U.S. patent application number 16/113569 was filed with the patent office on 2018-12-20 for methods and procedures for non-linear precoding based multiuser multiple input multiple output.
This patent application is currently assigned to INTERDIGITAL PATENT HOLDINGS, INC.. The applicant listed for this patent is INTERDIGITAL PATENT HOLDINGS, INC.. Invention is credited to Monisha Ghosh, Hanqing Lou, Robert L. Olesen, Oghenekome Oteri, Nirav B. Shah, Pengfei Xia.
Application Number | 20180367191 16/113569 |
Document ID | / |
Family ID | 50896495 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180367191 |
Kind Code |
A1 |
Xia; Pengfei ; et
al. |
December 20, 2018 |
METHODS AND PROCEDURES FOR NON-LINEAR PRECODING BASED MULTIUSER
MULTIPLE INPUT MULTIPLE OUTPUT
Abstract
A station may be used to implement non-linear coding based
multiuser multiple-input multiple-output (MU-MIMO). The station may
include a processor that may be configured to perform a number of
actions. For example, the processor may receive a null packet from
an access point (AP). Channel feedback may be generated using the
null packet. The channel feedback may be sent to the AP. QR
dependent information may be received from the AP. Data may be sent
to the AP according to the QR dependent information.
Inventors: |
Xia; Pengfei; (San Diego,
CA) ; Oteri; Oghenekome; (San Diego, CA) ;
Shah; Nirav B.; (San Diego, CA) ; Ghosh; Monisha;
(Chicago, IL) ; Lou; Hanqing; (Syosset, NY)
; Olesen; Robert L.; (Huntington, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTERDIGITAL PATENT HOLDINGS, INC. |
Wilmington |
DE |
US |
|
|
Assignee: |
INTERDIGITAL PATENT HOLDINGS,
INC.
Wilmington
DE
|
Family ID: |
50896495 |
Appl. No.: |
16/113569 |
Filed: |
August 27, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14777158 |
Sep 15, 2015 |
10063290 |
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PCT/US2014/025966 |
Mar 13, 2014 |
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16113569 |
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61794149 |
Mar 15, 2013 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/0417 20130101;
H04B 7/0452 20130101; H04B 7/0626 20130101; H04B 7/0456
20130101 |
International
Class: |
H04B 7/0417 20060101
H04B007/0417; H04B 7/0452 20060101 H04B007/0452; H04B 7/0456
20060101 H04B007/0456; H04B 7/06 20060101 H04B007/06 |
Claims
1. A station for multiuser multiple-input multiple-output (MU-MIMO)
operation, the station comprising: a memory; and a processor
configured to: receive a channel estimation packet from a base
station via a channel; generate channel feedback using the channel
estimation packet, wherein the channel feedback is associated with
the channel and the channel feedback is capable of being used by
the base station to generate matrix Q and matrix R (QR) dependent
information and user ordering information associated with the
station and at least one other station of the MU-MIMO operation,
the user ordering information comprising an order in which the
station and the at least one other station are processed, and
wherein the QR dependent information comprises diagonal loading
values and a modulo operation associated with the station; send the
channel feedback to the base station; receive the QR dependent
information and the user ordering information from the base
station; and receive non-linear precoded data from the base
station.
2. The station of claim 1, wherein the user ordering information
comprises a channel matrix of channel vectors from multiple
stations.
3. The station of claim 2, wherein the processor is further
configured to send data to the base station using the non-linear
precoded data in an order indicated in the user ordering
information.
4. The station of claim 1, wherein the QR dependent information
comprises transmission characteristics.
5. The station of claim 1, wherein the processor is further
configured to receive the QR dependent information via a code point
included in a signal (SIG) field of a MU-MIMO procedure packet data
unit (PPDU).
6. The station of claim 1, wherein the processor is further
configured to receive the QR dependent information via a primary
channel.
7. The station of claim 1, wherein the processor is further
configured to receive the QR dependent information via a pilot
signal.
8. The station of claim 1, wherein the processor is further
configured to subtract from the non-linear precoded data,
cross-interference from one or more other stations.
9. The station of claim 1, wherein the processor is further
configured to: receive a multi-user data stream from the base
station; and apply the diagonal loading values and the modulo
operation to the multi-user data stream.
10. The station of claim 9, wherein the processor is further
configured to perform demapping and decoding.
11. The station of claim 1, wherein the processor is further
configured to send an acknowledgement to the base station to
acknowledge receipt of the received non-linear precoded data.
12. A base station configured for multiuser multiple-input
multiple-output (MU-MIMO) operation, the base station comprising: a
memory; and a processor configured to: send a channel estimation
packet; receive a first feedback from a first station and a second
feedback from a second station, the first station and the second
station associated with the MU-MIMO operation; determine matrix Q
and matrix R (QR) dependent information and user ordering
information using the first feedback and the second feedback, the
user ordering information comprising an order in which the station
and the at least one other station are processed, wherein the QR
dependent information comprises diagonal loading values and a
modulo operation associated with the first station and the second
station, and wherein the user ordering information is associated
with the first station and the second station; send the QR
dependent information to the first station; and send a multi-user
data stream using nonlinear precoding and the user ordering
information.
13. The base station of claim 12, wherein the QR dependent
information comprises transmission characteristics.
14. The base station of claim 12, wherein the processor is further
configured to send the QR dependent information via a code point
included in a signal (SIG) field of a MU-MIMO procedure packet data
unit (PPDU).
15. The base station of claim 12, wherein the processor is further
configured to send the QR dependent information via a primary
channel.
16. The base station of claim 12, wherein the processor is further
configured to send the QR dependent information via a pilot
signal.
17. The base station of claim 12, wherein the processor is further
configured to send the QR dependent information to the second
station.
18. The base station of claim 12, wherein the user ordering
information comprises a channel matrix of channel vectors for the
first station and the second station.
19. The base station of claim 17, where in the processor is further
configured to apply the diagonal loading values and the modulo
operation to the multi-user data stream.
20. The base station of claim 12, wherein the processor is further
configured to perform demapping and decoding.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
application 61/794,149, filed on 15 Mar. 2013, the contents of
which are hereby incorporated by reference herein.
BACKGROUND
[0002] Due to an increasing demand for wireless communication
services and bandwidth capacities, wireless networks, for example
wireless local area networks (WLANs) may use multiple-input
multiple-output (MIMO) technologies. MIMO antennas may offer
improved data throughput and link range. However, performance of
existing MIMO technologies may be inadequate.
SUMMARY
[0003] Disclosed herein are systems, methods, and apparatus that
may be used to implement non-linear coding based multiuser
multiple-input multiple-output (MU-MIMO). For example, a station
may be used to receive non-linear coded MU-MIMO transmissions. The
station may include a processor that may be configured to perform a
number of actions. The processor may receive a null packet from an
access point (AP). Channel feedback may be generated using the null
packet. The channel feedback may be sent to the AP. QR dependent
information may be received from the AP. Data may be sent to the AP
according to the QR dependent information.
[0004] As another example, an access point (e.g. non-STA, a relay,
or the like) may be used to implement non-linear coding based
MU-MIMO. The access point may include a processor that may be
configured to perform a number of actions. The processor may send a
null packet. A first feedback may be received from a first station
and a second feedback may be received from a second station. QR
dependent information may be determined using the first feedback
and the second feedback. The QR dependent information may be sent
to the first station. A multi-user data stream may be received.
[0005] The Summary is provided to introduce a selection of concepts
in a simplified form that are further described in the Detailed
Description. This Summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used to limit the scope of the claimed subject
matter. Furthermore, the claimed subject matter is not limited to
any limitations that solve any or all disadvantages noted in any
part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] A more detailed understanding may be had from the following
description, given by way of example in conjunction with the
accompanying drawings.
[0007] FIG. 1 illustrates an exemplary multi-user transmission from
a single access point (AP) to multiple stations (STAs).
[0008] FIG. 2 illustrates an exemplary modulo operation for
quadrature phase shift keying (QPSK).
[0009] FIG. 3 illustrates an exemplary non-linear MU-MIMO
transmitter and receiver.
[0010] FIG. 4 illustrates an exemplary average per user bit-error
rate (BER) performance with no user ordering.
[0011] FIG. 5 illustrates an exemplary QPSK constellation.
[0012] FIG. 6 illustrates an exemplary extended demapper for QPSK
constellation.
[0013] FIG. 7 illustrates an exemplary block diagram of QR based
non-linear multi-user multiple input multiple output (NL
MU-MIMO).
[0014] FIG. 8 illustrates an exemplary transmitter block diagram
for a data field of a NL-MU-MIMO procedure protocol data unit
(PPDU).
[0015] FIG. 9 illustrates an exemplary receiver block for data
field of a NL-MU-MIMO PPDU.
[0016] FIG. 10 illustrates an exemplary NL-MU-MIMO in a wireless
local area network (WLAN).
[0017] FIG. 11 illustrates an exemplary average per user BER
performance with fixed user ordering.
[0018] FIG. 12(a) illustrates an exemplary aggregated channel from
an AP to four STAs.
[0019] FIG. 12(b) illustrates exemplary effective channels with no
ordering by the highlighted entries.
[0020] FIG. 12(c) illustrates exemplary the effective channels with
min-norm ordering.
[0021] FIG. 12(d) illustrates the effective channels with max-norm
ordering.
[0022] FIG. 13 illustrates an exemplary performance of various
schemes.
[0023] FIG. 14 illustrates an exemplary independent user ordering
for QR multi-user multiple input multiple output (QR-MU-MIMO).
[0024] FIG. 15 illustrates an exemplary independent user ordering
for QR-MU-MIMO in SC-FDE systems.
[0025] FIG. 16 illustrates an exemplary of max-log-MAP extended
demapping.
[0026] FIG. 17 illustrates an exemplary decision symbol sets for
the regular signal constellation.
[0027] FIG. 18 illustrates an exemplary extended demapping.
[0028] FIG. 19 illustrates an exemplary decision symbol sets of the
shifted/wrapped signal constellation.
[0029] FIG. 20 illustrates an exemplary transmitter diagram for
matched filtering implicit signaling.
[0030] FIG. 21 illustrates an exemplary differential signaling.
[0031] FIG. 22 illustrates an exemplary cumulative distribution
function (CDF) distribution of the gains.
[0032] FIG. 23 illustrates an exemplary explicit signaling frame
format.
[0033] FIG. 24A is a system diagram of an example communications
system in which one or more disclosed embodiments may be
implemented.
[0034] FIG. 24B is a system diagram of an example wireless
transmit/receive unit (WTRU) that may be used within the
communications system illustrated in FIG. 24A.
DETAILED DESCRIPTION
[0035] A detailed description of illustrative embodiments will now
be described with reference to the various figures. Although this
description provides a detailed example of possible
implementations, it should be noted that the details are intended
to be exemplary and in no way limit the scope of the
application.
[0036] Disclosed herein are systems, methods, and apparatus that
may be used to implement non-linear coding based multiuser
multiple-input multiple-output (MU-MIMO). For example, a station
may be used to implement non-linear coded based MU-MIMO
transmissions. The station may include a processor that may be
configured to perform a number of actions. The processor may
receive a null packet from an access point (AP). Channel feedback
may be generated using the null packet. The channel feedback may be
sent to the AP. QR dependent information may be received from the
AP. Data may be sent to the AP according to the QR dependent
information.
[0037] As another example, an access point may be used to implement
non-linear coding based MU-MIMO. The access point may include a
processor that may be configured to perform a number of actions.
