conditions by adaptively maximizing one or more
communication parameters based on a quality parameter. FIG. 2
illustrates the fundamental blocks of transmit unit 12 and one
receive unit 14 necessary to employ the method. Transmit unit 12
has a control unit 26 connected to a data processing block 28 for
receiving data 30 to be formatted, coded and mapped to antennas
18A, 18B, . . . , 18M for transmission therefrom. An up-conversion
and RF amplification block 32 supplies the transmit signals TS to
antennas 18A, 18B, . . . , 18M.
On the other side of the link, receiving unit 14 has N antennas
34A, 34B, . . . , 34N in its array 20 for receiving signals RS. An
RF amplification and down-conversion block 36 processes RS signals
and passes them to data processing block 38. A signal statistics
unit 40 assesses a quality parameter of RS signals and/or recovered
data 44 and feeds back quality parameter to control unit 26 of
transmitter 12. The feedback is indicated by dashed line 42. Using
this quality parameter, unit 26 controls data processing 28 to
ensure appropriate spatial multiplexing, diversity processing,
coding and mapping of data 30 such that a selected communication
parameter or parameters are continuously maximized.
The details of a preferred embodiment of a transmit unit 50 for
practicing the method of the invention are shown in FIG. 3. Data 52
to be transmitted is delivered to a data processing block 54, where
it first passes through an interleaver and pre-coder 56.
Interleaver and pre-coder 56 interleaves and pre-codes the stream
of data 52, as is known in the art and sends the interleaved and
pre-coded stream to serial to parallel converter 58. Converter 58,
produces from the single data stream a number k of
spatial-multiplexed streams SM.sub.i, where i=1 . . . k and k is a
variable, i.e., the number of streams SM.sub.i is variable, subject
to the condition that 1.ltoreq.k.ltoreq.N and also k.ltoreq.M. In
other words, the maximum number k of streams SM.sub.i is limited by
the smaller of the number M of transmit antennas TA.sub.1,
TA.sub.2, . . . , TA.sub.M and the number N of receive antennas
RA.sub.1, RA.sub.2, . . . , RA.sub.N (see FIG. 4).
The value of k is controlled by an adaptive controller 60, which is
part of control unit 62 and is connected to serial to parallel
converter 58. The decision on the number k of streams SM.sub.i can
be made locally by adaptive controller 60 or it can be communicated
from a receiver, as described below. In most systems, the decision
relies on feedback 64 from receiver indicating a quality parameter
or information from which adaptive controller 60 can derive the
quality parameter. In other systems, for example Time Division
Duplexed (TDD) system, where the channel is reciprocal, no extra
feedback is necessary. In those cases the feedback is obtained from
the transmit unit's own receive unit, as indicated in dashed
lines.
Each of the k streams SM.sub.i passes through a corresponding
Space-Time Coder 65 (S-T Coder) of an S-T Coding Unit 66. Each S-T
Coder produces k' coded streams CS.sub.h, where h=1 . . . k'. The
number k' is at least 1 and at most M, depending on the number of
streams SM.sub.i selected by adaptive controller 60. In fact,
adaptive controller 60 is also connected to S-T Coding unit 66 to
also control the number k'.
Space-time coding is a known technique which combines conventional
channel coding and antenna diversity. S-T coding splits an encoded
data stream, in this case each of spatial-multiplexed streams
SM.sub.i into k' dependent data streams, in this case coded streams
CS.sub.h, each of which is modulated and simultaneously transmitted
from a different transmit antenna TA. Various choices of mapping of
data to transmit antennas TA.sub.1, TA.sub.2, . . . , TA.sub.M can
be used. All transmit antennas TA can use the same modulation
format and carrier frequency. Alternatively, different modulation
or symbol delay can be used. Other approaches include the use of
different carrier frequencies (multi-carrier techniques) or
spreading codes. The concept of S-T coding is further described in
the literature (see, e.g., V. Tarokh et al., "Space-time codes for
high data rate wireless communication: Performance criterion and
code construction", IEEE Transactions on Information Theory, Vol.
44, No. 2, March 1998; and S. A. Alamouti, "A simple transmit
diversity technique for wireless communications", IEEE Journal on
selected areas in Communications, Vol. 16, pp. 1451-58, October
1998).
