US0074542l2B2
`
`(12) United States Patent
`Li et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 7,454,212 B2
`Nov. 18, 2008
`
`(54) OFDMA WITH ADAPTIVE
`SUBCARRIER-CLUSTER CONFIGURATION
`AND SELECTIVE LOADING
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`(75)
`
`Inventors: Xiaodong Li, Bellevue, WA (US); Hui
`Liu, Sammamish, WA (US); Kemin Li,
`Bellevue, WA (US); Wenzhong Zhang,
`Bellewes WA (US)
`(73) Assignee: Adaptix, Inc., Bellevue, WA (US)
`( * ) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`(21) Appl.No.: 11/199,586
`
`456705889 A
`
`6/1987 Hewitt et 31'
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`DE
`
`198 00 953
`
`7/1999
`
`(51)
`
`Filed:
`
`(22)
`(65)
`
`Aug. 8, 2005
`Prior Publication Data
`US 2006/0083210 A1
`Apr. 20, 2006
`.
`.
`Related U'S' Apphcatlon Data
`(63) Continuation of application No. 09/738,086, filed on
`Dec. 15, 2000, now Pat. No. 6,947,748.
`Int. Cl.
`(2006.01)
`H04B 17/00
`(2006.01)
`H04B 7/00
`(2006.01)
`H04Q 7/20
`(2006.01)
`H04Q 7/00
`(2006.01)
`H04Q 7/28
`(2006.01)
`H04M 1/00
`(2006.01)
`H04M 1/38
`(52) U.S. Cl.
`.................... .. 455/450; 455/67.11; 455/69;
`455/452.2; 455/464; 455/509; 455/550.1;
`455/556.2;455/561;370/329370/341
`(58) Field of Classification Search ............ .. 455/179.1,
`455/188.1, 422.1, 516_517, 67.11, 561, 5621,
`455/132435, 456.5i456.6, 455, 423i425,
`455/63.1_63.2, 6245, 41.2_41.3’ 443_453,
`455/463i464, 509510, 553, 512i513, 524i526,
`455/550.1, 168.1’ 176.1’ 69, 70, 266’ 403’
`455/500, 55 6'2; 370/203_210, 311, 346_347,
`370/465i480, 312%”, 319i322, 328i330,
`370/338, 341_344, 395.21’ 395.41’ 430’
`370/437, 447, 449, 458, 461—462, 913; 375/311,
`375/240, 240.07, 240.11
`See application file for complete search history.
`
`(Continued)
`OTHER PUBLICATIONS
`
`Wong et al. “Multiuser OFDM with Adaptive Subcarrier, Bit, and
`Power Allocation”, IEEE Journal on Selected Areas in Communica-
`ti0I1S.1EEE.NeWY0f1<,US, 1999, V01. 17, NR 10, PP~ 1747-1753
`Mexican Oflice Action issued for PiMa/2003/005311 dated Mar. 31,
`2006
`
`(Continued)
`
`Primary Examiner—Meless N Zewdu
`(74) Attorney, Agent, or Firm—Fulbright & Jaworski L.L.P.
`
`(57)
`
`ABSTRACT
`
`A method and apparatus for subcarrier selection for systems
`is described.
`In one embodiment,
`the system employs
`°“h°g°“a1.freq“e“°Y diViSi°“m“1‘iP1?a°°eSS(OFDMA?In
`one embodiment, a method for subcarrier selection comprises
`each of multiple subscribers measuring channeland interfer-
`ence information for subcarriers based on pilot symbols
`received from a base station, at least oneofsubscribers select-
`mg a set of candidate subcarriers, providing feedback infor-
`mation on the set of candidate subcarriers to the base station,
`and the one subscriber receiving an indication of subcarriers
`ofthe set ofsubcarriers selected by the base station for use by
`the One S“bS°“ber~
`
`33 Claims, 7 Drawing Sheets
`
`Rairainins
`Needed
`7
`
`Peiiudiraliy Broadcast Film
`OFDM Symbols in Subscribers
`
`Subscriber(s) Cunlinuously Monitors
`Pilul SymhoislMeasures SINR and/oi
`
`Each Suhsoriber Selects One nr More
`Clusters for Each Base Siaiion
`
`Ease Slat‘
`Clusie
`
`Selecis One or More
`I Each Subscriber
`
`Base Station Notifies me suhsnriber
`Regarding Cluslei Allacalion
`
`other Parameters
`
`
`101
`
`102
`
`103
`
`104
`
`105
`
`SPRINT 1118
`
`

