U.S. patent application number 13/736749 was filed with the patent office on 2013-08-01 for cooperative mimo in multicell wireless networks.
This patent application is currently assigned to ADAPTIX, INC.. The applicant listed for this patent is Adaptix, Inc.. Invention is credited to Hui Liu, Manyuan Shen, Guanbin Xing.
Application Number | 20130195000 13/736749 |
Document ID | / |
Family ID | 47780484 |
Filed Date | 2013-08-01 |
United States Patent
Application |
20130195000 |
Kind Code |
A1 |
Shen; Manyuan ; et
al. |
August 1, 2013 |
COOPERATIVE MIMO IN MULTICELL WIRELESS NETWORKS
Abstract
A method and system for cooperative multiple-input multiple
output (MIMO) transmission operations in a multicell wireless
network. Under the method, antenna elements from two or more base
stations are used to form an augmented MIMO antenna array that is
used to transmit and received MIMO transmissions to and from one or
more terminals. The cooperative MIMO transmission scheme supports
higher dimension space-time-frequency processing for increased
capacity and system performance.
Inventors: |
Shen; Manyuan; (Bellevue,
WA) ; Xing; Guanbin; (Issaquah, WA) ; Liu;
Hui; (Clyde Hill, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Adaptix, Inc.; |
Carrollton |
TX |
US |
|
|
Assignee: |
ADAPTIX, INC.
Carrollton
TX
|
Family ID: |
47780484 |
Appl. No.: |
13/736749 |
Filed: |
January 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12130277 |
May 30, 2008 |
8396153 |
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13736749 |
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11007570 |
Dec 7, 2004 |
7428268 |
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12130277 |
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Current U.S.
Class: |
370/312 |
Current CPC
Class: |
H04L 27/2626 20130101;
H04L 5/0023 20130101; H04B 7/0669 20130101; H04B 7/024 20130101;
H04L 2001/0092 20130101; H04W 4/06 20130101; H04L 1/0625 20130101;
H04B 7/10 20130101; H04B 7/068 20130101 |
Class at
Publication: |
370/312 |
International
Class: |
H04W 4/06 20060101
H04W004/06 |
Claims
1. A method comprising: employing antenna elements from a plurality
of base stations to support joint cooperative multiple-input
multiple-output (MIMO) transmissions in a wireless network, wherein
the joint cooperative MIMO transmissions are orthogonal frequency
division multiple access (OFDMA) MIMO transmissions; replicating a
data stream received from an information source; forwarding the
replication of the data stream to each base station of the
plurality of base stations; performing antenna signal processing
operations at each base station of the plurality of base stations
on the replication of the data stream it receives to generate
antenna signals; transmitting the antenna signals over selected
antenna elements of the antenna elements at each base station of
the plurality of base stations to form the joint cooperative MIMO
transmissions; and encoding, at respective base stations of the
plurality of base stations, the replication of the data stream
using one of space-time coding, space-frequency coding,
space-time-frequency coding, and spatial multiplexing to establish
the joint cooperative MIMO transmissions.
2. The method of claim 1, wherein the encoded joint cooperative
MIMO transmissions include subscriber MIMO channel information.
3. The method of claim 1, wherein the space-time coding comprises
space-time trellis coding.
4. The method of claim 1, wherein the space-time coding comprises
space-time block coding.
5. The method of claim 1, further comprising: encoding the joint
cooperative MIMO transmissions using space-time coding with delay
diversity.
6. The method of claim 1, wherein the joint cooperative MIMO
transmissions include downlink transmission s from the plurality of
base stations to terminals and uplink transmissions from the
terminals to the plurality of base stations.
7. The method of claim 1, further comprising: performing spatial
beamforming for selected ones of the joint cooperative MIMO
transmissions.
8. The method of claim 7, wherein the spatial beamforming is
performed in combination with one of space-time, space-frequency
and space-time-frequency coding of the selected ones of the joint
cooperative MIMO transmissions.
9. The method of claim 1, further comprising: transmitting the
joint cooperative MIMO transmissions to at least two terminals
simultaneously.
10. The method of claim 9, further comprising: performing spatial
beamforming on the joint cooperative MIMO transmissions such that
MIMO transmissions are directed toward intended users while spatial
nulling is effected toward unintended users.
11. The method of claim 1, further comprising: decoding, jointly,
uplink MIMO transmissions received from multiple terminals.
12. The method of claim 1, further comprising: decoding, jointly,
downlink MIMO transmissions received at multiple terminals.
13. The method of claim 1, further comprising: decoding,
separately, uplink MIMO transmissions received from multiple
terminals.
14. The method of claim 1, further comprising: encoding, jointly,
downlink MIMO transmissions sent to multiple terminals.
15. The method of claim 14, further comprising: decoding a jointly
encoded downlink MIMO transmission at a terminal of the multiple
terminals; and keeping portions of data sent via the jointly
encoded downlink MIMO transmission intended for the terminal, while
discarding other portions of the data that are not intended for the
terminal.
16. The method of claim 14, further comprising: separately
decoding, separately, the jointly encoded downlink transmissions at
each of the multiple terminals.
17. The method of claim 1, further comprising: synchronizing
performance of the antenna signal processing operations at the
plurality of base stations such that the antenna signals are
transmitted over the selected antenna elements at different base
stations of the plurality of base stations in synchrony.
18. The method of claim 1, further comprising: performing the joint
cooperative MIMO transmissions to facilitate terminal handoff
between wireless network cells or sectors.
19. The method of claim 1, further comprising: performing MIMO
encoding on another data stream to be transmitted over a
corresponding joint cooperative MIMO channel, the MIMO encoding
producing a respective set of encoded data sequences for each base
station of the plurality of base stations; sending to each base
station of the plurality of base stations the respective set of
encoded data sequences produced therefor; performing other antenna
signal processing operations to generate other antenna signals at
each base station of the plurality of base stations in view of the
respective sets of encoded data sequences received thereby; and
transmitting the other antenna signals over corresponding antenna
elements of the antenna elements at each base station of the
plurality of base stations to transmit the another data stream over
the corresponding joint cooperative MIMO channel.
20. The method of claim 19, further comprising: synchronizing the
performance of the other antenna signal processing operations at
the plurality of base stations such that the other antenna signals
are transmitted over the selected antenna elements at different
base stations of the plurality of base stations in synchrony.
21. A multicell wireless network, comprising: a plurality of base
stations each associated with a respective cell and having a
respective antenna array including at least one antenna element; a
joint cooperative multiple-input multiple-output (MIMO)
transmission mechanism that employs selected antenna elements from
the plurality of base stations to: form an augmented antenna array
used to support joint cooperative MIMO transmissions over the
wireless network, wherein the joint cooperative MIMO transmissions
are orthogonal frequency division multiple access (OFDMA) MIMO
transmissions; and encode, at respective base stations of the
plurality of base stations, the replication of the data stream
using one of space-time coding, space-frequency coding,
space-time-frequency coding, and spatial multiplexing to establish
the joint cooperative MIMO transmissions; a data replicator to:
replicate a data stream received from an information source; and
forward the replication of the data stream to each base station of
the plurality of base stations; and a set of antenna signal
processing components at each base station of the plurality of base
stations to perform antenna signal processing operations on the
data stream it receives to generate antenna signals, wherein the
antenna signals are transmitted over the selected antenna elements
to form a joint cooperative MIMO transmission at each base station
of the plurality of base stations.
