OAA
`
`US 20020163879A1
`
`as) United States
`a2) Patent Application Publication co) Pub. No.: US 2002/0163879 Al
`
` Li etal. (43) Pub. Date: Nov.7, 2002
`
`
`(54) MULTI-CARRIER COMMUNICATION WITH
`TIME DIVISION MULTIPLEXING AND
`CARRIER-SELECTIVE LOADING
`
`(76)
`
`Inventors: Xiaodong Li, Bellevue, WA (US); Hui
`Liu, Sammamish, WA (US); Hujun
`Yin, Seattle, WA (US)
`
`Related U.S. Application Data
`
`(60)
`
`Provisional application No. 60/262,828, filed on Jan.
`19, 2001.
`
`ee
`gps
`Publication Classification
`(SL) Unt. C17 ecssssnsennnnnsntnnnnneneesnee HO4J 11/00
`(52)
`UWS. C0.
`cescsesessesnsenee 370/200; 370/328; 370/411;
`455/560
`
`Correspondence Address:
`Christian A. Nicholes
`A methodfor subearrier allocation and loading for a multi-
`BLAKELY, SOKOLOFEF, TAYLOR & ZAFMAN
`carrier, multi-subscriber system is described. At least one
`LLP
`cluster in a first and second set ofclusters of subcarriers is
`Seventh Floor
`
`12400 Wilshire Boulevard associated for use in communication withafirst and second
`Los Angeles, CA 90025-1026 (US)
`subscriber, respectively. Then,for each cluster associated for
`use in communication with the first subscriber and the
`second subscriber, usage of that cluster
`is multiplexed
`between the first subscriber during a first time division and
`the second subscriber during a second time division.
`
`(21) Appl. No.:
`
`10/051,348
`
`(22)
`
`Filed:
`
`Jan. 17, 2002
`
`(57)
`
`ABSTRACT
`
`OFDM SYMBOLS TO SUBSCRIBERS
`
`[101
`
`MONITORS PILOT SYMBOLS/
`MEASURES SINR AND/OR
`OTHER PARAMETERS
`
`
` EACH SUBSCRIBER SELECTS ONE
`OR MORE CLUSTERS/FEEDBACK
`
` PERIODICALLY BROADCAST PILOT
`
`
`
`
`
` SUBSCRIBER(S) CONTINUOUSLY
`INFO TO BASE STATION
`
`
` 104
` BASE STATION SELECTS ONE OR
`MORE CLUSTERS FOR EACH
`
`SUBSCRIBER
`
`CLUSTER ALLOCATION
` BASE STATION NOTIFIES THE
` RETRAINING
`NEEDED?
`
`SUBSCRIBER REGARDING
`
`ee
`
`1
`
`GM 1007
`
`1
`
`GM 1007
`
`

`

`Patent Application Publication
`
`Nov. 7,2002 Sheet 1 of 7
`
`US 2002/0163879 Al
`
` PERIODICALLY BROADCAST PILOT=,101
`
`OFDM SYMBOLS TO SUBSCRIBERS
`
`
`
`104
`
` 102
`
`SUBSCRIBER(S) CONTINUOUSLY
`MONITORS PILOT SYMBOLS/
`MEASURESSINR AND/OR
`
`OTHER PARAMETERS
`
` EACH SUBSCRIBER SELECTS ONE
`103
`OR MORE CLUSTERS/FEEDBACK
`
`INFO TO BASE STATION
`
`
` BASE STATION SELECTS ONE OR
`MORE CLUSTERS FOR EACH
`
`
`SUBSCRIBER
`
` BASE STATION NOTIFIES THE
`»
`
`
`
`SUBSCRIBER REGARDING
`CLUSTER ALLOCATION
`
`RETRAINING
`NEEDED?
`
`
`
`FIG. 1
`
`2
`
`

`

`Patent Application Publication
`
`Nov. 7, 2002 Sheet 2 of 7
`
`US 2002/0163879 Al
`
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`Nov. 7, 2002 Sheet 3 of 7
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`Patent Application Publication
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`Nov. 7, 2002 Sheet 4 of 7
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`US 2002/0163879 Al
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`

`Patent Application Publication
`
`Nov. 7,2002 Sheet 5 of 7
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`US 2002/0163879 Al
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`601
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`
` MEDIA
`
`ACCESS
`CONTROLLER
`USER QUEUES:
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`

