(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization ;
`International Bureau
`
`(43) International Publication Date
`23 February 2006 (23.02.2006)
`
`
`
`NUMAA
`
`(10) International Publication Number
`WO 2006/019710 Al
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`(51)
`(21)
`
`(22)
`(25)
`(26)
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`(30)
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`(71)
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`(72)
`(75)
`
`International Patent Classification’:
`
`H04Q 7/38
`
`International Application Number:
`PCT/US2005/0246 14
`
`International Filing Date:
`Filing Language:
`
`11 July 2005 (11.07.2005)
`English
`
`English
`
`Publication Language:
`Priority Data:
`60/590,113
`11/020,457
`
`21 July 2004 (21.07.2004)
`22 December 2004 (22.12.2004)
`
`US
`US
`
`Applicant (for all designated States except US): QUAL-
`COMMINCORPORATED [US/US]; 5775 Morehouse
`Drive, San Diego, California 92121 (US).
`Inventors; and
`Inventors/Applicants (for US only): SUTIVONG, Arak
`[TH/US]; 8840 Costa Verde Boulevard, #3439, San Diego,
`California 92122 (US). TEAGUE, Edward Harrison
`[US/US]; 4614 Bryson Terrace, San Diego, California
`92130 (US). GOROKHOYV, Alexei [FR/US]; 12543 El
`Camino Real, San Diego, California 92130 (US).
`
`(74) Agents: WADSWORTH, Philip R. et al.; 5775 More-
`house Drive, San Diego, Califonia 92121 (US).
`
`(81)
`
`(84)
`
`Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ, CA, CH, CN,
`Co, CR, CU, CZ, DE, DK, DM, DZ, EC, EE, EG, ES, FI,
`GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE,
`KG, KM, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA,
`MD, MG, MK, MN, MW, MX, MZ, NA, NG, NI, NO, NZ,
`OM, PG, PH, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL,
`SM, SY, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC,
`VN, YU, ZA, 27M, ZW.
`
`Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI,
`FR, GB, GR, HU, TE, IS, IT, LT, LU, LV, MC, NL, PL, PT,
`RO, SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA,
`GN, GQ, GW, ML, MR, NE, SN, TD, TG).
`
`[Continued on next page]
`
`(54) Title: EFFICIENT SIGNALING OVER ACCESS CHANNEL
`
`400
`
`404
`
`408
`
`INFO OBSERVED
`
`410
`
`
`
`
`
`
`SEND PREAMBLE
`
`Ww/cal
`7416
`
`
`
`SEND ACK AT
`APPROPRIATE
`
`
`
`POWER LEVEL
`
`
`
`420
`SEND PAYLOAD
`
`
`
`
`An apparatus and
`(57) Abstract:
`method for transmitting an indicator
`of channel quality while minimizing
`the use of a broadcast channel
`is
`described. A metric of forward link
`geometry of observed transmission
`signals is determined. An indicator
`of channel quality value is determined
`as
`a
`function
`of
`the
`observed
`
`An access
`transmission signals.
`sequence is selected, randomly, from
`one group of a plurality of groups
`of access sequences, wherein each
`of the plurality of groups of access
`sequences
`correspond
`to different
`ranges of channel quality values.
