Adaptix, Inc. v. Apple Inc et al

Filing 1

COMPLAINT of Patent Infringement against Apple Inc, Cellco Partnership ( Filing fee $ 400, receipt number 0971-8036744.). Filed byAdaptix, Inc.. (Attachments: # 1 Exhibit A to Complaint, # 2 Exhibit B to Complaint, # 3 Civil Cover Sheet)(Shafer, Daniel) (Filed on 9/26/2013)

EXHIBIT B

US006947748B2

(12) United States Patent

(10) Patent N0.:
(45) Date of Patent:

Li et al.

(54)

OFDMA WITH ADAPTIVE SUBCARRIER
CLUSTER CONFIGURATION AND
SELECTIVE LOADING

Notice:

198 00 953 C1

DE

(73) Assignee: AdaptiX, Inc., Bothell, WA (US)
(*)

FOREIGN PATENT DOCUMENTS
DE

(75) Inventors: Xiaodong Li, Bellevue, WA (US); Hui
Liu, Sammamish, WA (US); Kemin Li,
Bellevue, WA (US); Wenzhong Zhang,
Bellevue, WA (US)
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35

US 6,947,748 B2
Sep. 20, 2005

19800953 Cl *

EP
EP
EP

EP
FR
GB
JP
W0
W0
W0

0 869 647 A2
0 926 912 A2
0 929 202 A1

0999658
2 777 407
2 209 858
06029922
WO 98/16077
WO 98/30047
W0 02 49305

7/1999
7/1999

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

10/1998
6/1999
7/1999

5/2000
A1
A

A2
A1
A2

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

U.S.C. 154(b) by 765 days.
OTHER PUBLICATIONS

(21) Appl. No.: 09/738,086
(22) Filed:
(65)

Vittoria Mignone et al. “CD3—OFDM: A Novel Demodula
tion Scheme for Fixed and Mobile Receives,” IEEE Trans
actions on Communications, Sep. 1996, vol. 44, No. 9.

Dec. 15, 2000
Prior Publication Data

US 2002/0119781 A1 Aug. 29, 2002
(51)
(52)

Int. Cl.7 .......................... .. H04Q 7/20; H04J 11/00
US. Cl. ..................... .. 455/450; 455/447; 455/453;

(58)

Bender et al., CDMA/HDR: A BandWidth—Ef?cient High—
Speed Wireless Data Service for Nomadic Users, IEEE
Communications Magazine, Jul. 2000, pp. 70—87.

Field of Search ............................... .. 455/447—453,

455/455; 455/464; 370/208

455/456.5, 456.6, 509, 512, 513, 524—526,
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188.1, 550.1, 553; 370/311, 347, 480, 203—206,
208, 210, 329; 375/132
(56)

5,507,034 A

5,515,378 A
5,555,268 A

*

3/1998 Frodigh et al. ........... .. 370/252

3/1998 KotZin et al.
*

interference information for subcarriers based on pilot sym
bols received from a base station, at least one of subscribers

selecting a set of candidate subcarriers, providing feedback

1/1998 Ritter

5,734,967 A

5,822,372 A

prises each of multiple subscribers measuring channel and

Bodin et al. ............. .. 455/34.1

12/1996 Schilling

5,708,973 A
5,774,808 A

one embodiment, a method for subcarrier selection com

5/1996 Roy, III et 211.
9/1996 Fattouche et 211.

5,588,020 A
5,726,978 A

4/1996

ABSTRACT

orthogonal frequency division multiple access (OFDMA). In

1/1994 Wang
12/1995 Chow et al.
4/1996 Chouly et 211.
*

(74) Attorney, Agent, or Firm—Fulbright & J aWorski LLP

Amethod and apparatus for subcarrier selection for systems
is described. In one embodiment, the system employs

U.S. PATENT DOCUMENTS
5,479,447 A
5,504,775 A

Primary Examiner—William Trost
Assistant Examiner—Meless ZeWdu

(57)

References Cited
5,280,630 A

(Continued)

6/1998 Sarkioja et al. ........... .. 455/436

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.

10/1998 Emami

23 Claims, 7 Drawing Sheets

(Continued)

Periodically Broadcast Pilot
OFDM Symbols to Suhscribevs

Subscribarls) Continuously MDIIihIrS
PllOl Mums/Measures SINR and/or
Other Parametels

Retraining

Nu

Each suhsm'ber Selects Om w Mora

Clusws to! Each Base Stallon

Needed
7

Base Station Setects One or More
Clusters tor Each Subsunher

Base Stallon Noti?es lb! Subsuibar

Regarding Cluster Allnnetton

US 6,947,748 B2
Page 2

US. PATENT DOCUMENTS
5,867,478 A
5,886,988 A
5,887,245 A

2/1999 Baum et al.
3/1999 Yun et al.
3/1999 Lindroth et al.

5,909,436 A
5,914,933 A
5,933,421 A

6/1999
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5,956,642 A
5,973,642 A

Engstrom et al.
Cimini et al.
Alamouti et al.
Larsson et al.
Li et al.

5,991,273 A

11/1999 Abu-Dayya

6,005,876
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6,064,692
6,064,694
6,067,290
6,108,374
6,111,919
6,131,016

12/1999
12/1999
2/2000
3/2000
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5/2000
5/2000
5/2000
8/2000
8/2000
10/2000

A
A
A
A
A
A
A
A
A
A
A
A

6,141,565 A

Cimini, Jr. et al.
Martinez et al.
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Farsakh

Chuang et al.
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Chow
Clark et al.
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Yonge, III
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6,144,696 A
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11/2000 Shively et al.
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6,298,092 B1 * 10/2001

6,307,851 B1

Heath, Jr. et al. ......... .. 375/267

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6,327,472 B1 * 12/2001
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Westroos et al. ......... .. 455/450
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4/2002 Harel et al.
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2003/0067890 A1
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4/2003 Goel et al.
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9/2003 Chayat

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 High—
Speed Wireless Data Service for Nomadic Users,” IEEE
Communications Magazine, Jul. 2000, pp. 70—87.
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Capacity Increase by DOA Sensitive Channel Allocation”,
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lishers, NL, vol. 11, No. 1, Oct. 1999, pp. 63—76,
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Wong, C.Y., et al., Multiuser OFDM With Adaptive Subcar
rier; 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

