BACKGROUND
Multiple-input-multiple-output (MIMO) systems represent an
5 advance in wireless communication. MIMO systems employ one or
more (e.g., multiple) antennas at the transmitting and receiving ends
of a wireless link to improve the data transmission rate, while holding
radio bandwidth and power constant.
A MIMO transmitter transmits an outgoing signal using multiple
0 service antennas by demultiplexing the outgoing signal into multiple
sub-signals and transmitting the sub-signals from separate antennas.
MIMO exploits the multiple signal propagation paths to increase
throughput, reduce bit error rates, and reduce transmission power.
FIG. 1 illustrates a multi-user multiple-input-multiple-output
5 (MIMO) wireless system having a conventional centralized architecture.
Referring to FIG. 1, a base station 100 includes a plurality of
service antennas 120 (i.e., antenna 120- 1 to antenna 120-M), one
central channel estimation unit 130, and one central pre-coding unit
140. The number of service antennas 120 in the conventional system
is typically 4 or 8, for example. After data to be transmitted has been
pre-coded by the central pre-coding unit 140 (as further explained
below), the base station 100 transmits an outgoing signal including
the pre-coded data using the plurality of antennas 120 by
demultiplexing the outgoing signal into multiple sub-signals and
transmitting the sub-signals from separate service antennas to a
plurality of independently-operated terminals 110 (i.e., terminal 110- 1
to terminal 110-K). The plurality of terminals 110 are equipped with
one or more antennas. For the sake of clarity, it is assumed that all
terminals 110 are equipped with only a single antenna.
A typical method of channel estimation in the conventional art
is the linear regression estimator and a typical method of pre-coding
in the conventional art is Zero-Forcing (ZF) via the pseudo-inverse,
which is further explained below.
The central channel estimation unit 130 estimates the
communication channel between the plurality of terminals 110 and
the plurality of antennas 120. For example, the central estimation
unit 130 may receive pilot sequences from the plurality of terminals
110 and estimate the channel condition based on the received pilot
sequences. For example, h may refer to the channel coefficient
between the i-th terminal of the plurality of terminals 110 and the j-th
antenna of the plurality of service antennas 120, where i-th refers to
any one of the terminals 110 and j-th refers to any one of the
antennas 120. That is, the signal sent by the i-th terminal to the j-th
antenna is multiplied by the channel coefficient h . Similarly, via
reciprocity, the signal sent by j-th antenna to the i-th terminal is also
multiplied by the channel coefficient hy . The channel estimation
vector for the j-th antenna may be denoted by:
The channel estimation between the plurality of service
antennas 120 and the plurality of terminals 110 may be denoted by
the matrix:
Eq. 2 : H= [h h2 ••• h ]
Matrix H is an K-by-M channel matrix, formed by the channel
vectors of the corresponding antennas.
During the pilot transmission phase, terminal 110- 1 through
terminal 110-K transmit pilot sequences {,•••, ^}, where each pilot
sequence is a column vector. It is advantageous for the different pilot
sequences to be substantially mutually orthogonal. For example, the
j-th antenna of the plurality of service antennas 120 receives the
following pilot sequence vector:
Eq. 3 : y j = h j hKj K + additive noise .
Referring to FIG. 1, the central channel estimation unit 130
collects all the vectors y j , where j=l,...,M, and forms the matrix:
Eq. 4 : Y = [ ••• y ]
Then, the central channel estimation unit 130 computes an
estimate of the ch nnel matrix H as follows:
Eq. 5 : H=
The superscript "T" refers to transposition and conjugation, and
c is a constant. In some implementations, such as minimum meansquare
estimation, a different constant is applied to each of the K
channel estimates.
The central estimation unit 130 transfers the channel estimate
H to the central pre-coding unit 140. The central pre-coding unit 130
receives data to be transferred to the plurality of service antennas (i.e.,
a n d pre-codes the data. The pre-coded data is then
transmitted via the plurality antennas 120. For instance, the plurality
of service antennas 120 transmits their respective coded signals (i.e.,
1, •, }) o the plurality of terminals 110. Pre-coding is generalized
beamforming that supports spatially-multiplexed transmission in
multi-user MIMO systems. Pre-coding enables multiple streams of
signals to be emitted from the transmit service antennas with
independent and appropriate weighting per each antenna such that
each terminal receives the data intended for itself with minimal
interference from data sent to other terminals.
