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BACKGROUND
[1001] The present application for Patent claimss priority of U.S. Provisional Application No. 60/409,820, filed Septemlaer 10, 2002, assigned to ttie assignee hereof and hereby expressly fncorporated by reference herein.
Field
[10021 The present dteclosed embodiments relate generally to wireless communications, and more specifically to reverse link rate scheduling in a communication system having a variable data transmission rate.
Background
£1003] The field ot communications has many appTicatiorte including, e.g., paging, wireless local loops, Internet telephony, and sateWite communication systems. An exemplary application is a cellular telephone system for mobile subscribers. (As used herein, the term "cellular" system encompasses both cellular and personal communications services (PCS) system frequencies.) Modem communication systems designed to aliow multiple users to access a common communications medium have been developed for such cellular systems. These modern communication systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), space division multiple access (SOMA), polarization division multiple access (PDMA), or other modulation techniques known in the art. Tfiese modulation techniques demodulate signals received from multiple users of a communication system, thereby enabling an increase in the capacity of the communication system. In connectbn therewith, various wireless systems have been established including, e.g.. Advanced Mobile Phone Service (AMPS), Global System for Mobile communication (GSM), and some otfier wireless systems. [1004] Ip FDMA systems, the total frequency spectrum is divided into a number of smaller sub-bands and each user is given its own sub-band to access
the cortununication medium. Altemativefy, in TDMA systems, each user is given the entire frequency spectrum during periodically recuning time slots. A CDMA system provides potential advantages over other types of systems, induding inaeased system capacity. In CDMA systems, each user is given the entire frequency spectmm for all of the time, but distinguishes its transmission throu^ the use of a unique code.
[1005] A CDMA system may be designed to support one or more CDI^flA standards such as (1) the 'T(A/ElA-95-B Mc^iiie Statiwi-Base Station Ckjmpatibility Standarcl for Dual-Mode Wideband Spread Spectrum Cellular System* (fte JS-95 standard), (2) the standard offered by a consortium named "3rd Generation Partriership Project (3GPP) and embodied in a set of documents including Oooument Nos. 3G TS 25.211, 3G TS 25.212,3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard ofiered by a consortium named "3rd Generation Partnership Proiiea 2" (3GPP2) and embodied in TR-46.5 Physical Layer Standard for cdnrvaZOOO Spread Spectrum Systems" (Ihe iS-2000 standard), and
(1006] In the above named CDMA communication systems and standards, the available ^lectmm is shared simultaneously among a number of users, and techniques such as soft handofl are employed to maintair\ sufficient quality to support delay-senstfjve services, such as voice. Data senfices are also available. More recently, systems have been proposed that enhance the capacity for data senflces by usmg higher order modulation, very fast feedback of C^er to Interference ratio {Cfi) from a mobile stetion, very fast sc^iedullng, and scheduling for services that have more relaxed delay requirements. An example of such a data-only communication system using these techniques, is the high data rate (HDR) system that conforms to the TIA/ElA/iS-856 standard (the 13-856 standard).
[lOOTJ In contrast to the ottwr above named standards, an IS-856 system uses the entire spectnjm available in each ce\] to transmit data to a single user al one lime. One factor used in determining virtiich user is served is link quality. By using link quality as a factor for selecting which user is served, the system spends a greater percentage of time sendir^ data at higher rates when the channel is
1
good, and thereby avoids committing resources to support transmission at Inefficient rates. The net effect is higiier data capacity, higher peak data rates, and higher average throughput,
[1008] Systems can incorporate support for deiay-sensitive data, such as voice channels or data channels supported in the [S-2000 standard, along with support for packet data services such as those described in the lS-856 standard. One such system is described in a proposal submitted by LG Electronics, LSI Logic, Lucent Technologies, Nortel Networks, QUALCOMM Incorporated, and Samsung to the 3rd Generation Partnership Project 2 (3GPP2). The proposal is detailed in documents entitled "Updated Joint Physical Layer Prqcrasal for IxEV-DV, submitted to 3GPP2 as document number C50-20010611-009, June 11, 2001; "Results of L3NQS Simulation Study", submitted to 3GPP2 as document number C50-20010820-011, August 20, 20O1; and "System Simulation Results for the L3NQS Framevwjrk Proposal for cdma2000 Ix-EVDV", submitted to 3GPP2 as document number C50-20010820-012, August 20, 2001. These are hereinafter refened to as the 1 xEV-DV proposal.
[1009] Multi-level scheduling may be useful for more efficient capacity utilization on the reverse link.
SUMMARY
110103 Embodiments disclosed herein address Hie above stated needs by providing a method and system for multilevel scheduling for rate assignment In a communication system.
[lOIIJ In an aspect, a method for estimating capacity used on a reverse link, comprises measuring a plurality of signal-to-noise ratios at a station for a plurality of rates, determining sector load based on the measured plurality of signal-to-ndse mtios, an as^gned tmnsmissic^ rate, and an expected transmissiCHi rate, and estimating capacity on the reverse link tsassd on the sector toad. [1012] In an aspect, a method of estimating load contritxjtion to a sector antenna, comprises assigning a transmission rate Ri on a first communication channel, determining an expected rate of transmission E[R] on a second communication channel, estimating a signal-to-noise ratfo of a station for the assigned transmission rate Ri on the first communication channel and the ejqaected rat© of transmlsston E[B] on a second communjcatton chann^, and estimating the load contribution based on the estimated sigr^t-to-noise ratio. [1013] in an aspect, a method for estimating capacity available to schedule, comprises measuring other-cell interference during a previous transmission (loc), determining thermal noise (No), determining sector load (Loadj), and determining rise-over-thermal (ROTj) based on the ratio of the measured other-cell interference over thermal noise, and based an the sector krad. [1014] In another aspeo, a method of distributing sector capacity across a base station (BS) and a base station controller (BSC), comprises measuring other-cell interference during a previous transmission (IM), determining tiiennal noise (No), detennining a maximum rise-over-thennal iROT(max)), detemilning an estimated assigned load at the BSC (Lcadj(BSC)), and detemninrng a sector capadty distributed to the base station based on the ratio of the measured other-cell interference over thermal noise, ttie maximum rise-over-thermal, and the estimated assigned load at the BSC.