`
`412
`
`APPLE 1003
`APPLE1003
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`WO2006/019710A.IMIINIIIUINNARIATINTIONMINCACA
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`

`

`WO 2006/019710 Al
`
`UUA
`
`Declarations under Rule 4.17:
`as to applicant's entitlement to apply for and be granted
`a patent (Rule 4.17(ii)) for the following designations AE,
`AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ,
`CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE,
`EG, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN,
`IS, JP, KE, KG, KM, KP, KR, KZ, LC, LK, LR, LS, LT, LU,
`LY MA, MD, MG, MK, MN, MW, MX, MZ, NA, NG, NI,
`NO, NZ, OM, PG, PH, PL, PT, RO, RU, SC, SD, SE, SG,
`SK, SL, SM, SY, TJ, TM, TN, TR, TT, TZ, UA, UG, UZ, VC,
`VN, YU, ZA, ZM, ZW, ARIPO patent (BW, GH, GM, KE,
`LS, MW. MZ, NA, SD, SL, 8Z, TZ, UG, 7M, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`patent (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl, FR,
`
`GB, GR, HU, LE, IS, IT, LT, LU, LV, MC, NL, PL, PT, RO,
`SE, SI, SK, TR), OAPI patent (BF, BJ, CF, CG, Cl, CM, GA,
`GN, GQ, GW, ML, MR, NE, SN, TD, TG)
`— as to the applicant’s entitlement to claim the priority of the
`earlier application (Rule 4.17(iii)) for all designations
`— as tothe applicant’s entitlement to claim the priority of the
`earlier application (Rule 4.17(iii)) for all designations
`
`Published:
`
`— with international search report
`
`For two-letter codes and other abbreviations, refer to the “Guid-
`ance Notes on Codes and Abbreviations" appearing at the begin-
`ning of each regular issue of the PCT Gazette.
`
`

`

`WO 2006/019710
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`PCT/US2005/024614
`
`EFFICIENT SIGNALING OVER ACCESS CHANNEL
`
`CROSS-REFERENCE TO RELATED APPLICATION
`
`[0001]
`
`This application claimspriority to U.S. Provisional Patent Application Serial
`
`No. 60/590,113, filed July 21, 2004, which is incorporated herein by referencein its
`
`entirety.
`
`Field
`
`BACKGROUND
`
`[0002]
`
`The invention relates generally to wireless communications, and more
`
`specifically to data transmission in a multiple access wireless communication system.
`
`Background
`
`[0003]
`
`An access channelis used on the reverse link by an access terminal for initial
`
`contact with an access point. The access terminal mayinitiate an access attempt in order
`
`to request dedicated channels,to register, or to perform a handoff, etc. Before initiating
`
`an access attempt, the access terminal receives information from the downlink channel
`
`in order to determinethe strongest signal strength from nearby access points and acquire
`
`downlink timing. The access terminalis then able to decode the information transmitted
`by the given access point on a broadcast channel regarding choice of parameters
`
`governing the access terminal’s access attempt.
`
`[0004]
`
`In some wireless communication systems, an access channel refers both to a
`
`probe and message being rendered.
`
`In other wireless communication systems,
`
`the
`
`access channel refers to the probe only. Once the probe is acknowledged, a message
`
`governing the access terminal’s access attemptis transmitted.
`
`[0005]
`
`In an orthogonal frequency division multiple access (OFDMA) system, an
`
`access terminal typically separates the access transmission to be transmitted on the
`
`access channel
`
`into parts, a preamble transmission and a payload transmission. To
`
`preventintra-cell interference due to lack of fine timing on the reverse link during the
`
`access preamble transmission, a CDM-based preamble transmission may be time-
`
`division-multiplexed with the rest of the transmissions(i.e., traffic, control, and access
`
`payload). To access the system,
`
`the access terminal then randomly selects one PN
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`WO 2006/019710
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`PCT/US2005/024614
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`sequence out of a group of PN sequences and sendsit as its preamble during the access
`
`slot.
`
`[0006]
`
`The access point searches for any preambles(i.e., all possible PN sequences)
`
`that may have been transmitted during the access slot. Access preamble transmission
`
`performance is measuredin termsofcollision probability, misdetection probability and
`
`false alarm probability. Collision probability refers to the probability that a particular
`
`pseudo-random (PN) sequence is chosen by more than one access terminal as its
`
`preamble in the same access slot. This probability is inversely proportional
`
`to the
`
`number of preamble sequences available. Misdetection probability refers to the
`
`probability that a transmitted PN sequence is not detected by the base station. False
`
`alarm probability refers to the probability that an access point erroneously declared that
`
`a preamble has been transmitted while no preamble is actually transmitted. This
`
`probability increases with the number of preambles available.
