Adaptix, Inc. v. Apple, Inc. et al

Filing 1

COMPLAINT against Apple, Inc., Cellco Partnership ( Filing fee $ 350 receipt number 0540-3484567.), filed by Adaptix, Inc.. (Attachments: # 1 Exhibit A - US 7,454,212, # 2 Exhibit B - US 6,947,748, # 3 Civil Cover Sheet)(Hill, Jack)

EXHIBIT B

111111111111111111111111111111111111111111111111111111111111111111111111111
US00694 7748B2

(54)

(75)

United States Patent

(10)

Li et ai.

(12)

(45)

OFDMA WITH ADAPTIVE SUBCARRIERCLUSTER CONFIGURATION AND
SELECTIVE LOADING
Inventors: Xiaodong Li, Bellevue, WA (US); Hui
Liu, Sammamish, WA (US); Kemin Li,
Bellevue, WA (US); Wenzhong Zhang,
Bellevue, WA (US)

FOREIGN PATENT DOCUMENTS

DE
DE
EP
EP
EP
EP
FR

GB
(73)

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

( *)

Notice:

(21)

Filed:

19800953
19800953
0869647
0926912
0929202
0999658
2777 407
2209858
06029922
WO 98/16077
WO 98/30047
WO 02 49305

C1
C1
A2
A2
A1
A1
A

7/1999

* 7/1999

........... H04B/7/005

10/1998
6/1999
7/1999
5/2000
10/1999
8/1997
2/1994
4/1998
7/1998
6/2002

Appl. No.: 09/738,086

(22)

Patent No.:
US 6,947,748 B2
Date of Patent:
Sep.20,200S

Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 765 days.

JP
WO
WO
WO

A2
A1
A2

OTHER PUBLICATIONS
Dec. 15, 2000
Prior Publication Data

(65)

US 2002/0119781 A1 Aug. 29, 2002

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(52)
(58)

Int. CI? ............................ H04Q 7/20; H04J 11/00
U.S. CI. ....................... 455/450; 455/447; 455/453;
455/455; 455/464; 370/208
Field of Search ................................. 455/447-453,
455/456.5, 456.6, 509, 512, 513, 524-526,
62, 63.1, 455, 463, 464, 168.1, 176.1, 179.1,
188.1, 550.1, 553; 370/311, 347, 480, 203-206,
208, 210, 329; 375/132
References Cited

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Emami

(Continued)

Vittoria Mignone et al. "CD3-0FDM: A Novel Demodulation Scheme for Fixed and Mobile Receives," IEEE Transactions on Communications, Sep. 1996, vol. 44, No.9.
Bender et aI., CDMA/HDR: A Bandwidth-Efficient HighSpeed Wireless Data Service for Nomadic Users, IEEE
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(Continued)

Primary Examiner-William Trost
Assistant Examiner-Meless Zewdu
(74) Attorney, Agent, or Firm-Fulbright & Jaworski LLP
ABSTRACT

(57)

A method and apparatus for sub carrier selection for systems
is described. In one embodiment, the system employs
orthogonal frequency division multiple access (OFDMA). In
one embodiment, a method for subcarrier selection comprises each of multiple subscribers measuring channel and
interference information for subcarriers based on pilot symbols received from a base station, at least one of subscribers
selecting a set of candidate subcarriers, providing feedback
information on the set of candidate subcarriers to the base
station, and the one subscriber receiving an indication of
subcarriers of the set of subcarriers selected by the base
station for use by the one subscriber.
23 Claims, 7 Drawing Sheets

101

102

103

104

105

US 6,947,748 B2
Page 2

U.S. PATENT DOCUMENTS
5,867,478
5,886,988
5,887,245
5,909,436
5,914,933
5,933,421
5,956,642
5,973,642
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6,131,016
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6,307,851
6,327,472
6,330,460
6,366,195
6,377,632
6,377,636
6,449,246
6,473,467
6,477,158
6,545,997
6,657,949
2003/0067890
2003/0169681
2003/0169824

A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
B1
B1
B1
B1
B1
B1
B1
B1
B1
B1
B1
B1
B1
A1
A1
A1

*
*
*
*
*

2/1999
3/1999
3/1999
6/1999
6/1999
8/1999
9/1999
10/1999
11/1999
12/1999
12/1999
2/2000
3/2000
4/2000
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12/2001
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455/560

375/267
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375/346

OlliER PUBLICATIONS
Frullone et aI., PRMA Performance 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 Services: 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).
Bender, et al. "CDMA/HDR: A Bandwidth Efficient HighSpeed Wireless Data Service for Nomadic Users," IEEE
Communications Magazine, Jul. 2000, pp. 70-87.
Frullone, et aI., "PRMA Performance in Cellular Environments with Self-Adaptive Channel Allocation Strategies,"
IEEE Transactions on Vehicular Technology, vol. 45, No.4,
Nov. 1996,pp. 657-665.
Farsakh, C. et aI., "Maximizing the SDMA Mobile Radio
Capacity Increase by DOA Sensitive Channel Allocation",
Wireless Personal Communications, Kluwer Academic Publishers, NL, vol. 11, No.1, Oct. 1999, pp. 63-76,
XP000835062, ISSN: 0929-6212.
Wong, c.Y, et aI., Multiuser OFDM With Adaptive Subcarriel; Bit, and Power Allocation, IEEE Journal on Selected
Areas in Communications, Oct. 1999, IEEE Inc., New York,
USA, vol. 17, Nr.1O,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. 1/2, 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:
0-7803-6463-5.
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. 48 th 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
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E77-B, NR. 3, Mar. 1994, pp. 396-402, XP0004510l4,
ISSN: 0916-8516.

* cited by examiner

u.s. Patent

Sep.20,200S

Sheet 1 of 7

US 6,947,748 B2

Subcarrier

101

FIG. 1A

f

PiiotOFDM
Symbols ~--t==
201

Occupied Clusters
a. Cell A

(A)

b. Cell B

(8)
f
201~~

c. Cell C

FIG. 2

(C)

u.s. Patent

Sep.20,200S

Sheet 2 of 7

(

US 6,947,748 B2

Begin)

