( 12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization :
`International Bureau
`
`(43) International Publication Date
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`23 February 2006 (23.02.2006)
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`
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`(10) International Publication Number
`
`WO 2006/019710 Al
`
`Agents: WADSWORTH. Philip R. el al.-, 5775 More—
`house Drive, San Diego, Califonia 92121 (US).
`
`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, Cl I, CN,
`CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE, EG, ES, FI,
`GB, GD, (iii, GH, GM, HR, HU, II), IL, IN, IS, JP, K15,
`KG, KM, KP, KR, [(2, LC, LK, LR, LS. LT, LU, LV. MA.
`MD, MG, MK, MN, MW, MX, MZ, NA, NG, NI, NO, NZ,
`OM, PG, I’ll, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL,
`SM, SY, TJ, TM, TN, TR, '['1", T2, U A, UG, US, UZ, VC,
`VN, YU, ZA, ZM, ZW.
`
`(51)
`(21)
`
`(22)
`I25)
`(26)
`
`(30)
`
`I71)
`
`I72)
`(75)
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`
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`WO2006/019710A1||||||||||||||||||||||l||||||||||||||||||||||||||l||||||||||||||l||||||||||||||l|||||||||||||||
`
`International Patent Classification-J:
`
`H04Q 7138
`
`(74)
`
`International Application Number:
`PCTi1]820030246 14
`
`{81)
`
`International Filing Date:
`Filing language:
`
`11 July 2005 (11.07.2005)
`[English
`
`English
`
`Publication Language:
`Priority Data:
`60590113
`1 ”020,457
`
`21 July 2004 (21.07.2004)
`22 December 2004 (22.12.2004)
`
`US
`US
`
`Applicant (for all designated States except USJ: QUAL-
`COML'I INCORPORATED [US/US]; 5775 Morehouse
`Drive, San Diego, California 92121 (US).
`Inventors; and
`lnventom‘Applicants (for US only): SU'I‘IVONG, Arak
`[’l‘l-IIUSI; 8840 Costa Verde Boulevard, #3439, San Diego,
`Calilornia 92122 (US). TEAGUE, Edward Harrison
`[USIUS]; 4614 Bryson Terrace, San Diego, California
`92130 (US). GOROKHOV, Alexei [WIS]; 12543 El
`Camino Real, San Diego, California 92130 (US).
`
`(84)
`
`Designated States (airless otherwise indicated. for every
`kind of regional protection available): ARIN) (BW, GH,
`GM. Kli, LS, MW, MZ, NA, SD, SL, SZ. 17.. 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, IIU, IE, 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, TI). TG).
`
`IConiiriued on next page}
`
`(54) Title: EFFICIENT SIGNALING OVER ACCESS CHANNEL
`
`400
`
`
`
`404
`
`
` 408
`{-
`INFO OBSERVED
`
`4 10
`
`W
`SEND PREAMBLE
`
`
`WICQI
`r416
`
`
`
`SEND ACK AT
`APPROPRIATE
`
`
`POWER LEVEL
`
`
`
`
`
`
`
`
`/42o
`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 iink
`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
`APPLE 1003
`
`