`
`[0007]
`
`The access point then transmits an acknowledgment for each of the preambles
`
`detected. The acknowledgement message may include a PN sequence detected, timing
`
`offset correction, and index of the channel for access payload transmission. Access
`
`terminal terminals whose PN sequenceis acknowledged can then transmit the respective
`
`access payload using the assigned resource.
`
`[0008]
`
`Because the access point has no prior knowledge of where the access terminal is
`
`in the system (i.e. what its power requirements, buffer level, or quality of service may
`
`be), the acknowledgement message is broadcasted at a power level high enough such
`
`that all access terminals in the given cell can decode the message. The broadcast
`
`acknowledgement is inefficient as it requires a disproportionate amount of transmit
`
`power and/or frequency bandwidth to close the link.
`
`Thus, there is a need to more
`
`efficiently send an acknowledgment message to access terminals in a given cell.
`
`SUMMARY
`
`[0009]
`
`Embodiments of the invention minimize use of a broadcast acknowledgement
`
`channel during its preamble transmission. Embodiments of the invention further
`
`addresses how information regarding forward link channel quality can beefficiently
`
`signaled over the access channel during access preamble transmission.
`
`In one embodiment, an apparatus and method for transmitting an indicator of
`
`channel quality minimizing the use of a broadcast channel is described. A metric of
`
`

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`WO 2006/019710
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`PCT/US2005/024614
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`forward link geometry of observed transmission signals is determined. An indicator of
`
`channel quality value is determined as a function of the observed transmission signals.
`
`An access sequenceis selected, randomly, from one group of a plurality of groups of
`
`access sequences, wherein each of the plurality of groups of access sequences
`
`correspondto different ranges of channel quality values.
`
`[0010]
`
`The metric of forward link geometry may be determined as a function of
`
`observed pilot signals, noise, and/or traffic on data channels. The quantity of access
`
`sequencesin the plurality of groups access sequencesare distributed non-uniformly.
`
`In
`
`an embodiment, the access sequencesare distributed to reflect the distribution of access
`terminals about the access point.
`In another embodiment, the access sequences are
`distributed in proportion to the number of access terminals that need a given amountof
`
`power neededto send an indicator of acknowledgmentto the access terminal.
`
`[0011]
`
`In another embodiment, a methodofpartitioning a plurality of access sequences,
`
`is described. A probability distribution of a plurality of access terminals about an
`
`access point is determined. The probability distribution is determinedas a function of a
`
`plurality of access terminals having CQI values within a predetermined ranges. Groups
`
`of access sequences are assigned in proportion to the probability distribution. Access
`
`sequencescan be reassignedas a function of a changein distribution of access terminals
`
`aboutthe accesspoint.
`
`[0012]
`
`In yet another embodiment, an apparatus and method of transmitting an
`
`acknowledgement of a detected access sequence is described. An access sequence is
`
`received. The access sequence can be looked-up in a look-up table, stored in memory,
`
`to determine at least one attribute of the given access terminal (as a function of the
`
`access sequence). The attribute can be information such as a channel quality indicator,
`
`a buffer level and a quality of service indicator.
`
`Information is then transmitted to the
`
`access terminal, where the information is commensurate and consistent with the
`
`attribute.
`
`Information transmitted may include an indicator of acknowledgment. The
`
`indicator of acknowledgment may be transmitted over a shared signalling channel
`
`(SSCH).
`
`[0013]
`
`Various aspects and embodiments of the invention are described in further detail]
`
`below.