[1015] In yet euiother aspect, a method of determining priority of a station, «Knprises determining pilot energy over noise plus interference ratio (Ecp/lsK), determining a soft iiandoff fador (SHOIactor), determining a fairness value (F), detemnrning a proportional fairness value (PF), determining a fairness factor a, ami detemiining *a maximum capac% utilization based on the pilot energy over noise plus interference ratio, tfie soft iiandoff factor, the fairness value, and the fairness factor a.
BRIEF DESCRIPTION OF THE DRAWINGS
[1016] FIG. 1 exemplifies an embodiment of a wireless commynication system
with three mobile stations and two base stations;
[10171 FIG. 2 shows set point adjustment due to rate transitions on R-SCH in
accordance with an embodiment.
[1018] FIG. 3 shows scheduling delay liming In accordance vWth an
embodiment;
[1019] FIG. 4 shows parameters associated in moWIe station scheduling on a
reverse ^rxK
[1020] FIG. 5 Is a flowchart of a scheduling process In accordance with an
embodiment;
[1021] FIG. 6 is a block diagram of a base station in accordance with an
emtwdlment; and
[1022] FIG. 7 Is a blocl
embodiment,
DETAILED DESCRIPTION
[1023] The word "exemplary" is used herein to mean "serving as an example^ instance, or illustration." Any embodiment described herein as "exemplai/ is not necessariiy to be construed as preferred or advantageous over other embodiments.
[1024] A wireless communtealion system may comprise multiple mobile stations and multiple base stations. Figure i exemplifies an embodiment of a vwrelGSs communication system with three mobile stations 10A, 10B and IOC and two baSB stations 12. In figure 1, the thrse mobile stations are shown as a mobiie t^ephone unit installed in a car 10A, a portable computer remote 10B, and a lixed (ocation unit 10C such as might be found in a wireless local loop or meter reading system. Mobile stations may be any type of communication unit such as, for example, hand-held pei^onal communication system units, port^le data units such as a personal data assistant, or fixed locaHon data units such as meter reading equipment. Figure 1 shows a forward link 14 from the base station 12 to the mobile stations 10 and a reverse link 16 from the mobile stations 10 to tfie base stations 12.
[1025] As a mobile station moves through the physical environment, the numljer of signal paihs and the strength ot the signals on these paths vary constantly, both as received at the mobile station and as received at the base station. Therefore, a receiver in an embodiment uses a special processing element called a searcher element, that continually scans the channel in the time domain to determine the existence, time offset, and the signal strength of signals in the multiple path environment A searcher element is also called a search wigine. The output of the searcher element provides the informaticffi for ensuring that demodulation elements are traddng the most advantageous paths. [1026] A method and system for assigning demodulation elements to a set of available signals for both mobile stations and base stations Is disclosed In U.S. Pat No. 5,490.165 entitled "DEMODULATION ELEMEI^ ASSIGNMENT IN A SYSTEM CAPABLE OF RECEIVING MULTIPLE SIGNALS." issued Feb. 6,1996, and assigned to the Assignee of the present.
[1027] When multiple mobiles transmit simultaneously, the radio transmission frcHTi one mobile acts as interference to the other mobile's radio transmission, thereby limiting throughput achievable on the reverse link (also called the uplink). For efficient capacity utilization on the reverse link, centralized scheduling at the base station has been recommended in U.S. Pat, No. 5,914,950 entitled -METHOD AND APPARATUS FOR REVERSE LINK RATE SCHEDULING,"
issued June 22, 1999, and U.S. Pat. No. 5,923,650 entitled "METHOD AND APPARATUS FOR REVERSE LINK RATE SCHEDULINS,' issued July 13,1999, both of which are assigned to the Assignee of the present. [1028] In an exemplary embodiment, multi-level scheduling is performed. In an embodiment, multi-level scheduling comprises base station level scheduling, selector level scheduling, and/or netwoilc level scheduling. [1029] In an embodiment, a detailed design of a flexible scheduling algorithm Is based on fundamental theoretical principles that limit reverse-linit system capacity, while using existing networic parameters available or measured by a base station.
[1030] In an embodiment, base-station estimation of each mobile's capacity contribution is based on measured signal-to-noise ratio (Snr) or pilot energy over noise plus interference ratio {Ecp/(lo+No)), collectively called (Ecp/Nl), given the cun^nt rate of transmission. Measurement (rf pilot Ecp/Nl from alt fingers in multi-path scenario is disdosed In U.S. application no. 10/011,519 entitled "METHOD AND APPARATUS FOR DETERMINING REVERSE LINK LOAD LEVEL FOR REVERSE LINK DATA RATE SCHEDULING IN A CDMA COMMUNICATION SYSTEM," filed November 5, 2001, and assigned to the assignee of ttie present invention.
[1031] From the measurement of pilot Ecp/Nt at cunent rates on different channels, capacity contrtbution of a mobile is estimated at new rates on these channels.
t1032] In an embodiment, mcAtile tec^ests for rate a«ocatior\ are prioritized. A list of all mobiles that a scheduler is responsible for scfteduling is maintained depending on which level the scheduling is performed. In an embodiment, there Is one list for all the mobiles. Alternatively, there are two lists for all mobiles. If the scheduler is responsible for scheduling all the base stations a mobile has in its Active Set, then the mobile belongs to a Rrst List. A separate Second List may be m^ntalned for those mobiles that have a base station in the Active Set that the scheduler is not responsible for sdieduiing. Prioritization of mobile rate requests is based on various reported, measured or known parameters that
maximize system throughput, while aliowtng for moblie fairness as well as their importance status.
[1033] In an ©mlsodiment, Greedy Filling is used. In Greedy Riling, a highest priority mobile obtains the available sector capacity. A highest rate that can be allocated to the mobile is detennined as the highest rate that the mobrie can transmit at. In an mnbodiment, the highest rates are determined teased on measured SNR. In an embodiment, the highest rates are determined based on Ecp/Nt. in an embodiment, the highest rates are detennined based also on Uniting parameters. In an embodiment, the highest rate is detemiined by a mobile's buftar estimate. The choice ot a high rate decreases the transmission delays and decreases interference that the transmitting mobile obsen/es. Remaining sector capacity can be allocated to ttie next lower priority mobile. This methodology helps in maximizing the gains due to interference reduction while maximizing the capadty utilization.
