Adaptix, Inc. v. T-Mobile USA, Inc.

Filing 1

COMPLAINT against T-Mobile USA, Inc. ( Filing fee $ 350 receipt number 0540-3620802.), filed by Adaptix, Inc.. (Attachments: # 1 Civil Cover Sheet, # 2 Exhibit A - U.S. PATENT NO. 7,146,172, # 3 Exhibit B - U.S. PATENT NO. 6,870,808, # 4 Exhibit C - U.S. PATENT NO. 7,573,851, # 5 Exhibit D - U..S. PATENT NO. 6,904,283, # 6 Exhibit E - U.S. PATENT NO. 7,072,315)(Hill, Jack)

EXHIBIT E

111111111111111111111111111111111111111111111111111111111111111111111111111
US007072315Bl

United States Patent

(10)

Liu et al.

(12)

(45)

(54)

MEDIUM ACCESS CONTROL FOR
ORTHOGONAL FREQUENCY-DIVISION
MULTIPLE-ACCESS (OFDMA) CELLULAR
NETWORKS

(75)

Inventors: Hui Liu, Sammamish, WA (US);
Xiaodong Li, Bellevue, WA (US); Fuqi
Mu, Issaquah, WA (US)

(73)

Notice:

5,933,421
5,956,642
5,973,642
5,991,273
6,005,876
6,026,123
6,041,237
6,052,594
6,061,568
6,064,692
6,064,694
6,067,290
6,091,717
6,108,374
6,119,011
6,131,016
6,144,696
6,226,320

Assignee: Adaptix, Inc., Seattle, WA (US)

( *)

Subject to any disclaimer, the tenn of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 944 days.

(21)

Appl. No.: 09/685,977

(22)

Filed:

(51)

Int. Cl.
H04Q 7/00
(2006.01)
H04J 11/00
(2006.01)
H04B 11/00
(2006.01)
U.S. Cl. ...................... 370/329; 370/208; 455/450;
455/69
Field of Classification Search ........ 370/203-210,
370/329,341,348,332; 3751147, 148,260,
375/264,346,348; 455/449-452.2,463-464,
455/561,69,63.1,67.13,509,512,513
See application file for complete search history.

(52)
(58)

Oct. 10, 2000

References Cited

(56)

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5,887,245
5,914,933

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A
A

*

811991
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Patent No.:
US 7,072,315 Bl
Date of Patent:
Jul. 4, 2006
A
A
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A
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Bl

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8/1999
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1111999
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212000
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Alamouti et al. ...........
Larsson et al. .............
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(Continued)
FOREIGN PATENT DOCUMENTS
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(Continued)
OTHER PUBLICATIONS
Bender et a!., CDMAlHDR: A Bandwidth-Efficient HighSpeed Wireless Data Service for Nomadic Users, IEEE
Communications Magazine, luI. 2000, pp. 70-87.
(Continued)
Primary Examiner-Steven Nguyen
(74) Attorney, Agent, or Firm-Fulbright & laworski LLP
(57)

ABSTRACT

A method and apparatus for controlling OFDMA cellular
networks is described. In one embodiment, the method
comprises receiving channel characteristics and noise-plusinterference infonnation measured at spatially distributed
subscribers and assigning traffic channels for an orthogonal
frequency-division multiple-access (OFDMA) network.
35 Claims, 9 Drawing Sheets

,.-600

TraffIC Channel
Register;
Channellnfe. Storage

US 7,072,315 Bl
Page 2

u.s. PATENT DOCUMENTS
6,298,092
6,366,195
6,377,632
6,442,130
6,445,916
6,477,158
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2003/0067890
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Bl
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Bl
Bl
Bl
Al
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*
*
*
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*

1012001
4/2002
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912002
1112002
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912003

Heath et al ................... 455/69
Harel et al.
Paulraj et al.
Jones et al. ................. 3701208
Rahman ..................... 455/423
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Jones et al. ................. 375/260
Alamouti et al. ........... 375/147
Barton et al. ............... 375/264
Sampath et al ............. 375/267
Goel et al.
Chayat

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0869647
0926912
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A2
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OTHER PUBLICATIONS
Frullone et aI., PRMA Perfonnance in Cellular Environments with Self-Adaptive Channel Allocation Strategies,
IEEE Transactions on Vehicular Technology, Nov. 1996, pp.
657-665 vol. 45, No.4.
Xu, Guanghan and Li, San-Qi, Throughput Multiplication of
Wireless Lans for Multimedia Sevices: SDMA Protocol
Design, 1994 IEEE, pp. 1326-1332.
Ward, James and Compton, R. Ted, Jr., High Throughput
Slotted ALOHA Packet Radio Networks with Adaptive
Arrays, IEEE Transactions on Communications, Mar. 1993,
pp. 460-470, vol. 41, No.3.
Tsoulos, G.y', Smart antennas for mobile communication
systems: benefits and challenges, Electronics & Communication Engineering Journal, Apr. 1999, pp. 84-94.
Shad et aI., Indoor SDMA Capacity Using a Smart Antenna
Basestation, 1997 IEEE, pp. 868-872.
Farsakh, Christof and Nossek, Josef A., On the Mobile
Radio Capacity Increase Through SDMA, no date (after
1997).
Farsakh, C. et aI., "Maximizing the SDMA Mobile Radio
Capacity Increase by DOA Sensitive Channel Allocation",
Wireless Personal Communications, Kluwer Academic Pub-