`
`

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`WO 2006/019710
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`PCT/US2003/024614
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0014]
`
`The features and nature of the present invention will become more apparent
`
`from the detailed description set forth below when taken in conjunction with the
`
`drawings in which like reference characters identify correspondingly throughout and
`
`wherein:
`
`[0015]
`
`[0016]
`
`[0017]
`
`[0018]
`
`[0019]
`
`[0020]
`
`FIG.1 illustrates a block diagram of a transmitter and a receiver;
`
`FIG. 2 illustrates the access probe structure and the access probe sequence;
`
`FIG.3 illustrates a traditional call flow between an access terminal and an access
`
`point;
`
`FIG. 4 illustrates an embodiment of the invention that avoids the use of the
`
`broadcast acknowledgement;
`
`FIG.5 illustrates a cell partitioned using uniform spacing;
`FIG.6 illustrates a diagram showing weighted partitioning based on quantized
`CQIvalues;
`
`[0021]
`
`FIG. 7 illustrates a table stored in memory that partitions the group of access
`
`sequences into sub-groups of access sequences based on a variety of factors; and
`
`[0022]
`
`FIG. 8 illustrates a process for dynamically allocating access sequences.
`
`DETAILED DESCRIPTION
`
`{0023]
`
`The word “exemplary”is used herein to mean “serving as an example, instance,
`or illustration.” Any embodiment or design described herein as “exemplary” is not
`
`necessarily to be construed as preferred or advantageous over other embodiments or
`
`designs.
`
`[0024]
`
`The techniques described herein for using multiple modulation schemes for a
`
`single packet may be used for various communication systems such as an Orthogonal
`
`Frequency Division Multiple Access (OFDMA) system, a Code Division Multiple
`
`Access (CDMA) system, a Time Division Multiple Access (TDMA) system, a
`
`Frequency Division Multiple Access (FDMA)system, an orthogonal frequency division
`
`multiplexing (OFDM)-based system, a single-input single-output (SISO) system, a
`
`multiple-input multiple-output (MIMO) system, and so on. These techniques may be
`
`used for systems that utilize incremental redundancy (IR) and systemsthat do notutilize
`
`IR (e.g., systems that simply repeats data).
`
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`[0025]
`
`Embodiments of the invention avoid use of a broadcast acknowledgement
`
`channel by having the access terminals indicate a parameter, such as forward link
`
`channel quality (i.e., CQI), buffer level requirements, quality of service requirements,
`
`etc., during its preamble transmission. By having the access terminals indicate forward
`
`link channel quality, the access point can transmit each acknowledgment on a channel
`
`using an appropriate amount of power for a given access terminal or group of access
`
`terminals.
`
`In the case of the acknowledgment message being transmitted to a group of
`
`access terminals, an acknowledgment messageis sent to multiple access terminals who
`
`have indicated the same or similar CQI values (within a range). Embodiments of the
`
`invention further address how CQIcan beefficiently signaled over the access channel
`during access preamble transmission.
`
`[0026]
`
`An “access terminal”refers to a device providing voice and/or data connectivity
`
`to a user. An access terminal may be connected to a computing device such as a laptop
`
`computer or desktop computer, or it may be a self contained device such as a personal
`
`digital assistant. An access terminal can also be called a subscriberstation, subscriber
`
`unit, mobile station, wireless device, mobile, remote station, remote terminal, user
`
`terminal, user agent, or user equipment. A subscriber station may be a cellular
`
`telephone, PCS telephone, a cordless telephone, a Session Initiation Protocol (SIP)
`
`phone, a wireless local
`
`loop (WLL)station, a personal digital assistant (PDA), a
`
`handheld device having wireless connection capability, or other processing device
`
`connected to a wireless modem.
`
`(0027]
`
`An “access point” refers to a device in an access network that communicates
`
`over the air-interface, through one or more sectors, with the access terminals or other
`
`access points. The accesspoint acts as a router between the access terminal andtherest
`
`of the access network, which may include an IP network, by converting received air-
`
`interface frames to IP packets. Access points also coordinate the management of
`
`attributes for the air interface. An access point may bea basestation, sectors of a base
`
`station, and/or a combination of a base transceiver station (BTS) andabasestation
`
`controller (BSC).
