(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0018336A1
`Sutivong et al.
`Jan. 26, 2006
`(43) Pub. Date:
`
`US 20060018336A1
`
`(54)
`
`(76)
`
`EFFICIENT SIGNALING OVER ACCESS
`CHANNEL
`
`Inventors: Arak Sutivong, San Diego, CA (US);
`Edward Harrison Teague, San Diego,
`CA (US); Alexei Gorokhov, San Diego,
`CA (US)
`Correspondence Address:
`QUALCOMM, INC
`5775 MOREHOUSE DR.
`SAN DIEGO, CA 92121 (US)
`
`(21)
`(22)
`
`Appl. No.:
`
`11/020,457
`
`Filed:
`
`Dec. 22, 2004
`
`Related U.S. Application Data
`
`(60)
`
`Provisional application No. 60/590,113, filed on Jul.
`21, 2004.
`
`800
`
`
`
`Publication Classification
`
`(51) Int. Cl
`(2006.01)
`H04I 3/14
`(2006.01)
`H04I 3/16
`(2006.01)
`H04I 3/22
`(2006.01)
`H04L 12/26
`(2006.01)
`H04J III6
`(2006.01)
`H04L I/00
`(2006.01)
`H04B 7/216
`(52) U.S. Cl. ........................... 370/437; 370/252; 370/465
`(57)
`ABSTRACT
`An apparatus and 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 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 chan
`nel quality values.
`
`SETIRESENTIAL
`PARTIONSZE
`
`804
`
`808
`COUNACCESS r
`AtteMSN
`EACHSUBSET
`
`UPDAE
`XECED
`82
`WALUES BASED ON r
`ACCSS
`AttMPS
`RECEWEON
`EACHSUBSET
`
`–
`
`816
`
`DETERMINE NEW SUBSE /
`SIES
`
`
`
`ARENEWSIZES
`SUBSANTIALLY OFFEREN
`
`
`
`820
`
`/
`
`824
`
`YES
`
`832
`MAINANCURRENT r
`SUBSETSIZES
`
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`Patent Application Publication Jan. 26, 2006 Sheet 1 of 8
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`US 2006/0018336A1
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`B?2C] XX
`
`JOSS0001)
`
`JOSS30OJE
`?OunOS
`
`e?BC] XL
`
`e?eC]
`
`Z!!
`
`JOSS90OJc3
`
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`Patent Application Publication Jan. 26, 2006 Sheet 2 of 8
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`US 2006/0018336A1
`
`GD
`
`2
`
`2.
`
`
`
`CN
`
`a -
`
`Fig. 2
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`Patent Application Publication Jan. 26, 2006 Sheet 3 of 8
`
`US 2006/0018336A1
`
`300
`
`
`
`304
`
`/
`SEND PREAMBLE
`
`308
`
`312
`
`316
`/
`BROADCAST
`ACCESS GRANT
`
`320
`
`/
`SEND PAYLOAD
`
`FIG. 3
`
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`Patent Application Publication Jan. 26, 2006 Sheet 4 of 8
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`US 2006/0018336A1
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`400
`
`
`
`404
`
`412
`
`408
`/
`NFO OBSERVED
`
`410
`/
`SEND PREAMBLE
`W/CQI
`-416
`SEND ACK AT
`APPROPRIATE
`POWER LEVEL
`
`-420
`SEND PAYLOAD
`
`FIG. 4
`
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`Patent Application Publication Jan. 26, 2006 Sheet 5 of 8
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`US 2006/0018336A1
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`500
`
`
`
`FIGURE 5
`
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`Patent Application Publication Jan. 26, 2006 Sheet 6 of 8
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`US 2006/0018336A1
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`600
`
`
`
`FIGURE 6
`
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`Patent Application Publication Jan. 26, 2006 Sheet 7 of 8
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`US 2006/0018336A1
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`700
`
`
`
`PACKETSIZE
`
`BWRECUEST
`
`BUFFER
`LEVEL
`
`AS . . .
`
`FIGURE 7
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`Patent Application Publication Jan. 26, 2006 Sheet 8 of 8
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`US 2006/0018336A1
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`800
`
`N
`
`
`
`SETIRESET INTIAL
`PARTIONSIZE
`
`804
`
`COUNT ACCESS
`ATTEMPTSN
`EACHSUBSET
`
`UPDATE
`EXPECTED
`VALUES BASED ON
`ACCESS
`ATTEMPTS
`RECEIVED IN
`EACHSUBSET
`
`DETERMINE NEW SUBSET
`SIZES
`
`808
`
`812
`
`816
`
`ARENEW SIZES
`SUBSTANTIALLY DIFFERENT
`
`/ 82O
`
`824
`
`YES
`
`MANTAIN CURRENT
`SUBSET SIZES
`
`832
`
`FIGURE 8
`
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`US 2006/0018336A1
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`Jan. 26, 2006
`
`EFFICIENT SIGNALING OVER ACCESS
`CHANNEL
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`0001. This application claims priority to U.S. Provisional
`Patent Application Ser. No. 60/590,113, filed Jul. 21, 2004,
`which is incorporated herein by reference in its entirety.