The processor may send a null packet. A first feedback may be
received from a first station and a second feedback may be received
from a second station. QR dependent information may be determined
using the first feedback and the second feedback. The QR dependent
information may be sent to the first station. A multi-user data
stream may be received.
[0038] FIG. 1 illustrates an exemplary multi-user transmission from
a single access point (AP) to multiple stations (STAs). As shown in
FIG. 1, wireless local area network (WLAN) 100 may be in an
infrastructure basic service set (IBSS) mode. The WLAN may have an
access point (AP) for a basic service set (BSS). One or more
stations (STAs) may be in communication with the AP. For example,
STA 207, STA 205, and/or STA 203 may be in communication with AP
209.
[0039] An AP, such as AP 209, may have access or interface to a
wired or wireless network, such as a distribution system (DS), that
may carry traffic into and out of the BSS. A STA, such as STA 205,
may receive traffic via an AP. For example, traffic from outside
the BBS may arrive at AP 209 and AP 209 may deliver the traffic to
STA 205. A STA may send traffic to destinations outside the BSS via
the AP. For example, STA 205 may send traffic to AP 102 and AP 102
may deliver the traffic to a destination outside the BSS.
[0040] Traffic between STAs within the BSS may be sent via the AP.
For example, STA 205 may send traffic to AP 209 and the AP 209 may
deliver the traffic to STA 203. The traffic between STAs within a
BSS may be peer-to-peer traffic. Peer-to-peer traffic may be sent
directly between a source STA and a destination STA using, for
example, a direct link setup (DLS) such as an IEEE 802.11e DLS, an
IEEE 802.11z tunneled DLS (TDLS), or the like. A WLAN using an IBSS
mode may not have an AP and the STAs may communicate directly with
each other. This mode of communication may be referred to as an
ad-hoc mode.
[0041] Using the IEEE 802.11 infrastructure mode of operation, AP
209 may transmit a beacon on a channel, which may be a primary
channel. The channel may be 20 MHz wide, and may be the operating
channel of the BSS. The channel may be used by the STAs to
establish a connection with AP 209. For example, STA 205 may use
the channel to establish a connection with AP 209. When using the
IEEE 802.11 infrastructure mode, channel access may be Carrier
Sense Multiple Access with Collision Avoidance (CSMA/CA). When
using CSMA/CA an STA and/or an AP may sense the primary channel. If
the channel is detected to be busy, the STA or AP may back off.
This may be done, for example, to avoid collisions by allow a STA
or an AP to transmit within a BBS when the channel is free.
[0042] WLAN 100 may use IEEE 802.11 AC, or a later amendment to it.
A STA, such as STA 207, STA 205, and STA 203 may be a very high
throughput (VHT) STA. In IEEE 802.11ac, a VHT STA may support,
e.g., 20 MHz, 40 MHz, 80 MHz, and/or 160 MHz wide channels. The 40
MHz, and 80 MHz, channels may be formed, for example, by combining
contiguous 20 MHz channels. A 160 MHz channel may be formed, for
example, by combining eight contiguous 20 MHz channels, or by
combining two non-contiguous 80 MHz channels (which may be referred
to as an 80+80 configuration). For an 80+80 configuration, the data
may be passed through a segment parser that may divide it into two
streams. Inverse fast Fourier transform (IFFT) and/or time domain
processing may be performed on a stream. The streams may be mapped
onto two channels and the data may be transmitted. At the receiver,
this mechanism may be reversed, and the combined data may be sent
to the media access control (MAC).
[0043] WLAN 100 may use IEEE 802.11af, IEEE 802.11ah, or similar
sub-6 GHz specification. IEEE 802.11af and IEEE 802.11ah may
support sub 1 GHz modes of operation. For these specifications, the
channel operating bandwidths reduced relative to those used in IEEE
802.11n, and IEEE 802.11ac. IEEE 802.11af may support 5 MHz, 10 MHz
and/or 20 MHz bandwidths in the TV White Space (TVWS) spectrum.
IEEE 802.11ah may support 1 MHz, 2 MHz, 4 MHz. 8 MHz, and/or 16 MHz
bandwidths, for example, using non-TVWS spectrum. IEEE 802.11ah may
support Meter Type Control (MTC) devices in a macro coverage area.
MTC devices may have capabilities including, for example, support
for limited bandwidths, and long battery life.
[0044] WLAN 100 may support multiple channels and/or channel widths
using, for example, IEEE 802.11n, IEEE 802.11ac, IEEE 802.11af,
IEEE 802.11ah, and/or a later amendment. WLAN 100 may include a
channel that may be designated as a primary channel. The bandwidth
of the primary channel may be set according to the ability of one
or more STA(s). For example, the primary channel may have a
bandwidth that may be equal to a common operating bandwidth
supported by the STAs in the BSS. As another example, the primary
channel may have a bandwidth that may support the smallest
bandwidth operating mode of the STAs in the BSS. For example, in
IEEE 802.11ah, the primary channel may be 1 MHz wide when there may
be a STA (such as a MTC type devices) that may support a 1 MHz
mode. This may occur even though other APs and/or STAs in the BSS
may support other channel bandwidth operating mode, such as a 2 MHz
mode, a 4 MHz mode, a 8 MHz mode, a 16 MHz mode, or the like. The
carrier sensing, and network allocation vector (NAV) settings, may
depend on the status of the primary channel. If the primary channel
is busy, for example, due to a STA supporting a 1 MHz operating
mode transmitting to the AP, the available frequency bands may be
considered busy even though the bands may be available.
[0045] The bandwidth available for IEEE 802.11ah may be 6 MHz to 26
MHz and may depend on the country code. For example, in the United
States the available frequency bands that may be used by IEEE
802.11ah may be from 902 MHz to 928 MHz. As another example, in
Korea it may be from 917.5 MHz to 923.5 MHz. As another example, in
Japan it may be from 916.5 MHz to 927.5 MHz.
[0046] Downlink multi-user (MU) multiple input multiple output
(MIMO) transmissions, such as downlink MU IEEE 802.11ac based
transmission, may support multiple users. For example, downlink MU
transmissions may support four users. Downlink MU-MIMO may support
multiple space-time streams (STS), such as eight STS, and may allow
a user to support multiple STS, such as four STS. Downlink MU-MIMO
may be considered, for example, where receivers for a user may be
separate from the receivers of other users and may not be able to
cooperate with each other. Transmitters for a user (for example, a
STA) may be co-located at an AP and may be able to cooperate with
each other.
[0047] In DL-MU-MIMO in IEEE 802.11ac, there may be eight streams
transmitted from a beamformer, which may be an AP, and the
space-time streams may be divided between one or more STAs. For
example, referring to FIG. 1. AP 209 may transmit eight STS and STA
may receive four STS. IEEE 802.11ac may use a linear precoding at
the transmitter, such as at AP 209. A received signal vector at a
beamformee, which may be a STA such as STA 207, may be separable
from the signals transmitted to other STAs. The linear precoder may
be designed to minimize interference between multiple STAs. For
example, for a STA u on subcarrier k, with N.sub.Rx.sub.u receive
antennas, the received signal may be written as,
y.sub.k,u=H.sub.k,uQ.sub.k,uX.sub.k+n.sub.u
[0048] where y.sub.k,u may be an N.sub.Rx.sub.u.times.1 vector
representing the received signal at STA u, H.sub.k,u, may be an
N.sub.Rx.sub.u.times.N.sub.Tx matrix representing the channel
matrix from AP to STA to STA u, Q.sub.k,u may be an
N.sub.Tx.times.N.sub.STS,u steering matrix for user u, X.sub.k may
be an N.sub.U.times.1 vector (for example, where N.sub.U may be the
total number of STS for each of the transmitted users .SIGMA..sub.u
N.sub.STS,u) representing the data transmitted to each of the users
on subcarrier k and n.sub.u may be an N.sub.Rx.sub.u.times.1 vector
representing the additive white noise (and interference) for user
u. A DL-MU-MIMO steering matrix (Q.sub.k) may be derived using
beamforming feedback, which may include the signal-to-noise ratio
(SNR) information for a subcarrier.
[0049] Signaling information may be indicated in the VHT preamble.
This may ensure that a STA may be able to decode a STS that may be
meant for it. The signaling information may include a parameter
indicating the packet may be a MU-transmission, a group-ID
indicating the beamformees or STAs that belong to a group for a
MU-MIMO STA addresses within the group, relative positions of STS,
number of STS, a modulation and coding schemes (MCS) used for a
STA, or the like.
[0050] Using this or similar signaling, the STA STS ordering may be
similar across a transmission bandwidth. For example, a STA's
ordering on sub-carrier n may match the ordering on sub-carrier m.
As a STA may be able to identify the STS intended for other
interfering STAs and may be able to estimate the channel, the STA
may use attempt to reduce the effect of interference from other
STAs.
[0051] To enable an AP, which may be a beamformer, to calculate the
preferred steering matrix, one or more STAs in an addressed group
may send feedback to the AP about the channel state measured at the
STA's location. A compressed beamforming feedback method, such as a
Given's rotation method, may be used. Upon receipt of a VHT null
data packet sounding physical (PHY) layer convergence procedure
Protocol Data Unit (PPDU), a beamformee may feed back the channel,
and an associated SNR, using a codebook phase quantization level,
such as the codebook phase quantization level defined in 8-53c of
the 802.11ac specification.
[0052] A precoding steering matrix design and signaling may be
provided. The MU-MIMO precoding used for calculation of the
steering matrix may be linear. The MU-MIMO precoding may assume may
be assumed that N.sub.T.sub.x>N.sub.Rx.sub.u. The MU-MIMO
precoding may include a zero forcing MU-MIMO, a regularized channel
inversion, a block diagonalization, a leakage based precoding, or
the like.
[0053] A zero forcing MU-MIMO may be used. N.sub.Rx.sub.u=1 (e.g.,
a receive antenna or stream) may be assumed for each of the STAs.
The steering matrix Q may be calculated as:
Q=H.sup.H(HH.sup.H).sup.-1
where H may be the composite channel from the AP to the associated
STAs. The interference between STAs may be eliminated by using a
linear precoder.
[0054] A regularized channel inversion may be used.
N.sub.Rx.sub.u=1 may be assumed for each of the STAs. The steering
matrix Q may be calculated as:
Q=H.sup.H(HH.sup.H+.alpha.1).sup.-1,.alpha.=K/.rho.
where H may be the composite channel from the AP to each of the
STAs, K may be the number of STAs and .rho. may be the operating
SNR. A level of residual interference between STAs may be
allowed.
[0055] A block diagonalization may be used. N.sub.Rx.sub.u>1 may
be assumed and each receiver may be allowed to orthogonally
coordinate its processing between antennas. A leakage based
precoding may be used. N.sub.Rx.sub.u>1 may be assumed and
interference between STAs may be allowed. A precoding may be used
at a transmitter.
[0056] NL MU-MIMO may be provided. The sum-rate capacity of a
downlink MU-MIMO system may be achieved by using dirty paper coding
(DPC). DPC may be a non-linear precoding technique. A modulo
operation may be used to reduce the complexity of implementing a
DPC in a wireless system. For example, a modulo operation may be
utilized in non-linear precoding for a MU-MIMO system.
[0057] An implementation of non-linear DPC may result in a QAM
symbol that may be transmitted outside constellation boundaries,
which may increase the overall transmit power of the transmitted
signal. A modulo operation may be used at a transmitter and at a
receivers to map a resulting signal back within the boundaries of
the original constellation.