`

`WO 2006/019710 A1
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`|I||||||||I||||||l|||||||||||||||||||||||||||||||||||||Illlllllll|||||||||I|||||||||||||||||
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`GB. GR. ill). ”5. l5. lT. LT. LU. Uri MC. NL. PL. PI R0.
`Declarations under Rule 4.17:
`SE. Sl. SK. TR). GAPlparent (BF. BJ. CF. CG. Cl. CM. GA.
`— as to applicantir entitlement to apply for and be granted
`(2N. GQ. GW ML. MR. NE. SN. TD. TG)
`a patent (Rule 4.1 7{ii)j for the following designations AE.
`AG. AL. AM. AT: AU. AZ. BA. 83. BG. BR. BW. BY. BZ. — as to the applicant's entitlement to claim the priority of the
`CA. CH. CN. CO. CR. CU. CZ. DE. DK. DM. DZ. EC. EE.
`earlier application (Rule 4.l7{iii}J for all designations
`EG. ES. Fl. GB. GD. GE. Gil. (PM. HR. ”U. H). lit, lN. — as to the applicant's entitlement to claim the priority of the
`lS. JR KE. KG. KM. KP. KR. KZ. LC. LK. LR. LS. LT: LU.
`earlier application (Rule 4.l7(iii}}for all designations
`LI”: MA. MD. MG. MK. MN. MW. MX. MZ. NA. NG. Ni.
`Published:
`NO. NZ. OM. PG. PH. PL. PT: R0. RU. SC. SD. SE. SG.
`SK. SL. SM. SY. TJ. TM. TN. TR. TI: 12. UA. U0. UZ. VC. — with international search report
`VN. YU. ZA. ZM. ZW. ARH’O patent (SW. GH. GM. KE.
`LS. MW MZ. NA. SD. SL. SZ, TA. UG. KM. ZW). Eurasian
`patent (AM. AZ. BY. KG. KZ. MD. RU. TJ. TM). European
`patent (AT. BE. BC. CH. CY. CZ. DE. DK. EE. ES. Fl. FR.
`
`Fortwo—lettenrodes and other abbreviations. refer to the "Guid—
`anee Notes on Codes and Abbreviatiotir" appearing at tlte begin—
`ning ofeaclt regular isa'ue afthe PCT Gazette.
`
`

`

`W0 20061019710
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`EFFICIENT SIGNALING OVER ACCESS CHANNEL
`
`CROSS-REFERENCE TO RELATED APPLICATION
`
`[0001]
`
`This application claims priority to U.S. Provisional Patent Application Serial
`
`No. 60590,]13, filed July 21, 2004, which is incorporated herein by reference in 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 channel is used on the reverse link by an access terminal for initial
`
`contact with an access point. The access terminal may initiate 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 determine the strongest signal strength from nearby access points and acquire
`
`downlink timing. The access terminal is then able to decode the information transmitted
`
`by the given access point on a broadcast channel regarding choice of parameters
`
`governing the access terrninal’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 attempt is transmitted.
`
`[00051
`
`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
`
`prevent intra—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
`
`

`

`W0 20061019710
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`PCTIUSZOOSIOZ-l-Gl-l
`
`sequence out of a group of PN sequences and sends it 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 measured in terms of collision 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 3 PN sequence detected, timing
`
`offset correction, and index of the channel for access payload transmission. Access
`
`terminal terminals whose PN sequence is 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 (Le. 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 andfor 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 be efficiently
`
`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
`
`

`

`W0 20061019710
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`PCTIUSZOOSIOZ-l-Gl-l
`
`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 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.
`
`[0010]
`
`The metric of forward link geometry may be determined as a fimction of
`
`observed pilot signals, noise, andfor traffic on data channels. The quantity of access
`
`sequences in the plurality of groups access sequences are distributed non-uniformly.
`
`In
`
`an embodiment, the access sequences are 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 amount of
`
`power needed to send an indicator of acknowledgment to the access terminal.
`
`[00111
`
`In another embodiment, a method of partitioning 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 determined as 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
`
`sequences can be reassigned as a function of a change in distribution of access terminals
`
`about the access point.
`
`[00121
`
`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 iooked—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.
`
`

`

`W0 20061019710
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`PCTIUSZflflSi’OZJfil-l
`
`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
`
`CQI values;
`
`[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
`
`10023]
`
`The word “exemplary” is used herein to mean “serving as an example, instance,
`1|
`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 (8180) system, a
`
`multiple-input multiple-output (MIMO) system, and so on. These techniques may be
`
`used for systems that utilize incremental redundancy (IR) and systems that do not utilize
`
`IR (e.g., systems that simply repeats data).
`
`

`

`W0 2006ffll9710
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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 message is sent to multiple access terminals who
`
`have indicated the same or similar CQI values (within a range). Embodiments of the
`
`invention further address how CQI can be efficiently signaled over the access channel
`
`during access preamble transmission.
`
`[0026]
`
`An “access terminal” refers to a device providing voice andx'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 subscriber station, 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 (FDA), 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 access point acts as a router between the access terminal and the rest
`
`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 be a base station, sectors of a baSe
`
`station, andz’or a combination of a base transceiver station (BTS) and a base station
`
`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 mode selected 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 scheme to 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 symbol blocks (6. 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, andfor
`
`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 having a 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 fithher
`
`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 fi‘om an antenna 224 and via a communication channel to 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 dcmodulates) 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 SlNR 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 may be represented 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
`
`

