U.S. patent application number 12/534423 was filed with the patent office on 2009-12-17 for exploiting multiuser diversity through phase modulation multiplexing.
This patent application is currently assigned to Adaptix, Inc.. Invention is credited to Hui Liu, Manyuan Shen, Guanbin Xing.
Application Number | 20090310700 12/534423 |
Document ID | / |
Family ID | 36565371 |
Filed Date | 2009-12-17 |
United States Patent
Application |
20090310700 |
Kind Code |
A1 |
Liu; Hui ; et al. |
December 17, 2009 |
Exploiting multiuser diversity through phase modulation
multiplexing
Abstract
A method and apparatus for combining signals of multiple users
onto a common channel is disclosed. In one embodiment, the method
comprises identifying one or more traffic channels that are of one
or more predetermined quality levels to a plurality of subscriber
units based on channel profiles of the plurality of subscriber
units and transmitting phase modulation multiplexed signals to the
plurality of subscriber units through a common set of one or more
channels having higher quality than the one or more predetermined
quality levels.
Inventors: |
Liu; Hui; (Clyde Hill,
WA) ; Shen; Manyuan; (Bellevue, WA) ; Xing;
Guanbin; (Issaquah, WA) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI L.L.P
2200 ROSS AVENUE, SUITE 2800
DALLAS
TX
75201-2784
US
|
Assignee: |
Adaptix, Inc.
Carrollton
TX
|
Family ID: |
36565371 |
Appl. No.: |
12/534423 |
Filed: |
August 3, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11001939 |
Dec 1, 2004 |
7606596 |
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12534423 |
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Current U.S.
Class: |
375/267 |
Current CPC
Class: |
Y02D 30/50 20200801;
H04J 13/0077 20130101; Y02D 50/10 20180101; H04L 1/0003 20130101;
H04L 1/0017 20130101; H04L 1/0009 20130101; H04J 13/00
20130101 |
Class at
Publication: |
375/267 |
International
Class: |
H04B 7/02 20060101
H04B007/02 |
Claims
1. A method comprising: identifying at least one traffic channel
having a maximum achievable data rate above a predetermined
threshold, said traffic channel being utilized below said
threshold; identifying a plurality of low rate subscriber units,
said identification of low rate subscriber units based, at least in
part, upon a data rate of said subscriber unit over a period of
time; and transmitting phase modulation multiplexed signals on said
at least one identified traffic channel to said plurality of
identified low rate subscriber units, wherein said at least one
traffic channel is shared by said plurality of low rate
subscribers.
2. The method of claim 1 wherein said identification of low rate
subscriber units is based upon collecting the channel profiles of
said low rate subscriber units.
3. The method of in claim 1 wherein the low rate subscriber units
comprise voice only subscriber units.
4. The method of claim 1 wherein identifying at least one traffic
channel is based on periodic traffic pattern analysis.
5. (canceled)
6. The method of claim 1 further comprising one of said plurality
of low rate subscriber units demodulating at least a portion of the
modulated multiplexed signals to obtain data for the one subscriber
unit.
7. The method of claim 6 wherein the one subscriber unit
demodulates and decodes all of the modulated multiplexed signals to
obtain data designated for the one subscriber unit.
8-16. (canceled)
17. A communication system comprising: a base station transmitting
phase modulation multiplexed signals to a plurality of low rate
subscriber units over at least one traffic channel, at least two of
said plurality of low rate subscriber units sharing at least one of
said traffic channels; said base station also transmitting signals
to high rate subscriber units utilizing adaptive code modulation;
wherein said plurality of low rate subscriber units are identified
as those having a data rate over a period of time below a
threshold; and wherein said high rate subscriber units are
identified as those having a data rate over a period of time above
said threshold.
18. The communication system of claim 17 wherein the base station
comprises: a multiplexer to multiplex phase modulated signals for a
plurality of low rate subscriber units onto a shared traffic
channel; and an adaptive coded modulation unit to transmit adaptive
code modulated signals to high rate subscriber units.