According to the method of the invention, each S-T code is imposed
by corresponding S-T coder 65 and output in the form of k' streams
CS.sub.h. The constraint length of the code and value k' can be
decided depending upon the computational complexity which can be
afforded in the operation of the communication system. The coding
rate and the modulation rate should be chosen depending upon the
characteristics of the channel, i.e., depending on the
communication parameter as reflected by the value of the quality
parameter.
In the preferred embodiment a database 68 in control unit 62
contains the set of S-T codes to be used depending on the number k'
and the quality parameter. Database 68 is connected to S-T Coding
Unit 66 for supplying these S-T codes to the latter. Adaptive
controller 60 is connected to database 68 to control the transfer
of the S-T codes to S-T Coding Unit 66.
Each of the S-T codes stored in database 68 has an associated
coding scheme and modulation scheme. The coding rate and modulation
rate of the different S-T codes may be chosen to be different, such
that each S-T code is suitable to given channel conditions, as
indicated by the quality parameter. The choice of coding rates and
modulation rates of the S-T codes can be further dictated by what
communication parameter of the channel is to be optimized.
Specifically, communication parameter such as data throughput
requires that the S-T code with higher rate modulation and code be
chosen.
For example, if the quality parameter which is fed back is SINR and
the aim is to improve the throughput, then database 68 will contain
the performance curves (BER versus SINR) for different S-T codes
for all possible transmit/receive configurations in terms of number
M of transmit antennas TA.sub.1, TA.sub.2, . . . , TA.sub.M and
number N of receive antennas RA.sub.1, RA.sub.2, . . . , RA.sub.N.
FIG. 8 shows the performance of three typical S-T codes. As can be
seen, to achieve a BER of value q, which is suitable for the
application (e.g., voice data transmission), when the prevailing
average SINR has to have a value p or less, only S-T codes 1 and 2
are suitable. S-T code 3 is not suitable because at SINR value p
its BER is too high. Now, when the communication parameter to be
maximized is the throughput, an additional choice is to be made
between S-T code 1 and S-T code 2, and the one maximizing
throughput is selected. A person of average skill in the art will
see that this process or a similar process can be employed to
maximize any of the communication parameters. In addition,
preferably, database 68 contains the necessary performance curves
to select the proper S-T codes, values of k and G(z) matrix sets to
use. However, empirically collected data may also be used.
In the preferred embodiment, k' is equal to the number M of
transmit antennas TA.sub.1, TA.sub.2, . . . , TA.sub.M. Each S-T
coder 65 uses the S-T code indicated by adaptive controller 60 and
the codes used by individual S-T coders 65 can be the same or
different. Alternatively, the k spatial-multiplexed streams
SM.sub.i can also be S-T coded jointly to provide only one set of
k' coded streams CS.sub.h. Joint S-T coding typically incurs a
higher computational complexity as opposed to separate S-T coding.
Joint S-T coding is preferable if the computational complexity is
acceptable. A person of average skill in the art will be able to
make the appropriate design choice in any given case.
A transmit processing unit 72 receives coded streams CS.sub.h and
produces M transmit signals TS.sub.1, TS.sub.2, . . . , TS.sub.M
for transmission. An Up-conversion and RF Amplification unit 74, as
is well-known in the art, receives the M transmit signals TS.sub.p,
prepares them as necessary, and transmits them from antennas
TA.
The conversion of coded streams CS.sub.h is performed by the
application of k M.times.M space-time (or alternatively
space-frequency) filtering matrix set G(z) to all inputs (M=k').
The choice of matrix set G(z) is based on the quality parameter.
For this reason adaptive controller 60 is connected to unit 72 to
adaptively control the selection of matrix set G(z).