Periodically Broadcast Pilot
OFDM Symbols to Subscribers

Subscriber(s) Continuously Monitors
Pilot Symbols/Measures SINR and/or
Other Parameters

~~~
Needed
?

v 101

h,..,

102

Each Subscriber Selects One or More r- 103
Clusters for Each Base Station

~

oor

Base Station Selects One or More
Clusters for Each Subscriber

--

104

,
Base Station Notifies the Subscriber
Regarding Cluster Allocation

FIG.1B

t- 105

u.s. Patent

Sep.20,200S

303

302

Request Selected
Clusters and Coding!
Modulation Rates

FIG. 3

401

Per-cluster SINR
Estimation in
Pilot Periods

402

Per-cluster
Power Calculation
in Pilot Periods

+

Per-cluster
Power Calculation
in Data Periods

Cluster Orderingl
Selection Based on
404
SINR and Power
Difference

403

502 ~

Cluster
ID1

304

Cluster Ordering
and Rate
Prediction

Trafficll nterference
Analysis in Date
Periods

I,

US 6,947,748 B2

301

Channelll nterference
Estimation in Pilot
Periods

501

Sheet 3 of 7

Request Selected
Clusters and Coding!
Modulation Rates

FIG.4

503 ~
Cluster
ID2

SINR1

406

504 ' .

504'~
SINR2

504

'---..

Cluster
ID3

SINR3

a a'a

FIG. 5
Group 3

Group 4

/~

It \.

\.

./

----.... ( , -

Group 1

--

~'\

'"

"""

-

__

"-

.-/
~r--

Group 2

FIG. 6

f

../

u.s. Patent

Group
101

SINR1

Sep.20,200S

SINR2

SINR3

Sheet 4 of 7

Group
102

FIG.7

FIG. 8

SINR1

US 6,947,748 B2

SINR2

SINR3

•••

u.s. Patent

Sep.20,200S

Sheet 5 of 7

US 6,947,748 B2

1-8: Diverse Clusters
9-16: Plain Clusters

1

9

f
,

10

11

It

12

13

14 1

15 16

a. CeliA
f

~

1

9

10

1

IIII
ITI

11

"

1

13

14

P1

15 . 16

b.CeliB

..f
1

lit

12

9

10

1

11

12

1 13

14

15

16

c. CeliC

FIG.9

f

Time 1
Time 2
Time 3
Time 4
a.CeiIA

b. Cell B

FIG. 10

f

u.s. Patent

Sep.20,200S

Sheet 6 of 7

Channel/Interference
Variation Detection

US 6,947,748 B2

1101

No

Yes

1104

1103
Select Diversity

Select Coherence

Clusters

Clusters

FIG. 11

f

--1

111
1 10 1

111 12 1
1

Ir

a. CeliA

FIG. 12

111 14 1
1

111

16

u.s. Patent

Sep.20,200S

Sheet 7 of 7

US 6,947,748 B2

~

J~

~

J

J

d,

User Data Buffer Information
1311

,I.

,I.

~

~

User 1 - N

\
Multi-user Data
Buffer

-

1301)

(
Admission Control
1310

Ir

Cluster Allocation and
Load Scheduling
Controller

r--... 1302

h

~

A'

,.

j~

,

.Ir

,

,

,if

~

.
-

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Multiplexer
j~

,

,

Ir

,

.It

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Transmission and
Receiving Buffer

SINRlRate
..../' Indices
1313

,~

"

7

~

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,.

CI uster 1 - M

V

,~

,

A

j~

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,

,

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,

OFDM Transceiver

r--- 1305

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Cluster Allocation
1312

OFDM Signal
•

FIG. 13

US 6,947,748 B2
1

2

OFDMA WITH ADAPTIVE SUBCARRIERCLUSTER CONFIGURATION AND
SELECTIVE LOADING

existing subscribers is dropped off the network or a new
subscribers is added onto the network. This is often impractical in real wireless system, mainly due to the bandwidth
cost for updating the subscriber information and the computation cost for the joint optimization.

FIELD OF THE INVENTION
The invention relates to the field of wireless communications; more particularly, the invention relates to multi -cell,
multi-subscriber wireless systems using orthogonal frequency division multiplexing (OFDM).

SUMMARY OF THE INVENTION
10

BACKGROUND OF THE INVENTION
Orthogonal frequency division multiplexing (OFDM) is
an efficient modulation scheme for signal transmission over
frequency-selective channels. In OFDM, a wide bandwidth
is divided into multiple narrow-band subcarriers, which are
arranged to be orthogonal with each other. The signals
modulated on the subcarriers are transmitted in parallel. For