19. The communication system of claim 18 wherein the adaptive coded
modulation unit jointly encodes the data stream to generate encoded
data and maps the encoded data onto a QAM constellation.
20. The communication system of claim 18 wherein the adaptive coded
modulation unit comprises: a channel encoder to channel code data
from the data stream to generate encoded data; and a modulator to
perform modulation on the encoded data for wireless transmission on
the traffic channel.
21. The communication system of claim 20 wherein the modulator
comprises a QAM modulator.
22. The communication system of claim 21 wherein the channel
encoder comprises a convolutional code encoder.
23. The communication system of claim 21 wherein the channel
encoder comprises a LDPC encoder.
24. The communication system of claim 21 wherein the channel
encoder comprises a Turbo encoder.
25. The communication system of claim 21 wherein the channel
encoder comprises a TPC encoder.
26.-46. (canceled)
47. A method comprising: receiving, at a subscriber unit, low rate
data transmissions from a base station; transmitting, at said
subscriber unit, channel profile information to said base station;
receiving, at said subscriber station and in response to said
transmitting, phase modulation multiplexed signals from said base
station on at least one traffic channel, said at least one traffic
channel being shared by at least one other subscriber unit; and
decoding and demodulating said phase modulated multiplexed signals
at said subscriber station.
48. The method of claim 47 wherein said subscriber unit decodes and
demodulates a portion of the modulated multiplexed signals to
obtain data for said subscriber unit.
49. The method of claim 47 wherein said subscriber unit decodes and
demodulates all of the modulated multiplexed signals to obtain data
for said subscriber unit.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of wireless
communications; more particularly, the present invention relates to
the use of multi-user diversity in orthogonal multiple access
wireless communications systems.
BACKGROUND OF THE INVENTION
[0002] Modern broadband wireless networks have to support
heterogeneous users with a large variation in service requirements.
While the peak data rate of most systems increases with the
bandwidth, the number of simultaneous users a system can support
does not always increase proportionally due to the system
granularity issue. TDMA (time-division multiple-access) and CDMA
(code-division multiple-access) are known to have limited
granularity and thus suffer from decreased spectrum efficiency when
the system is heavily loaded. Other performance parameters that may
be affected by coarse granularity include packet delays and
jittering.
[0003] By partitioning the radio resource in both the frequency
domain and the time domain, orthogonal frequency-division
multiple-access (OFDMA) offers flexibility and granularity over
either TDMA or CDMA. Similar to TDMA and synchronous CDMA with
orthogonal spreading codes, each traffic channel in OFDMA is
exclusively assigned to a single user, eliminating intracell
interference in a system. A salient feature of orthogonal multiple
access schemes such as OFMDA, TDMA, SCDMA is its capability to
explore the so-called multiuser diversity in a wireless network (R.
Knopp and P. A. Humblet, "Information capacity and power control in
single-cell multiuser communications," in Proc. IEEE Int. Conf.
Comm. 1995, Seattle, Wash., June 1995, pp. 331-335).
[0004] Adaptive coded modulation (ACM) and dynamic channel
allocation (DCA) are well-known in the art. For example, for more
information on DCA, see U.S. Pat. No. 6,606,499, "Dynamic channel
allocation method in a cellular radio communication network."
[0005] When orthogonal multiple access schemes are combined with
adaptive coded modulation (ACM) and dynamic channel allocation
(DCA), the spectrum efficiency of these approaches their theoretic
bounds. As a matter of fact, it can be proved that in terms of
total system capacity, OFDMA is indeed optimal in broadband
downlink transmission. For more information, see Jiho Jang and
Kwang Bok Lee, "Transmit power adaptation for multiuser OFDM
systems," IEEE Journal on Selected Areas in Communication, vol. 21,
no. 2, February 2003.
[0006] On the other hand, the benefits of ACM and DCA cannot be
fully captured without taking into account the actual traffic
patterns of the users. For a system with many low and constant-rate
users (e.g., voice), the need for individual user based ACM
vanishes. High-qualify traffic channels are sometimes wasted,
especially in downlink transmission where power control is less
feasible. Consider a situation involving a number of voice users
with QPSK+1/2 coding as the default coding and modulation scheme.