[0058] FIG. 2 illustrates an exemplary modulo operation for
quadrature phase shift keying (QPSK). As shown in FIG. 2 a
non-linear operation may result in a transmit signal outside
constellation boundaries 204, 206, 208, and/or 210. For example, at
202, a non-linear operation may have resulted in the transmit
signal being outside constellation boundary 206 and constellation
boundary 208. A modulo operation may result in a transmit signal
within constellation boundaries 204, 206, 208, and/or 210. For
example, at 212, a modulo operation may result in a transmit signal
within constellation boundaries 204, 206, 208, and/or 210.
[0059] A modulo operation may be defined for each real or imaginary
dimension of a constellation as
mod ( a , .tau. ) = a - a + .tau. 2 .tau. .tau. , .tau. = 2 ( d max
+ .DELTA. / 2 ) , ##EQU00001##
where d.sub.max may be the distance from the origin to the farthest
constellation point, based on the modulation scheme used, and
.DELTA. may be the maximum distance between two constellation
points.
[0060] FIG. 3 illustrates an exemplary non-linear MU-MIMO
transmitter and receiver. MU-MIMO Transmitter 312 may include a
number of modules that may be used to transmit a signal. For
example, MU-MIMO Transmitter 312 may include channel coding and
modulation 302, non-linear precoding 310, and/or single
carrier/ODFM processing 308. Non-linear precoding 310 may include
non-linear operation 304 and/or modulo operation 306.
[0061] Receiver 314 may include a number of modules that may be
used to receive a signal. For example, receiver 314 may include
single carrier/ODFM processing 318, equalization 320, modulo
operation 322, and/or symbol demapping and decoding. Receiver 316
may include a number of modules that may be used to receive a
signal. For example, receiver 316 may include single carrier/ODFM
processing 318, equalization 320, modulo operation 330, and/or
symbol demapping and decoding 332.
[0062] A number of non-linear MU-MIMO schemes may be used and may
include ordered, or unordered, zero forcing dirty paper coding
(ZF-DPC) with Tomlinson-Harashima precoding (THP); ordered or
un-ordered minimum mean square error DPC (MMSE-DPC) with THP;
vector perturbation using sphere encoding; linear lattice encoder
using lentra-lentra-lovasz (LLL) decomposition, or the like.
[0063] Ordered, or unordered, Zero Forcing Dirty Paper Coding
(ZF-DPC) with Tomlinson-Harashima Precoding (THP) may be used as a
non-linear MU-MIMO scheme. In ordered or unordered ZF-DPC with THP,
interference may be pre-subtracted at the transmitter for a STA,
such that less error precoding errors may be minimized at the STA.
For example, interference pre-cancellation may occur.
Pre-subtraction may be performed in a zero forcing manner (e.g., by
forcing no crosstalk between beamformees). Scalar THP may be
performed to ensure that a transmitted signal may satisfy the
transmit power requests of a system. The signal for a user may be
designed individually and independently of a signal for another
user. The pre-subtraction may be ordered to improve performance.
The channel may be decomposed into a lower triangular and a matrix
using, for example, QR decomposition, LU decomposition, and/or
Cholesky decomposition. The inverse of the matrix may be used to
linearly pre-multiply the channel. The effective channel may be a
triangular matrix, and the input signal may be non-linearly
pre-distorted, or pre-subtracted, so that the diagonal elements of
the effective channel may be seen by each receiver.
[0064] Ordered or un-ordered MMSE-DPC with THP may be used as a
non-linear MU-MIMO scheme. Ordered or un-ordered MMSE-DPC with THP
may be similar to the ZF-DPC, but pre-subtraction may be done to
minimize the mean square error between the transmitted signal and
desired signal as opposed to minimizing cross-talk
interference.
[0065] Vector perturbation may be used as a non-linear MU-MIMO
scheme. Vector perturbation using sphere encoding may pre-subtract
the interference so that an error may not be seen at a receiver.
The signal for a user may be designed with another user. The
transmitter may perform a regularized channel inverse and may add
an integer vector offset to a transmitted signal. The vector
perturbation to the transmitted signal may reduce the transmitted
power. A sphere encoder may be used to solve lattice closest
problem at transmitter.
[0066] Linear lattice encoder using lentra-lentra-lovasz (LLL)
decomposition may be used as a non-linear MU-MIMO scheme. Linear
lattice encoder using LLL decomposition may be similar to vector
perturbation with sphere encoding. LLL decomposition may solve a
lattice closest problem by using an LLL algorithm to create a
reduced basis with orthogonal columns. A transmitter that may
implement linear lattice encoder using LLL decomposition may be
less complex than a transmitter that may implement vector
perturbation.
[0067] QR decomposition based MU-MIMO precoding with THP QR
multiuser multiple input multiple output (QR-MU-MIMO) may be
disclosed. QR-MU-MIMO may be applied to a WLAN.
[0068] NL MU-MIMO may be used to provide performance improvements
over linear MU-MIMO in WLAN. To use NL MU-MIMO in a WLAN system,
non-linear precoding may be used at an AP. While implementing the
NL MU-MIMO, legacy specifications may be retained.
[0069] FIG. 4 illustrates an exemplary average per user bit-error
rate (BER) performance with no user ordering. When QR NL-MU-MIMO is
used, ordering of the user at the transmitter (e.g., AP) side may
impact system performance. FIG. 4 may illustrate an average per
user BER performance when no particular user ordering may be used.
The performance of one or more users may be different. A user with
low performance may become a bottleneck for the system performance.
In some scenarios, a user performance imbalance may be desirable.
In other scenarios, a user performance balance may be preferred.
Methods may be used to address user ordering for QR NL-MU-MIMO to
address system performance, such as the balance of per-user
performance relative to other users.
[0070] FIG. 5 illustrates an exemplary QPSK constellation. FIG. 5
illustrates a demapper for QPSK modulation, in which a received
signal may fall outside a constellation boundary that may be
dictated by a modulo operation. For example, a non-linear operation
may result in a transmit signal outside constellation boundaries
504, 506, 508, and/or 510. At 502, a non-linear operation may have
resulted in the transmit signal being outside constellation
boundary 506 and constellation boundary 508. A modulo operation may
result in a transmit signal within constellation boundaries 504,
506, 508, and/or 510. For example, at 512, a modulo operation may
result in a transmit signal within constellation boundaries 504,
506, 508, and/or 510.
[0071] If no modulo operation occurs, a binary 0 may be detected
for the first bit (e.g., the I-branch), and its log likelihood
ratio (LLR) may be positive with a large absolute value. If modulo
operation does occur, the received signal at 512 may be flipped
inside the constellation boundaries, a binary 1 may be detected for
the first bit, and its soft LLR may be negative with a large
absolute value. The demapper may become ineffective when the modulo
operation may be present and an extended demapper may be used.
[0072] FIG. 6 illustrates an exemplary extended demapper for QPSK
constellation. As shown in FIG. 6, an extended demapper may include
a number of constellation boundaries, such as 602, 604, 606, and/or
608. The constellation boundaries may be created by a modulo
operation. Constellation points, such as constellation points 610
and 614 may be extended outside the constellation boundaries. Under
the modulo operation each of the numbered dot with may translate to
the same numbered dot inside the dot and dashed enclosed boundary.
For example, constellation point 610, which may have a binary value
of 10, may be extended at 612. As another example, constellation
point 614, which may have a binary value of 00, may be extended at
616.
[0073] When a modulo operation occurs, the received signal at 618
may be compared with an extended constellation point, such as
extended constellation point 612. A constellation point may be
cloned due to constellation expansion. For example, constellation
point 610 may be extended at 612. A binary 1 may be detected, and
its soft LLR may be negative. The LLR may have a small absolute
value, which may be due to the extended constellation. The extended
demapper may be used when a modulo operation may be requested at
the receiver side. When a demapper is used, a soft bit LLR may be
derived for subsequent processing in a receiver.
[0074] Downlink signaling and procedures may be provided. When
QR-MU-MIMO QRMU may be used at a transmitter, a user may feed its
own channel estimate back to the AP. The AP may collect the channel
estimate, may perform QR decomposition, and may perform precoding
operations. At the receiver side, a user (e.g., the receiver) may
obtain a scalar G to perform proper modulo operation/demapper
operation.
[0075] For user i, the scalar G_i may depend on user i's channel
and may depend on the channel of other users. The scalars may be
subcarrier dependent. A scalar G may be signaled to a user that may
use the scalar G.
[0076] QR decomposition based downlink NL MU-MIMO for application
to WLAN (QR-MU-MIMO) may be provided. This may be done, for
example, address user ordering, extend demapping, or the like.
[0077] FIG. 7 illustrates an exemplary block diagram of QR based NL
MU-MIMO. A transmitter may include a modulo module at 706, a Q
matrix at 704, and/or a feedback filter F at 708. At 702, the MIMO
channel between a transmitter and a receiver maybe QR decomposed
as:
H'=QRH=R'Q'=LQ'
where A' may be the Hermitian of the matrix A and L may be a lower
triangular matrix and Q may be a unitary matrix at 704. For a
subcarrier,
y = HX + n = LQ ' QX + n = LX + n ##EQU00002## L = [ l 11 0 0 0 l
12 l 22 0 0 l 13 l 23 l 33 0 l 14 l 24 l 34 l 44 ]
##EQU00002.2##
where l.sub.ij may be the ith column and jth row of the matrix L,
where L may be a lower triangular matrix. For a subcarrier, the
first user may transmit signals without interference. The
subsequent users, to whom the signals may be transmitted to, may
pre-subtract the cross-interference from users to whom the signals
were transmitted to earlier. The channel seen by a user i may be
l.sub.ii, the crosstalk or interference to the user may be
l.sub.ij. The pre-subtraction process may reduce the effect of the
cross-talk at the transmitter, such that the desired signal on the
channel may be received by the intended user.
[0078] For example, in a two user MU-MIMO system, with the desired
information S, the transmitted information X and received signal Y,
the matrix L may be given as:
L = [ l 11 0 l 12 l 22 ] ; [ x 1 x 2 ] = [ s 1 - l 12 l 22 s ^ 1 +
s 2 ] ; Y = [ l 11 s 1 l 22 s 2 ] ##EQU00003##
[0079] A receiver may operate as if it may be the only receiver in
the channel. The relationship between the channel l.sub.ii, and the
cross-talk channels l.sub.ij may depend on the orthogonality of the
channels to each of the users. The more orthogonal the channels may
be, the less cross-talk there may be between the users. For
example, if STA i and STA j may be orthogonal, then l.sub.ij=0. If
STA i and STA j may be aligned, l.sub.ii=l.sub.ij and l.sub.jj=0.
STA i and STA j may be inseparable. A STA selector or scheduler may
select users that may be orthogonal (e.g., similar to the selection
criterion for the linear zero forcing receiver).
[0080] FIG. 8 illustrates an exemplary transmitter block diagram
for transmitting a data field of a NL-MU-MIMO procedure protocol
data unit (PPDU). Transmitter block 800 may include N_STS_total
transmit chains 872, transmitted associated functions 842, and
N_Tx_transmit chains 874.
[0081] N_STS_total transmit chains 872 may include a transmit chain
for a user, such as user 802, user 804, and user 806. A transmit
chain for user 802 may include PHY padding 808, scrambler 810,
encoder 812, interleaver 814, and/or constellation mapper 816. A
transmit chain for user 804 may include PHY padding 818, scrambler
820, encoder 822, interleaver 824, constellation mapper 826, and/or
Cyclic Shift Diversity (CSD (cyclic shift delay)) per STS 828. A
transmit chain for user 806 may include PHY padding 830, scrambler
832, encoder 834, interleaver 836, constellation mapper 838, and/or
CSD per STS 840.