`
`[0028]
`
`FIG.1 illustrates a block diagram of a transmitter 210 and a receiver 250 in a
`
`wireless communication system 200. At transmitter 210, a TX data processor 220
`
`receives data packets from a data source 212. TX data processor 220 processes(e.g.,
`
`formats, encodes,partitions, interleaves, and modulates) each data packet in accordance
`
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`with a modeselected for that packet and generates up to T blocks of data symbols for
`the packet. The selected mode for each data packet may indicate (1) the packet size
`
`(i.e., the number of information bits for the packet) and (2) the particular combination of
`
`code rate and modulation schemeto use for each data symbol block of that packet. A
`
`controller 230 provides various controls to data source 212 and TX data processor 220
`for each data packet based on the selected mode. TX data processor 220 provides a
`stream of data symbolblocks(e.g., one block for each frame), where the blocks for each
`
`packet may be interlaced with the blocks for one or more other packets.
`
`(0029)
`
`A transmitter unit (TMTR) 222 receives the stream of data symbol blocks from
`
`TX data processor 220 and generates a modulated signal.
`
`Transmitter unit 222
`
`multiplexes in pilot symbols with the data symbols (e.g., using time, frequency, and/or
`
`code division multiplexing) and obtains a stream of transmit symbols. Each transmit
`
`symbol may be a data symbol, a pilot symbol, or a null symbol havinga signal value of
`
`zero. Transmitter unit 222 may perform OFDM modulation if OFDM is used by the
`
`system. Transmitter unit 222 generates a stream of time-domain samples and further
`
`conditions (e.g., converts to analog, frequency upconverts, filters, and amplifies) the
`
`sample stream to generate the modulated signal.
`
`The modulated signal
`
`is then
`
`transmitted from an antenna 224 and via a communication channelto receiver 250.
`
`[0030]
`
`At receiver 250, the transmitted signal is received by an antenna 252, and the
`
`received signal
`
`is provided to a receiver unit (RCVR) 254. Receiver unit 254
`
`conditions, digitizes, and pre-processes (e.g., OFDM demodulates) the received signal
`
`to obtain received data symbols and received pilot symbols. Receiver unit 254 provides
`the received data symbols to a detector 256 and the received pilot symbols to a channel
`estimator 258. Channel estimator 258 processes the received pilot symbols and
`
`provides channel estimates (e.g., channel gain estimates and SINR estimates) for the
`
`communication channel. Detector 256 performs detection on the received data symbols
`
`with the channel estimates and provides detected data symbols to an RX data processor
`
`260. The detected data symbols mayberepresented by log-likelihood ratios (LLRs) for
`
`the code bits used to form the data symbols (as described below) or by other
`
`representations. Whenever a new block of detected data symbols is obtained for a given
`data packet, RX data processor 260 processes (e.g., deinterleaves and decodes) all
`
`detected data symbols obtained for that packet and provides a decoded packet to a data
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`/
`
`[0031]
`
`[0032]
`
`[0033]
`
`sink 262. RX data processor 260 also checks the decoded packet and provides the
`packetstatus, which indicates whether the packet is decodedcorrectly orin error.
`A controller 270 receives the channel estimates from channelestimator 258 and
`the packet status from RX data processor 260. Controller 270 selects a mode for the
`next data packet to be transmitted to receiver 250 based on the channel estimates.
`Controller 270 also assembles feedback information. The feedback information is
`processed by a TX data processor 282, further conditioned by a transmitter unit 284, and
`transmitted via antenna 252 to transmitter 210.