22. The multicell wireless network of claim 21, wherein the encoded
joint cooperative MIMO transmissions include subscriber MIMO
channel information.
23. The multicell wireless network of claim 21, wherein the
space-time coding comprises space-time trellis coding.
24. The multicell wireless network of claim 21, wherein the
space-time coding comprises space-time block coding.
25. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmission mechanism encodes the joint
cooperative MIMO transmissions using space-time coding with delay
diversity.
26. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmissions include downlink transmissions from
the plurality of base stations to terminals and uplink
transmissions from the terminals to the plurality of base
stations.
27. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmission mechanism performs spatial beam
forming for selected ones of the joint cooperative MIMO
transmissions.
28. The multicell wireless network of claim 27, wherein the joint
cooperative MIMO transmission mechanism performs the spatial
beamforming in combination with one of space-time, space-frequency
and space-time-frequency coding of the selected ones of the joint
cooperative MIMO transmissions.
29. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmission mechanism performs transmitting the
joint cooperative MIMO transmissions to at least two terminals
simultaneously.
30. The multicell wireless network of claim 29, wherein the joint
cooperative MIMO transmission mechanism further perforins spatial
beamforming on the joint cooperative MIMO transmissions such that
MIMO transmissions are directed toward intended users while spatial
nulling is effected toward unintended users.
31. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmission mechanism further performs jointly
decoding uplink MIMO transmissions received from multiple
terminals.
32. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmission mechanism further performs separately
decoding uplink MIMO transmissions received from multiple
terminals.
33. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmission mechanism further performs jointly
encoding downlink MIMO transmissions sent to multiple
terminals.
34. The multicell wireless network of claim 21, further comprising:
a synchronizing mechanism to synchronize the antenna signal
processing operation s at the plurality of base stations such that
the antenna signals are transmitted over the selected antenna
elements at different base stations of the plurality of base
stations in synchrony.
35. The multicell wireless network of claim 21, further comprising:
a master encoder to: perform MIMO encoding on another data stream
to be transmitted over a corresponding joint cooperative MIMO
channel, the MIMO encoding producing a respective set of encoded
data sequences for each base station of the plurality of base
stations; and send to each base station of the plurality of base
stations the respective set of encoded data sequences produced
therefor; and a set of other antenna signal processing components
at each base station of the plurality of base stations to perform
other antenna signal processing operations on the respective sets
of encoded data sequences received thereby to generate other
antenna signals, wherein the other antenna signals are transmitted
over the selected antenna elements at each base station of the
plurality of base stations to form the joint cooperative MIMO
transmissions over the corresponding joint cooperative MIMO
channel.
36. The multicell wireless network of claim 35, further comprising:
a synchronizing mechanism to synchronize the other antenna signal
processing operations at the plurality of base stations such that
the other antenna signals are transmitted over the selected antenna
elements at different base stations of the plurality of base
stations in synchrony.
37. The multicell wireless network of claim 21, wherein the joint
cooperative MIMO transmission mechanism performs the joint
cooperative MIMO transmissions to facilitate terminal handoff
between wireless network cells or sectors.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims priority to
U.S. patent application Ser. No. 12/130,277 entitled COOPERATIVE
MIMO IN MULTICELL WIRELESS NETWORKS, filed on May 30, 2008; which
is a continuation-in-part of and claims priority to U.S. patent
application Ser. No. 11/007,570, now U.S. Pat. No. 7,428,268, filed
on Dec. 7, 2004; all of the disclosures of which are expressly
incorporated by reference herein.
TECHNICAL FIELD
[0002] The present invention relates to the field of communications
systems; more particularly, the present invention relates to
techniques for performing MIMO operations in a multicell wireless
network.
BACKGROUND OF THE INVENTION
[0003] With high-speed wireless services increasingly in demand,
there is a need for more throughput per bandwidth to accommodate
more subscribers with higher data rates while retaining a
guaranteed quality of service (QoS). In point-to-point
communications, the achievable data rate between a transmitter and
a receiver is constrained by the available bandwidth, propagation
channel conditions, as well as the noise-plus-interference levels
at the receiver. For wireless networks where a base-station
communicates with multiple subscribers, the network capacity also
depends on the way the spectral resource is partitioned and the
channel conditions and noise-plus-interference levels of all
subscribers. In current state-of-the-art, multiple-access
protocols, e.g., time-division multiple access (TDMA),
frequency-division multiple-access (FDMA), code-division
multiple-access (CDMA), are used to distribute the available
spectrum among subscribers according to subscribers' data rate
requirements. Other critical limiting factors, such as the channel
fading conditions, interference levels, and QoS requirements, are
ignored in general.
[0004] The fundamental phenomenon that makes reliable wireless
transmission difficult to achieve is time-varying multipath fading.
Increasing the quality or reducing the effective error rate in a
multipath fading channel may be extremely difficult. For instance,
consider the following comparison between a typical noise source in
a non-multipath environment and multipath fading. In environments
having additive white Gaussian noise (AWGN), it may require only 1-
or 2-db higher signal-to-noise ratio (SNR) using typical modulation
and coding schemes to reduce the effective bit error rate (BER)
10.sup.-2 from 10.sup.-3. Achieving the same reduction in a
multipath fading environment, however, may require up to 10 db
improvement in SNR. The necessary improvement in SRN may not be
achieved by simply providing higher transmit power or additional
bandwidth, as this is contrary to the requirements of next
generation broadband wireless systems.
[0005] One set of techniques for reducing the effect of multipath
fading is to employ a signal diversity scheme, wherein a combined
signal is received via independently fading channels. Under a space
diversity scheme, multiple antennas are used to receive and/or send
the signal. The antenna spacing must be such that the fading at
each antenna is independent (coherence distance). Under a frequency
diversity scheme, the signal is transmitted in several frequency
bands (coherence BW). Under a time diversity scheme, the signal is
transmitted in different time slots (coherence time). Channel
coding plus interleaving is used to provide time diversity. Under a
polarization diversity scheme, two antennas with different
polarization are employed for reception and/or division.
[0006] Spatial diversity is commonly employed in modern wireless
communications systems. To achieve spatial diversity, spatial
processing with antenna arrays at the receiver and/or transmitter
is performed. Among many schemes developed to date, multiple-input
multiple-output (MIMO) and beamforming are the two most studied and
have been proved to be effective in increase the capacity and
performance of a wireless network, (see, e.g., Ayman F. Naguib,
Vahid Tarokh, Nambirajan Seshadri, A. Robert Calderbank, "A
Space-Time Coding Modem for High-Data-Rate Wireless
Communications", IEEE Journal on Selected Areas in Communications,
vol. 16, no. 8, October 1998 pp. 1459-1478). In a block
time-invariant environment, it can be shown that in a system
equipped with Nt transmit antennas and Nr receive antennas, a well
designed space-time coded (STC) systems can achieve a maximum
diversity of Nr*Nt. Typical examples of STC include space-time
trellis codes (STTC) (see, e.g., V. Tarokh, N. Seshadri, and A. R.