~~~~::~~~il~e~~!:~~:, t~i~~~~h~~oa:~ ~:~~~~~~

:o:e
Division Multiplexing," IEEE Trans. Commun., vol. COM33, no. 7, July 1985, pp. 665-75; Chuang and Sollenberger,
"Beyond 3G: Wideband Wireless Data Access Based on

~~~f':n:n~a~r~i:~\T;tC;;: ~~i~~:~ni;_1;~~u~0~~~.One way to use OFDM to support multiple access for
multiple subscribers is through time division multiple access
(TDMA), in which each subscriber uses all the subcarriers
within its assigned time slots. Orthogonal frequency division
multiple access (OFDMA) is another method for multiple
access, using the basic format of OFDM. In OFDMA,
multiple subscribers simultaneously use different
subcarriers, in a fashion similar to frequency division multiple access (FDMA). For more information, see Sari and
Karam, "Orthogonal Frequency-Division Multiple Access
and its Application to CATV Networks," European Transactions on Telecommunications, Vol. 9 (6), pp. 507-516,
November/December 1998 and Nogueroles, Bossert,
Donder, and Zyablov, "Improved Performance of a Random
OFDMA Mobile Communication System,", Proceedings of
IEEE VTC'98, pp. 2502-2506.
Multipath causes frequency-selective fading. The channel
gains are different for different subcarriers. Furthermore, the
channels are typically uncorrelated for different subscribers.
The sub carriers that are in deep fade for one subscriber may
provide high channel gains for another subscriber.
Therefore, it is advantageous in an OFDMA system to
adaptively allocate the sub carriers to subscribers so that each
subscriber enjoys a high channel gain. For more
information, see Wong et aI., "Multiuser OFDM with Adaptive Subcarrier, Bit and Power Allocation," IEEE J. Select.
Areas Commun., Vol. 17(10), pp. 1747-1758, October 1999.
Within one cell, the subscribers can be coordinated to
have different subcarriers in OFDMA. The signals for different subscribers can be made orthogonal and there is little
intracell interference. However, with aggressive frequency
reuse plan, e.g., the same spectrum is used for multiple
neighboring cells, the problem of intercell interference
arises. It is clear that the intercell interference in an OFDMA
system is also frequency selective and it is advantageous to
adaptively allocate the subcarriers so as to mitigate the effect
of intercell interference.
One approach to sub carrier allocation for OFDMA is a
joint optimization operation, not only requiring the activity
and channel knowledge of all the subscribers in all the cells,
but also requiring frequent rescheduling every time an

15

20

25

30

35

40

45

50

55

A method and apparatus for subcarrier selection for
systems is described. In one embodiment, the system
employs orthogonal frequency division multiple access
(OFDMA). In one embodiment, a method for subcarrier
selection comprises a subscriber measuring channel and
interference information for subcarriers based on pilot symboIs received from a base station, the subscriber selecting a
set of candidate subcarriers, providing feedback information
on the set of candidate subcarriers to the base station, and
receiving an indication of subcarriers of the set of subcarriers selected by the base station for use by the subscriber.
BRIEF DESCRIPTION OF THE DRAWINGS
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. 1A illustrates subcarriers and clusters.
FIG. 1B is a flow diagram of one embodiment of a process
for allocating subcarriers.
FIG. 2 illustrates time and frequency grid of OFDM
symbols, pilots and clusters.
FIG. 3 illustrates subscriber processing.
FIG. 4 illustrates one example of FIG. 3.
FIG. 5 illustrates one embodiment of a format for arbitrary cluster feedback.
FIG. 6 illustrates one embodiment of a partition the
clusters into groups.
FIG. 7 illustrates one embodiment of a feedback format
for group-based cluster allocation.
FIG. 8 illustrates frequency reuse and interference in a
multi-cell, multi-sector network.
FIG. 9 illustrates different cluster formats for coherence
clusters and diversity clusters.
FIG. 10 illustrates diversity clusters with subcarrier hopping.
FIG. 11 illustrates intelligent switching between diversity
clusters and coherence clusters depending on subscribers
mobility.
FIG. 12 illustrates one embodiment of a reconfiguration
of cluster classification.
FIG. 13 illustrates one embodiment of a base station.
DETAILED DESCRIPTION OF THE PRESENT
INVENTION

60

65

A distributed, reduced-complexity approach for subcarrier allocation is described. The techniques disclosed herein
are described using OFDMA (clusters) as an example.
However, they are not limited to OFDMA-based systems.
The techniques apply to multi-carrier systems in general,
where, for example, a carrier can be a cluster in OFDMA, a
spreading code in CDMA, an antenna beam in SDMA
(space-division multiple access), etc. In one embodiment,
subcarrier allocation is performed in each cell separately.

US 6,947,748 B2

3

4

Within each cell, the allocation for individual subscribers
(e.g., mobiles) is also made progressively as each new
subscriber is added to the system as opposed to joint
allocation for subscribers within each cell in which allocation decisions are made taking into account all subscribers in
a cell for each allocation.
For downlink channels, each subscriber first measures the
channel and interference information for all the subcarriers
and then selects multiple subcarriers with good performance
(e.g., a high signal-to-interference plus noise ratio (SINR))
and feeds back the information on these candidate subcarriers to the base station. The feedback may comprise channel
and interference information (e.g., signal-to-interferenceplus-noise-ratio information) on all subcarriers or just a
portion of subcarriers. In case of providing information on
only a portion of the subcarriers, a subscriber may provide
a list of subcarriers ordered starting with those subcarriers
which the subscriber desires to use, usually because their
performance is good or better than that of other subcarriers.
Upon receiving the information from the subscriber, the
base station further selects the subcarriers among the
candidates, utilizing additional information available at the
base station, e.g., the traffic load information on each
subcarrier, amount of traffic requests queued at the base
station for each frequency band, whether frequency bands
are overused, and/or how long a subscriber has been waiting
to send information. In one embodiment, the subcarrier
loading information of neighboring cells can also be
exchanged between base stations. The base stations can use
this information in subcarrier allocation to reduce inter-cell
interference.
In one embodiment, the selection by the base station of
the channels to allocate, based on the feedback, results in the
selection of coding/modulation rates. Such coding/
modulation rates may be specified by the subscriber when
specifying subcarriers that it finds favorable to use. For
example, if the SINR is less than a certain threshold (e.g., 12
dB), quadrature phase shift keying (QPSK) modulation is
used; otherwise, 16 quadrature amplitude modulation
(QAM) is used. Then the base station informs the subscribers about the subcarrier allocation and the coding/
modulation rates to use.
In one embodiment, the feedback information for downlink sub carrier allocation is transmitted to the base station
through the uplink access channel, which occurs in a short
period every transmission time slot, e.g., 400 microseconds
in every lO-millisecond time slot. In one embodiment, the
access channel occupies the entire frequency bandwidth.
Then the base station can collect the uplink SINR of each
subcarrier directly from the access channel. The SINR as
well as the traffic load information on the uplink subcarriers
are used for uplink subcarrier allocation.
For either direction, the base station makes the final
decision of sub carrier allocation for each subscriber.
In the following description, a procedure of selective
subcarrier allocation is also disclosed, including methods of
channel and interference sensing, methods of information
feedback from the subscribers to the base station, and
algorithms used by the base station for sub carrier selections.
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, terms, numbers, or
the like.
It should be bome 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.
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.
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.
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 machinereadable 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.

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US 6,947,748 B2
5

6

Subcarrier Clustering
The techniques described herein are directed to subcarrier
allocation for data traffic channels. In a cellular system, there
are typically other channels, pre-allocated for the exchange
of control information and other purposes. These channels
often include down link and up link control channels, uplink
access channels, and time and frequency synchronization
channels.
FIG. 1Aillustrates multiple subcarriers, such as subcarrier
101, and cluster 102. A cluster, such as cluster 102, is defined
as a logical unit that contains at least one physical subcarrier,
as shown in FIG. 1A. A cluster can contain consecutive or
disjoint subcarriers. The mapping between a cluster and its
subcarriers can be fixed or reconfigurable. In the latter case,
the base station informs the subscribers when the clusters are
redefined. In one embodiment, the frequency spectrum
includes 512 subcarriers and each cluster includes four
consecutive subcarriers, thereby resulting in 128 clusters.
An Exemplary Subcarrier/Cluster Allocation Procedure
FIG. 1B is a flow diagram of one embodiment of a process
for allocation clusters to subscribers. The process is performed by processing logic that may comprise hardware
(e.g., dedicated logic, circuitry, etc.), software (such as that
which runs on, for example, a general purpose computer
system or dedicated machine), or a combination of both.
Referring to FIG. 1B, each base station periodically
broadcasts pilot OFDM symbols to every subscriber within
its cell (or sector) (processing block 101). The pilot symbols,
often referred to as a sounding sequence or signal, are
known to both the base station and the subscribers. In one
embodiment, each pilot symbol covers the entire OFDM
frequency bandwidth. The pilot symbols may be different for