[1034] By the choice of different prioritization functions, the Greedy Filling algorithm can be tuned to the conventional round-robin, proportionally fair or most imf^r scheduling based on a specified cost metric. Under tiie ciasa ot scheduling considered, the atrave method helps aid manmum edacity utilization. [1035] The mobile station initiates a call by transmitting a request message to the t>ase station. Once the mobile receives a channel assignment message from base station, it can use logical dedicated channel for further communicaticKi with the base-station. In a scheduled system, virfien the nx^ile station has data to trariantt, it can initiate the hlgh-sp^d data transmission on the reverse link by transmitting a request message on the reverse link.
[1036] Rate request and rate allocation stmcture curently specified in IS 2000 Release C Is considered. However, it would be apparent to those sl
Mobile station Procedures
[1037] In an embodiment, mobile stations (MS) at least support the simultaneous operation of ttie followir>g channels:
1. Reverse Fundamental Channel (R-FCH)
2. Reverse Supplemental Channel (R-SCH)
Reverse Fundamental Channel (R-FCH): When a voiceHanly MS has an active voice-call, it is carried on the R-FCH. For data-only MS, R-FCH carries signaling and data. Exemplary R-FCH channel frame size, coding, modulation and interieaving are specified in TIA/ElA-lS-2000.2, "Mobile Station-Base Station Compatibility Standanj for Dual-Mode Wideband Spread Spectaim Cellular System," June, 2002.
[1038] In an exemplary embodiment, R-FCH at a null rate is used for outer-loop power contToS (PC), when an MS is not transmitting voice, data or signaling on R-FCH. Null rate means a lowest rate. R-FCH at a lowest rate may be used to maintain outer-loop power control even when there is no transmission on R-SCH.
[1039] Reverse Supplemenlai Channel (R-SCH): The MS supports one R-SCH for packet data transmissions In acrordance with an embodiment. In an exemplary embodiment, the R-SCH uses rates specified by radio configuration (RC3) in TIA/EIA-IS-2000.2.
[1040] In an embodiment where only single data channel (R-SCH) is supported, the signaling and power control can be done on a control channel. Alternatively, signaling can be carried over R-SCH and outer-loop PC can be carried on R-SCH whenever it Is present.
[1041] In an embodiment, the following procedures are followed by mobile stations:
• Multiple Channel Adjustment Gain
• Discontinuous Transmission and Variable Supplemental Adjustment Gain
• Overhead transmission of R-CQICH and other control channels
• Closed-loop Power Control (PC) command
• Rate request using a Supplemental Channel Request Mini Message (SCRMM) on a 5-ma R-FCH or a Supplemental Channel Request Message (SCRM) on a 20-ms R-FCH
[10421 Multiple Channel Adjustment Gain: When the R-FCH and the R-SCH are simultaneously active, multiple channel gain table adjustment as specified In TlA/EIA-IS-2000.2 is perfomied to maintain con-ect transmission power of the R-FCH. The trafflc-to-pilot (T/P) ratios for all channel rate are also specified in the Nominal Atblbute Gain table in appendix A as Nomina) Attribute Gain values. Trattic-to^ilot ratio means the ratio of traffic channel power to pilot channel power.
[1043] DiscondnucHJS Transmission and Variable Supplemental Adjustment Gsun; The MS may be as^ned an R-SCH rate by a sctieduler during each scheduling period. When the MS is not assigned an R-SCH rate, it will not transmit anything on the R-SCH. If the MS is assigned to transmit on the R-SCH, but it does not have any data or sufficient power to transmit at the assigned rate, it disables transmission {DTX) on the R-SCH. If the system ^lows It, the MS may be ti^nsmitting on the R-SCH at a rate lower than the assigned one autonomously. In an embodiment, this variable-rate R-SCH operation is accompanied tiy tV» variable rale SCH gain acHustment as spetiatied in TIA/EIA-IS-2000.2. R-FCH T/P is adjusted assuming the received pilot SNR is high enough to support the assigned rate on R-SCH.
[1044] Ororhead transmission of R-CQICH and other control channels: A data-only MS transmits extra power on CQICH and/or other control channels at a CQlCH-to-pilot (or control-to-pilot) (C/P) ratio with multi-ctxannel gain adjustnrrent perfoitned to maintain correct transmission power of the R-CQIGH (or control channels). (C/P) value may be different for MS in soft-handott from those not in
soft handoff. (C/P) represent the ratio of total power used by the control channels
to the pilot power without multichannel gain adjustment.
[1045] Closed-loop Power Control (PC) command: In an embodiment, an MS
receives one PC command per power control group (PCG) at a rate of 800Hz
from all base stetions (BSs) (n the MS's Active Set. A PCG is a 1.25 ms tnteival
on the Reverse Trafto Channel and the Reverse Pilot Channel. Pilot power is
updated by +-1 dB based on an "Or-of-Downs" rule, after combining of the PC
commands from co-located BSs (sectors in a given cell).
[1046] Rate request Is dwie vrfth one of two methods. In a first method, rate
request is perfomned using a Supplemental Channel Request Mini Message
(SCRMM) on a 5-ms R-FCH as specified in TlA/BA-IS-2000.5.
£1047] Supplemental Channel Request Mini Message (SCRMM) on a 5-ms R-
FCH: In an embodiment, each SCRMM transmission is 24 bits (or 48 bits with the
physica! layer frame overhead in each 5-ms FCH frame at 9.6 kbps).
[1048} The MS sends the SCRMM in any periodic interval of 5 ms. If a 5-ms
SCRMM needs to be transmitted, the MS intenupts Its transmission of tire current
20-ms R-FCH frame, and instead sends a 5-ms frame on the R-FCH. After the 5-
ms frame is sent, any remaining time in the 20-ms period on the R-FCH is not
transmitted. "TTie discontinued transmission of the 20-ms i^FCH is re-est^lished
at the start of next 20-ms frame.
[1049] In a second method, rate request is perfomned using a Supplemental
Channel Request Message (SCRM) on a 20-ms R-FCH.
