`Li et al.
`
`USOO6904283B2
`(10) Patent No.:
`US 6,904,283 B2
`(45) Date of Patent:
`Jun. 7, 2005
`
`(54) MULTI-CARRIER COMMUNICATIONS
`WITH GROUP-BASED SUBCARRIER
`ALLOCATION
`
`(75) Inventors: Xiaodong Li, Bellevue, WA (US); Hui
`Liu, Sammamish, WA (US); Hujun
`Yin, Seattle, WA (US); Guanbin Xing,
`Bellevue, WA (US); Fuqi Mu,
`Issaquah, WA (US)
`
`(73) ASSignee: Adaptix, Inc., Bothell, WA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 727 days.
`
`(21) Appl. No.: 09/837,337
`(22) Filed:
`Apr. 17, 2001
`(65)
`Prior Publication Data
`US 2003/0169681 A1 Sep. 11, 2003
`2
`Related U.S. Application Data
`
`(63) Saygin part of application No. 09/738,086, filed on
`(51) Int. Cl. ............................ H04B 7/00, H04B 1/38,
`HO4O 7/20; HO4M 1.00, HO4. 1100
`(52) U.S. Cl
`455,450. 45569. 455/.447
`455,448; 455/561; 455,550.1; 370/208
`(58) Field of Search ................................. 375/133, 135,
`375/260, 267; 370/203, 208, 210, 482,
`484, 431, 319-321, 328, 329, 332, 342,
`344, 345; 455/69, 434, 455, 463, 422.1,
`447-450, 452.1, 452.2, 453. 42,500, 512
`s
`s
`s
`513, 103-105
`
`(56)
`
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`Primary Examiner-William Trost
`Assistant Examiner Meless Zewdu
`(74) Attorney, Agent, or Firm-Blakely, Sokoloff, Taylor &
`Zafman LLP
`ABSTRACT
`(57)
`A method and apparatus for Subcarrier Selection for Systems
`is described. In one embodiment, a method for Subcarrier
`Selection for a System employing orthogonal frequency
`division multiple access (OFDMA) comprises partitioning
`Subcarriers into groups of at least one cluster of Subcarriers,
`receiving an indication of a Selection by the Subscriber of
`one or more groups in the groups, and allocating at least one
`cluster in the one or more groups of clusterS Selected by the
`Subcarrier for use in communication with the Subscriber.
`
`119 Claims, 7 Drawing Sheets
`
`Periodically Broadcast Pilot
`OFDM Symbolsto Subscribers
`
`Subscribers) Continuously Monitors
`Plot symbols. MeasuressINRandlor -102
`Othel Farameters
`
`Retraining
`Needed
`
`Each Subscribe? Selects One or More
`Custers for each Base Station
`
`103
`
`Base Station Selects One or More
`Cisters for East Subscribef
`
`04
`
`
`
`Base Station Motifies the Subscriber
`Regarding Cluster Allocation
`
`15
`
`IPR2018-1581
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`Access for the OFDM Transmission Technique”, Wireless
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`Motegi, M. et al.: “Optimum Band Allocation According to
`Subband Condition for BST-OFDM' 11" IEEE Interna
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`Kapoor, S. et al.: "Adaptive Interference Suppression in
`Multiuser Wireless OFDM Systems. Using Antenna Arrays'
`IEEE Transactions on Signal Processing, vol. 47, No. 12,
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`York, USA, ISSN: 1053-587X.
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`tions, 1999. (MOMUC99). 1999 IEEE International Work
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`Access with Demand-ASSignment Using Multicarrier
`Modulation for Indoor Wireless Communications Systems”,
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`ISSN: O916-8516.