After receiving the channel estimation H , the central pre-coding
unit 140 calculates the following pre-coding matrix (e.g., the pseudoinverse
of the channel estimate) :
Eq. 6 : = ? •- (ή •) 1
P is a normalization constant that defines the base station
transmission power.
Based on the pre-coding matrix A, the central pre-coding unit
140 precodes signals { ,•••, } by computing the following vector:
Signals ¾ to sM are transferred to their respective service
antennas for transmission. For example, signal ¾ is transferred to
antenna 120- 1 and signal sM is transferred to antenna 120-M.
As described above, the conventional system includes a small
number of antennas 120, which are all connected to the channel
estimation unit 130 and the pre-coding unit 140. However, if the
number of service antennas is increased to a number substantially
larger than 4 or 8, the complexity of the conventional system greatly
increases. For example, as the number of service antennas increases,
the complexity of computing Eqs. 6 and 7 in the pre-coding unit 140
grows quadratically with the number of antennas.
In a multi-user MIMO system having a conventional centralized
architecture, data is typically transmitted over the reverse-link as
follows. Each of the K terminals transmits a data symbol, and each of
the M service antennas receives a combination of all K data symbols
as modified by the channel. The j-th service antenna receives the
signal Xj =¾•h +--- + qK -hKj + additive noise . A central de-coding unit
uses the channel estimates to decode the M received signals. The socalled
zero-forcing receiver utilizes the pseudo-inverse of the channel
estimate to obtain estimates for the K data symbols as follows,
[q ]=[ ••• ii T HH . Other commonly-used decoding
schemes includes minimum mean-square estimation, and successive
nulling and cancellation. All of these decoding schemes require that a
centralized decoder have access to all of the Mreceived signals as well
as the channel estimates. The computational burden of these
decoding schemes grows quadratically with the number of service
antennas.
SUMMARY
Embodiments provide a MIMO system having a plurality of
service antennas and method for data transmission and reception.
The system includes a plurality of service antennas, where each
service antenna is configured to simultaneously serve a plurality of
terminals, and independently receive a pilot sequence from the
plurality of terminals. The system further includes a plurality of
channel estimation units, where each channel estimation unit is
associated with a different one of the plurality of service antennas and
configured to independently generate an antenna- specific channel
estimate based on the received pilot sequence. The antenna-specific
channel estimate is a channel estimate between the plurality of
terminals and a respective one of the plurality of service antennas.
The system further includes a plurality of pre-coding units, where
each pre-coding unit is associated with a different one of the plurality
of channel estimation units and configured to receive a set of data
symbols to be transmitted and a respective generated antenna- specific
channel estimate. Each pre-coding unit is configured to
independently generate a coded signal to be transmitted to the
plurality of terminals via a respective service antenna based on the set
of data symbols and the antenna- specific channel estimate.
Each pre-coding unit generates the coded signal based on a
conjugate-transpose of the antenna- specific channel estimate.
Further, each pre-coding unit generates the coded signal by
calculating an inner product between the conjugate-transpose of the
antenna-specific channel estimate and the set of data symbols.
In one embodiment, the plurality of service antennas are
randomly distributed in at least two different location areas.
Alternatively, the plurality of service antennas are arranged in one of
(i) a single group and (ii) a plurality of groups, each group
corresponding to a different location area.
In one embodiment, a ratio between a number of the plurality of
service antennas and a number of the plurality of terminals is equal to
or above a threshold level.
The system may further include a data controller configured to
independently transmit the set of data symbols to each pre-coding
unit.
In another embodiment, a first pre-coding unit may receives the
set of data symbols from a data controller and transmits the set of
data symbols to a second pre-coding unit, and the receiving and
transmitting operations are repeated until a last pre-coding unit of the
plurality of pre-coding units.
The system may include a plurality of service antennas, where
each service antenna is configured to simultaneously serve a plurality
of terminals and independently receive a pilot sequence from the
plurality of terminals. The system further includes a plurality of
channel estimation units, where each channel estimation unit is
associated with a different one of the plurality of service antennas and
configured to independently generate an antenna- specific channel
estimate based on the received pilot sequence. The antenna-specific
channel estimate is a channel estimate between the plurality of
terminals and a respective one of the plurality of service antennas.