[1050] Depending on different embodiments, different information can be sent
on a request message. In IS2000, SupptementcU Channel Request Mini Message
(SCRMM) or a Supplemental Channel Request Message (SCRM) Is sent on the
reverse-linK tor rate request.
[1051] In an embodiment, the following infonnation shall be reported by the
MS to the BS on each SCRM/SCRMM transmission:
• Maximum Requested Rate
• Queue Information
[1052] Maximum Requested Rate: It can be the maximum data rate an MS is capable of transmitting at the cun"ent cheinnei conditions leaving headroom for fast channel variations. An MS may detemiine Its maximum rate using the following equation:
after power constraints on the MS side are applied in case of power outage, ^^NormAvPiTxiPCG,) ,.3 ^ normalized average transmit pilot power. An MS may be more conservative or aggressive In its choice of headroom and determination of maximum requested rate depending on what is pennitted fay ttie
BS.
[A(^3] In an emiaodiment, the MS receives grant information by on© ot the two
following methods:
[1054] Method a: Enhanced supplemental channel assignment mini message
(ESCAMM) from BS on 5-ms fonward dedicated control channel (F-DCCH) with
rate assignment for specified scheduling duration.
[1055] Method b: Enhanced supplemental channel assignnriwit message
(ESCAM) from BS on forward physical data channel (F-PDCH) with rate
assignn^nt for specified scheduling duration.
[1056] The assignment delays depend on the bactthaul and transmission
delays and are different depending on which method is used for rate grant.
During the scheduled duration, the following procedures are perfonned:
• In an embodiment virtiere R-FCH is used to transmit autonomous data and for outer-loop FK;, the MS transmfts data at an autonomous rate of 9600 bps if it lias some data in its buffer. Otlienwise, ttie MS sends a null R-FCH frame at a rate of 1500 bps.
• 7^0 MS transmits at the assigned R-SCH rate in a given 20-ms period if the MS has more data than can be carried on the R-FCH and if the MS has decided that it would have sufficient power to transmit at the assigned rate (keeping headroom for channel variations). Otherwise, there is no transmission on the R-SCH during the frame or the MS transmits at a lower rate which satisfies the power constraint. The MS decides that it has sufficient power to transmit on the R-SCH at the assigned rate R in a given 20-ms period Encode_Delay before the beginning of that 20-ms period if the followtng equation is satisfied:
Pref{R)*NomAvPiTic{PCG,) l+fX'P),+({TIF), +(C/P))( ^^^^'M
' L " I P«fW )} HeadroomJTx
Where Pref(R) is the "Pilot Reference Level" value specified in the Attribute Gain Table In T1WE)A-1S-2000.2, ^ormMPiTx^PCC;) ^^ ^^ norniafeed average transmit pilot power, (T/P)R is ttie traffic to pilot ratio that corresponds to rate R and for ail trfiannei rates is specified in the Nominal Attribute Gain table in appendix A as Nominal Attribute Gain values, (T/P)RreH is the traffic to pilot ratio on FCH, (C/P) is ii^ ratio of total power used by the control channels to the pilot power without multichannel gain adjustment, Tx(max) is the maximum MS transmit power, and Headroom_Tx is the headroom the MS keeps to allow for channel variation.
[1057] The DTX determination is done once every frame, Encode_Deiay PCGs before the R-SCH transmission, (f the MS disables transnilssion on the R-SCH, it transmits at the following powen
T>cPwr(PCG,) = PiTxI'wr{PCGi) l + (iT/P)„^+(C/P)) -^rfflffislj
V rrej{K) y_
[1058] An MS encodes the transmission frame Encode_Delay before the actual transmission.
Base Station Procedures
[1059] In an embodiment, the 68 performs the following essential functions:
• Decoding of R-FCH/R-SCH
• Power control
Decoding of R-FCH/R-SCH
[1060] When there are multiple traffic channels transmitted by the MS simultaneously, each of the traffic channels is decoded after correlating with the con-esponding Walsh sequence. Power-cOTitrol
[1061] Power control in a CDMA system is essential to maintain the desired quality of service (QoS). In lS-2000, the RL pilot channel (R-PICH) of each MS is closed-loop power controlled to a desired threshold. At the BS, this threshold, called iinwer contrel set point, is compared against the received Ecp/Nt to ^nerate power control command (closed-toop PC), where Ecp is the pilot channd energy per chip. To achieve the desired QoS on ttie traffic channel, the threshold at the BS Is changed with erasures on the traffic channel, and has to be adjusted when the data rate changes.
[1062] Set point corrections occur due to:
• Outer-loop power coitrol
• Rate Transitions
[1063] Outer-loop power control: If the R-FCH is present, the power control set point is conrected based on erasures of the R-FCH. If R-FCH is not present, the outer-loop PC is conected based on erasures of some control channel or R-SCH when ttie MS is transmitting data.
[1064] Rate Transitions: Different data rates on the R-SCH require different optimal set point of the reverse pilot channel. When data rate changes on the R-
SCH, the BS changes the MS's received Ecp/Nt by the Pilot Reference Levels (Pref(R)) difference between the current and the next R-SCH data rate. In an embodiment, the Pilot Reference Level for a given data rate R, Pref(R), Is spedfied in the Nominal Attribute Gain Table in C.S0002-C. Since the closed-loop power control brings the received pilot Ecp/Nt to the set point, the BS adjusts the outer loop set point according to the next assigned R-SCH data rate:
A = PrefiRnew) - Fref{Rold)
[1065] Set point adjustnwnt te done '^' PCGs in advance of the new R-SCH data rate H Rrm> > Row- Otherwise, this adjustment occurs at the R-SGH frame boundary. TTie pilot power thus ramps up or down to the correct level approximately in 1 dB step sizes of the closed loop as shown in tigure 2. [1066] Figure 2 shows set point adjustment due to rate transttions on R-SCH in accordance with an embodiment. The vertical axis of figure 2 shows a setpoint of a base station controHer (BSC) 202, a base transceiver subsystem (BTS) receiver pilot power 204, and the mobile station rate 206. The 1^8 rate is initially at Ro 208. When the R-SCH data rate increases, i.e., R1>R0 210, then the setpoint Is adjusted according to Prei(Ri)-Pref{l=lo) 212. When the R-SCH data rate decreases, i.e., R2P«KRi)216.
