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

Filing 1

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

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EXHIBIT A 111111111111111111111111111111111!I I I,11,1111111111111111111111111 (12) United States Patent (10) Patent No.: US 7,146,172 B2 (45) Date of Patent: *Dec. 5, 2006 Li et al. (54) MULTI-CARRIER COMMUNICATIONS ADAPTIVE CLUSTER CONFIGURATION AND SWITCHING 5,507,034 A 5,515,378 A 5,555,268 A 5,588,020 A 5,708,973 A 5,726,978 A 5,734,967 A 5,774,808 A 5,822,372 A 5,867,478 A 5,886,988 A 5,887,245 A 5,909,436 A 5,914,933 A 5,933,421 A 5,956,642 A WITH (75) Inventors: Xiaodong Li, Bellevue, WA (US); Hui Liu, Sammamish, WA (US); Wenzhong Zhang, Bellevue, WA (US); Kemin Li, Bellevue, WA (US) Assignee: Adaptix, Inc., Seattle, WA (US) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 758 days. This patent is subject to a terminal disclaimer. DE 198 00 953 Prior Publication Data US 2002/0147017 Al * Bodin et al. Roy et al. Fattouche et al. Schilling Ritter Frodigh et al. Kotzin et al. Sarkioja et al. Emami Baum et al. Yun et al. Lindroth et al. Engstrom et al. Cimini et al. Alamouti et al. Larsson et al. 455/452.2 370/334 375/141 370/337 455/62 370/252 455/63.1 455/436 375/260 370/203 370/208 455/449 FOREIGN PATENT DOCUMENTS Apr. 17, 2001 (65) * * * * * * * 4/1996 5/1996 9/1996 12/1996 1/1998 3/1998 3/1998 6/1998 10/1998 2/1999 3/1999 3/1999 6/1999 6/1999 8/1999 9/1999 (Continued) (21) Appl. No.: 09/837,701 (22) Filed: * * 7/1999 (Continued) Oct. 10, 2002 OTHER PUBLICATIONS Related U.S. Application Data (63) Continuation-in-part of application No. 09/738,086, filed on Dec. 15, 2000. Mignone et al., CD3-OFDM: A Novel Demodulation Scheme for Fixed and Mobile REceivers, IEEE Trnasations on Communications, vol. 44, No. 9, Sep. 1996.* (Continued) (51) Int. Cl. HO4Q 7/20 (52) U.S. Cl. (58) (56) (2006.01) 455/452.1; 455/450; 455/452.2; 455/447; 455/448 Field of Classification Search 455/447, 455/450, 452.1, 452.2, 453; 310/203, 208, 310/343, 480, 205, 439, 210, 299, 347; 375/276 See application file for complete search history. References Cited U.S. PATENT DOCUMENTS 5,280,630 A * 1/1994 Wang 5,479,447 A * 12/1995 Chow et al. 5,504,775 A * 4/1996 Chouly et al. 455/452.2 375/260 370/210 Primary Examiner—Temica Beamer Assistant Examiner Joy Contee (74) Attorney, Agent, or Firm—Fulbright & Jaworski LLP (57) ABSTRACT A method and apparatus for allocating subcarriers in an orthogonal frequency division multiple access (OFDMA) system is described. In one embodiment, the method comprises allocating at least one diversity cluster of subcarriers to a first subscriber and allocating at least one coherence cluster to a second subscriber. 13 Claims, 7 Drawing Sheets Cl.v. Detection o) /101_ ASH Yes Select Diversity Clusters —110/ No Select Coherence Clusters I 1 0.1 US 7,146,172 B2 Page 2 U.S. PATENT DOCUMENTS 5,973,642 A 10/1999 Li et al 5,991,273 A 11/1999 Abu-Dayya 6,005,876 A 12/1999 Cimini, Jr. et al. 6,009,553 A 12/1999 Martinez et al. 6,026,123 A 2/2000 Williams 6,041,237 A 3/2000 Farsakh 6,052,594 A 4/2000 Chuang et al. 6,061,568 A 5/2000 Dent 6,064,692 A 5/2000 Chow 6,064,694 A 5/2000 Clark et al. 6,067,290 A 5/2000 Paulraj et al. 6,108,374 A 8/2000 Balachandran et al. 6,111,919 A 8/2000 Yonge, III 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 BI 5/2001 Hakkinen et al. 6,282,185 BI * 8/2001 Hakkinen et al. 6,298,092 31 10/2001 Heath, Jr. 6,307,851 31 * 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 BI 4/2002 Hard et al. 6,377,632 BI 4/2002 Paulraj et al. 6,377,636 31 4/2002 Paulraj et al. 6,449,246 31 9/2002 Barton et al. 6,473,467 B1 10/2002 Wallace et al. 6,477,158 31 11/2002 Take 6,545,997 BI 4/2003 Bohnke et al. 6,657,949 Bl* 12/2003 Jones et al. 6,726,297 31 * 4/2004 Uesugi 2003/0067890 Al 4/2003 Goel et al. 2003/0169681 Al * 9/2003 Li et al. 2003/0169824 Al 9/2003 Chayat 2005/0025099 Al * 2/2005 Heath et al. 342/378 370/525 455/450 455/450 375/219 375/224 370/329 370/342 370/342 455/562.1 370/205 375/260 370/203 370/334 FOREIGN PATENT DOCUMENTS DE EP EP EP EP FR GB JP WO WO WO 198 00 953 Cl 7/1999 0 869 647 A2 10/1998 0 926 912 A2 6/1999 0 929 202 Al 7/1999 0 999 658 A2 5/2000 2 777 407 Al 10/1999 2 209 858 A 8/1997 06029922 2/1994 WO 98/16077 A2 4/1998 WO 98/30047 Al 7/1998 WO 02 49305 A2 6/2002 OTHER PUBLICATIONS Farsakh, C. et al.. "Maximizing the SDMA Mobile Radio Capacity Increase by DOA Sensitive Channel Allocation". Wireless Personal Communications, Kluwer Academic Publishers, NL, vol. 11, No. 1, Oct. 1999, pp. 63-76, XP000835062, ISSN: 0929-6212. Wong, C.Y., et al., Multiuser OFDM With Adaptive Subcarrier, Bit, and Power Allocation. IEEE Journal on Selected Areas in Communications, Oct. 1999, IEEE Inc., New York, USA, vol. 17, Nr. 10, pp. 1747-1758, XP000854075, ISSN: 0733-8716 Sections I and II abstract. Gruenheid, R. et al: "Adaptive Modulation and Multiple Access for the OFDM Transmission Technique", Wireless Personal Communications, Kluwer Academic Publishers, NL, vol. 13, NR. 1/2, Year 2000, pp. 5-13 XP000894156, ISSN: 0929-6212, no month listed. Motegi, M. et al.: "Optimum Band Allocation According to Subband Condition for BST-OFDM" 11e IEEE International Symposium on Personal Indoor and Mobile Radio Communications, vol. 2, Sep. 18-21, 2000, pp. 1236-1240, XP002213669, Piscataway, NJ, USA, ISBN: 0-7803-6463-5. Kapoor, S. et al.: "Adaptive Interference Suppression in Multiuser Wireless OFDM Systems Using Antenna Arrays" IEEE Transactions on Signal Processing, vol. 47, No. 12, Dec. 1999, pp. 33813391, XP000935422, IEEE, New York, USA, ISSN: 1053-587X. Ye Li, et al.: "Clustered OFDM with channel estimation for high rate wireless data", Mobile Multimedia Communications, 1999. (MOMUC '99). 1999 IEEE International Workshop on San Diego, CA, USA, IEEE, US, Nov. 15, 1999, pp. 43-50, XP010370695, ISBN: 0-7803-5904-6. Nogueroles, R. et al.: "Improved Performance of a Random OFDMA Mobile Communication System" Vehicular Technology Conference, 1998. VTC 98. 48th IEEE Ottawa, Ontario, Canada, May 18-21, 1998, pp. 2502-2506, XP010288120, ISBN: 0-78034320-4. 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 Electronics Information and Comm. Eng. Tokyo, Japan, vol. E77-B, NR. 3, Mar. 1994, pp. 396-402, XP000451014, ISSN: 0916-8516. Bender et al., CDMA/HDR: A Bandwidth-Efficient 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: Benefits And Challenges, Electronics & Communication Engineering Journal, Apr. 1999, pp. 84-94. Shad et al., Indoor SDMA Capacity Using a Smart Antenna Basestation, 1997 IEEE, pp. 868-872, no month listed. Farsakh, Christof and Nossek, Josef A., On the Mobile Radio Capacity Increase Through SDMA, no date (after 1997). Frullone et al., PRMA Performance in Cellular Environments with Self-Adaptive Channel Allocation Strategies, IEEE Transactions on Vehicular Technology, Nov. 1996, pp. 657-665 vol. 45, No. 4. Xu, Guanghan and Li, San-Qi, Throughput Multiplication of Wireless Lans for Multimedia Services: SDMA Protocol Design, 1994 IEEE, pp. 1326-1332, no month listed. 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. Wong et al. "Multiuser OFDM with Adaptive Subcarrier, Bit, and Power Allocation", IEEE Journal on Selected Areas in Communications. IEEE. New York, US, 1999, vol. 17. NR. 10, pp. 17471758, no month listed. Mexican Office Action issued for PA/a/2003/005311 dated Mar. 31, 2006. * cited by examiner U.S. Patent US 7,146,172 B2 Sheet 1 of 7 Dec. 5, 2006 Subcarrier Cluster 10) ladk Figure lA s vrts-.- Pilot OFDM Symbols 111s 11111•a•s • 2.0 4111 .P . 440 1PIIIPP.' Occupied Clusters a.Cell A ( 4) f t b.Cell B ( b) t Figure 2 c. Cell C U.S. Patent r Dec. 5, 2006 Sheet 2 of 7 US 7,146,172 B2 • *-A Pue C)F" D ao. sl,...4,64 4 S J 6rr-.ws At) y (Air c...tr ; 6 vsv-49 Ger."ts ...ro a vli la.  11,,,..4* Ls/ e b l VE . 1 lift, 0 6144. rr el1/44.4hary "6 S SI Pill.. atLa...- r .F.41:01 ,-,......--&-v-s -s ,...c. or es info to ItAs Esneri.e) gETPAieJ eJ 31C NVE.ve..P Pt* OW C.. J 7 -c rrs. ervw de' F00- L•4 c. toy E. 0-- 1r 1 g I ar STA-L-60 pal- LES 1- 4 CA—k• A o-Di4 S. Or SC•ergi.4.