Efficient signaling over access channel

multi-access wireless communication system.

Background of the Invention An access channel is used on a reverse link by an access terminal for initial contact with an access point. The access terminal may initiate an access attempt to request dedicated channels, for registration, or to perform a handover, etc. Before initiating an access attempt, the access terminal receives information from the downlink to determine the highest signal strength from nearby access points and acquire downlink timing. The access terminal is then able to decode information transmitted by the given access point over the broadcast channel regarding the selection of parameters for regulating the access terminal's access attempt.

[0003] In some wireless communication systems, an access channel relates to both the probe and the message being provided. In other wireless communication systems, the access channel only refers to the probe. Once the probe is acknowledged, a message is transmitted to regulate the access terminal's access attempt.

[0004] In an orthogonal frequency division multiple access (OFDMA) system, an access terminal typically

Separates the access transmission to be transmitted on the part access channel, preamble transmission and data block transmission. To prevent intracellular interference due to the lack of accurate timing on the reverse link during access preamble transmission, the CDM based preamble transmission may be time division multiplexed with the rest of the transmission (i.e. traffic, control and access payload). To access the system, the access terminal then randomly selects one PN sequence from the PN sequence group and sends it as its preamble during the access slots.

[0005] The access point searches for any preambles (ie, all possible PN sequences) that may have been access slots. The access performance is measured as the collision probability, the false-false probability and the transmitted during the preamble transmission.

relates to detection and probability

Collision probability probability that a specific pseudorandom (PN) sequence is selected by more than one access terminal as its preamble in the same access slot. The probability is inversely proportional to the number of preamble sequences available. Mis-detection probability refers to the probability that the transmitted PN sequence is not detected by the base station. The false alarm probability refers to the probability that the access point erroneously determined that the preamble was transmitted when no preamble is actually transmitted.

This probability increases with the number of preambles available.

[0006] The access point then transmits an acknowledgment for each of the detected preambles. A confirmation message may

Include the detected PN sequence, timing offset correction, and channel index for transmission of access data blocks. Access terminals whose PN sequences are confirmed may then transmit the appropriate access data blocks using the assigned resources.

[0007] Since the access point has no prior knowledge of where the access terminal is in the system (i.e. what its power requirement, buffer level, or quality of service may be), an acknowledgment message is transmitted at a sufficiently high power level such that all terminals cells in a given cell can decode the message. A transmit acknowledgment is inefficient as it requires a disproportionate amount of transmit power and / or bandwidth to close the link. Therefore, there is a need to more efficiently send an acknowledgment message to the access terminals in a given cell.

[0008] In the application document US 2002/0003792 A1, a technique is described which can select a frequency from the available frequency spectrum, the frequency being identified by an index. The patent document US 6674787 B1 describes an example of using an access channel.

SUMMARY OF THE INVENTION This need is met by the independent claims. Embodiments minimize the use of the acknowledge channel when transmitting their preamble. The inventive examples consider how information can be efficiently signaled via the access channel during transmission of the access preamble regarding the quality of the forward link channel.

In one embodiment, an apparatus and method for transmitting a channel quality indicator minimizing broadcast channel utilization is described. The metric of the forward link geometry of the observed transmission signals is determined. The channel quality value indicator is determined as a function of the observed transmission signals. The access sequence is randomly selected from one group of a plurality of access sequence groups, each of the plurality of access sequence groups corresponding to a different range of channel quality values.

[0010] The metric of downlink geometry may be determined as a function of observed pilots, noise, and / or traffic on data channels. The number of access sequences in the plurality of access sequence groups is unevenly distributed. In an embodiment, the access sequences are spaced to reflect the distribution of access terminals around the access point. In another embodiment, the access sequences are proportional to the number of access terminals that require a given amount of power to send an acknowledgment indicator to the access terminal.

[0011] Moreover, a method of splitting multiple access sequences is described. A probability distribution of a plurality of access terminals around an access point is determined. The probability distribution is determined as a function of a plurality of access terminals with CQI values ​​within predetermined ranges. Access sequence groups are assigned in proportion to the probability distribution. Access sequences may be reassigned as functions of changing the layout of the access terminals around the access point.