Scheduler Procedures
[1067] A scheduler may be collocated with the BSC, or BTS or at some element in the netw(xk layer. A Sclieduler may be niuWIevei with each part responsible for scheduling those IWSs that share the lower layer resources. For example, the MS not in soft-handoff (SHO) may be scheduled by BTS while the MS in SHO may be scheduled by part of the scheduler collocated with BSC. The reverse-Iinl
[10&8] In an embodiment, the following assumptions are used for ttie scheduler and \reuious parameters associated with sctieduHng in accordance with an embodimwit:
1. Centralized Scheduling: The scheduler is co-located with the BSC, and is responsible for simultEuieous scheduling of MSs across multiple ceils.
2. Synchronous Scheduling; All R-SCH data rate transmissions are time aligned. Ail data rate ^signments are for the duration of one scheduling period, which is time aligned for all the MSs in the system. The scheduling duration period is denoted SCH_PRD.
3. Vt^ce and Autonomous R-SCH transmissions: Before allocattng capacity to transmissions on R-SCH through rate assignments, the scheduler looks at the per^dlng rate requests from the MSs and discounts for voice ar>d autonwnmjs transmissions in a given cell.
4. Rate Request Delay: The uplink request delay associated wi^ rate rec^esting via SCRf^SCRMM Is denoted as D„RL(request). It is the delay from the time the request is sent to when it is available to the scheduler. D_RL(rBquest) includes delay segments lor over-ths-air transmission of the request, decode time of the request at the cells, and b^khaul delay from the cells to the BSC, and is modeled as a unifomily distributed random variable.
5. Rate Assignment Delay: The downlink assignment delay associated with rate assignment via ESCAM/ESCAMM is denoted as D_FL(assign). It is the time between the moment the rate decision is made and the time the MS receiving the resultant assignment. D_R.(assign) includes backhaul delay from the scheduler to the cells, over-ths-alT transmission time of the assignn^t (based on method chosen), and its decode time at ^e MS.
6. Available Ecp^t Measurement: The Ecp/Nt measurement used ui the scheduler shall be the latest available to it at ttie last frame boundary. The me^ured Ecp/Nt is reported to the scheduler by the BTS receiver periodically and so it Is delayed for a BSC receiver.
[1069] FIG. 3 shows scheduling delay timing in accordance with an embodiir^nt. The numbere shown are an example of typical nurrtaers thai may
be used by a BSC located scheduler though the actual numbers are dependent on backhaul delays and loading scenario of the deployed system. [1070] The horizontal axis shows an SCH frame boundary 250, a last SCH frame boundary before a point A 252, a point A 254, a scheduling time 256, and an action time 258. An Ec/Nt measurement window 260 is shown starting at the SCH frame boundary 2S0 and ending at the last SCH frame boundary before point A 252. A time to last frame boundary 262 is shown from the last SCH frame boundary before point A 252 to prant A 254. A time to get Infomiation from the BTS to the BSC (6 PCGs) 264 Is shown starting at point A 254 and ending at ttie scheduling time 256. ActlonTlmelDelay (25 PCGs for Method a, 62 PCGs for Metiiod b) 266 is shown to start at the scheduling time 256 and ending at the action time 258.
Scheduling, Rate Assignment and Transmission Timeline
[1071] Given the assumed synchronous scheduling, most events related to request, grant and transmission are periodic with period SCH^PRD. 11072] Figure 4 illustrates the timing diagram of a rate request, scheduling and rate allocation in accordance with an embodiment. The vertical axes show the time lines for the BSC (scheduler) 402 and the mobile 404. The MS creates an SCRMM 406 and sends a rate request to the BSC (scheduler) 408. The rate request is included in the SCRMM, which is sent on R-FCH. The uplink request delay associated with rate requesting via SCRM/SCRMM is denoted as D_RHrequest) 410. A scheduling decision 412 is made once every scheduUng period 414. After ttie scheduling decision 412, an ESCAM/ESCAMM 416 is sent on a forward channel from the BSC to the MS indfcating a rate assignment 418. D_FL 420 is the downlink assignment delay associated with rate assignment via ESCAM/ESCAMM. Turnaround time 422 Is the time it takes to turnaround a rate request. It is the time from the rate request to rate assignment.
[1073] The following characterizes ttie timeline:
• Scheduling Timing
• Scheduled Rate Transmissions
• MS R-SCH Rate Requests
[1074] Scheduling Timing: The scheduler operates once every scheduling period. If the first scheduling decision is performed at ', then the scheduter operates at'" ' ^SCH^PRD, t, +2SCli^Pm..
[1075] Scheduled Rate Transmissions: Given that the MSs have to be notified
of the scheduling decisions with sufficient lead-time, a scheduling decision has to
be reached at Action Time of ttie ESCAM/ESCAMM message minus a fixed
delay, ActionTimeD^ay. Typical values of ActionTimeDelay for Methods a and b
are given in Table 1.
[1076] MS R-SCH Rate Requests: R-SCH rate requests are triggered as
described below:
[1077] Before the beginning of each SCRM/SCRMM frame encode boundary,
the MS checks if either of the following three condftions are satisfied:
1. New data arrives and data in the MS's buffer exceeds a certain buffer deptti (BUF„DEPTH), and the MS has sufficient power to transmit at a non¬zero rate; OR
2. If the last SCRM/SCRMM was sent at time ^', and the cun^nt time
is greater than or equal to ^' "*" ^^^ -^^, and if the MS has data in Its buffer that exceeds the BUF_DEPTH, arid the MS has sufficient power to transmit at a non¬zero rate; OR
3. If the last SCRM/SCRMM was sent at time ^', and the current time
is greater than or equal to ^' '^ ^^^ - ^^, and if the current assigned rate at the MS side based on received E5CAMM/ESCAM is non-zero (irrespecHve of the facS that the MS may not have data or power to request a nwi-zero rate). "Current assigned rate" Is the assigned rate applic^le for the current rate transmission. If no ESCAM is received for the cun^nt scheduled duration, then the assigned rate Is corraidered 0. The rate assigned in the ESCAM/ESCAMM message with Action Time at some later time takes effect after the Action Time.