If only one user is allowed in each traffic channel, the maximum
throughput of each traffic channel is fixed as 1 bit/s/Hz,
regardless of the traffic channel condition. Note that the problem
cannot be solved by buffering (and burst transmission) due to the
delay constraints in voice communications.
SUMMARY OF THE INVENTION
[0007] A method and apparatus for combining signals of multiple
users onto a common channel is disclosed. In one embodiment, the
method comprises identifying one or more traffic channels that are
of one or more predetermined quality levels to a plurality of
subscriber units based on channel profiles of the plurality of
subscriber units and transmitting phase modulation multiplexed
signals to the plurality of subscriber units through a common set
of one or more channels having higher quality than the one or more
predetermined quality levels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention will be understood more fully from the
detailed description given below and from the accompanying drawings
of various embodiments of the invention, which, however, should not
be taken to limit the invention to the specific embodiments, but
are for explanation and understanding only.
[0009] FIG. 1 illustrates a wireless networks where users' channel
conditions are vastly different, due to different propagation
losses, interference patterns, and multipath reflections.
[0010] FIG. 2 depicts channel profiles of two users and the
achievable rates in each traffic channels.
[0011] FIG. 3A is a block diagram of one embodiment of a phase
modulation multiplexer that multiplexes data from multiple low rate
users into a high rate stream for high-dimensional coded
modulation.
[0012] FIG. 3B illustrates another embodiment of phase modulation
multiplexing logic.
[0013] FIG. 4 illustrates increasing the granularity of a wireless
system with phase modulation multiplexing.
[0014] FIG. 5 is a block diagram of one embodiment of a dynamic
channel multiplexing logic unit that utilizes DCA, ACM, and
PMM.
[0015] FIG. 6 is a flow diagram of one embodiment of a process for
performing dynamic channel multiplexing.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0016] A method and apparatus for exploiting multiuser diversity in
orthogonal multiplexing/multiple access (e.g., OFDMA, TDMA, SCDMA)
wireless broadband networks are described. In one embodiment, data
for two or more low rate subscriber units are combined (e.g.,
multiplexed) into one (or more) high quality channels. The channels
that are being combined for low rate subscriber units may be voice
channels. In one embodiment, the high quality channels are
identified based on channel profiles and periodic traffic pattern
analysis of the channels used by the group of subscriber units. The
data for multiple subscriber units is combined into a single
channel in order to use the single channel more fully or,
potentially, at full capacity.
[0017] In one embodiment, an intelligent traffic allocation scheme
enables sharing of high-quality orthogonal traffic channel(s)
through PMM-based dynamic data aggregation. In one embodiment, the
PMM is performed according to U.S. Pat. No. 6,295,273 entitled,
"Phase modulation multiplexing transmission unit and phase
modulation multiplexing method," issued Sep. 25, 2001. Using phase
modulation multiplexing (PMM) takes advantage of the common set of
high-quality traffic channels associated with multiple low rate
subscribers. This increases the system granularity, and more
importantly, guarantees increased, and potentially maximum, usage
of high-quality traffic channels irrespective of the traffic loads
of individual users. As a result, the highest achievable rate can
be reached on each traffic channel. Note that this approach is
distinct from the orthogonal multiplexing/multiple access schemes
in prior art where each traffic channel is assigned to only one
user.
[0018] A method and apparatus that combines phase modulation
multiplexing (PMM) with DCA and ACM is described. The techniques
set forth herein increase the granularity of a broadband network
and at the same time, increases, and potentially maximizes, the
system spectrum efficiency under stringent QoS constraints (e.g.,
rate, delay, and jitter).
[0019] The techniques capture the multiuser diversity not available
in existing systems with a large number of constant-rate users.
Note there is no prior art that discloses the dynamic aggregation
using phase modulation multiplexing based on the users' channel and
traffic characteristics. In one embodiment, no additional hardware
is required at the base station. In addition, it also overcomes the
drawbacks in prior art that employs bursty transmission--no delays
and jittering are created to low rate traffics.
