HK1105750B - Efficient signaling over access channel - Google Patents

Description

Efficient signaling over an access channel

Cross Reference to Related Applications

This application claims priority to U.S. provisional application No. 60/590,113, filed on 21/7/2004, the latter of which is incorporated by reference herein in its entirety.

Technical Field

The present disclosure relates generally to wireless communications, and more specifically to data transmission in a multiple access wireless communication system.

Technical Field

The access terminal initially contacts the access point on the reverse link using the access channel. An access terminal may initiate an access attempt to request a dedicated channel, register or perform a handover, etc. Prior to initiating an access attempt, the access terminal receives information from the downlink channel to determine the strongest signal strength from nearby access points and to acquire a downlink opportunity. The access terminal may then decode information transmitted by a given access point on the broadcast channel that is relevant to the selection of parameters that control the access terminal's access attempt.

In some wireless communication systems, the access channel refers to both probe messages and submitted messages. In other wireless communication systems, the access channel refers only to the probe message. Once the probe message is acknowledged, a message is transmitted that controls access attempts by the access terminal.

In an Orthogonal Frequency Division Multiple Access (OFDMA) system, an access terminal typically divides an access transmission to be transmitted on an access channel into two parts, a preamble transmission and a payload transmission. To prevent intra-cell interference due to lack of precise timing on the reverse link during access preamble transmission, CDM based transmission can be time division multiplexed with the other remaining transmissions (i.e., traffic, control, and access payloads). To access the system, the access terminal then randomly selects a PN sequence from a set of PN sequences and transmits it as its preamble in the access slot.

The access point searches for any preamble (i.e., all possible PN sequences) that may be transmitted in the access slot. Access preamble transmission performance is measured in terms of collision probability, false detection probability, and false alarm probability. The collision probability refers to the probability of selecting a particular pseudo-random sequence (PN) as a respective preamble in the same access slot by multiple access terminals. This probability is inversely proportional to the number of available preamble sequences. The false detection probability refers to the probability that the base station does not detect the transmitted PN sequence. The false alarm probability refers to the probability of an access point falsely declaring that a preamble was transmitted when it was not actually transmitted. This probability increases with the number of available preambles.

The access point then transmits an acknowledgement message for each detected preamble. The acknowledgement message may include the detected PN sequence, time offset correction, and channel index for access payload transmission. Those access terminals whose PN sequences have been acknowledged may then terminate to transmit the corresponding access payload using the assigned resources.

Because the access point does not know the location of the access terminal in the system in advance (i.e., what its power requirements, buffer level, or quality of service is), the acknowledgment message is broadcast at a power level high enough so that all access terminals within a given cell can decode the message. This broadcast acknowledgement is inefficient because it requires a disproportionate amount of transmission power and/or frequency bandwidth to close the link. Therefore, there is a need to more efficiently send acknowledgement messages to access terminals within a given cell.

Disclosure of Invention

Embodiments of the present invention minimize the use of a broadcast acknowledgement channel during preamble transmission. Embodiments of the present invention also address the problem of how to efficiently transmit information about forward link channel quality over an access channel during access preamble transmission.

In one embodiment, an apparatus and method for transmitting channel quality indicators while minimizing the use of broadcast channels is described. A metric of forward link geometry (geometry) of an observed transmission signal is determined. An indicator of channel quality value is determined based on the observed transmission signal. One access sequence is randomly selected from one of a plurality of sets of access sequences, wherein each of the plurality of sets of access sequences corresponds to a different range of channel quality values.

A metric of forward link geometry may be determined based on observed pilot signals, noise, and/or traffic on the data channel. The plurality of access sequences in the plurality of sets of access sequences are non-uniformly distributed. In one embodiment, access sequences are assigned to reflect the distribution of access terminals around an access point. In another embodiment, the access sequence is allocated in proportion to the number of access terminals that require a given amount of power to send the acknowledgement indicator to the access terminals.

In another embodiment, a method for partitioning a plurality of access sequences is described. A probability distribution is determined for a plurality of access terminals located around an access point. The probability distribution is determined based on a plurality of access terminals having CQI values within a predetermined range. According to the probability distribution, an access sequence group is assigned. The access sequences may be reallocated according to changes in the distribution of access terminals located around the access point.