Ii shers , NL, vol. 11, No.1, Oct. 1999, pp. 63-76,
XP000835062, ISSN: 0929-6212.
Wong, c.Y., et aI., Multiuser OFDM With Adaptive Subcarrier, Bit, and Power Allocation, IEEE Journal on Selected
Areas in Communications, Oct. 1999, IEEE Inc., New York,
USA, vol. 17, Nr. 10, pp. 1747-1758, XP000854075, ISSN:
0733-8716 Sections I and II abstract.
Gruenheid, R. et al: "Adaptive Modulation and Multiple
Access for the OFDM Transmission Technique", Wireless
Personal Communications, Kluwer Academic Publishers,
NL, vol. 13, NR. 112, Year 2000, pp. 5-13 XP000894156,
ISSN: 0929-6212.
Motegi, M. et al.: "Optimum Band Allocation According to
Subband Condition for BST-OFDM" 11th IEEE International Symposium on Personal Indoor and Mobile Radio
Communications, vol. 2, Sep. 18-21,2000, pp. 1236-1240,
XP002213669, Piscataway, NJ, USA, ISBN: 0-7803-64635.
Kapoor, S. et al.: "Adaptive Interference Suppression in
Multiuser Wireless OFDM Systems Using Antenna Arrays"
IEEE Transactions on Signal Processing, vol. 47, No. 12,
Dec. 1999, pp. 3381-3391, XP000935422, IEEE, New York,
USA, ISSN: 1053-587X.
Ye Li, et al.: "Clustered OFDM with channel estimation for
high rate wireless data", Mobile Multimedia Communications, 1999. (MOMUC '99).1999 IEEE International Workshop on San Diego, CA, USA, IEEE, US, Nov. 15, 1999, pp.
43-50, XP010370695, ISBN: 0-7803-5904-6.
Nogueroles, R. et al.: "Improved Performance of a Random
OFDMA Mobile Communication System" Vehicular Technology Conference, 1998. VTC 98. 48th IEEE Ottawa,
Ontario, Canada, May 18-21, 1998, pp. 2502-2506,
XPOl0288120, ISBN: 0-7803-4320-4.
Kinugawa, Y. et al.: "Frequency and Time Division Multiple
Access with Demand-Assignment Using Multicarrier
Modulation for Indoor Wireless Communications Systems",
IEICE Transactions on Communications, Institute of
Electonics Infonnation and Comm. Eng. Tokyo, Japan, vol.
E77-B, NR. 3, Mar. 1994, pp. 396-402, XP000451014,
ISSN: 0916-8516.
PCT Written Opinion mailed Sep. 18, 2003, International
Application No. PCT/US01l31766 (5 pages).
Chinese Office Action issued for 01817199.0 dated Apr. 22,
2005.

* cited by examiner

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US 7,072,315 Bl
1

2

MEDIUM ACCESS CONTROL FOR
ORTHOGONAL FREQUENCY-DIVISION
MULTIPLE-ACCESS (OFDMA) CELLULAR
NETWORKS

1747-1758, October 1999. These references indicate that
there is a problem for multi-user communications and show
that a full extent of centralized resource allocation in the
context of OFDMA can substantially increase the capacity
of a wireless network.
Existing approaches for wireless traffic channel assignment are subscriber-initiated and single-subscriber (pointto-point) in nature. Since the total throughput of a multipleaccess network depends on the channel fading profiles,
noise-plus-interference levels, and in the case of spatially
separately transceivers, the spatial channel characteristics,
of all active subscribers, distributed or subscriber-based
channel loading approaches as fundamentally sub-optimum.
Furthermore, subscriber-initiated loading algorithms are
problematic when multiple transceivers are employed as the
base-station, since the signal-to-noise-plus-interference ratio
(SINR) measured based on an omni-directional sounding
signal does not reveal the actual quality of a particular traffic
channel with spatial processing gain. In other words, a "bad"
traffic channel measured at the subscriber based on the
omni-directional sounding signal may very well be a "good"
channel with proper spatial beamforming from the basestation. For these two reasons, innovative information
exchange mechanisms and channel assignment and loading
protocols that acconnt for the (spatial) channel conditions of
all accessing subscribers, as well as their QoS requirements,
are highly desirable. Such "spatial-channel-and-QoS-aware"
allocation schemes can considerably increase the spectral
efficiency and hence data throughput in a given bandwidth.
Thus, distributed approaches, i.e., subscriber-initiated
assignment are thus fundamentally sub-optimum.

FIELD OF THE INVENTION
The present invention relates to the field of cellular
networks; more particularly, the present invention relates to
using medium access control for orthogonal frequencydivision multiple-access (OFDMA) cellular networks.