[0012] In another embodiment, an apparatus and method for transmitting a detected acknowledgment is described

-6 access sequences. Access sequence is received. An access sequence may be searched from a lookup table stored in memory to determine at least one attribute of a given access terminal (as a function of the access sequence). The attribute may be information such as channel quality indicator, buffer level, and service indicator quality. The information is then transmitted to the access terminal where the information is proportional to and consistent with the attribute. The information transmitted may include an acknowledgment indicator. The acknowledgment indicator may be transmitted on a shared signaling channel (SSCH).

[0013] Various aspects and embodiments of the invention are described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS The features and characteristics of the present invention will become more apparent from the following detailed description when considered in conjunction with the drawings, wherein the same reference numerals serve for identification, respectively, and wherein:

[0015] FIG. 1 shows a block diagram of a transmitter and receiver;

[0016] FIG. 2 shows an access probe structure - an access probe sequence;

[0017] FIG. 3 shows a traditional link flow between an access terminal and an access point;

[0018] FIG. 4 illustrates an embodiment of the invention that avoids the use of transmit acknowledgment;

[0019] FIG. 5 shows a cell divided with uniform spacing;

[0020] FIG. 6 is a diagram showing weighted partitioning based on quantized CQI values;

[0021] FIG. 7 shows a table stored in memory that subdivides access sequence groups into access sequence subgroups based on various coefficients; and [0022] FIG. 8 shows a flow for a dynamically allocated access sequence.

DETAILED DESCRIPTION [0023] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or structure described herein as "exemplary" need not necessarily be construed as being preferred or advantageous over the other embodiment or structure.

[0024] The techniques described herein for using multiple modulation schemes in a single packet may be used for various communication systems, such as an Orthogonal Frequency Division Multiple Access (CDMA) system. - (Code Division Multiple Access), Time Division Multiple Access (TDMA) - (Time Division Multiple Access), Frequency Division Multiple Access system (OFDM) - (orthogonal frequency division multiplexing), single-input single-output (SISO) system ), multiple-input multipleoutput (MIMO) - (multiple-input multipleoutput), and so on. These techniques can be applied to systems that use incremental redundancy (IR)

-8- (incremental redundancy) and systems that do not use IR (for example, systems that just repeat data).

[0025] Embodiments of the invention avoid using a transmit acknowledgment channel by having access terminals indicating a parameter such as downlink channel quality (i.e., CQI), buffer level requirements, quality of service requirements, etc., when transmitting their preamble. By having the access terminals indicating the channel quality of the forward link, the access point may transmit each acknowledgment on the channel using the appropriate amount of power for a given access terminal or group of access terminals. In the case where an acknowledgment message is transmitted to a group of access terminals, an acknowledgment message is sent to the plurality of access terminals that have indicated the same or similar CQI values ​​(within a range). Embodiments of the invention consider how a CQI can be efficiently signaled via an access channel during transmission of an access preamble.

[0026] "Access Terminal" refers to a device that provides voice and / or data communications to a user. The access terminal may be connected to a computing device such as laptop computers or a desktop computer, or it may be a standalone device such as a personal digital assistant. An access terminal may also be called a subscriber station, subscriber unit, cellular station, wireless device, cellular telephone, remote station, remote terminal, user terminal, user agent, or user equipment. The subscriber station can be a mobile phone, a PCS telephone, a telephone

-9 wireless, Session Initiation Protocol (SIP) telephone

- (Session Initiation Protocol), a wireless local loop station (WLL) - (Wireless Local Loop), a personal digital assistant (PDA) - (Personal Digital Assistant), a wireless capable mobile device, or other processing device connected to a wireless modem.

[0027] "Access point" refers to a device in an access network that communicates over the air interface over one or more sectors with 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 the IP network, by converting the received air interface frames into IP packets. Access points also coordinate attribute management for the air interface. The access point may be a base station, base station sectors, and / or a combination of a Base Transceiver Station (BTS) and a Base Station Controller (BSC).