`US 2002/0163879 Al
`
`Nov. 7, 2002
`
`MULTI-CARRIER COMMUNICATION WITH TIME
`DIVISION MULTIPLEXING AND
`CARRIER-SELECTIVE LOADING
`
`RELATED APPLICATIONS
`
`(0001] This application claims priority to the provisional
`application titled Multi-Carrier Communication With Time
`Division Multiplexing And Carrier-Selective Loading,filed
`Jan. 19, 2001, serial No. 60/262,828, whichis incorporated
`by reference herein.
`
`FIELD OF THE INVENTION
`
`(0002] The present invention relates to the field of com-
`munication systems; more particularly, the present invention
`relates to multi-subscriber, multi-carrier systems.
`
`BACKGROUND OF THE INVENTION
`
`In a multi-subscriber, single-carrier communica-
`{0003]
`tion system employing time division multiplexing (TDM), a
`channel may be shared by multiple subscribers in a time
`division fashion; that is, the channel may be used by one
`subscriber at one time and by another subscriber al another
`time.
`
`[0004] The time usage allocation for TDM maybefixed or
`variable. For fixed usage, each subscriber utilizes the chan-
`nel at a fixed, pre-scheduled timeslot, typically seen in time
`division multiple access (TDMA) systems. Therefore, no
`frequent scheduling/rescheduling is needed. However,fixed
`channel usage may lead to resource waste, especially in
`bursty packet data transmission, because the subscriber may
`have nothing to transmit duringits assigned time slot. On the
`other hand, with variable time usage, a channel may be used
`by one subscriber for a variable period of time (e.g., depend-
`ing on its data load) and then used by another subscriber,
`With careful scheduling, variable time usage achieves sta-
`tistical multiplexing gain and is typically more efficient. For
`examples of TDM with variable time usage, see Bender,
`Black, Grob, Padovani, Sindhushayana,
`and Viterbi,
`“CDMA/HDR: A Bandwidth-Efficient High-Speed Wireless
`Data Service for Nomadic Users,” IEEE Communications
`Magazine, Vol. 38, No. 7, pp. 70-77, July, 2000.
`
`In a multi-carrier communication system, each
`(0005]
`subscriber may be allocated multiple carriers and can use the
`multiple carriers simultaneously. For a specific subscriber,
`the transmission rate/reliability (performance) of different
`carriers may be different. Furthermore, for a specific carrier,
`the transmissionrate/reliability for different subscribers may
`be different. One example of such is orthogonal frequency
`division multiple access (OFDMA). In OFDMA, multiple
`subscribers simultaneously use different frequency subcar-
`riers in a manner 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/
`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.
`[0006] Due to the unique properties of multi-carrier sys-
`tems described above,
`the TDM scheduling algorithms
`designed for single-carrier systems may not directly apply.
`This is at least partially because, in a multi-carrier system,
`unlike in a single-carrier system,
`the operation of each
`
`carrier is to some extent dependent on each other carrier;
`each carrier impacts each of the others, In a single-carrier
`system, unlike in a multi-carrier system, there are no com-
`plications regarding orderings of packets amongcarriers. In
`a mullti-carrier system, varying delays associated with mul-
`tiple carriers introduce complexities unfathomedin a single-
`carrier system. In a single-carrier system, unlike a multi-
`carrier system, there needs not be any consideration given
`toward allocating data packets among more than one carrier.
`The algorithms needed to potentially optimize overall
`throughput in a multi-carrier system are inherently different
`from algorithms used in a single-carrier system.
`
`SUMMARY OF THE INVENTION
`
`(0007] A methodfor subcarrier allocation and loading for
`a multi-carrier, multi-subscriber system is described. Atleast
`one cluster in a first and second set of clusters of subcarriers
`is associated for use in communication with a first and
`second subscriber, respectively, Then, for each cluster asso-
`ciated for use in communication with the first subscriber and
`the second subscriber, usage of that cluster is multiplexed
`between the first subscriber during a first time division and
`the second subscriber during a second time division.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`invention will be understood more
`[0008] The present
`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 explana-
`tion and understanding only.
`
`[0009] FIG. 1 is a flow diagram of one embodiment of a
`process for allocating subcarriers.
`
`(0010) FIG. 2 illustrates time and frequency grid of
`OFDM symbols, pilots and clusters.
`
`[0011] FIG. 3 illustrates subscriber processing.
`[0012]
`FIG.4 illustrates one example of FIG. 3.
`
`(0013] FIG. 5 illustrates one embodiment of a format for
`arbitrary cluster feedback.
`[0014] FIG. 6 is a block diagram of one embodiment ofa
`base station of a multi-subscriber, multi-carrier system
`employing time-division multiplexing.
`
`[0015] FIG. 7 is a block diagram of another embodiment
`of a base station with single-segment cluster queues.
`
`FIG.8 is a block diagram of one embodiment ofa
`[0016]
`transmitter,
`
`[0017] FIG. 9 is a block diagram of one embodimentof a
`receiver.
`
`DETAILED DESCRIPTION
`
`[0018] A high-performance multi-carrier, TDM system,
`including carrier allocation, carrier loading, TDM signaling,
`and many other aspects, is disclosed.
`[0019] The methods disclosed herein are described using
`the example of OFDMA,wherea carrier is correspondingto
`a cluster, containing multiple OFDM frequency subcarriers.
`However, it should be noted that the methods are not limited
`to just OFDMA. The methods directly apply to much more
`
`9
`
`