10

BACKGROUND OF THE INVENTION
With high-speed wireless services increasingly in
demand, there is a need for more throughput per bandwidth
to accommodate more subscribers with higher data rates
while retaining a guaranteed quality of service (QoS). In
point-to-point communications, the achievable data rate
between a transmitter and a receiver is constrained by the
available bandwidth, propagation channel conditions, as
well as the noise-plus-interference levels at the receiver. For
wireless networks where a base-station commnnicates with
multiple subscribers, the network capacity also depends on
the way the spectral resource is partitioned and the channel
conditions and noise-plus-interference levels of all subscribers. In current state-of-the-art, multiple-access protocols,
e.g., time-division multiple access (TDMA), frequencydivision multiple-access (FDMA), code-division multipleaccess (CDMA) , are used to distribute the available spectrum among subscribers according to subscribers' data rate
requirements. Other critical limiting factors, such as the
channel fading conditions, interference levels, and QoS
requirements, are ignored in general.
Recently, there is an increasing interest in orthogonal
frequency-division multiplexing (OFDM) based frequency
division multiple access (OFDMA) wireless networks. One
of the biggest advantages of an OFDM modem is the ability
to allocate power and rate optimally among narrowband
sub-carriers. From a theoretical standpoint, OFDM was
known to closely approximate the "water-filling" solutions
of information theory that are capacity achieving. Some
early work of Hirosaki, "An Orthogonally Multiplexed
QAM System Using the Discrete Fourier Transform," IEEE
Trans. Communications, vol. 29, July 1981, pp. 982-989,
based on an FFT implementation of OFDM achieved complexity and decoded bit count that was comparable to
single-carrier connterparts. This inherent potential ofOFDM
achieved fruition in the design of discrete multi-tone systems (DMT) for xDSLIADSL applications pioneered by J.
Cioffi et aI., "A discrete multi-tone transceiver system for
HDSL applications," IEEE Journal on Selected Areas in
Communications, vol. 9, no. 6 Aug. 1991, pp 909-91.
OFDMA allows for multi-access capability to serve
increasing number of subscribers. In OFDMA, one or a
cluster OFDM sub-carriers defines a "traffic channel", and
different subscribers access to the base-station simultaneously by using different traffic channels. For more information, see Cheng and Verdu, "Gaussian multiaccess channels with lSI: Capacity region and multiuser water-filling,"
IEEE Trans. Info. Theory, Vol. 39(3), pp 773-785, May
1993; Tse and Hanly, "Multiaccess fading channels-part I:
Polymatriod structure, optimal resource allocation and
throughput capacities," IEEE Trans. Info. Theory, Vol.
44(7), pp 2796-2815, November 1998; and Wong et aI.,
"Multiuser OFDM with adaptive subcarrier, bit and power
allocation," IEEE J. Select. Areas Commnn., Vol. 17(10), pp

15

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SUMMARY OF THE INVENTION
35

40

A method and apparatus for controlling OFDMA cellular
networks is described. In one embodiment, the method
comprises receiving channel characteristics and noise-plusinterference information measured at spatially distributed
subscribers and assigning traffic channels for an orthogonal
frequency-division multiple-access (OFDMA) network.
BRIEF DESCRIPTION OF THE DRAWINGS

45

50

55

60

65

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.
FIG. 1 is a block diagram of one embodiment of a
multiple access wireless network with a base-station and
multiple subscribers.
FIG. 2 shows different propagation conditions resulting in
different channel responses in the frequency domain for
different subscribers.
FIG. 3 shows an exemplary channel allocation of the
OFDMA spectrum with joint channel assignment for a pair
of users.
FIG. 4 is a flow diagram of one embodiment of a basic
traffic channel assignment process between a base-station
and multiple subscribers.
FIG. 5 is a block diagram of one embodiment of a
subscriber.
FIG. 6 is a block diagram of one embodiment of a
base-station.

US 7,072,315 Bl

3

4

FIG. 7 shows the beam-pattem of omni-directional sounding signal and the beam-pattem of directional transmission
and reception.
FIG. 8 shows an examplary frame structure for use during
link initiation.
FIG. 9 shows base-stations in a multi-cell network to
perform joint traffic channel allocation.

prove convenient to construct more specialized apparatus to
perfonn 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.
A machine-readable medium includes any mechanism for
storing or transmitting infonnation 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 fonn of propagated signals (e.g.,
carrier waves, infrared signals, digital signals, etc.); etc.

DETAILED DESCRIPTION OF THE PRESENT
INVENTION
A protocol for allocating chaunels is described. In the
following description, numerous details are set forth to
provide a thorough understanding 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.
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, tenns, numbers, or the like.
It should be borne in mind, however, that all of these and
similar tenns 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 tenns 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 transfonns 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 infonnation storage, transmission or display devices.
The present invention also relates to apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may
comprise a general purpose computer selectively activated
or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer
readable storage medium, such as, but is not limited to, any
type of disk including floppy disks, optical disks, CDROMs, and magnetic-optical disks, read-only memories
(ROMs), random access memories (RAMs), EPROMs,
EEPROMs, magnetic or optical cards, or any type of media
suitable for storing electronic instructions, and each coupled
to a computer system bus.
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

10

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65

Overview
A medium access control protocol is described that centralizes broadband chaunel characteristics and noise-plusinterference infonnation measured at spatially distributed
subscribers and assigns traffic chaunels for orthogonal frequency-division multiple-access (OFDMA) network. In one
embodiment, the assigument is made using spatial multiplexing (beamforming).
In one embodiment, the medium access control protocol
controls channel information feedback from multiple subscribers to the base-station, estimates spatial processing
gains for both uplink (subscriber to base-station) and downlink (base-station to subscriber) communications, and performs joint traffic channel assigument.
In one embodiment, a base-station in a wireless network
collects broadband channel and noise-plus-interference
information measured at multiple subscribers, estimates
space-time-frequency diversity gains afforded by spatially
separated antennas at the base-station, detennines the uplink
and downlink OFDMA traffic channel conditions, and
jointly assigns traffic channels to needed subscribers. The
assigument may be made to substantially increase the network throughput.
In one embodiment, standby subscribers initially listen to
an omni-directional sounding signal broadcast by a basestation in the cell network. The sounding signal may comprise a signal having a data sequence known to the basestation and the subscribers. Each subscriber estimates
channel gains and noise-plus-interference levels of a set of
OFDMA traffic channels. In one embodiment, the set of
OFDMA traffic channels are different for different subscribers. When one or more subscribers are paged or when one or
more subscribers have packets to transmit to the basestation, such subscribers transmit measured channel and
noise-plus-interference infonnation to the base-station
through pre-allocated access channels. Those subscribers
with links to the base-station already allocated need not
resend their information unless the base-station is performing retraining (globally reallocating). The access channels
are preallocated by the base station.
The base-station demodulates the access signals and estimates the broadband spatial processing gains across all
available OFDMA traffic channels for each of the accessing
subscribers (subscribers sending or desiring to send information to the base station). The results, together with the
feedback channel and noise-plus-interference information,
are used to detennine the optimum set of uplink and downlink traffic channels for accessing and/or ongoing subscribers.