Further, the system includes a plurality of de-coding units, where
each de-coding unit is associated with a different one of the plurality
of channel estimation units and configured to receive a set of databearing
signals from the plurality of terminals and a respective
antenna- specific channel estimate. Each de-coding unit is configured
to independently generate a decoded signal for each of the plurality of
terminals based on the set of data-bearing signals and the antennaspecific
channel estimate.
Each de-coding unit generates the decoded signal based on a
conjugate-transpose of the antenna- specific channel estimate.
Further, each de-coding unit generates the decoded signal by
multiplying the set of data-bearing signals with the conjugatetranspose
of the antenna- specific channel estimate.
The system may further include a summation unit configured to
receive each decoded signal from the plurality of de-coding units and
sum each decoded signal to produce a resulting summed signal.
Alternatively, the system may include a first de-coding unit that
transmits a first decoded signal to a second de-coding unit, and the
second de-coding unit adds the first decoded signal with a second
decoded signal, and the transmitting and adding operations are
repeated until a last de-coding unit in the plurality of de-coding unit.
The last de-coding unit generates a resulting summed signal.
In one embodiment, the plurality of service antennas are
randomly distributed in different location areas. Alternatively, the
plurality of service antennas are arranged in one of (i) a single group
and (ii) a plurality of groups, each group corresponding to a different
location area.
In one embodiment, a ratio between a number of the plurality of
service antennas and a number of the plurality of terminals is equal to
or above a threshold level.
The method may include independently receiving, by each
service antenna, a pilot sequence from the plurality of terminals,
independently generating, by each channel estimation unit, an
antenna-specific channel estimate based on the received pilot
sequence, where the antenna- specific channel estimate is a channel
estimate between the plurality of terminals and a respective one of the
plurality of service antennas, receiving, by each pre-coding unit, a set
of data symbols to be transmitted and a respective generated antennaspecific
channel estimate, and independently generating, by each precoding
unit, a coded signal to be transmitted to the plurality of
terminals via a respective service antenna based on the set of data
symbols and the respective antenna- specific channel estimate.
The independently generating step generates the coded signal
based on a conjugate-transpose of the antenna- specific channel
estimate. Further, the independently generating step generates the
coded signal by calculating an inner product between the conjugatetranspose
of the antenna- specific channel estimate and the set of data
symbols.
The method may also include independently receiving, by each
service antenna, a pilot sequence from the plurality of terminals,
independently generating, by each channel estimation unit, an
antenna-specific channel estimate based on the received pilot
sequence, where the antenna- specific channel estimate is a channel
estimate between the plurality of terminals and a respective one of the
plurality of service antennas, receiving, by each de-coding unit, a set
of data-bearing signals from the plurality of terminals and a respective
antenna-specific channel estimate, and independently generating, by
each de-coding unit, a decoded signal based on the set of data-bearing
signals and the antenna- specific channel estimate.
The independently generating step generates the decoded signal
based on a conjugate-transpose of the antenna- specific channel
estimate. Further, the independently generating step generates the
decoded signal by multiplying the set of data-bearing signals with the
conjugate-transpose of the antenna- specific channel estimate.
BRIEF DESCRIPTION OF THE DRAWINGS
Example embodiments will become more fully understood from
the detailed description given herein below and the accompanying
drawings, wherein like elements are represented by like reference
numerals, which are given by way of illustration only and thus are not
limiting , and wherein:
FIG. 1 illustrates a multi-user multiple-input-multiple-output
(MIMO) wireless system having a conventional architecture;
FIG. 2 illustrates a multi-user MIMO wireless system for data
transmission and reception according to an embodiment;
FIG. 3 illustrates a portion of the multi-user MIMO wireless
system including a plurality of channel estimation units according to
an embodiment;
FIG. 4 illustrates a portion of the multi-user MIMO wireless
system including a plurality of pre-coding units for transmission on
the forward-link according to an embodiment;
FIG. 5 illustrates a portion of the multi-user MIMO wireless
system including the plurality of pre-coding units for data
transmission on the forward-link according to another embodiment;
FIG. 6 illustrates a portion of the multi-user MIMO wireless
system including a plurality of de-coding units for data reception on
the reverse-link according to an embodiment; and
FIG. 7 illustrates a portion of the multi-user MIMO wireless
system including the plurality of de-coding units for data reception on
the reverse-link according to another embodiment.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Various example embodiments will now be described more fully
with reference to the accompanying drawings in which some example
embodiments are shown. Like numbers refer to like elements
throughout the description of the figures.
