(12) United States Patent
`Li et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,904,283 B2
`Jun. 7, 2005
`
`US006904283B2
`
`(54) MULTI-CARRIER COMMUNICATIONS
`WITH GROUP-BASED SUBCARRIER
`ALLOCATION
`
`(75) Inventors: Xiaodong Li, Bellevue, WA (US); Hui
`Liu, Sammamish, WA (US); Hujun
`Yin, Seattle, WA (US); Guanbin Xing,
`Bellevue, WA (Us); Fuqi Mu,
`Issaquah> WA (Us)
`
`(73) Assignee: AdaptiX, IIlC., Bothell, WA (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 727 days.
`
`_
`(21) Appl' No" 09/837’337
`(22) Filed:
`Apt 17’ 2001
`
`4/1996 Bodin et al.
`5,507,034 A
`5/1996 ROY, III 61 ‘IL
`5,515,378 A
`9/1996 Fattouche et al.
`5,555,268 A
`5,588,020 A * 12/1996 Schilling .................. .. 370/337
`5708973 A
`1/1998 Rmer
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`198 00 953 c1
`7/1999
`0 869 647 A2 * 10/1998
`0 926 912 A2
`6/1999
`0 929 202 A1
`7/1999
`0 999 658 A2 * 5/2000
`2 777 407 A1 10/1999
`2 209 858 A
`8/1997
`06029922
`2/1994
`WO 98/16077 A2
`4/1998
`WO 98/30047 A1
`7/1998
`W0 02 49305 A2
`6/2002
`
`......... .. H04L/27/26
`
`__________ __ H04B/7/02
`
`DE
`EP
`EP
`EP
`EP
`FR
`GB
`JP
`W0
`W0
`W0
`
`(65)
`
`Prior Publication Data
`
`OTHER PUBLICATIONS
`
`Us 2OO3/0169681 A1 Sep 11 2003
`7
`Related US Application Data
`
`(63) ggrcltirlnsljatzigrégnpart of application No. 09/738,086, ?led on
`
`(52) U S C]
`
`(51) Int. c1.7 .......................... .. H04B 7/00- H04B 1/38'
`H04Q 7/20. H04M H00’. H04] 11/06
`455/450 455/’69 455/447
`455/448; 455/561; 455/550.1; 370/208
`(58) Field of Search ............................... .. 375/133, 135,
`375/260, 267; 370/203, 208, 210, 482,
`484, 431, 319_321, 328, 329, 332, 342,
`344, 345; 455/69, 434, 455, 463, 4221,
`447_450, 4521, 4522, 453, 42, 500, 512,
`513, 102_105
`
`(56)
`
`References Cited
`
`US PATENT DOCUMENTS
`5 280 630 A
`1/1994 Wang
`5,479,447 A * 12/1995 Chow et al. .............. .. 375/260
`5,504,775 A
`4/1996 Chouly et al.
`
`Vittoria Mignone et al., “CD3—OFDM: A Novel Demodu
`lation Scheme for Fixed and Mobile Receivers,” IEEE
`Transactions on Communications, Sep. 1996, pp.
`1144—1151, vol. 44, No. 9, IEEE.
`(Continued)
`
`Primary Examiner—w?liam Trost
`Assistant Examiner—Meless ZeWdu
`(74) Attorney, Agent, or Firm—Blakely, Sokoloff, Taylor &
`Zafman LLP
`(57)
`
`ABSTRACT
`_
`_
`Amethod and apparatus for subcarr1er selection for systems
`is described. In one embodiment, a method for subcarrier
`selection for a system employing orthogonal frequency
`division multiple access (OFDMA) comprises partitioning
`subcarriers into groups of at least one cluster of subcarriers,
`receiving an indication of a selection by the subscriber of
`one or more groups in the groups, and allocating at least one
`cluster in the one or more groups of clusters selected by the
`subcarrier for use in communication With the subscriber.
`
`119 Claims, 7 Drawing Sheets
`
`Begin
`
`Periodically Broadcast Pilot
`OFDM Symbols to Subscribers
`
`Subscribe/(s) Continuously Monitors
`Pilot Symbols/Measures SINR and/or ~1°2
`Ollie! Parameters
`
`1
`
`Nu
`
`Each Subscriber Selects One or More
`Clusters lor Each Base Station
`
`Retraining
`Needed
`7
`
`Base Station Selects One or More {104
`Clusters for Each Subscriber
`
`i
`
`Base Station Noti?es tne Subscriber
`Regarding Cluster Allocation
`
`~105
`
`____l
`
`ERIC-1002
`Ericsson v IV
`Page 1 of 24
`
`