In another embodiment, an apparatus and method for transmitting an acknowledgement of a detected access sequence is described. An access sequence is received. The access sequence may be looked up in a look-up table stored in memory to determine at least one attribute (in terms of access sequence) for a given access terminal. The attributes may be information such as channel quality indicator, buffer level and quality of service indicator. Information is then transmitted to the access terminal, wherein the information matches and conforms to the attribute. The transmitted information may include an acknowledgement indicator. The acknowledgement indicator may be transmitted over a Shared Signaling Channel (SSCH).

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

Drawings

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:

fig. 1 shows a block diagram of a transmitter and a receiver;

fig. 2 shows an access probe message structure and an access probe sequence;

fig. 3 illustrates a conventional call flow between an access terminal and an access point;

FIG. 4 illustrates one embodiment of the present invention that avoids the use of broadcast acknowledgements;

FIG. 5 shows a cell divided with uniform spacing;

FIG. 6 is a diagram illustrating weighted partitioning based on quantized CQI values;

fig. 7 illustrates a table stored in memory that divides a set of access sequences into a plurality of access sequence sub-sets based on a plurality of factors; and

fig. 8 shows a process for dynamically allocating an access sequence.

Detailed Description

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.

The techniques described herein for employing multiple modulation schemes for a single packet may be used in various communication systems such as Orthogonal Frequency Division Multiple Access (OFDMA) systems, Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiplexing (OFDM) based systems, Single Input Single Output (SISO) systems, Multiple Input Multiple Output (MIMO) systems, and so on. These techniques may be used in systems that employ Incremental Redundancy (IR) as well as systems that do not employ IR (e.g., systems that merely duplicate data).

Embodiments of the present invention avoid the use of broadcast acknowledgements by having the access terminal indicate parameters such as forward link channel quality (i.e., CQI), buffer level requirements, quality of service requirements, etc., during preamble transmission. By having the access terminal indicate the forward link channel quality, the access point can transmit each acknowledgment on the channel with the appropriate amount of power for a given access terminal or group of access terminals. In the case of transmission of an acknowledgement message to a group of access terminals, the acknowledgement message is sent to a plurality of access terminals that specified the same or similar CQI value (within a certain range). Embodiments of the present invention also address the problem of how to efficiently send CQI on the access channel during access preamble transmission.

An "access terminal" refers to a device that provides voice and/or data connectivity to a user. The access terminal may be connected to a computing device such as a laptop or desktop computer, or it may be a stand-alone 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 agent, or user device. A subscriber station may be a portable telephone, a 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.

An "access point" refers to a device in an access network that communicates over the air-interface, through one or more sectors, with access terminals or other access points. The access point acts as a router between the access terminal and other parts of the access network, which may include an IP network, and converts received air-interface frames into IP packets. The access point may also assist in the management of attributes for the air interface. An access point may be comprised of a base station, a sector of a base station, and/or a Base Transceiver Station (BTS) and a Base Station Controller (BSC).

Fig. 1 shows 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, codes, partitions, interleaves, and modulates) each data packet in accordance with a mode selected for that packet and generates T blocks of data symbols for that packet. The mode selected for each data packet may indicate: (1) a packet size (i.e., the number of bits of the information bits of the packet), and (2) a particular combination of code rate and modulation scheme employed per block of data symbols of the packet. The controller 230 controls the data source 212 and TX data processor 220 for each data packet based on the selected mode. TX data processor 220 provides a series of blocks of data symbols (e.g., one block per frame), where the blocks of each packet may be interleaved with the blocks of one or more other packets.

A transmitter unit (TMTR)222 receives the series of blocks of data symbols from TX data processor 220 and generates a modulated signal. Transmitter unit 222 multiplexes pilot symbols with the data symbols (e.g., using time, frequency, and/or code division multiplexing) and obtains a stream of transmission symbols. Each transmission symbol may be a data symbol, a pilot symbol, or a null symbol having a signal value of 0. If the system employs OFDM, transmitter unit 222 may perform OFDM modulation. Transmitter unit 222 generates a time-domain sample stream and also processes (e.g., converts to analog, frequency upconverts, filters, and amplifies) the sample stream to generate a modulated signal. The modulated signal is then transmitted from antenna 224 and transmitted over a communication channel to receiver 250.