It will be understood that, although the terms first, second, etc.
may be used herein to describe various elements, these elements
should not be limited by these terms. These terms are only used to
distinguish one element from another. For example, a first element
could be termed a second element, and, similarly, a second element
could be termed a first element, without departing from the scope of
example embodiments. As used herein, the term "and/or" includes
any and all combinations of one or more of the associated listed items.
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
example embodiments. As used herein, the singular forms "a," "an"
and "the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood that
the terms "comprises," "comprising," "includes" and/ or "including,"
when used herein, specify the presence of stated features, integers,
steps, operations, elements and/ or components, but do not preclude
the presence or addition of one or more other features, integers, steps,
operations, elements, components and/ or groups thereof.
It should also be noted that in some alternative
implementations, the functions/ acts noted may occur out of the order
noted in the figures. For example, two figures shown in succession
may in fact be executed concurrently or may sometimes be executed
in the reverse order, depending upon the functionality/ acts involved.
Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which example
embodiments belong. It will be further understood that terms, e.g.,
those defined in commonly used dictionaries, should be interpreted as
having a meaning that is consistent with their meaning in the context
of the relevant art and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
In the following description, illustrative embodiments will be
described with reference to acts and symbolic representations of
operations (e.g., in the form of flowcharts) that may be implemented as
program modules or functional processes that include routines,
programs, objects, components, data structures, etc., that when
executed perform particular tasks or implement particular abstract
data types and may be implemented using existing hardware at
existing network elements. Such existing hardware may include one
or more Central Processing Units (CPUs), digital signal processors
(DSPs), application-specific-integrated-circuits, field programmable
gate arrays (FPGAs) computers or the like machines that once
programmed become particular machines.
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, or as is apparent from the
discussion, terms such as "generating", "summing", "configuring" 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.
As used herein, the term "terminal" may be considered
synonymous to, and may hereafter be occasionally referred to, as a
client, mobile unit, mobile station, mobile user, user equipment (UE),
subscriber, user, remote station, access terminal, receiver, etc., and
may describe a remote user of wireless resources in a wireless
communication network. In the MIMO system, a terminal may have
one or more antennas.
Similarly, as used herein, the term "base station" may be
considered synonymous to, and may hereafter be occasionally referred
to, as a Node B, base transceiver station (BTS), etc., and may describe
a transceiver in communication with and providing wireless resources
to mobiles in a wireless communication network. As discussed herein,
base stations may have all functionally associated with conventional,
well-known base stations in addition to the capability to perform the
methods discussed herein.
Embodiments of the present disclosure provide a multi-user
multiple-input and multiple-output (MIMO) system for data
transmission and reception that utilizes a relatively large number of
service antennas in relation to the number of independently operated
terminals.
The inventors of the present disclosure have recognized the
benefits of using a large number of service antennas in relation to the
number of independently operated terminals. An architecture of using
such a large number of service antennas provides improved
throughput and spectral efficiency. For example, this type of
architecture may simultaneously transmit signals of information to
many terminals at once using the same time-frequency slots (e.g., in
spatial multiplexing). Further, because many different signals are
transmitted over the communication channel, the beamforming of
these signals may be more focused, and, as a result, decrease the
amount of radiated power.
Further, the inventors of the present disclosure have recognized
as the number of service antennas, M, grows large as compared with
the number of terminals being served, K, the M-component
propagation vectors to different terminals, as functions of frequency,
become asymptotically orthogonal. This permits the pseudo-inverse
pre-coder of the conventional art (which is the source of the
complexity of the conventional system) to be replaced by a simpler
pre-coder, which may be a scaled conjugate-transpose of the
estimated channel matrix, as further described below. The pre-coder
of the embodiments allows a more decentralized architecture in which
a ) each service antenna retains its own channel estimate for the
communication channel between itself and the K terminals and shares
this information with no other service antenna, and b ) each antenna
performs pre-coding independently of the pre-coding performed by the
other antennas (apart from amplitude scaling for power control).
Similar benefits of operating with a large excess of service antennas
compared with the number of terminals exist for up-link transmission
of data.