(-2-2 c- A I tf5 U.S. Patent Dec. 5, 2006 US 7,146,172 B2 Sheet 3 of 7 Channel/Interference Estimation in Pilot Periods Cluster '.ordering and Rate —IPI Prediction V Traffic/Interference Analysis in Data Periods Request Selected Clusters & Coding/ Modulation Rates 3401 I 3b3 Figure 3 Per-Cluskr S 1WK —11wEstirnation PAD+ periods (Lioi Cluster Ordering/ Selection Based on 4 1 10 Request Selected Clusters & Coding/ —11Modulation Rates Power Difference Per-Cluster Power Calculation in Pilot Periods r-fa b al- yo 5 Per-Cluster Power Calculation in Data Periods f 9.3 Figure 4 f Cluster ID1 " Se C L FO I t Cluster ID2 SINR1 5°3 1 SINR2 5 ' 1 Sc'`( I Cluster 103 r 51 . SINR3 • • • Figure 5 Group 4 Group 3 111s 11s s s s s s s s s 111s •=1s — 111s 01. 1111011, —111111s Group 1 Figure 6 Group 2 U.S. Patent Group 101 Figure 7 Figure 8 SINR-I US 7,146,172 B2 Sheet 4 of 7 Dec. 5, 2006 SINR2 SINR3 II . I 51,4 0-1 Dr-44-1- U.S. Patent Dec. 5, 2006 US 7,146,172 B2 Sheet 5 of 7 1-8: Diverse Clusters 9-16: Plain Clusters —..--345678 9 10 12 34 56 76 92 11 12 34 5 78 7 9 1 2 3 4, 5 6 13 14 13 1 2 3 4 5 6 78 15 16 14 67 81 3 45 15 16 2 3 4 5 6 7 81 1 15 16 a. CEA A 1254 56 T8 9 10 8 128 45 6 7 12 11 i 1 1 b. COB 56 78 12 34 9 10 45 67 81 23 92 11 34 56 78 1 2 13 14 C. Cell C Figure 9 I /— ; z :i:5 4 3 . i .4'1; 4, 3.144 3 'i 3 I 214 , 4. a Cell A .3141 H Yl 3 4i 1 2 . 41 t I ..) I 1 ' 71Al'. b. Cell a Figure 10 A iZ3 , 234 3 ! U.S. Patent Dec. 5, 2006 US 7,146,172 B2 Sheet 6 of 7 2 Detection —,1 6 ) Yes V Select Coherence Clusters Select Diversity Clusters Figure 11 123 45 67 B9 111 13 5 10 12 345 67 89 111 13 5 12 a. Gel A Figure 12 11 123 4 56 7891 135 14 1 2 34 567891 1 1 135 16 U.S. Patent Dec. 5, 2006 Tr- ser Data Buffert U Information :all CVimission Control 131. V Cluster Allocation and Load Scheduling Controller Sheet 7 of 7 W: 2M: US 7,146,172 B2 User 1 - N Multi-User Data Buffer 11.-1_ Multiplexer A A A A 1 II YIF Ir T —1.703 Cluster 1 - M Multi-Cluster Transmission and Receiving Buffer OFDM Tra hsceiver (Control Signal/ ciws4, Alf 0.a:.... 1312_ OFDM Signal 1 1 i>....s.. 13 Is US 7,146,172 B2 1 2 MULTI-CARRIER COMMUNICATIONS WITH ADAPTIVE CLUSTER CONFIGURATION AND SWITCHING 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 impractical in real wireless system, mainly due to the bandwidth cost for updating the subscriber information and the computation cost for the joint optimization. This patent application is a Continuation-in-part (CIP) of patent application Ser. No. 09/738,086 filed Dec. 15, 2000, entitled "OFDMA with Adaptive Subcarrier-Cluster Configuration and Selective Loading." FIELD OF THE INVENTION The invention relates to the field of wireless communications; more particularly, the invention relates to multi-cell, multi-subscriber wireless systems using orthogonal frequency division multiplexing (OFDM). 5 10 SUMMARY OF THE INVENTION 15 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 20 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 25 Division Multiplexing," IEEE Trans. Commun., vol. COM33, no. 7, July 1985, pp. 665 75; Chuang and Sollenberger, "Beyond 3G: Wideband Wireless Data Access Based on OFDM and Dynamic Packet Assignment," IEEE Communications Magazine, Vol. 38, No. 7, pp. 78-87, July 2000. 30 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 35 access, using the basic format of OFDM. In OFDMA, multiple subscribers simultaneously use different subcarriers, in a fashion similar to frequency division multiple access (FDMA). For more information, see Sari and Karam, "Orthogonal Frequency-Division Multiple Access and its 40 Application to CATV Networks," European Transactions on Telecommunications, Vol. 9 (6), pp. 507-516, November/ December 1998 and Nogueroles, Bossed, Donder, and Zyablov, "Improved Performance of a Random OFDMA Mobile Communication System,", Proceedings of IEEE 45 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 50 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 Adaptive Subcarrier, Bit and 55 Power Allocation," IEEE J. Select. Areas Commun., Vol. 17(10), pp. 1747-1758, October 1999. Within one cell, the subscribers can be coordinated to have different subcarriers in OFDMA. The signals for different subscribers can be made orthogonal and there is little so 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. A method and apparatus for allocating subcarriers in an orthogonal frequency division multiple access (OFDMA) system is described. In one embodiment, the method comprises allocating at least one diversity cluster of subcarriers to a first subscriber and allocating at least one coherence cluster to a second subscriber. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only. FIG. 1A illustrates subcarriers and clusters. FIG. 1B is a flow diagram of one embodiment of a process for allocating subcarriers. FIG. 2 illustrates time and frequency grid of OFDM symbols, pilots and clusters. FIG. 3 illustrates subscriber processing. FIG. 4 illustrates one example of FIG. 3. FIG. 5 illustrates one embodiment of a format for arbitrary cluster feedback. FIG. 6 illustrates one embodiment of a partition the clusters into groups. FIG. 7 illustrates one embodiment of a feedback format for group-based cluster allocation. FIG. 8 illustrates frequency reuse and interference in a multi-cell, multi-sector network. FIG. 9 illustrates different cluster formats for coherence clusters and diversity clusters. FIG. 10 illustrates diversity clusters with subcarrier hopping. FIG. 11 illustrates intelligent switching between diversity clusters and coherence clusters depending on subscribers mobility. FIG. 12 illustrates one embodiment of a reconfiguration of cluster classification. FIG. 13 illustrates one embodiment of a base station. DETAILED DESCRIPTION OF THE PRESENT INVENTION A method and apparatus for allocating subcarriers in an orthogonal frequency division multiple access (OFDMA) system is described. In one embodiment, the method comprises allocating at least one diversity cluster of subcarriers to a first subscriber and allocating at least one coherence cluster to a second 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 US 7,146,172 B2 3 4 CDMA, an antenna beam in SDMA (space-division multiple Some portions of the detailed descriptions which follow access), etc. In one embodiment, subcarrier allocation is are presented in terms of algorithms and symbolic repreperformed in each cell separately. Within each cell, the sentations of operations on data bits within a computer allocation for individual subscribers (e.g., mobiles) is also memory. These algorithmic descriptions and representations made progressively as each new subscriber is added to the 5 are the means used by those skilled in the data processing system as opposed to joint allocation for subscribers within arts to most effectively convey the substance of their work each cell in which allocation decisions are made taking into to others skilled in the art. An algorithm is here, and account all subscribers in a cell for each allocation. generally, conceived to be a self-consistent sequence of steps For downlink channels, each subscriber first measures the leading to a desired result. The steps are those requiring channel and interference information for all the subcarriers 0 physical manipulations of physical quantities. Usually, and then selects multiple subcarriers with good performance though not necessarily, these quantities take the form of (e.g.. a high signal-to-interference plus noise ratio (SINR)) electrical or magnetic signals capable of being stored, transand feeds back the information on these candidate subcarferred, combined, compared, and otherwise manipulated. It riers to the base station. The feedback may comprise channel has proven convenient at times, principally for reasons of and interference information (e.g., signal-to-interference- 15 common usage, to refer to these signals as bits, values, plus-noise-ratio information) on all subcarriers or just a elements, symbols, characters, terms, numbers, or the like. portion of subcarriers. In case of providing information on It should be borne