`
`US 6,904,283 B2
`Page 2
`
`US. PATENT DOCUMENTS
`
`3/1998 Frodigh et al.
`5,726,978 A
`3/1998 Kotzin et al.
`5,734,967 A
`6/1998 Sarkioja et al.
`5,774,808 A
`5,822,372 A * 10/1998 Emami ..................... .. 375/260
`5,867,478 A
`2/1999 Baum et al.
`5,886,988 A
`3/1999 Yun et al.
`5,887,245 A
`3/1999 Lindroth et al.
`5,909,436 A * 6/1999 Engstrom et al. ......... .. 370/343
`5,914,933 A * 6/1999 Cimini et al. ............. .. 370/208
`5,933,421 A
`8/1999 Alamouti et al.
`5,956,642 A * 9/1999 Larsson et al. ........... .. 455/449
`5,973,642 A 10/1999 Li et al. ................... .. 342/378
`5,991,273 A 11/1999 Abu-Dayya
`6,005,876 A 12/1999 Cimini, Jr. et al. ....... .. 370/525
`6,009,553 A * 12/1999 Martinez et al. .......... .. 714/784
`6,026,123 A
`2/2000 Williams
`6,041,237 A
`3/2000 Farsakh .................... .. 455/450
`6,052,594 A
`4/2000 Chuang et al. ........... .. 455/450
`6,061,568 A
`5/2000 Dent
`6,064,692 A
`5/2000 Chow ....................... .. 375/219
`
`5/2000 Clark et al. . . . . .
`. . . .. 375/224
`6,064,694 A
`5/2000 Paulraj et al. ............ .. 370/329
`6,067,290 A
`8/2000 Balachandran et al.
`6,108,374 A
`6,111,919 A * 8/2000 Yonge, III ................ .. 375/260
`6,131,016 A 10/2000 Greenstein et al.
`6,141,565 A 10/2000 Feuerstein et al.
`6,144,696 A 11/2000 Shively et al.
`6,226,320 B1
`5/2001 Hakkinen et al.
`6,282,185 B1 * 8/2001 Hakkinen et al. ......... .. 370/335
`6,298,092 B1
`10/2001 Heath, Jr. et al.
`6,307,851 B1
`10/2001 Jung et al.
`6,327,472 B1
`12/2001 Westroos et al.
`6,330,460 B1
`12/2001 Wong et al.
`6,366,195 B1
`4/2002 Harel et al.
`6,377,632 B1
`4/2002 Paulraj et al.
`6,377,636 B1
`4/2002 Paulraj et al.
`6,449,246 B1
`9/2002 Barton et al.
`6,473,467 B1
`10/2002 Wallace et al.
`6,477,158 B1
`11/2002 Take
`6,545,997 B1 * 4/2003 Bohnke et al. ........... .. 370/347
`6,567,383 B1 * 5/2003 Bohnke .................... .. 370/280
`6,657,949 B1
`12/2003 Jones, IV et al.
`6,726,297 B1 * 4/2004 Uesugi ..................... .. 375/260
`2002/0114269 A1 * 8/2002 Onggosanusi et al. .... .. 370/208
`2003/0067890 A1
`4/2003 Goel et al.
`2003/0169681 A1
`9/2003 Li et al.
`9/ 2003 Chayat
`2003/ 0169824 A1
`
`OTHER PUBLICATIONS
`
`Bender et al., CDMA/HDR: A Bandwidth—E?icient High—
`Speed Wireless Data Service for Nomadic Users, IEEE
`Communications Magazine, Jul. 2000, pp. 70—87.
`Tsoulos, G.V., Smart Antennas For Mobile Communication
`Systems: Bene?ts And Challenges, Electronics & Commu
`nication Engineering Journal, Apr. 1999, pp. 84—94.
`Shad et al., Indoor SDll/[A Capacity Using a Smart Antenna
`Basestation, 1997 IEEE, pp. 868—872.
`Farsakh, Christof and Nossek, Josef A., On the Mobile
`Radio Capacity Increase Through SDIVIA, no date (after
`1997).
`
`Frullone et al., PRMA Performance in Cellular Environ
`ments 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: SDll/[A 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.
`Farsakh, C. et al., “Maximizing the SDMA Mobile Radio
`Capacity Increase by DOA Sensitive Channel Allocation”,
`Wireless Personal Communications, KluWer Academic Pub
`lishers, NL, vol. 11, No. 1, Oct. 1999, pp. 63—76,
`XP000835062, ISSN: 0929—6212.
`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
`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 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.
`Ye Li, et al.: “Clustered OFDM With channel estimation for
`high rate Wireless data”, Mobile Multimedia Communica
`tions, 1999. (MOMUC ’99). 1999 IEEE International Work
`shop 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 Tech
`nology Conference, 1998. VTC 98. 48th IEEE OttaWa,
`Ontario, Canada, May 18—21, 1998, pp. 2502—2506,
`XP010288120, ISBN: 0—7803—4320—4.
`KinugaWa, Y et al.: “Frequency and Time Division Multiple
`Access With Demand—Assignment Using Multicarrier
`Modulation for Indoor Wireless Communications Systems”,
`IEICE Transactions on Communications, Institute of Elec
`tronics Information and Comm. Eng. Tokyo, Japan, vol.
`E77—B, NR. 3, Mar. 1994, pp. 396—402, XP000451014,
`ISSN: 0916—8516.
`
`* cited by examiner
`
`ERIC-1002 / Page 2 of 24
`
`