`

`US 7,454,212 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`2005/0025099 A1
`
`2/2005 Heath et al.
`
`5,280,630
`5,437,054
`5,479,447
`5,504,775
`5,507,034
`5,515,378
`5,555,268
`5,588,020
`5,708,973
`5,726,978
`5,734,967
`5,774,808
`5,822,372
`5,839,074
`5,867,478
`5,886,988
`5,887,245
`5,909,436
`5,914,933
`5,933,421
`5,956,642
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`6,005,876
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`6,131,016
`6,141,565
`6,144,696
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`6,282,185
`6,298,092
`6,307,851
`6,327,472
`6,330,460
`6,366,195
`6,377,632
`6,377,636
`6,411,186
`6,415,153
`6,449,246
`6,473,467
`6,477,158
`6,526,281
`6,545,997
`6,553,011
`6,567,383
`6,657,949
`6,726,297
`6,904,283
`6,920,122
`6,985,432
`7,047,011
`7,373,151
`2002/0114269
`2003/0067890
`2003/0169681
`2003/0169824
`
`>D>>>D>>>>D>>>>>>>D>>>>D>D>D>D>>D>D>D>>D>D>>D>D>D>>D>D>>D>
`
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`
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`B1
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`A1
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`FOREIGN PATENT DOCUMENTS
`
`DE
`DE
`DE
`EP
`EP
`EP
`EP
`EP
`EP
`FR
`JP
`KR
`W0
`W0
`W0
`
`198 00 953 C1
`*
`19800953
`019800953 C1 *
`0 869 647 A2
`0882377 B1
`0 926 912 A2
`0 929 202 A1
`0 999 658
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`
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`ISSN: 0733-8716 Sections I and II
`abstract.**
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`
`

`

`US 7,454,212 B2
`Page 3
`
`Nogueroles, R. et al.: Improved Performance of a Random OFDMA
`Mobile Communications System: Vehicular Technology Confer-
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`**
`
`Kinugawa, Y.et al.: “Frequency and Time Division Multiple Access
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`Japan, vol. E77-B, NR. 3, Mar. 1994, pp. 396-402,
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`
`Wong et al. “Multiuser OFDM with Adaptive Subcarrier, Bit, and
`Power Allocation”, IEEE Journal on Selected Areas in Communica-
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`Mexican Office Action issued for P1Ma/2003/005311 dated Mar. 31,
`2006.
`Ye Li et al.; “Clustered OFDM with Channel Estimation for High
`Rate Wireless Data”; Mobile Multimedia Communications, 1999.
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`7007961, dated Sep. 27, 2006.
`
`* cited by examiner
`
`

`

`U.S. Patent
`
`Nov. 18,2008
`
`Sheet 1 of7
`
`US 7,454,212 B2
`
`Subcarrier
`
`101
`
`Cluster
`
`102
`
`FIG. 1A
`
`
`
`
`
`Pilot OFDM
`Symbols
`
`2m
`
`
`
`!§§!!§!§!!
`
`-§§--§-N--
`
`
`t
`Occupied Clusters
`
`a. Cell A
`
`f
`
`
`
`f
`
`f
`
`f
`
`(A)
`!§:!§~.\\3:!!§\f!!_-_
`!§!§!!§!!!
`!§!§!!§!!!
`-§-&\V--§\‘---
`
`
`t
`
`
`
`b. Cell B
`(B)
`
`
`
`
`
`—————
`§IIIIi§ii§
`.--__-jn...-__j_.j_:—-_--...__—j.._---
`
`FIG. 2
`
`(C)
`
`201
`
`201
`
`