different cells ( or sectors). The pilot symbols can serve
multiple purposes: time and frequency synchronization,
channel estimation and signal-to-interference/noise (SINR)
ratio measurement for cluster allocation.
Next, each subscriber continuously monitors the reception
of the pilot symbols and measures the SINR and/or other
parameters, including inter-cell interference and intra-cell
traffic, of each cluster (processing block 102). Based on this
information, each subscriber selects one or more clusters
with good performance (e.g., high SINR and low traffic
loading) relative to each other and feeds back the information on these candidate clusters to the base station through
predefined uplink access channels (processing block 103).
For example, SINR values higher than 10 dB may indicate
good performance. Likewise, a cluster utilization factor less
than 50% may be indicative of good performance. Each
subscriber selects the clusters with relatively better performance than others. The selection results in each subscriber
selecting clusters they would prefer to use based on the
measured parameters.
In one embodiment, each subscriber measures the SINR
of each subcarrier cluster and reports these SINR measurements to their base station through an access channel. The
SINR value may comprise the average of the SINR values
of each of the subcarriers in the cluster. Alternatively, the
SINR value for the cluster may be the worst SINR among
the SINR values of the subcarriers in the cluster. In still
another embodiment, a weighted averaging of SINR values
of the subcarriers in the cluster is used to generate an SINR
value for the cluster. This may be particularly useful in
diversity clusters where the weighting applied to the subcarriers may be different.
The feedback of information from each subscriber to the
base station contains a SINR value for each cluster and also
indicates the coding/modulation rate that the subscriber

desires to use. No cluster index is needed to indicate which
SINR value in the feedback corresponds to which cluster as
long as the order of information in the feedback is known to
the base station. In an alternative embodiment, the information in the feedback is ordered according to which clusters
have the best performance relative to each other for the
subscriber. In such a case, an index is needed to indicate to
which cluster the accompanying SINR value corresponds.
Upon receiving the feedback from a subscriber, the base
station further selects one or more clusters for the subscriber
among the candidates (processing block 104). The base
station may utilize additional information available at the
base station, e.g., the traffic load information on each
sub carrier, amount of traffic requests queued at the base
station for each frequency band, whether frequency bands
are overused, and how long a subscriber has been waiting to
send information. The subcarrier loading information of
neighboring cells can also be exchanged between base
stations. The base stations can use this information in
subcarrier allocation to reduce inter-cell interference.
After cluster selection, the base station notifies the subscriber about the cluster allocation through a downlink
common control channel or through a dedicated downlink
traffic channel if the connection to the subscriber has already
been established (processing block 105). In one
embodiment, the base station also informs the subscriber
about the appropriate modulation/coding rates.
Once the basic communication link is established, each
subscriber can continue to send the feedback to the base
station using a dedicated traffic channel (e.g., one or more
predefined uplink access channels).
In one embodiment, the base station allocates all the
clusters to be used by a subscriber at once. In an alternative
embodiment, the base station first allocates multiple clusters,
referred to herein as the basic clusters, to establish a data link
between the base station and the subscriber. The base station
then subsequently allocates more clusters, referred to herein
as the auxiliary clusters, to the subscriber to increase the
communication bandwidth. Higher priorities can be given to
the assignment of basic clusters and lower priorities may be
given to that of auxiliary clusters. For example, the base
station first ensures the assignment of the basic clusters to
the subscribers and then tries to satisfy further requests on
the auxiliary clusters from the subscribers. Alternatively, the
base station may assign auxiliary clusters to one or more
subscribers before allocating basic clusters to other subscribers. For example, a base station may allocate basic and
auxiliary clusters to one subscriber before allocating any
clusters to other subscribers. In one embodiment, the base
station allocates basic clusters to a new subscriber and then
determines if there are any other subscribers requesting
clusters. If not, then the base station allocates the auxiliary
clusters to that new subscriber.
From time to time, processing logic performs retraining
by repeating the process described above (processing block
106). The retraining may be performed periodically. This
retraining compensates for subscriber movement and any
changes in interference. In one embodiment, each subscriber
reports to the base station its updated selection of clusters
and their associated SINRs. Then the base station further
performs the reselection and informs the subscriber about
the new cluster allocation. Retraining can be initiated by the
base station, and in which case, the base station requests a
specific subscriber to report its updated cluster selection.
Retraining can also be initiated by the subscriber when it
observes channel deterioration.

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US 6,947,748 B2
7
Adaptive Modulation and Coding
In one embodiment, different modulation and coding rates
are used to support reliable transmission over channels with
different SINR. Signal spreading over multiple subcarriers
may also be used to improve the reliability at very low
SINR.
An example coding/modulation table is given below in
Table 1.

8

cells are broadcast at the same time, they will interfere with
each other (because they occupy the entire frequency band).
This collision of pilot symbols may be used to determine the
amount of interference as a worst case scenario. Therefore,
in one embodiment, the above SINR estimation using this
method is conservative in that the measured interference
level is the worst-case scenario, assuming that all the interference sources are on. Thus, the structure of pilot symbols
is such that it occupies the entire frequency band and causes
TABLE 1
10 collisions among different cells for use in detecting the worst
case SINR in packet transmission systems.
Scheme
Modulation
Code Rate
During data traffic periods, the subscribers can determine
liz
QPSK, lfg Spreading
the level of interference again. The data traffic periods are
liz
QPSK, 1/4 Spreading
used to estimate the intra-cell traffic as well as the inter-cell
liz
QPSK, 1/2 Spreading
2
15 interference level. Specifically, the power difference during
liz
QPSK
213
the pilot and traffic periods may be used to sense the
4
8PSK
16QAM
5
'14
(intra-cell) traffic loading and inter-cell interference to select
5;6
64QAM
the desirable clusters.
The interference level on certain clusters may be lower,
In the example above, 1fs spreading indicates that one 20 because these clusters may be unused in the neighboring
QPSK modulation symbol is repeated over eight subcarriers.
cells. For example, in cell A, with respect to cluster A there
The repetition/spreading may also be extended to the time
is less interference because cluster A is unused in cell B
domain. For example, one QPSK symbol can be repeated
(while it is used in cell C). Similarly, in cell A, cluster B will
over four subcarriers of two OFDM symbols, resulting also
experience lower interference from cell B because cluster B
1fs spreading.
25 is used in cell B but not in cell C.
The coding/modulation rate can be adaptively changed
The modulation/coding rate based on this estimation is
according to the channel conditions observed at the receiver
robust to frequent interference changes resulted from bursty
after the initial cluster allocation and rate selection.
packet transmission. This is because the rate prediction is
Pilot Symbols and SINR Measurement
based on the worst case situation in which all interference
In one embodiment, each base station transmits pilot 30 sources are transmitting.
symbols simultaneously, and each pilot symbol occupies the
In one embodiment, a subscriber utilizes the information
entire OFDM frequency bandwidth, as shown in FIGS.
available from both the pilot symbol periods and the data
2A-C. Referring to FIGS. 2A-C, pilot symbols 201 are
traffic periods to analyze the presence of both the intra-cell
shown traversing the entire OFDM frequency bandwidth for
traffic load and inter-cell interference. The goal of the
cells A, Band C, respectively. In one embodiment, each of 35 subscriber is to provide an indication to the base station as
the pilot symbols have a length or duration of 128 microto those clusters that the subscriber desires to use. Ideally,
seconds with a guard time, the combination of which is
the result of the selection by the subscriber is clusters with
approximately 152 microseconds. After each pilot period,
high channel gain, low interference from other cells, and
there are a predetermined number of data periods followed
high availability. The subscriber provides feedback inforby another set of pilot symbols. In one embodiment, there 40 mation that includes the results, listing desired clusters in
are four data periods used to transmit data after each pilot,
order or not as described herein.
and each of the data periods is 152 microseconds.
FIG. 3 illustrates one embodiment of subscriber processA subscriber estimates the SINR for each cluster from the
ing. The processing is performed by processing logic that
pilot symbols. In one embodiment, the subscriber first
may comprise hardware (e.g., dedicated logic, circuitry,
estimates the channel response, including the amplitude and 45 etc.), software (such as that which runs on, for example, a
general purpose computer system or dedicated machine), or
phase, as if there is no interference or noise. Once the
channel is estimated, the subscriber calculates the