`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 1 0f 7
`
`US 6,904,283 B2
`
`FIG. 1A
`
`Pilot OFDM
`Symbols
`201
`
`201
`
`201
`
`FIG. 2
`
`t
`
`t
`
`t
`
`7
`
`Cluster A
`Cluster B
`
`Occupied Clusters
`a. Cell A
`(A)
`
`b. Cell B
`(B)
`
`C.
`C
`(C)
`
`f
`
`f
`
`f
`
`ERIC-1002 / Page 3 of 24
`
`

`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 2 0f 7
`
`US 6,904,283 B2
`
`Periodically Broadcast Pilot
`OFDM Symbols to Subscribers
`
`_/ 101
`
`Subscriber(s) Continuously Monitors
`Pilot Symbols/Measures SINR and/or ‘v 102
`Other Parameters
`
`l
`
`l
`
`Each Subscriber Selects One or More
`Clusters for Each Base Station
`
`l
`
`Base Station Selects One or More
`Clusters for Each Subscriber
`
`-/104
`
`l
`
`Base Station Noti?es the Subscriber
`Regarding Cluster Allocation
`
`~105
`
`FIG. 1B
`
`ERIC-1002 / Page 4 of 24
`
`

`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 3 0f 7
`
`US 6,904,283 B2
`
`Channel/interference ~/ 301
`-—> Estimation in Pilot
`Penods
`+
`Traffic/Interference
`——> Analysis in Date
`Periods
`
`I
`
`I
`
`I
`
`’\ 302
`
`( 303
`Cluster Ordering
`and Rate
`Prediction
`
`K 304
`Request Selected
`——> Clusters and Coding! —>
`Modulation Rates
`
`3
`
`-->
`
`Per-cluster SINR $01
`Estimation in —>
`PM Periods
`Cluster Ordering/
`Selection Based on
`402
`"i 404 SINR and Power
`Difference
`
`Per-cluster
`—> Power Calculation
`in Pilot Periods
`
`-
`
`_/‘405
`
`405
`F
`Request Selected
`—-> Clusters and Coding/ —>
`Modulation Rates
`
`Per-cluster
`—> Power Calculation
`in Data Periods ’\ 403
`
`4
`
`501 \ 502 \ 503 \ 504 \ 504 q 504 —\
`Cluster
`Cluster
`Cluster
`‘D1
`‘D2
`m3
`
`SINRZ
`
`SINR3
`
`- ~
`
`SlNRl
`
`Group 3
`
`Group 4
`
`/" \ x K’ \ a)
`t
`
`L J \ / \ J
`Y \ W/’'
`x\ //J
`t
`Group 1
`Group 2
`
`ERIC-1002 / Page 5 of 24
`
`