`

`U.S. Patent
`
`Nov. 18,2008
`
`Sheet 2 of7
`
`US 7,454,212 B2
`
`
`
`
`
`Subscriber(s) Continuously Monitors
`Pilot Symbols/Measures SINR andlor
`
`Periodically Broadcast Pilot
`OFDM Symbols to Subscribers
`
`Other Parameters
`
`
`Each Subscriber Selects One or More
`Clusters for Each Base Station
`
`101
`
`102
`
`103
`
`104
`
`
`Regarding Cluster Allocation 105
`
`
`
`
`Base Station Selects One or More
`Clusters for Each Subscriber
`
`
`
`Base Station Notifies the Subscriber
`
`FIG. 1B
`
`

`

`U.S. Patent
`
`Nov. 18,2008
`
`Sheet 3 of7
`
`US 7,454,212 B2
`
`Channel/Interference
`
`
`
` Cluster Ordering
`Request Selected
`Clusters and Codingl
`Modulation Rates
`Prediction '
` Traffic/Interference
`
`
`Analysis in Date
`
`Penods
`
`3” FIG. 3
`
`
`
`
`
`and Rate
`
`Estimation in Pilot
`Penods
`
`
`
`
`
`Per-cluster SINR
`
`Estimation in
`
`405
`
`
`
`
`
`
`
`
`
`Power Calculation
`in Data Periods
`
`
`FIG. 4
`
`501
`
`502
`
`503
`
`504
`
`504
`
`504
`
`Cluster
`
`Cluster
`
`Cluster
`
`FIG. 5
`
`
`
`
`
`Pilot Periods
`
`Per-cluster
`Power Calculation
`
`Cluster Orderingl
`404 Selection Based on
`Request Selected
`_
`SINR and Power
`Clusters and Codingl
`
`A Difference
`Modulation Rates
`in Pilot Periods
`
`Per-cluster
`
`

`

`U.S. Patent
`
`Nov. 18,2008
`
`Sheet 4 of7
`
`US 7,454,212 B2
`
`
`
`
`
`
`
`&
`
`
`
`
`
`
`
`
`
`FIG. 8
`
`
`
`
`
`
`
`
`

`

`00002m
`
`.SWmSNmMCmmC.e....m.
`
`U.S. Patent
`
`.WIa...DP
`
`4|9
`
`g!
`
`7:105LI.6ehS
`
`2.}454.}7SU
`
`2B2
`
`1f
`
`24|.
`
`I‘!3 Ami‘:
`16
`111l.1l1II|11.1l1lII
`
`a. Cell A
`
`H
`.D. IIiII.HmI
`
`d
`
`IiI
`
`II
`
`III!|IIII
`
`01.
`
`II
`
`Ii
`
`ll.
`
`I‘
`
`FIG. 9
`
`1 ~
`? 13
`|1111lIl
`!IBIul
`
`II
`
`1 !IIIWOI
`
`
`16
`
`
`!111. I15.I
`
`!I
`
`!I
`
`II
`
`!I
`
`lo.
`
`In
`
`1 4| III
`
`
`
`“lidmmuRN51».»n...m
`
`
`
`
`
`nmsu.sn..LmWIIU§u.uw.....m«nun.Nvuunavy
`
`nun.»VVS.h$u\..\N
`
`III
`
`
`
`
`
`vvm“HNSU.9n...S.u.I\|\
`
`nahi..08w\.uu..S
`
`
`
`08SEno»3”_VHSnahawn.fiwvm
`
`IIIIIIIISm“nasuvuxuN.I‘U
`
`
`
`3:;“mmnfimvu‘INN
`
`Subcarner 1
`
`Subcarrier 2
`
`
`
`finn.H:....u‘umm
`
`mmmbumammm.“
`
`.329...:hasme:
`E...Q.“S.u..MM.
`
`
`
`HNNUvvsRVswu.II3”“nahwms\N.I~l\
`
`vmknusu»w«E
`
`.
`
`
`
`mtvmsn.IIh\"mmnvmxnwuu"mu.hovu
`
`
`
`
`
`a. Cell A
`
`En.En.“nmuhsusIIIIIIII
`
`uwfian.mmusmac.
`IIIIIIII.-us«.5KKK“em.QNum.§HVI§wmm:Emu
`
`Numbn.§wumm“INNIIIIIIIIIIII
`
`
`
`n.4\ksum.“with.wnn
`
`b. Ce||B
`
`FIG. 10
`
`
`
`
`
`