a combination of both.
Referring to FIG. 3, channel/interference estimation prointerference/noise from the received signal.
cessing block 301 performs channel and interference estiThe estimated SINR values may be ordered from largest
to smallest SINRs and the clusters with large SINR values 50 mation in pilot periods in response to pilot symbols. Traffic/
are selected. In one embodiment, the selected clusters have
interference analysis processing block 302 performs traffic
SINR values that are larger than the minimum SINR which
and interference analysis in data periods in response to
signal information and information from channel!
still allows a reliable (albeit low-rate) transmission supinterference estimation block 301.
ported by the system. The number of clusters selected may
Cluster ordering and rate prediction processing block 303
depend on the feedback bandwidth and the request trans- 55
mission rate. In one embodiment, the subscriber always tries
is coupled to outputs of channel/interference estimation
to send the information about as many clusters as possible
processing block 301 and traffic/interference analysis profrom which the base station chooses.
cessing block 302 to perform cluster ordering and selection
along with rate prediction.
The estimated SINR values are also used to choose the
appropriate coding/modulation rate for each cluster as dis- 60
The output of cluster ordering processing block 303 is
cussed above. By using an appropriate SINR indexing
input to cluster request processing block 304, which requests
scheme, an SINR index may also indicate a particular coding
clusters and modulation/coding rates. Indications of these
and modulation rate that a subscriber desires to use. Note
selections are sent to the base station. In one embodiment,
the SINR on each cluster is reported to the base station
that even for the same subscribers, different clusters can
65 through an access channel. The information is used for
have different modulation/coding rates.
Pilot symbols serve an additional purpose in determining
cluster selection to avoid clusters with heavy intra-cell traffic
interference among the cells. Since the pilots of multiple
loading and/or strong interference from other cells. That is,

US 6,947,748 B2
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9
a new subscriber may not be allocated use of a particular
cluster if heavy intra -cell traffic loading already exists with
respect to that cluster. Also, clusters may not be allocated if
the interference is so strong that the SINR only allows for
low-rate transmission or no reliable transmission at all.
The channel/interference estimation by processing block
301 is well-known in the art by monitoring the interference
that is generated due to full-bandwidth pilot symbols being
simultaneously broadcast in multiple cells. The interface
information is forwarded to processing block 302 which
uses the information to solve the following equation:

PN , with no signal and interference
PD =

P s + PN , with signal only

j

PI + P N , with interference only
Ps + PI + PN, with both signal and interference
Ps + PI, with no signal and interference

10

PI, with signal only

Pp-PD =

j

Ps , with interference only

0, with both signal and interference

where Si represents the signal for subcarrier (freq. band) i,
Ii is the interference for subcarrier i, ni is the noise associated
with subcarrier i, and Yi is the observation for subcarrier i.
In the case of 512 subcarriers, i may range from 0 to 511.
The Ii and ni are not separated and may be considered one
quantity. The interference/noise and channel gain Hi are not
know. During pilot periods, the signal Si representing the
pilot symbols, and the observation Yi are knowns, thereby
allowing determination of the channel gain Hi for the case
where there is no interference or noise. Once this is known,
it may be plugged back into the equation to determine the
interference/noise during data periods since Hi' Si and Yi are
all known.
The interference information from processing blocks 301
and 302 are used by the subscriber to select desirable
clusters. In one embodiment, using processing block 303,
the subscriber orders clusters and also predicts the data rate
that would be available using such clusters. The predicted
data rate information may be obtained from a look up table
with precalculated data rate values. Such a look up table may
store the pairs of each SINR and its associated desirable
transmission rate. Based on this information, the subscriber
selects clusters that it desires to use based on predetermined
performance criteria. Using the ordered list of clusters, the
subscriber requests the desired clusters along with coding
and modulation rates known to the subscriber to achieve
desired data rates.
FIG. 4 is one embodiment of an apparatus for the selection of clusters based on power difference. The approach
uses information available during both pilot symbol periods
and data traffic periods to perform energy detection. The
processing of FIG. 4 may be implemented in hardware, (e.g.,
dedicated logic, circuitry, etc.), software (such as is run on,
for example, a general purpose computer system or dedicated machine), or a combination of both.
Referring to FIG. 4, a subscriber includes SINR estimation processing block 401 to perform SINR estimation for
each cluster in pilot periods, power calculation processing
block 402 to perform power calculations for each cluster in
pilot periods, and power calculation processing block 403 to
perform power calculations in data periods for each cluster.
Subtractor 404 subtracts the power calculations for data
periods from processing block 403 from those in pilot
periods from processing block 402. The output of subtractor
404 is input to power difference ordering (and group
selection) processing block 405 that performs cluster ordering and selection based on SINR and the power difference
between pilot periods and data periods. Once the clusters
have been selected, the subscriber requests the selected
clusters and the coding/modulation rates with processing
block 406.
More specifically, in one embodiment, the signal power of
each cluster during the pilot periods is compared with that
during the traffic periods, according to the following:

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where Pp is the measured power corresponding to each
cluster during pilot periods, PD is the measured power
during the traffic periods, Psis the signal power, PI is the
interference power, and PN is the noise power.
In one embodiment, the subscriber selects clusters with
relatively large Pp/(Pp-PD ) (e.g., larger than a threshold
such as 10 dB) and avoids clusters with low Pp/(Pp-PD )
(e.g., lower than a threshold such as 10 dB) when possible.
Alternatively, the difference may be based on the energy
difference between observed samples during the pilot period
and during the data traffic period for each of the subcarriers
in a cluster such as the following:

Thus, the subscriber sums the differences for all subcarriers.
Depending on the actual implementation, a subscriber
may use the following metric, a combined function of both
SINR and Pp-PD , to select the clusters:

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where f is a function of the two inputs. One example of f is
weighted averaging (e.g., equal weights). Alternatively, a
subscriber selects a cluster based on its SINR and only uses
the power difference Pp-PD to distinguish clusters with
similar SINR. The difference may be smaller than a threshold (e.g., 1 dB).
Both the measurement of SINR and Pp-PD can be averaged over time to reduce variance and improve accuracy. In
one embodiment, a moving-average time window is used
that is long enough to average out the statistical abnormity
yet short enough to capture the time-varying nature of
channel and interference, e.g., 1 millisecond.
Feedback Format for Downlink Cluster Allocation
In one embodiment, for the downlink, the feedback contains both the indices of selected clusters and their SINR. An
exemplary format for arbitrary cluster feedback is shown in
FIG. 5. Referring to FIG. 5, the subscriber provides a cluster
index (ID) to indicate the cluster and its associated SINR
value. For example, in the feedback, the subscriber provides
cluster IDl (501) and the SINR for the cluster, SINRl (502),
cluster ID2 (503) and the SINR for the cluster, SINR2 (504),
and cluster ID3 (505), and the SINR for the cluster, SINR3
(506), etc. The SINR for the cluster may be created using an
average of the SINRs of the subcarriers. Thus, multiple
arbitrary clusters can be selected as the candidates. As
discussed above, the selected clusters can also be ordered in
the feedback to indicate priority. In one embodiment, the
subscriber may form a priority list of clusters and sends back
the SINR information in a descending order of priority.
Typically, an index to the SINR level, instead of the SINR
itself is sufficient to indicate the appropriate coding/
modulation for the cluster. For example, a 3-bit field can be

US 6,947,748 B2
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12

used for SINR indexing to indicate 8 different rates of
adaptive coding/modulation.
An Exemplary Base Station
The base station assigns desirable clusters to the subscriber making the request. In one embodiment, the availability of the cluster for allocation to a subscriber depends on
the total traffic load on the cluster. Therefore, the base station
selects the clusters not only with high SINR, but also with
low traffic load.
FIG. 13 is a block diagram of one embodiment of a base
station. Referring to FIG. 13, cluster allocation and load
scheduling controller 1301 (cluster allocator) collects all the
necessary information, including the downlink/uplink SINR
of clusters specified for each subscriber (e.g., via SINR/rate
indices signals 1313 received from OFDM transceiver 1305)
and user data, queue fullness/traffic load (e.g., via user data
buffer information 1311 from multi-user data buffer 1302).
Using this information, controller 1301 makes the decision
on cluster allocation and load scheduling for each user, and
stores the decision information in a memory (not shown).
Controller 1301 informs the subscribers about the decisions
through control signal channels (e.g., control signal/cluster
allocation 1312 via OFDM transceiver 1305). Controller
1301 updates the decisions during retraining.