`* cited by examiner
`
`IPR2018-1581
`HTC EX1003, Page 2
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`
`
`U.S. Patent
`
`Jun. 7, 2005
`
`Sheet 1 of 7
`
`US 6,904,283 B2
`
`Subcarrier
`101
`
`m
`
`Cluster
`2102
`
`FIG. 1A
`
`f
`
`
`
`
`
`
`
`t
`
`Cluster A
`Cluster B
`ŠSS
`E"MSNN
`201 NNNP
`Š Š Š
`Occupied Clusters
`a. Cell A
`(A)
`Finns==N=== f
`2012 PNNNPP
`N N T N
`
`2012(NPSIN SNS
`NINN
`Š
`Š Š
`t
`C. Cell C
`(C)
`
`t
`
`b. Cell B
`(B)
`
`
`
`
`
`N axe was a
`
`rare as
`
`a
`
`stN to as Y wasy as
`
`f
`
`
`
`FIG 2
`
`IPR2018-1581
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`U.S. Patent
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`Jun. 7, 2005
`
`Sheet 2 of 7
`
`US 6,904,283 B2
`
`Periodically Broadcast Pilot
`OFDM Symbols to Subscribers
`
`W
`
`101
`
`Subscriber(s) Continuously Monitors
`Pilot Symbols/Measures SINR and/or Y 102
`Other Parameters
`
`
`
`Retraining
`Needed
`
`Each Subscriber Selects One or More
`Clusters for Each Base Station
`
`103
`
`Base Station Selects One Or More
`Clusters for Each SubSCriber
`
`104
`
`Base Station Notifies the SubSCriber
`Regarding Cluster Allocation
`
`105
`
`FIG. 1B
`
`IPR2018-1581
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`U.S. Patent
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`Jun. 7, 2005
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`Sheet 3 of 7
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`US 6,904,283 B2
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Channel Interference
`Estimation in Pilot
`Periods
`
`
`
`
`
`Traffic/Interference
`Analysis in Date
`Periods
`
`Cluster Ordering
`and Rate
`Prediction
`
`
`
`Request Selected
`Clusters and Coding?
`Modulation Rates
`
`
`
`Per-cluster SNR 401
`Estimation in
`Pilot Periods
`Per-cluster
`Power Calculation
`in Pilot Periods
`
`404
`
`Cluster Ordering
`Selection Based On
`SNR and POWer
`Difference
`
`405
`
`406
`Request Selected
`Clusters and Codingl
`Modulation Rates
`
`Per-Cluster
`Power Calculation
`in Data Periods
`
`403
`
`FIG. 4
`
`502
`
`501
`Cluster
`
`503
`Cluster
`
`504
`
`504
`
`504
`Cluster
`
`
`
`Group 3
`
`Group 4
`
`IPR2018-1581
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`U.S. Patent
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`Jun. 7, 2005
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`Sheet 4 of 7
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`US 6,904,283 B2
`
`Gyp SNR1 SINR2 SINR3 Gyp SNR1 SINR2 SINR3 o O e
`
`
`
`
`
`
`
`FIG. 8
`
`IPR2018-1581
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`U.S. Patent
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`Jun. 7, 2005
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`Sheet 5 of 7
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`US 6,904,283 B2
`
`1-8: Diverse Clusters
`9-16: Plain Clusters
`
`A.
`
`a. Cell A
`
`12
`
`b. Cell B
`
`| t
`HeHale H He
`H M
`
`682314
`
`10 4567812
`
`45678.12 13
`
`2345678 15
`
`A.
`
`16
`
`Subcarrier 1
`
`an
`
`RSR S.
`N
`
`FIG. 9
`
`a. Cell A
`
`b. Cell B
`
`FIG 10
`
`
`
`
`
`
`
`
`
`
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`U.S. Patent
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`Jun. 7, 2005
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`Sheet 6 of 7
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`US 6,904,283 B2
`
`Channel/interference
`Variation Detection
`
`1101
`
`Yes
`
`
`
`
`
`1104
`
`Select Diversity
`ClusterS
`
`1102
`
`
`
`
`
`Any
`Significant Variation
`Detected
`
`1103
`
`Select Coherence
`Clusters
`
`FIG. 11
`
`
`
`HHHH.
`H. H. H. H.
`
`
`
`a. Cell A
`FIG. 12
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`Jun. 7, 2005
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`Sheet 7 of 7
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`US 6,904,283 B2
`
`USer 1 - N
`
`Multi-user Data
`Buffer
`
`1302
`
`User Data Buffer information
`1311
`
`
`
`
`
`
`
`1301
`
`Admission Control
`1310
`
`Cluster Allocation and
`Load Scheduling
`Controller
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`SINRJRate
`indices
`1313
`
`Multi-cluster
`Transmission and
`Receiving Buffer
`
`
`
`Cluster 1 - M
`
`1304
`
`OFDM Transceiver
`
`1305
`
`
`
`OFDM Signal
`
`Control Signal
`Cluster Allocation
`1312
`
`F.G. 13
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`US 6,904,283 B2
`
`1
`MULTI-CARRIER COMMUNICATIONS
`WITH GROUP-BASED SUBCARRIER
`ALLOCATION
`
`2
`One approach to Subcarrier allocation for OFDMA is a
`joint optimization operation, not only requiring the activity
`and channel knowledge of all the Subscribers in all the cells,
`but also requiring frequent rescheduling every time an
`existing SubscriberS is dropped off the network or a new
`subscribers is added onto the network. This is often imprac
`tical in real wireleSS System, mainly due to the bandwidth
`cost for updating the Subscriber information and the com
`putation cost for the joint optimization.