Preferably, database 68 is also connected to unit 72 and contains
stored parameters of suitable matrix sets G(z) for any given
channel conditions or the matrix sets G(z) themselves. In the
latter case adaptive controller 60, which is also connected to
database 68, instructs database 68 to download the appropriate
matrix set G(z) into transmit processing unit 72 as the channel
conditions change. The choice of matrix set G(z) is made to
facilitate the salability of the k spatial-multiplexed streams
SM.sub.i at the receiver. Matrix set G(z) can incorporate diversity
techniques such as delay/switched diversity or any other combining
techniques known in the art. For example, when no channel
information is available at transmit unit 50, e.g., at system
initialization or at any other time, then matrix set G(z) (which
consists of k M.times.M matrices) is made up of k matrices of rank
M*k such that the subspaces spanned by thee matrices are mutually
orthogonal to ensure separability of k stems at receive unit 80.
The task of finding such matrices can be performed by a person of
average skill in the art. During operation, as the quality
parameter changes, other sets of matrices G(z) can be also
used.
It is important to note, that S-T Coding Unit 66 and transmit
processing unit 72 together operate on the k spatial-multiplexed
streams SM.sub.i to map them into transmit signals TS.sub.p, where
p=1 . . . M, which are assigned to the corresponding transmit
antennas TA.sub.1, TA.sub.2, . . . , TA.sub.M. In other words, S-T
Coding Unit 66 in conjunction with transmit processing unit 72 form
an antenna mapping unit which maps streams SM.sub.i to transmit
antennas TA.sub.1, TA.sub.2, . . . , TA.sub.M in accordance with
the above-described rules. The mapping is adjusted by adaptive
controller 60 with the aid of S-T codes and matrices G(z) stored in
database 68 as a function of the quality parameter indicative of
the channel conditions.
Transmit unit 50 preferably also has a training unit 70 drawn in
dashed lines to include training data, as is known in the art. The
training data can be inserted at any appropriate location before or
after S-T Coding Unit 66 and delivered to transmit processing unit
72. The training data can be sent in a separate control channel or
together with data 52. A person of average skill in the art will be
familiar with the necessary techniques and requirements.
FIG. 4 shows the block diagram of a corresponding receiver 80 for
receiving signals transmitted from transmit unit 50. Specifically,
receiver 80 has an array of N receive antennas RA.sub.1, RA.sub.2,
. . . , RA.sub.N to receive RS.sub.j receive signals, where j=1 . .
. N. An RF amplification and down-conversion block 82 amplifies and
converts signals RS.sub.j and performs any other required
operations (e.g., sampling, analog-to-digital conversion). Then,
signals RS.sub.j are passed on to both a matrix channel estimator
84 and a receive processing unit 86.
Matrix channel estimator 84 estimates the channel coefficients
using known training patterns, e.g., the training patterns provided
by training unit 70 in accordance with known techniques. In the
present case, the output of estimator 84 is A(z): A(z)=G(z)H(z),
where G(z) is the matrix applied by transmit processing block 72,
and H(z) is the matrix of pure channel coefficients. G(z) is a set
of M.times.M matrices while H(z) is an M.times.N matrix. The
resulting matrix A(z) is an M.times.N matrix and represents channel
estimates for received signals RS.sub.1, RS.sub.2, . . . , RS.sub.N
after digitization. The channel estimates supplied to receive
processing block 86 by estimator 84 are used by the latter to
recover the k spatial-multiplexed streams SM.sub.i. In fact, any of
the well-known receive processing techniques such as zero-forcing
(ZF), MMSE, LS, ML etc. can be used for processing received signals
RS.sub.1, RS.sub.2, . . . , RS.sub.N.
The recovered k coded streams are supplied to both an S-T Decoding
Unit 88 and to a signal statistics of receive streams unit 90. S-T
Decoding Unit 88 has S-T decoders 89 which reverse the coding of
S-T coders 65 of transmit unit 50. The S-T codes to be applied are
supplied to unit 88 by a database 92. S-T decoding will be
discussed in more detail below in reference to FIG. 5. Signal
statistics unit 90 analyzes receive signals RS.sub.j converted to k
streams by receive processing block 86 to assess the quality
parameter. In the preferred embodiment, unit 90 is an averaging
unit which averages signal statistics over time. Unit 90 computes
the signal statistics of each of the k streams including
signal-to-interference noise ratio (SINR), signal-to-noise ratio
(SNR), power level, level crossing rate (LCR), level crossing
duration at a given signal threshold and reception threshold or
other signal parameters.