[0082] Interference cancellation block 842 may include a number of
modules that may be used for NL-MU-MIMO. For example, 842 may
include user ordering 844, feedback filter coefficients 848,
pre-subtract interference 846, pre-subtract interference 850,
modulo 852, and/or modulo 854.
[0083] N_Tx_transmit chains 874 may include a transmit chain for a
user, such as user 802, user 804, and user 806. A transmit chain
may include triangularizing filter 856, which may be a Q' filter,
an inverse (U) filter, an inverse (C) filter, or the like. A
transmit chain may include spatial mapping 858. A transmit chain
may include an IDFT module, such as 872, 874, and 876; an insert GI
and window module, such as 874, 868, and 860; and an analog and RF
module, such as 876, 870, and 864.
[0084] FIG. 9 illustrates an exemplary receiver block for
transmitting a data field of a NL-MU-MIMO PPDU. Receiver 900 may
include a number of modules that may be used for NL-MU-MIMO. For
example, receiver 900 may include analog and RF 902,
serial-to-parallel 904, GI removal 906, FFT 908, equalizer 910,
modulo 912, demapper 914, de-interleaver 916, parallel-to-serial
918, decoder 920, descrambler 922, and the like.
[0085] NL-MU-MIMO may be used in WLAN systems. FIG. 10 illustrates
an exemplary NL-MU-MIMO in a wireless local area network (WLAN). As
shown in FIG. 10, AP 1002 may send out a null data packet
announcement (NDPA) to announce the sending of an NDP packet to
arrive at 1010. The AP may send out the NDP to enable accurate
channel estimation at a receiver.
[0086] STA 1004 may estimate its channel and may send back channel
feedback at feedback 1014. STA 1006 may estimate its channel and
may send back channel feedback at 1016.
[0087] AP 1002 may collect channel estimates from one or more users
and may perform QR-based signal processing at 1018. For example, AP
1002 may receive feedback from STA 1004 and/or feedback from STA
1006. AP 1002 may compute the feed-forward filter Q, the feedback
filter F, and/or the diagonal loadings G.
[0088] At 1020, AP 1002 may signal the QR information to a STA. For
example, AP 1002 may signal diagonal loading values and a modulo
choice, which may be MCS dependent. This information may include,
for example, codepoints, which may be included in the SIG field;
information transmitted in a side channel such as a primary
channel; information that may be in a pilot signal; and the
like.
[0089] At 1022, AP 1002 may send a MU-transmission. AP 1002 may use
the feed-forward filter Q and feedback filter F to filter the
multi-user data streams.
[0090] A receiver (e.g., a STA) may apply the diagonal loading and
modulo based on AP signaling. The receiver may separate
demapping/decoding. Extended de-mapper may be used to account for
the effect of modulo operation. A STA may send a separate ACK to
the AP to acknowledge successful receipt of the transmission. For
example, at 1024 STA 1004 may send an ACK to AP 1002 and at 1026
STA 1006 may send an ACK to AP 1002. QR-MU-MIMO may rely on
implicit feedback, where a NDP or feedback packet may not be
requested.
[0091] User ordering for NL-MU-MIMO may be provided and a number of
user ordering strategies may be utilized. User ordering for
NL-MU-MIMO may be applied to systems having any number of transmit
antennas, any number of receivers, or any combination thereof. For
example, the methods for user ordering described herein may be
applied to a system that may have a different number of antennas
per receiver.
[0092] For QRMU modulation, the transmitter (e.g., the AP) may
group multiple receivers (e.g., the STAs) for joint downlink
transmissions. For example, an AP may have four transmit antennas
and four receiver. A receivers may have a receive antenna, e.g. the
four receives may each have one receive antenna. For example, h1
may be the channel vector for receiver 1, h2 may be the channel
vector for receiver 2, h3 may be the channel vector for receiver 3,
and h4 may be the channel vector for receiver 4. A channel vector
may be a row vector, e.g., of size 1.times.4.
[0093] The AP may receive channel feedback of h1 from receiver 1,
h2 from receiver 2, h3 from receiver 3, and/or h4 from receiver 4.
The AP may have flexibility in grouping multiple users and in
selecting the order in which the users may be processed within the
group.
[0094] The AP may order the user as (user 1, user 2, user 3, and
user 4) such that the AP may form the channel matrix
H 1 = [ h 1 h 2 h 3 h 4 ] ##EQU00004##
for processing. H1 may be a 4.times.4 matrix. QR decomposition of
this channel matrix may be given by:
Q.sub.1.times.R.sub.1=H.sub.1', where Q1 may be a unitary 4.times.4
matrix, and
R 1 = [ r 11 r 12 r 13 r 14 0 r 22 r 23 r 24 0 0 r 33 r 34 0 0 0 r
44 ] ##EQU00005##
may be a upper-triangular with real diagonal values and complex
off-diagonal values. Pre-cancellation of other user signals based
on R1 may be carried out and may be followed by unitary precoding
of the pre-cancelled signals based on Q1. For such a user ordering,
the error rate performance for a user may be illustrated in FIG.
11.
[0095] FIG. 11 illustrates an exemplary average per user BER
performance with fixed user ordering. In FIG. 11, line 1102 may be
for user 1, 1104 may be for user 2, 1106 may be for user 3, and
1108 may be for user 4. As shown at 1102, user 1 may be a first
place and may get better performance than other users, while at
1108 user 4 may be in a last place may have lower performance. The
worst user (e.g., user 4 here) may become a performance
bottleneck.
[0096] The AP may order the user in an arbitrary way (e.g. user 3,
user 2, user 1, and user 4) such that AP may form the channel
matrix
H 2 = [ h 3 h 2 h 1 h 4 ] ##EQU00006##
for further processing. The matrix H2 may be a 4.times.4 matrix. QR
decomposition of this channel matrix may be given by:
Q.sub.2R.sub.2=H'.sub.2, where Q2 is a unitary 4.times.4 matrix,
and
R 2 = [ t 11 t 12 t 13 t 14 0 t 22 t 23 t 24 0 0 t 33 t 34 0 0 0 t
44 ] ##EQU00007##
may be upper-triangular with real diagonal values and complex
off-diagonal values. Pre-cancellation of other user signals based
on R2 may be carried out, followed by unitary precoding of the
pre-cancelled signals based on Q2.
[0097] Each user's performance may depend (e.g., solely) on the
diagonal entries. If the ordering of user 1, user 2, user 3, user 4
may be used, user 1's performance may depend on the diagonal entry
of r.sub.11, user 2's performance may depend on the diagonal entry
of r.sub.22, user 3's performance may depend on the diagonal entry
of r.sub.33, and user 4's performance may depend on the diagonal
entry of r.sub.44. Due to channel estimation error and/or
quantization errors, the performance of each user may depend on
other factors.
[0098] If the ordering of user 3, user 2, user 1, user 4 may be
used, user 3's performance may depend on the diagonal entry of
t.sub.11, user 2's performance may depend on the diagonal entry of
t.sub.22, user 1's performance may depend on the diagonal entry of
t.sub.11, and user 4's performance may depend on the diagonal entry
of t.sub.44.
[0099] The four users may experience different error rate
performance. The AP may find an ordering such that the
minimum-SNR-user's performance is maximized or the
maximum-SNR-user's performance is minimized, which may have the
same purpose of having balanced performance across multiple users.
For example,
H = [ h 1 h 2 h 3 h 4 ] ##EQU00008##
where H may be an arbitrary ordering of the channel vectors. To
determine an ordering of channel vector number a channel
correlation matrix may be computed as: A=H*H'. An matrix inverse
inv(A) may be calculated. A may be a Hermitian matrix and with
probability 1, and A may be invertible. Diagonal entries of inv(A)
may be sorted in (e.g., a descending order). The ordering output of
inv(A) may be used to sort users for final QRMU operation. For
example, in Matlab mathematics, this may be expressed as:
sort(diag(inv(H*H')),`descend`)
[0100] One matrix inverse may be needed to find the max-min
ordering. A numerical performance evaluation may show that the
max-min-SNR ordering may be close to an optimal ordering. The QRMU
with max-min-SNR ordering may outperform the QRMU scheme with no
ordering.
[0101] Min-row-norm ordering may be provided. For min-row-norm
ordering, ordering by sorting the users based on their row norms
may be used as a proxy for sorting the users based on their
effective channels after QR decomposition. This may approximate
optimal ordering. Sorting based on the diagonal R elements may
require a search, a determination of possible orders, or an
iterative operation. The norm of the rows of the effective channel
created by aggregating the channels to a user may be computed and
sorted in an ascending order. This may, for example, provide a low
complexity ordering of the channel vectors.
[0102] FIG. 12(a) illustrates an aggregated channel from an AP to
four STAs. FIG. 12(b) illustrates the effective channels with no
ordering. The effective channels may be the channels at 1202, 1204,
1206, and 1208. FIG. 12(c) illustrates the effective channels with
min-norm ordering. The effective channels may be the channels at
1210, 1212, 1214, and 1216. FIG. 12(d) illustrates the effective
channels with max-norm ordering. The effective channels may be the
channels at 1218, 1220, 1222, and 1224.
[0103] As shown in FIGS. 12(a)-12(d), with min-norm ordering, the
effective channel of a user that may be experiencing decreased
performance (e.g., minimal of the absolute values of the diagonal
entries) may be improved with min-row-norm ordering. The effective
channel of that user may worsen with max-row-norm ordering. The
min-row-norm ordering may achieve performance that may be better
than no ordering, but not be as good as max-min-SNR ordering.
[0104] FIG. 13 illustrates an exemplary performance various
schemes. 1302 may use a NLP MU-MIMO with max-min SNR ordering. 1304
may use a NLP MU-MIMO with min-row-norm ordering. 1306 may use a
NLP MU-MIMO without ordering. 1308 may use a zero forcing (ZF)
precoding scheme.
[0105] To perform the min-row-norm ordering, the norms of the
individual rows of an effective channel H may be calculated. For
example, given an effective channel
H = [ h 1 h 2 h 3 h 4 ] ##EQU00009##
the norms of the individual rows of H, |h1|, . . . , |hn| may be
computed. The row norm values of H may be sorted in an ascending
order. The rows of the channel may be re-ordered to form a new
effective channel based on the row order. For example, if the
sorted order is 2, 3, 1, and 4 effective channels may be given
as:
H -- new = [ h 2 h 3 h 1 h 4 ] ##EQU00010##
Non-linear QR precoding may be performed on the new effective
channel. The ordering output from the non-linear QR precoding may
be used to sort users in a QRMU operation.
[0106] Ordering based on a received SNR for a ZF precoding may be
provided. A user ordering for a non-linear precoding may be based
on channels at a receiver. The received SNR using a zero forcing
(ZF) precoder may be an indicator of how the users may be ordered
for non-linear precoding. A channel pseudo-inverse may be computed
by: Q=H.sup.H(HH.sup.H).sup.-1. Each column of Q may be normalized
to form QN. QN may be the ZF precoder normalized such that each
user may transmit the same power. The received power vector may be:
P=|diag(H*QN)|. The entries of P may be sorted in ascending order.
This may be the order in which the channel matrix may be ordered
prior to QR decomposition.
[0107] Ordering across multiple frequency tones may be provided.