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A subscriber unit that communicates with a base-station
using OFDMA is also disclosed. In one embodiment, the
subscriber unit includes a channel and noise-pIus-interference estimator, an access signal generator, and an OFDM
modem. The channel and noise-plus-interference estimator
estimates channel gains and noise-plus-interference levels in
a pre-detennined set of traffic channels, possibly announced
by the base-station. This infonnation is the SINRs corresponding to the pre-determined set of traffic channels. The
predetermined set of channels may comprise all the channels
or some portion of channels. The portion of channels may be
the even channels, odd channels, every ith channel (where i
is an integer from 3 or above, such that the portion of
channels comprises every 3 rd channel, or every 4th channel,
etc.), or a number of channels that are not selected from a
regular pattern such as every ith channel.
The access signal generator encodes the channel and
noise-plus-interference infonnation to fonn an access signal.
The OFDM modem modulates the access signal and transmits the modulated signal through an access channel. The
access channel is comprised of all or a subset of traffic
channels during an access time slot. The accessing signal
from the subscriber is used by the base-station to perfonn
spatial channel and spatial processing gain estimation for all
or a subset of traffic channels and traffic channel assignment.
A base-station that communicates with multiple subscribers using OFDMA protocol is also disclosed. In one embodiment, the base-station includes one or more spatially separated transceivers, an access signal detector and
demodulator, a broadband spatial channel and spatial gain
estimator, an uplink and downlink signal-to-noise-plus-interference calculator, a multi-user traffic channel allocator,
and an OFDM modem. The access signal detector and
demodulator detects access signals transmitted from subscribers and demodulates the feedback channel gain and
noise-plus-interference infonnation measured at the subscribers. Based on the received accessing signals, the spatial
channel and spatial gain estimator estimates the broadband
spatial channel, i.e., the spatial characteristics of all or a
subset of traffic channel, between the base-station and each
of the accessing subscribers. The broadband spatial channel
estimates, together with the measured channel and noiseplus-interference infonnation feedback from the access subscribers, are used by the multi-user traffic channel allocator
to detennine a traffic channel assignment and code and
modulation combination for each of the accessing subscribers.
The coding and modulation scheme may be selected
based on the SINR values. For example,
if SINR >=6 dB: QPSK with 112 coding, yielding 1
bit/sec/HZ
if SINR >=12 dB: 16 QAM with 3/4 coding, yielding 3
bits/sec/HZ, where the fractional numbers refer to code rates
(=# of information bits/# of coded bits). Therefore, 112
coding means that 1 infonnation bit generates 2 coded bits,
adding 100% redundancy. For example, if one wants to
transmit 100 bits over wireless link, one first codes them
(adding 100% redundancy) and generates 200 coded bits,
then modulates the 200 bits using QPSK. At the receiver
side, the decoder removes the redundancy and recovers the
100 infonnation bits. The 3/4 coding simply means 3
information bits generates 4 coded bits (33% redundancy).
The OFDM modem modulates the decision regarding
traffic channel assignments and code and modulation combinations and transmits the modulated decision to the subscribers. The modulated decision may comprise a channel
index or channel indices for channels allocated to the

subscriber or an indication of the same (e.g., a compressed
version of a channel index, bit pattern indicative of the
channel to be used or not to be used, etc.).
For the spatial channel and spatial gain estimator, a
process for estimating uplink and downlink spatial gains
from the access signals, in conjunction with the channel and
noise-plus-interference infonnation feedback from the subscribers, is disclosed. The process may be perfonned by
processing logic that comprises hardware (e.g., dedicated
logic), software (such as that which runs on a general
purpose computer or on a dedicated machine), or a combination of both. In one embodiment, the process includes
processing logic that first estimates the broadband spatial
channels across all or a pre-specified set of OFDMA traffic
channels for each accessing subscriber based on the accessing channel received. The results detennine the uplink and
downlink "spatial processing" gain on each of the OFDMA
traffic channels. Processing logic adds the spatial processing
gain to the downlink signal strength feedback (e.g., the
channel and noise-plus-interference infonnation) from the
subscriber to predict the signal to noise-plus-interference
ratio (SINR) for uplink and downlink transmission with
spatial processing (e.g., beamforming) over each of the
available OFDMA traffic channels. The available OFDMA
traffic channels may comprise all the traffic channels or may
comprise all or some portion of the unused traffic channels.
Using the SINRs values for all active subscribers and
accessing subscribers, processing logic determines a traffic
channel assignment. In one embodiment, such a traffic
channel assignment may be the optimum traffic channel
assignment.
In another embodiment, the protocol for channel assignment incorporates priority (based on, for example, an
amount of money paid by the subscriber) and QoS requirements. In one such embodiment, the base-station first estimates the uplink and downlink SINRs across all OFDMA
traffic channels for all active (subscriber already linked to
the base-station but not currently transmitting) and accessing
subscribers, while factoring in the QoS requirements (e.g.,
data rate (e.g., buffer size), time-out, bit error rate, waiting
time (how long the subscriber has been waiting)) to determine the optimum traffic channel allocation. Such infonnation may be combined in a weighted fashion. For example,
in one embodiment, a gain may be combined with weighted
buffer size and time out requests.
In another embodiment, the protocol for channel assignment that involves multiple base-stations is disclosed. In
such an embodiment, in a multi-cell environment, the basestation within each cell first estimates the uplink and downlink SINRs across all OFDMA traffic channels for all active
and accessing subscribers. Each base-station may also buffer
the QoS requirements (e.g., data rate, time-out, bit error rate,
waiting time). Base-stations in neighboring cells exchange
such information before perfonning a traffic channel allocation jointly for multiple subscribers.
Thus, the present invention may be used to answer a
primary challenge for next generation wireless networks by
supporting integrated multimedia type traffic over a unified
network platform. Also, given the stringent constraints on
bandwidth, power and cost relative to increasing end-user
expectations, design optimization approaches described
herein for the air interface (involving multiple access/modem issues) exploit space-time-frequency resources and yet
provide a feasible low-cost/low-power solution to mobility
support is a critical imperative.