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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 Interna
tional 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.
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Nogueroles, R. et al.: “Improved Performance of a Random
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* cited by examiner

U.S. Patent

Sep. 20,2005

Sheet 1 0f 7

US 6,947,748 B2

FIG. 1A

Pilot OFDM
Symbols

201

________ _ _ ........... ._

\

U.S. Patent

Sep. 20,2005

Sheet 2 0f 7

US 6,947,748 B2

Periodically Broadcast Pilot

/ 101

OFDM Symbols to Subscribers

l
Subscriber(s) Continuously Monitors
Pilot Symbols/Measures SINR and/or V102
Other Parameters

l
Each Subscriber Selects One or More

Retraining

Clusters for Each Base Station

~ 103

Needed
7

‘_ '

l
‘

Base Station Selects One or More

Clusters for Each Subscriber

l
Base Station Noti?es the Subscriber

Regarding Cluster Allocation

FIG. 1B

- 105

U.S. Patent

Sep. 20,2005

Sheet 3 of 7

US 6,947,748 B2

Channel/Interference ~/ 301

—> Estimation in Pilot

(- 303

Penods
+
Traf?cjlmerference
—n Analysis in Date
Periods

_. Cluster Ordering
__>
and Rate
Prediction

K 304

Request Selected
—> Clusters and Coding/ —->
Modulation Rates

'\ 302

Per-cluster SINR J01
——>

Estimation in

——>

./ 405

PM Peliods

Cluster Ordering!
402

Per-cluster

406

Selection Based on

(

‘i 404 SINR and Power

—> Power Calculation

Difference

in Pilot Periods

Request Selected
—> Clusters and Coding! —>

-

Modulation Rates

Per-cluster
—H Power Calculation

in Data Periods

501 \
Cluster

‘D1

502 -\

"\ 403

503 \

SINR1

Group 3

Cluster

‘D2

G 4

504 \

SlNRZ

504 \

504 \

Cluster

‘D3

_ "

SlNR3

Group 4
f

Yt \ 7% /"J
Group 1
Group 2
FIG. 6

U.S. Patent

Sep. 20,2005

Sheet 5 0f 7

US 6,947,748 B2

1-8: Diverse Clusters
9-16: Plain Clusters
12

9

101|2

f
*z 11

V1 7

12 12

13

14 12

15

16

a. CellA

f
>

12

9 1o 1

711 121ia1z+1 13 146711112

v1

b.CellB

15 16

'

f
)

51b 1.5419

10

V1

7'12311

12

16

c.CellC

FIG.9
Subcarrier1
Subcarrier2

f

'Fme1
1”1me2
Time3
11me4
1

a. Cell A

t

b. Cell B

FIG. 10

U.S. Patent

Sep. 20,2005

Sheet 6 0f 7

US 6,947,748 B2

Channel/Interference / 1101
Variation Detection
1102

Any
Signi?cant Variation
Detected
'?

1104»

(1103

Select Diversity
Clusters

Select Coherence
Clusters

FIG. 11

1

12a 61 e1“ 1012

67 91“ 1212

68191“ 14 12

a. Cell A

FIG. 12

a

1111s

U.S. Patent

Sep. 20,2005

Sheet 7 of 7

US 6,947,748 B2

User Data Bilge; Information I I I I I User1~N
3
Multi-user Data

__?___>

,\ 1302

Buffer

Admission Control
Cluster Allocation and

Load Scheduling

—>

Controller

Multiplexer

I13”

1 I I I I Cluster1~M
Multi-cluster
Transmission and

S'NR/Rate

1304
~/‘

Receiving Buffer

lndices

Hill

1313

(

>

0FDM Transceiver

Control Signal/

\/ 1305

I QFDM Signal

Cluster Allocation
1312

FIG. 13

US 6,947,748 B2
1

2

OFDMA WITH ADAPTIVE SUBCARRIER
CLUSTER CONFIGURATION AND
SELECTIVE LOADING

existing subscribers is dropped off the netWork or a neW

subscribers is added onto the netWork. This is often imprac
tical in real Wireless system, mainly due to the bandWidth
cost for updating the subscriber information and the com

putation cost for the joint optimiZation.
FIELD OF THE INVENTION
SUMMARY OF THE INVENTION

The invention relates to the ?eld of Wireless communi
cations; more particularly, the invention relates to multi-cell,

multi-subscriber Wireless systems using orthogonal fre
quency division multiplexing (OFDM).

10

BACKGROUND OF THE INVENTION
an efficient modulation scheme for signal transmission over

employs orthogonal frequency division multiple access
(OFDMA). In one embodiment, a method for subcarrier

Orthogonal frequency division multiplexing (OFDM) is
frequency-selective channels. In OFDM, a Wide bandWidth
is divided into multiple narroW-band subcarriers, Which are

A method and apparatus for subcarrier selection for
systems is described. In one embodiment, the system

15

selection comprises a subscriber measuring channel and
interference information for subcarriers based on pilot sym
bols 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 subcar
riers selected by the base station for use by the subscriber.

arranged to be orthogonal With each other. The signals
modulated on the subcarriers are transmitted in parallel. For

more information, see Cimini, Jr., “Analysis and Simulation

of a Digital Mobile Channel Using Orthogonal Frequency
Division Multiplexing,” IEEE Trans. Commun., vol. COM

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention Will be understood more fully from
the detailed description given beloW and from the accom

33, no. 7, July 1985, pp. 665—75; Chuang and Sollenberger,
“Beyond 3G: Wideband Wireless Data Access Based on

OFDM and Dynamic Packet Assignment,” IEEE Commu
nications Magazine, Vol. 38, No. 7, pp. 78—87, July 2000.

panying draWings of various embodiments of the invention,
25

One Way to use OFDM to support multiple access for

understanding only.

multiple subscribers is through time division multiple access

FIG. 1A illustrates subcarriers and clusters.