For example, a number of ordering strategies may be used for a
subcarrier or a flat fading channel. As another example, ordering
strategies for multi-carrier modulation and its variants may be
provided.
[0108] FIG. 14 illustrates an exemplary independent user ordering
for QR-MU-MIMO, which may be used in an OFDM system. When QRMU may
be applied in a multi-carrier communication system, such as an OFDM
system, a determination may be made as to whether user ordering may
be performed. It may also be determined when user ordering may be
performed. As different users may experience different channels in
a frequency domain, the optimal ordering for a subcarrier may be
different. And uniform ordering may not provide a performance
benefit for one or more users.
[0109] As shown in FIG. 14, independent user ordering may be used
to enable QRMU across multiple orthogonal sub-carriers, such as
subcarrier 1432, 1434, and 1436. For example, for each subcarrier
k, the AP may perform one or more of the following. The AP may find
a good ordering for a subcarrier k. For example, the AP may
determine a data ordering at 1404, 1412, and/or 1420. To find an
ordering, the AP may stack multiple row channel vectors from
multiple users in an arbitrary order to obtain an initial channel
matrix H(k). For example, the AP may obtain an channel estimate
H(k) at 1402, 1410, and/or 1418. The AP may compute
A(k)=H(k)*H(k)'. The AP may find an matrix inverse inv(A(k)). The
AP may sort the diagonal entries of inv(A(k)), e.g., in a
descending order. The AP may reorder data symbols that may be
transmitted on subcarrier k. The data symbols may be reordered
using the ordering indices given by inv(A(k)), e.g., in a
descending order. The AP may obtain a reordered channel matrix
Hr(k) by recording rows of the channel matrix H(k). The AP may
compute a QR decomposition of Hr(k), and may obtain Q(k) and/or
R(k). The AP may perform pre-cancellation of other user signals
based on the upper-triangular matrix R(k). The AP may perform
unitary precoding of other user signals based on an unitary
precoding matrix Q(k). For example, the AP may perform precoding at
1408, 1416, and/or 1424. The AP may perform inverse FFT (IFFT)
operation on precoded signals that may be sent on a transmit
antenna. For example, the AP may perform an IFFT operation at 1426,
1428, and/or 1430. The inverse FFT output may be upconverted,
filtered, and/or sent from a transmit antenna. Similar user
ordering may be carried out for other variants of multi-carrier
modulations.
[0110] FIG. 15 illustrates an exemplary independent user ordering
for QR-MU-MIMO in a single-carrier with frequency domain
equalization (SC-FDE), where parallel to serial conversion with
cyclic prefix insertion (P2S/CP) may be used. As shown in FIG. 15,
independent user ordering may be used to enable QRMU across
multiple orthogonal sub-carriers, such as subcarrier 1532, 1534,
and 1536. For example, for each subcarrier k, the AP may perform
one or more of the following. The AP may find a good ordering for a
subcarrier k. For example, the AP may determine a data ordering at
1504, 1512, and/or 1520. To find an ordering, the AP may stack
multiple row channel vectors from multiple users in an arbitrary
order to obtain an initial channel matrix H(k). For example, the AP
may obtain an channel estimate H(k) at 1502, 1510, and/or 1518. The
AP may compute A(k)=H(k)*H(k)'. The AP may find an matrix inverse
inv(A(k)). The AP may sort the diagonal entries of inv(A(k)), e.g.,
in a descending order. The AP may reorder data symbols that may be
transmitted on subcarrier k. The data symbols may be reordered
using the ordering indices given by inv(A(k)), e.g., in a
descending order. The AP may obtain a reordered channel matrix
Hr(k) by recording rows of the channel matrix H(k). The AP may
compute a QR decomposition of Hr(k), and may obtain Q(k) and/or
R(k). The AP may perform pre-cancellation of other user signals
based on the upper-triangular matrix R(k). The AP may perform
unitary precoding of other user signals based on an unitary
precoding matrix Q(k). For example, the AP may perform precoding at
1508, 1516, and/or 1524. The AP may perform a P2S/CP operation on
precoded signals that may be sent on a transmit antenna. For
example, the AP may perform a P2S/CP operation at 1526, 1528,
and/or 1530. The P2S/CP operation output may be upconverted,
filtered, and/or sent from a transmit antenna.
[0111] Uniform user ordering may be provided. Independent ordering
may be used to improve the performance of a user. In some cases,
the AP may not improve the performance of each of the users. The
ordering strategy may consider MAC layer requirements, such as the
quality of service (QoS) requirements, (e.g., delay, latency
requirements), the packet size requirements, fairness requirements,
and the like. The AP may enhance the performance of a user or a
group of users. For example, one user may have more data to
transmit and the AP may choose to provide this user with better
performance. The AP may the user as a first user as the performance
of first user may be better than the rest of users. Uniform
ordering may be based on a criterion that may be averaged over the
entire frequency band, e.g., users may have the same ordering for
the sub-carriers.
[0112] To provide a uniform ordering one or more of the following
may be performed. For each sub-carrier k, an AP may calculate a
metric according to pre-selected criterion. For example, the AP may
compute A(k)=H(k)*H(k)', find the matrix inverse inv(A(k)), and
define the per sub-carrier metric as C(k)=diag(inv(A(k))). The AP
may compute A(k)=H(k)*H(k)', and define the per sub-carrier metric
as C(k)=diag(A(k)). The AP may average the metric over each of the
sub-carriers such that C=mean(C(k)). The AP may sort C in a
descending or ascending order depending on the definition of the
per sub-carrier metric C(k). The AP may order user using the
sorting index obtained while sorting C.
[0113] Extended demapping may be provided for 16QAM and/or 64 QAM.
When extended demapper may be used for 16QAM and 64QAM, a soft bit
LLR may be calculated for a received symbol. This may be done, for
example, by counting the probability of receiving the received
symbol given the constellation points in a constellation. The
computation complexity may increase with the number of bits (e.g.,
4 bit for 16QAM and 6 bit for 64QAM). The complexity may increase
for a demapper, and for an extended demapper. For an extended
demapper, a constellation point may be more than a clone due to the
constellation extension. The max-log-MAP approximation may be
utilized in calculating the soft bit LLRs, for example, when
extended demapper may be used for 16QAM and 64QAM. The max-log-MAP
may be used to reduce demapping complexity.
[0114] FIG. 16 illustrates exemplary max-log-MAP extended
demapping. As shown in FIG. 16, demapper 1608 may include a number
of modules such as equalizer 1602, modulus 1604, and regular
demapper max-log-MAP 1606. Extended demapper 1618 may include a
number of modules such as equalizer 1610, extended demapper
max-log-MP 1612, signal constellation mapping 1614, and decision
symbol set update 1616.
[0115] FIG. 17 illustrates an exemplary decision symbol sets for
the regular signal constellation. In case of extended demapping for
16QAM modulations, the soft bit decisions may be given by:
LLR ( b l , k ) = log .SIGMA. .alpha. .di-elect cons. S l , k 1 p (
r [ i ] | a [ i ] = .alpha. ) .SIGMA. .alpha. .di-elect cons. S l ,
k 0 p ( r [ i ] | a [ i ] = .alpha. ) ##EQU00011##
where b.sub.l,k may represent the kth bit in I-branch, r[i] may
represent the received signal at i, a[i] may represent the
transmitted QAM symbol at, S.sub.l,k.sup.1 such as at 1702 and 1704
may be a set of transmitted symbols that may have a 1 in the kth
bit of I-branch, while S.sub.i,k.sup.0 such as at 1706, 1708, and
1710 may be a set of symbols that have a 0 in the kth bit of
I-branch. The same may apply to bit b.sub.Q,k, which may be the kth
bit in Q-branch.
[0116] The max-log-MAP approximation may be used, leading to
LLR ( b l , k ) .apprxeq. log max .alpha. .di-elect cons. S l , k 1
p ( r [ i ] | a [ i ] = .alpha. ) max a .di-elect cons. S l , k 0 p
( r [ i ] | a [ i ] = .alpha. ) ##EQU00012##
[0117] With y[i] being the equalized signal (e.g., zero-forcing
equalization), the soft bits may be given by:
LLR ( b l , k ) = | G ch ( i ) | 2 4 { min .alpha. .di-elect cons.
S l , k 0 | y [ i ] - .alpha. | 2 - min .alpha. .di-elect cons. S l
, k 1 | y [ i ] - .alpha. | 2 } ##EQU00013##
[0118] The performance metric D.sub.l,k may be:
D l , k = min .alpha. .di-elect cons. S l , k 0 | y [ i ] - .alpha.
| 2 - min .alpha. .di-elect cons. S l , k 1 | y [ i ] - .alpha. | 2
##EQU00014##
the soft bit decision task may be performed by evaluating
{D.sub.l,k} for various bit index k on I/Q branch. The symbol sets
S.sub.l,k.sup.0 and S.sub.l,k.sup.1 may dictate the end result of
{D.sub.l,k}.
[0119] For 16QAM constellations, for example, the symbol sets and
the performance metrics {D.sub.l,k} may be fixed. For extended
demapper, the signal constellation may move with the received
signal. For example, the decision symbol sets
{S.sub.l,k.sup.0,S.sub.l,k.sup.1} may move with the received
signal. The performance metric may be modified accordingly.
[0120] FIG. 18 illustrates an extended demapping signal
constellation. As illustrated in FIG. 18, the square at 1802 may
represent a 16QAM signal constellation and may have a symbol sets
{S.sub.l,k.sup.0,S.sub.l,k.sup.1}, which may be further illustrated
in FIG. 17.
[0121] Referring again to FIG. 18, a received signal may be within
the square at 1804 before a modulo operation and the constellation
at 1804 may used. The decision symbol sets
{S.sub.l,k.sup.0,S.sub.l,k.sup.1} may change. For example, the
decision symbol may be changed from the decision symbol sets in
FIG. 17 to FIG. 19. FIG. 19 illustrates an exemplary decision
symbol sets of the shifted/wrapped signal constellation. Although a
difference may be seen in the I-branch, the decision symbol set
{S.sub.Q,k.sup.0,S.sub.Q,k.sup.1} may also be different.
Additionally, the I-branch and Q-branch may be orthogonal and may
be treated independently. Although the methods herein may be
discussed in terms of the I-branch, the methods herein may be
applied to the Q-branch.
[0122] Referring again to FIG. 18, as the decision symbol sets
{S.sub.l,k.sup.0,S.sub.l,k.sup.1} change, the expressions of the
max-log-MAP soft bit LLRs may change. For example, if y may be the
equalized signal on the I and/or Q branch with scaling, the
demapping may include one or more of the following. A signal
constellation mapping that may be used to calculate max-log-MAP
soft bit LLRs may be decided. The signal constellation mapping may
be a circularly wrapped and shifted version of an original
constellation mapping. The signal constellation mapping may depend
on the value of an equalized signal.
[0123] Depending on the value of the equalized signal y, an
offseted signal z may be formed (e.g., properly) as: [0124] z=y
when -1<=y<=1, [0125] z=y-2 when 1<=y<=3, [0126] z=y-4
when 3<=y<=5, [0127] z=y-6 when 5<=y<=7, [0128] z=y+8
when -9<=y<=-7 [0129] z=y+6 when -7<=y<=-5, [0130]
z=y+4 when -5<=y<=-3, [0131] z=y+2 when -3<=y<=-1,
[0132] . . .