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OFDMA with Multi-User Uploading
Orthogonal frequency-division multiplexing (OFDM) is a
form of modulation that transmits high-speed data via multiple parallel traffic channels. In broadband applications
where the communication channels are frequency selective,
OFDM is known to closely approximate the "water-filling"
solutions of information theory that are capacity-achieving
via appropriate power-per-bit allocations to each sub-carrier.
For wireless systems with multiple subscribers, many
existing schemes combine OFDM with static time-division
multiple access (TDMA), and handle multiple-access by
letting users communicate with the base-station in separate
time slot(s). Within each time slot, OFDM with water-filling
can be employed to maximize the capacity. While the
OFDMlTDMA scheme offers a capacity increase over the
conventional TDMA scheme with fixed modulation, channel
adaptation here is limited to single-user loading. Notice that
in point-to-point OFDM, narrowband traffic channels (subcarriers) that experience deep fade are wasted because they
are not power-efficient to carry any information bit. However in a multiple-access environment, this portion of subcarriers is unlikely to be in deep fade for all users. FIG. 1
illustrates broadband channel fading patterns that are dramatically different from one subscriber to the other. From a
theoretical viewpoint, an orthogonal frequency-division
multiple access (OFDMA) that allows simultaneous data
transmission from multiple subscribers over different traffic
channels can offer a substantially larger capacity increase
over OFDMlTDMA. To achieve such gain however, coordination between the base-station and subscribers is of
paramount importance.

FIG. 4 illustrates one embodiment of an MAC protocol.
Referring to FIG. 4, standby subscribers, e.g., subscriber #i,
listens to an omni-directional sounding signal 401 broadcast
from the base-station. In one embodiment, sounding signal
401 is transmitted periodically, and through all or a majority
of OFDMA traffic channels. Based on the known sounding
signal pattern, the subscriber estimates the channel gains at
each of the OFDMA traffic channel. The subscriber also
estimates the noise-plus-interference information in a similar fashion using signal processing techniques such as, for
example, maximum likelihood channel and noise parameter
estimation algorithms, FFT-based channel gain and noiseplus-interference power estimators, and decision directed
channel estimation algorithms.
Until the subscriber has packets to transmit, or when it is
paged by the base-station, the subscriber continues updating
its channel and noise-plus-interference estimates based on
new sounding signals received. Once paged or when it has
packets to transmit, the subscriber encodes the estimated
channel and noise-plus-interference information corresponding to all or a part of the OFDMA traffic channels into
an access signal. The subscriber knows, prior to encoding,
the OFDMA channels for which to encode information. The
access signal is transmitted to the base-station through one
or more access channels within a dedicated access time slot,
such as with signal 402. Each access channel may consist of
all OFDMA traffic channels or a subset of OFDMA traffic
channels across the spectrum.
During this processing, other standby subscribers, e.g.,
subscriber #j, performs the same operations and may transmit another access signal, such as signal 403, through the
same or different access channel to the base-station. In some
cases, multiple access signals may collide on a particular
access channel. The base-station may resolve both access
signals using multi-user detection techniques well-known in
the art.
Once the access signal(s) are received, the base-station
estimates the uplink and downlink SINRs corresponding to
the OFDMA traffic channels being allocated for accessing
subscribers. If antenna arrays are employed at the basestation, accessing signals are also used for estimating uplink
and downlink broadband spatial gains, which determine the
uplink and downlink SINRs of OFDMA traffic channels.
The base-station then performs joint traffic channel
assignment, based on subscribers' channel and noise-plusinterference characteristics, and broadband spatial gains
provided that spatially separated antennas are employed at
the base-station. Other factors, such as, for example, subscribers' data rates, time-off limitations, waiting time, buffer
status, service type (voice, video, email, multi-media) and
other QoS requirements, may be considered in conjunction
with the channel and noise-plus-interference characteristics
to perform joint traffic channel assignment. The decision is
sent back, using signal 404, for example, to accessing and/or
ongoing subscriber(s) at a predetermined time to initial or
update wireless links. The determination of when to update
the information and repeat the allocation process depends
upon the mobility of the subscribers. For subscribers that
move frequently, reallocation may occur more often.
FIG. 5 is a block diagram of one embodiment of a
subscriber. Referring to FIG. 5, subscriber 500 comprises a
receiving antenna (array) and RF receivers 501, storage 502
for received base-band sonnding signal, an OFDM demodulator 503, a channel and noise-plus-interference estimator
504, a subscriber information register 506, an encoder 505,
a serial-to-parallel converter 507, an OFDM modulator 508,
RF transmitter( s) and transmission antennae s) 509.