Calderbank, "Space-time codes for high data rate wireless
communication: performance criterion and code construction", IEEE
Trans. Inform. Theory, 44:744-765, March 1998) and space-time block
codes from orthogonal design (STBC-OD) (see, e.g., V. Tarokh, H.
Jafarkhani, and A. R. Calderbank, "Space-time block codes from
orthogonal designs", IEEE Trans. Inform. Theory, 45:1456-1467, July
1999.)
[0007] Since the capacity and performance of an MIMO system depends
critically on its dimension (i.e., Nt and Nr) and the correlation
between antenna elements, larger size and more scattered antenna
arrays are desirable. On the other hand, costs and physical
constraints prohibit the use of excessive antenna arrays in
practice.
BRIEF SUMMARY OF THE INVENTION
[0008] A method and system is disclosed herein for cooperative
multiple-input multiple output (MIMO) transmission operations in a
multicell wireless network. Under one embodiment, antenna elements
from two or more base stations are used to form an augmented MIMO
antenna array that is used to transmit and receive MIMO
transmissions to and from one or more terminals.
[0009] The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter which form the subject of the claims
of the invention. It should be appreciated by those skilled in the
art that the conception and specific embodiment disclosed may be
readily utilized as a basis for modifying or designing other
structures for carrying out the same purposes of the present
invention. It should also be realized by those skilled in the art
that such equivalent constructions do not depart from the spirit
and scope of the invention as set forth in the appended claims. The
novel features which are believed to be characteristic of the
invention, both as to its organization and method of operation,
together with further objects and advantages will be better
understood from the following description when considered in
connection with the accompanying figures. It is to be expressly
understood, however, that each of the figures is provided for the
purpose of illustration and description only and is not intended as
a definition of the limits of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawing, in which:
[0011] FIG. 1 depicts a multicell scenario where antenna elements
from multiple base-stations are augmented to form a higher
dimension MIMO transceiver array;
[0012] FIG. 2 shows a generic channel matrix H used for modeling
the capacity of MIMO systems;
[0013] FIG. 3 shows the capacity increase of an MIMO system with
respect to the number of transmitting antennas;
[0014] FIG. 4a shows a cooperative MIMO architecture under which
antenna arrays from two base stations are employed in a cooperative
MIMO transmission scheme to transmit downlink signals to one
terminal;
[0015] FIG. 4b shows aspects of the cooperative MIMO architecture
of FIG. 4a employed for transmitting and processing uplink signals
received by the augmented antenna array;
[0016] FIG. 5 shows an extension to the cooperative MIMO
architecture of FIG. 4a, wherein beamforming is used to direct a
MIMO transmission toward one terminal while performing spatial
nulling towards another terminal;
[0017] FIG. 6 shows a cooperative MIMO architecture under which two
base stations performing multiuser MIMO with two terminals
simultaneously using joint encoding and decoding;
[0018] FIG. 7a shows a block diagram of an MIMO OFDM
encoder/transmitter;
[0019] FIG. 7b shows the block diagram of an MIMO OFDM
encoder/transmitter with beamforming;
[0020] FIG. 8 shows a block diagram of an MIMO OFDM
receiver/decoder;
[0021] FIG. 9 shows a block diagram used to model a space-time
coding transmission;
[0022] FIG. 10 shows an exemplary PSK-based space-time trellis code
(SITC) encoder;
[0023] FIG. 11 shows an exemplary QAM-based STTC encoder;
[0024] FIG. 12 shows a block diagram used to model a space-time
block coding (STBC) transmission scheme;
[0025] FIG. 13a shows a block diagram modeling an STTC delay
diversity scheme;
[0026] FIG. 13b shows a block diagram modeling an STBC delay
diversity scheme;
[0027] FIG. 14 is a block diagram of an exemplary PSK-based SITC
delay diversity encoder;
[0028] FIG. 15 is a schematic diagram illustrating a cooperative
MIMO architecture under which STC encoding operations are performed
at a master encoder;
[0029] FIG. 16 is a schematic diagram illustrating a cooperative
MIMO architecture under which STC encoding operations are performed
on respective instances of replicated data streams at multiple base
stations;
[0030] FIG. 17a shows a cooperative MIMO architecture under which
antenna arrays from multiple terminals are employed in a
cooperative MIMO transmission scheme to transmit uplink signals to
one or more base stations;
[0031] FIG. 17b shows aspects of the cooperative MIMO architecture
of FIG. 17a employed for transmitting and processing downlink
signals received by the augmented antenna array;
[0032] FIG. 18 shows a cooperative MIMO architecture under which
multiple terminals perform multiuser MIMO with multiple base
stations simultaneously using joint encoding and decoding;
[0033] FIG. 19a shows a block diagram of another MIMO OFDM
encoder/transmitter;
[0034] FIG. 19b shows the block diagram of another MIMO OFDM
encoder/transmitter with beamforming; and
[0035] FIG. 20 shows a block diagram of another MIMO OFDM
receiver/decoder.
DETAILED DESCRIPTION OF THE INVENTION
[0036] In accordance with aspects of the present invention, a
method and apparatus to augment antenna elements from two or more
base-stations and/or terminals to perform higher dimensional MIMO
operations is disclosed. In one implementation, MIMO/joint
space-time coding is employed across multiple base stations in a
cellular environment, wherein the cooperative transmission of
signals is performed at the modulation and coding level. According
to another embodiment, MIMO/joint space-time coding is employed
across multiple terminals in a similar fashion. This novel approach
introduces additional diversities and capacities to existing
network components with minimal additional costs. Because of the
increase in the number of transmit antennas, the number of
simultaneous users increases, leading to better spectrum
efficiency.
[0037] In the following description, numerous details are set forth
to provide a more thorough explanation of the present invention. It
will be apparent, however, to one skilled in the art, that the
present invention may be practiced without these specific details.
In other instances, well-known structures and devices are shown in
block diagram form, rather than in detail, in order to avoid
obscuring the present invention.
[0038] Some portions of the detailed descriptions which follow are
presented in terms of algorithms and symbolic representations of
operations on data bits within a computer memory. These algorithmic
descriptions and representations are the means used by those
skilled in the data processing arts to most effectively convey the
substance of their work to others skilled in the art. An algorithm
is here, and generally, conceived to be a self-consistent sequence
of steps leading to a desired result. The steps are those requiring
physical manipulations of physical quantities. Usually, though not
necessarily, these quantities take the foiin of electrical or
magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
[0039] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise as apparent from
the following discussion, it is appreciated that throughout the
description, discussions utilizing terms such as "processing" or
"computing" or "calculating" or "determining" or "displaying" or
the like, refer to the action and processes of a computer system,
or similar electronic computing device, that manipulates and
transforms data represented as physical (electronic) quantities
within the computer system's registers and memories into other data
similarly represented as physical quantities within the computer
system memories or registers or other such information storage,
transmission or display devices.
[0040] The present invention also relates to apparatus for
performing the operations herein. This apparatus may be specially
constructed for the required purposes, or it may comprise a
general-purpose computer selectively activated or reconfigured by a
computer program stored in the computer. Such a computer program
may be stored in a computer readable storage medium, such as, but
is not limited to, any type of disk including floppy disks, optical
disks, CDROMs, and magnetic-optical disks, read-only memories
(ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or
optical cards, or any type of media suitable for storing electronic
instructions, and each coupled to a computer system bus.