`

`U.S. Patent
`
`Nov. 18,2008
`
`Sheet 6 of7
`
`US 7,454,212 B2
`
`Channel/Interference
`
`1101
`
`Variation Detection
`
`1102
`
`No
`
`1103
`
`Select Coherence
`
`Clusters
`
`
`
`«
`
`f
`
`
`
`
`
`
`
`.
`Any
`Significant Variation
`Detected
`
`
`
`
`
`
`
`?
`
`F I G. 1 1
`
`a. Cell A
`
`FIG. 12
`
`Yes
`
`1104
`
`Select Diversity
`Clusters
`
`
`
`t
`
`
`
`
`
`

`

`U.S. Patent
`
`Nov. 18,2008
`
`Sheet 7 of7
`
`US 7,454,212 B2
`
`1311
`
`User Data Buffer Information
`
`
`
`
`Admission Control
`1301
`1310
`
`Cluster Allocation and
`
`Load Scheduling
`Controller
`
`Cluster 1 ~ M
`
`
`
`
`
` Multi-cluster
`Transmission and
`
`Receiving Buffer
`
`OFDM Transceiver
`
`1 OFDM Signal
`
`Control Signal/
`Cl_uster‘A||ocation
`1 312
`
`FIG. 13
`
`1304
`
`1305
`
`