Protocols for Centralized Channel Assignment
In one embodiment, the broadband channel characteristics
of each subscriber, as well as the noise-plus-interference
experienced across all OFDMA traffic channels, are known
to the base-station for joint uplink and downlink traffic
channel allocation. Secondly, if the spatial diversity afforded
by base-station antenna array is to be exploited at the
base-station, as done in almost all wireless networks, an
additional information exchange is required to estimate the
downlink channel characteristics associated with each subscriber. This is because before a wireless link is established,
only sounding signals transmitted onmi-directional from the
base-station can be detected by stand by subscribers. Channel characteristics or signal strengths estimated at the subscriber based on the sonnding signals do not reflect the
actual downlink channel conditions after spatial processing
is applied. Thirdly, each subscriber is subject to interference
from neighboring cells in a multi-cell setup. To increase, and
potentially maximize, the spectral efficiency for ever-changing traffic, coordination among base-stations and subscribers
is considered in traffic channel assignment.
FIG. 2 illustrates that the channel gain for different
channels changes based on the sub carrier being examined.
For example, while channels 1 and 2 has good gain at certain
subchannels, they also have poorer gains at others. The
present invention makes intelligent decisions about channel
assignments for multi-users so that multiple channels are
jointly allocated to multiple subscribers based on which
channels have desirable characteristics (e.g., higher gains,
lower interference, etc.) for each particular subscriber. FIG.
3 illustrates the performance of multiple sub carriers (channels) for two users, user 1 and user 2, and the resulting
allocation for those users based, at least in part, on the
channel conditions.

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Sounding signals received at receiving antenna(s)501A
are down-converted to base-band by RF receiver(s) 501B.
The down-converted sounding signals are stored in storage
502 for processing.
OFDM demodulator 503 demodulates data infonnation
embedded in the sounding signals. The demodulated information, along with the raw sounding signals stored, is
forwarded to channel and noise-plus-interference estimator
504 for channel and noise-plus-interference estimation. Estimator 504 formats the estimated infonnation into, for
example, the signal-to-noise-plus-interference ratios, and
together with the subscriber's infonnation (e.g., subscriber
ID infonnation; requested data rate, etc.) from the subscriber
information register 506, forwards the information to
encoder 505.
Encoder 505 encodes the infonnation and passes it to a
serial to parallel converter 507, which converts the data from
serial to parallel. The parallel data is then sent to OFDM
modulator 508, which modulates the data. The output of
OFDM modulator 508 forms an encoded accessing signal,
which is then up-converted by the RF transmitter(s) 509A
and transmitted out through the transmission antenna (array)
509B.
FIG. 6 is a block diagram of one embodiment of a
base-station. Referring to FIG. 6, base-station 600 includes
a receiving antenna (array) 601, storage 602 for uplink
accessing signals, an OFDM demodulator 603, a broadband
channel and noise-plus-interference estimator 604, a traffic
channel register and storage 606 for estimated channel and
noise-plus-interference characteristics, a joint traffic channel
allocator 605A, a feedback signal generator 605B, a downlink data stream interface 608, an OFDM modulator 607, a
RF transmitter (array) 609B and a transmitting antenna
(array) 609A.
Uplink signals from subscribers, including accessing signals, are received by receiving antenna (array) 609A and
down-converted to base-band by RF receiver(s) 609B. The
accessing signals received during the dedicated access time
slot are stored in storage 602. The row accessing signals are
fed to a broadband channel and noise-plus-interference
estimator 604, which, together with OFDM demodulator
603, estimates the broadband channel and noise-plus-interference characteristics and decodes the feedback infonnation encoded in the accessing signals. In one embodiment,
the feedback infonnation includes, but is not limited to,
downlink channel and noise-plus-interference characteristics under onmi-directional transmission and the data rate
requests and other QoS requirements of accessing subscribers. Such infonnation, along with that for ongoing subscribers stored in the traffic channel register and broadband
channel infonnation storage 606, as forwarded to joint traffic
channel allocator 605A for channel assignment. The results
are coded into feedback message signals by feedback signal
generator 605B. The feedback signals intended for accessing
subscriber, and a portion or all ongoing subscribers, are
mixed with downlink data streams for data designated for
other subscribers from the downlink data streams interface
608 and modulated using OFDM modulator 607. The mixing may occur prior to OFDM modulator 607 using a
mixing. The modulated OFDM signal is up-converted by RF
transmitter(s) 609B and transmitted through antenna (array)
609A.
In one embodiment, a sonnding signal generator 630 is
also included in the base-station FIG. 6.

Uplink and Downlink Broadband Spatial Channel Estimation
Spatial processing (e.g., beamforming) using multiple
antennas is among the most efficient ways to combat interference in wireless commnnications. When combined properly with joint traffic loading, uplink and downlink beamforming can significantly increase the capacity of an
OFDMA network. To achieve such a gain, however, it is
essential that the base-station has knowledge of "broadband"
uplink and downlink spatial channel characteristics before
perfonning spatially selective beamfonning.
Before a link is established for a subscriber, the location
or the spatial channel of the subscriber is nnknown to the
base-station, sonnding signals can be broadcast onmi-directionally from the base-station. Once the location of a subscriber has been determined, then the base-station may use
beamforming to communicate with the subscriber. The difference between an omni-directional beam pattern and a
spatial selective beam pattern is illustrated in FIG. 7. Referring to FIG. 7, an onmi-directional sounding signal beam
pattern 701 is shown being broadcast from base-station
antenna array 710. Once target subscriber 712 communicates with the base-station, the base-station, using spatially
selective beamfonning beam pattern 702, which is created in
a manner well-known in the art, may detennine the channel
characteristics and commnnicate thereafter with subscriber
712 (using beamforming). For this reason, OFDMA traffic
channel conditions detennined at the subscriber based on
sounding signals does not reflect the actual traffic channel
conditions if downlink beamfonning is perfonned. In other
words, a "bad" downlink traffic channel for omni-directional
sounding signals may very well be a "good" channel for real
data traffic with downlink beamfonning.
In one embodiment, a base-station detennines the downlink traffic channel conditions under spatial beamforming.
Such a base-station may perfonn the following operations.
First, a standby subscriber listens to the omni-directional
sounding signal and detennines the signal to noise-plusinterference ratio for each of the OFDMA traffic channels:
SINR_i, i=l, ... , K,