`

`US 2002/0163879 Al
`
`Nov. 7, 2002
`
`generic multi-carrier systems, where a carrier can be, for
`example, a frequency cluster in OFDMA,a spreading code
`in CDMA, an antenna beam in SDMA (space-division
`multiple access) system, a data stream from one transmit
`antenna in a multi-input multi-output (MIMO) employing
`antenna arrays at both the transmit and receiving sides.
`Indeed, the methods can be applied to a much broader area
`of data networking systems containing multi-input, multi-
`output multiplexers (switches) with a property that
`the
`transmission rate of each output port depends on the con-
`nected input port.
`
`In the following description, numerous details are
`[0020]
`sel forth, to provide a thorough understanding ofthe 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.
`
`[0021] Some portions of the detailed descriptions which
`follow are presented in terms of algorithms and symbolic
`representations 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 oftheir work
`to others skilled in the art. An algorithm is here, and
`generally, conceivedto 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, trans-
`ferred, 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
`(0022]
`these and similar terms are to be associated with the appro-
`priate physical quantities and are merely convenient labels
`applied to these quantities. Unless specifically stated other-
`wise as apparent from the following discussion, it is appre-
`ciated that throughout the description, discussions utilizing
`terms such as “processing” or “computing” or “calculating”
`or “determining” or “displaying” or the like, refer to the
`action and processes of a computer system, or similar
`electronic computing device,
`that manipulates and trans-
`forms data represented as physical (electronic) quantities
`within the computer system’s registers and memories into
`other data similarly represented as physical quantities within
`the computer system memories or registers or other such
`information storage, transmission or display devices.
`
`(0023] The present invention also relates to apparatus for
`performing the operations herein. This apparatus may be
`specially 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.
`
`[0024] The algorithms and displays presented herein are
`not inherently related to any particular computer or other
`apparatus. Various general purpose systems may be used
`with programs in accordance with the teachingsherein, or it
`may prove convenient to construct more specialized appa-
`ratus to perform 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 program-
`ming languages may be used to implement the teachings of
`the invention as described herein.
`
`[0025] A machine-readable medium includes any mecha-
`nism 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.); ete.
`
`(0026] An Exemplary Subcarrier/Cluster Allocation Pro-
`cedure
`
`[0027] FIG. 1 is a flow diagram of one embodiment of a
`processfor allocating clusters to subscribers. The process is
`performed 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 ofboth.
`
`[0028] Referring to FIG. 1, each basestation 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
`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.
`
`[0029] 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 (c.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 clusterutilization factorless
`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
`[0030]
`SINR of each subcarrier cluster and reports these SINR
`measurements to their base station through an access chan-
`nel. The SINR value may comprise the average of the SINR
`values of each ofthe subcarriers in the cluster. Alternatively,
`
`10
`
`10
`
`