`

`US 7,454,212 B2
`
`1
`OFDMA WITH ADAPTIVE
`SUBCARRIER-CLUSTER CONFIGURATION
`AND SELECTIVE LOADING
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`This is a continuing application of application Ser. No.
`09/738,086, entitled “OFDMA WITH ADAPTIVE SUB-
`CARRIER-CLUSTER CONFIGURATION AND SELEC-
`TIVE LOADING,” filed Dec. 15, 2000, the disclosure of
`which is hereby incorporated herein by reference thereto.
`
`FIELD OF THE INVENTION
`
`The invention relates to the field of wireless communica-
`
`tions; more particularly, the invention relates to multi-cell,
`multi-subscriber wireless systems using orthogonal
`fre-
`quency division multiplexing (OFDM).
`
`BACKGROUND OF THE INVENTION
`
`Orthogonal frequency division multiplexing (OFDM) is an
`efiicient modulation scheme for signal transmission over fre-
`quency-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 modu-
`lated on the subcarriers are transmitted in parallel. For more
`information, see Cimini, Jr., “Analysis and Simulation of a
`Digital Mobile Charmel Using Orthogonal Frequency Divi-
`sion Multiplexing,” IEEE Trans. Commun., vol. COM-33,
`no. 7, Jul. 1985, pp. 665-75; Chuang and Sollenberger,
`“Beyond 3G: Wideband Wireless Data Access Based on
`OFDM and Dynamic Packet Assignment,” IEEE Communi-
`cations 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, mul-
`tiple subscribers simultaneously use different subcarriers, in a
`fashion similar
`to frequency division multiple access
`(FDMA). For more information,
`see Sari and Karam,
`“Orthogonal Frequency-Division Multiple Access and its
`Application to CATV Networks,” European Transactions on
`Telecommunications, Vol. 9(6), pp. 507-516, November/De-
`cember 1998 and Nogueroles, Bossert, Donder, and Zyablov,
`“Improved Performance of a Random OFDMA Mobile Com-
`munication 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 allo-
`cate 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
`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 canbe 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,
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`the problem of intercell interference arises. It is clear that the
`intercell interference in an OFDMA system is also frequency
`selective and it is advantageous to adaptively allocate the
`subcarriers so as to mitigate the effect of intercell interfer-
`ence.
`
`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 exist-
`ing subscribers is dropped off the network or a new subscrib-
`ers is added onto the network. This is often impractical in real
`wireless system, mainly due to the bandwidth cost for updat-
`ing the subscriber information and the computation cost for
`the joint optimization.
`
`SUMMARY OF THE INVENTION
`
`A method and apparatus for subcarrier selection for sys-
`tems is described. In one embodiment, the system employs
`orthogonal frequency division multiple access (OFDMA). In
`one embodiment, a method for subcarrier selection comprises
`a subscriber measuring charmel and interference information
`for subcarriers based on pilot symbols received from a base
`station, the subscriber selecting a set of candidate subcarriers,
`providing feedback information on the set of candidate sub-
`carriers to the base station, and receiving an indication of
`subcarriers of the set of subcarriers selected by the base
`station for use by the subscriber.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The present invention will be understood more fully from
`the detailed description given below and from the accompa-
`nying 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 under-
`standing 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 sym-
`bols, 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 ofa 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 reconfiguration of
`cluster classification.
`FIG. 13 illustrates one embodiment of a base station.
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`US 7,454,212 B2
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`3
`DETAILED DESCRIPTION OF THE PRESENT
`INVENTION
`
`A distributed, reduced-complexity approach for subcarrier
`allocation is described. The techniques disclosed herein are 5
`described using OFDMA (clusters) as an example. However,
`they are not limited to OFDMA-based systems. The tech-
`niques 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 alloca-
`tion 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.
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`For downlink charmels, each subscriber first measures the
`channel and interference information for all the subcarriers
`
`and then selects multiple subcarriers with good performance
`(e.g., a high signal-to-interference plus noise ratio (SINR))
`and feeds back the information on these candidate subcarriers
`
`to the base station. The feedback may comprise channel and
`interference information (e.g., signal-to-interference-plus-
`noise-ratio information) on all subcarriers or just a portion of
`subcarriers. In case of providing information on only a por-
`tion 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 candi-
`dates, utilizing additional information available at the base
`station, e.g., the trafiic load information on each subcarrier,
`amount of trafiic 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 informa-
`tion. 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 subcar-
`rier 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/modula-
`tion rates may be specified by the subscriber when specifying
`subcarriers that it finds favorable to use. For example, if the
`SINR is less than a certain threshold (e.g., 12 dB), quadrature
`phase shift keying (QPSK) modulation is used; otherwise, 16
`quadrature amplitude modulation (QAM) is used. Then the
`base station informs the subscribers about the subcarrier allo-
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`cation and the coding/modulation rates to use.
`In one embodiment, the feedback information for down-
`link subcarrier allocation is transmitted to the base station
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`through the uplink access channel, which occurs in a short
`period every transmission time slot, e.g., 400 microseconds in
`every l0-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 charmel. The SINR as well 60
`as the traffic load information on the uplink subcarriers are
`used for uplink subcarrier allocation.
`For either direction, the base station makes the final deci-
`sion of subcarrier allocation for each subscriber.
`
`In the following description, a procedure of selective sub-
`carrier allocation is also disclosed,
`including methods of
`channel and interference sensing, methods of information
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`4
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`feedback from the subscribers to the base station, and algo-
`rithms 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 specific
`details. In other instances, well-known structures and devices
`are shown in block diagram form, rather than in detail, in