`
`SUMMARY OF THE INVENTION
`A method and apparatus for Subcarrier Selection for
`Systems is described. In one embodiment, a method for
`Subcarrier Selection for a System employing orthogonal
`frequency division multiple access (OFDMA) comprises
`partitioning Subcarriers into groups of at least one cluster of
`Subcarriers, receiving an indication of a Selection by the
`Subscriber of one or more groups in the groups, and allo
`cating at least one cluster in the one or more groups of
`clusterS Selected by the Subcarrier for use in communication
`with the Subscriber.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The present invention will be understood more fully from
`the detailed description given below and from the accom
`panying drawings of various embodiments of the invention,
`which, however, should not be taken to limit the invention
`to the 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 arbi
`trary cluster feedback.
`FIG. 6 illustrates one embodiment of a partition the
`clusters into groups.
`FIG. 7 illustrates one embodiment of a feedback format
`for group-based cluster allocation.
`FIG. 8 illustrates frequency reuse and interference in a
`multi-cell, multi-Sector network.
`FIG. 9 illustrates different cluster formats for coherence
`clusters and diversity clusters.
`FIG. 10 illustrates diversity clusters with Subcarrier hop
`ping.
`FIG. 11 illustrates intelligent Switching between diversity
`clusters and coherence clusters depending on Subscribers
`mobility.
`FIG. 12 illustrates one embodiment of a reconfiguration
`of cluster classification.
`FIG. 13 illustrates one embodiment of a base station.
`
`DETAILED DESCRIPTION OF THE PRESENT
`INVENTION
`An approach for Subcarrier allocation is described. A
`method and apparatus for Subcarrier Selection for Systems is
`described. In one embodiment, a method for Subcarrier
`Selection for a System employing orthogonal frequency
`division multiple access (OFDMA) comprises partitioning
`Subcarriers into groups of at least one cluster of Subcarriers,
`
`5
`
`15
`
`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 Con
`figuration and Selective Loading.”
`FIELD OF THE INVENTION
`The invention relates to the field of wireless communi
`cations, 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 efficient modulation Scheme for Signal transmission over
`frequency-selective channels. In OFDM, a wide bandwidth
`is divided into multiple narrow-band Subcarriers, which are
`arranged to be orthogonal with each other. The Signals
`modulated on the Subcarriers are transmitted in parallel. For
`more information, See Cimini, Jr., “Analysis and Simulation
`of a Digital Mobile Channel Using Orthogonal Frequency
`25
`Division Multiplexing.” IEEE Trans. Commun., vol. COM
`33, no. 7, July 1985, pp. 665–75; Chuang and Sollenberger,
`“Beyond 3G: Wideband Wireless Data Access Based on
`OFDM and Dynamic Packet Assignment,” IEEE Commu
`nications Magazine, Vol. 38, No. 7, pp. 78-87, July 2000.
`One way to use OFDM to support multiple access for
`multiple Subscribers is through time division multiple access
`(TDMA), in which each subscriber uses all the subcarriers
`within its assigned time slots. Orthogonal frequency division
`multiple access (OFDMA) is another method for multiple
`35
`access, using the basic format of OFDM. In OFDMA,
`multiple Subscribers Simultaneously use different
`Subcarriers, in a fashion Similar to frequency division mul
`tiple access (FDMA). For more information, see Sari and
`Karam, “Orthogonal Frequency-Division Multiple Access
`and its Application to CATV Networks,” European Trans
`actions on Telecommunications, Vol. 9 (6), pp. 507–516,
`November/December 1998 and Nogueroles, Bossert,
`Donder, and Zyablov, “Improved Performance of a Random
`OFDMA Mobile Communication System,”, Proceedings of
`IEEE VTC 98, pp. 2502–2506.