in mind, however, that all of these and only a portion of the subcarriers, a subscriber may provide a list of subcarriers ordered starting with those subcarriers similar terms are to be associated with the appropriate which the subscriber desires to use, usually because their 20 physical quantities and are merely convenient labels applied performance is good or better than that of other subcarriers. to these quantities. Unless specifically stated otherwise as Upon receiving the information from the subscriber, the apparent from the following discussion, it is appreciated that base station further selects the subcarriers among the canthroughout the description, discussions utilizing terms such didates, utilizing additional information available at the base as "processing" or "computing" or "calculating" or "deterstation, e.g., the traffic load information on each subcarrier, 25 mining" or "displaying" or the like, refer to the action and amount of traffic requests queued at the base station for each processes of a computer system, or similar electronic comfrequency band, whether frequency bands are overused, puting device, that manipulates and transforms data repreand/or how long a subscriber has been waiting to send sented as physical (electronic) quantities within the cominformation. In one embodiment, the subcarrier loading puter system's registers and memories into other data information of neighboring cells can also be exchanged 30 similarly represented as physical quantities within the combetween base stations. The base stations can use this inforputer system memories or registers or other such informamation in subcarrier allocation to reduce inter-cell interfertion storage, transmission or display devices. ence. The present invention also relates to apparatus for perIn one embodiment, the selection by the base station of the channels to allocate, based on the feedback, results in the 35 forming the operations herein. This apparatus may be speselection of coding/modulation rates. Such coding/modulacially constructed for the required purposes, or it may tion rates may be specified by the subscriber when specifycomprise a general purpose computer selectively activated ing subcarriers that it finds favorable to use. For example, if or reconfigured by a computer program stored in the comthe SINR is less than a certain threshold (e.g., 12 dB), puter. Such a computer program may be stored in a computer quadrature phase shift keying (QPSK) modulation is used; 40 readable storage medium, such as, but is not limited to, any otherwise, 16 quadrature amplitude modulation (QAM) is type of disk including floppy disks, optical disks, CDused. Then the base station informs the subscribers about the ROMs, and magnetic-optical disks, read-only memories subcarrier allocation and the coding/modulation rates to use. (ROMs), random access memories (RAMs), EPROMs, In one embodiment, the feedback information for downEEPROMs, magnetic or optical cards. or any type of media link subcarrier allocation is transmitted to the base station 4 5 suitable for storing electronic instructions, and each coupled through the uplink access channel, which occurs in a short to a computer system bus. period every transmission time slot, e.g., 400 microseconds The algorithms and displays presented herein are not in every 10-millisecond time slot. In one embodiment, the inherently related to any particular computer or other appaaccess channel occupies the entire frequency bandwidth. Then the base station can collect the uplink SINR of each so ratus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may subcarrier directly from the access channel The SINR as prove convenient to construct more specialized apparatus to well as the traffic load information on the uplink subcarriers perform the required method steps. The required structure are used for uplink subcarrier allocation. for a variety of these systems will appear from the descripFor either direction, the base station makes the final 55 tion below. In addition, the present invention is not decision of subcarrier allocation for each subscriber. described with reference to any particular programming In the following description, a procedure of selective language. It will be appreciated that a variety of programsubcarrier allocation is also disclosed, including methods of ming languages may be used to implement the teachings of channel and interference sensing, methods of information the invention as described herein. feedback from the subscribers to the base station, and algorithms used by the base station for subcarrier selections. so A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a In the following description, numerous details are set machine (e.g., a computer). For example, a machine-readforth to provide a thorough understanding of the present able medium includes read only memory ("ROM"); random invention. It will be apparent, however, to one skilled in the access memory ("RAM"); magnetic disk storage media; art, that the present invention may be practiced without these specific details. In other instances, well-known structures 65 optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., and devices are shown in block diagram form, rather than in carrier waves, infrared signals, digital signals. etc.); etc. detail, in order to avoid obscuring the present invention. US 7,146,172 B2 5 6 Subcarrier Clustering indicates the coding/modulation rate that the subscriber desires to use. No cluster index is needed to indicate which The techniques described herein are directed to subcarrier SINR value in the feedback corresponds to which cluster as allocation for data traffic channels In a cellular system, there long as the order of information in the feedback is known to are typically other channels, pre-allocated for the exchange of control information and other purposes. These channels 5 the base station. In an alternative embodiment, the information in the feedback is ordered according to which clusters often include down link and up link control channels, uplink have the best performance relative to each other for the access channels, and time and frequency synchronization subscriber. In such a case, an index is needed to indicate to channels. which cluster the accompanying SINR value corresponds. FIG. lA illustrates multiple subcarriers, such as subcarrier Upon receiving the feedback from a subscriber, the base 101, and cluster 102. A cluster, such as cluster 102. is defined 10 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 disjoint subcarriers. The mapping between a cluster and its base station, e.g., the traffic load information on each subsubcarriers can be fixed or reconfigurable. In the latter case, the base station informs the subscribers when the clusters are 15 carrier, amount of traffic requests queued at the base station for each frequency band, whether frequency bands are redefined. In one embodiment, the frequency spectrum overused, and how long a subscriber has been waiting to includes 512 subcarriers and each cluster includes four send information. The subcarrier loading information of consecutive subcarriers, thereby resulting in 128 clusters. neighboring cells can also be exchanged between base An Exemplary Subcarrier/Cluster Allocation Procedure 20 stations. The base stations can use this information in FIG. 1B is a flow diagram of one embodiment of a process subcarrier allocation to reduce inter-cell interference. for allocation clusters to subscribers. The process is perAfter cluster selection, the base station notifies the subformed by processing logic that may comprise hardware scriber about the cluster allocation through a downlink (e.g.. dedicated logic, circuitry, etc.). software (such as that common control channel or through a dedicated downlink which runs on, for example, a general purpose computer 25 traffic channel if the connection to the subscriber has already system or dedicated machine), or a combination of both. been established (processing block 105). In one embodiReferring to FIG. 1B, each base station periodically ment, the base