[0133] The offseted signal z may bring the equalized signal y to
the origin. The center of the constellation labeling may be no
longer the same as the constellation labeling in the original
constellation. For example, center of 1804 may not be the center of
1802. The max-log-MAP bit decision may be performed using the
offseted signal z and the signal constellation. Example soft bit
LLRs may be illustrated in Table 1. For example, Table 1 may
illustrate exemplary 16 QAM max-log-MAP soft bit LLRs.
[0134] As shown in Table 1, D.sub.1.sup.A and D.sub.2.sup.A may be
the max-log-MAP soft bit LLRs for the first and second bit with the
original signal constellation labeling. With different equalized
signals (and different offsets), the soft bit LLRs may be
sign-flipped and position-flipped.
TABLE-US-00001 TABLE 1 Region 1 Region 2 Region 3 Region 4
Equalized -1 <= y <= 1 1 <= y <= 3 3 <= y <= 5 5
<= y <= 7 signal Offseted z = y z = y - 2 z = y - 4 z = y - 6
signal Equalized -9 <= y <= -7 -7 <= y <= -5 -5 <= y
<= -3 -3 <= y <= -1 signal Offseted z = y + 8 z = y + 6 z
= y + 4 z = y + 2 signal D1 D.sub.1.sup.A = z D2 -[z] D1 -[z] D2 z
D2 D.sub.2.sup.A = -|z| + 2 D1 -|z| + 2 D2 -[-|z| + 2] D1 -[-|z| +
2] 1.sup.st bit LLR D.sub.1.sup.A D.sub.2.sup.A -D.sub.1.sup.A
-D.sub.2.sup.A 2.sup.nd bit LLR D.sub.2.sup.A -D.sub.1.sup.A
-D.sub.2.sup.A D.sub.1.sup.A
[0135] For 16QAM extended demapper, depending on whether it is in
region 1, 2, 3, or 4, 1st bit LLR and the 2nd bit LLR of the
extended demapper may be approximated by one of the following
values: [0136] {D.sub.1.sup.A, -D.sub.1.sup.A, D.sub.2.sup.A,
-D.sub.2.sup.A}
[0137] Similar max-log-MAP soft bit LLRs may be carried out for
64QAMs. For example, depending on the value of the equalized
signal, a signal constellation mapping that may be used to
calculate max-log-MAP soft bit LLRs may be decided. The signal
constellation mapping may be a circularly shifted version of an
original constellation mapping. Depending on the value of the
equalized signal y, the offseted signal z may be formed as: [0138]
z=y when -21<=y<=2, [0139] 1, z=y-42 when 21<=y<=6,
[0140] 3, z=y-84 when 63<=y<=10, [0141] 5, z=y-126 when
105<=y<=14, [0142] 7, z=y+168 when -189<=y<=-14, [0143]
7, z=y+126 when -147<=y<=-10, [0144] z=y+8 when
-10<=y<=-6, [0145] 5, z=y+4 when -65<=y<=-3, z=y+2 when
-3<=y<=-2.
[0146] The offseted signal z may bring the equalized signal y to
center of the constellation. The max-log-MAP bit decision may be
performed using the offseted signal z and the signal constellation.
The soft bit LLRs in this case may be illustrated in Table 2, which
may illustrate exemplary 64 QAM max-log-MAP soft bit LLRs.
TABLE-US-00002 TABLE 2 Region 1 Region 2 Region 3 Region 4 -2 <=
y <= 2 2 <= y <= 6 6 <= y <= 10 10 <= y <= 14
z = y z = y - 4 z = y - 8 z = y - 12 -18 <= y <= -14 -14
<= y <= -10 -10 <= y <= -6 -6 <= y <= -2 z = y +
16 z = y + 12 z = y + 8 z = y + 4 1.sup.st bit LLR D.sub.1.sup.A
D.sub.2.sup.A -D.sub.1.sup.A -D.sub.2.sup.A 2.sup.nd bit LLR
D.sub.2.sup.A -D.sub.1.sup.A -D.sub.2.sup.A D.sub.1.sup.A 3.sup.rd
bit LLR D.sub.3.sup.A -D.sub.3.sup.A D.sub.3.sup.A
-D.sub.3.sup.A
[0147] For 64QAM extended demapper, depending on whether it is in
region 1, 2, 3, or 4, 1st bit LLR and 2nd bit LLR of the extended
demapper may be approximated by one of the following values: [0148]
{D.sub.1.sup.A, -D.sub.1.sup.A, D.sub.2.sup.A, -D.sub.2.sup.A)}
[0149] The 3rd bit LLR of the extended demapper may be approximated
by one of the following values: [0150] {D.sub.3.sup.A,
-D.sub.3.sup.A}
[0151] Downlink signaling may be provided. A receiver may have
knowledge of the scalar G (e.g., a real-valued number) to scale
and/or equalize a signal before demapping the signal. For example,
in a multi-carrier scenario, each subcarrier may have a scalar G.
The scalar G may differ from one user to another. Downlink
signaling may be implicit or explicit.
[0152] FIG. 20 illustrates an exemplary transmitter diagram for
matched filtering implicit signaling. In implicit downlink
signaling, the AP may send out a set of precoded long training
fields (LTFs) (e.g., linearly precoded LTFs). Users (e.g., STAs)
may receive the LTFs and may detect the scalar G for one or more
data frequencies in the LTF. The LTF sequence may be known by the
STAs.
[0153] LTFs may be used by the transmitter to enable channel
estimation at the receiver side. For QR-MU-MIMO, channel estimation
may not be performed. The LTFs may be used to carry downlink
signaling.
[0154] LTF may be generated at the AP. For example, precoded LTFs
may be generated by using a sequence such as a length-Nf 802.11n/ac
LTF sequence, a low peak-to-average-power ratio (PAPR) sequence,
and the like. The sequence may vary based on the system bandwidth.
For example, LTF-28-28 may be used for 20 MHz transmissions,
LTF-58, 58 may be used for 40 MHz transmissions, etc. For example,
the sequence, LTF-28,28={1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1,
1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 0, 1, -1, -1, 1, 1,
-1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1,
1, 1, -1, -1} and the sequence, LTF-58,58={1, 1, -1, -1, 1, 1, -1,
1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1,
-1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1,
-1, 1, -1, 1, 1, 1, 1, -1, -1, -1, 1, 0, 0, 0, -1, 1, 1, -1, 1, 1,
-1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1,
1, -1, 1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1,
1, 1, -1, -1, -1, -1, 1, -1, 1, 1, 1}. The sequence length, Nf may
depend on the number of data sub-carriers as part of the system
design.
[0155] Elements of the sequence may be multiplied by an Nt.times.Ns
matrix P to create a three dimensional matrix (e.g.,
space-time-frequency matrix). The LTF sequence may span the
frequency domain, and the matrix P may span the space and the time
domains. A row of the P matrix may spread the LTF sequence to one
or more layers of MU-MIMO transmission. A column of the P matrix
may spread the LTF sequence to one or more LTF symbols in the time
domain. For example, orthogonal space-time spread 2004, 2012, 2020
may be used to spread the LTF symbol 2002, 2010, and/or 2018 in the
time domain.
[0156] The dimension of this matrix P may be selected according to
the number of users in a downlink. For example, P2.times.2 may be
used for 2 users in a 2-transmit antenna setup, while P4.times.4
may be used for 3 or 4 users in a 4-transmit antenna setup.
P 2 .times. 2 = [ 1 - 1 1 1 ] ##EQU00015## P 4 .times. 4 = [ 1 - 1
1 1 1 1 - 1 1 1 1 1 - 1 - 1 1 1 1 ] ##EQU00015.2##
[0157] In the 4.times.4 example, P(1,1), P(1,2) P(1,3), P(1,4) may
be the four symbols that may be transmitted on the four layers
(e.g., at the same time). P(1,1), P(2,1) P(3,1), P(4,1) may be the
four symbols on layer 1, e.g., in time slot 1, 2, 3, and/or 4.
Other orthogonal P matrix such as a Hadamard matrix may be used.
The orthogonally spread LTF sequence may be precoded by a unitary
matrix Q. For example, output from orthogonal space-time spread
2004, 2012, and/or 2020 may be precoded by unitary precede 2006,
2014, and/or 2020. The unitary precoder may be obtained from QR
decomposition of the channel matrix on the particular sub-carrier,
and may be obtained after user ordering. The unitary precoder Q
matrix may be channel dependent. The unitary precoder Q may be
frequency dependent. IFFT output may be generated at 2008, 2016,
and/or 2022 by performing IFFT operation on the precoded LTF
sequence for each of the subcarriers.
[0158] A participating STA may estimate its own scaling parameter G
on one or more of the subcarrier. The STA may use blind detection
to estimate its scaling parameter G. For example, using a 4.times.4
(e.g., 4 transmit antennas to serve 4 users at the same time). This
may be generalized for number of antennas or number of users.
[0159] For each subcarrier, a channel H may be written as:
H'=QRH=LQ'
where L may be lower triangular, Hermitian transpose of the
upper-triangular matrix R.
[0160] The received signal (e.g., ignoring subcarrier index) may be
written as:
Y=HQPs+n=LPs+N
where may be the LTF symbol on the subcarrier and N may be additive
white Gaussian noise. In this example, the dimensions of Y, H, Q,
and P may be 4.times.4. With Y a 4.times.4 matrix
Y = [ y 11 y 12 y 13 y 14 y 21 y 22 y 23 y 24 y 31 y 32 y 33 y 34 y
41 y 42 y 43 y 44 ] ##EQU00016##
[0161] The first STA may receive y11, y12, y13 and y14 over time
slot 1, 2, 3, and 4 for a subcarrier. The second STA may receive
y21, y22, y23, y24 over time slot 1, 2, 3, and 4 for the
subcarrier. The third STA may receive y31, y32, y33 and y34 over
time slot 1, 2, 3, and 4 for the subcarrier. The fourth STA may
receive y41, y.sup.42, y43, y44 over time slot 1, 2, 3, and 4 for
the subcarrier.
[0162] The STAs may perform the same matched filtering by
multiplying the P' matrix to the received symbols
Z = YP ' = LPP ' s + NP ' = Ls + NP ' ##EQU00017## L = [ l 11 0 0 0
l 12 l 22 0 0 l 13 l 23 l 33 0 l 14 l 24 l 34 l 44 ]
##EQU00017.2##
[0163] The diagonal entries of the matrix L may be real-valued
numbers, the upper-triangular entries of L may be 0, and the
lower-triangular entries of L may be complex-valued numbers.
Because of the orthogonality of the matrix P', the noise NP' may
not be amplified as compared to the noise N. After matched
filtering on the subcarriers, the filter outputs Z may be written
as the original LTF symbol s multiplied by the lower-triangular
matrix L. Since G=Inverse(Diag(Diag(L))), the diagonal entries of
the matrix L may be estimated.
[0164] Users may not know which row of Z they may be receiving,
which may be due to independent user ordering. Such information may
be obtained by using the structure of the lower triangular matrix
L.
[0165] Each of the STAs may perform a blind detection with the
matched filter output {zi1,zi2, zi3, zi4}, where i may be the row
index to be detected on the particular subcarrier. A STA may use
matched filter output {zi1, zi2, zi3, zi4} to perform a blind
detection via hypothesis testing.