`

`W0 20061019710
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`PC TlUSZOUSfOZ-lfil 4
`
`'/
`
`sink 262. RX data processor 260 also checks the decoded packet and provides the
`
`packet status, which indicates whether the packet is decoded correctly or in error.
`A controller 270 receives the channel estimates from channel estimator 258 and
`
`[0031]
`
`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.
`
`[00321
`
`the transmitted signal from receiver 250 is received by
`At transmitter 210,
`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 ACKJ’NAK to control
`
`the IR
`
`transmission of the packet being sent to receiver 250, and uses the selected mode to
`
`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.
`
`[0033]
`
`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 Np probes.
`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
`
`layer with a number of elements, including, but not
`protocol provides the physical
`limited to, the power level, access sequence identification, pilot PN of the sector to
`
`which the access probe is to be transmitted, a timing offset field and a control segment
`field. Each probe in a sequence is 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 of the first probe of all 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 sequences and sends 308 the preamble during the access slot to the access
`
`

`

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`PCTlUS20051’02461-l
`
`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
`
`acloiowledgement
`
`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 because the 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 resources allocated in the access grant.
`
`[0035]
`
`The broadcast acknowledgement
`
`transmission described above is relatively
`
`inefficient as it requires a diSproportionate amount of transmit power andfor 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 predetermined set 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
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`during its initial access attempt with the access point 412, the access point 412 has the
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`knowledge needed to transmit 416 each aclcnowledgement on a channel using an
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`appropriate amount of power
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`for
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`the designated access terminal 404.
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`In an
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`embodiment, the acknowledgment message may be sent to a group of access terminals
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`having the same or similar CQI values. This may be through use of the SSCH. Thus,
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`based on the power level needed for the access terminal to successfiilly receive the
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`transmission, the access point sends the acknowledgement message in the apprOpriate
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`section of the SSCH message.
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`[0033]
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`In addition to CQI information, the access terminal may send other information
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`of interest to the access point during the initial access phase. For example, the access
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`terminal may send a buffer level indicator, indicating the amount of data the access
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`terminal intends to send to the access point. With such knowledge, the access point is
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`able to appropriately dimension initial resource assignments.
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`[0039]
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`The access terminal may also send information regarding priority groups or
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`quality of service. This information may be used to prioritize access terminals in the
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`event of limited access point capability or system overload.
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`[0040]
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`Upon receipt of the access grant message by the access terminal, the access
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`terminal 404 sends 420 payload as per the resources defined in the access grant
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`message. By receiving additional information during the initial access phase, the access
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`point will be able to take advantage of knowing the CQI, buffer level and quality of
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`service information as part of the access grant message.
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`[0041]
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`FIG. 5 illustrates a cell 500 partitioned using uniform spacing. The cell is
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`divided into a number of regions R, wherein each region is defined by having a
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`probability of observed metrics within a given range.
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`In an embodiment, observations
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`of forward link geometry are used. For example, metrics such as CH, where C is the
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`received pilot power and l is the observed noise, may be used. Also, C!(C+I) may be
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`used.
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`In other words, some measure that utilizes observed signal power and noise is
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`used. These observed metrics correspond to given CQI values, or value ranges, which
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`thus define the region.
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`For example, Region R; defines a Region having CQI values
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`corresponding to power andr'or noise levels greater than P1. Region R2 defines a region
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`having CQI values corresponding to power andfor noise levels such that P2 > R2 > P;.
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`Similarly, Region R3 defines a Region having CQI values corresponding to power
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`andtor noise levels such that P; > R; > P2, and so on. Region Rm has CQI values
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`corresponding to power andfor noise levels such that they fall in the range of P, > R m
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`> P,.. Similarly, Region RN has CQI values corresponding to power andfor noise levels
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`observed < PX.
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`[0042]
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`Theoretically, by choosing to transmit one of N possible preamble sequences, up
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`to logz(N) bits of information may be conveyed. For example, when N = 1024, as many
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`as log2(1024) = 10 bits may be conveyed. Thus, by choosing which preamble sequence
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`to transmit, it is possible for user dependent information to be embedded as part of the
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`preamble transmission.
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`[00431
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`A commonly used technique is to partition then N preamble sequences into M
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`distinct sets, labeled {1,2,---,M} To signal one of log2(M) possibilities (i.c., log2(M) bits),