[0028] FIG. 1 shows a block diagram of a transmitter 110 and a receiver 150 in a wireless communication system 100. Transmitter 110, a TX data processor 120, receives data packets from data source 112. TX data processor 120 processes (e.g., formats, encodes, splits, interleaved, and modulates) each data packet according to the mode selected for that packet and generates up to T data symbol blocks for the packet. The selected mode for each data packet may indicate (1) the packet size (that is, the number of information bits for the packet) and (2) a specific combination of code rate and modulation scheme to be used for each data symbol block of that packet. The controller 130 provides various controls for the data source 112 and the TX data processor 120

-10 for each data packet based on the selected mode.

TX data processor 120 provides a stream of data symbol blocks (e.g., one block for each frame) where blocks for each packet may be interleaved with blocks for one or more other packets.

[0029] The transmitter unit 122 (TMTR) receives a stream of data symbol blocks from the TX data processor 120 and generates a modulated signal. Transmitter unit 122 multiplexes in pilot symbols with 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 with a signal value of zero. Transmitter unit 122 may perform OFDM modulation if OFDM is used by the system. Transmitter unit 122 generates a stream of time-domain samples and further aligns (e.g., converts to analog, upconverts, filters, and amplifies) the sample stream to generate a modulated signal. The modulated signal is then transmitted from the antenna 124 and via the communication channel to the receiver 150.

[0030] At receiver 150, the transmitted signal is received by the antenna 152 and the received signal is provided to the receiver unit 154 (RCVR). Receiver unit 154 matches, digitizes, and pre-processes (e.g., demodulates OFDM) the received signal to obtain received data symbols and received pilot symbols. Receiver unit 154 provides the received data symbols to the detector 156 and the received pilot symbols to the channel estimator 158. The channel estimator 158 processes the received pilot symbols and provides channel estimates (e.g., estimates

-11 channel gain and SINR estimate) for the communication channel.

The detector 156 performs a detection on the received data symbols with the channel estimates and provides the detected data symbols to RX data processor 160. The detected data symbols may be represented by log-likelihood ratios (LLR) for the code bits used to form the data symbols (as described below) or by other representations. As soon as a new block of detected data symbols is received for a given data packet, RX data processor 160 processes (e.g., deinterleaved and decodes) all detected data symbols obtained for that packet and delivers the decoded packet to data sink 162. RX data processor 160 also checks the decoded packet and provides a packet status that indicates whether the packet is decoded correctly or incorrectly.

[0031] A controller 170 receives the channel estimates from the channel estimator 158 and packet status from RX data processor 160. Controller 170 selects a mode for the next data packet to be transmitted to receiver 150 based on the channel estimates. The controller 170 also collects feedback information. The feedback information is processed by TX data processor 182, further conditioned by transmitter unit 184, and transmitted via antenna 152 to transmitter 110.

At transmitter 110, the transmitted signal from receiver 150 is received by antenna 124, conditioned by receiver unit 142, and further processed by RX data processor 144 to recover feedback information sent by receiver 150. Controller 130 receives the received information about feedback, uses ACK / NAK to control the IR transmission of the packet that is sent to receiver 150, and

12 uses the selected mode to process the next data packet to be sent to the receiver 150. Controllers 130 and 170 direct operation at transmitter 110 and receiver 150, respectively. Memory units 132 and 172 provide storage for program codes and data used by controllers 130 and 170, respectively. [0033] FIG. 2 shows an access probe structure and an access probe sequence 200. In FIG. 2, Ns probe sequences are shown where each probe sequence has Np probes. The Media Access Control (MAC) layer protocol broadcasts the access probes by instructing the physical layer to transmit the probe. With this instruction, the MAC access channel protocol provides the physical layer with a number of elements including, but not limited to, power level, access sequence identification, sector pilot PN to which the access probe can be transmitted, timing offset field, and field. control segment. Each probe in the sequence is transmitted with increasing power until the access terminal receives an access grant. Transmission is terminated if the protocol has received a deactivation command, or if the maximum number of probes per sequence has been transmitted. Before transmitting the first probe of all probe sequences, the access terminal creates a persistence test that is used to control congestion on the access channel.