`
`BACKGROUND
`
`0002) 1. Field
`0003. The invention relates generally to wireless com
`munications, and more specifically to data transmission in a
`multiple access wireleSS communication System.
`0004 2. Background
`0005. 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 terminals acceSS
`attempt.
`0006. 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 terminals
`access attempt is transmitted.
`0007. In an orthogonal frequency division multiple
`access (OFDMA) system, an access terminal typically sepa
`rates 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
`Sequence out of a group of PN sequences and Sends it as its
`preamble during the access slot.
`0008 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 per
`formance is measured in terms of collision probability,
`misdetection probability and false alarm probability. Colli
`sion 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 pre
`amble 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.
`0009. The access point then transmits an acknowledg
`ment for each of the preambles detected. The acknowledge
`ment message may include a PN sequence detected, timing
`offset correction, and index of the channel for acceSS pay
`load transmission. Access terminal terminals whose PN
`Sequence is acknowledged can then transmit the respective
`access payload using the assigned resource.
`0010 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 acknowl
`edgement 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
`0011 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.
`0012. 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 forward
`link geometry of observed transmission signals is deter
`mined. 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.
`0013 The metric of forward link geometry may be deter
`mined as a function of observed pilot Signals, noise, and/or
`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.
`0014.
`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 COI values within a predetermined ranges. Groups
`of access Sequences are assigned in proportion to the prob
`ability distribution. AcceSS Sequences can be reassigned as a
`function of a change in distribution of access terminals about
`the access point.
`0015. In yet another embodiment, an apparatus and
`method of transmitting an acknowledgement of a detected
`
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`US 2006/0018336A1
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`Jan. 26, 2006
`
`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 signal
`ling channel (SSCH).
`0016 Various aspects and embodiments of the invention
`are described in further detail below.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0.017. 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:
`0.018
`FIG. 1 illustrates a block diagram of a transmitter
`and a receiver;
`0.019
`FIG. 2 illustrates the access probe structure and the
`CCCSS probe Sequence,
`0020 FIG.3 illustrates a traditional call flow between an
`access terminal and an access point;
`0021
`FIG. 4 illustrates an embodiment of the invention
`that avoids the use of the broadcast acknowledgement;
`0022 FIG. 5 illustrates a cell partitioned using uniform
`Spacing,
`0023 FIG. 6 illustrates a diagram showing weighted
`partitioning based on quantized COI values,
`0024 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
`0.025
`FIG. 8 illustrates a process for dynamically allo
`cating acceSS Sequences.
`
`DETAILED DESCRIPTION
`0026. 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.
`0027. 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 tech
`niques may be used for Systems that utilize incremental
`redundancy (IR) and Systems that do not utilize IR (e.g.,
`Systems that simply repeats data).
`
`0028 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., COI), 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 COI values (within a range). Embodiments
`of the invention further address how COI can be efficiently
`Signaled over the acceSS channel during acceSS preamble
`transmission.
`0029. 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 termi
`nal can also be called a Subscriber Station, Subscriber unit,
`mobile Station, wireleSS device, mobile, remote Station,
`remote terminal, user terminal, user agent, or user equip
`ment. 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.
`0030. 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, and/or
`a combination of a base transceiver station (BTS) and a base
`station controller (BSC).
`0031
`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 with a mode
`Selected for that packet and generates up to Tblocks 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 com
`bination 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
`(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.
`0032) 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 multi
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`plexes 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
`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 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 channel to receiver 250.
`0033. 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 SIR 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 representa
`tions. 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 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.
`0034. A controller 270 receives the channel estimates
`from channel estimator 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 feed
`back information. The feedback information is processed by
`a TX data processor 282, further conditioned by a transmit
`ter unit 284, and transmitted via antenna 252 to transmitter
`210.
`0035. 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 transmis
`Sion 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.
`0.036
`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.
`0037. 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 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.
`0038 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 point 312. Upon receipt, the
`access point 312 then transmits 316 an access grant, includ
`ing a broadcast acknowledgement, for each of the preambles
`detected. This acknowledgement is a broadcasted acknowl
`edgement 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 knowl
`edge 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.
`0039 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 embodi
`ment 400 that avoids the use of the broadcast acknowledge
`ment. 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.
`0040. 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 knowl
`edge of forward link channel quality (CQI). COI informa
`tion may be transmitted as within the preamble, or appended
`to it. In another embodiment, an access Sequence is ran
`domly chosen out of a plurality of groups of access
`Sequences, where each group of acceSS Sequences is desig
`nated for a range of COI values. For example, indications of
`forward link channel quality may be observed pilot Signal
`power. The observed pilot Signal power may be quantized to
`COI values based on a predetermined set of values. Thus, a
`given range of received pilot signal power may correspond
`to a given COI value. Accordingly, the access point 412 may
`determine the COI of a given access terminal by virtue of the
`acceSS Sequence chosen by the acceSS terminal.