`Multipath causes frequency-Selective fading. The channel
`gains are different for different Subcarriers. Furthermore, the
`channels are typically uncorrelated for different Subscribers.
`The Subcarriers that are in deep fade for one subscriber may
`provide high channel gains for another Subscriber.
`Therefore, it is advantageous in an OFDMA system to
`adaptively allocate the Subcarriers to SubscriberS So that each
`Subscriber enjoys a high channel gain. For more
`information, see Wong et al., “Multiuser OFDM with Adap
`55
`tive Subcarrier, Bit and Power Allocation.” IEEE J. Select.
`Areas Commun., Vol. 17(10), pp. 1747–1758, October 1999.
`Within one cell, the Subscribers can be coordinated to
`have different subcarriers in OFDMA. The signals for dif
`ferent Subscribers can be made orthogonal and there is little
`intracell interference. However, with aggressive frequency
`reuse plan, e.g., the same Spectrum is used for multiple
`neighboring cells, the problem of intercell interference
`arises. It is clear that the intercell interference in an OFDMA
`System is also frequency Selective and it is advantageous to
`65
`adaptively allocate the Subcarriers So as to mitigate the effect
`of intercell interference.
`
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`3
`receiving an indication of a Selection by the Subscriber of
`one or more groups in the groups, and allocating at least one
`cluster in the one or more groups of clusterS Selected by the
`Subcarrier for use in communication with the Subscriber.
`The techniques disclosed herein are described using
`OFDMA (clusters) as an example. However, they are not
`limited to OFDMA-based systems. The techniques apply to
`multi-carrier Systems in general, where, for example, a
`carrier can be a cluster in OFDMA, a spreading code in
`CDMA, an antenna beam in SDMA(space-division multiple
`access), etc. In one embodiment, Subcarrier allocation is
`performed in each cell Separately. Within each cell, the
`allocation for individual Subscribers (e.g., mobiles) is also
`made progressively as each new Subscriber is added to the
`System as opposed to joint allocation for Subscribers within
`each cell in which allocation decisions are made taking into
`account all Subscribers in a cell for each allocation.
`For downlink channels, each Subscriber 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 Subcar
`riers to the base Station. The feedback may comprise channel
`and interference information (e.g., Signal-to-interference
`plus-noise-ratio information) on all Subcarriers or just a
`portion of Subcarriers. In case of providing information on
`only a portion of the Subcarriers, a Subscriber may provide
`a list of Subcarriers ordered Starting with those Subcarriers
`which the Subscriber desires to use, usually because their
`performance is good or better than that of other Subcarriers.
`Upon receiving the information from the Subscriber, the
`base Station further Selects the Subcarriers among the
`candidates, utilizing additional information available at the
`base Station, e.g., the traffic load information on each
`Subcarrier, amount of traffic requests queued at the base
`Station for each frequency band, whether frequency bands
`are overused, and/or how long a Subscriber has been waiting
`to Send information. In one embodiment, the Subcarrier
`loading information of neighboring cells can also be
`eXchanged between base Stations. The base Stations can use
`this information in Subcarrier allocation to reduce inter-cell
`interference.
`In one embodiment, the selection by the base station of
`the channels to allocate, based on the feedback, results in the
`Selection of coding/modulation rates. Such coding/
`modulation rates may be specified by the subscriber when
`Specifying Subcarriers that it finds favorable to use. For
`example, if the SINR is less than a certain threshold (e.g., 12
`dB), quadrature phase shift keying (QPSK) modulation is
`used; otherwise, 16 quadrature amplitude modulation
`(QAM) is used. Then the base station informs the subscrib
`ers about the Subcarrier allocation and the coding/
`modulation rates to use.
`In one embodiment, the feedback information for down
`link Subcarrier allocation is transmitted to the base Station
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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 10-millisecond time slot. In one embodiment, the
`access channel occupies the entire frequency bandwidth.
`Then the base station can collect the uplink SINR of each
`Subcarrier directly from the access channel. The SINR as
`well as the traffic load information on the uplink subcarriers
`are used for uplink Subcarrier allocation.
`For either direction, the base Station makes the final
`decision of Subcarrier allocation for each Subscriber.