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where SINR_i is the signal to noise-plus-interference ratio
on the ith traffic channel, and K is the total number of traffic
channels allowed by the base-station.
Once paged or when the standby subscriber has packets to
transmit, the subscriber sends back the measured SINR
information to the base-station though one of the access
channels. A broadband spatial channel estimator at the
base-station estimates the uplink spatial channels:
(a_Ii, a_2i, ... , a_Mi) , i=l, ... , K
where a_ml is the antenna response ofthe ith traffic channel
from the mth antenna, M is the total number of antenna
elements.
Based on the spatial channel estimated, the base-station
predicts the "additional" spatial gain of beamfonning over
omni-directional transmission as, for example,
G_i=lO log 1O(la_lil'2+la_2il'2+ ... +la_Mil'2)/la_Ii+
a_2i+ ... +a_Mil'2[dBJ, i=l, ... , K.
Many other approaches can be used to estimate the spatial
processing gains over omni-directional transmission. Once
G_i is calculated, the expected SINR_i over traffic channel
i with downlink beamfonning can be determined as
SINR_i,new=SINR_i+G_i, i=l, ... , K
The above information is used by the traffic channel
allocator of the base-station to detennine a channel assignment.

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FIG. S illustrates and frame structure of a time-division
duplex network where the above operations are performed
before traffic channel assignment. Referring to FIG. S,
initially, onmi-directional sounding signals are transmitted
from the base-station (SOl). Downlink data streams are
delivered in a spatially selectively fashion to ongoing subscribers using downlink beamforming (S02). Thus, a portion
of the downstream traffic (e.g., 5%, 10%, etc.) is dedicated
to the transfer of information to facilitate the channel
allocation process for new subscribers. Accessing subscribers listen to the sonnding signal and send back the measured
SINR_i of all available traffic channels through a dedicated
access channel drawing a random access time period (S03).
The base-station estimates, based on the accessing signal
and feedback SINR information, e.g., the SINR for accessing subscribers with downlink beamforming. After rate
negotiation and initial hand-shaking, the accessing subscribers are assigned traffic channels through which data streams
are transmitted with uplink and downlink beamforming. The
uplink transfer of information (S04) represents the remaining portion of the uplink time window.

from the plurality of subscribers and OFDMA channel
information collected from at least one of the other base
stations, and in collaboration with said at least one
other base station to provide joint OFDMA channel
allocation to multiple ones of said plurality of subscribers.
2. The network defined in claim 1 wherein the logic
calculates spatial gains of uplink and downlink channels
based on responses of spatially separated receivers at the
base station.
3. The network defined in claim 1 wherein the feedback
information comprises channel fading information and noise
and interference levels for each of the plurality of candidate
OFDMA traffic channels.
4. The network defined in claim 1 wherein the plurality of
subscribers send the feedback information in response to a
sounding signal from each of one or more of the base
stations.
5. The network defined in claim 1 wherein said logic
selects a combination of modulation and coding schemes
based on the SINR of the selected traffic channel for each
accessing subscriber.
6. The network defined in claim 1 wherein the logic
comprises medium access control (MAC) logic.
7. A method comprising:
sending sonnding signals to a plurality of subscribers
from a plurality of base stations;
receiving, at each base station, channel condition information for a plurality of OFDMA traffic channels from
at least one of said subscribers and at least one other
base station; and
performing OFDMA multi-user traffic channel assignment to assign OFDMA traffic channels from the
plurality ofOFDMA traffic channels to the plurality of
subscribers, based on the OFDMA channel condition
information received from at least one of said subscribers and at least one other of said base stations and
estimated spatial gains for the uplink and downlink
signals for the plurality of subscribers, and in collaboration with said at least one other of said base stations
to provide joint OFDMA channel allocation to multiple
ones of said plurality of subscribers.
S. The method defined in claim 7 wherein the channel
condition information comprises information regarding estimated channel gains and channel interference for the plurality of OFDMA traffic channels.
9. The method defined in claim 7 wherein performing
traffic channel assignment is based on channel conditions
between one or more antennas at a base station and one or
more antennas at subscriber locations.
10. The method defined in claim 7 further comprising
estimating spatial gains for uplink and downlink signals.
11. The method defined in claim 10 further comprising
estimating signal-to-noise-plus-interference rates (SINRs)
for the uplink and downlink signals, and wherein performing
channel assignment is based on the SINRs for the uplink and
downlink signals.
12. The method defined in claim 11 wherein estimating
SINRs for the uplink and downlink signals is performed on
all OFDMA traffic channels for all active and accessing
subscribers.
13. The method defined in claim 11 wherein performing
channel assignment is based on quality of service (QoS)
requirements.
14. The method defined in claim 13 wherein the QoS
requirements include one or more of the following: data rate,
time-out, bit error rate, and writing time.