11078] If Brther of the above three conditions are satisfied, the MS sends a SCRMM/SCRM rate request.
|;1079J In an embodimenf, an SCRM/SCRMM request made at ^' is made available to the scheduler after a random delay at ^i+^^-^Li^equest) ^^ another embodiment, different combinations of change in MS data buffer, change in MS ma)dmum supportable rate and MS last request time out may be used to detem^ine the time when a rate request is sent.
Scheduler Description and Procedures
[1080} In an embodiment, there is one centralized scheduler element for a large number of cells. The scfieduler maintains a list of all MSs in the system and BSs in each MS's Active 8et. Associated with each MS, the scheduler stores an
estimate of an MS's queue size (^) and niaximum scheduled rate (Rmax(s)).
11081] The queue size estimate ^ is updated after any o1 the fc^lowing events happen:
1. An SCRMI\fl/SCRM is receh/ed: SCRMM/SCRM is received after a
delay of D_RL(request). ^ is updated to:
Q = Queue Size reported in SCRMM
If ttie SCRMM/SCRM is lost, the scheduler uses the previous (and the latest) information it has.
2. After each R-FCH and R-SCH frame decoding:
Q = Q-DataJFCH) + DalaJSCli)
where ^^^'^^^CH) g^d Dm^(SCH) ^^ J,^Q ^^^^ transmitted in the last R-FCH and R-SCH frame, respectively (If flie frame is decoded correcHy) after discounting the physical layer overhead and RLP layer overhead.
3. At the scheduling instant ', scheduler estimates the maximum
scheduled rate for the MS in accordance with an embodiment. The buffer size
estimation is done as:
[1085] ■"'s™^ is the rate assigned during current scheduling period and R^ is the rate transmitted on R-SCH during current scheduling period. R„^^ +1 is rate one higher than what is currently assigned to the MS and R^^ -1 is a rate one lower than what is currently assigned to the MS, Rijeported) is the maximum rate repwted by the MS in rate request message tike SCRM/SCRMM. The above method may be used when Rireported) by tlie MS is not related to the maximum rate that MS is capable of transmitting at its current power constraints. [1086] Arg max provides the maximum supportable rate by the scheduler.
Capacity Computation
(1087] Tfw sector capacity at the itt\ sector Is estimated from the measuved MSs' Sinrs. The Sinr is the average pilot-weighted combined Sinr per antenna. In an embodiment, the combining per power-control group (PCG) is pilot-weighted combining over multlpia fingers and different antennas of the sector of interest. In an embodiment, the combining per power-control group (PCG) is maximal ratio comWning over multiple fingers and different antennas. The combining is not over different sectors in the case of a softer-handoff MS. The averaging can be over the duration of a frame or it can be a filtered average over a couple of PCGs. [1088] The following formula (s used for estimating Load contnTaution to a sector antenna:
where ^'"'J^^'^^'^^^is the estimated Sinr if the MS is assignedarate ^' on R-
SCH and ^^'™ ^ is the expected rate of transmission on the R-FCH.
[1089] Let the measured pilot Sinr (frame average or filtered average pilot Sinr
averaged over two antennas) be ^ f'"ih^ while it is assigned a rate of BMSign(SCH) on the R-SCH. Then,
scheduler has two scheduling elements, one at a BTS and the other at a BSC, let the estimated ^signed Load at BSC be LoadjiBSC) and the estimated assigned
load at BTS be LoadjiBTS). Then,
Loadj{BSC)-i-LoadjiBTS)
I
[1094] Since the timing delay in scheduling at BSC is greater than BTS, estimated assigned load at BSC Loadj(BSC) can be known at BTS prior to
scheduling at BTS. BTS scheduler prior to scheduling then has following constraint on the assigned ioad:
Load J iBTS)
Scheduling Algorithm
[1095] The scheduling algorithm has the following crfiaracteristics:
a) scheduling least number of MS for increasing TDM geJns,
b) CDM few users for maximum capacity utilization, and
c) prioritization of MS rate requests.
[1096] Prioritization of mobWes can be based on one or more of tha varied
reported or measured quantities. A priority function that increases system
throughput can have one or many of the following diaracteristics:
[1097] The higher the measured pilot Ecp/Nt (normalized), the lower Is the
mt^ile's priority. Instead of using a measured Ecp/Nt, a pilot Eqj/Nt set-point that
the base-station maintains for power control outer-loop could be used. A lower
Ecp/Nt (measured or set-point) implies a better instantaneous channel and hence
increased throughput If channel variations are small.
[1098] For a mobile in SHO, pilot Ecp/Nt (nieasured or Set-point) can be
weighted by an SHO factor to reduce the other-cell interference. For example, if
average received pilot powers at all SHO legs is available, 2!ii','(*)/Pf'(/)can senre as an SHO factor, where f;"(*)i3 frie average recerved pilot power of the ^
mobile by the A"' base station in its Active Set, P," (;') is the average received piiot
power of the f^ mobile by the strongest, ^ base station in its Active Set, and M is
the number of base stations In the m(*ile's AcWve Set (set of base stations in soft
handoff wtth the nrolwle)
[1099] Higher the measured or estimated propagation loss, lesser is the
priority. Propagation Loss can be calculated from the measured received pilot
power if the mobile periodice^ly reports ^suismitted pilot power in the request
message like SCRM. Or othenvise, it can estimate which mobile sees better
propagation loss based on ftie reported strength of the FL Ecp/Ni
[11001 Velocity based priority function; If the base-station estimated velocity of
a moving mobile using some velocity estimation algorithm, then stationary
mobiles are given ttie highest priority, and middle velocity mobiles are glv«i the
least priority.
[1101] Priority function based on above measured or reported parameter is
an unfair priority function aimed at increasing the reverse-link system throughput.
In addtion, priority can be irwreased or decreased by a cost metric that is decided
by what grade of eetvk^ a user is registered for. In addition to the above, a
certain degree of fairness could be provided by a Fairness factor. Two different
kinds of Fairness are described tietow:
[1102] Proportional Fairness (PF): PF Is the ratio of maximum requested rate
to average achieved transmission rate. Thus,PF = j?,™'//e,'*", where Rl^ is the
requested rate and Rf^ Is the average rate allocated by \he scheduler.