[0020] The new technique can be utilized in wireless communications
systems employing a variety of multiple-access schemes such as, for
example, OFDMA, TDMA, FDMA, CDMA, SDMA, and any combinations of
these multiple-access schemes.
[0021] In the following description, numerous details are set forth
to provide a more thorough explanation of the present invention. It
will be apparent, however, to one skilled in the art, that the
present invention may be practiced without these specific details.
In other instances, well-known structures and devices are shown in
block diagram form, rather than in detail, in order to avoid
obscuring the present invention.
[0022] Some portions of the detailed descriptions which follow are
presented in terms of algorithms and symbolic representations of
operations on data bits within a computer memory. These algorithmic
descriptions and representations are the means used by those
skilled in the data processing arts to most effectively convey the
substance of their work to others skilled in the art. An algorithm
is here, and generally, conceived to be a self-consistent sequence
of steps leading to a desired result. The steps are those requiring
physical manipulations of physical quantities. Usually, though not
necessarily, these quantities take the form of electrical or
magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
[0023] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise as apparent from
the following discussion, it is appreciated that throughout the
description, discussions utilizing terms such as "processing" or
"computing" or "calculating" or "determining" or "displaying" or
the like, refer to the action and processes of a computer system,
or similar electronic computing device, that manipulates and
transforms data represented as physical (electronic) quantities
within the computer system's registers and memories into other data
similarly represented as physical quantities within the computer
system memories or registers or other such information storage,
transmission or display devices.
[0024] The present invention also relates to apparatus for
performing the operations herein. This apparatus may be specially
constructed for the required purposes, or it may comprise a general
purpose computer selectively activated or reconfigured by a
computer program stored in the computer. Such a computer program
may be stored in a computer readable storage medium, such as, but
is not limited to, any type of disk including floppy disks, optical
disks, CD-ROMs, and magnetic-optical disks, read-only memories
(ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or
optical cards, or any type of media suitable for storing electronic
instructions, and each coupled to a computer system bus.
[0025] The algorithms and displays presented herein are not
inherently related to any particular computer or other apparatus.
Various general purpose systems may be used with programs in
accordance with the teachings herein, or it may prove convenient to
construct more specialized apparatus to perform the required method
steps. The required structure for a variety of these systems will
appear from the description below. In addition, the present
invention is not described with reference to any particular
programming language. It will be appreciated that a variety of
programming languages may be used to implement the teachings of the
invention as described herein.
[0026] A machine-readable medium includes any mechanism for storing
or transmitting information in a form readable by a machine (e.g.,
a computer). For example, a machine-readable medium includes read
only memory ("ROM"); random access memory ("RAM"); magnetic disk
storage media; optical storage media; flash memory devices;
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waves, infrared signals, digital signals, etc.);
etc.
[0027] FIG. 1 illustrates a typical wireless network where
subscriber units 101-103 are geometrically spread in a cell,
leading to different channel characteristics between the
base-station 110 and subscriber units 101-103. Note that for the
purposes herein, the terms "subscriber" and "subscriber unit" are
used interchangeably with the term "user." In this particular
example, two users (subscribers 101 and 102) are closer to
base-station 110 while the other user (subscriber 103) is farther
away than subscriber 101 and 102. The distance between a subscriber
and base-station 110, coupled with other factors such as multipath
reflections, the interference and shadowing effects, determines the
signal-to-interference-and-noise-ration (SINR) received at each
subscriber unit during downlink operation. Depending on the
adaptive coded modulation (ACM) scheme employed, the SINR value
dictates the achievable data rate at a given traffic channel.
Assuming the downlink transmission power on individual traffic
channels is fixed, the overall system capacity (or spectrum
efficiency) can be increased if increased, or potentially maximum,
throughput can be delivered over each traffic channel using
adaptive coded modulation.