[0166] For example, a STA may be user 1 on a subcarrier if without
noise, zi1 may be real (e.g., imaginary part of zi1 is zero); zi2
may be zero (e.g., real and imaginary parts of zi2 may be zeros);
zi3 may be zero (e.g., real and imaginary parts of zi3 may be
zeros); and/or zi4 may be zero (e.g., real and imaginary parts of
zi4 may be zeros). As another example, a STA may be user 2 on this
subcarrier, without noise, zi1 may be complex (e.g., imaginary part
of zi1 may be nonzero); zi2 may be real (e.g., imaginary part of
zi2 may be zero); zi3 may be zero (e.g., real and imaginary parts
of zi3 may be zeros); and zi4 may be zero (e.g., real and imaginary
parts of zi4 may be zeros). As another example, a STA may be user 3
on the subcarrier if, without noise, zi1 may be complex (e.g.,
imaginary part of zi1 may be nonzero); zi2 may be complex (e.g.,
imaginary part of zi2 may be nonzero); zi3 may be real (e.g.,
imaginary part of zi3 may be zero); and zi4 may be zero (e.g., real
and imaginary parts of zi4 may be zeros). As another example, the
STA may be user 4 on the subcarrier if, without noise, zi1 may be
complex (e.g., imaginary part of zi1 may be nonzero); zi2 may be
complex (e.g., imaginary part of zi2 may be nonzero); zi3 may be
complex (e.g., imaginary part of zi3 may be nonzero); and zi4 may
be zero real (e.g., imaginary part of zi4 may be zero).
[0167] The STA may blindly detect the row index (e.g.,
corresponding to user ordering) on a subcarrier, for example, by
analyzing the real parts and imaginary parts of matched filter
output {zi1, zi2, zi3, zi4}.
[0168] The STA may estimate the diagonal entry of L by
incorporating the row index info (e.g., user ordering info)
obtained from blind decoding with the matched filter output. The
STA may estimate the value G by inverting the diagonal entry of the
matrix L.
[0169] The blind detection and estimation may be repeated for the
sub-carriers and for the STAs (e.g., independently). Sub-carrier
ordering may be grouped together at the AP to improve the detection
probability at the receiver.
[0170] Implicit signaling may be used to allow a STA to determine a
scalar G. LTFs may be non-linearly precoded. The STAs may estimate
its effective channel I.sub.ii (e.g., independently of the
cross-talk from each of the channels). The AP may use similar LTFs
for the users.
[0171] For example, in case of two users, for a specific
sub-carrier, the received signal (e.g., effective received signal)
for a STA may be modeled after QR-MU-MIMO precoding as:
[ y 1 y 2 ] = [ l 11 0 l 12 l 22 ] [ s 1 s 2 ] + [ n 1 n 2 ]
##EQU00018##
where y.sub.i may be the signal received at STA i and s.sub.i is
the effective pilot signal used by STA i to estimate the channel.
The effective channel, l.sub.ii may be estimated independent of the
cross talk l.sub.ij. For a LTF sequence s, s.sub.i may be set such
that the effective channel seen by STA i, may be:
y.sub.i=l.sub.iis+n.sub.i
which may enable the STA to estimate the effective channel as:
l 11 ^ = y i s ##EQU00019##
In the exemplary two user case,
y.sub.1=l.sub.11s.sub.1+n.sub.1s.sub.1=s
y 2 = l 12 s 1 + l 22 s 2 + n 2 = l 22 s s 2 = ( l 22 - l 12 ) l 22
s ##EQU00020##
[0172] For a large number of STAs, the channel may be generalized.
The vector S may be normalized to satisfy the power requirements of
the transmitter. The modulo for the duration of the LTF
transmission may be removed.
[0173] LTF signal generation and/or channel estimation may include
one or more of the following. The precoded LTFs may be generated by
using a length-Nf 802.11n/ac LTF sequence a low
peak-to-average-power ratio (PAPR) sequence, or the like. The
sequence may vary based on the system bandwidth. For example,
LTF-28-28 may be used for 20 MHz transmissions, LTF-58, 58 may be
used for 40 MHz transmissions, etc. For example, the sequence,
LTF-28,28={1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1,
-1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 0, 1, -1, -1, 1, 1, -1, 1, -1,
1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1, 1, 1, 1, 1, -1,
-1} and the sequence, LTF-58,58={1, 1, -1, -1, 1, 1, -1, 1, -1, 1,
1, 1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1,
1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, -1, 1, -1, 1, -1,
1, 1, 1, 1, -1, -1, -1, 1, 0, 0, 0, -1, 1, 1, -1, 1, 1, -1, -1, 1,
1, -1, 1, -1, 1, 1, 1, 1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1,
1, 1, 1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1,
-1, 1, -1, 1, -1, 1, 1, 1, 1}. The sequence length, Nf may depend
on the number of data sub-carriers as part of the system
design.
[0174] The NL-MU-MIMO preceding order may be decided. For STAs 2, .
. . , n, for example, the LTF may be pre-distorted, as shown in the
equations, to enable the STAs to estimate their effective channel
free of crosstalk. The normalization factor may be calculated to
satisfy transmit power requirements. A modified SIG-A may be sent
with a normalization factor. A normalization factor may be sent for
each of the sub-carriers. A normalization factor may be sent for
each sub-carrier, which may incur overhead that may be a fraction
(e.g., 1/N) of the overhead to send the data. Each STA may estimate
its effective channel over the transmitted bandwidth. The LTF
signal generation and channel estimation technique may be
generalized where N, the number of STAs, may be greater than
two.
[0175] Differential signaling may be used, e.g., instead of using
blind detection for the determination of one or more parameters.
FIG. 21 illustrates an exemplary differential signaling. As shown
at 2102, an additional LTF may be used as a reference LTF. With the
extra overhead of 1 LTF, a user may estimate G for each
sub-carrier.
[0176] Generation of LTF may occur at the AP. A non-precoded LTF
may be sent in the first OFDM symbol, which may be used as a
reference LTF. The reference LTF may be followed by LTFs multiplied
by Gu (1.times.nSC) for each user u. The LTF symbols may be
multiplied by the scalar G in an element-wise fashion (e.g., each
element may correspond to a frequency subcarrier). Instead of
multiplied by the scalar G, a direct function of G may be used.
(n+1) LTFs may be used for signaling to n users in a system that
may employ differential signaling.
[0177] LTF ordering per user may use signaling of the order. The
signaling may include, for example, incorporation of the
parameter(s) as part of the VHT-SIG-B field, and/or SIG
definition(s), e.g., a VHT-SIG-C field. The signaling may not be
the per sub-carrier ordering, but may indicate which user may use
which LTF to estimate G for each of the sub-carriers.
[0178] A STA procedure for estimation of a G may be provided. A STA
may finds it's index, i, e.g., from the SIG or in a way it was
transmitted. A STA may use the reference (e.g., 1st) and (i+1)th
reference LTF to compute G for the sub-carrier using simple
division: Gi(k)=LTF(i+1)(k)/LTF1(k), for each sub-carrier k. MMSE
estimate may be used. The Gs may be used to decode the rest of the
packet
[0179] Transparent signaling may be provided. The LTFs may be
precoded (e.g., non-linearly precoded) in a similar manner as for
the data. For example, in a four user system with one receive
antenna for each user, the SIG-A field in the preamble may label
the users in an order. The four distinct LTFs may be labeled in the
same order. User 1, for example, may use LTF 1 to estimate its
parameters. At the AP, the user ordering per sub-carrier may be
determined from the channel matrix. The user ordering may be
applied to the LTFs, which may be non-linearly precoded. At a
receiver, the user may decode its LTF to estimate its desired gain
parameters. The received signal model for the ith user on the kth
sub-carrier may be: r.sub.ik=G.sub.ik(a.sub.ik+v.sub.ik)+n.sub.ik
where a.sub.ik may be the known LTF symbol, n.sub.ik may be the
additive noise and v.sub.ik may be the unknown additive element
that may be due to the modulo operation at the transmitter. The
gain G.sub.ik and v.sub.ik may be unknown and G.sub.ik may not be
estimated from r.sub.ik. G.sub.ik may be real, may be a function of
the channel and sorting of the channel matrix on sub-carrier k, and
may be bounded as illustrated in FIG. 22. FIG. 22 illustrates an
exemplary cumulative distribution function (CDF) distribution of
the gains. If the receiver has more than one LTF symbols, the
ambiguity about v.sub.ik may be resolved and the gain G.sub.ik may
be determined.
[0180] The scalar Gs may be signaled in the downlink. FIG. 23
illustrates an exemplary signaling frame format. As shown in FIG.
23, the signaling frame formal may include number of users 2302,
user index 2304, quantization resolution 2314, signaling content
2306, user index 2308, quanization resolution 2310, and/or
signaling content 2312. For a user, the real values (G) may be
uniformly and/or non-uniformly quantized within a certain range and
represented by binary bits. The binary signaling bits for a user
may follow a user index (e.g., the STA address) control field and a
quantization resolution control field.
[0181] Upon receiving the signaling frame, a user may identify its
own user index (e.g., the STA address) and recover the signaling
content that may follow.
[0182] In explicit downlink signaling, the LTFs may be generated a
similar manner as in explicit signaling. Instead of relying on
blind detection and estimation, explicit signaling may be used to
signal the row index (e.g., user ordering) info for a subcarrier.
The user ordering info may take lesser bits (e.g. 2 bit for a
4-user system) than direct signaling of the real-valued G.
[0183] With the user ordering explicitly signaled, a STA may
directly proceed to estimate the diagonal entry of the matrix L and
the corresponding Gs. The frame format of explicit signaling the
user ordering index may be similar to frame format of explicit
signaling of the real-valued Gs, described herein.
[0184] FIG. 24A is a diagram of an example communications system
100 in which one or more disclosed embodiments may be implemented.
The communications system 100 may be a multiple access system that
provides content, such as voice, data, video, messaging, broadcast,
etc., to multiple wireless users. The communications system 100 may
enable multiple wireless users to access such content through the
sharing of system resources, including wireless bandwidth. For
example, the communications systems 100 may employ one or more
channel access methods, such as code division multiple access
(CDMA), time division multiple access (TDMA), frequency division
multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier
FDMA (SC-FDMA), and the like.
[0185] As shown in FIG. 24A, the communications system 100 may
include wireless transmit/receive units (WTRUs) 102a, 102b, 102c,
and/or 102d (which generally or collectively may be referred to as
WTRU 102), a radio access network (RAN) 103/104/105, a core network
106/107/109, a public switched telephone network (PSTN) 108, the
Internet 110, and other networks 112, though it will be appreciated
that the disclosed embodiments contemplate any number of WTRUs,
base stations, networks, and/or network elements. Each of the WTRUs
102a, 102b, 102c, 102d may be any type of device configured to
operate and/or communicate in a wireless environment. By way of
example, the WTRUs 102a, 102b, 102c, 102d may be configured to
transmit and/or receive wireless signals and may include wireless
transmit/receive unit (WTRU), a mobile station, a fixed or mobile
subscriber unit, a pager, a cellular telephone, a personal digital
assistant (PDA), a smartphone, a laptop, a netbook, a personal
computer, a wireless sensor, consumer electronics, and the
like.
[0186] The communications systems 100 may also include a base
station 114a and a base station 114b. Each of the base stations
114a, 114b may be any type of device configured to wirelessly
interface with at least one of the WTRUs 102a, 102b, 102c, 102d to
facilitate access to one or more communication networks, such as
the core network 106/107/109, the Internet 110, and/or the networks
112. By way of example, the base stations 114a, 114b may be a base
transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a
Home eNode B, a site controller, an access point (AP), a wireless
router, and the like. While the base stations 114a, 114b are each
depicted as a single element, it will be appreciated that the base
stations 114a, 114b may include any number of interconnected base
stations and/or network elements.