(TDMA), in Which each subscriber uses all the subcarriers

FIG. 1B is a How diagram of one embodiment of a process

Within its assigned time slots. Orthogonal frequency division
multiple access (OFDMA) is another method for multiple

for allocating subcarriers.
FIG. 2 illustrates time and frequency grid of OFDM
symbols, pilots and clusters.
FIG. 3 illustrates subscriber processing.

access, using the basic format of OFDM. In OFDMA,
multiple subscribers simultaneously use different
subcarriers, in a fashion similar to frequency division mul
tiple access (FDMA). For more information, see Sari and

Karam, “Orthogonal Frequency-Division Multiple Access

35

trary cluster feedback.
FIG. 6 illustrates one embodiment of a partition the
clusters into groups.
40

Multipath causes frequency-selective fading. The channel

FIG. 8 illustrates frequency reuse and interference in a

multi-cell, multi-sector netWork.
45

The subcarriers that are in deep fade for one subscriber may

Therefore, it is advantageous in an OFDMA system to
adaptively allocate the subcarriers to subscribers so that each
subscriber enjoys a high channel gain. For more
information, see Wong et al., “Multiuser OFDM With Adap
tive Subcarrier, Bit and PoWer Allocation,” IEEE J. Select.

p1ng.

FIG. 11 illustrates intelligent sWitching betWeen diversity
clusters and coherence clusters depending on subscribers

mobility.
FIG. 12 illustrates one embodiment of a recon?guration

Areas Commun., Vol. 17(10), pp. 1747—1758, October 1999.

of cluster classi?cation.

Within one cell, the subscribers can be coordinated to
55

neighboring cells, the problem of intercell interference

A distributed, reduced-complexity approach for subcar

arises. It is clear that the intercell interference in an OFDMA

rier allocation is described. The techniques disclosed herein
are described using OFDMA (clusters) as an example.
HoWever, they are not limited to OFDMA-based systems.

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 subcarrier allocation for OFDMA is a

and channel knoWledge of all the subscribers in all the cells,
but also requiring frequent rescheduling every time an

FIG. 13 illustrates one embodiment of a base station.

DETAILED DESCRIPTION OF THE PRESENT
INVENTION

intracell interference. HoWever, With aggressive frequency
reuse plan, e.g., the same spectrum is used for multiple

joint optimiZation operation, not only requiring the activity

FIG. 9 illustrates different cluster formats for coherence

clusters and diversity clusters.
FIG. 10 illustrates diversity clusters With subcarrier hop

provide high channel gains for another subscriber.

have different subcarriers in OFDMA. The signals for dif
ferent subscribers can be made orthogonal and there is little

FIG. 7 illustrates one embodiment of a feedback format

for group-based cluster allocation.

IEEE VTC’98, pp. 2502—2506.
gains are different for different subcarriers. Furthermore, the
channels are typically uncorrelated for different subscribers.

FIG. 4 illustrates one example of FIG. 3.
FIG. 5 illustrates one embodiment of a format for arbi

and its Application to CATV Networks,” European Trans
actions 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

Which, hoWever, should not be taken to limit the invention
to the speci?c embodiments, but are for explanation and

The techniques apply to multi-carrier systems in general,
Where, for example, a carrier can be a cluster in OFDMA, a
65

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 alloca
tion decisions are made taking into account all subscribers in

Some portions of the detailed descriptions Which folloW
are presented in terms of algorithms and symbolic repre
sentations 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

a cell for each allocation.

For doWnlink channels, each subscriber ?rst 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))

10

physical manipulations of physical quantities. Usually,
though not necessarily, these quantities take the form of
electrical or magnetic signals capable of being stored,

and feeds back the information on these candidate subcar

riers to the base station. The feedback may comprise channel

and interference information (e.g., signal-to-interference

transferred, combined, compared, and otherWise manipu

plus-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.

lated. It has proven convenient at times, principally for
15 reasons of common usage, to refer to these signals as bits,

values, elements, symbols, characters, terms, numbers, or
the like.
It should be borne in mind, hoWever, that all of these and
similar terms are to be associated With the appropriate

Upon receiving the information from the subscriber, the

physical quantities and are merely convenient labels applied

base station further selects the subcarriers among the

to these quantities. Unless speci?cally stated otherWise as

candidates, utiliZing additional information available at the

apparent from the folloWing discussion, it is appreciated that
throughout the description, discussions utiliZing terms such

base station, e.g., the traf?c load information on each

as “processing” or “computing” or “calculating” or “deter

subcarrier, amount of traf?c requests queued at the base

station for each frequency band, Whether frequency bands

25

mining” or “displaying” or the like, refer to the action and

are overused, and/or hoW long a subscriber has been Waiting

processes of a computer system, or similar electronic com

to send information. In one embodiment, the subcarrier

puting device, that manipulates and transforms data repre

loading information of neighboring cells can also be

sented as physical (electronic) quantities Within the com
puter system’s registers and memories into other data
similarly represented as physical quantities Within the com

exchanged betWeen base stations. The base stations can use
this information in subcarrier allocation to reduce inter-cell
interference.

puter system memories or registers or other such informa
tion storage, transmission or display devices.
The present invention also relates to apparatus for per

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 speci?ed by the subscriber When

35

specifying subcarriers that it ?nds 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 subscrib
ers about the subcarrier allocation and the coding/

40

forming the operations herein. This apparatus may be spe
cially constructed for the required purposes, or it may
comprise a general purpose computer selectively activated
or recon?gured by a computer program stored in the com
puter. 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 ?oppy disks, optical disks,
CD-ROMs, and magnetic-optical disks, read-only memories

modulation rates to use.

(ROMs), random access memories (RAMs), EPROMs,

In one embodiment, the feedback information for doWn
link subcarrier allocation is transmitted to the base station
through the uplink access channel, Which occurs in a short

EEPROMs, magnetic or optical cards, or any type of media
45

period every transmission time slot, e.g., 400 microseconds

The algorithms and displays presented herein are not
inherently related to any particular computer or other appa
ratus. Various general purpose systems may be used With
programs in accordance With the teachings herein, or it may

in every 10-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 traf?c load information on the uplink subcarriers
are used for uplink subcarrier allocation.
For either direction, the base station makes the ?nal
decision of subcarrier allocation for each subscriber.

prove convenient to construct more specialiZed apparatus to

perform the required method steps. The required structure

55

In the folloWing description, a procedure of selective
subcarrier allocation is also disclosed, including methods of
channel and interference sensing, methods of information

for a variety of these systems Will appear from the descrip
tion beloW. In addition, the present invention is not
described With reference to any particular programming
language. It Will be appreciated that a variety of program

ming languages may be used to implement the teachings of
the invention as described herein.

feedback from the subscribers to the base station, and

Amachine-readable medium includes any mechanism for
storing or transmitting information in a form readable by a

algorithms used by the base station for subcarrier selections.

machine (e.g., a computer). For example, a machine
readable medium includes read only memory (“ROM”);
random access memory (“RAM”); magnetic disk storage

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
speci?c 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.

suitable for storing electronic instructions, and each coupled
to a computer system bus.

media; optical storage media; ?ash memory devices;
65

electrical, optical, acoustical or other form of propagated

signals (e.g., carrier Waves, infrared signals, digital signals,
etc.); etc.