`

`US 2002/0163879 Al
`
`Nov. 7, 2002
`
`the SINR value for the cluster may be the worst SINR
`among the SINR values of the subcarriers in the cluster. In
`sull 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
`subcarriers may be different.
`
`[0031] 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.
`
`[0032] 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 basestation may utilize additional information available
`at the base station, e.g., the traffic load information on each
`subcarrier, amount of traflic 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.
`
`[0033] After cluster selection, the base station notifies the
`subscriber 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 embodi-
`ment, the base station also informs the subscriber about the
`appropriate modulation/coding rates.
`
`[0034] Once the basic communication link is established,
`each subscriber can continue to send the feedbackto 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
`(0035]
`the clusters to be used by a subscriber at once.
`In an
`alternative embodiment, the base station first allocates mul-
`tiple 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 priorities may be giventothat ofauxiliary
`clusters. For example,
`the base station first ensures the
`assignment of the basic clusters to the subscribers and then
`tries to satisfy further requests on the auxiliary clusters from
`the subscribers. Alternatively, the base station may assign
`auxiliary clusters to one or more subscribers before allocat-
`ing basic clusters to other subscribers. For example, a base
`station may allocate basic and auxiliary clusters to one
`subscriber before allocating any clusters to other subscrib-
`ers.
`In one embodiment,
`the base station allocates basic
`clusters to a new subscriber and then determinesifthere are
`
`any other subscribers requesting clusters. If not, then the
`base station allocates the auxiliary clusters to that new
`subscriber.
`
`From time to time, processing logic performs
`[0036]
`retraining by repeating the process described above (pro-
`cessing block 106). The retraining may be performed peri-
`odically. This retraining compensates for subscriber move-
`ment and any changesin interference. In one embodiment,
`each subscriber
`reports to the base station its updated
`selection of clusters and their associated SINRs. Then the
`
`base station further performs the reselection and informs the
`subscriber about the new cluster allocation. Retraining can
`be initiated by the base station, and in which case, the base
`station requests a specific subscriber to report
`its updated
`cluster selection. Retraining can also be initiated by the
`subscriber when it observes channel deterioration.
`
`[0037] Adaptive Modulation and Coding
`
`In one embodiment, different modulation and cod-
`[0038]
`ing rates are used to support reliable transmission over
`channels with different SINR. Signal spreading over mul-
`tiple subcarriers may also be used to improve the reliability
`at very low SINR.
`
`[0039] An example coding/modulation table is given
`below in Table 1.
`
`TABLE 1
`
`Scheme
`
`Modulation
`
`Code Rate
`
`0
`1
`2
`3
`4
`5
`6
`
`OPSK, \ Spreading
`QPSK,'4 Spreading
`QPSK, 2 Spreading
`OPSK
`SPSK
`16QAM
`64QAM
`
`4
`ee)
`“%
`“4
`24
`Ms
`Ye
`
`In the example above, s spreading indicates that
`[0040]
`one OPSK modulation symbol is repeated over eight sub-
`carriers. The repetition/spreading may also be extended to
`the time domain. For example, one QPSK symbol can be
`repeated over
`four subcarriers of two OFDM symbols,
`resulting also /s spreading.
`
`(0041] The coding/modulation rate can be adaptively
`changed according to the channel conditions observed at the
`receiver after the initial cluster allocation and rate selection.
`
`[0042]
`
`Pilot Symbols and SINR Measurement
`
`In one embodiment, each base station transmits
`(0043]
`pilot symbols simultaneously, and each pilot symbol occu-
`pies the entire OFDM frequency bandwidth, as shown in
`FIGS. 2A-C. Referring to FIG. 2A-C, pilot symbols 201 are
`showntraversing the entire OFDM frequency bandwidth for
`cells A, B and C, respectively. In one embodiment, each of
`the pilot symbols have a length or duration of 128 micro-
`seconds with a guard time,
`the combination of which is
`approximately 152 microseconds. After each pilot period,
`there are a predetermined numberof data periods followed
`by another set of pilot symbols. In one embodiment, there
`are four data periods used to transmit data after each pilot,
`and each of the data periods is 152 microseconds.
`
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`
`[0044] A subscriber estimates the SINR for each cluster
`from the pilot symbols. In one embodiment, the subscriber
`first estimates the channel response, including the amplitude
`and phase, as if there is no interference or noise. Once the
`channel is estimated, the subscriber calculates the interfer-
`ence/noise from the received signal.
`
`[0045] The estimated SINR values may be ordered from
`largest to smallest SINRsand the clusters with large SINR
`values are selected. In one embodiment, the selected clusters
`have SINR values that are larger than the minimum SINR
`which still allows a reliable (albeit low-rate) transmission
`supported by the system. The number of clusters selected
`may depend on the feedback bandwidth and the request
`transmissionrate. In one embodiment, the subscriber always
`tries to send the information about as many clusters as
`possible from which the base station chooses.
`
`[0046] The estimated SINR values are also used to choose
`the appropriate coding/modulation rate for each cluster as
`discussed above. By using an appropriate SINR indexing
`scheme, an SINR index mayalso indicate a particular coding
`and modulation rate that a subscriber desires to use. Note
`that even for the same subscribers, different clusters can
`have different modulation/coding rates.