`At transmitter 210,
`the transmitted signal from receiver 250 is received by
`antenna 224, conditioned by a receiver unit 242, and further processed by an RX data
`processor 244 to recover the feedback information sent by receiver 250. Controller 230
`obtains the received feedback information, uses the ACK/NAK to control
`the IR
`transmission of the packet being sent to receiver 250, and uses the selected modeto
`process the next data packet to send to receiver 250. Controllers 230 and 270 direct the
`operation at transmitter 210 and receiver 250, respectively. Memory units 232 and 272
`provide storage for program codes and data used by controllers 230 and 270,
`respectively.
`FIG.2 illustrates the access probe structure and the access probe sequence 200.
`In FIG. 2, Ns probe sequences are shown, where each probe sequence has Npprobes.
`The media access control layer (MAC) protocol transmits access probes by instructing
`the physical layer to transmit a probe. With the instruction, the access channel MAC
`protocol provides the physical
`layer with a number of elements, including, but not
`limited to, the power level, access sequence identification, pilot PN of the sector to
`which the access probeis to be transmitted, a timing offset field and a control segment
`field. Each probe in a sequenceis transmitted at increasing power until the access
`terminal receives an access grant. Transmission is aborted if the protocol received a
`deactivate command, or if a maximum number of probes per sequence have been
`transmitted. Prior to transmission ofthe first probe ofall probe sequences, the access
`terminal forms a persistence test which is used to control congestion on the access
`channel.
`
`[0034]
`
`FIG.3 illustrates a traditional call flow between an access terminal and an access
`point 300. Access terminal 304 randomly selects a preamble, or PN sequence, out of a
`group of PN sequencesand sends 308 the preamble during the access slot to the access
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`point 312. Upon receipt, the access point 312 then transmits 316 an access grant,
`
`including a broadcast acknowledgement, for each of the preambles detected. This
`
`acknowledgement
`
`is a broadcasted acknowledgement
`
`transmitted at a high enough
`
`power such that all of the access terminals in a given cell are able to decode the
`
`broadcast acknowledgement. This is deemed necessary becausethe access point has no
`prior knowledge where the access terminals are in the system, and thus - has no
`knowledge as to the power level necessary for the access terminal to decode the
`
`broadcasted acknowledgement. On receipt of the accent grant 316, access terminal 304
`
`sends 320 the payload as per the defined resourcesallocated in the accessgrant.
`
`[0035]
`
`The broadcast acknowledgement
`
`transmission described above is relatively
`
`inefficient as it requires a disproportionate amount of transmit power and/or frequency
`
`bandwidth to close the link. FIG 4 illustrates an embodiment 400 that avoids the use of
`
`the broadcast acknowledgement. An access terminal observes 408 transmissions from
`
`access points.
`
`In observing, the access terminal determines the power of transmissions
`
`it receives. These observations typically involve determining forward link channel
`
`quality from observed acquisition pilot signal transmissions or pilot transmissions as
`
`part of a shared signalling channel (SSCH)channel.
`
`[0036]
`
`The access terminal 404 then randomly selects a preamble, or access sequence,
`
`out of a group of access sequences and sends the preamble 410 to the access point 412.
`
`This preamble is transmitted along with some knowledge of forward link channel
`
`quality (CQI). CQI information may be transmitted as within the preamble, or
`
`appended to it. In another embodiment, an access sequence is randomly chosen out of a
`
`plurality of groups of access sequences, where each group of access sequences is
`
`designated for a range of CQI values. For example, indications of forward link channel
`
`quality may be observed pilot signal power. The observed pilot signal power may be
`
`quantized to CQI values based on a predeterminedset of values. Thus, a given range of
`
`received pilot signal power may correspond to a given CQI value. Accordingly, the
`
`access point 412 may determine the CQI of a given access terminal by virtue of the
`
`access sequence chosen by the access terminal.
`
`[0037]
`
`Because the access terminal sends an indicator of forward link channel quality
`
`duringits initial access attempt with the access point 412, the access point 412 has the
`
`knowledge needed to transmit 416 each acknowledgement on a channel using an
`
`appropriate amount of power
`
`for
`
`the designated access terminal 404.