US 6,947,748 B2
6

5
Subcarrier Clustering

desires to use. No cluster index is needed to indicate Which
SINR value in the feedback corresponds to Which cluster as

The techniques described herein are directed to subcarrier
allocation for data traffic channels. In a cellular system, there

long as the order of information in the feedback is knoWn to
the base station. In an alternative embodiment, the informa
tion in the feedback is ordered according to Which clusters
have the best performance relative to each other for the

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. 1A illustrates multiple subcarriers, such as subcarrier
101, and cluster 102. Acluster, such as cluster 102, is de?ned

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

as a logical unit that contains at least one physical subcarrier,

among the candidates (processing block 104). The base

as shoWn in FIG. 1A. A cluster can contain consecutive or

station may utiliZe additional information available at the
base station, e.g., the traf?c load information on each

disjoint subcarriers. The mapping betWeen a cluster and its

subcarriers can be ?xed or recon?gurable. In the latter case,
subcarrier, amount of traf?c requests queued at the base
the base station informs the subscribers When the clusters are 15 station for each frequency band, Whether frequency bands

rede?ned. In one embodiment, the frequency spectrum
includes 512 subcarriers and each cluster includes four

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

consecutive subcarriers, thereby resulting in 128 clusters.
An Exemplary Subcarrier/Cluster Allocation Procedure

stations. The base stations can use this information in

FIG. 1B is a How diagram of one embodiment of a process
for allocation clusters to subscribers. The process is per

subcarrier allocation to reduce inter-cell interference.

After cluster selection, the base station noti?es the sub
scriber about the cluster allocation through a doWnlink

formed 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.

common control channel or through a dedicated doWnlink
25

Referring to FIG. 1B, each base station periodically
broadcasts pilot OFDM symbols to every subscriber Within

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.

its cell (or sector) (processing block 101). The pilot symbols,

Once the basic communication link is established, each

often referred to as a sounding sequence or signal, are
knoWn to both the base station and the subscribers. In one

subscriber can continue to send the feedback to the base
station using a dedicated traf?c channel (e.g., one or more

embodiment, each pilot symbol covers the entire OFDM

prede?ned uplink access channels).

frequency bandwidth. The pilot symbols may be different for
different cells (or sectors). The pilot symbols can serve

In one embodiment, the base station allocates all the

multiple purposes: time and frequency synchronization,
channel estimation and signal-to-interference/noise (SINR)

clusters to be used by a subscriber at once. In an alternative
35

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

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
traf?c, of each cluster (processing block 102). Based on this

embodiment, the base station ?rst allocates multiple clusters,
referred to herein as the basic clusters, to establish a data link

ratio measurement for cluster allocation.

With good performance (e.g., high SINR and loW traf?c

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

loading) relative to each other and feeds back the informa
tion on these candidate clusters to the base station through

station ?rst ensures the assignment of the basic clusters to
the subscribers and then tries to satisfy further requests on

40

information, each subscriber selects one or more clusters

prede?ned uplink access channels (processing block 103).

45

subscribers before allocating basic clusters to other subscrib
ers. 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

mance than others. The selection results in each subscriber
selecting clusters they Would prefer to use based on the

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

measured parameters.
In one embodiment, each subscriber measures the SINR
of each subcarrier cluster and reports these SINR measure
ments to their base station through an access channel. The
SINR value may comprise the average of the SINR values

clusters to that neW subscriber.
55

of each of the subcarriers in the cluster. Alternatively, the

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

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 sub
carriers 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

the auxiliary clusters from the subscribers. Alternatively, the
base station may assign auxiliary clusters to one or more

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 perfor

65

speci?c subscriber to report its updated cluster selection.
Retraining can also be initiated by the subscriber When it
observes channel deterioration.

US 6,947,748 B2
8

7
Adaptive Modulation and Coding

cells are broadcast at the same time, they Will interfere With

In one embodiment, different modulation and coding rates

each other (because they occupy the entire frequency band).

are used to support reliable transmission over channels With

This collision of pilot symbols may be used to determine the

different SINR. Signal spreading over multiple subcarriers

amount of interference as a Worst case scenario. Therefore,

may also be used to improve the reliability at very loW

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 inter

SINR.

An example coding/modulation table is given beloW in
Table 1.

ference sources are on. Thus, the structure of pilot symbols

is such that it occupies the entire frequency band and causes
collisions among different cells for use in detecting the Worst
case SINR in packet transmission systems.
During data traffic periods, the subscribers can determine
the level of interference again. The data traffic periods are

TABLE 1
Scheme

Modulation

Code Rate

0
1
2

QPSK, 1/2 Spreading
QPSK, ‘A Spreading
QPSK, l/2 Spreading

1/2
1/2
1/2

3

QPSK

1/2

4

SPSK

2/3

the pilot and traffic periods may be used to sense the

5
6

16QAM
64QAM

%
5/6

(intra-cell) traf?c loading and inter-cell interference to select

used to estimate the intra-cell traffic as Well as the inter-cell
15

the desirable clusters.
The interference level on certain clusters may be loWer,
because these clusters may be unused in the neighboring
cells. For example, in cell A, With respect to cluster A there
is less interference because cluster A is unused in cell B

In the example above, 1/8 spreading indicates that one
QPSK modulation symbol is repeated over eight subcarriers.
The repetition/spreading may also be extended to the time
domain. For example, one QPSK symbol can be repeated
over four subcarriers of tWo OFDM symbols, resulting also

1/8 spreading.