[0041] The algorithms and displays presented herein are not
inherently related to any particular computer or other apparatus.
Various general-purpose systems may be used with programs in
accordance with the teachings herein, or it may prove convenient to
construct more specialized apparatus to perform the required method
steps. The required structure for a variety of these systems will
appear from the description below. In addition, the present
invention is not described with reference to any particular
programming language. It will be appreciated that a variety of
programming languages may be used to implement the teachings of the
invention as described herein.
[0042] A machine-readable medium includes any mechanism for storing
or transmitting information in a form readable by a machine (e.g.,
a computer). For example, a machine-readable medium includes read
only memory ("ROM"); random access memory ("RAM"); magnetic disk
storage media; optical storage media; flash memory devices;
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waves, infrared signals, digital signals, etc.);
etc.
Overview
[0043] FIG. 1 depicts three cells 100, 102, and 104 for a typical
wireless network with multiple base stations BS1, BS2 and BS3 and
terminals A, B, and C. Each of base stations BS1 and BS2 includes a
4-element circular antenna array, while terminal A has two antennas
1 and 2.
[0044] From a theoretical viewpoint, the capacity between a
transmitter and a receiver for a MIMO transmission scheme is
determined by the vector channel H, which is also referred to as
the channel matrix. As illustrated in FIG. 2, the channel matrix H
includes M rows and N columns, wherein M is the number of receiver
antennas (Rx) and N is the number of transmitter antennas (Tx). In
the illustrated channel matrix H, each entry .alpha..sub.ij is the
complex channel gain from the i-th transmit antenna to the j-th
receive antenna.
[0045] The channel capacity for a Single-Input Single-Output (SISO)
channel is,
C=log.sub.2(1+p) bits/sec/use (1),
where p is the signal to noise ratio. The channel capacity for a
MIMO channel is,
C = log 2 det [ I + P N HH * ] . ( 2 ) ##EQU00001##
From the above, the outage capacity can be shown to be,
C = 1 2 M log 2 ( 1 + .sigma. { h } 2 p ) . ( 3 ) ##EQU00002##
[0046] It is observed that under equation (3), the capacity
increases linearly with the number of receive antennas when M is
large. The channel capacity limit grows logarithmically when adding
an antenna array at the receiver side (Single-Input
Multiple-Output--SIMO). Meanwhile, the channel capacity limit grows
as much as linearly with min(M, N), which is the maximum number of
spatial eigenmodes, in the case of a MIMO system. An illustration
of a MIMO system capacity as a function of channel matrix dimension
is shown in FIG. 3.
[0047] Since the system capacity is dictated by the dimension
(number of antennas) and the condition (correlation between antenna
elements) of the channel, it is desirable to have large size
antenna array with more scattered elements. However, there is a
point of diminishing return, wherein the costs of adding antenna
elements and corresponding processing complexity for a given base
station or terminal exceeds the benefit of the incremental increase
in system capacity. Furthermore, to obtain the added benefit of
extra capacity, it may be necessary to add additional antenna
elements to many or all base stations or terminals within a given
wireless network.
[0048] Embodiments of the present invention take advantage of the
benefit of having large size antenna arrays with more scattered
elements without requiring additional antenna elements. This is
accomplished by augmenting the operations of antenna elements from
two or more transmitters to form a larger size antenna array. The
augmented array performs "cooperative MIMO" transmission operations
for one or more receivers. For example, FIG. 1 shows an exemplary
use of a cooperative MIMO transmission scheme, wherein the antenna
elements for base stations BS1 and BS2 are augmented to
cooperatively communicate via receive antennas 1 and 2 for terminal
A.
[0049] FIG. 4a depicts a block diagram of one embodiment of a
downlink (from base stations to terminals) cooperative MIMO
architecture 400. For illustrative purposes, the architecture shown
in FIG. 4a include two base stations 402 and 404 and a single
terminal 406. It will be understood that an actual implementation
of MIMO architecture 400 may include two or more base stations that
transmit signals that are received by one or more terminals.
[0050] In the illustrated embodiment of FIG. 4a, base station 402
has an antenna array including Nt.sub.1 transmit antennas, while
base station 404 has an antenna array including Nt.sub.2 antennas
and terminal 406 includes Nr antennas. In view of the foregoing
MIMO definitions, the cooperative use of the base station antennas
increases the MIMO dimension to (Nt.sub.1+Nt.sub.2)*Nr. This
increase in dimension is accomplished without requiring any
additional antenna elements at the base stations, as well as the
components use to drive the antennas.
[0051] According to aspects of various embodiments of the invention
described herein, an information bit sequence corresponding to data
to be transmitted to a subscriber (e.g. terminal 406) may be
space-time, space-frequency, or space-time-frequency coded, as
depicted by a block 408 in FIG. 4a. In some embodiments,
space-time, space-frequency, or space-time-frequency codes may be
augmented to support delay diversity, as described below. After
appropriate encoding is performed in block 408, the coded data is
then passed to the base stations, whereupon it is transmitted via
applicable antenna elements at those base stations. The two or more
base stations then perform joint MIMO transmissions (depicted as
signals 410 and 412) towards the subscriber (e.g. a user operating
terminal 406) in view of applicable MIMO channel configuration
parameters. For example, signals 410 and 412 transmitted from base
stations 402 and 404 may employ selected antenna elements for each
of the base stations based on the coding scheme and/or MIMO scheme
that is currently employed for a particular subscriber. In general,
cooperative MIMO transmissions can be performed during regular
communication, or during handoff, where a subscriber moves across
the boundary between cells.
[0052] In one embodiment, space-time coding is employed. For
example, incoming information bits are space-time coded (using
e.g., space-time block or trellis codes) at block 408, and the
encoded data are forwarded to each of base stations 402 and 404.
Further details of space-time block encoding and the use of
space-time trellis codes are discussed below.
[0053] In one embodiment, the space-time (or space-frequency, or
space-time-frequency) coding is performed at a master encoder. In
another embodiment, the space-time (or space-frequency, or
space-time-frequency) is performed at separate locations (e.g.,
within the base stations) based on a common (replicated)
information bit sequence received at each of the separate
locations.
[0054] FIG. 4b shows uplink signal processing aspects of
cooperative MIMO architecture 400. In this instance, an uplink
signal 414 is transmitted from terminal 406 via selected antennas
from among transmit antennas 1-Nt. The uplink signal 414 is
received by the respective receive antenna arrays (1-Nr.sub.1,
1-Nr.sub.2) for base stations 402 and 404. (It is noted that the
same antennas may be used for both transmit and receive operations
for some embodiments, while separate sets of transmit and receive
antennas may be employed for other embodiments.) Upon being
received at the base stations, initial signal processing is
performed on the uplink signals, and the processed signals are
forwarded to a block 416 to perform joint MIMO decoding and
demodulation, thus extracting the information bits corresponding to
the data transmitted by terminal 406. In general, the components
for performing the operations of block 416 may be implemented in a
master decoder that is centrally located with respect to multiple
base stations (e.g., base stations 402 and 404), or may be located
at one of the multiple base stations.