In one embodiment, controller 1301 also performs admission control to user access since it knows the traffic load of
the system. This may be performed by controlling user data
buffers 1302 using admission control signals 1310.
The packet data of User I-N are stored in the user data
buffers 1302. For downlink, with the control of controller
1301, multiplexer 1303 loads the user data to cluster data
buffers (for Cluster I-M) waiting to be transmitted. For the
uplink, multiplexer 1303 sends the data in the cluster buffers
to the corresponding user buffers. Cluster buffer 1304 stores
the signal to be transmitted through OFDM transceiver 1305
(for downlink) and the signal received from transceiver
1305. In one embodiment, each user might occupy multiple
clusters and each cluster might be shared by multiple users
(in a time-division-multiplexing fashion).
Group-Based Cluster Allocation
In another embodiment, for the downlink, the clusters are
partitioned into groups. Each group can include multiple
clusters. FIG. 6 illustrates an exemplary partitioning. Referring to FIG. 6, groups 1-4 are shown with arrows pointing
to clusters that are in each group as a result of the partitioning. In one embodiment, the clusters within each group are
spaced far apart over the entire bandwidth. In one
embodiment, the clusters within each group are spaced apart
farther than the channel coherence bandwidth, i.e. the bandwidth within which the channel response remains roughly
the same. A typical value of coherence bandwidth is 100 kHz
for many cellular systems. This improves frequency diversity within each group and increases the probability that at
least some of the clusters within a group can provide high
SINR. The clusters may be allocated in groups. Goals of
group-based cluster allocation include reducing the data bits
for cluster indexing, thereby reducing the bandwidth
requirements of the feedback channel (information) and
control channel (information) for cluster allocation. Groupbased cluster allocation may also be used to reduce inter-cell
interference.
After receiving the pilot signal from the base station, a
subscriber sends back the channel information on one or
more cluster groups, simultaneously or sequentially. In one
embodiment, only the information on some of the groups is
sent back to the base station. Many criteria can be used to
choose and order the groups, based on the channel

information, the inter-cell interference levels, and the intracell traffic load on each cluster.
In one embodiment, a subscriber first selects the group
with the best overall performance and then feedbacks the
SINR information for the clusters in that group. The subscriber may order the groups based on their number of
clusters for which the SINR is higher than a predefined
threshold. By transmitting the SINR of all the clusters in the
group sequentially, only the group index, instead of all the
cluster indices, needs to be transmitted. Thus, the feedback
for each group generally contains two types of information:
the group index and the SINR value of each cluster within
the group. FIG. 7 illustrates an exemplary format for indicating a group-based cluster allocation. Referring to FIG. 7,
a group ID, IDl, is followed by the SINR values for each of
the clusters in the group. This can significantly reduce the
feedback overhead.
Upon receiving the feedback information from the
subscriber, the cluster allocator at the base station selects
multiple clusters from one or more groups, if available, and
then assigns the clusters to the subscriber. This selection
may be performed by an allocation in a media access control
portion of the base station.
Furthermore, in a multi-cell environment, groups can
have different priorities associated with different cells. In
one embodiment, the subscriber's selection of a group is
biased by the group priority, which means that certain
subscribers have higher priorities on the usage of some
groups than the other subscribers.
In one embodiment, there is no fixed association between
one subscriber and one cluster group; however, in an alternative embodiment there may be such a fixed association. In
an implementation having a fixed association between a
subscriber and one or more cluster groups, the group index
in the feedback information can be omitted, because this
information is known to both subscriber and base station by
default.
In another embodiment, the pilot signal sent from the base
station to the subscriber also indicates the availability of
each cluster, e.g., the pilot signal shows which clusters have
already been allocated for other subscribers and which
clusters are available for new allocations. For example, the
base station can transmit a pilot sequence 1111 1111 on the
subcarriers of a cluster to indicate that the cluster is
available, and 1111-1-1-1-1 to indicate the cluster is not
available. At the receiver, the subscriber first distinguishes
the two sequences using the signal processing methods
which are well known in the art, e.g., the correlation
methods, and then estimates the channel and interference
level.
With the combination of this information and the channel
characteristics obtained by the subscriber, the subscriber can
prioritize the groups to achieve both high SINR and good
load balancing.
In one embodiment, the subscriber protects the feedback
information by using error correcting codes. In one
embodiment, the SINR information in the feedback is first
compressed using source coding techniques, e.g., differential encoding, and then encoded by the channel codes.
FIG. 8 shows one embodiment of a frequency reuse
pattern for an exemplary cellular set up. Each cell has
hexagonal structure with six sectors using directional antennas at the base stations. Between the cells, the frequency
reuse factor is one. Within each cell, the frequency reuse
factor is 2 where the sectors use two frequencies alternatively. As shown in FIG. 8, each shaded sector uses half of
the available OFDMA clusters and each unshaded sector

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uses the other half of the clusters. Without loss of generality,
the clusters used by the shaded sectors are referred to herein
as odd clusters and those used by the unshaded sectors are
referred to herein as even clusters.
Consider the downlink signaling with omni-directional
antennas at the subscribers. From FIG. 8, it is clear that for
the downlink in the shaded sectors, Cell A interferes with
Cell B, which in turn interferes with Cell C, which in turn
interferes with Cell A, namely, A->B->C->A. For the
unshaded sectors, Cell A interferes with Cell C, which in
turn interferes with Cell B, which in turn interferes with Cell
A, namely, A->C->B->A.
Sector Al receives interference from Sector Cl, but its
transmission interferes with Sector BI. Namely, its interference source and the victims with which it interferes are not
the same. This might cause a stability problem in a distributed cluster-allocation system using interference avoidance:
if a frequency cluster is assigned in Sector Bl but not in
Sector Cl, the cluster may be assigned in Al because it may
be seen as clean in AI. However, the assignment of this
cluster Al can cause interference problem to the existing
assignment in BI.
In one embodiment, different cluster groups are assigned
different priorities for use in different cells to alleviate the
aforementioned problem when the traffic load is progressively added to a sector. The priority orders are jointly
designed such that a cluster can be selectively assigned to
avoid interference from its interference source, while
reducing, and potentially minimizing, the probability of
causing interference problem to existing assignments in
other cells.
Using the aforementioned example, the odd clusters (used
by the shaded sectors) are partitioned into 3 groups: Group
1, 2, 3. The priority orders are listed in Table 2.

Table 4 shows the priority orders for the unshaded sectors,
which are different from those for the shaded sectors, since
the interfering relationship is reversed.
TABLE 4
Priority ordering for the downlink of the unshaded sectors.
Priority Ordering
10

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25

30

35

TABLE 2
Priority ordering for the downlink of the shaded sectors.
Priority Ordering

CellA

Cell B

Cell C

2

Group 1
Group 2
Group 3

Group 3
Group 1
Group 2

Group 2
Group 3
Group 1

Consider Sector AI. First, the clusters in Group 1 are
selectively assigned. If there are still more subscribers
demanding clusters, the clusters in Group 2 are selectively
assigned to subscribers, depending on the measured SINR
(avoiding the clusters receiving strong interference from
Sector Cl). Note that the newly assigned clusters from
Group 2 to Sector Al shall not cause interference problem
in Sector Bl, unless the load in Sector Bl is so heavy that
the clusters in both Group 3 and 1 are used up and the
clusters in Group 2 are also used. Table 3 shows the cluster
usage when less than 2/3 of all the available clusters are used
in Sector AI, Bl, and CI.

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55

TABLE 3
Cluster usage for the downlink of the shaded sectors
with less than Y3 of the full load
Cluster Usage

CellA

Cell B

Cell C

2

Group 1
Group 2

Group 3
Group 1

60

Group 2
Group 3

65

CellA

Cell B

Cell C

2

Group 1
Group 2
Group 3

Group 2
Group 3
Group 1

Group 3
Group 1
Group 2

Intelligent Switching between Coherence and
Diversity Clusters
In one embodiment, there are two categories of clusters:
coherence clusters, containing multiple subcarriers close to
each other and diversity clusters, containing multiple subcarriers with at least some of the subcarriers spread far apart
over the spectrum. The closeness of the multiple subcarriers
in coherence clusters is preferably within the channel coherence bandwidth, i.e. the bandwidth within which the channel
response remains roughly the same, which is typically
within 100 kHz for many cellular systems. On the other
hand, the spread of subcarriers in diversity clusters is
preferably larger than the channel coherence bandwidth,
typically within 100 kHz for many cellular systems. Of
course, the larger the spread, the better the diversity.
Therefore, a general goal in such cases is to maximize the
spread.
FIG. 9 illustrates exemplary cluster formats for coherence
clusters and diversity clusters for Cells A-C. Referring to