station also informs the subscriber about the broadcasts pilot OFDM symbols to every subscriber within 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 30 subscriber can continue to send the feedback to the base known to both the base station and the subscribers. In one station using a dedicated traffic channel (e.g., one or more embodiment, each pilot symbol covers the entire OFDM predefined uplink access channels). frequency bandwidth. The pilot symbols may be different for In one embodiment, the base station allocates all the different cells (or sectors). The pilot symbols can serve clusters to be used by a subscriber at once. In an alternative multiple purposes: time and frequency synchronization, 35 embodiment, the base station first allocates multiple clusters, channel estimation and signal-to-interference/noise (SINR) referred to herein as the basic clusters, to establish a data link ratio measurement for cluster allocation. between the base station and the subscriber. The base station Next, each subscriber continuously monitors the reception then subsequently allocates more clusters, referred to herein of the pilot symbols and measures the SINR and/or other as the auxiliary clusters, to the subscriber to increase the parameters, including inter-cell interference and intra-cell 40 communication bandwidth. Higher priorities can be given to traffic, of each cluster (processing block 102). Based on this the assignment of basic clusters and lower priorities may be information, each subscriber selects one or more clusters given to that of auxiliary clusters. For example, the base with good performance (e.g.. high SINR and low traffic station first ensures the assignment of the basic clusters to loading) relative to each other and feeds hack the informathe subscribers and then tries to satisfy further requests on tion on these candidate clusters to the base station through 45 the auxiliary clusters from the subscribers. Alternatively, the predefined uplink access channels (processing block 103). base station may assign auxiliary clusters to one or more For example, SINR values higher than 10 dB may indicate subscribers before allocating basic clusters to other subscribgood performance. Likewise, a cluster utilization factor less ers. For example, a base station may allocate basic and than 50% may be indicative of good performance. Each auxiliary clusters to one subscriber before allocating any subscriber selects the clusters with relatively better perfor- 50 clusters to other subscribers. In one embodiment, the base mance than others. The selection results in each subscriber station allocates basic clusters to a new subscriber and then selecting clusters they would prefer to use based on the determines if there are any other subscribers requesting measured parameters. clusters. If not, then the base station allocates the auxiliary In one embodiment, each subscriber measures the SINR clusters to that new subscriber. of each subcarrier cluster and reports these SINR measure- 55 From time to time, processing logic performs retraining ments to their base station through an access channel The by repeating the process described above (processing block SINR value may comprise the average of the SINR values 106). The retraining may be performed periodically. This of each of the subcaniers in the cluster. Alternatively, the retraining compensates for subscriber movement and any SINR value for the cluster may be the worst SINR among changes in interference. In one embodiment, each subscriber the SINR values of the subcarriers in the cluster. In still so reports to the base station its updated selection of clusters another embodiment, a weighted averaging of SINR values and their associated SINRs. Then the base station further of the subcarriers in the cluster is used to generate an SINK performs the reselection and informs the subscriber about value for the cluster. This may be particularly useful in the new cluster allocation. Retraining can be initiated by the diversity clusters where the weighting applied to the subbase station, and in which case, the base station requests a carriers may be different. 65 specific subscriber to report its updated cluster selection. The feedback of information from each subscriber to the Retraining can also be initiated by the subscriber when it base station contains a SINR value for each cluster and also observes channel deterioration. US 7,146,172 B2 7 8 Adaptive Modulation and Coding Pilot symbols serve an additional purpose in determining interference among the cells. Since the pilots of multiple In on embodiment, different modulation and coding rates cells are broadcast at the same time, they will interfere with are used to support reliable transmission over channels with each other (because they occupy the entire frequency band). different SINR. Signal spreading over multiple subcarriers may also be used to improve the reliability at very low 5 This collision of pilot symbols may be used to determine the amount of interference as a worst case scenario. Therefore, SINR. in one embodiment, the above SINR estimation using this An example coding/modulation table is given below in method is conservative in that the measured interference Table 1. level is the worst-case scenario, assuming that all the intern) ference sources are on. Thus, the structure of pilot symbols TABLE 1 is such that it occupies the entire frequency band and causes Scheme Modulation Code Rate collisions among different cells for use in detecting the worst case SINR in packet transmission systems. 0 QPSK, 1/2 Spreading 1/2 During data traffic periods, the subscribers can determine QPSK, V4 Spreading 1/2 2 QPSK, 1 Spreading 1/2 is the level of interference again. The data traffic periods are 1/2 3 QPSK 1/2 used to estimate the intra-cell traffic as well as the inter-cell 2h 4 8 PSK interference level. Specifically, the power difference during 5 16 QAM 3 '4 / the pilot and traffic periods may be used to sense the 6 64 QAM 5 /6 (intra-cell) traffic loading and inter-cell interference to select 20 the desirable clusters. In the example above, 1/8 spreading indicates that one The interference level on certain clusters may be lower, QPSK modulation symbol is repeated over eight subcarriers. because these clusters may be unused in the neighboring The repetition/spreading may also be extended to the time cells. For example. in cell A, with respect to cluster A there domain. For example, one QPSK symbol can be repeated is less interference because cluster A is unused in cell B over four subcarriers of two OFDM symbols, resulting also 25 (while it is used in cell C). Similarly, in cell A, cluster B will 1/8 spreading. experience lower interference from cell B because cluster B The coding/modulation rate can be adaptively changed is used in cell B but not in cell C. according to the channel conditions observed at the receiver The modulation/coding rate based on this estimation is after the initial cluster allocation and rate selection. robust to frequent interference changes resulted from bursty 30 packet transmission. This is because the rate prediction is Pilot Symbols and SINR Measurement based on the worst case situation in which all interference In one embodiment, each base station transmits pilot sources are transmitting. symbols simultaneously, and each pilot symbol occupies the In one embodiment, a subscriber utilizes the information entire OFDM frequency bandwidth, as shown in FIGS. available from both the pilot symbol periods and the data 2A—C. Referring to FIG. 2A-C, pilot symbols 201 are shown 35 traffic periods to analyze the presence of both the intra-cell traversing the entire OFDM frequency bandwidth for cells traffic load and inter-cell interference. The goal of the A, B and C, respectively. In one embodiment, each of the subscriber is to provide an indication to the base station as pilot symbols have a length or duration of 128 microseconds to those clusters that the subscriber desires to use. Ideally, with a guard time, the combination of which is approxithe result of the selection by the