`In the following description, a procedure of Selective
`Subcarrier allocation is also disclosed, including methods of
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`channel and interference Sensing, methods of information
`feedback from the Subscribers to the base station, and
`algorithms used by the base Station for Subcarrier Selections.
`In the following description, numerous details are Set
`forth to provide a thorough understanding of the present
`invention. It will be apparent, however, to one skilled in the
`art, that the present invention may be practiced without these
`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 repre
`Sentations of operations on data bits within a computer
`memory. These algorithmic descriptions and representations
`are the means used by those skilled in the data processing
`arts to most effectively convey the substance of their work
`to otherS Skilled in the art. An algorithm is here, and
`generally, conceived to be a Self-consistent Sequence of steps
`leading to a desired result. The Steps are those requiring
`physical manipulations of physical quantities. Usually,
`though not necessarily, these quantities take the form of
`electrical or magnetic Signals capable of being Stored,
`transferred, combined, compared, and otherwise manipu
`lated. It has proven convenient at times, principally for
`reasons of common usage, to refer to these signals as bits,
`values, elements, Symbols, characters, terms, numbers, or
`the like.
`It should be borne in mind, however, that all of these and
`Similar terms are to be associated with the appropriate
`physical quantities and are merely convenient labels applied
`to these quantities. Unless Specifically Stated otherwise as
`apparent from the following discussion, it is appreciated that
`throughout the description, discussions utilizing terms Such
`as “rprocessing” or “computing or "calculating” or “deter
`mining” or “displaying or the like, refer to the action and
`processes of a computer System, or Similar electronic com
`puting device, that manipulates and transforms data repre
`Sented as physical (electronic) quantities within the com
`puter System's registers and memories into other data
`Similarly represented as physical quantities within the com
`puter System memories or registers or other Such informa
`tion Storage, transmission or display devices.
`The present invention also relates to apparatus for per
`forming the operations herein. This apparatus may be spe
`cially constructed for the required purposes, or it may
`comprise a general purpose computer Selectively activated
`or reconfigured by a computer program Stored in the com
`puter. Such a computer program may be Stored in a computer
`readable Storage medium, Such as, but is not limited to, any
`type of disk including floppy disks, optical disks,
`CD-ROMs, and magnetic-optical disks, read-only memories
`(ROMs), random access memories (RAMs), EPROMs,
`EEPROMs, magnetic or optical cards, or any type of media
`Suitable for Storing electronic instructions, and each coupled
`to a computer System bus.
`The algorithms and displays presented herein are not
`inherently related to any particular computer or other appa
`ratus. Various general purpose Systems may be used with
`programs in accordance with the teachings herein, or it may
`prove convenient to construct more specialized apparatus to
`perform the required method steps. The required Structure
`for a variety of these Systems will appear from the descrip
`tion below. In addition, the present invention is not
`described with reference to any particular programming
`language. It will be appreciated that a variety of program
`ming languages may be used to implement the teachings of
`the invention as described herein.
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`IPR2018-1581
`HTC EX1003, Page 11
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`A machine-readable medium includes any mechanism for
`Storing or transmitting information in a form readable by a
`machine (e.g., a computer). For example, a machine
`readable medium includes read only memory (“ROM”);
`random access memory (“RAM), magnetic disk storage
`media, optical Storage media; flash memory devices;
`electrical, optical, acoustical or other form of propagated
`Signals (e.g., carrier Waves, infrared signals, digital signals,
`etc.), etc.
`Subcarrier Clustering
`The techniques described herein are directed to Subcarrier
`allocation for data traffic channels. In a cellular System, there
`are typically other channels, pre-allocated for the exchange
`of control information and other purposes. These channels
`often include down link and up link control channels, uplink
`access channels, and time and frequency Synchronization
`channels.
`FIG. 1A illustrates multiple subcarriers, such as Subcarrier
`101, and cluster 102. A cluster, Such as cluster 102, is defined
`as a logical unit that contains at least one physical Subcarrier,
`as shown in FIG. 1A. A cluster can contain consecutive or
`disjoint Subcarriers. The mapping between a cluster and its
`Subcarriers can be fixed or reconfigurable. In the latter case,
`the base station informs the Subscribers when the clusters are
`redefined. In one embodiment, the frequency spectrum
`includes 512 Subcarriers and each cluster includes four
`consecutive Subcarriers, thereby resulting in 128 clusters.