`
`Pilot symbols serve an additional purpose in deter-
`(0047]
`mining interference among the cells. Since the pilots of
`multiple cells are broadcast at
`the same time,
`they will
`interfere with each other (because they occupy the entire
`frequency band). This collision of pilot symbols may be
`used to determine the amountof interference as a worst case
`scenario. Therefore, in one embodiment, the above SINR
`estimation using this method is conservative in that
`the
`measured interference level
`is the worst-case scenario,
`assuming that all the interference sources are on. Thus, the
`structure of pilot symbols is such that it occupies the entire
`frequency band and causes collisions among different cells
`for use in detecting the worst case SINR in packet trans-
`mission systems.
`
`the subscribers can
`[0048] During data traffic periods,
`determine the level of interference again. The data traffic
`periods are used to estimate the intra-cell traffic as well as
`the inter-cell interference level. Specifically, the power dif-
`ference during the pilot and traflic periods may be used to
`sense the (intra-cell) traffic loading and inter-cell interfer-
`ence to select the desirable clusters.
`
`[0049] The interference level on certain clusters may be
`lower, because these clusters may be unused in the neigh-
`boring cells. For example, in cell A, with respect to cluster
`A thereis less interference because cluster Ais unusedin cell
`B (while it is used in cell C). Similarly, in cell A, cluster B
`will experience lower interference from cell B because
`cluster B is used in cell B but not in cell C.
`
`[0050] The modulation/coding rate based onthis estima-
`tion is robust to frequent interference changes resulted from
`bursty packet transmission. This is because the rate predic-
`tion is based on the worst case situation in which all
`interference sources are transmitting.
`
`In one embodiment, a subscriber utilizes the infor-
`[0051]
`mation available from both the pilot symbol periods and the
`data traffic periods to analyze the presence of both the
`intra-cell traffic load and inter-cell interference. The goal of
`the subscriber is to provide an indication to the base station
`
`as to those clustersthat the subscriber desires to use. Ideally,
`the result of the selection by the subscriber is clusters with
`high channel gain, low interference from other cells, and
`high availability. The subscriber provides feedback infor-
`mation that includes the results, listing desired clusters in
`order or not as described herein.
`
`[0052] FIG. 3 illustrates one embodiment of subscriber
`processing. The processing is performed 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.
`
`(0053] Referring to FIG. 3, channel/interference estima-
`tion processing block 301 performs channel andinterference
`estimation in pilot periods in response to pilot symbols.
`Traffic/interference analysis processing block 302 performs
`traffic and interference analysis in data periods in response
`to signal information and information from channel/inter-
`ference estimation block 301.
`
`[0054] Cluster ordering and rate prediction processing
`block 303 is coupled to outputs of channel/interference
`estimation processing block 301 and traffic/interference
`analysis processing block 302 to perform cluster ordering
`and selection along with rate prediction.
`
`[0055] The output of cluster ordering processing block
`303 is input to cluster request processing block 304, which
`requests clusters and modulation/coding rates. Indications of
`these selections are sent to the base station. In one embodi-
`ment, the SINR on each cluster is reported to the base station
`through an access channel. The information is used for
`cluster selection to avoid clusters with heavy intra-cell traffic
`loading and/or strong interference from othercells. That is,
`a new subscriber may not be allocated use of a particular
`cluster if heavy intra-cell traffic loading already exists with
`respectto 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.
`
`[0056] 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:
`
`A,Sltney,
`
`[0057] where S, represents the signal for subcarrier (freq.
`band)i, 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 I; and n; are not separated and may be
`considered one quantity. The interference/noise and channel
`gain H; are not know. During pilot periods, the signal 5;
`representing the pilot symbols, and the observation y, are
`knowns, thereby allowing determination of the channel gain
`H, for the case 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.
`
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`US 2002/0163879 Al
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`
`interference information from processing
`[0058] The
`blocks 301 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 with precalculated data rate values. Such a look up
`table may store the pairs of each SINR andits 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 subscriber requests the desired clusters along
`with coding and modulation rates knownto the subscriber to
`achieve desired data rates.
`
`[0059] FIG. 4 is one embodiment of an apparatus for the
`selection of clusters based on power difference. The
`approach uses information available during both pilot sym-
`bol periods and data traffic periods to perform energy
`detection. The processing of FIG. 4 may be implemented in
`hardware, (¢.g., dedicated logic, circuitry, etc.), software
`(such as is run on, for example, a general purpose computer
`system or dedicated machine), or a combination of both.
`
`(0060] Referring to FIG. 4, a subscriber includes SINR
`estimation processing block 401 to perform SINRestimation
`for each cluster in pilot periods, power calculation process-
`ing block 402 to perform power calculations for each cluster
`in pilot periods, and power calculation processing block 403
`to perform