(While it is used in cell C). Similarly, in cell A, cluster B Will
25

The coding/modulation rate can be adaptively changed

based on the Worst case situation in Which all interference
sources are transmitting.
In one embodiment, a subscriber utiliZes the information

symbols simultaneously, and each pilot symbol occupies the

available from both the pilot symbol periods and the data
traffic periods to analyZe the presence of both the intra-cell
traffic load and inter-cell interference. The goal of the
35

high channel gain, loW interference from other cells, and
high availability. The subscriber provides feedback infor

there are a predetermined number of data periods folloWed
40

FIG. 3 illustrates one embodiment of subscriber process

ing. The processing is performed by processing logic that
may comprise hardWare (e.g., dedicated logic, circuitry,
45

phase, as if there is no interference or noise. Once the

channel is estimated, the subscriber calculates the
interference/noise from the received signal.
The estimated SINR values may be ordered from largest
to smallest SINRs and the clusters With large SINR values

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. 3, channel/interference estimation pro
cessing block 301 performs channel and interference esti
mation in pilot periods in response to pilot symbols. Traf?c/

interference analysis processing block 302 performs traffic

are selected. In one embodiment, the selected clusters have
SINR values that are larger than the minimum SINR Which

still alloWs a reliable (albeit loW-rate) transmission sup
ported by the system. The number of clusters selected may
depend on the feedback bandWidth and the request trans
mission rate. In one embodiment, the subscriber alWays tries

mation that includes the results, listing desired clusters in
order or not as described herein.

A subscriber estimates the SINR for each cluster from the

pilot symbols. In one embodiment, the subscriber ?rst
estimates the channel response, including the amplitude and

subscriber is to provide an indication to the base station as
to those clusters that the subscriber desires to use. Ideally,

the result of the selection by the subscriber is clusters With

approximately 152 microseconds. After each pilot period,
by another set of pilot symbols. In one embodiment, there
are four data periods used to transmit data after each pilot,
and each of the data periods is 152 microseconds.

experience loWer interference from cell B because cluster B
is used in cell B but not in cell C.
The modulation/coding rate based on this estimation is

robust to frequent interference changes resulted from bursty
packet transmission. This is because the rate prediction is

according to the channel conditions observed at the receiver
after the initial cluster allocation and rate selection.
Pilot Symbols and SINR Measurement
In one embodiment, each base station transmits pilot

entire OFDM frequency bandwidth, as shown in FIGS.
2A—C. Referring to FIGS. 2A—C, pilot symbols 201 are
shoWn traversing the entire OFDM frequency bandWidth for
cells A, B and C, respectively. In one embodiment, each of
the pilot symbols have a length or duration of 128 micro
seconds With a guard time, the combination of Which is

interference level. Speci?cally, the poWer difference during

and interference analysis in data periods in response to
signal information and information from channel/
interference estimation block 301.
55

to send the information about as many clusters as possible

from Which the base station chooses.

Cluster ordering and rate prediction processing block 303
is coupled to outputs of channel/interference estimation
processing block 301 and traffic/interference analysis pro
cessing block 302 to perform cluster ordering and selection

along With rate prediction.
The output of cluster ordering processing block 303 is
input to cluster request processing block 304, Which requests

The estimated SINR values are also used to choose the

appropriate coding/modulation rate for each cluster as dis

cussed above. By using an appropriate SINR indexing
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
that even for the same subscribers, different clusters can

selections are sent to the base station. In one embodiment,

Pilot symbols serve an additional purpose in determining

the SINR on each cluster is reported to the base station
through an access channel. The information is used for
cluster selection to avoid clusters With heavy intra-cell traf?c

interference among the cells. Since the pilots of multiple

loading and/or strong interference from other cells. That is,

have different modulation/coding rates.

65

US 6,947,748 B2
9

10

a neW subscriber may not be allocated use of a particular

cluster if heavy intra-cell traf?c 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

PN, With no signal and interference

P; + PN, With signal only

loW-rate transmission or no reliable transmission at all.
P

The channel/interference estimation by processing block

D

301 is Well-knoWn in the art by monitoring the interference

=

P, + PN , With interference only

Pg + P, + PN, With both signal and 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:

Pg + P1, With no signal and interference
10

P], with signal only
Pp — PD =

P5, 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.

15

Where PP is the measured poWer corresponding to each

cluster during pilot periods, PD is the measured poWer
during the traffic periods, P5 is the signal poWer, P, is the

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 H- are not

interference poWer, and PN is the noise poWer.
In one embodiment, the subscriber selects clusters With

knoW. During pilot periods, the signal Si representing the

relatively large PP/(PP—PD) (e.g., larger than a threshold

pilot symbols, and the observation yi are knoWns, thereby
alloWing determination of the channel gain H- for the case

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

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

difference betWeen observed samples during the pilot period
25

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,

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:

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

and during the data traffic period for each of the subcarriers
in a cluster such as the folloWing:

35

Where f is a function of the tWo inputs. One example of f is

performance criteria. Using the ordered list of clusters, the
subscriber requests the desired clusters along With coding

Weighted averaging (e.g., equal Weights). Alternatively, a

and modulation rates knoWn to the subscriber to achieve
desired data rates.
FIG. 4 is one embodiment of an apparatus for the selec
tion of clusters based on poWer difference. The approach

the poWer difference PP— D to distinguish clusters With
similar SINR. The difference may be smaller than a thresh

subscriber selects a cluster based on its SINR and only uses
40

old (e.g., 1 dB).
Both the measurement of SINR and PP—PD can be aver

uses information available during both pilot symbol periods

aged over time to reduce variance and improve accuracy. In
one embodiment, a moving-average time WindoW is used

and data traffic periods to perform energy detection. The

processing of FIG. 4 may be implemented in hardWare, (e.g.,

45

dedicated logic, circuitry, etc.), softWare (such as is run on,
for example, a general purpose computer system or dedi

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 con
tains both the indices of selected clusters and their SINR. An

cated machine), or a combination of both.
Referring to FIG. 4, a subscriber includes SINR estima

tion processing block 401 to perform SINR estimation for

each cluster in pilot periods, poWer calculation processing

exemplary format for arbitrary cluster feedback is shoWn in

block 402 to perform poWer calculations for each cluster in

FIG. 5. Referring to FIG. 5, the subscriber provides a cluster
index (ID) to indicate the cluster and its associated SINR

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

55

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 order

(506), etc. The SINR for the cluster may be created using an
average of the SINRs of the subcarriers. Thus, multiple

ing 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 speci?cally, 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:

value. For example, in the feedback, the subscriber provides
cluster ID1 (501) and the SINR for the cluster, SINR1 (502),
cluster ID2 (503) and the SINR for the cluster, SINR2 (504),
and cluster ID3 (505), and the SINR for the cluster, SINR3