`An Exemplary Subcarrier/Cluster Allocation Procedure
`FIG. 1B is a flow diagram of one embodiment of a process
`for allocation clusters to Subscribers. The process is per
`formed by processing logic that may comprise hardware
`(e.g., dedicated logic, circuitry, etc.), Software (such as that
`which runs on, for example, a general purpose computer
`System or dedicated machine), or a combination of both.
`Referring to FIG. 1B, each base station periodically
`broadcasts pilot OFDM symbols to every subscriber within
`its cell (or sector) (processing block 101). The pilot symbols,
`often referred to as a Sounding Sequence or Signal, are
`known to both the base station and the Subscribers. In one
`embodiment, each pilot symbol covers the entire OFDM
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`frequency bandwidth. The pilot symbols may be different for
`different cells (or sectors). The pilot symbols can serve
`multiple purposes: time and frequency Synchronization,
`channel estimation and Signal-to-interference/noise (SINR)
`ratio measurement for cluster allocation.
`Next, each Subscriber continuously monitors the reception
`of the pilot symbols and measures the SINR and/or other
`parameters, including inter-cell interference and intra-cell
`traffic, of each cluster (processing block 102). Based on this
`information, each Subscriber Selects one or more clusters
`with good performance (e.g., high SINR and low traffic
`loading) relative to each other and feeds back the informa
`tion on these candidate clusters to the base Station through
`predefined uplink access channels (processing block 103).
`For example, SINR values higher than 10 dB may indicate
`good performance. Likewise, a cluster utilization factor leSS
`than 50% may be indicative of good performance. Each
`subscriber selects the clusters with relatively better perfor
`mance than others. The Selection results in each Subscriber
`Selecting clusters they would prefer to use based on the
`measured parameters.
`In one embodiment, each Subscriber measures the SINR
`of each Subcarrier cluster and reports these SINR measure
`ments to their base Station through an access channel. The
`SINR value may comprise the average of the SINR values
`of each of the Subcarriers in the cluster. Alternatively, the
`SINR value for the cluster may be the worst SINR among
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`the SINR values of the Subcarriers in the cluster. In still
`another embodiment, a weighted averaging of SINR values
`of the Subcarriers in the cluster is used to generate an SINR
`value for the cluster. This may be particularly useful in
`diversity clusters where the weighting applied to the Sub
`carriers may be different.
`The feedback of information from each Subscriber to the
`base station contains a SINR value for each cluster and also
`indicates the coding/modulation rate that the Subscriber
`desires to use. No cluster indeX is needed to indicate which
`SINR value in the feedback corresponds to which cluster as
`long as the order of information in the feedback is known to
`the base Station. In an alternative embodiment, the informa
`tion in the feedback is ordered according to which clusters
`have the best performance relative to each other for the
`Subscriber. In Such a case, an indeX is needed to indicate to
`which cluster the accompanying SINR value corresponds.
`Upon receiving the feedback from a Subscriber, the base
`Station further Selects one or more clusters for the Subscriber
`among the candidates (processing block 104). The base
`Station may utilize additional information available at the
`base Station, e.g., the traffic load information on each
`Subcarrier, amount of traffic requests queued at the base
`Station for each frequency band, whether frequency bands
`are overused, and how long a Subscriber has been waiting to
`Send information. The Subcarrier loading information of
`neighboring cells can also be exchanged between base
`Stations. The base Stations can use this information in
`Subcarrier allocation to reduce inter-cell interference.
`After cluster Selection, the base Station notifies the Sub
`Scriber about the cluster allocation through a downlink
`common control channel or through a dedicated downlink
`traffic channel if the connection to the subscriber has already
`been established (processing block 105). In one
`embodiment, the base station also informs the Subscriber
`about the appropriate modulation/coding rates.
`Once the basic communication link is established, each
`Subscriber can continue to Send the feedback to the base
`Station using a dedicated traffic channel (e.g., one or more
`predefined uplink access channels).
`In one embodiment, the base Station allocates all the
`clusters to be used by a Subscriber at once. In an alternative
`embodiment, the base Station first allocates multiple clusters,
`referred to herein as the basic clusters, to establish a data link
`between the base station and the Subscriber. The base station
`then Subsequently allocates more clusters, referred to herein
`as the auxiliary clusters, to the Subscriber to increase the
`communication bandwidth. Higher priorities can be given to
`the assignment of basic clusters and lower pr