For example, when receive processing is performed with the ZF
(zero-forcing) method, unit 90 computes SINR in accordance with the
following algorithm:
##EQU00001## where the brackets denotes the expectation value, X is
the transmitted sequence and Y is the received sequence. LCR is the
rate at which the signal level goes below a set level. LCR can be
computed for different signal level thresholds. SINR and LCR both
give an indication of the error properties of the channel. The
window size (duration) over which these statistics are computed and
averaged by unit 90 can be changed depending upon the kind of
channel receive unit 80 sees.
For a given threshold level and LCR the error probability will
depend upon the type of S-T codes used (which includes the coding
and modulation aspects of the S-T codes) and the number k of
spatial-multiplexed streams SM.sub.i used by transmit unit 50. The
value of k is dictated by the separability of spatial signatures at
receive unit 50.
Thus, the choice of S-T codes for k separable spatial-multiplexed
streams SM.sub.i can be based on the LCR and LC duration at a given
threshold level and a maximum acceptable error rate. Average SINR
can also give similar kind of information. This error information
is used directly by unit 90 as the quality parameter or is used to
derive the quality parameter. The other signal criteria can be used
in a similar fashion to be employed by unit 90 directly as the
quality parameter or to derive a quality parameter.
Alternatively, and preferably in addition to unit 90 a signal
statistics of output streams unit 94 is used to analyze
reconstructed streams SM.sub.i obtained from S-T Decoding Unit 88.
Once again, unit 94 can perform the same statistical computations
of reconstructed streams SM.sub.i to obtain signal statistics
including signal-to-interference noise ratio (SINR),
signal-to-noise ratio (SNR), power level, level crossing rate
(LCR), level crossing duration and reception threshold or other
signal parameters. Meanwhile, reconstructed streams SM.sub.i are
converted to a serial stream by parallel to serial converter 96.
Then, they are de-interleaved and decoded by de-interleaver and
decoder 98 to recover data 52' (the prime indicates that the
recovered data may differ from original data 52 due to transmission
errors) originally transmitted from transmit unit 50.
The method of the invention employs the quality parameter or
parameters obtained as described above to adjust at least the
number k of spatial-multiplexed streams SM.sub.i generated by
serial to parallel converter 58 of transmit unit 50. Preferably,
the quality parameter or parameters are also used to control the
S-T coding of unit 66, e.g., the selection of number k', and
transmit processing, i.e., the selection of matrix set G(z) of
transmit processing unit 72 of transmit unit 50.
During regular operation, transmit unit 50 selects G(z), k, k' and
S-T codes at system initialization. These parameters are then
updated as the channel changes. Transmit unit 50 sends control
information 102 (see FIG. 5A), including the S-T codes used, the
value k, the matrix set G(z) being applied by transmit processing
unit 72 etc. regularly to receive unit 80. Alternatively, this
information may be transmitted only once during initialization of a
communication session and then updated as required (e.g., only when
one of these pieces of information changes).
FIG. 5A illustrates in more detail how adaptive control of G(z), k,
k' and S-T codes is accomplished. Streams S.sub.1 through S.sub.k
are supplied to unit 90 while reconstructed spatial-multiplexed
streams SM.sub.1 through SM.sub.k are supplied to unit 94. Both
units 90, 94 compute the signal statistics as described above.
Then, units 90, 94 communicate their signal statistics or quality
parameters to an S-T Code Lookup block 100. Based on these block
100 makes a decision on the most suitable S-T code and value of k
to be used. This decision is passed on as feedback 64 to
transmitter 50. Alternatively, block 100 passes on the signal
statistics as feedback 64 to adaptive control 60 of transmit unit
50. In this case, adaptive control 60 selects the appropriate S-T
codes and k value. The decisions on the use of appropriate matrix
set G(z) is also made by adaptive control 60 based on feedback
64.
Of course, in order to recover data 52, receiver 80 has to use the
appropriate S-T codes and know the number k. This information is
available to it either from block 100, which can supply this
information to database 92 of S-T codes which is connected to S-T
Decoding Unit 88 (see FIG. 4) or from control channel information
102 transmitted by transmit unit 50, as mentioned above. In case
control channel information 102 is used, an S-T code, k indicator
104 receives the information and communicates it to database 92.