[1103] Round Robin Fairness (RRF): Round robin scheduling tries to provide equal transmission (^portunlties to all the users. When a mobile enters the system, RRF is initialized to some value, say 0. Each scheduling period ttie rate Is not allocated to the mobile, RRF is incremented by one. Every time some rate (or the requested rate) is allocated to the mobile, RRF is reset to the Initial value 0. This emulates the process v^iere mobiles scheduled in the last scheduling period are last In the queue.
[1104] Fairness can be used together with Priority function to detemnine the priorily of the mobile in the Prioritization list. When Faimess is used alone to prioritize mobiles, it provides proportional fair or round-robin scheduling that is
throughput optimal for reverse-link as well as allowing multiple transmissions for full capacity utilization.
[1105] An embodimen! which uses different aspects of previously defined priority functions and proportional fairness may have a priority of the i'*' user determined as:
where the parametero called Fairness factor can be used to Irade-off fairness for system throughput. As a increases, fairness gets worse. Schedulers witii higher a yield higher throughput.
[1106] Next we consider a parQcular embodiment where the scheduler wakes up every scheduling period and makes rale allocation decisions based on pending rate requests. The scheduling algorithm looks like the one described betow.
[1107] Initialization: lYi& MS rate requests are prtorltized. Associatsd vMn each
MS is a priority count PRIORITY. PRIORITY of an IVlS is initialized to 0 in the
beglnrtng. When a new MS enters the system with sector j as the primary
sector, Its PRIORtTV (s set equal to the
mintPRIORlTY,. Vi soch that MSi has sector j as the primary sector}
1. Let the Load constraint be i^'i/^i«axl^>ad^ ^^^^ U^^^ ^ ^^^ over-thermal overshoot above a certain threshold is limited. For the calibration purposes, max Load value of 0-45 will be used by the scheduler. The capacity consumed due to pilot transmissions and transmissions on fundamental channets (due to voice or data) Is confuted and the available capacity is computed as
Cav(j) = max Load ~ > —
where max Load Is the maximum Load for which rise-over-themnal outage criteria specified is satisfied.
MS rate requests are prioritized in decreasing onjer of their PRIORITY. So MSs with highest PRIORITY are at the top of the queue. When multiple MSs
with iderrtical PRIORITY values are at Ihe top of the queue, the scheduler makes a equally-likely random choice among these MSs.
2. Setk=1,
3. The data-only MS at tiie kth position in the queue is assigned the
[1108] It would be apparent to those skilled in the art that other values can be used for the parameters in table 1. It would also be apparent to those skilled in the art that more or less parametere may be used for a particular Implementation. [1109] Figure 5 is a flowchart of a scheduling process in an embodiment, in an embodiment, a mobile i and a mobile j send a request rate to a scheduler in step 300. Alternatively, a mobile i and a mobile j send a request rate to a scheduler in step 310.
[11103 In step 300, the scheduler creates a list of mobiles (Mi) thai it will schedule. Then, the scheduler creates a list of base stations (BTSs) the scheduler is responsible for scheduling. Also, the scheduler creates a list of mot»les that are not in the list of base stations the scheduler is responsible for scheduling and that are in soft handoff (SHO) with base stations the scheduler Is responsible for scheduling (Ui). The flow of control goes to step 302.
11111] The BTS supplies the scheduler with a reported DTX by a mobile. In step 302, a check Is made to determine whether a mobile, which is scheduled, reported a DTX, in which case resources can be reallocated from the scheduled m
[1112] In step 308, the scheduler is supplied by the BTSs witti an estimate of loc and piolot Ec/Nt of {MOunlon{Ui}. The capadty of each Bi is initialized given the loc estimates. For each Bi, subtracting from ttie available capacity, the voice users contribution to capacity given voice activity and autonomous transmission on R-FCH/R-DCCH. The measurement used for the amount subtracted is the pilot Ecp/Nt Also for each Bi, subtracted from the available capacity is the expected contribution by {Ui}. Then, the flow of control goes to step 310. [1113] In step 310, pilot Ec^t of (Mj) and set-point and Rx pilot power are provided to the scheduler and are used by a prioritization function. The mc^ile rate requests are prioritized in a prioritization queue, in an embodiment, a prioritization function is used in which measured and reported information is used. In an embodiment, a prioritization function provides for fairness. The flow of centred goes to step 312.
[1114] In step 312, a maximum rate is assigned to a highest priority mobile such that a capacity constraint of all BSs in soft handoff is not violated. TTie maximum rate is the maximum rate supported by the highest priority mobile. The highest priority mobile Is placed last in the prioritization queue. The available capacity is updated by subtracting the mobile contribution to capacity at an assigned maximum rate. The flow of control goes to step 314. [1115] In step 314, a checit is made to detemiine whether all the mobiles in tiie {Mi} list have been scanned. If all the mobiles in the {Mi} list have not been
scanned, then the flow of control goes to step 312. If all the mobiles in the {M\} list have been scanned, then the ftow of control goes to step 302. [1116] Those of skill in the art would understand that method steps could be interchanged without departing from the scope of the invention. Those of skill in the art would also understand that infonmation and signals might be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, Infomiation, signals, bits, symbols, and chips tiiat may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
11117] Those of skill in the art would understand that Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instnjcttons, commands, infonnafcn, signals, bits, symbols, and chips that may be referenced throughout the above descripti(»i may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. [1118] Figure 6 is a blocl
[1119] Figure 7 is a block diagram of an MS 106 in accordance with an embodiment. The downlink signal Is received by an antenna 712, routed through a duplexer 714, and provided to a receiver (RCVR) unit 722, Receiver unit 722 condlttons (e.g., filters, amplifies, and frequency downconverts) the received
signal and further digitizes tiie conditioned signal to provide samples. A demodulator 724 then receives and processes (e.g., descrambles, channelizes, and data demodulates) ftie samples to provide symbols. Demodulator 724 may implement a rake receiver that can process multiple instances (or multipath components) of the received si^al and provide combined symbols. A receive (RX) data processor 726 then decodes the symbols, checics the received pacl
[1120] On the uplink, data for the uplink, pilot data, and feedback information are processed (e.g., formatted, encoded, and so on) by a transmit (TX) data procMsor 742, further processed (e.g., channelized, scrambled, and so on) by a modulator (MOD) 744, and conditioned (e.g., converted to analog signals, amplified, filtered, and frequency upconverted) by a transmitter unit 746 to provide an uplink signal. The data processing for the uplink is described by standard documents. The uplink signal is routed through duplexer 714 and transmitted via antenna 712 to one or more BSs 12.