FIG. 9, for cells A-C, the labeling of frequencies
(subcarriers) indicates whether the frequencies are part of
coherence or diversity clusters. For example, those frequencies labeled 1-8 are diversity clusters and those labeled 9-16
are coherence clusters. For example, all frequencies labeled
1 in a cell are part of one diversity cluster, all frequencies
labeled 2 in a cell are part of another diversity cluster, etc.,
while the group of frequencies labeled 9 are one coherence
cluster, the group of frequencies labeled 10 are another
coherence cluster, etc. The diversity clusters can be configured differently for different cells to reduce the effect of
inter-cell interference through interference averaging.
FIG. 9 shows example cluster configurations for three
neighboring cells. The interference from a particular cluster
in one cell are distributed to many clusters in other cells,
e.g., the interference from Cluster 1 in Cell A are distributed
to Cluster 1, 8, 7, 6 in Cell B. This significantly reduces the
interference power to any particular cluster in Cell B.
Likewise, the interference to any particular cluster in one
cell comes from many different clusters in other cells. Since
not all cluster are strong interferers, diversity clusters, with
channel coding across its subcarriers, provide interference
diversity gain. Therefore, it is advantageous to assign diversity clusters to subscribers that are close (e.g., within the
coherent bandwidth) to the cell boundaries and are more
subject to inter-cell interference.
Since the subcarriers in a coherence cluster are consecutive or close (e.g., within the coherent bandwidth) to each
other, they are likely within the coherent bandwidth of the
channel fading. Therefore, the channel gain of a coherence
cluster can vary significantly and cluster selection can
greatly improve the performance. On the other hand, the
average channel gain of a diversity cluster has less of a
degree of variation due to the inherent frequency diversity
among the multiple subcarriers spread over the spectrum.

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With channel coding across the subcarriers within the
cluster, diversity clusters are more robust to cluster misselection (by the nature of diversification itself), while
yielding possibly less gain from cluster selection. Channel
coding across the subcarriers means that each codeword
contains bits transmitted from multiple subcarriers, and
more specifically, the difference bits between codewords
(error vector) are distributed among multiple subcarriers.
More frequency diversity can be obtained through subcarrier hopping over time in which a subscriber occupies a
set of subcarriers at one time slot and another different set of
subcarriers at a different time slot. One coding unit (frame)
contains multiple such time slots and the transmitted bits are
encoded across the entire frame.
FIG. 10 illustrates diversity cluster with sub carrier hopping. Referring to FIG. 10, there are four diversity clusters
in each of cells A and B shown, with each subcarrier in
individual diversity clusters having the same label (1, 2, 3,
or 4). There are four separate time slots shown and during
each of the time slots, the subcarriers for each of the
diversity clusters change. For example, in cell A, subcarrier
1 is part of diversity cluster 1 during time slot 1, is part of
diversity cluster 2 during time slot 2, is part of diversity
cluster 3 during time slot 3, and is part of diversity cluster
4 during time slot 4. Thus, more interference diversity can
be obtained through sub carrier hopping over time, with
further interference diversity achieved by using different
hopping patterns for different cells, as shown in FIG. 10.
The manner in which the subscriber changes the subcarriers (hopping sequences) can be different for different cells
in order to achieve better interference averaging through
coding.
For static subscribers, such as in fixed wireless access, the
channels change very little over time. Selective cluster
allocation using the coherence clusters achieves good performance. On the other hand, for mobile subscribers, the
channel time variance (the variance due to changes in the
channel over time) can be very large. A high-gain cluster at
one time can be in deep fade at another. Therefore, cluster
allocation needs to be updated at a rapid rate, causing
significant control overhead. In this case, diversity clusters
can be used to provide extra robustness and to alleviate the
overhead of frequent cluster reallocation. In one
embodiment, cluster allocation is performed faster than the
channel changing rate, which is often measured by the
channel Doppler rate (in Hz), i.e. how many cycles the
channel changes per second where the channel is completely
different after one cycle. Note that selective cluster allocation can be performed on both coherence and diversity
clusters.
In one embodiment, for cells containing mixed mobile
and fixed subscribers, a channel/interference variation detector can be implemented at either the subscriber or the base
station, or both. Using the detection results, the subscriber
and the base station intelligently selects diversity clusters to
mobile subscribers or fixed subscribers at cell boundaries,
and coherence clusters to fixed subscribers close to the base
station. The channel/interference variation detector measures the channel (SINR) variation from time to time for
each cluster. For example, in one embodiment, the channell
interference detector measures the power difference between
pilot symbols for each cluster and averages the difference
over a moving window (e.g., 4 time slots). A large difference
indicates that channel/interference changes frequently and
subcarrier allocation may be not reliable. In such a case,
diversity clusters are more desirable for the subscriber.

FIG. 11 is a flow diagram of one embodiment of a process
for intelligent selection between diversity clusters and
coherence clusters depending on subscribers mobility. The
process is performed by processing logic that may comprise
hardware (e.g., circuitry, dedicated logic, etc.), software
(such as that which runs on, for example, a general purpose
computer system or dedicated machine), or a combination of
both.
Referring to FIG. 11, processing logic in the base station
performs channel/interference variation detection
(processing block 1101). Processing logic then tests whether
the results of the channel/interference variation detection
indicate that the user is mobile or in a fixed position close to
the edge of the cell (processing block 1102). If the user is not
mobile or is not in a fixed position close to the edge of the
cell, processing transitions to processing block 1103 where
processing logic in the base station selects coherence clusters; otherwise, processing transitions to processing block
1104 in which processing logic in the base station selects
diversity clusters.
The selection can be updated and intelligently switched
during retraining.
The ratio/allocation of the numbers of coherence and
diversity clusters in a cell depends on the ratio of the
population of mobile and fixed subscribers. When the population changes as the system evolves, the allocation of
coherence and diversity clusters can be reconfigured to
accommodate the new system needs. FIG. 12 illustrates a
reconfiguration of cluster classification which can support
more mobile subscribers than that in FIG. 9.
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.
We claim:
1. A method for sub carrier selection for a system employing orthogonal frequency division multiple access
(OFDMA) comprising:
a subscriber measuring channel and interference information for a plurality of subcarriers based on pilot symbols received from a base station, wherein the subscriber measuring channel and interference information
comprises
the subscriber continuously monitoring reception of the
pilot symbols known to the base station and measuring
signal-plus-interference-to-noise ratio (SINR) of each
cluster of subcarriers, and
the subscriber measuring intra -cell traffic;
the subscriber selecting a set of candidate subcarriers,
wherein the subscriber selects candidate subcarriers
based, at least in part, on the intra-cell traffic load
balancing;
the subscriber providing feedback information on the set
of candidate subcarriers to the base station; and
the subscriber receiving an indication of subcarriers of the
set of subcarriers selected by the base station for use by
the subscriber.
2. The method defined in claim 1 further comprising the
base station selecting the subcarriers in order to balance
intra -cell traffic load on each cluster.
3. A method for sub carrier selection for a system employing orthogonal frequency division multiple access
(OFDMA) comprising:

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a subscriber measuring channel and interference information for a plurality of subcarriers based on pilot symbols received from a base station, wherein the subscriber measuring channel and interference information
comprises using information from pilot symbol periods
and data periods to measure channel and interference
information;
the subscriber selecting a set of candidate subcarriers
based on the SINR of a cluster of subcarriers and a
difference between measured power corresponding to
each cluster during pilot periods and measured power
during data periods;
the subscriber providing feedback information on the set
of candidate subcarriers to the base station; and
the subscriber receiving an indication of subcarriers of the
set of subcarriers selected by the bas station for use by
the subscriber.
4. The method defined in claim 3 further comprising the
subscriber using the power difference to distinguish, during
selection, clusters of subcarriers having substantially similar
SINRs.
5. A method for sub carrier selection for a system employing orthogonal frequency division multiple access
(OFDMA) comprising:
a subscriber measuring channel and interference information for a plurality of subcarriers based on pilot symbols received from a base station, wherein the subscriber measuring channel and interference information
comprises
using information from pilot symbol periods and data
periods to measure channel and interference
information, and
using information from pilot symbol periods and data
traffic periods to analyze presence of intra-cell traffic