`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 4 0f 7
`
`US 6,904,283 B2
`
`Group
`‘D1
`
`S|NR1 SINRZ SINR3
`
`Group
`I02
`
`SINR1 SINR2 SINR3 0 0 0
`
`\\\\\\\\\\Q\
`
`g \ Q
`
`FIG. 8
`
`ERIC-1002 / Page 6 of 24
`
`

`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 5 0f 7
`
`US 6,904,283 B2
`
`f
`>
`
`f
`)
`
`f
`>
`
`f
`
`1-8: Diverse Clusters
`946: Plain Clusters
`1
`1
`
`1234,511111 9
`
`10 12341516718‘ 11
`
`12 12314
`
`8' 13
`
`14 1234511815 16
`
`Vt
`
`a. CellA
`
`123
`
`I8 9
`
`10 812
`
`711 12 7812345613 14 b 1234515 115
`
`H
`
`b. CellB
`
`5111! 1234! 9
`
`10 41511:
`
`123 11
`
`12 3411b! 12 13
`
`14 2
`
`0/111 15
`
`16
`
`H
`
`c.CellC
`
`Subcarrier1
`Subcarrier2
`
`Time1
`Time2
`Time3
`T1me4
`
`1
`
`t
`
`a. CeIIA
`
`b. Cell B
`
`FIG. 10
`
`ERIC-1002 / Page 7 of 24
`
`

`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 6 0f 7
`
`US 6,904,283 B2
`
`Channel/Interference
`Variation Detection
`
`/ 1101
`
`1102
`
`Any
`Signi?cant Variation
`Detected
`?
`
`FIG. 11
`
`(1103
`
`Select Coherence
`Clusters
`
`“04v
`
`Select Diversity
`Clusters
`
`124156191“ 10 23451679}11 12 123%5167 H’ 14 122141111 91“ 1e
`
`Vt
`
`a. CeilA
`
`r
`>
`
`ERIC-1002 / Page 8 of 24
`
`

`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 7 0r 7
`
`US 6,904,283 B2
`
`User Data Buffer Information
`1311
`
`User 1 ~ N
`
`1301
`
`__(.___>
`Admission Control
`
`Multi-user Data
`Buffer
`
`\ 1302
`
`Cluster Allocation and
`Load Scheduling ———> Multiplexer
`Controller
`A
`
`f 1303
`
`I I I I I Cluster1~M
`
`SmR/Rate
`~/\ lndices
`
`Multi-cluster
`Transmission and f 1304
`Receiving Buffer
`
`(
`
`> OFDM Transceiver
`
`\/ 1305
`
`Control Signal/
`
`Cluster Allocation
`1312
`
`1 OFDM signal
`
`-
`
`FIG. 13
`
`ERIC-1002 / Page 9 of 24
`
`

`
`US 6,904,283 B2
`
`1
`MULTI-CARRIER COMMUNICATIONS
`WITH GROUP-BASED SUBCARRIER
`ALLOCATION
`
`This patent application is a Continuation-in-part (CIP) of
`patent application Ser. No. 09/738,086 ?led Dec. 15, 2000,
`entitled “OFDMA With Adaptive Subcarrier-Cluster Con
`?guration and Selective Loading.”
`
`FIELD 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
`
`15
`
`2
`One approach to subcarrier 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
`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.
`
`SUMMARY OF THE INVENTION
`
`A method and apparatus for subcarrier selection for
`systems is described. In one embodiment, a method for
`subcarrier selection for a system employing orthogonal
`frequency division multiple access (OFDMA) comprises
`partitioning subcarriers into groups of at least one cluster of
`subcarriers, receiving an indication of a selection by the
`subscriber of one or more groups in the groups, and allo
`cating at least one cluster in the one or more groups of
`clusters selected by the subcarrier for use in communication
`With the subscriber.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The present invention Will be understood more fully from
`the detailed description given beloW and from the accom
`panying draWings of various embodiments of the invention,
`Which, hoWever, should not be taken to limit the invention
`to the speci?c embodiments, but are for explanation and
`understanding only.
`FIG. 1A illustrates subcarriers and clusters.
`FIG. 1B is a How 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 arbi
`trary 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 hop
`ping.
`FIG. 11 illustrates intelligent sWitching betWeen diversity
`clusters and coherence clusters depending on subscribers
`mobility.
`FIG. 12 illustrates one embodiment of a recon?guration
`of cluster classi?cation.
`FIG. 13 illustrates one embodiment of a base station.
`
`DETAILED DESCRIPTION OF THE PRESENT
`INVENTION
`
`An approach for subcarrier allocation is described. A
`method and apparatus for subcarrier selection for systems is
`described. In one embodiment, a method for subcarrier
`selection for a system employing orthogonal frequency
`division multiple access (OFDMA) comprises partitioning
`subcarriers into groups of at least one cluster of subcarriers,
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`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
`more information, see Cimini, Jr., “Analysis and Simulation
`of a Digital Mobile Channel Using Orthogonal Frequency
`Division Multiplexing,” IEEE Trans. Commun., vol. COM
`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.
`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 mul
`tiple access (FDMA). For more information, see Sari and
`Karam, “Orthogonal Frequency-Division Multiple Access
`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
`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 subcarriers 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 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.
`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 dif
`ferent 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
`65
`adaptively allocate the subcarriers so as to mitigate the effect
`of intercell interference.
`
`55
`
`60
`
`ERIC-1002 / Page 10 of 24
`
`