[1121] Refening back to FIG. 6, at BS 12. the uplink signal is received by antenna 624, routed through duplexer 622, and provided to a receiver unit 628. Receiver unit 628 conditions (e.g., frequency downconverts, filters, and amplifies) the received signal and further digitizes the conditioned signal to provkle a stream of samples.
[1122] In the embodiment shown in FIG. 6, BS 12 irwiudes a number of channel proc^sors 630a through 630n. Each channel processor 630 may be assigned to process the sanple steam for one MS to recover the data and feedback infonnation transmitted on the uplink by the assigned MS. Each channel processor 630 includes a (1) demodulator 632 that processes (e.g., descrambles, channelizes, and so on) the samples to provkle symbols, and (2) a RX data processor 634 ttiat ftjrther processes the symbols to pnavide the decoded data fw the assigned MS.
[1123] Controllers 640 and 730 control the processing at the BS and the MS, respectively. Each controller may also be designed to implement all or a portion
of the scheduling process. Program codes and data required by controllers 640 mti 730 may be stored In memory units 642 and 732, respectively. 11124] Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the en^)odiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly Illustrate this intercrfiangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally In terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints Imposed on the overall system. Skilled artisans may implement the described functfonality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
[1125] The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, disoete hardware components, or any combination thereof designed to perform the funcUons described herein. A gerwral purpose processor may be a microprowssor, but in the alternative, the processor may be any conventional processor, controlier, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction w^th a DSP core, or any other such configuration. [1126] Tiw steps of a method or algorithm described in connection with the embodiments disclosed herein may be enrtrodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An ex^nplary
storage medium is coupled to the processor such the processor can read infomiatfon from, and write infomiation to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the dtemative, the processor and the storage medium may reside as discrete components in a user temiinal.
[1127] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the wkiest scope consistent vrith the principles and novel features disclosed herein.
WE CLAIM :
I A method for estimating capacity used on a reverse link, comprising the steps of:
measuring a plurality of signal-to-noise ratios at a station for a pluralit)' of rates; determining sector load based on the measured piurality of signal-to-tioise ratios, an assigned transmission rate, and an expected transmission rate; and estimating capacilj' on the reverse link based on the sector load.
2. The method as claimed in claim i, wherein the measured plurality of signal-to-
noise ratios is averaged.
3. The method as claimed in claim 2, wherein the measured plurality of signaUto-noise ratios is averaged over a duration of a frame.
4. The method as claimed ia claim 2, wherein the measured plurality of signal-to-noise ratios
is averaged over a plurality of pilot controi groups.
5. The method as claimed in claim 2, wherein the station is a base station.
6. A method of estimating load contribution to a sector antenna, comprising the steps of:
assigning a transmission rate R1 on a first communication channel;
determining an expected rate of transmission E[R] on a second communication
charmei;
estimating a signal-to-noise ratio of a station for the assigned transmission rate R, on the first communication channel and the expected rate of transmission E[R] on a second communication channel; and
estimating the load contribution based on the estimated signal-to-noise ratio. 7 The method as claimed in claim 6, wherein the first communication channel is a .verse
supplemental channel and the second communication channel is a reverse link fundamental channel.
8. A method for estimating capacity available to schedule, comprising the steps of:
measuring other-cell interference during a previous transmission (loc); determining thermal noise (No); determining sector load (Loadj); and
determining rise-over-thermal (ROTj) based on the ratio of the measured other-ceil interference over thermal noise, and based on the sector load.
9. A method of distributing sector capacity across a base station (BS) and a base station
controller (BSC), comprising the steps of:
measuring other-cell interference during a previous transmission (loc-);
determining thermal noise (No);
determining a maximum rise-over-thermal (ROT(max));
determining an estimated assigned load at the BSC (Loadj(BSC)); and
determining a sector capacity distributed to the base station based on the ratio of the measured other-cell interference over thermal noise, the maximum rise-over-thermal, and the estimated assigned load at the BSC.
10. A method of determining priority of a station, comprising:
determining pilot energy over noise plus interference ratio (Ecp/Ni);
determining a soft handoff factor (SHOfactor);
determining a fairness value (F); determining a proportional fairness value (PF); determining a fairness factor a; and
determining priority of a station based on the pilot energy over noise plus interference ratio, the soft handotT factor, the fairness value, and the fairness factor a.
11. The method as claimed in claim 10, wherein determining the soft handoff factor is based
on average received pilot powers.
12. The method as claimed in claim 10, wherein the fairness value is a proportional fairness value.
13. The method as claimed in claim 10, wherein the fairness value is a round robin fairness value.
14. The method as claimed in claim 12, wherein determining the proportional fairness value is based on a ratio of a maximum requested rate to an average transmission rate.
15. A station, comprising :
an antenna for receiving and transmitting a plurality of signals;
a receiver coupled to the antenna, the receiver receives the plurality of receive signals;
a controller (640) coupled to the receiver, the controller
measiu-es a plurality of signal-to-noise ratios for a plurality of rates;
determines sector load based on the measured plurality of signal-to-noise ratios, an assigned transmission rate, and an expected transmission rate; and
estimates capacity on the reverse link based on the sector load; and a transmitter coupled to tile controller, the transmitter conditions the capacity estimation for transmission.
16.The station of claim 15, wherein the station is a base station.
17. A station comprising :
an antenna for receiving and transmitting a plurality of signals;
a receiver coupled to the antenna, the receiver receives the plurality of receive signals;
a controller (640) coupled to the receiver, the controller
assigns a transmission rate Rj on a first communication channel;
determines an expected rate of transmission E[R] on a second communication channel;
estimates a signal-to-noise ratio of a station for the assigned transmission rate Ri on the first commimication channel and the expected rate of transmission E[R] on a second communication channel; and
estimates the load contribution based on the estimated signal-to-noise ratio; and
a transmitter coupled to the controller, the transmitter conditions the load contribution estimation for transmission.
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