FIG. 2 illustrates a multi-user MIMO wireless system 200 for
data transmission and reception according to an embodiment.
The MIMO wireless system 200 includes a data controller 260,
a plurality of channel estimation units 230 (e.g., a first channel
estimation unit 230- 1 to a last channel estimation unit 230-M), a
plurality of pre-coding/de-coding units 240 (e.g., a first precoding/
de-coding unit 240- 1 to a last pre-coding/de-coding unit 240-
M), a plurality of service antennas 220 (e.g., a first service antenna
220- 1 to a last service antenna 220-M), and a plurality of
independently operated terminals 2 10 (e.g., a first terminal 2 10- 1 to a
last terminal 2 10-K). When the "coding unit" is de-coding a signal,
the unit 240 is referred to as a de-coding unit, and when the "coding
unit" is pre-coding a signal, the unit 240 is referred to a pre-coding
unit.
The MIMO system 200 may include a time division duplexing
(TDD) orthogonal frequency division multiplexing (OFDM) system.
Under TDD, data transmissions in the uplink (from terminal to base
station) and downlink (from base station to terminal) occupy disjoint
intervals of time, and utilize the same frequency band. Time-division
duplex operation is particularly efficient for the acquisition of
downlink channel information by the service antennas, because the
time occupied by the pilot sequences is then independent of the
number of service antennas. However, it will be understood that
embodiments may be implemented in other MIMO systems as well as
other wireless communication systems and/or schemes. For example,
methods discussed herein may be implemented in connection with a
frequency division duplexing (FDD) or similar scheme.
As shown in FIG. 2, a separate channel estimation unit 230 and
separate pre-coding/de-coding unit 240 are independently provided
for each service antenna 220. In other words, each channel
estimation unit 230 is associated with a different service antenna 220,
and each pre-coding/ de-coding unit 240 is associated with a different
channel estimation unit 230.
Alternatively, each channel estimation unit 230 may be
indirectly or directly connected to a different service antenna 220, and
each pre-coding/de-coding unit 240 may be indirectly or directly
connected to a different channel estimation unit 230. As such, one
channel estimation unit, one pre-coding/de-coding unit, and one
service antenna may be bundled as a block. In this embodiment, the
MIMO wireless system 200 includes a plurality of blocks, where each
block has the capacity to independently estimate the channel
condition, pre-code or de-code a signal, and transmit and/or receive
the signal on the reverse/ forward link communication channel
without the intervention of the other blocks.
The MIMO wireless system 200 may include other components
that are well known to one of ordinary skill in the art. For example,
FIG. 2 illustrates a base-band representation of the operation of the
system, and certain customary features are not shown, including
modules for assembling and disassembling OFDM pulses, modules for
adding or removing cyclic prefixes, up-converters and down-converters,
and power amplifiers and pre-amplifiers. In addition, a separate
modulation/demodulation unit may be provided for each precoding/
de-coding unit.
The plurality of service antennas 220 may be provided in a
single location area such as a centrally located base station.
Alternatively, the plurality of service antennas 220 may be arranged in
at least two different location areas such as two different base stations
located in different areas. Further, the plurality of antennas 220 may
be randomly distributed in one or more location areas.
A ratio between a number of the plurality of service antennas
220 and a number of the plurality of terminals 2 10 may be equal to or
above a threshold level. For example, the number of service antennas
220 may be 400 and the number of terminals 2 10 may be 40. As
such, in one particular embodiment, the ratio of service antennas to
terminals is the threshold level of 10. However, the embodiments
encompass any type of value for the threshold value such that the
ratio of the number of service antennas 220 to the number of
terminals 2 10 is relatively large.
The plurality of service antennas 220 are configured to
simultaneously serve the plurality of terminals 2 10 through multi
user MIMO. Forward-link data transmission includes the
simultaneous (over frequency and over time) transmission of K
separate data streams to the K terminals 2 10 over an air interface.
The air interface may include any type of radio-based communication
link between two network elements according to any type of standard
that is well known to one of ordinary skill in the art. Reverse-link
data transmission comprises the simultaneous (over frequency and
over time) transmission of separate data streams by the K terminals
10 to the service antennas 220 over the air interface.