[0034] FIG. 3 shows the traditional call flow between the access terminal and access point 300. Access terminal 304 randomly selects a preamble, or PN sequence, from the PN sequence group and sends 308 the preamble during the access slot to access point 312. Upon receipt of it, access point 312 then transmits 316

Access grant including transmit acknowledgment for each of detected preambles. This acknowledgment is a transmitted acknowledgment transmitted at sufficiently high power such that all access terminals in a given cell are able to decode the transmit acknowledgment. This is considered necessary because the access point does not know in advance where the access terminals are in the system and thus has no knowledge of the power level required for the access terminal to decode a transmit acknowledgment. Upon receipt of access 316, the access terminal 304 sends 320 a payload in accordance with the determined resources allocated in the access granted.

[0035] The transmit acknowledgment described above is relatively inefficient as it requires a disproportionate amount of transmit power and / or bandwidth to close the link. Fig. 4 shows an embodiment 400 to avoid the use of transmit acknowledgment. The access terminal watches 408 transmissions from access points. Upon observation, the access terminal determines the power of the transmissions it is receiving. These observations typically involve determining the quality of the downlink channel from an observed pilot fetch transmission or pilot transmission as part of a shared signaling channel (SSCH).

[0036] The access terminal 404 then randomly selects a preamble, or access sequence, from the access sequence group and sends the preamble 410 to the access point 412. The preamble is transmitted with some forward link quality (CQI) knowledge. CQI information may be transmitted within or combined with a preamble. In a further embodiment, the access sequence is randomly selected from a plurality of access sequence groups, each access sequence group being designated for

-14 range of CQI values. For example, the downlink channel quality indicators may be observed pilot power. The observed pilot power may be quantized to a CQI value based on a predetermined set of values. Thus, a given range of received pilot power may correspond to a given CQI value. Accordingly, the access point 412 can determine the CQI of a given access terminal due to the access sequence selected by the access terminals.

[0037] Since the access terminal sends the forward link channel quality indicator during its initial access attempt with access point 412, the access point 412 has the necessary knowledge to transmit 416 each acknowledgment on the channel using the appropriate amount of power for the designated access terminal 404. In an exemplary embodiment, the message is an acknowledgment may be sent to a group of access terminals with the same or similar CQI values. This can be done by using the SSCH. Thus, based on the power level necessary for the access terminal to successfully receive the transmission, the access point sends an acknowledgment message in the appropriate section of the SSCH message.

[0038] In addition to the CQI information, the access terminal may send other information relevant to the access point during the initial access phase. For example, the access terminal may send a buffer level indicator that indicates the amount of data the access terminal intends to send to the access point. With such knowledge, the access point is able to appropriately size the initial resource allocations.

[0039] The access terminal may also send priority groups or quality of service, this may be used to determine information

Priorities information

-15 access terminals in the event of limited capabilities of the access point or system overload.

[0040] Upon receipt of the access grant message by the access terminal, the access terminal 404 sends 420 a 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 use the CQI knowledge, buffer level, and information service quality as part of the access grant message.

R is determined by the observed metrics of the exemplary embodiment, [0041] FIG. 5 shows a cell 500 divided using even spacing. The cell is divided into a number of R regions in which each region has a probability within a given range. Observations of the forward link geometry are used. For example, metrics such as C / I can be used, where C is the received pilot power and I is the observed noise. Also, C / (C + I) can be used. In other words, some activities are used that use the observed signal strength and noise. These observed metrics correspond to the given CQI values ​​or ranges of values, which thus define the region. For example, Region R1 defines a Region with CQI values ​​corresponding to power and / or noise levels greater than P1. The R2 region defines a region with CQI values ​​corresponding to the power and / or noise levels such that P2> R2> P1. Similarly, Region R3 defines a Region with CQI values ​​corresponding to power and / or noise levels such that P3> R3> P2, and so on. The RN-1 region has CQI values ​​corresponding to power and / or noise levels such that they fall within the range Px> RN-1> Py. Likewise, the RN Region has CQI values

-16 corresponding to the power and / or noise levels observed <Px.