[0055] FIG. 5 depicts a multi-user cooperative MIMO architecture
500. Under this embodiment, the augmented antenna array (comprising
selected transmit antenna elements for base stations 502 and 504)
is used to perform MIMO operation towards one or more intended
subscribers while limiting the radio signal at the
location/direction of un-intended subscribers using a beamforming
and nulling scheme. For example, techniques are known for steering
transmitted signals toward selected locations, while transmitted
signals sent toward other directions are nullified due to signal
canceling effects and/or fading effects. Collectively, these
selective transmission techniques are referred to as beamforming,
and are accomplished by using appropriate antenna elements (an
augmented array of antennas hosted by two or more base stations
under the embodiments herein) and applicable control of the signals
transmitted from those antenna elements (e.g., via weighted inputs
derived from feedback returned from a targeted terminal). Under
beamforming embodiments of the invention, current techniques
employed for antenna arrays located at a single base stations (see,
e.g., D. J. Love, R. W. Heath Jr., and T. Strohmer, "Grassmannian
Beam forming for Multiple-Input Multiple-Output Wireless Systems,"
IEEE Transactions on Information Theory, vol. 49, pp. 2735-2747,
October 2003) are extended to support beamforming operations via
selected antenna elements hosted by multiple base stations. As
described below, it may be necessary to employ signal
synchronization between multiple base stations to obtain the
desired beamforming results.
[0056] In the embodiment of FIG. 5, information bits are encoded
using one of space-time, space-frequency, or space-time-frequency
coding schemes in a block 514. Block 514 is also employed to
perform beamforming operations, as describe below in further detail
with reference to FIG. 7b. The encoded output of block 514 is then
provided to each of base stations 502 and 504, which in turn
transmit respective signals 516 and 518. As depicted by lobes 520,
522, and 524, the channel characteristics of the combined signals
516 and 518 produce areas of higher gain in certain directions. At
the same time, the gain of the combined signals 516 and 518 in
other directions, such as depicted by a null direction 526, may be
greatly reduced (e.g., to the point at which the signal cannot be
decoded) due to spatial nulling. In one embodiment, spatial nulling
is performed at the direction of un-intended subscribers.
[0057] For example, under the scenario illustrated in FIG. 5, the
combined signals 516 and 518 are controlled so as to produce a high
gain within lobe 522. As such, terminal 506 receives a good signal
at its antenna array, and can decode the combined MIMO signal using
appropriate MIMO decoding techniques that are well-known in the
wireless communication system arts. Meanwhile, the strength of the
combined signal received at a terminal 528 is nulled using spatial
nulling. Accordingly, data corresponding to the information bits
received at block 514 is transmitted to only terminal 506, and is
not received by terminal 528.
[0058] FIG. 6 depicts another multi-user cooperative MIMO
architecture 600. Instead of forming nulls to un-intended
terminals, information from multiple users is jointed encoded,
transmitted from multiple base stations via the augmented MIMO
antenna array, and then decoded at the receiving terminals. In one
embodiment of the invention, the information is decoded at the user
ends independently. The signals intended for other users are
treated as interference. In another embodiment, the information
from all users are decoded jointly. In yet another embodiment, the
information received at different user locations are consolidated
for joint decoding.
[0059] The embodiment of FIG. 6 shows an example of joint decoding.
In this instance, information to be sent to terminals 1 (606) and 2
(628) is jointly encoded using one of space-time, space-frequency,
or space-time-frequency coding in a block 630. For clarity, the
respective information to be sent to terminals 1 and 2 is depicted
as data A and data B. The jointly encoded output of block 630 is
provided as inputs to each of base stations 602 and 604. The base
stations then transmit the jointly encoded data via selected
antennas (corresponding to MIMO channels assigned to terminals 1
and 2) to terminals 606 and 628. Upon receipt of the jointly
encoded data, it is decoded via operations performed in a block 632
for each of terminals 606 and 628. Upon being decoded, information
intended for each recipient terminal is kept, while other
information is discarded. Accordingly, terminal 606 keeps data A
and discards data B, while terminal 628 keeps data B and discards
data A. In one embodiment, information to keep and discard is
identified by packet headers corresponding to packets that are
extracted from the decoded data received at a given terminal.
[0060] A block diagram corresponding to one embodiment of an OFDMA
(Orthogonal Frequency Division Multiple Access)
encoding/transmitter module 700A for a base station having N.sub.t
transmit antennas is shown in FIG. 7a. Information bits for each of
1-N subcarriers are received at respective space-time coding (STC)
blocks 704.sub.1-N. The size of the STCs is a function of the
number of transmit antennas Nt. In general, the space-time codes
may comprise space-time trellis codes (STTC), space-time block
codes (STBC), as well as STTC or STBC with delay diversity, details
of which are described below. Based on the applicable STC, each of
blocks 704.sub.1-p outputs a set of code words c.sub.1[j,k] to
c.sub.Nt[j,k], wherein j represents the sub-channel index and k is
the time index. Each of the code words is then forwarded to an
appropriate Fast Fourier Transform (FFT) blocks 706.sub.1-Nt. The
outputs of the FFT blocks 706.sub.1-Nt are then fed to parallel to
serial (P/S) conversion blocks 708.sub.1-Nt, and cyclic prefixes
are added via add cyclic prefix (CP) blocks 710.sub.1-Nt. The
outputs of add CP blocks 710.sub.1-Nt are then provided to transmit
antennas 1-Nt to be transmitted as downlink signals to various
terminals within the base station's coverage area.
[0061] A block diagram corresponding to one embodiment of an OFDMA
receiver/decoder module 800 for a terminal having N.sub.r receive
antennas is shown in FIG. 8. The signal processing at the receive
end of a downlink signal is substantially the inverse of the
process used for encoding and preparing the signal for
transmission. First, the cyclic prefix for each of the signals
received at respective receive antennas 1-Nr is removed by a
respective remove CP block blocks 810.sub.1-Nr. The respective
signals are then fed into respective serial-to-parallel (S/P)
conversion blocks 808.sub.1-Nt to produce parallel sets of data,
which are then provided as inputs to FFT blocks 806.sub.1-Nr. The
outputs of FFT blocks 806.sub.1-Nr are then forwarded to
appropriate STC decoding blocks 804.sub.1-N for decoding. The
decoded data is then output at the information bits for subcarriers
1-N.
[0062] A block diagram corresponding to one embodiment of an OFDMA
encoding/beamforming/transmitter module 700B that performs
beamforming is shown in FIG. 7b. As depicted by like-numbered
blocks, much of the signal processing performed by the embodiments
of FIGS. 7a and 7b is similar. In addition to these processing
operations, OFDMA encoding/beamforming/transmitter module 700B
further includes beamforming blocks 705.sub.1-N. Each of these
beamforming blocks applies a weighted value W.sub.1-N to its
respective inputs in view of control information provided by a
beamforming control block 712, which is generated in response to
beamforming feedback data 714. Further differences between the
embodiments of FIGS. 7a and 7b include STC blocks 704A.sub.1-N,
which now employ STCs having a size L, which represents the number
of beamforming channels.
[0063] It should be appreciated that the cooperative MIMO concepts
described herein, both in the downlink and the uplink, also apply
at the terminal side of a network. Virtual antenna arrays at the
terminals, comprising one or more antenna elements from a plurality
of terminals, enable cooperative downlink reception and cooperative
uplink transmission. FIGS. 17a and 17b show components of a
wireless network according to various embodiments of the inventions
described herein that enable terminal side cooperative MIMO
applications.