65

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 ?eld can be

US 6,947,748 B2
11

12

used for SINR indexing to indicate 8 different rates of

information, the inter-cell interference levels, and the intra

adaptive coding/modulation.

cell traf?c load on each cluster.
In one embodiment, a subscriber ?rst selects the group

An Exemplary Base Station
The base station assigns desirable clusters to the sub
scriber making the request. In one embodiment, the avail

With the best overall performance and then feedbacks the
SINR information for the clusters in that group. The sub

ability of the cluster for allocation to a subscriber depends on
the total traf?c load on the cluster. Therefore, the base station

scriber may order the groups based on their number of

clusters for Which the SINR is higher than a prede?ned
threshold. By transmitting the SINR of all the clusters in the

selects the clusters not only With high SINR, but also With
loW traf?c load.
FIG. 13 is a block diagram of one embodiment of a base

10

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 speci?ed for each subscriber (e.g., via SINR/rate
indices signals 1313 received from OFDM transceiver 1305)

15

and user data, queue fullness/traf?c 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

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 indi
cating a group-based cluster allocation. Referring to FIG. 7,
a group ID, ID1, is folloWed by the SINR values for each of
the clusters in the group. This can signi?cantly 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

through control signal channels (e.g., control signal/cluster

may be performed by an allocation in a media access control

allocation 1312 via OFDM transceiver 1305). Controller

portion of the base station.

1301 updates the decisions during retraining.
In one embodiment, controller 1301 also performs admis

Furthermore, in a multi-cell environment, groups can
25

have different priorities associated With different cells. In

sion control to user access since it knoWs the traf?c load of

one embodiment, the subscriber’s selection of a group is

the system. This may be performed by controlling user data
buffers 1302 using admission control signals 1310.
The packet data of User 1~N are stored in the user data

biased by the group priority, Which means that certain
subscribers have higher priorities on the usage of some
groups than the other subscribers.

buffers 1302. For doWnlink, With the control of controller
1301, multiplexer 1303 loads the user data to cluster data

In one embodiment, there is no ?xed association betWeen
one subscriber and one cluster group; hoWever, in an alter

buffers (for Cluster 1~M) Waiting to be transmitted. For the

native embodiment there may be such a ?xed association. In
an implementation having a ?xed association betWeen a

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

subscriber and one or more cluster groups, the group index
35

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

40

each cluster, e.g., the pilot signal shoWs Which clusters have
already been allocated for other subscribers and Which

(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. Refer
ring to FIG. 6, groups 1—4 are shoWn With arroWs pointing
to clusters that are in each group as a result of the partition

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
45

available, and 1111-1-1-1-1 to indicate the cluster is not

ing. In one embodiment, the clusters Within each group are
spaced far apart over the entire bandWidth. In one

available. At the receiver, the subscriber ?rst distinguishes
the tWo sequences using the signal processing methods

embodiment, the clusters Within each group are spaced apart
farther than the channel coherence bandWidth, ie the band
Width Within Which the channel response remains roughly
the same. Atypical value of coherence bandWidth is 100 kHZ

Which are Well knoWn in the art, e.g., the correlation

for many cellular systems. This improves frequency diver
sity 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 55

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. Group
based 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 65
sent back to the base station. Many criteria can be used to
choose and order the groups, based on the channel

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 ?rst

compressed using source coding techniques, e.g., differen
tial 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 anten
nas 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 alterna
tively. As shoWn in FIG. 8, each shaded sector uses half of
the available OFDMA clusters and each unshaded sector

US 6,947,748 B2
14

13

Table 4 shoWs the priority orders for the unshaded sectors,

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

Which are different from those for the shaded sectors, since

the interfering relationship is reversed.

referred to herein as even clusters.

Consider the doWnlink signaling With omni-directional

TABLE 4

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

Priority ordering for the doWnlink of the unshaded sectors.

Priority Ordering

Cell A

Cell B

Cell C

1
2
3

Group 1
Group 2
Group 3

Group 2
Group 3
Group 1

Group 3
Group 1
Group 2

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 A1 receives interference from Sector C1, but its
transmission interferes With Sector B1. Namely, its interfer
ence source and the victims With Which it interferes are not 15

the same. This might cause a stability problem in a distrib

Intelligent SWitching betWeen Coherence and
Diversity Clusters
In one embodiment, there are tWo categories of clusters:

uted cluster-allocation system using interference avoidance:

coherence clusters, containing multiple subcarriers close to
each other and diversity clusters, containing multiple sub

if a frequency cluster is assigned in Sector B1 but not in
Sector C1, the cluster may be assigned in A1 because it may
be seen as clean in A1. HoWever, the assignment of this
cluster A1 can cause interference problem to the existing

assignment in B1.

carriers 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 coher
ence bandWidth, i.e. the bandWidth Within Which the channel

In one embodiment, different cluster groups are assigned
different priorities for use in different cells to alleviate the

Within 100 kHZ for many cellular systems. On the other

aforementioned problem When the traffic load is progres
sively 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

response remains roughly the same, Which is typically
25

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

reducing, and potentially minimiZing, the probability of
causing interference problem to existing assignments in

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 frequen

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.

cies 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 con?g
ured differently for different cells to reduce the effect of

TABLE 2
Priority ordering for the doWnlink of the shaded sectors.

Priority Ordering

Cell A

Cell B

Cell C

1
2
3

Group 1
Group 2
Group 3

Group 3
Group 1
Group 2

Group 2
Group 3
Group 1

Consider Sector A1. First, the clusters in Group 1 are
selectively assigned. If there are still more subscribers

45

inter-cell interference through interference averaging.
FIG. 9 shoWs example cluster con?gurations 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 CellA are distributed

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 C1). Note that the neWly assigned clusters from
Group 2 to Sector A1 shall not cause interference problem
in Sector B1, unless the load in Sector B1 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

hand, the spread of subcarriers in diversity clusters is
preferably larger than the channel coherence bandWidth,

to Cluster 1, 8, 7, 6 in Cell B. This signi?cantly 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
55

diversity gain. Therefore, it is advantageous to assign diver
sity clusters to subscribers that are close (e.g., Within the

in Sector A1, B1, and C1.

coherent bandWidth) to the cell boundaries and are more

subject to inter-cell interference.