Protocols for Multiple Base-Stations
One application of joint traffic channel assignment is
multi-cell OFDMA networks. In such setup, the network
capacity can benefit significantly from dynamic loading/
adaptive modulation that increases, and potentially maximizes, the throughput in any given situation. Essentially,
multiple cells can share the overall spectral resources and
provide "on-demand" traffic channel allocation in a dynamic
network.
To enable joint multi-cell traffic channel allocation, the
base-station within each cell performs uplink and downlink
traffic channel estimation using the protocols and schemes
described above. In addition, as illustrated in FIG. 9, neighboring base-stations exchange such information through the
base-station controller, or dedicated links between basestations. Traffic channel conditions, assignment tables, as
well as QoS requirements of all accessing subscribers of
neighboring cells, may be accounted for in performing traffic
channel assignment. For example, if two base stations know
two subscribers near to each other in different cells can be
allocated any of channels 1-10 (there are channels with high
gain for these subscribers), then one base station may
allocate channels 1-5 to its subscriber and the other base
station may allocate channels 6-10 to its subscriber.
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 nnderstood that any particular embodi ment 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.
We claim:
1. A cellular network comprising:
a plurality of subscribers each of said subscribers communicating with one base station of a plurality of base
stations using orthogonal frequency division multiple
access (OFDMA);
each of said base stations having logic to coordinate
multiple-access and information exchange between the
base station and the plurality of subscribers, the logic
selecting a set of OFDMA traffic channels from a
plurality of candidate OFDMA traffic channels, based
on feedback OFDMA channel information collected

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15. The method defined in claim 13 wherein performing
channel assignment is based on priority.
16. The method defined in claim 7 further comprising
determining a combination of coding and modulation
schemes when performing channel assignments.
17. The method defined in claim 7 wherein performing
traffic channel assignments comprises said plurality of base
stations coordinating to perform the traffic channel assignment.
18. The method defined in claim 17 wherein each of the
plurality of base stations is within a cell and estimates SINRs
for uplink and downlink signals across all OFDMA traffic
channels for accessing subscribers.
19. The method defined in claim 18 when the plurality of
base stations perform estimates for active and accessing
subscribers.
20. The method defined in claim 7 wherein the sounding
signal is onmi-directional.
21. The method defined in claim 7 wherein estimating
spatial gains for uplink and downlink signals comprises:
estimating broadband spatial channels across the plurality
of OFDMA traffic channels for each accessing subscriber;
determining the spatial processing gains for uplink and
downlink signals on each of the plurality of OFDMA
traffic channels;
predicting signal-to-noise-plus-interference ratio (SINR)
for uplink and downlink transmission with spatial processing over each of available OFDMA traffic channels
by adding the spatial processing gain to downlink
signal strength feedback from one or more subscribers.
22. A method comprising:
receiving, at one of a plurality of base stations, OFDMA
channel characteristics and noise-plus-interference
information measured at spatially distributed subscribers;
receiving OFDMA channel characteristics information for
at least one other base station; and
assigning OFDMA traffic channels for an OFDMA network, based on received OFDMA channel characteristics and noise-plus-interference information measured
at the spatially distributed subscribers and the OFDMA
channel characteristics information from the at least
one other base station, and in collaboration with at least
said one other base station to provide joint OFDMA
channel allocation to multiple ones of said subscribers.
23. The method defined in claim 22 wherein assigning
traffic channels is performed for the OFDMA network that
uses spatial multiplexing.
24. A method comprising:
each of a plurality of subscribers estimating channel gains
and noise-plus-interference levels of a set of OFDMA
traffic channels in response to a sounding signal;
the plurality of subscribers transmitting to a first base
station measured OFDMA channel and noise-plusinterference information;
receiving, by one of said subscribers, an allocation of one
or more OFDMA traffic channels allocated, in response
to the measured channel and noise-plus-interference
information and OFDMA channel information from a
plurality of base stations including a second base
station other than the first base station, and in collaboration with at least said second base station to provide
joint OFDMA channel allocation to multiple ones of
said plurality of subscribers;

at least one of the plurality of subscribers transmitting
packets using one or more allocated OFDMA traffic
channels.
25. The method defined in claim 24 wherein the plurality
of subscribers transmit the measured channel and noiseplus-interference information on pre-allocated channels.
26. The method defined in claim 24 wherein the plurality
of subscribers transmits the measured channel and noiseplus-interference information when paged or when one or
more of the plurality of subscribers have a packet to transmit
to the first base station.
27. An apparatus comprising:
an OFDMA channel and noise-plus-interference estimator;
an access signal generator coupled to the estimator;
an OFDM modem coupled to the generator; and
a radio frequency transmitter to transmit information on
OFDMA traffic channels jointly allocated to a plurality
of subscribers through a collaborative OFDMA channel
assignment among multiple base stations.
28. The apparatus defined in claim 27 wherein the estimator estimates channel gains and noise-plus-interference
levels in a pre-determined set of traffic channels.
29. The apparatus defined in claim 28 wherein the generator encodes channel and noise-plus-interference information to form an access signal.
30. The apparatus defined in claim 29 wherein the OFDM
modem modulates the access signal and transmits a modulated version of the access signal through an access channel.
31. The apparatus defined in claim 30 wherein the access
channel comprises at least a subset of all traffic channels
during and access time slot.
32. An apparatus comprising:
at least one spatially separated transceiver;
an access signal detector and demodulator coupled to the
at least one spatially separated transceivers;
a spatial channel and spatial gain estimator;
an uplink and downlink signal-to-noise-plus-interference
estimator;
a multi-user traffic channel allocator coupled to said
estimators to determine OFDMA channel assignment
based on broadband spatial channel estimates and measured OFDMA channel and noise-plus-interference
information feedback from subscribers and from at
least two base stations to provide joint OFDM channel
allocation to multiple subscribers; and
an OFDM modem coupled to the allocator.
33. The apparatus defined in claim 32 wherein the allocator determines traffic channel assignment and a code and
modulation combination for each accessing subscriber, and
the OFDM modem modulates the traffic channel assignment
and transmits a modulated version of the traffic channel
assignment to at least one subscriber.
34. The apparatus defined in claim 32 wherein the broadband spatial channel estimates comprise the broadband
spatial channel between a base station and each accessing
subscriber.
35. The apparatus defined in 32 wherein the access signal
detector and demodulator detects access signals transmitted
by subscribers and demodulates the measured channel and
noise-plus-interference information feedback from subscribers.

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