[0064] FIG. 17b shows downlink signal processing aspects of
cooperative MIMO architecture 1700. As shown, network 1700
comprises a plurality of terminals, e.g., terminals 1706, 1708, and
1710, each having antenna arrays where terminal 1706 has Nt.sub.1
transmit antennas and Nr.sub.1 receive antennas, terminal 1708 has
Nt.sub.2 transmit antennas and Nr.sub.2 receive antennas, and
terminal 1710 has Nt.sub.3 transmit antennas and Nr.sub.3 receive
antennas. Base station 1702 has an antenna array including Nt.sub.1
transmit antennas and Nr.sub.1 receive antennas and base station
1704 has an antenna array including Nt.sub.2 transmit antennas and
Nr.sub.2 receive antennas. In view of the foregoing MIMO
definitions, the cooperative use of the base station antennas
increases the MIMO dimension to
(Nt.sub.1+Nt.sub.2+Nt.sub.3)*(Nr.sub.1+Nr.sub.2+Nr.sub.3).
[0065] According to a preferred embodiment, cooperative MIMO
downlink reception is achieved by exchanging data between a
plurality of terminals, e.g., terminals 1706, 1708, and 1710. Data
exchange between terminals is executed via a short distance, high
throughput radio link 1712. According to a preferred embodiment,
short distance radio link 1712 is a link according to the IEEE
802.15 standard (e.g., Bluetooth), wireless USB, and the like.
According to other embodiments, data may be exchanged between
terminals using in-band radio communications, where, for example,
one or more terminals functions as a relay.
[0066] Downlink signals, e.g., downlink signal 1714, are
transmitted from base stations 1702 and/or base station 1704 via
selected transmit antennas among available transmit antennas at
each of base station 1702 and base station 1704, i.e., 1-Nt.sub.1
transmit antennas at base station 1702 and 1-Nt.sub.2 transmit
antennas at 1704. Downlink signal 1714 is received by the receive
antenna arrays (1-Nr.sub.1, 1-Nr.sub.2, 1-Nr.sub.3) for terminals
1706, 1708, and 1710, respectively. As discussed above, it should
be appreciated that the same antennas may be used for both transmit
and receive operations for some embodiments, while separate sets of
transmit and receive antennas may be employed for other
embodiments.
[0067] Upon being received at the terminals, initial signal
processing is performed on the downlink signals at terminals 1706,
1708, and 1710, and the processed signals are forwarded to a block
1716 to perform joint MIMO decoding and demodulation, thus
extracting the information bits corresponding to the data
transmitted by base stations 1702 and/or 1704. According to a
preferred embodiment, the components for performing the operations
of block 1716 are located at each terminal; that is, decoder 1716
is co-located at each terminal. In such case decoder 1716 decodes
only bit streams targeted for the specific terminal at which it is
located. This is accomplished using signals from its own antennas
as well as antenna signals exchanged from other terminals. In
another embodiment, the components for performing the operations of
block 1716 may be implemented in a master decoder that is centrally
located with respect to multiple terminals (e.g., 1706, 1708, and
1710), or may be co-located at one of the terminals.
[0068] According to another embodiment of the invention described
herein, one or more terminals receives downlink signals, determines
whether the downlink signals comprise cooperative MIMO signals or
signals from a single base station, and decodes the received
signals according to that determination. In such case, decoding may
be performed at the receiving terminal or performed at centralized
location, e.g., a centralized master decoder.
[0069] FIG. 17a depicts a block diagram of one embodiment of an
uplink cooperative MIMO architecture 1700. Similar to downlink
concepts discussed herein, cooperative MIMO uplink concepts are
particularly useful in cases where there is a weak signal path
between a base station and a first terminal. In such case, a
second, cooperative terminal having a strong signal path between
the base station is used to relay signals between the first
terminal and the base station. As a practical matter, this is
likely to occur where the first terminal is subject to severe
channel fading while a second terminal is not, or where is a clear
line of sight between the second terminal and base station, but not
between the first terminal and the base station.
[0070] For illustrative purposes, the architecture shown in FIG.
17a include two base stations 1702 and 1704 and terminals 1706,
1708, and 1710. In the illustrated embodiment of FIG. 17a, terminal
1706 has an antenna array including Nt.sub.1 transmit antennas,
terminals 1708 has an antenna array including Nt.sub.2 transmit
antennas, and terminal 1710 has an array including Nt.sub.3
transmit antennas. Base station 1702 includes Nr.sub.1 receive
antennas and base station 1704 includes Nr.sub.2 receive antennas.
In view of the foregoing MIMO definitions, the cooperative use of
the terminal antennas increases the MIMO dimension to
(Nt.sub.1+Nt.sub.2+Nt.sub.3)*(Nr.sub.1+Nr.sub.2). This increase in
dimension is accomplished without requiring any additional antenna
elements at the terminals, as well as the components use to drive
the antennas.
[0071] According to aspects of various embodiments of the invention
described herein, an information bit sequence corresponding to data
to be transmitted to a base station may be space-time,
space-frequency, or space-time-frequency coded, as depicted by a
block 1718 in FIG. 17a. Space-time, space-frequency, or
space-time-frequency codes may be augmented to support delay
diversity. After appropriate encoding is performed in block 1718,
the coded data is then passed to the terminals, whereupon it is
transmitted via applicable antenna elements at those terminals. The
terminals then perform joint MIMO transmissions (depicted as
signals 1720, 1722, and 1724) towards the base stations in view of
applicable MIMO channel configuration parameters. For example,
signals 1720, 1722, and 1724 transmitted from terminals 1706, 1708,
and 1710 may employ selected antenna elements for each of the base
stations based on the coding scheme and/or MIMO scheme that is
currently employed for a particular base station. In general,
cooperative MIMO transmissions can be performed during regular
communication, or during handoff, where a terminal moves across the
boundary between cells.
[0072] In one embodiment, space-time coding is employed. For
example, incoming information bits are space-time coded (using
e.g., space-time block or trellis codes) at block 1718, and the
encoded data are forwarded to each of terminals 1706, 1708, and
1710. Further details of space-time block encoding and the use of
space-time trellis codes are discussed below.
[0073] In one embodiment, the space-time (or space-frequency, or
space-time-frequency) coding is performed at a master encoder. In
another embodiment, the space-time (or space-frequency, or
space-time-frequency) is performed at separate locations (e.g.,
separate from each terminal, but typically co-located at a
particular terminal) based on a common (replicated) information bit
sequence received at each of the separate locations.
[0074] It should be further appreciated that augmented antenna
arrays can be used in uplink communications by employing the
beamforming techniques described above with respect to downlink
communications. Likewise, the techniques known for steering
transmitted signals toward selected locations, while transmitted
signals sent toward other directions are nullified due to signal
canceling effects and/or fading effects may be fully employed for
transmission from terminals to base stations. Similar to the
discussion above, it may be necessary to employ signal
synchronization between multiple terminals to obtain the desired
beamforming results.