[0042] In theory, up to log2 (N) information bits can be conveyed by selecting to transmit one of the N possible preamble sequences. For example, when N = 1024, not less than log2 (1024) = 10 bits can be carried. Thus, by choosing which preamble sequence to transmit, it is possible for the user to obtain dependent information embedded as part of the preamble transmission.

[0043] A commonly used technique is to then divide N preamble sequences into M distinct sets, denoted as {1,2, ..., M}. To signal one of the log2 (M) possibilities (e.g., log2 (M) bits), a sequence in the appropriate set is selected and transmitted. For example, to signal the message index ke {1,2, ..., M}, a sequence in the kth set is (randomly) selected and transmitted. Assuming proper detection at the receiver, transmitted information (i.e. log2 (M) bit message) can be obtained based on the index of the set to which the received sequence belongs.

[0044] In the partitioning strategy, where the N preamble sequences are evenly divided into M groups (i.e. each group contains N / M sequences). Based on the measured CQI values, one of the preamble sequences from the appropriate set is selected and transmitted.

The collision probability then depends on the mapping / quantization of the measured CQI and a number of simultaneous access attempts.

[0045] This can be represented by considering a simple 2-level quantization of CQI (i.e., M = 2), with Pr (M (CQI) = 1) = a and Pr (M (CQI) = 1) = α, where M (x ) is a quantization function that maps the measured CQI value at one of two levels.

[0046] With the access sequence partitioning evenly, the N preamble sequences are split into two sets with N / 2 sequences in each set. As an example, suppose there are two simultaneous access attempts (that is, exactly two access terminals are trying to access the system in each access slot). The collision probability is expressed as:

<img file="PL1774822T3_D0001.tif" />

[0047] With probability α², the two access terminals want to send M = 1 (i.e. both have a quantized CQI = 1). Since there are N / 2 preamble sequences to choose from in the first set, the collision probability (given that both access terminals select their sequence from that set) is 1 / (N / 2). By the same logic, a collision probability for another set can be derived. [0048] Thus, the overall collision probability depends on the parameter α and the number of simultaneous access attempts. The collision probability can be as high as

2 / Ν (α = 0.1) or as low as 1 / N (a = 0.5). Thus, the best choice of α in this case is α = 0.5. However, it is unclear whether the CQI quantization function resulting in α = 0.5 is the desired function.

[0049] The access point transmits a channel acknowledgment at the power level required to close the link as indicated by the CQI level. In this example, with probability α, the access point must transmit at a power corresponding to that of the broadcast channel, and with probability 1-α, the access point may transmit at some lower power. Thus, at α = 0.5, half the time

-18 access point must transmit channel confirmation. On the other hand, by selecting α = 0.5, the access point is forced to transmit channel acknowledgment less frequently, but with an increase in transmit power in the remaining time and a higher overall collision probability.

[0050] FIG. 6 is a diagram showing a weighted partition 600 based on quantized CQI values. The region is divided into different regions that are not uniformly spaced but rather divided based on quantized CQI values ​​that are weighted. By weighting the regions, additional preamble sequences are available in regions that have a greater probability of access terminals that are in that region (ie, a higher mass function). For example, regions 604, 608, and 612 are larger regions which can correspond to having more access sequences available. Conversely, regions 616 and 620 are smaller regions that can indicate fewer users present and thus fewer access sequences available. Thus, regions can be subdivided based on some prior knowledge of the C / I distribution or received power over a certain range in a given cell. It is contemplated that geographic regions may not always represent the user concentration within given CQI ranges. Instead, the graphic representations of non-uniform spacing are intended to indicate non-uniform distribution of access sequences over a given region of the cell.

[0051] In an embodiment, the probability distribution of access terminals within a 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 day or otherwise.

Adapted as the concentration function of the current access terminals in a given CQI region.

[0052] Thus, the available sequences for initial access are divided into N number of slots. The access terminal determines the interval to be used for an access attempt based on at least the observed pilot strength and buffer level. It is believed that this split may also be determined on several other factors such as packet size, traffic type, bandwidth request, or quality of service. Once a interval is determined, the access terminals select the ID sequence using the even probability over the interval. Of the available sequences for access, a sequence member is reserved for active file operations, and subsequent sequence subsets are available for initial access. In one embodiment, sequences 0, 1, and 2 are reserved for active set operations, and sequences by the total number of access sequences are available for initial access.