`
`US 6,904,283 B2
`
`3
`receiving an indication of a selection by the subscriber of
`one or more groups in the groups, and allocating at least one
`cluster in the one or more groups of clusters selected by the
`subcarrier for use in communication With the subscriber.
`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. 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 ?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))
`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
`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.
`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 traf?c load information on each
`subcarrier, amount of traf?c 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 speci?ed by the subscriber When
`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/
`modulation rates to use.
`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
`period every transmission time slot, e.g., 400 microseconds
`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.
`In the folloWing description, a procedure of selective
`subcarrier allocation is also disclosed, including methods of
`
`10
`
`15
`
`25
`
`35
`
`40
`
`45
`
`55
`
`65
`
`4
`channel and interference sensing, methods of information
`feedback from the subscribers to the base station, and
`algorithms used by the base station for subcarrier 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
`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.
`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
`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 manipu
`lated. 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 borne in mind, hoWever, that all of these and
`similar terms are to be associated With the appropriate
`physical quantities and are merely convenient labels applied
`to these quantities. Unless speci?cally stated otherWise as
`apparent from the folloWing discussion, it is appreciated that
`throughout the description, discussions utiliZing terms such
`as “rprocessing” or “computing” or “calculating” or “deter
`mining” or “displaying” or the like, refer to the action and
`processes of a computer system, or similar electronic com
`puting device, that manipulates and transforms data repre
`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
`puter system memories or registers or other such informa
`tion storage, transmission or display devices.
`The present invention also relates to apparatus for per
`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
`(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 appa
`ratus. 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 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.
`
`ERIC-1002 / Page 11 of 24
`
`

`
`US 6,904,283 B2
`
`10
`
`35
`
`25
`
`5
`Amachine-readable medium includes any mechanism for
`storing or transmitting information in a form readable by a
`machine (e.g., a computer). For example, a machine
`readable medium includes read only memory (“ROM”);
`random access memory (“RAM”); magnetic disk storage
`media; optical storage media; ?ash memory devices;
`electrical, optical, acoustical or other form of propagated
`signals (e.g., carrier Waves, infrared signals, digital signals,
`etc.); etc.
`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. 1A illustrates multiple subcarriers, such as subcarrier
`101, and cluster 102. Acluster, such as cluster 102, is de?ned
`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 ?xed or recon?gurable. In the latter case,
`the base station informs the subscribers When the clusters are
`rede?ned. 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 How diagram of one embodiment of a process
`for allocation clusters to subscribers. The process is per
`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.
`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
`40
`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
`traf?c, 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 traf?c
`loading) relative to each other and feeds back the informa
`tion on these candidate clusters to the base station through
`prede?ned 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 perfor
`mance 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 measure
`ments 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
`
`45
`
`55
`
`65
`
`6
`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
`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 informa
`tion 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 traf?c load information on each
`subcarrier, amount of traf?c 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 noti?es the sub
`scriber 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 traf?c channel (e.g., one or more
`prede?ned 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 ?rst 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 alloc