[0075] FIG. 18 depicts cooperative MIMO architecture 1800 for
uplink transmissions. Information from multiple terminals is
jointly encoded, transmitted from multiple terminals via the
augmented MIMO antenna array, and then decoded at the receiving
base stations. In one embodiment of the invention, the information
is decoded at the base stations independently. The signals received
at a base station but intended for another base station is treated
as interference. In another embodiment, the information from all
terminals is decoded jointly at the base stations. In yet another
embodiment, the information received at different base stations is
consolidated for joint decoding.
[0076] The embodiment of FIG. 18 shows an example of joint
decoding. In this instance, information to be sent to multiple base
stations, e.g., base station 1806 and 1828, is jointly encoded
using one of space-time, space-frequency, or space-time-frequency
coding in a block 1830. For clarity, the respective information to
be sent to base station 1806 and 1828 is depicted as data A and
data B. The jointly encoded output of block 1830 is provided as
inputs to each of base stations 1806 and 1828. The terminals then
transmit the jointly encoded data via selected antennas
(corresponding to MIMO channels assigned to respective base
stations) to base stations 1806 and 1828. Upon receipt of the
jointly encoded data, it is decoded via operations performed in a
block 1832 for each of base stations 1806 and 1828. Upon being
decoded, information intended for each recipient base station is
kept, while other information is discarded. Accordingly, base
station 1806 keeps data A and discards data B, while base station
1828 keeps data B and discards data A. In one embodiment,
information to keep and discard is identified by packet headers
corresponding to packets that are extracted from the decoded data
received at a given base station.
[0077] A block diagram corresponding to one embodiment of an OFDMA
(Orthogonal Frequency Division Multiple Access)
encoding/transmitter module 1900A for a terminal having Nt transmit
antennas is shown in FIG. 19a. Information bits for each of 1-N
subcarriers are received at respective space-time coding (STC)
blocks 1904.sub.1-N. The size of the STCs is a function of the
number of transmit antennas Nt. In general, the space-time codes
may comprise space-time trellis codes (STTC), space-time block
codes (STBC), as well as STTC or STBC with delay diversity, details
of which are described below. Based on the applicable STC, each of
blocks 1904.sub.1-p outputs a set of code words to c.sub.1[j,k] to
c.sub.Nt[j,k], wherein j represents the sub-channel index and k is
the time index. Each of the code words is then forwarded to an
appropriate Fast Fourier Transform (FFT) blocks 1906.sub.1-Nt. The
outputs of the FFT blocks 1906.sub.1-Nt are then fed to parallel to
serial (PIS) conversion blocks 1910.sub.1-Nt, and cyclic prefixes
are added via add cyclic prefix (CP) blocks 1910.sub.1-Nt. The
outputs of add CP blocks 1910.sub.1-Nt are then provided to
transmit antennas 1-Nt to be transmitted as uplink signals to
various base stations for which the terminal is communicating.
[0078] A block diagram corresponding to one embodiment of an OFDMA
receiver/decoder module 2000 for a base station having Nr receive
antennas is shown in FIG. 20. The signal processing at the receive
end of an uplink signal is substantially the inverse of the process
used for encoding and preparing the signal for transmission. First,
the cyclic prefix for each of the signals received at respective
receive antennas 1-Nr is removed by a respective remove CP block
blocks 2010.sub.1-Nr. The respective signals are then fed into
respective serial-to-parallel (SIP) conversion blocks 2008.sub.1-Nt
to produce parallel sets of data, which are then provided as inputs
to FFT blocks 2006.sub.1-Nr. The outputs of FFT blocks
2006.sub.1-Nr are then forwarded to appropriate STC decoding blocks
2004.sub.1-N for decoding. The decoded data is then output at the
information bits for subcarriers 1-N.
[0079] A block diagram corresponding to one embodiment of an OFDMA
encoding/beamforming/transmitter module 1900B that performs uplink
beamforming is shown in FIG. 19b. As depicted by like-numbered
blocks, much of the signal processing performed by the embodiments
of FIGS. 19a and 19b is similar. In addition to these processing
operations, OFDMA encoding/beamforming/transmitter module 1900B
further includes beamforming blocks 1905.sub.1-N. Each of these
beam forming blocks applies a weighted value W.sub.1-N to its
respective inputs in view of control information provided by a
beamforming control block 1912, which is generated in response to
beamforming feedback data 1914. Further differences between the
embodiments of FIGS. 19a and 19b include STC blocks 1904A.sub.1-N
which now employ STCs having a size L, which represents the number
of beamforming channels.
Space Time Encoding.
[0080] Space-Time Codes (STC) were first introduced by Tarokh et
at. from AT&T research labs (Y. Tarokh, N. Seshadri, and A. R.
Calderbank, "Space-time codes for high data rates wireless
communications: Performance criterion and code construction," IEEE
Trans. Inform. Theory, vol. 44, pp. 744-765, 1998) in 1998 as a
novel means of providing transmit diversity for the
multiple-antenna fading channel. There are two main types of STCs,
namely space-time block codes (STBC) and space-time trellis codes
(STTC). Space-time block codes operate on a block of input symbols,
producing a matrix output whose columns represent time and rows
represent antennas. Space-time block codes do not generally provide
coding gain, unless concatenated with an outer code. Their main
feature is the provision of full diversity with a very simple
decoding scheme. On the other hand, space-time trellis codes
operate on one input symbol at a time, producing a sequence of
vector symbols whose length represents antennas. Like traditional
TCM (trellis coded modulation) for a single-antenna channel,
space-time trellis codes provide coding gain. Since they also
provide full diversity gain, their key advantage over space-time
block codes is the provision of coding gain. Their disadvantage is
that they are difficult to design and generally require high
complexity encoders and decoders.
[0081] FIG. 9 shows a block diagram of as STC MIMO transmission
model. Under the model, data from an information source 900 is
encoded using a STBC or SITC code by a space-time encoder 902. The
encoded data is then transmitted over a MIMO link 904 to a receiver
906. The received signals are then decoded at the receiver to
extract the original data.
[0082] An exemplary 8-PSK 8-state space-time trellis code for two
antennas is shown in FIG. 10, while an exemplary 16-QAM 16-state
SITC for two antennas is shown in FIG. 11. The encoding for SITCs
are similar to TCM, except that at the beginning and the end of
each frame, the encoder is required to be in the zero state. At
each time t, depending on the state of the encoder and the input
bits, a transition branch is selected. If the label of the
transition branch is c.sub.i.sup.t; c.sub.2.sup.t; . . . ;
c.sub.n.sup.t, then transmit antenna i is used to send the
constellation symbols c.sub.i.sup.t=1; 2; . . . ; n and all these
transmissions are in parallel. In general, an SITC encoder may be
implemented via a state machine programmed with states
corresponding to the trellis code that is to be implemented.
[0083] FIG. 12 shows a block diagram corresponding to an STBC model
employing two antennas. As before, data is received from an
information source 1200. Space time block encoding is then
performed by the operations of space time block code 1202 and
constellation maps 1204A and 1204B.
[0084] In further detail, an STBC is defined by a pxn transmission
matrix G, whose entries are linear combinations of x.sub.j; . . . ;
x.sub.k and their conjugates x.sub.1*; . . . ; x.sub.k*, and whose
columns are pairwise-orthogonal. In the case when p=n and {x.sub.i}
are real, G is a linear processing orthogonal design which
satisfies the condition that G.sup.TG=D where D is a diagonal
matrix with the (i;i) th diagonal element of the form
(l.sub.1.sup.ix+l.sub.2.sup.ix.sub.2.sup.2+ . . .