On the forward link, the data controller 260 transmits the data
streams to the plurality of pre-coding/de-coding units 240, while on
the reverse link the data controller 260 receives data streams from the
plurality of pre-coding/de-coding units 240.. The operation of the
data controller 260 is further described with reference to FIGS. 4 and
5.
Intra-cell interference (i.e. interference among the K data
streams) is reduced to acceptable levels through linear pre-coding by
the pre-coding/de-coding units 240 on the forward-link, and through
linear combining by the pre-coding/de-coding units 240 on the
reverse-link.
The pre-coding/de-coding units 240 require a channel estimate
for the forward and the reverse-link channel, respectively. For a large
numbers of service antennas 220, this channel-state information can
be obtained by employing time-division duplex operation such that the
forward and reverse-link channels are reciprocal, and scheduling an
interval of time for the K terminals 2 10 to transmit pilot sequences on
the reverse-link, as further explained below.
FIG. 3 illustrates a portion of the MIMO wireless system 200
including the plurality of channel estimation units 230 according to
an embodiment.
Each channel estimation unit 230 independently generates an
antenna- specific channel estimate based on received pilot sequences.
The antenna- specific channel estimate is a channel estimate between
the plurality of terminals 2 10 and a respective one service antenna
220 (e.g., a first service antenna 220- 1). For example, each channel
estimation unit 230 independently receives pilot sequences from the
plurality of terminals 2 10 over the air interface and independently
estimates the channel condition based on the received pilot sequences.
For example, as shown in FIG. 3, the plurality of terminals 2 10
transmit substantially orthogonal pilot sequences ,••• on the
reverse link, where each pilot sequence is a column vector. The co
efficient hjj may refer to the channel coefficient between the i-th
terminal of the plurality of terminals 2 10 and the j-th service antenna
of the plurality of service antennas 220, where the i-th terminal is any
one of the plurality of terminals 2 10 and the j-th service antenna is
any one of the plurality of service antennas 220. That is, the signal
sent by the i-th terminal to the j-th antenna is multiplied by the
channel coefficient . Similarly, via reciprocity, the signal sent by j -
th antenna to the i-th terminal is also multiplied by the channel
coefficient ¾ . The channel vector for the j-th antenna may be
denoted by Eq. 1, as described above (e.g., h ). As such, the j -
th service antenna of the plurality of service antennas 220 receives the
pilot sequence vector j as described in Eq. 3 (e.g.,
y j = hji • hj K K + additive noise ).
However, according to the embodiments, each channel
estimation unit 230 computes its own antenna- specific channel
estimation, independently from all other channel estimation units 230.
In one embodiment, each channel estimation unit 230 computes the
antenna-specific channel estimation based on the following equation:
The superscript "T" refers to transposition and conjugation, and
c is a constant.
In one example, the first channel estimation unit 230- 1 receives
the pilot sequence - +additive noise from the
plurality of terminals 2 10. Because the transmitted pilot sequence
{ , } is known to the first channel estimation unit 230- 1, the first
channel estimation unit 230- 1 is able to compute the antenna- specific
channel estimate based on Eq. 8 above. For example, as shown in
FIG. 3, the first channel estimation unit 230- 1 generates the antennaspecific
channel estimate , ---hK , where each channel coefficient in
the antenna- specific channel estimate refers to a corresponding
channel coefficient between a respective terminal and the first service
antenna 220. The same operation is repeated for each of the plurality
of channel estimation units 230.
FIG. 4 illustrates a portion of the MIMO wireless system 200
including the plurality of pre-coding units 240 for transmission on the
forward-link according to an embodiment.
As shown in FIG. 4, each pre-coding unit 240 receives a
respective antenna- specific channel estimate corresponding to its
associated channel estimation unit 230 of FIG. 3. Further, each precoding
unit 240 receives a set of data symbols to be transmitted (e.g.,
{ 7i , •••½ ) to the plurality of terminals 2 10 on the forward-link. The
distribution of the set of data symbols may be controlled by the data
controller 260 of FIG. 2. In the embodiment shown in FIG. 4, the data
controller 260 independently transmits the set of data symbols to each
of the pre-coding units 240. According to the embodiments, each precoding
unit 240 independently generates a pre-coded signal to be
transmitted to the plurality of antennas 2 10 via a respective service
antenna 220 based on the set of data symbols to be transmitted and
the antenna- specific channel estimate, as further explained below.