`order to avoid obscuring the present invention.
`Some portions of the detailed descriptions which follow
`are presented in terms of algorithms and symbolic represen-
`tations 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, con-
`ceived to be a self-consistent sequence of steps leading to a
`desired result. The steps are those requiring physical manipu-
`lations ofphysical quantities. Usually, though not necessarily,
`these quantities take the form of electrical or magnetic signals
`capable of being stored, transferred, combined, compared,
`and otherwise manipulated. It has proven convenient at times,
`principally for reasons of common usage, to refer to these
`signals as bits, values, elements, symbols, characters, terms,
`numbers, or the like.
`It should be borne in mind, however, that all of these and
`similar terms are to be associated with the appropriate physi-
`cal quantities and are merely convenient labels applied to
`these quantities. Unless specifically stated otherwise as
`apparent from the following discussion, it is appreciated that
`throughout the description, discussions utilizing terms such
`as “processing” or “computing” or “calculating” or “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 computer
`system’s registers and memories into other data similarly
`represented as physical quantities within the computer sys-
`tem memories or registers or other such information storage,
`transmission or display devices.
`The present invention also relates to apparatus for perform-
`ing the operations herein. This apparatus may be specially
`constructed for the required purposes, or it may comprise a
`general purpose computer selectively activated or reconfig-
`ured by a computer program stored in the computer. Such a
`computer program may be stored in a computer readable
`storage medium such as, but is not limited to, any type of disk
`including floppy disks, optical disks, CD-ROMs, and mag-
`netic-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 sys-
`tem bus.
`
`The algorithms and displays presented herein are not inher-
`ently related to any particular computer or other apparatus.
`Various general purpose systems may be used with programs
`in accordance with the teachings herein, or it may prove
`convenient to construct more specialized apparatus to per-
`form the required method steps. The required structure for a
`variety of these systems will appear from the description
`below. In addition, the present invention is not described with
`reference to any particular programming language. It will be
`appreciated that a variety of programming languages may be
`used to implement the teachings of the invention as described
`herein.
`
`A machine-readable medium includes any mechanism for
`storing or transmitting information in a form readable by a
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`US 7,454,212 B2
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`5
`machine (e.g., a computer). For example, a machine readable
`medium includes read only memory (“ROM”); random
`access memory (“RAM”); magnetic disk storage media; opti-
`cal storage media; flash memory devices; electrical, optical,
`acoustical or other form of propagated signals (e.g., carrier
`waves, infrared signals, digital signals, etc.); etc.
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`may be particularly useful in diversity clusters where the
`weighting applied to the subcarriers may be different.
`The feedback of information from each subscriber to the
`base station contains a SINR value for each cluster and also
`
`the subscriber
`indicates the coding/modulation rate that
`desires to use. No cluster index is needed to indicate which
`
`Subcarrier Clustering
`The techniques described herein are directed to subcarrier
`allocation for data trafiic 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 charmels, uplink access
`channels, and time and frequency synchronization channels.
`FIG. 1A illustrates multiple subcarriers, such as subcarrier
`101, and cluster 102. A cluster, such as cluster 102, is defined
`as a logical unit that contains at least one physical subcarrier,
`as shown in FIG. 1A. A cluster can contain consecutive or
`
`disjoint subcarriers. The mapping between a cluster and its
`subcarriers can be fixed or reconfigurable. In the latter case,
`the base station informs the subscribers when the clusters are
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`the frequency spectrum
`In one embodiment,
`redefined.
`includes 512 subcarriers and each cluster includes four con-
`
`secutive subcarriers, thereby resulting in 128 clusters.
`
`An Exemplary Subcarrier/Cluster Allocation Procedure
`FIG. 1B is a flow diagram of one embodiment of a process
`for allocation clusters to subscribers. The process is 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 broad-
`casts pilot OFDM symbols to every subscriber within its cell
`(or sector) (processing block 101). The pilot symbols, often
`referred to as a sounding sequence or signal, are known to
`both the base station and the subscribers. In one embodiment,
`each pilot symbol covers the entire OFDM frequency band-
`width. 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
`trafiic, of each cluster (processing block 102). Based on this
`information, each subscriber selects one or more clusters with
`good performance (e.g., high SINR and low traffic loading)
`relative to each other and feeds back the information on these
`
`candidate clusters to the base station through predefined
`uplink access channels (processing block 103). For example,
`SINR values higher than 10 dB may indicate good perfor-
`mance. Likewise, a cluster utilization factor less than 50%
`may be indicative of good performance. Each subscriber
`selects the clusters with relatively better performance than
`others. The selection results in each subscriber selecting clus-
`ters they would prefer to use based on the measured param-
`eters.
`
`In one embodiment, each subscriber measures the SIR of
`each subcarrier cluster and reports these SINR measurements
`to their base station through an access charmel. The SINR
`value may comprise the average ofthe SINR values ofeach of
`the subcarriers in the cluster. Alternatively, the SINR value for
`the cluster may be the worst SINR among the SINR values of
`the subcarriers in the cluster. In still another embodiment, a
`weighted averaging of SINR values of the subcarriers in the
`cluster is used to generate an SINR value for the cluster. This
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`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-
`0 tion in the feedback is ordered according to which clusters
`have the best performance relative to each other for the sub-
`scriber. 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
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`among the candidates (processing block 104). The base sta-
`tion may utilize additional information available at the base
`station, e.g., the traffic load information on each subcarrier,
`amount of trafiic 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 loadin