+l.sub.n.sup.ix.sub.n.sup.2) with the coefficients l.sub.1.sup.i,
l.sub.2.sup.i, . . . l.sub.n.sup.i>0. An example of a 2.times.2
STBC code is shown in FIG. 12.
[0085] Another signal diversity scheme is to employ a combination
of STC with delay. For example, FIGS. 13a and 13b respectively show
models corresponding to an STTC with delay transmission scheme and
an STBC with delay transmission scheme. In FIG. 13a, data from an
information source 1300 is received by a code repetition block
1302, which produces a pair of replicated symbol sequences that are
generated in view of the data. A first sequence of symbols is
forwarded to an STTC encoder 1304A for encoding. Meanwhile, the
replicated sequence of symbols is fed into a delay block 1306,
which produces a one-symbol delay. The delayed symbol sequence
output of delay block 1306 is then forwarded to STTC encoder 1304B
for encoding. An exemplary 8-PSK 8-state delay diversity code for
two antennas is shown in FIG. 14. As illustrated, the symbol
sequence for transmission antenna Tx2 is synchronized with the
input sequence, while the symbol sequence for transmission antenna
Tx1 is delayed by one symbol.
[0086] Under the signal diversity scheme of FIG. 13b, data from
information source 1300 is received at best block code selection
logic 1308, which outputs replicated block codes to produce two
block code sequences. The first block code sequence is forwarded to
constellation mapper 1310A for encoding, while the second block
code sequence is delayed by one symbol via a delay block 1312 and
then forwarded to constellation mapper 1310B for encoding. The
encoded signals are then transmitted via first and second transmit
antennas.
[0087] The foregoing STTC and STBC schemes are depicted herein in
accordance with conventional usage for clarity. Under such usage,
the various encoded signals are transmitted using multiple antennas
at the same transmitter, e.g., a single base station. In contrast,
embodiments of the invention employ selective antenna elements in
antenna arrays from multiple transmitters, e.g., multiple base
stations and/or multiple terminals to form an augmented MIMO
antenna array.
[0088] In order to implement an STC transmission scheme using
multiple transmitters, additional control elements may be needed.
For example, if the transmitters are located at different distances
from a master encoder facility, there may need to be some measure
to synchronize the antenna outputs in order to obtain appropriate
MIMO transmission signals. Likewise, appropriate timing must be
maintained when implementing a delay diversity scheme using antenna
arrays at transmitters at different locations.
[0089] FIG. 15 shows an example cooperative MIMO architecture 1500
that employs a master encoder 1502 serving base stations 402 and
404. However, it should be appreciated that a master encoder could
also serve multiple terminals, e.g., 1706, 1708, etc. In general,
the master encoder 1502 may be located at a separate facility from
base stations or terminals, or may be co-located with one of the
base stations or terminals. In respective embodiments, master
encoder 1502 performs STC encoding and signal processing operations
similar to the operations performed by the OFDMA
encoding/transmitter module 700A of FIG. 7A (as depicted in FIG.
15) or OFDMA encoding/beamforming/transmitter module 700B of FIG.
7B. However, the transmission output are not fed directly to the
transmission antennas, since the transmission antennas for at least
one of the base stations or terminals will be located at a separate
facility. Rather, master encoder 1502 produces respective sets of
antenna drive signals 1504 and 1506 for base stations 402 and 404.
Upon receipt of the antenna drive signals, corresponding downlink
signals are transmitted by selected antennas hosted by base
stations 402 and 404 based on the different MIMO channels supported
by the system. Control inputs to master encoder 1502 corresponding
to the MIMO channels are provided by a subscriber MIMO channel
assignment register 1508.
[0090] If necessary, signal synchronization is performed by one or
more sync/delay blocks 1510. According to the example embodiment of
FIG. 15, two sync/delay blocks 1510A and 1510B are shown, with each
being employed at a respective base station. In other embodiments,
some base stations or terminals may not require a delay block,
particularly if a co-located master encoder is employed. In
general, the sync/delay blocks for a system are employed to
synchronize the antenna signals or synchronize the delay of antenna
signals (when delay diversity is employed).
[0091] Signal synchronization may be performed in any number of
ways using principles known in the communication arts. For example,
in one embodiment separate timing signals or sequences are provided
to each of the base stations in a cooperative MIMO system. The
timing signals or sequences contain information from which
corresponding antenna drive signals may be synchronized. To perform
such synchronization, each sync/delay blocks add an appropriate
delay to its antenna signals. Synchronization feedback information
may also be employed using well-known techniques.
[0092] Under one embodiment of a variation of architecture 1500,
antenna signal processing operations corresponding to the FFT, PIS,
and add CP blocks are implemented at the respective base stations
or respective terminals. In this instance, STC code sequences are
provided to each of the base stations or terminals, with further
antenna signal processing being performed at the base stations or
terminals. Under this approach, timing signals or the like may be
embedded in the data streams containing the code sequences.
[0093] Another approach for implementing a cooperative MIMO system
is depicted by cooperative MIMO architecture 1600 in FIG. 16. Under
this architecture, replicated instances of input information
streams for multiple channel subscribers are generated by a block
1602 and provided to each of the base stations used to form the
augmented MIMO antenna array. In this case, the STC encoding and
signal processing operations are performed at each base station in
a manner similar to that described with respect to the OFDMA
encoding/transmitter module 700A of FIG. 7A (as depicted in FIG.
16) or OFDMA encoding/beamforming/transmitter module 700B of FIG.
7B. Again, however, it should be appreciated that architecture 1600
can also be implemented at the terminal side of a network, where
input information streams generated by a block 1602 would be
provided to each terminal and used to form an augmented MIMO
antenna array.
[0094] In one embodiment, subscriber MIMO channel information is
embedded in the input data streams received at each base station.
Accordingly, there is a need to determine which antenna elements
are used to support each MIMO channel. This information is stored
in a subscriber MIMO channel register 1604, and is used to control
signal processing in a collaborative manner at the base
stations.
[0095] As before, there may be a need to synchronize the antenna
signals. For example, if the components used to perform the
operations of block 1602 are located at different distances from
the base stations, the input streams will be received at different
times. In response, the corresponding antenna signals will be
generated at different times. To address this situation, one or
more sync/delay blocks 1606 may be employed (e.g., as depicted by
sync/delay blocks 1606A and 1606B in FIG. 16B. In one embodiment,
timing signals are encoded in the input data streams using one of
many well-known schemes. The timing signals, which may typically
comprise timing frames, timing bits, and/or timing sequences, are
extracted by 1606A and 1606B. In view of the timing information, a
variable delay is applied by sync/delay block for the data streams
that are received earlier, such that at the point the data streams
are ready received at the STC blocks, they have been
resynchronized.
[0096] In general, the processing operations performed by the
process blocks depicted herein may be performed using known
hardware and/or software techniques. For example, the processing
for a given block may be performed by processing logic that may
comprise hardware (circuitry, dedicated logic, etc.), software
(such as is run on a general purpose computer system or a dedicated
machine), or a combination of both.
[0097] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods, and steps described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure of the present invention, processes, machines,
manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
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