[0053] The size of each bin is determined by the access sequence interval field in the system information block. Usually it is part of a sector parameter. The determined N number of bins includes sequence identifiers ranging from a low threshold, a low N interval, to a high threshold, an upper N interval. Both thresholds are determined using the size of the ranges, some of which are given in Table 1 below:

<td rowspan="2">Access sequence interval</td><td colspan="8">The N size of the interval (N from 1 to 8)</td>

<td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td>

<td> 00000</td><td> 0</td><td> 0</td><td> 0</td><td> 0</td><td> 0</td><td> 0</td><td> 0</td><td> 0</td>

<td> 00001</td><td>S2</td><td>S2</td><td>S2</td><td>S2</td><td>S2</td><td>S2</td><td>S2</td><td>S2</td>

<td> 00010</td><td>S3</td><td>S3</td><td>NS</td><td>S1</td><td>S1</td><td>S1</td><td>S1</td><td>S1</td>

<td> 00011</td><td>S1</td><td>S1</td><td>S1</td><td>S3</td><td>S3</td><td>S3</td><td>S1</td><td>S1</td>

<td> 00100</td><td>S1</td><td>S1</td><td>S1</td><td>S1</td><td>S1</td><td>S1</td><td>S3</td><td>S3</td>

<td> 00101</td><td>S3</td><td>S1</td><td>S1</td><td>S3</td><td>S1</td><td>S1</td><td>S3</td><td>S1</td>

<td> 00101</td><td>S1</td><td>S3</td><td>S1</td><td>S1</td><td>S3</td><td>S1</td><td>S1</td><td>S3</td>

<td> 00110</td><td>S1</td><td>S1</td><td>S3</td><td>S1</td><td>S1</td><td>S3</td><td>S1</td><td>S1</td>

<td> 00111</td><td>S3</td><td>S3</td><td>S1</td><td>S3</td><td>S1</td><td>S1</td><td>S1</td><td>S1</td>

<td> 01000</td><td>S1</td><td>S1</td><td>S1</td><td>S3</td><td>S3</td><td>S1</td><td>S3</td><td>S1</td>

[0054] Thus, in this embodiment, the access terminal selects its pilot level based on a ratio, measured in decibels, of fetch pilot power from the sector where the access attempt is made to the total power received in the time slot of the download channel. The pilot thresholds are determined based on the pilot strength segmentation field of the system information message.

[0055] Embodiments describe a technique whereby the access sequence spacing is divided according to the statistics of a quantized CQI. More precisely,

<img file="PL1774822T3_D0002.tif" />

is the probability mass function of the quantized CQI values, where

VfiCQl = 1) = _AND,? t (CQI = 2) = ρ₂, ~ ·,? FiCQI = M) = p_at}

The access sequence interval is then divided to have a similar probability mass function. That is, the ratio of the number of access sequences in each set to the total number of access sequences should be proportional such that [0056]

<img file="PL1774822T3_D0003.tif" />

<img file="PL1774822T3_D0004.tif" />

<img file="PL1774822T3_D0005.tif" />

<td>where</td><td>Nk</td><td>is a number</td><td>sequence</td><td>access in</td><td>harvest</td>

<td colspan="2">Ke {1,2, .., M}</td><td></td><td></td><td></td><td></td>

<td> [0057]</td><td>IN</td><td>example</td><td>describing</td><td>2 — level,</td><td>function</td>

<td colspan="2">quantization</td><td>CQI brings</td><td>following:</td><td></td><td></td>

Pr {M (CQn = 1) = a Pr (M (C2 /) = 2) = 1 - a

The sequence number corresponding to (a) N collisions is accessed wi (1 — α) N.

every set is, therefore

The result of probability

<img file="PL1774822T3_D0006.tif" />

¹ _ ^g , about-^g) ((la) JV) Ν N

N * which is the lowest possible collision probability.

[0058] For a more general setup with M possible CQI levels and U simultaneous trials, the analytical expression of the collision probability becomes more complex.