subscriber is clusters with mately 152 microseconds. After each pilot period, there are 40 high channel gain, low interference from other cells, and a predetermined number of data periods followed by another high availability. The subscriber provides feedback inforset of pilot symbols. In one embodiment, there are four data mation that includes the results, listing desired clusters in periods used to transmit data after each pilot, and each of the order or not as described herein. data periods is 152 microseconds. FIG. 3 illustrates one embodiment of subscriber processA subscriber estimates the SINR for each cluster from the 45 ing. The processing is performed by processing logic that pilot symbols. In one embodiment, the subscriber first may comprise hardware (e.g., dedicated logic, circuitry, estimates the channel response, including the amplitude and etc.), software (such as that which runs on, for example, a phase, as if there is no interference or noise. Once the general purpose computer system or dedicated machine), or channel is estimated, the subscriber calculates the interfera combination of both. ence/noise from the received signal. so Referring to FIG. 3, channel/interference estimation proThe estimated SINR values may be ordered from largest cessing block 301 performs channel and interference estito smallest SINRs and the clusters with large SINR values mation in pilot periods in response to pilot symbols. Traffic/ are selected. In one embodiment, the selected clusters have interference analysis processing block 302 performs traffic SINR values that are larger than the minimum SINR which and interference analysis in data periods in response to still allows a reliable (albeit low-rate) transmission sup- 55 signal information and information from channel/interferported by the system. The number of clusters selected may ence estimation block 301. depend on the feedback bandwidth and the request transCluster ordering and rate prediction processing block 303 mission rate. In one embodiment, the subscriber always tries is coupled to outputs of channel/interference estimation to send the information about as many clusters as possible processing block 301 and traffic/interference analysis profrom which the base station chooses. 6c) cessing block 302 to perform cluster ordering and selection The estimated SINR values are also used to choose the along with rate prediction. appropriate coding/modulation rate for each cluster as disThe output of cluster ordering processing block 303 is cussed above. By using an appropriate SINR indexing input to cluster request processing block 304, which requests scheme, an SINR index may also indicate a particular coding clusters and modulation/coding rates. Indications of these and modulation rate that a subscriber desires to use. Note 65 selections are sent to the base station. In one embodiment, that even for the same subscribers, different clusters can the SINR on each cluster is reported to the base station have different modulation/coding rates. through an access channel. The information is used for US 7,146,172 B2 9 cluster selection to avoid clusters with heavy intra-cell traffic loading and/or strong interference from other cells. That is, a new subscriber may not be allocated use of a particular cluster if heavy intra-cell traffic loading already exists with respect to that cluster. Also, clusters may not be allocated if the interference is so strong that the SINR only allows for low-rate transmission or no reliable transmission at all. The channel/interference estimation by processing block 301 is well-known in the art by monitoring the interference that is generated due to full-bandwidth pilot symbols being simultaneously broadcast in multiple cells. The interface information is forwarded to processing block 302 which uses the information to solve the following equation: 10 More specifically, in one embodiment. the signal power of each cluster during the pilot periods is compared with that during the traffic periods, according to the following: 5 PP = PS +PI + PN, PN, with no signal and interference Ps + PN, with signal only PD = + PN, 10 with interference only Ps + Pi + PN, with both signal and interference Ps + PI, with no signal and interference P1, with signal only PP = PD = 15 where S, represents the signal for subcarrier (freq. band) i, is the interference for subcarrier i, n, is the noise associated with subcarrier i, and y, is the observation for subcarrier i. In the case of 512 subcarriers, i may range from 0 to 511. The 20 I, and ff are not separated and may be considered one quantity. The interference/noise and channel gain H, are not know. During pilot periods, the signal S, representing the pilot symbols, and the observation y, are knowns, thereby allowing determination of the channel gain H, for the case 25 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 H, S, and y, are all known. The interference information from processing blocks 301 30 and 302 are used by the subscriber to select desirable clusters. In one embodiment, using processing block 303, the subscriber orders clusters and also predicts the data rate that would be available using such clusters. The predicted data rate information may be obtained from a look up table 35 with precalculated data rate values. Such a look up table may store the pairs of each SINR and its associated desirable transmission rate. Based on this information, the subscriber selects clusters that it desires to use based on predetermined performance criteria. Using the ordered list of clusters, the 40 subscriber requests the desired clusters along with coding and modulation rates known to the subscriber to achieve desired data rates. FIG. 4 is one embodiment of an apparatus for the selection of clusters based on power difference. The approach 45 uses information available during both pilot symbol periods and data traffic periods to perform energy detection. The processing of FIG. 4 may be implemented in hardware, (e.g., dedicated logic, circuitry, etc.), software (such as is run on, for example, a general purpose computer system or dedi- 50 cated machine), or a combination of both. Referring to FIG. 4, a subscriber includes SINR estimation processing block 401 to perform SINR estimation for each cluster in pilot periods, power calculation processing block 402 to perform power calculations for each cluster in 55 pilot periods, and power calculation processing block 403 to perform power calculations in data periods for each cluster. Subtractor 404 subtracts the power calculations for data periods from processing block 403 from those in pilot periods from processing block 402. The output of subtractor 60 404 is input to power difference ordering (and group selection) processing block 405 that performs cluster ordering and selection based on SINR and the power difference between pilot periods and data periods. Once the clusters have been selected, the subscriber requests the selected 65 clusters and the coding/modulation rates with processing block 406. Ps, with interference only 0, with both signal and interference where Pp is the measured power corresponding to each cluster during pilot periods, PD is the measured power during the traffic periods, P c is the signal power, P1 is the interference power, and P„ is the noise power. In one embodiment, the subscriber selects clusters with relatively large Pp/(Pp—PD) (e.g., larger than a threshold such as 10 dB) and avoids clusters with low PAPF—PD) (e.g., lower than a threshold such as 10 dB) when possible. Alternatively, the difference may be based on the energy difference between observed samples during the pilot period and during the data traffic period for each of the subcarriers in a cluster such as the following: o =1YrI — IYT)I 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 SINK and pp—PD, to select the clusters: fi=ftsINR, pit/(Pp-PD) where f is a function of the two inputs. One example of f is weighted averaging (e.g., equal weights). Alternatively, a subscriber selects a cluster based on its SINR and only uses the power difference PP PD to