TABLE 3

Since the subcarriers in a coherence cluster are consecu
Cluster usage for the doWnlink of the shaded sectors
With less than 2/3 of the full load

Cluster Usage

Cell A

Cell B

Cell C

1
2

Group 1
Group 2

Group 3
Group 1

Group 2
Group 3

3

tive 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 signi?cantly 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.

US 6,947,748 B2
15

16

With channel coding across the subcarriers Within the
cluster, diversity clusters are more robust to cluster mis

FIG. 11 is a How diagram of one embodiment of a process

for intelligent selection betWeen diversity clusters and
coherence clusters depending on subscribers mobility. The

selection (by the nature of diversi?cation itself), While
yielding possibly less gain from cluster selection. Channel

process is performed by processing logic that may comprise
hardWare (e.g., circuitry, dedicated logic, etc.), softWare

coding across the subcarriers means that each codeWord

(such as that Which runs on, for eXample, a general purpose
computer system or dedicated machine), or a combination of
both.

contains bits transmitted from multiple subcarriers, and
more speci?cally, the difference bits betWeen codeWords

(error vector) are distributed among multiple subcarriers.
More frequency diversity can be obtained through sub

Referring to FIG. 11, processing logic in the base station
performs channel/interference variation detection
(processing block 1101). Processing logic then tests Whether

carrier hopping over time in Which a subscriber occupies a
set of subcarriers at one time slot and another different set of

the results of the channel/interference variation detection

subcarriers at a different time slot. One coding unit (frame)
contains multiple such time slots and the transmitted bits are

indicate that the user is mobile or in a ?Xed position close to

the edge of the cell (processing block 1102). If the user is not

encoded across the entire frame.

FIG. 10 illustrates diversity cluster With subcarrier hop
ping. Referring to FIG. 10, there are four diversity clusters

mobile or is not in a ?Xed position close to the edge of the
15

in each of cells A and B shoWn, With each subcarrier in

individual diversity clusters having the same label (1, 2, 3,

diversity clusters.

or 4). There are four separate time slots shoWn and during
each of the time slots, the subcarriers for each of the

The selection can be updated and intelligently sWitched

during retraining.

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 subcarrier hopping over time, With

cell, processing transitions to processing block 1103 Where
processing logic in the base station selects coherence clus
ters; otherWise, processing transitions to processing block
1104 in Which processing logic in the base station selects

25

The ratio/allocation of the numbers of coherence and
diversity clusters in a cell depends on the ratio of the
population of mobile and ?Xed subscribers. When the popu
lation changes as the system evolves, the allocation of
coherence and diversity clusters can be recon?gured to
accommodate the neW system needs. FIG. 12 illustrates a

further interference diversity achieved by using different

recon?guration of cluster classi?cation Which can support

hopping patterns for different cells, as shoWn in FIG. 10.
The manner in Which the subscriber changes the subcar
riers (hopping sequences) can be different for different cells
in order to achieve better interference averaging through

more mobile subscribers than that in FIG. 9.
Whereas many alterations and modi?cations of the
present invention Will no doubt become apparent to a person

coding.

description, it is to be understood that any particular embodi

For static subscribers, such as in ?xed Wireless access, the
channels change very little over time. Selective cluster

of ordinary skill in the art after having read the foregoing
ment shoWn and described by Way of illustration is in no
35

allocation using the coherence clusters achieves good per
formance. 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

40

a subscriber measuring channel and interference informa
tion for a plurality of subcarriers based on pilot sym
bols received from a base station, Wherein the sub

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

scriber 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

different after one cycle. Note that selective cluster alloca
tion can be performed on both coherence and diversity
clusters.
In one embodiment, for cells containing miXed mobile
and ?Xed subscribers, a channel/interference variation detec

cluster of subcarriers, and
the subscriber measuring intra-cell traf?c;

tor can be implemented at either the subscriber or the base
55

the subscriber selecting a set of candidate subcarriers,
Wherein the subscriber selects candidate subcarriers
based, at least in part, on the intra-cell traf?c 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.

mobile subscribers or ?Xed subscribers at cell boundaries,
and coherence clusters to ?Xed subscribers close to the base
station. The channel/interference variation detector mea
sures the channel (SINR) variation from time to time for

each cluster. For example, in one embodiment, the channel/

2. The method de?ned in claim 1 further comprising the
base station selecting the subcarriers in order to balance

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). Alarge difference
subcarrier allocation may be not reliable. In such a case,
diversity clusters are more desirable for the subscriber.

ing orthogonal frequency division multiple access

(OFDMA) comprising:

can be used to provide eXtra robustness and to alleviate the
overhead of frequent cluster reallocation. In one

indicates that channel/interference changes frequently and

ences 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. Amethod for subcarrier selection for a system employ

allocation needs to be updated at a rapid rate, causing
signi?cant control overhead. In this case, diversity clusters

station, or both. Using the detection results, the subscriber
and the base station intelligently selects diversity clusters to

Way intended to be considered limiting. Therefore, refer

intra-cell traf?c load on each cluster.
65

3. Amethod for subcarrier selection for a system employ

ing orthogonal frequency division multiple access

(OFDMA) comprising:

US 6,947,748 B2
17

18

a subscriber measuring channel and interference informa
tion for a plurality of subcarriers based on pilot sym
bols received from a base station, Wherein the sub

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 modu
lation rates that the subscriber desires to employ for

scriber measuring channel and interference information

comprises using information from pilot symbol periods
and data periods to measure channel and interference

each cluster; and

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

10

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.

employing orthogonal frequency division multiple access

(OFDMA) comprising:
a subscriber measuring channel and interference informa
tion for a plurality of subcarriers based on pilot sym
bols 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

4. The method de?ned in claim 3 further comprising the

subscriber using the poWer difference to distinguish, during
selection, clusters of subcarriers having substantially similar
SINRs.
5. Amethod for subcarrier selection for a system employ

ing orthogonal frequency division multiple access

(OFDMA) comprising:
a subscriber measuring channel and interference informa
tion for a plurality of subcarriers based on pilot sym
bols received from a base station, Wherein the sub

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 de?ned 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