In one embodiment, each pre-coding unit 240 generates the
coded signal based on a conjugate-transpose of the antenna- specific
channel estimate. For example, each pre-coding unit 240 generates
the coded signal by calculating an inner product between the
conjugate-transpose of the antenna- specific channel estimate and the
set of data symbols. For instance, each pre-coding unit 240 generates
an antenna- specific pre-coding vector based on the following equation:
The parameter p is a normalization factor, and ay is a row
vector with K entries. The K entries correspond to the K terminals
2 10.
Next, each pre-coding unit 240 generates its coded signal (e.g.
Sj ) for its respective service antenna 220 based on the following
equation:
<1Eq. 10: s = a
l
According to an embodiment, the operations in one pre-coding
unit 240 and its associated channel estimation units 230 are
performed without any coordination with other the pre-coding units
and associated channel estimated units.
Thereafter, each service antenna 220 transmits its coded signal
to the plurality of terminals 2 10.
FIG. 5 illustrates a portion of the MIMO wireless system 200
including the plurality of pre-coding units 240 for data transmission
on the forward-link according to another embodiment. The difference
between FIG. 5 and FIG. 4 is the way the pre-coding units 240 receive
the set of data symbols to be transmitted. In FIG. 5, the first precoding
unit 240- 1 receives the set of data symbols to be transmitted
(e.g., ) from the data controller 260 over a communication
link, and then transmits the set of data symbols to the second precoding
unit 240-2, and the receiving and transmitting operations are
repeated until a last pre-coding unit 240-M. In other words, the set of
data symbols to be transmitted are distributed to the pre-coding units
240 in a daisy-chain manner. Thereafter, the pre-coding units 240
operate in the same manner as previously described with reference to
FIG. 4.
A backhaul communication network may be provided in the
MIMO system 200 to allow communication between each pre-coding
unit 240 and/or each service antenna 220. For example, because the
service antennas 220 may be randomly distributed in a de-centralized
manner, the backhaul communication network provides the
communication between each service antenna 220. The backhaul
network could comprise any sort of conventional communications
links, including wire, optical fiber, free-space optical, or wireless.
FIG. 6 illustrates a portion of the MIMO wireless system 200
including the plurality of de-coding units 240 for data reception on the
reverse-link according to an embodiment.
Each of the k terminals 2 10 transmits a data symbol to each of
the service antennas 220 on the reverse-link. As such, each service
antenna 220 receives a data-bearing signal corresponding to this
antenna. For example, the first antenna 220- 1 receives the databearing
signal = q - ¾ +••• + ¾ • K + additive noise resulting from the
transmission of the plurality of data symbols from the plurality of
terminals 2 10 corresponding to the first antenna 220- 1. The other
antennas 220 operate in the same manner.
According to an embodiment, each de-coding unit 240 receives a
data-bearing signal and a respective antenna- specific channel
estimate. The antenna- specific channel estimate is provided from an
associated channel estimation unit 230. Each de-coding unit 240 is
configured to independently generate a decoded signal for each of the
K terminals based on the set of data-bearing signals and the antennaspecific
channel estimate. The de-coding units 240 operate in a
similar manner to the pre-coding units 240, as illustrated FIG. 5,
except that the de-coding units 240 decode the data symbols
transmitted through the communication channel. For example,
similar to the pre-coding units 240, each de-coding unit 240 generates
its decoded signal based on a conjugate-transpose of the antennaspecific
estimate. For instance, each de-coding unit 240 generates the
decoded signal by multiplying the data-bearing signal with the
conjugate-transpose of the antenna- specific channel estimate.
In one example, the first de-coding unit 240- 1 receives a databearing
signal ¾ corresponding to data symbols from the terminals
2 10 associated with the first service antenna 240- 1. Also, the first d e
coding unit 240- 1 receives the antenna- specific channel estimate
associated with the terminals 2 10 and the first service antenna 240- 1
(e.g., ¾ ,--- K . The computation of the first service antenna channel
estimate is the same as previously explained with reference to FIG. 3.
The first de-coding unit 240- 1 generates its de-coded data by
multiplying with ••• h , e.g.,
[q ]=¾• ••• hK . The other de-coding units operate in
the same manner.