distinguish clusters with similar SINR. The difference may be smaller than a threshold (e.g., 1 dB). Both the measurement of SINR and Pp—PE, can be averaged over time to reduce variance and improve accuracy. In one embodiment, a moving-average time window is used that is long enough to average out the statistical abnormity yet short enough to capture the time-varying nature of channel and interference. e.g., 1 millisecond. Feedback Format for Downlink Cluster Allocation In one embodiment, for the downlink, the feedback contains both the indices of selected clusters and their SINR. An exemplary format for arbitrary cluster feedback is shown in FIG. 5. Referring to FIG. 5, the subscriber provides a cluster index (ID) to indicate the cluster and its associated SINR value. For example, in the feedback, the subscriber provides cluster 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 (506), etc. The SINR for the cluster may be created using an average of the SINRs of the subcarriers. Thus, multiple arbitrary clusters can be selected as the candidates. As US 7,146,172 B2 11 discussed above, the selected clusters can also be ordered in the feedback to indicate priority. In one embodiment, the subscriber may form a priority list of clusters and sends back the SINR information in a descending order of priority. Typically, an index to the SINR level, instead of the SINR itself is sufficient to indicate the appropriate coding/modulation for the cluster. For example, a 3-bit field can be used for SINR indexing to indicate 8 different rates of adaptive coding/modulation. An Exemplary Base Station The base station assigns desirable clusters to the subscriber making the request. In one embodiment, the availability of the cluster for allocation to a subscriber depends on the total traffic load on the cluster. Therefore, the base station selects the clusters not only with high SINR, but also with low traffic load. FIG. 13 is a block diagram of one embodiment of a base station. Referring to FIG. 13, cluster allocation and load scheduling controller 1301 (cluster allocator) collects all the necessary information, including the downlink/uplink SINR of clusters specified for each subscriber (e.g., via SINR/rate indices signals 1313 received from OFDM transceiver 1305) and user data, queue fullness/traffic load (e.g., via user data buffer information 1311 from multi-user data buffer 1302). Using this information, controller 1301 makes the decision on cluster allocation and load scheduling for each user, and stores the decision information in a memory (not shown). Controller 1301 informs the subscribers about the decisions through control signal channels (e.g., control signal/cluster allocation 1312 via OFDM transceiver 1305). Controller 1301 updates the decisions during retraining. In one embodiment, controller 1301 also performs admission control to user access since it knows the traffic load of the system. This may be performed by controlling user data buffers 1302 using admission control signals 1310. The packet data of User 1—N are stored in the user data buffers 1302. For downlink, with the control of controller 1301, multiplexer 1303 loads the user data to cluster data buffers (for Cluster 1-4\4) waiting to be transmitted. For the uplink, multiplexer 1303 sends the data in the cluster buffers to the corresponding user buffers. Cluster buffer 1304 stores the signal to be transmitted through OFDM transceiver 1305 (for downlink) and the signal received from transceiver 1305. In one embodiment. each user might occupy multiple clusters and each cluster might be shared by multiple users (in a time-division-multiplexing fashion). Group-Based Cluster Allocation In another embodiment. for the downlink, the clusters are partitioned into groups. Each group can include multiple clusters. FIG. 6 illustrates an exemplary partitioning. Referring to FIG. 6, groups 1-4 are shown with arrows pointing to clusters that are in each group as a result of the partitioning. In one embodiment, the clusters within each group are spaced far apart over the entire bandwidth. In one embodiment, the clusters within each group are spaced apart farther than the channel coherence bandwidth, i.e. the bandwidth within which the channel response remains roughly the same. A typical value of coherence bandwidth is 100 kHz for many cellular systems. This improves frequency diversity within each group and increases the probability that at least some of the clusters within a group can provide high SINR. The clusters may be allocated in groups. Goals of group-based cluster allocation include reducing the data bits for cluster indexing, thereby reducing the bandwidth requirements of the feedback channel (informa- 12 tion) 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 5 subscriber sends back the channel information on one or more cluster groups, simultaneously or sequentially. In one embodiment, only the information on some of the groups is sent back to the base station. Many criteria can be used to choose and order the groups, based on the channel inform mation, the inter-cell interference levels, and the intra-cell traffic load on each cluster. In one embodiment, a subscriber first selects the group with the best overall performance and then feedbacks the SINR information for the clusters in that group. The subis scriber may order the groups based on their number of clusters for which the SINR is higher than a predefined threshold. By transmitting the SINR of all the clusters in the group sequentially. only the group index, instead of all the cluster indices, needs to be transmitted. Thus, the feedback 20 for each group generally contains two types of information: the group index and the SINR value of each cluster within the group. FIG. 7 illustrates an exemplary format for indicating a group-based cluster allocation. Referring to FIG. 7, a group ID, IDE is followed by the SINR values for each of 25 the clusters in the group. This can significantly reduce the feedback overhead. Upon receiving the feedback information from the subscriber, the cluster allocator at the base station selects multiple clusters from one or more groups, if available, and 30 then assigns the clusters to the subscriber. This selection may be performed by an allocation in a media access control portion of the base station. Furthermore, in a multi-cell environment, groups can have different priorities associated with different cells. In 35 one embodiment, the subscriber's selection of a group is biased by the group priority, which means that certain subscribers have higher priorities on the usage of some groups than the other subscribers. In one embodiment, there is no fixed association between 40 one subscriber and one cluster group; however, in an alternative embodiment there may be such a fixed association. In an implementation having a fixed association between a subscriber and one or more cluster groups, the group index in the feedback information can be omitted, because this 45 information is known to both subscriber and base station by default. In another embodiment, the pilot signal sent from the base station to the subscriber also indicates the availability of each cluster, e.g., the pilot signal shows which clusters have so already been allocated for other subscribers and which clusters are available for new allocations. For example, the base station can transmit a pilot sequence 1111 1111 on the subcarriers of a cluster to indicate that the cluster is available, and 1111-1-1-1-1 to indicate the cluster is not avail55 able. At the receiver, the subscriber first distinguishes the two sequences using the signal processing methods which are well known in the art, e.g., the correlation methods, and then estimates the channel and interference level. With the combination of this information and the channel so 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 embodi65 ment, the SINR information in the feedback is first compressed using source coding techniques, e.g., differential encoding, and then encoded by the channel codes. US 7,146,172 B2 14 13 FIG. 8 shows one