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`a sequence in an appropriate set is chosen and transmitted. For instance, to signal
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`message index k€{1,2,---, M}, a sequence in the it” set is (randomly) chosen and
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`transmitted. Assuming correct detection at the receiver, the transmitted information (i.e.,
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`the log2(M) -bit message) can be obtained based on the index of the set that the received
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`sequence belongs to.
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`[0044]
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`In a uniform partitioning strategy, where the N preamble . sequences are
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`uniformly partitioned into M groups (i.e., each group contains MM sequences). Based
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`on the measured CQI value, one of the preamble sequences from an appropriate set is
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`selected
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`and
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`transmitted. The
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`collision
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`probability,
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`then,
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`depends
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`on
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`the
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`mapping/quantization of the measured CQI and the number of simultaneous access
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`attempts.
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`[0045]
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`This can be illustrated by considering a simple 2-level quantization of CQI
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`(i.e.,M=2), with Pr(M(CQI)=1)=a and Pr(M(CQI)=1)=o., where M(x) is a quantization
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`function mapping the measured CQI value into one of the two levels.
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`[0046]
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`With uniform access sequence partitioning,
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`the N preamble sequences are
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`partitioned into two sets with Nf2 sequences in each set. As by example, assume that
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`‘ there are two simultaneous access attempts (i.e., exactly two access terminals are trying
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`to access the system in each access slot). The collision probability is given by
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`r152;+(1—c:)2—1
`it]
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`[0047]
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`With probability (12, the two access terminals wish to send M=I(i.e., they both
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`have quantized CQI level = 1). Since there are N12 preamble sequences to choose from
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`in the first set, the collision probability (given that both access terminals choose their
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`sequence from this set) is IKNIZ). Following the same logic, the collision probability
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`for the other set can be derived.
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`[0048]
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`Thus, the overall collision probability depends on the parameter 0. and number
`
`of simultaneous access attempts. The collision probability can be as high as ZEN
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`(a =0,1) or as low as UN (0. = 0.5). Thus, the best choice of o. in this case is (1 =0.5.
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`However, it is unclear whether the CQI quantization function that results in (1 =05 is a
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`desirable function.
`
`[0049]
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`The access point will transmit the acknowledgment channel at the power level
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`required to close the link as indicated by the CQI level. In this example, with probability
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`a, the access point has to transmit at the power correSponding to that of a broadcast
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`channel and with probability 1-0., the access point can transmit at some lower power.
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`Thus, with u = 0.5, half the time the access point has to broadcast the acknowledgment
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`channel. On the other hand, by choosing a = 0.5, the access point is forced to broadcast
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`the acknowledgement channel less frequently but incurring an increase in the transmit
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`power in the remaining of the time and higher overall collision probability.
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`[0050}
`
`FIG. 6 illustrates a diagram showing weighted partitioning 600 based on
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`quantized CQI values. The region is partitioned into various regions that are not of a
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`uniform space, but are rather partitioned based on quantized CQI values that are
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`weighted. By weighting the regions, additional preamble sequences are available in
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`regions that have a higher probability of access terminals being in that region (Le, a
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`higher mass function). For example, regions 604, 608, and 612 are larger regions that
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`may correspond to having a larger number of access sequences available. Conversely,
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`regions 616 and 620 are smaller regions that may indicate smaller quantities of users
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`present and thus fewer access sequences available. Thus, the regions may be partitioned
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`having some prior knowledge as to the distribution of CH or received power
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`in a
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`specified range in a given cell.
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`It is contemplated that geographic regions may not
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`always represent concentrations of users within given CQI ranges. Rather, the graphical
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`representations of non-uniform spacing is to indicate the non-uniform distribution of
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`access sequences through a given cell region.
`
`[0051]
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`In an embodiment, the probability distribution of access terminals within the cell
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`may be dynamic based on the distribution of access terminals over time. Accordingly,
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`certain partitioned regions may be larger or smaller based on the absence or presence of
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`access terminals at a given time of the day, or otherwise adjusted as a fimction of the
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`concentration of access terminals present in a given CQI region.
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`[0052]
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`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
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`attempt based on a