At receiver 250, an antenna 252 receives the transmitted signal and provides a received signal to a receiver unit 254 (RCVR). Receiver unit 254 conditions, digitizes, and pre-processes (e.g., OFDM demodulates) the received signal to obtain received digital symbols and received pilot symbols. Receiver unit 254 provides the received data symbols to a detector 256 and the received pilot symbols to a channel estimator 258. Channel estimator 258 processes the received pilot symbols and provides channel estimates (e.g., channel gain estimates and SINR estimates) for the communication channel. Detector 256 uses the channel estimates to detect the received data symbols and provides detected data symbols to an RX data processor 260. The detected data symbols may be represented by log-likelihood ratios (LLRs) of the code bits used to form the data symbols, as described below, or by other representations. Once a new block of detected data symbols is acquired for a given data packet, RX data processor 260 processes (e.g., deinterleaves and decodes) all detected data symbols acquired for the packet and provides a decoded packet to data receiver 262. RX data processor 260 also examines the decoded packet and provides a packet status indicating whether the decoding of the packet is correct or erroneous.

A controller 270 receives the channel estimates from the channel estimator 258 and the packet status from the RX data processor 260. Controller 270 selects a mode for the next data packet to be transmitted based on the channel estimate. The controller 270 also aggregates the feedback information. The feedback information is processed by a TX data processor 282, further conditioned by a transmitter unit 284, and transmitted via antenna 252 to transmitter 210.

At transmitter 210, the transmission signal is received from receiver 250 via antenna 224, conditioned by a receiver unit 242, and processed by an RX data processor 244 to recover the feedback information sent by receiver 250. Controller 230 obtains the received feedback information, controls the IR transmission of packets to be sent to receiver 250 with the ACK/NAK, and processes the next data packet to be sent to receiver 250 using the selected mode. Controllers 230 and 270 control operation at transmitter 210 and receiver 250, respectively. Memory units 232 and 272 store program codes and data used by controllers 230 and 270, respectively.

Fig. 2 shows an access probe message structure and access probe sequence 200. In fig. 2, Ns probe sequences are shown, with Np probe messages per probe sequence. The medium access control layer (MAC) protocol transmits access probe messages by instructing the physical layer to transmit probe messages. With this instruction, the access channel MAC protocol provides many elements to the physical layer including, but not limited to: power class, access sequence identification, pilot PN of the sector to which the access probe message is to be transmitted, time offset field, and control field. Each probe message in a sequence is transmitted at an incremental power until an access grant is received by the access terminal. If the protocol receives a deactivate command or if a maximum number of probe messages per sequence have been transmitted, the transmission is terminated. The access terminal performs a persistence test for controlling congestion on the access channel prior to transmitting the first probe message of all probe sequences.

Fig. 3 illustrates a conventional call flow between an access terminal and an access point 300. The access terminal 304 randomly selects a preamble or PN sequence from a set of PN sequences and then transmits the preamble to the access point 312(308) in an access slot. Upon receipt, the access point 312 then transmits an access grant including a broadcast acknowledgement for each detected preamble (316). The acknowledgement is a broadcast acknowledgement transmitted at a higher power sufficient for all access terminals within a given cell to decode the broadcast acknowledgement. This is believed necessary because the access point does not know the location of the access terminal in the system in advance and therefore does not know the power level required for the access terminal to decode the broadcast acknowledgement. Upon receiving the access grant (316), the access terminal 304 transmits a payload in accordance with the defined resources allocated in the access grant (320).

Since the broadcast acknowledgment transmissions described above require a disproportionate amount of transmission power and/or frequency bandwidth in order to close the link, they are relatively inefficient. Fig. 4 illustrates an embodiment 400 that avoids the use of broadcast acknowledgements. The access terminal observes transmissions from the access point (408). In observation, the access terminal determines the power of the transmission it receives. Such observations typically involve determining the forward link channel quality from the observed acquisition pilot signal transmission or the pilot transmission as part of a common signaling channel (SSCH).

The access terminal 404 then randomly selects a preamble or access sequence from a set of access sequences and transmits the preamble 410 to the access point 412. The preamble is transmitted along with some information of the forward link Channel Quality (CQI). The CQI information may be transmitted within or in addition to the preamble. In another embodiment, an access sequence is randomly selected from a plurality of sets of access sequences, wherein each set of access sequences is assigned a range corresponding to a CQI value. For example, the forward link channel quality indicator may be an observed pilot signal power. The observed pilot signal power may be quantized to a CQI value according to a set of predetermined values. Thus, a given range of received pilot signal power may correspond to a given CQI value. Thus, the access point 412 can determine the CQI for a given access terminal through the access sequence selected by the access terminal.