embodiment of a frequency reuse pattern for an exemplary cellular set up. Each cell has hexagonal structure with six sectors using directional antennas at the base stations. Between the cells, the frequency reuse factor is one. Within each cell, the frequency reuse factor is 2 where the sectors use two frequencies alternatively. As shown in FIG. 8, each shaded sector uses half of the available OFDMA clusters and each unshaded sector uses the other half of the clusters. Without loss of generality, the clusters used by the shaded sectors are referred to herein as odd clusters and those used by the unshaded sectors are referred to herein as even clusters. Consider the downlink signaling with omni-directional antennas at the subscribers. From FIG. 8, it is clear that for the downlink in the shaded sectors, Cell A interferes with Cell B, which in turn interferes with Cell C, which in turn interferes with Cell A, namely, A->B->C->A. For the unshaded sectors, Cell A interferes with Cell C. which in turn interferes with Cell B, which in turn interferes with Cell A, namely, A->C->B->A. Sector Al receives interference from Sector Cl, but its transmission interferes with Sector Bl. Namely, its interference source and the victims with which it interferes are not the same. This might cause a stability problem in a distributed cluster-allocation system using interference avoidance: if a frequency cluster is assigned in Sector B1 but not in Sector Cl, the cluster may be assigned in Al because it may be seen as clean in Al. However, the assignment of this cluster Al can cause interference problem to the existing assignment in Bl. In one embodiment, different cluster groups are assigned different priorities for use in different cells to alleviate the aforementioned problem when the traffic load is progressively added to a sector. The priority orders are jointly designed such that a cluster can be selectively assigned to avoid interference from its interference source, while reducing, and potentially minimizing, the probability of causing interference problem to existing assignments in other cells. Using the aforementioned example, the odd clusters (used by the shaded sectors) are partitioned into 3 groups: Group 1, 2, 3. The priority orders are listed in Table 2. TABLE 2 Priority ordering for the downlink of the shaded sectors. Priority Ordering 1 2 3 Cell A Cell B Cell C Group 1 Group 2 Group 3 Group 3 Group 1 Group 2 Group 2 Group 3 Group 1 Consider Sector Al. First, the clusters in Group 1 are selectively assigned. If there are still more subscribers demanding clusters, the clusters in Group 2 are selectively assigned to subscribers, depending on the measured SINR (avoiding the clusters receiving strong interference from Sector Cl). Note that the newly assigned clusters from Group 2 to Sector Al shall not cause interference problem in Sector Bl, unless the load in Sector Bl is so heavy that the clusters in both Group 3 and 1 are used up and the clusters in Group 2 are also used. Table 3 shows the cluster usage when less than 2/3 all the available clusters are used in Sector Al, Bl, and Cl. TABLE 3 5 Cluster usage for the downlink of the shaded sectors with less than 2/3 of the full load. Cluster Usage 1 2 3 Cell A Cell B Cell C Group 1 Group 2 Group 3 Group 1 Group 2 Group 3 10 Table 4 shows the priority orders for the unshaded sectors, which are different from those for the shaded sectors, since the interfering relationship is reversed. 15 TABLE 4 Priority ordering for the downlink of the unshaded sectors. Priority Ordering Cell A Cell B Cell C Group 1 Group 2 Group 3 Group 2 Group 3 Group 1 Group 3 Group 1 Group 2 20 1 2 3 25 Intelligent Switching between Coherence and Diversity Clusters In one embodiment, there are two categories of clusters: coherence clusters. containing multiple subcarriers close to each other and diversity clusters, containing multiple sub30 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 coherence bandwidth, i.e. the bandwidth within which the channel response remains roughly the same, which is typically 35 within 100 kIIz for many cellular systems. On the other hand, the spread of subcarriers in diversity clusters is preferably larger than the channel coherence bandwidth, typically within 100 kHz for many cellular systems. Of course, the larger the spread, the better the diversity. There40 fore, a general goal in such cases is to maximize the spread. FIG. 9 illustrates exemplary cluster formats for coherence clusters and diversity clusters for Cells A—C. Referring to FIG. 9, for cells A—C, the labeling of frequencies (subcar45 riers) indicates whether the frequencies are part of coherence or diversity clusters. For example. those frequencies labeled 1-8 are diversity clusters and those labeled 9-16 are coherence clusters. For example, all frequencies labeled 1 in a cell are part of one diversity cluster, all frequencies labeled 2 in sr) a cell are part of another diversity cluster, etc., while the group of frequencies labeled 9 are one coherence cluster, the group of frequencies labeled 10 are another coherence cluster, etc. The diversity clusters can be configured differently for different cells to reduce the effect of inter-cell 55 interference through interference averaging. FIG. 9 shows example cluster configurations for three neighboring cells. The interference from a particular cluster in one cell are distributed to many clusters in other cells, e.g.. the interference from Cluster 1 in Cell A are distributed so to Cluster 1, 8. 7, 6 in Cell B. This significantly reduces the interference power to any particular cluster in Cell B. Likewise, the interference to any particular cluster in one cell comes from many different clusters in other cells. Since not all cluster are strong interferers. diversity clusters, with 65 channel coding across its subcarriers, provide interference diversity gain. Therefore, it is advantageous to assign diversity clusters to subscribers that are close (e.g., within the US 7,146,172 B2 15 16 coherent bandwidth) to the cell boundaries and are more station. The channel/interference variation detector measubject to inter-cell interference. sures the channel (SINR) variation from time to time for Since the subcarriers in a coherence cluster are consecueach cluster. For example, in one embodiment, the channel; tive or close (e.g., within the coherent bandwidth) to each interference detector measures the power difference between other, they are likely within the coherent bandwidth of the 5 pilot symbols for each cluster and averages the difference channel fading. Therefore, the channel gain of a coherence over a moving window (e.g., 4 time slots). A large difference cluster can vary significantly and cluster selection can indicates that channel/interference changes frequently and greatly improve the performance. On the other hand, the subcarrier allocation may be not reliable. In such a case, average channel gain of a diversity cluster has less of a diversity clusters are more desirable for the subscriber. degree of variation due to the inherent frequency diversity m FIG. 11 is a flow diagram of one embodiment of a process among the multiple subcarriers spread over the spectrum. for intelligent selection between diversity clusters and With channel coding across the subcarriers within the cluscoherence clusters depending on subscribers mobility. The ter, diversity clusters are more robust to cluster mis-selection process is performed by processing logic that may comprise (by the nature of diversification itself), while yielding poshardware (e.g., circuitry, dedicated logic, etc.), software sibly less gain from cluster selection Channel coding across 15 (such as that which runs on, for example, a general purpose the subcarriers means that each codeword contains bits computer system or dedicated machine), or a combination of transmitted from multiple subcarriers, and more specifically, both. the difference bits between codewords (error vector) are Referring to FIG. 11, processing logic in the base station distributed among multiple subcarriers. performs channel/interference variation detection (processMore frequency diversity can be obtained through sub- 20 ing block 1101). Processing logic then tests whether the carrier hopping over time in which a subscriber occupies a results of the channel/interference variation detection indiset of subcarriers at one time slot and another different set of cate that the user is mobile or in a fixed position close to the subcarriers at a different time slot. One coding unit (frame) edge of the cell (processing block 1102). If the user is not contains multiple such time slots and the transmitted bits are mobile or is not in a fixed position close to the edge of the encoded across the entire frame. 