During system start-up indicator 104 can either start with the last
used configuration or start with value k=1 and a particular S-T
code and G(z) matrix set. Alternatively, it can start with any
agreed upon configuration. Of course, the configuration will be
updated during the session to maximize a communication
parameter.
The adjustment of k, S-T codes and selection of matrix set G(z),
whether suggested by block 100 or determined by adaptive control
60, is made to maximize or optimize a communication parameter under
the changing channel conditions. Typically, the communication
parameter to be maximized is either the channel capacity, signal
quality, SNR or throughput. Channel capacity will be maximized by
selecting the largest possible value of k and a high throughput S-T
code (high modulation rate and low coding overhead). The reduction
of k increases the order of diversity. In this case, the signal
quality improves but throughput decreases. The SNR will be
maximized if k=1, but this, will minimize the channel capacity.
Hence adaptive control 60 (or block 100) has to decide an optimum k
if both channel capacity and signal quality are to be
maximized.
In addition, in case the method of the invention is implemented in
a system with frequency re-use, e.g., a cellular network with
frequency re-use, the receive unit is likely to see interference.
In addition, the method of invention is preferably implemented in
conjunction with interference mitigation, as is known in the art.
In that case, the choice of S-T codes, the number k and matrix set
G(z) should be done in such a way that interference mitigation is
also carried out side by side. When the method of the invention is
implemented with interference mitigation some reduction of order of
diversity or spatial multiplexing may occur.
In an alternative embodiment, S-T Decoding Unit 88 can be a joint
S-T decoder for producing k reconstructed streams SM.sub.i rather
than the group of S-T decoders 89 as shown in FIG. 4. Joint or
separate decoding strategy depends upon the coding strategy
employed by transmit unit 50 and can be reconfigured.
In alternative embodiments different types of coders can replace
the S-T coders. For example, the decoding unit can be a
space-frequency coder, and adaptive modulation rate coder or other
suitable coding device. The space-time and space-frequency coders
can use different coding and modulation rates.
In yet another embodiment, as shown in FIG. 5B, receive unit 80 can
take advantage of additional data analysis blocks 110 and 112 to
compute additional data statistics after parallel to serial
conversion and after the de-interleaving and final de-coding steps.
These data statistics could be BER or packet error rate. This
information can also be fed back to transmit unit 50 to adjust the
parameters k, k', S-T coding and selection of matrix set G(z).
Alternatively, this information can be sent to unit 100 for local
determination of the parameters.
The system can be based on any multiple access technique including
TDMA, FDMA, CDMA and OFDMA. For example, the adaptations necessary
to transmit unit 50 and receive unit 80 for implementation in an
OFDM system are illustrated in FIGS. 6 and 7. Specifically, FIG. 6
illustrates the adaptation of transmit unit 50 to operate in an
OFDM system. In this case transmit signals from transmit processing
unit 72 have to be converted to parallel by serial-to-parallel
converters (S/P) 120. In this case, training unit 70 also provides
the training patterns directly to S/P converters 120 in this case.
Next, the parallel transmit signals are inverse fast Fourier
transformed by IFFT's 122 and again transformed to serial by
parallel-to-serial converters (P/S) 124. Then, the signals are
up-converted and amplified for RF transmission from transmit
antennas TA.sub.1, . . . , TA.sub.M.
FIG. 7 illustrates the adaptation to receive unit 80 necessary to
receive OFDM signals as transmitted for transmit unit 50 adapted as
shown in FIG. 6. Specifically, receive signals are received by
receive antennas RA.sub.1, . . . , RAN and the down-converted and
amplified by the corresponding blocks. Then, the signals are
converted from serial to parallel by S/P converters 126. Fast
Fourier transform (FFT) blocks 128 1 through N then transform the
signals and pass them on to both a space-frequency (S-F) matrix
channel estimator 130 and to the receive processing block 132. From
there, the processing of the receive signals proceeds as in receive
unit 80.
It will be clear to one skilled in the art that the above
embodiment may be altered in many ways without departing from the
scope of the invention. Accordingly, the scope of the invention
should be determined by the following claims and their legal
equivalents.
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