The MIMO wireless system 200 may also include a summation
unit 260 that is configured to receive each decoded signal from the
plurality of de-coding units 240, and sum each decoded signal to
produce a resulting data signal, i.e.,
fei ••• ••• ]+••• + [¾ ••• to] •
FIG. 7 illustrates a portion of the MIMO wireless system 200
including the de-coding units 240 for data reception on the reverselink
according to another embodiment.
Instead of providing a summation unit 260 as shown in FIG. 6,
the MIMO wireless system 200 may sum the decoded signals from the
plurality of de-coding units 240 in a daisy chain manner. For example,
a first de-coding unit 240- 1 transmits a first decoded signal,
[< K I >
to second de-coding unit 240-2, and the second decoding
unit 240-2 adds the first decoded signal with a second decoded
signal, [¾ ••• (i- e
>
tne second decoded signal being generated
by the second de-coding unit 240-2), to obtain the sum,
[< i]+[¾ fe _ n the transmitting and adding operating
are repeated until a last de-coding unit 240-M. The last de-coding
unit 240-M produces the resulting summed signal, ••• .
What is claimed:
1. A multiple-input and multiple-output (MIMO) system (200) for
data transmission, the system comprising:
a plurality of service antennas (220), each service antenna
configured to simultaneously serve a plurality of terminals (2 10), each
service antenna configured to independently receive a pilot sequence
from the plurality of terminals;
a plurality of channel estimation units (230), each channel
estimation unit being associated with a different one of the plurality of
service antennas and configured to independently generate an
antenna-specific channel estimate based on the received pilot
sequence, the antenna- specific channel estimate being a channel
estimate between the plurality of terminals and a respective one of the
plurality of service antennas; and
a plurality of pre-coding units (240), each pre-coding unit being
associated with a different one of the plurality of channel estimation
units and configured to receive a set of data symbols to be transmitted
and a respective generated antenna- specific channel estimate, each
pre-coding unit configured to independently generate a coded signal to
be transmitted to the plurality of terminals via a respective service
antenna based on the set of data symbols and the antenna- specific
channel estimate.
2. The system of claim 1, wherein each pre-coding unit generates the
coded signal based on a conjugate-transpose of the antenna- specific
channel estimate.
3. The system of claim 2, wherein each pre-coding unit generates the
coded signal by calculating an inner product between the conjugatetranspose
of the antenna- specific channel estimate and the set of data
symbols.
4. The system of claim 1, wherein a ratio between a number of the
plurality of service antennas and a number of the plurality of
terminals is equal to or above a threshold level.
5. The system of claim 1, further comprising:
a data controller (260) configured to independently transmit the
set of data symbols to each pre-coding unit.
6. The system of claim 1, wherein a first pre-coding unit (240- 1)
receives the set of data symbols from a data controller (260) and
transmits the set of data symbols to a second pre-coding unit (240-2),
and the receiving and transmitting operations are repeated until a last
pre-coding unit (240-M) of the plurality of pre-coding units.
7. A multiple-input and multiple-output (MIMO) system (200) for data
reception, the system comprising:
a plurality of service antennas (220), each service antenna
configured to simultaneously serve a plurality of terminals (2 10), each
service antenna configured to independently receive a pilot sequence
from the plurality of terminals;
a plurality of channel estimation units (230), each channel
estimation unit being associated with a different one of the plurality of
service antennas and configured to independently generate an
antenna-specific channel estimate based on the received pilot
sequence, the antenna- specific channel estimate being a channel
estimate between the plurality of terminals and a respective one of the
plurality of service antennas; and
a plurality of de-coding units (240), each de-coding unit being
associated with a different one of the plurality of channel estimation
units and configured to receive a set of data-bearing signals from the
plurality of terminals and a respective antenna- specific channel
estimate, each de-coding unit configured to independently generate a
decoded signal for each of the plurality of terminals based on the set
of data-bearing signals and the antenna- specific channel estimate.
8. The system of claim 7, wherein each de-coding unit generates the
decoded signal based on a conjugate-transpose of the antenna- specific
channel estimate.
9. The system of claim 9, wherein each de-coding unit generates the
decoded signal by multiplying the set of data-bearing signals with the
conjugate-transpose of the antenna- specific channel estimate.
10. The system of claim 7, further comprising:
a summation unit (260) configured to receive each decoded
signal from the plurality of de-coding units and sum each decoded
signal to produce a resulting summed signal.