`
`In an
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`embodiment, the acknowledgment message maybesent to a group of access terminals
`
`having the same or similar CQI values. This may be through use of the SSCH. Thus,
`
`based on the power level needed for the access terminal to successfully receive the
`
`transmission, the access point sends the acknowledgement message in the appropriate
`
`section of the SSCH message.
`
`[0038]
`
`In addition to CQI information, the access terminal may send other information
`
`of interest to the access point during the initial access phase. For example, the access
`
`terminal may send a buffer level indicator, indicating the amount of data the access
`
`terminal intends to send to the access point. With such knowledge, the access pointis
`
`able to appropriately dimension initial resource assignments.
`
`[0039]
`
`The access terminal may also send information regarding priority groups or
`
`quality of service. This information may be used to prioritize access terminals in the
`
`event of limited access point capability or system overload.
`
`[0040]
`
`Upon receipt of the access grant message by the access terminal, the access
`
`terminal 404 sends 420 payload as per the resources defined in the access grant
`
`message. By receiving additional information during the initial access phase, the access
`
`point will be able to take advantage of knowing the CQI, buffer level and quality of
`
`service informationas part of the access grant message.
`
`[0041]
`
`FIG. 5 illustrates a cell 500 partitioned using uniform spacing. The cell is
`
`divided into a number of regions R, wherein each region is defined by having a
`
`probability of observed metrics within a given range.
`
`In an embodiment, observations
`
`of forward link geometry are used. For example, metrics such as C/I, where C is the
`
`received pilot power andI is the observed noise, may be used. Also, C/(C+I) may be
`
`used.
`
`In other words, some measure that utilizes observed signal power and noise is
`
`used. These observed metrics correspond to given CQI values, or value ranges, which
`
`thus define the region.
`
`For example, Region R, defines a Region having CQI values
`
`corresponding to power and/or noise levels greater than P;. Region R2 defines a region
`
`having CQI values corresponding to power and/or noise levels such that P2 > R2 > P).
`
`Similarly, Region R; defines a Region having CQI values corresponding to power
`
`and/or noise levels such that P; > R; > P2, and so on. Region Ry.; has CQI values
`
`corresponding to power and/or noise levels such that they fall in the range of P, > R w-1
`
`> Py. Similarly, Region Ry has CQI values corresponding to powerand/ornoise levels
`
`observed < P,.
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`[0042]
`
`Theoretically, by choosing to transmit one of N possible preamble sequences, up
`
`to log2(N) bits of information may be conveyed. For example, when N = 1024, as many
`
`as log2(1024) = 10 bits may be conveyed. Thus, by choosing which preamble sequence
`
`to transmit, it is possible for user dependent information to be embedded as part ofthe
`
`preamble transmission.
`
`[0043]
`
`A commonly used techniqueis to partition then N preamble sequences into M
`
`distinct sets, labeled {1,2,--,4}To signal one of log2(M) possibilities (1.¢., log2(M) bits),
`
`a sequence in an appropriate set is chosen and transmitted. For instance, to signal
`message index k€{1,2,--, M}, a sequence in the K" set is (randomly) chosen and
`transmitted. Assuming correct detection at the receiver, the transmitted information(i.e.,
`
`the log,(M) -bit message) can be obtained based on the index ofthe set that the received
`
`[0044]
`
`sequence belongsto.
`In a uniform partitioning strategy, where the N preamble “sequences are
`uniformly partitioned into M groups(i.e., each group contains N/M sequences). Based
`
`on the measured CQIvalue, one of the preamble sequences from an appropriate set is
`
`selected
`
`and
`
`transmitted. The
`
`collision
`
`probability,
`
`then,
`
`depends
`
`on
`
`the
`
`mapping/quantization of the measured CQI and the number of simultaneous access
`
`attempts.