25 cell, processing transitions to processing block 1103 where FIG. 10 illustrates diversity cluster with subcarrier hopprocessing logic in the base station selects coherence clusping. Referring to FIG. 10, there are four diversity clusters ters; otherwise, processing transitions to processing block in each of cells A and B shown, with each subcarrier in 1104 in which processing logic in the base station selects individual diversity clusters having the same label (1, 2, 3, diversity clusters. or 4). There are four separate time slots shown and during 30 In one embodiment, the base station determines whether each of the time slots, the subcarriers for each of the a subscriber is mobile or fixed by detecting a rate of change diversity clusters change. For example, in cell A, subcarrier of pilot signals, or the normalized channel variation, and 1 is part of diversity cluster 1 during time slot 1. is part of determining that the rate of change is greater than a predediversity cluster 2 during time slot 2, is part of diversity termined threshold. The normalized instantaneous difference cluster 3 during time slot 3, and is part of diversity cluster 35 between channels may be represented as 4 during time slot 4. Thus, more interference diversity can be obtained through subcarrier hopping over time. with further interference diversity achieved by using different 11 - 112 -li hopping patterns for different cells, as shown in FIG. 10. The manner in which the subscriber changes the subcar- 40 riers (hopping sequences) can be different for different cells in order to achieve better interference averaging through where 1-1, represents the channel and i is the index to coding. represent the individual channels. For static subscribers, such as in fixed wireless access. the The threshold is system dependent. For example, the rate channels change very little over time. Selective cluster 45 of change is greater than 10% (although any precentage allocation using the coherence clusters achieves good per(e.g., 20%) could be used), then the base station concludes formance. On the other hand, for mobile subscribers, the that the subscriber is mobile. In one embodiment, if the channel time variance (the variance due to changes in the constant period in signaling is not greater than a multiple of channel over time) can be very large. A high-gain cluster at one time can be in deep fade at another. Therefore, cluster 50 the round trip delay (e.g., 5 times the round trip delay), then the base station determines that the subscriber is mobile and allocation needs to be updated at a rapid rate, causing allocates diversity clusters; otherwise, the base station allosignificant control overhead. In this case, diversity clusters cates coherence clusters. can be used to provide extra robustness and to alleviate the The selection can be updated and intelligently switched overhead of frequent cluster reallocation. In one embodiment, cluster allocation is performed faster than the channel 55 during retraining. The ratio/allocation of the numbers of coherence and changing rate, which is often measured by the channel diversity clusters in a cell depends on the ratio of the Doppler rate (in Hz), i.e. how many cycles the channel population of mobile and fixed subscribers. When the popuchanges per second where the channel is completely differlation changes as the system evolves, the allocation of ent after one cycle. Note that selective cluster allocation can 60 coherence and diversity clusters can be reconfigured to be performed on both coherence and diversity clusters. accommodate the new system needs. FIG. 12 illustrates a In one embodiment, for cells containing mixed mobile reconfiguration of cluster classification which can support and fixed subscribers, a channel/interference variation detecmore mobile subscribers than that in FIG. 9. tor can be implemented at either the subscriber or the base station, or both. Using the detection results, the subscriber Whereas many alterations and modifications of the and the base station intelligently selects diversity clusters to 65 present invention will no doubt become apparent to a person mobile subscribers or fixed subscribers at cell boundaries, of ordinary skill in the art after having read the foregoing and coherence clusters to fixed subscribers close to the base description, it is to be understood that any particular embodi- US 7,146,172 B2 17 18 ment shown and described by way of illustration is in no 7. The method defined in claim 1 wherein subcarriers of way intended to be considered limiting. Therefore, referone coherence cluster are within the coherent bandwidth of ences to details of various embodiments are not intended to a channel between a base station and a subscriber. limit the scope of the claims which in themselves recite only 8. The method defined in claim I further comprising 5 those features regarded as essential to the invention. updating allocation of clusters to the subscriber. We claim: 9. The method defined in claim 1 further comprising 1. A method for use in allocating subcarriers in an reconfiguring cluster classification when population of OFDMA system comprising mobile and fixed subscribers in a cell changes. allocating at least one diversity cluster of subcarriers to a first subscriber; and 10 10. The method defined in claim 1 wherein the at least one allocating at least one coherence cluster to a second diversity cluster is configured to reduce the effect of intersubscriber. such that communication with the first and cell interference. second subscribers is able to occur by simultaneously 11. The method defined in claim 1 further comprising using the at least one diversity cluster and the at least determining characteristics of the first subscriber and the one coherence cluster, respectively. 15 second subscriber, wherein allocating the at least one diver2. The method defined in claim 1 wherein the first sity cluster of subcarriers to the first subscriber and allocatsubscriber comprises a mobile subscriber and the second ing the at least one coherence cluster to the second subsubscriber comprises a fixed subscriber. scriber are based on determined characteristics of the first 3. The method defined in claim 1 wherein the first and second subscribers. subscriber comprises a fixed subscriber located at a cell 2 0 12. The method defined in claim 11 wherein the characedge. teristics comprise whether the first and second subscribers 4. The method defined in claim 1 further comprising are fixed or mobile subscribers. transmitting information using one diversity cluster while 13. The method defined in claim 1 further comprising performing frequency hopping. 5. The method defined in claim 1 wherein using one 25 adaptively switching allocation of clusters to either the first or second subscriber so that the first subscriber is allocated diversity cluster includes channel coding across subcarriers at least one coherence cluster of subcarriers or the second of the one diversity cluster. subscriber is allocated at least one diversity cluster of 6. The method defined in claim 1 further comprising subscribers based on channel conditions and subscriber transmitting codewords in which each codeword contains bits transmitted from multiple subcarriers and with differ- 30 characteristics. ence bits between codewords being distributed among multiple subcarriers.

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