[0028] In FIG. 1, if both subscriber 101 and subscriber 102 are
low, fixed-rate voice users and the typical data rate of voice
communications is 8 kbps or lower, then to accommodate this type of
traffic, only low dimensional modulation (e.g., QPSK+1/2
coding.fwdarw.1 bit/s/Hz) is needed, regardless of the actual
channel SINR value. As a result, high-quality channels suitable for
higher dimensional modulations (e.g., 64QAM+5/6 coding.fwdarw.5
bit/s/Hz) will be under-used, leading to a waste of spectrum
resources. This problem is particularly evident in orthogonal
multiplexing/multiple-access schemes such as TDMA, OFDMA, and
synchronous CDMA (SCDMA) with one user in each traffic channel (a
time slot, a cluster of sub-carriers, or an orthogonal spreading
code). According to one embodiment of the present invention, the
aforementioned problem is solved by combining dynamic channel
allocation (DCA), adaptive coded modulation (ACM), and phase
modulation multiplexing (PMM).
[0029] FIG. 2 illustrates a dynamic channel allocation technique in
combination of PMM for multiple subscriber units sharing a common
set of high-quality traffic channels. Referring to FIG. 2, the
channel characteristics of two low rate users with basic rate
requirement <2 bit/s/Hz are illustrated with some high-quality
traffic channels are common to both users. The y-axis shows the
achievable data rate (e.g., the ACM rate based on the SINR value)
in bit/s/Hz. As shown, both users favor traffic channel #3 where
the achievable rate is .about.4 bit/s/Hz. In this case, channel
allocation logic is one embodiment of the present invention assigns
the same traffic channel to both subscriber units using PMM. By
aggregating the traffic loads of both subscriber units, the traffic
channel is utilized with increased, and potentially full, capacity,
resulting in much higher system spectrum efficiency.
[0030] FIG. 3A is a block diagram of one embodiment of phase
modulation multiplexing logic to aggregate two or more low rate
users using a PMM scheme. Referring to FIG. 3A, subscriber units
301.sub.1-N are multiplexed into a high-rate stream 302 using
multiplexer 310. In one embodiment, subscriber units 301.sub.1-N
have rates of 2-bit/unit time, 1-bit/unit time, and 3-bit/unit
time, respectively, while high-rate data stream has a rate of
6-bit/unit time.
[0031] An adaptive coded modulator 320 receives high-rate stream
302. In one embodiment, adaptive coded modulator 320 comprises a
channel encoder 311 and a modulator 312 (e.g., QAM). Channel
encoder 311 performs channel coding 311 on data in high-rate steam
302 to produce channel coded data. Channel encoder 311 may comprise
a convolutional coder, an LDPC coder, a Turbo coder, a TPC coder, a
block coder and/or a trellis coder. Modulator 312 receives and
modulates the channel coded data. In one embodiment, modulator 312
modulates the channel coded data using QAM, which maps the channel
coded data onto a QAM constellation. Adaptive coded modulator 320
then loads the resulting coded and modulated signals onto a traffic
channel 303.
[0032] FIG. 3B illustrates another embodiment of a phase modulation
multiplexing logic. Referring to FIG. 3B, low-rate data streams
from different subscribers 351.sub.1-N are first encoded separately
using the same or different encoders 361.sub.1-N to generate
encoded data streams. The encoding may be performed using, for
example, a convolutional encoder. Multiplexer 370 multiplexes the
encoded streams into a high-rate stream 371, which is then
modulated using modulator 372. In one embodiment, modulator 372
maps high-rate data stream 371 onto a QAM constellation.
[0033] In yet another embodiment, modulator 372 maps high-rate data
stream 371 onto a hierarchical QAM constellation to allow different
detection thresholds at the user ends. This may be accomplished
using the technique disclosed in U.S. Pat. No. 5,966,412,
"Apparatus and Method for Processing a Quadrature Amplitude
Modulated (QAM) Signal," issued Oct. 12, 1999.
[0034] In yet another embodiment, other orthogonal phase modulation
multiplexing schemes such as, for example, the orthogonal waveform
modulation are used to multiplex the low rate data streams from
different users.