[0059] In another example, consider M = 6, U = 8, and

N = 1024. Suppose the CQI values ​​are quantized in step

- 5dB. The quantized CQI values ​​are given by [-3, 1,

5, 10, 15, 20] dB with the following probability mass function [0.05, 0.25, 0.25 0.20 0.15 0.10]. That is 5% of the time, users will report CQI values ​​less than 3 dB, 25% of the time with a CQI value between -3 and 1 dB, and so on. The access point may then adjust the power for the channel acknowledgment based on the reported CQI. [0060] Using the proposed access sequence splitting technique, the result of the collision probability is approximately 2.5%. The collision probability using uniform access sequence split is compared to 3.3%. However, to obtain a similar collision probability when uniform partitioning of the access sequence is used, the total number of sequences must be increased by 25% to 1280. Accordingly, the greater number of access sequences for the search directly translates into a higher degree of complexity and a higher probability of false positives. alarm.

This partitioning strategy may also be used when signaling other information such as packet size, traffic type, and bandwidth request over the access channel. This is especially useful when an access channel (preamble part) is used as a means for users to return to the system or request resources. If the information on the statistics of the information to be conveyed is known (e.g., the percentage of connection time of certain traffic (http, ftp, SMS) is requested or how much bandwidth is frequently required, etc.), then this information may be used in determining the interval of the access preamble sequence.

[0062] FIG. 7 shows a table 700 stored in memory that subdivides access sequence groups into access sequence subgroups based on various coefficients. The factors include CQI ranges, buffer level, quality of service, packet size, bandwidth request, or other factors. The number of access sequences in a given subgroup may be initially determined from past statistics of the past concentration of users in a given cell as a function of the coefficients that are taken into account. Thus, each cell may have a predetermined access sequence mass distribution for combinations of different coefficients. In this way, the collision probability of multiple users selecting the same access sequence is minimized.

[0063] In an embodiment, the number of access sequences assigned to different combinations of coefficients may change dynamically based on changes in the composition of user needs. Thus, if more users migrate to a region with a CQI within a given range, and a buffer level of a certain amount, and other different factors, then the region may be assigned additional access sequences. The dynamic allocation of access sequences thus mimics an optimal scenario whereby the likelihood of collisions is minimized.

[0064] FIG. 8 shows such a flow 800. Initial partitions are set 804, thereby dividing a plurality of access sequences into a number of access sequence groups. These groups can be based on ranges of CQI values. In an embodiment, the initial set may be based on uniform distributions of access sequences. In another embodiment, the initial interval sizes may be based on historical data. Counter 808 counts access attempts in each subset. Counter can track

- 24 time access attempts to determine if there are patterns of varying heavy or light usage. Based on these access attempts over time, the expected value of the access attempts in the given subsets may be updated 812. The expectation value may be represented by the following equation:

<img file="PL1774822T3_D0007.tif" />

where Em is the expected value, m is the number of access sequences in a given subset, and β is the forgetting factor. The forgetfulness factor calculates the mean recursively so that it gives more weight to more recent data and less weight to less recent data.

Based on the new expectation value, the new subset size may be determined as 816. In an embodiment, the subset size is determined by the following equation:

<img file="PL1774822T3_D0008.tif" />

where Nm is the new size of the subset, Ek is the "old" expectation value for the kth subset, m is a given subset of M integer subsets.

[0066] A determination is made 820 as to whether the newly determined subset size is substantially different from the predetermined subset size. The threshold that is "substantially different" is configurable. if

A determination is made, and the newly determined subset size is substantially different 824, then the subset sizes are reset. If not (828), current member sizes are kept 832.

[0067] Various aspects and features of the present invention have been described above with reference to specific embodiments. As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to be construed as not exclusively including elements or limitations that follow those terms. Accordingly, the system, method, or other embodiments that include the set of elements are not limited to those elements, and may include other elements not specifically mentioned or which are peculiar to the claimed embodiment.

[0068] While the present invention has been described with reference to specific embodiments, it is to be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and corrections to the above-described embodiments are possible. These variations, modifications, additions and corrections are contemplated to fall within the scope of the invention as defined in the following claims.