25

the subscriber;
the base station allocating a ?rst portion of the subcarriers
to establish a data link betWeen the base station and the

scriber measuring channel and interference information

subscriber; and then
the base station allocating a second portion of the sub

comprises
using information from pilot symbol periods and data

carriers to the subscriber to increase communication

periods to measure channel and interference

bandWidth Wherein, due to subscriber priority, the base
station allocates the second portion before allocating

information, and
using information from pilot symbol periods and data
traf?c periods to analyZe presence of intra-cell traf?c
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. Amethod for subcarrier selection for a system employ

each subscriber in the cell subcarriers to establish their
data link to the base station.
35

40

back information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a ?rst base station in the ?rst cell, in response to receiving
inter-cell interference information, coordinates With
other cells to make a cluster assignment decision, the
?rst base station performing subcarrier allocation for

45

OFDMA to allocate OFDMA subcarriers in clusters to
the plurality of subscribers based on inter-cell interfer
ence avoidance and intra-cell traf?c load balancing in
response to the feedback information.

ing orthogonal frequency division multiple access

(OFDMA) comprising:
a subscriber measuring channel and interference informa
tion for a plurality of subcarriers based on pilot sym
bols 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

11. An apparatus comprising:
a plurality of subscribers in a ?rst cell to generate feed

12. An apparatus comprising:
a plurality of subscribers in a ?rst cell to generate feed

back information indicating clusters of subcarriers
desired for use by the plurality of subscribers; and

providing feedback information comprises arbitrarily

a ?rst base station in the ?rst cell, the ?rst base station to
allocate OFDMA subcarriers in clusters to the plurality

ordering the set of candidate of subcarriers as clusters

of subcarriers, and further Wherein the feedback infor

of subscribers;

mation includes an indeX indication of a candidate 55

each of a plurality of subscribers to measure channel and

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 de?ned in claim 6 Wherein each indeX is
indicative of a coding and modulation rate.
8. Amethod for subcarrier selection for a system employ

interference information for the plurality of subcarriers
based on pilot symbols received from the ?rst base
station, Wherein each of the plurality of subscribers

ing orthogonal frequency division multiple access

sures intra-cell traf?c, and further Wherein at least one

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 mea

(OFDMA) comprising:
a subscriber measuring channel and interference informa
tion for a plurality of subcarriers based on pilot sym
bols received from a base station;

65

subscriber of the plurality of subcarriers based, at least
in part, on the intra-cell traf?c load balancing, and the
one subscriber to provide feedback information on the
set of candidate subcarriers to the base station and to

US 6,947,748 B2
19

20

receive an indication of subcarriers form the set of

base station for use by the one subscriber, Wherein the

subcarriers selected by the ?rst base station for use by

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 de?ned in claim 19 Wherein each indeX
is indicative of a coding and modulation rate.

the one subscriber.

13. The apparatus de?ned in claim 12 Wherein the base
station selects subcarriers in order to balance intra-cell traf?c
load on each cluster of subcarriers.

14. An apparatus comprising:
a plurality of subscribers in a ?rst cell to generate feed

21. An apparatus comprising:

back inforrnation indicating clusters of subcarriers
desired for use by the plurality of subscribers; and

a plurality of subscribers in a ?rst cell to generate feed

back inforrnation indicating clusters of subcarriers
desired for use by the plurality of subscribers; and

a ?rst base station in the ?rst cell, the ?rst base station to
allocate OFDMA subcarriers in clusters to the plurality

a ?rst base station in the ?rst cell, the ?rst base station to
allocate OFDMA subcarriers in clusters to the plurality

of subscribers;
each of a plurality of subscribers to measure channel and

of subscribers;

interference information for the plurality of subcarriers
based on pilot syrnbols received from the ?rst base
station, Wherein at least one subscriber of the plurality

each of a plurality of subscribers to measure channel and

interference information for the plurality of subcarriers
based on pilot syrnbols received from the ?rst base

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 peri
ods 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 25
receive an indication of subcarriers from the set of

subcarriers selected by the ?rst base station for use by
the one subscriber.

15. The apparatus de?ned in claim 14 Wherein the one

subscriber distinguishes, during selection, cluster of subcar
riers having substantially similar SINRs based on the poWer
difference.
16. The apparatus de?ned in claim 14 Wherein the at least
one subscriber uses information from pilot syrnbol periods
and data traf?c periods to analyZe presence of intra-cell
traf?c load and inter-cell interference.
17. The apparatus de?ned in claim 14 Wherein the pilot
syrnbols occupy an entire OFDM frequency bandWidth.
18. The apparatus de?ned in claim 17 Wherein at least one
other pilot syrnbol from a different cell transmitted at the
same time as the pilot syrnbols received from the base
station collide With each other.

23. An apparatus comprising:
a plurality of subscribers in a ?rst cell to generate feed
35

of subscribers; and
each of a plurality of subscribers to measure channel and
40

a plurality of subscribers in a ?rst cell to generate feed
45

a ?rst base station in the ?rst cell, the ?rst base station to
allocate OFDMA subcarriers 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 syrnbols received from the ?rst 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 feed
back inforrnation on the set of candidate subcarriers to
the base station and to receive an indication of subcar
riers from the set of subcarriers selected by the ?rst

back inforrnation indicating clusters of subcarriers
desired for use by the plurality of subscribers; and
a ?rst base station in the ?rst cell, the ?rst base station to
allocate OFDMA subcarriers in clusters to the plurality

19. An apparatus comprising:
back inforrnation indicating clusters of subcarriers
desired for use by the plurality of subscribers; and

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 feed
back inforrnation on the set of candidate subcarriers to
the base station and to receive an indication of subcar
riers from the set of subcarriers selected by the ?rst
base station for use by the one subscriber, Wherein the
one subscriber sends an indication of coding and rnodu
lation rates that the one subscriber desires to employ.
22. The apparatus de?ned in claim 21 Wherein the indi
cation of coding and modulation rates comprises an SINR
indeX indicative of a coding and modulation rate.

interference information for the plurality of subcarriers
based on pilot syrnbols received from the ?rst 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 feed
back inforrnation on the set of candidate subcarriers to
the base station and to receive an indication of subcar
riers from the set of subcarriers selected by the ?rst
base station for use by the one subscriber;
Wherein the base station allocates a ?rst portion of the
subcarriers to establish a data link betWeen the base

station, the base station allocates a second portion of
the subcarriers to the subscriber to increase communi

55

cation bandWidth, and due to subscriber priority, the
base station allocates the second portion before allo
cating each subscriber in the cell subcarriers to estab
lish their data link to the base station.