[0035] FIG. 4 illustrates the use of PPM to improve the granularity
of an orthogonal multiplexing/multiple access scheme. The added
dimension in phase modulation enables simultaneous transmission of
data intended for multiple users without causing interference.
[0036] FIG. 5 is a block diagram of one embodiment of dynamic
channel multiplexing logic at a base-station. Referring to FIG. 5,
a channel profile estimator 501 estimates the channel
characteristics (time, frequency, and spatial responses) of users.
The channel characteristics may be based on either users' feedback,
uplink channel estimation, or both. In response to this input,
channel profile estimator 501 generates a profile for each channel
in a manner well-known in the art.
[0037] Traffic channel allocator 502 receives the channel profiles.
Traffic channel allocator 502 also receives user data rate
information and optionally other QoS parameters, such as, for
example, delay and bit-error-rate requirements. In response to
these inputs, traffic channel allocator 502 makes traffic channel
allocation decisions for users. Traffic channel allocator 502
signals phase modulation multiplexer 504 to cause the low-rate
users to be phase modulation multiplexed onto a common set of one
or more traffic channels. Traffic channel allocator 502 also
controls adaptive coded modulator 505 with respect to a high-rate
user.
[0038] After all traffic channels are loaded from phase modulation
modulator 504 and adaptive coded modulator 505, a frame former and
transmitter 506 consolidates the modulated signals from all traffic
channels into data frames (e.g., TDMA, OFDMA, SCDMA, SDMA) and
performs data transmission.
[0039] In one embodiment, the dynamic channel multiplexing logic in
FIG. 5 updates the channel allocation and ACM schemes periodically
based on a fixed or a variable time interval.
[0040] Several channel allocation and phase modulation multiplexing
criteria can be considered. FIG. 6 is a flow diagram of one
embodiment of a process for selecting traffic channels. The process
is performed by processing logic that may comprise hardware
(circuitry, dedicated logic, etc.), software (such as is run on a
general purpose computer system or a dedicated machine), or a
combination of both.
[0041] Referring to FIG. 6, processing logic stores a list of
unallocated traffic channels in an available traffic channel
register (processing block 601). In one embodiment, processing
logic constantly updates the list in the traffic channel register
every time a traffic channel is assigned or released.
[0042] Processing logic evaluates each available traffic channel at
different achievable rates, starting at the highest: ACM_1, to the
lowest: ACM_K. To that end, processing logic sets the channel at
the highest rate (processing block 602) and then tests whether the
achievable rate of the users is greater than or equal to the rate
being tested (processing block 603). In one embodiment, a users'
channel profile register 610 provides the latest channel
characteristics of the users. If one or more users are qualified at
ACM_1, processing logic selects the traffic channel and updates the
available channel register to move the assigned traffic channel.
Otherwise, processing logic updates the index (processing block
605) and repeats the process by reducing the rate to ACM_2, ACM_3,
. . . , ACM_K, until the number of qualified users becomes
non-zero.
[0043] In one embodiment, from the list the qualified users,
processing logic selects a subset or all of users from a list of
qualified users based on their associated traffic information
(e.g., data rate, delay, buffered data, other QoS parameters, etc.)
stored in a data buffer register 620 in the, or accessible by the
base station (processing block 604). Thus, PPM is performed to
multiplex the selected users' data steams onto the traffic channel
being evaluated.
[0044] When the subscriber unit receives the combined high rate
stream, they demodulate and decode the modulated and channel
encoded high rate stream to obtain the data that is designated for
them. In an alternate embodiment, instead of demodulating and
decoding the entire modulated and channel encoded high rate stream,
each subscriber unit only demodulates and decodes its designated
portion thereof. Note that identifying a portion of the stream
designated for a particular subscriber unit is well-known in the
art.
[0045] Whereas many alterations and modifications of the present
invention will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that any particular embodiment shown and described
by way of illustration is in no way intended to be considered
limiting. Therefore, references to details of various embodiments
are not intended to limit the scope of the claims which in
themselves recite only those features regarded as essential to the
invention.
* * * * *