load and inter-cell interference;
the subscriber selecting a set of candidate subcarriers;
the subscriber providing feedback information on the set
of candidate subcarriers to the base station; and
the subscriber receiving an indication of subcarriers of the
set of subcarriers selected by the base station for use by
the subscriber.
6. A method for sub carrier selection for a system employing orthogonal frequency division multiple access
(OFDMA) comprising:
a subscriber measuring channel and interference information for a plurality of subcarriers based on pilot symbols received from a base station;
the subscriber selecting a set of candidate subcarriers;
the subscriber providing feedback information on the set
of candidate subcarriers to the base station, wherein
providing feedback information comprises arbitrarily
ordering the set of candidate of subcarriers as clusters
of subcarriers, and further wherein the feedback information includes an index indication of a candidate
cluster with its SINR value; and
the subscriber receiving an indication of subcarriers of the
set of subcarriers selected by the base station for use by
the subscriber.
7. The method defined in claim 6 wherein each index is
indicative of a coding and modulation rate.
8. A method for sub carrier selection for a system employing orthogonal frequency division multiple access
(OFDMA) comprising:
a subscriber measuring channel and interference information for a plurality of subcarriers based on pilot symbols received from a base station;

the subscriber selecting a set of candidate subcarriers;
the subscriber providing feedback information on the set
of candidate subcarriers to the base station;
the subscriber sending an indication of coding and modulation rates that the subscriber desires to employ for
each cluster; and
the subscriber receiving an indication of subcarriers of the
set of subcarriers selected by the base station for use by
the subscriber.
9. The method defined in claim 8 wherein the indication
of coding and modulation rates comprises an SINR index
indicative of a coding and modulation rate.
10. A method for subcarrier selection for a system
employing orthogonal frequency division multiple access
(OFDMA) comprising:
a subscriber measuring channel and interference information for a plurality of subcarriers based on pilot symbols received from a base station;
the subscriber selecting a set of candidate subcarriers;
the subscriber providing feedback information on the set
of candidate subcarriers to the base station;
the subscriber receiving an indication of subcarriers of the
set of subcarriers selected by the base station for use by
the subscriber;
the base station allocating a first portion of the subcarriers
to establish a data link between the base station and the
subscriber; and then
the base station allocating a second portion of the subcarriers to the subscriber to increase communication
bandwidth wherein, due to subscriber priority, the base
station allocates the second portion before allocating
each subscriber in the cell subcarriers to establish their
data link to the base station.
11. An apparatus comprising:
a plurality of subscribers in a first cell to generate feedback information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a first base station in the first cell, in response to receiving
inter-cell interference information, coordinates with
other cells to make a cluster assignment decision, the
first base station performing subcarrier allocation for
OFDMA to allocate OFDMA subcarriers in clusters to
the plurality of subscribers based on inter-cell interference avoidance and intra-cell traffic load balancing in
response to the feedback information.
12. An apparatus comprising:
a plurality of subscribers in a first cell to generate feedback information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a first base station in the first cell, the first base station to
allocate OFDMAsubcarriers in clusters to the plurality
of subscribers;
each of a plurality of subscribers to measure channel and
interference information for the plurality of subcarriers
based on pilot symbols received from the first base
station, wherein each of the plurality of subscribers
continuously monitors reception of the pilot symbols
known to the base station and the plurality of
subscribers, measures signal-plus-interference-to-noise
ratio (SINR) of each cluster of subcarriers and measures intra-cell traffic, and further wherein at least one
subscriber of the plurality of subcarriers based, at least
in part, on the intra -cell traffic load balancing, and the
one subscriber to provide feedback information on the
set of candidate subcarriers to the base station and to

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receive an indication of subcarriers form the set of
subcarriers selected by the first base station for use by
the one subscriber.
13. The apparatus defined in claim 12 wherein the base
station selects subcarriers in order to balance intra -cell traffic
load on each cluster of subcarriers.
14. An apparatus comprising:
a plurality of subscribers in a first cell to generate feedback information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a first base station in the first cell, the first base station to
allocate OFDMAsubcarriers in clusters to the plurality
of subscribers;
each of a plurality of subscribers to measure channel and
interference information for the plurality of subcarriers
based on pilot symbols received from the first base
station, wherein at least one subscriber of the plurality
of subscribers select a set of candidate subcarriers from
the plurality of subcarriers based, at least in part, on
SINR of the cluster and a difference between measured
power corresponding to each cluster during pilot periods and measured power during data periods, and the
one subscriber to provide feedback information on the
set of candidate subcarriers to the base station and to
receive an indication of subcarriers from the set of
subcarriers selected by the first base station for use by
the one subscriber.
15. The apparatus defined in claim 14 wherein the one
subscriber distinguishes, during selection, cluster of subcarriers having substantially similar SINRs based on the power
difference.
16. The apparatus defined in claim 14 wherein the at least
one subscriber uses information from pilot symbol periods
and data traffic periods to analyze presence of intra -cell
traffic load and inter-cell interference.
17. The apparatus defined in claim 14 wherein the pilot
symbols occupy an entire OFDM frequency bandwidth.
18. The apparatus defined in claim 17 wherein at least one
other pilot symbol from a different cell transmitted at the
same time as the pilot symbols received from the base
station collide with each other.
19. An apparatus comprising:
a plurality of subscribers in a first cell to generate feedback information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a first base station in the first cell, the first base station to
allocate OFDMAsubcarriers in clusters to the plurality
of subscribers;
each of a plurality of subscribers to measure channel and
intcrference information for the plurality of subcarriers
based on pilot symbols received from the first base
station and at least one of the plurality of subscribers to
select a set of candidate subcarriers from the plurality
of subcarriers, and the one subscriber to provide feedback information on the set of candidate subcarriers to
the base station and to receive an indication of subcarriers from the set of subcarriers selected by the first

base station for use by the one subscriber, wherein the
plurality of subscribers provide feedback information
that comprises an arbitrarily ordered set of candidate
subcarriers as clusters of subcarriers, and further
wherein the feedback information includes an index
indication of a candidate cluster with it SINR value.
20. The apparatus defined in claim 19 wherein each index
is indicative of a coding and modulation rate.
21. An apparatus comprising:
a plurality of subscribers in a first cell to generate feedback information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a first base station in the first cell, the first base station to
allocate OFDMAsubcarriers in clusters to the plurality
of subscribers;
each of a plurality of subscribers to measure channel and
interference information for the plurality of subcarriers
based on pilot symbols received from the first base
station and at least one of the plurality of subscribers to
select a set of candidate subcarriers from the plurality
of subcarriers, and the one subscriber to provide feedback information on the set of candidate subcarriers to
the base station and to receive an indication of subcarriers from the set of subcarriers selected by the first
base station for use by the one subscriber, wherein the
one subscriber sends an indication of coding and modulation rates that the one subscriber desires to employ.
22. The apparatus defined in claim 21 wherein the indication of coding and modulation rates comprises an SINR
index indicative of a coding and modulation rate.
23. An apparatus comprising:
a plurality of subscribers in a first cell to generate feedback information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a first base station in the first cell, the first base station to
allocate OFDMAsubcarriers in clusters to the plurality
of subscribers; and
each of a plurality of subscribers to measure channel and
interference information for the plurality of subcarriers
based on pilot symbols received from the first base
station and at least one of the plurality of subscribers to
select a set of candidate subcarriers from the plurality
of subcarriers, and the one subscriber to provide feedback information on the set of candidate subcarriers to
the base station and to receive an indication of subcarriers from the set of subcarriers selected by the first
base station for use by the one subscriber;
wherein the base station allocates a first portion of the
subcarriers to establish a data link between the base
station, the base station allocates a second portion of
the sub carriers to the subscriber to increase communication bandwidth, and due to subscriber priority, the
base station allocates the second portion before allocating each subscriber in the cell subcarriers to establish their data link to the base station.

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