`0041
`Because the access terminal sends an indicator of
`forward link channel quality during its initial acceSS attempt
`with the access point 412, the acceSS point 412 has the
`
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`Jan. 26, 2006
`
`knowledge needed to transmit 416 each acknowledgement
`on a channel using an appropriate amount of power for the
`designated acceSS terminal 404. In an embodiment, the
`acknowledgment message may be sent to a group of acceSS
`terminals having the same or similar COI 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.
`0042. In addition to COI 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 point is able
`to appropriately dimension initial resource assignments.
`0043. The access terminal may also send information
`regarding priority groups or quality of Service. This infor
`mation may be used to prioritize access terminals in the
`event of limited acceSS point capability or System overload.
`0044) 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 COI, buffer level and quality of service infor
`mation as part of the access grant message.
`004.5 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 and I 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 COI values, or value
`ranges, which thus define the region. For example, Region
`R defines a Region having COI values corresponding to
`power and/or noise levels greater than P. Region R defines
`a region having COI values corresponding to power and/or
`noise levels such that PaRa-P. Similarly, Region R
`defines a Region having COI values corresponding to power
`and/or noise levels. Such that P>R>P, and So on. Region
`RN has COI values corresponding to power and/or noise
`levels such that they fall in the range of P->RN >P.
`Similarly, Region RN has COI values corresponding to
`power and/or noise levels observed <P.
`0046) Theoretically, by choosing to transmit one of N
`possible preamble Sequences, up to log(N) bits of informa
`tion 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 of the pre
`amble transmission.
`0047 A commonly used technique is to partition then N
`preamble sequences into M distinct sets, labeled {1,2,. . .
`To signal one of log2(*) possibilities (i.e., log2(M) bits), a
`Sequence in an appropriate Set is chosen and transmitted. For
`instance, to signal message index kE1.2, .
`. . , M, a
`sequence in the k" set is (randomly) chosen and transmitted.
`
`ASSuming correct detection at the receiver, the transmitted
`information (i.e., the log2(M)-bit message) can be obtained
`based on the index of the Set that the received Sequence
`belongs to.
`0048. In a uniform partitioning strategy, where the N
`preamble Sequences are uniformly partitioned into Mgroups
`(i.e., each group contains N/M sequences). Based on the
`measured COI value, 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.
`0049. This can be illustrated by considering a simple
`2-level quantization of CQI (i.e.,M-2), with Pr(M(COI)=
`1)=C. and Pr(M(COI)=1)=C, where M(x) is a quantization
`function mapping the measured COI value into one of the
`two levels.
`0050. With uniform access sequence partitioning, the N
`preamble Sequences are partitioned into two Sets with N/2
`Sequences in each Set. AS by example, assume that 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 = -- + (1 - a)--
`()
`()
`
`0051) With probability of, the two access terminals wish
`to send M=1 (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 choose their sequence from this set) is 1/(N/2).
`Following the same logic, the collision probability for the
`other set can be derived.
`0052 Thus, the overall collision probability depends on
`the parameter C. and number of Simultaneous access
`attempts. The collision probability can be as high as 2/N
`(C=0,1) or as low as 1/N (C=0.5). Thus, the best choice of
`C. in this case is C=0.5. However, it is unclear whether the
`CQI quantization function that results in C=0.5 is a desirable
`function.
`0053. The access point will transmit the acknowledgment
`channel at the power level required to close the link as
`indicated by the COI level. In this example, with probability
`C, the acceSS point has to transmit at the power correspond
`ing to that of a broadcast channel and with probability 1-C,
`the acceSS point can transmit at Some lower power. Thus,
`with CL=0.5, half the time the access point has to broadcast
`the acknowledgment channel. On the other hand, by choos
`ing C=0.5, the access point is forced to broadcast the
`acknowledgement channel leSS frequently but incurring an
`increase in the transmit power in the remaining of the time
`and higher overall collision probability.
`0054 FIG. 6 illustrates a diagram showing weighted
`partitioning 600 based on quantized COI values. The region
`is partitioned into various regions that are not of a uniform
`Space, but are rather partitioned based on quantized COI
`values that are weighted. By weighting the regions, addi
`
`Optis Wireless Ex 2006-p. 13
`Apple v Optis Wireless
`IPR2020-00466
`
`

`

`US 2006/0018336A1
`
`Jan. 26, 2006
`
`tional 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 regions that 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
`Sequences available. Thus, the regions may be partitioned
`having Some prior knowledge as 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 rep
`resent concentrations of users within given COI ranges.
`Rather, the graphical representations of non-uniform Spac
`ing is to indicate the non-uniform distribution of acceSS
`Sequences through a given cell region.
`0055. 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 may be larger or Smaller based on
`the absence or 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 COI
`region.
`0056 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 number of 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 available for initial access. In one embodi
`ment, Sequences 0, 1 and 2 are reserved for active Set
`operations, and Sequences 3 through the total number of
`access Sequences are available for initial access.
`0057 The size of each partition is determined by the