`
`[0045]
`
`This can be illustrated by considering a simple 2-level quantization of CQI
`
`(i.e.,.M=2), with Pr(M(CQD=1)=a and Pr(M(CQD=1)=0a, where M(x) is a quantization
`
`function mapping the measured CQIvalue into oneof the twolevels.
`
`[0046]
`
`With uniform access sequence partitioning,
`
`the N preamble sequences are
`
`partitioned into two sets with N/2 sequences in each set. As by example, assumethat
`
`_there are two simultaneous access attempts(i.e., exactly two access terminals are trying
`to access the system in each access slot). The collision probability is given by
`a? 40-o
`=).
`G)
`
`[0047]
`
`With probability a, the two access terminals wish to send M=/(i.e., they both
`
`have quantized CQI level = 1). Since there are N/2 preamble sequences to choose from
`
`in the first set, the collision probability (given that both access terminals choosetheir
`
`sequence from this set) is 1/(N/2). Following the samelogic, the collision probability
`
`for the other set can be derived.
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`[0048]
`
`Thus, the overall collision probability depends on the parameter & and number
`
`of simultaneous access attempts. The collision probability can be as high as 2/N
`
`(a =0,1) or as low as 1/N (a = 0.5). Thus, the best choice of @ in this case is & =0.5.
`
`However, it is unclear whether the CQI quantization function that results in & =0.5 is a
`
`desirable function.
`
`[0049}
`
`The access point will transmit the acknowledgment channel at the power level
`
`required to close the link as indicated by the CQIlevel. In this example, with probability
`
`Q, the access point has to transmit at the power corresponding to that of a broadcast
`
`channel and with probability 1-0, the access point can transmit at some lower power.
`
`Thus, with o = 0.5, half the time the access point has to broadcast the acknowledgment
`
`channel. On the other hand, by choosing &@ = 0.5, the access point is forced to broadcast
`
`the acknowledgement channelless frequently but incurring an increase in the transmit
`
`powerin the remaining of the time and higher overall collision probability.
`FIG. 6 illustrates a diagram showing weighted partitioning 600 based on
`
`[0050]
`
`quantized CQI values. The region is partitioned into various regions that are not of a
`
`uniform space, but are rather partitioned based on quantized CQI values that are
`
`weighted. By weighting the regions, additional preamble sequences are available in
`
`regions that have a higher probability of access terminals being in that region (i.e., a
`
`higher mass function). For example, regions 604, 608, and 612 are larger regionsthat
`
`may correspond to having a larger number of access sequences available. Conversely,
`
`regions 616 and 620 are smaller regions that may indicate smaller quantities of users
`
`present and thus fewer access sequencesavailable. Thus, the regions maybe partitioned
`
`having some prior knowledgeas to the distribution of C/I or received power
`
`in a
`
`specified range in a given cell.
`
`It is contemplated that geographic regions may not
`
`always represent concentrations of users within given CQI ranges. Rather, the graphical
`representations of non-uniform spacing is to indicate the non-uniform distribution of
`
`access sequences through a given cell region.
`
`[0051]
`
`In an embodiment, the probability distribution of access terminals within the cell
`
`may be dynamic based on the distribution of access terminals over time. Accordingly,
`
`certain partitioned regions maybe larger or smaller based on the absenceor presence of
`
`access terminals at a given time of the day, or otherwise adjusted as a function of the
`
`concentration of access terminals present in a given CQIregion.
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`
`[0052]
`
`Thus, the sequences available for initial access are divided into N number of
`
`partitions. The access terminal determines the partition to be used for the access
`
`attempt based on at least the observed pilot power and buffer level.
`
`It is contemplated
`
`that the partition may also be determined on a numberof other factors, such as packet
`
`size,
`
`traffic type, bandwidth request, or quality of service. Once the partition is
`
`determined, the access terminals select the sequence ID using a uniform probability
`
`over that partition. Of the available sequences for access, a subset of sequences is
`
`reserved for active set operations, and another subset of sequences are availab