[0187] The base station 114a may be part of the RAN 103/104/105,
which may also include other base stations and/or network elements
(not shown), such as a base station controller (BSC), a radio
network controller (RNC), relay nodes, etc. The base station 114a
and/or the base station 14b may be configured to transmit and/or
receive wireless signals within a particular geographic region,
which may be referred to as a cell (not shown). The cell may
further be divided into cell sectors. For example, the cell
associated with the base station 114a may be divided into three
sectors. Thus, in one embodiment, the base station 114a may include
three transceivers, i.e., one for each sector of the cell. In an
embodiment, the base station 114a may employ multiple-input
multiple output (MIMO) technology and, therefore, may utilize
multiple transceivers for each sector of the cell.
[0188] The base stations 114a, 114b may communicate with one or
more of the WTRUs 102a, 102b, 102c, 102d over an air interface
115/116/117, which may be any suitable wireless communication link
(e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet
(UV), visible light, etc.). The air interface 115/116/117 may be
established using any suitable radio access technology (RAT).
[0189] More specifically, as noted above, the communications system
100 may be a multiple access system and may employ one or more
channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA,
and the like. For example, the base station 114a in the RAN
103/104/105 and the WTRUs 102a, 102b, 102c may implement a radio
technology such as Universal Mobile Telecommunications System
(UMTS) Terrestrial Radio Access (UTRA), which may establish the air
interface 115/116/117 using wideband CDMA (WCDMA). WCDMA may
include communication protocols such as High-Speed Packet Access
(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed
Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet
Access (HSUPA).
[0190] In an embodiment, the base station 114a and the WTRUs 102a,
102b, 102c may implement a radio technology such as Evolved UMTS
Terrestrial Radio Access (E-UTRA), which may establish the air
interface 115/116/117 using Long Term Evolution (LTE) and/or
LTE-Advanced (LTE-A).
[0191] In an embodiment, the base station 114a and the WTRUs 102a,
102b, 102c may implement radio technologies such as IEEE 802.16
(i.e., Worldwide Interoperability for Microwave Access (WiMAX)),
CDMA2000, CDMA2000 1.times., CDMA2000 EV-DO, Interim Standard 2000
(IS-2000), Interim Standard 95 (IS-95), Interim Standard 856
(IS-856), Global System for Mobile communications (GSM), Enhanced
Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the
like.
[0192] The base station 114b in FIG. 24A may be a wireless router.
Home Node B, Home eNode B, or access point, for example, and may
utilize any suitable RAT for facilitating wireless connectivity in
a localized area, such as a place of business, a home, a vehicle, a
campus, and the like. In one embodiment, the base station 114b and
the WTRUs 102c, 102d may implement a radio technology such as IEEE
802.11 to establish a wireless local area network (WLAN). In an
embodiment, the base station 114b and the WTRUs 102c, 102d may
implement a radio technology such as IEEE 802.15 to establish a
wireless personal area network (WPAN). In yet an embodiment, the
base station 114b and the WTRUs 102c, 102d may utilize a
cellular-based RAT (e.g, WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to
establish a picocell or femtocell. As shown in FIG. 24A, the base
station 114b may have a direct connection to the Internet 110.
Thus, the base station 114b may not be required to access the
Internet 110 via the core network 106/107/109.
[0193] The RAN 103/104/105 may be in communication with the core
network 106/107/109, which may be any type of network configured to
provide voice, data, applications, and/or voice over internet
protocol (VoIP) services to one or more of the WTRUs 102a, 102b,
102c, 102d. For example, the core network 106/107/109 may provide
call control, billing services, mobile location-based services,
pre-paid calling, Internet connectivity, video distribution, etc.,
and/or perform high-level security functions, such as user
authentication. Although not shown in FIG. 24A, it will be
appreciated that the RAN 103/104/105 and/or the core network
106/107/109 may be in direct or indirect communication with other
RANs that employ the same RAT as the RAN 103/104/105 or a different
RAT. For example, in addition to being connected to the RAN
103/104/105, which may be utilizing an E-UTRA radio technology, the
core network 106/107/109 may also be in communication with a RAN
(not shown) employing a GSM radio technology.
[0194] The core network 106/107/109 may also serve as a gateway for
the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the
Internet 110, and/or other networks 112. The PSTN 108 may include
circuit-switched telephone networks that provide plain old
telephone service (POTS). The Internet 110 may include a global
system of interconnected computer networks and devices that use
common communication protocols, such as the transmission control
protocol (TCP), user datagram protocol (UDP) and the internet
protocol (IP) in the TCP/IP internet protocol suite. The networks
112 may include wired or wireless communications networks owned
and/or operated by other service providers. For example, the
networks 112 may include a core network connected to one or more
RANs, which may employ the same RAT as the RAN 103/104/105 or a
different RAT.
[0195] Some or all of the WTRUs 102a, 102b, 102c, 102d in the
communications system 100 may include multi-mode capabilities,
i.e., the WTRUs 102a, 102b, 102c, 102d may include multiple
transceivers for communicating with different wireless networks
over different wireless links. For example, the WTRU 102c shown in
FIG. 24A may be configured to communicate with the base station
114a, which may employ a cellular-based radio technology, and with
the base station 114b, which may employ an IEEE 802 radio
technology.
[0196] FIG. 24B is a system diagram of an example WTRU 102. As
shown in FIG. 24B, the WTRU 102 may include a processor 118, a
transceiver 120, a transmit/receive element 122, a
speaker/microphone 124, a keypad 126, a display/touchpad 128,
non-removable memory 130, removable memory 132, a power source 134,
a global positioning system (GPS) chipset 136, and other
peripherals 138. It will be appreciated that the WTRU 102 may
include any sub-combination of the foregoing elements while
remaining consistent with an embodiment. Also, embodiments
contemplate that the base stations 114a and 114b, and/or the nodes
that base stations 114a and 114b may represent, such as but not
limited to transceiver station (BTS), a Node-B, a site controller,
an access point (AP), a home node-B, an evolved home node-B
(eNodeB), a home evolved node-B (HeNB), a home evolved node-B
gateway, and proxy nodes, among others, may include some or each of
the elements depicted in FIG. 24B and described herein.
[0197] The processor 118 may be a general purpose processor, a
special purpose processor, a conventional processor, a digital
signal processor (DSP), a plurality of microprocessors, one or more
microprocessors in association with a DSP core, a controller, a
microcontroller, Application Specific Integrated Circuits (ASICs),
Field Programmable Gate Array (FPGAs) circuits, any other type of
integrated circuit (IC), a state machine, and the like. The
processor 118 may perform signal coding, data processing, power
control, input/output processing, and/or any other functionality
that enables the WTRU 102 to operate in a wireless environment. The
processor 118 may be coupled to the transceiver 120, which may be
coupled to the transmit/receive element 122. While FIG. 24B depicts
the processor 118 and the transceiver 120 as separate components,
it will be appreciated that the processor 118 and the transceiver
120 may be integrated together in an electronic package or
chip.
[0198] The transmit/receive element 122 may be configured to
transmit signals to, or receive signals from, a base station (e.g.,
the base station 114a) over the air interface 115/116/117. For
example, in one embodiment, the transmit/receive element 122 may be
an antenna configured to transmit and/or receive RF signals. In an
embodiment, the transmit/receive element 122 may be an
emitter/detector configured to transmit and/or receive IR, UV, or
visible light signals, for example. In yet an embodiment, the
transmit/receive element 122 may be configured to transmit and
receive both RF and light signals. It will be appreciated that the
transmit/receive element 122 may be configured to transmit and/or
receive any combination of wireless signals.
[0199] In addition, although the transmit/receive element 122 is
depicted in FIG. 24B as a single element, the WTRU 102 may include
any number of transmit/receive elements 122. More specifically, the
WTRU 102 may employ MIMO technology. Thus, in one embodiment, the
WTRU 102 may include two or more transmit/receive elements 122
(e.g., multiple antennas) for transmitting and receiving wireless
signals over the air interface 115/116/117.
[0200] The transceiver 120 may be configured to modulate the
signals that are to be transmitted by the transmit/receive element
122 and to demodulate the signals that are received by the
transmit/receive element 122. As noted above, the WTRU 102 may have
multi-mode capabilities. Thus, the transceiver 120 may include
multiple transceivers for enabling the WTRU 102 to communicate via
multiple RATs, such as UTRA and IEEE 802.11, for example.
[0201] The processor 118 of the WTRU 102 may be coupled to, and may
receive user input data from, the speaker/microphone 124, the
keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal
display (LCD) display unit or organic light-emitting diode (OLED)
display unit). The processor 118 may also output user data to the
speaker/microphone 124, the keypad 126, and/or the display/touchpad
128. In addition, the processor 118 may access information from,
and store data in, any type of suitable memory, such as the
non-removable memory 130 and/or the removable memory 132. The
non-removable memory 130 may include random-access memory (RAM),
read-only memory (ROM), a hard disk, or any other type of memory
storage device. The removable memory 132 may include a subscriber
identity module (SIM) card, a memory stick, a secure digital (SD)
memory card, and the like. In an embodiment, the processor 118 may
access information from, and store data in, memory that is not
physically located on the WTRU 102, such as on a server or a home
computer (not shown).
[0202] The processor 118 may receive power from the power source
134, and may be configured to distribute and/or control the power
to the other components in the WTRU 102. The power source 134 may
be any suitable device for powering the WTRU 102. For example, the
power source 134 may include one or more dry cell batteries (e.g.,
nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride
(NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and
the like.
[0203] The processor 118 may also be coupled to the GPS chipset
136, which may be configured to provide location information (e.g.,
longitude and latitude) regarding the current location of the WTRU
102. In addition to, or in lieu of, the information from the GPS
chipset 136, the WTRU 102 may receive location information over the
air interface 115/116/117 from a base station (e.g., base stations
14a, 14b) and/or determine its location based on the timing of the
signals being received from two or more nearby base stations. It
will be appreciated that the WTRU 102 may acquire location
information by way of any suitable location-determination method
while remaining consistent with an embodiment.
[0204] The processor 118 may further be coupled to other
peripherals 138, which may include one or more software and/or
hardware modules that provide additional features, functionality
and/or wired or wireless connectivity. For example, the peripherals
138 may include an accelerometer, an e-compass, a satellite
transceiver, a digital camera (for photographs or video), a
universal serial bus (USB) port, a vibration device, a television
transceiver, a hands free headset, a Bluetooth.RTM. module, a
frequency modulated (FM) radio unit, a digital music player, a
media player, a video game player module, an Internet browser, and
the like.
[0205] Although features and elements are described above in
particular combinations, one of ordinary skill in the art will
appreciate that each feature or element may be used alone or in any
combination with the other features and elements. In addition, the
methods described herein may be implemented in a computer program,
software, or firmware incorporated in a computer-readable medium
for execution by a computer or processor. Examples of
computer-readable media include electronic signals (transmitted
over wired or wireless connections) and computer-readable storage
media. Examples of computer-readable storage media include, but are
not limited to, a read only memory (ROM), a random access memory
(RAM), a register, cache memory, semiconductor memory devices,
magnetic media such as internal hard disks and removable disks,
magneto-optical media, optical media such as CD-ROM disks, and
digital versatile disks (DVDs). A processor in association with
software may be used to implement a radio frequency transceiver for
use in a WTRU, WTRU, terminal, base station, RNC, or any host
computer.
* * * * *