Because the access terminal sends an indicator of the forward link channel quality during its initial attempt to access the access point 412, the access point 412 knows the information needed to transmit each acknowledgment 416 on the channel, with each acknowledgment being transmitted with the appropriate power for the given access terminal 404. In one embodiment, the confirmation message may be sent to a group of access terminals having the same or similar CQI value. This can be achieved by using SSCH. Thus, the access point sends the acknowledgment message in the appropriate portion of the SSCH message, depending on the power level required for the access terminal to successfully receive the transmission.

In addition to CQI information, the access terminal may also transmit other useful information during the initial access phase. For example, the access terminal may send a buffer level indicator to indicate the amount of data that the access terminal intends to send to the access point. With these messages, the access point can appropriately determine the initial resource allocation amount.

The access terminal may also send information about the priority group or quality of service. This information may be used to prioritize access terminals in the event of limited access point capability or system overload.

Once the access terminal receives the access grant message, the access terminal 404 transmits the payload 420 according to the resources defined in the access grant message. By receiving additional information during the initial access phase, the access point can utilize the known CQI, buffer level, and quality of service information as part of the access grant message.

Fig. 5 shows a cell 500 partitioned with uniform spacing. The cell is divided into a number of regions R, where each region is defined by the probability of the observation metric falling within a given range. In one embodiment, forward link geometry observations are employed. For example, a metric such as C/I may be employed, where C is the received pilot power and I is the observed noise. C/(C + I) may also be employed. In other words, some metric used takes advantage of the observed signal power and noise. These observation metrics correspond to a given CQI value or range of values, so it can define a region. For example, the region R₁CQI values for defined regions corresponding to power and/or noise levels greater than P₁. Region R₂The CQI value of a defined region satisfies P corresponding to a power and/or noise level₂＞R₂＞P₁. Similarly, the region R₃The CQI value of a defined region satisfies P corresponding to a power and/or noise level₃＞R₃＞P₂And so on. Region R_N-1Having a power and/or noise level for the CQI value falling within the range P_x＞R_N-1＞P_yAnd (4) the following steps. Similarly, the region R_NHaving a CQI value corresponding to a power and/or observed noise level less than P_x。

Theoretically, by selecting one of N possible preamble sequences for transmission, a maximum of log can be transmitted₂(N) bits of information. For example, when N102At 4 hours, log can be transmitted₂(1024) 10 bits. Thus, by selecting which preamble sequence to transmit, user-dependent information can be embedded as part of the preamble transmission.

One common technique is to divide the N preamble sequences into M different sets, labeled 1, 2, …, M. Selecting and transmitting a sequence in an appropriate set to send log₂(M) possibilities (i.e., log)₂(M) bits). For example, to send a message index k e {1, 2, …, M }, one sequence in the kth set is (randomly) selected and transmitted. Assuming correct detection at the receiver, the transmission information (i.e., the log) can be obtained from the index of the set to which the received sequence belongs₂(M) bit message).

In the uniform partitioning strategy, the N preamble sequences are evenly partitioned into M groups (i.e., each group includes N/M sequences). Based on the measured CQI value, a preamble sequence is selected from an appropriate set and transmitted. The collision probability then depends on the mapping/quantization of the measured CQI value and the number of simultaneous access attempts.

This can be illustrated by considering a simple 2-level quantization of the CQI (i.e., M ═ 2), in which case Pr (M (CQI) ═ 1) ═ α and Pr (M (CQI) ═ 1) ═ α, where M (x) is a quantization function that maps the measured CQI values onto one of the two levels.

With uniform access sequence partitioning, the N preamble sequences are partitioned into two sets, where each set includes N/2 sequences. For example, assume that there are two access attempts at the same time (i.e., exactly two access terminals attempting to access the system in each access slot). The collision probability is represented by the following formula:

due to the probability a²Both access terminals want to send M1 (i.e., they both quantize the CQI level to 1). Since there are N/2 preamble sequences to select from the first set, the collision probability (meaning that both access terminals select their sequences from this set) is 1/(N/2). The collision probabilities for other sets may also be derived, according to the same logic.

The total collision probability thus depends on the parameter a and the number of simultaneous access attempts. The access collision may be as high as 2/N (α ═ 0, 1), or as low as 1/N (α ═ 0.5). Therefore, in this case, the optimum choice of α is 0.5. However, it is unclear whether the CQI quantization function that yields α of 0.5 is a desired function.

The access point will transmit a channel confirmation based on the power level required to close the link as indicated by the CQI level. In this example, the access point is to transmit at a power corresponding to the broadcast channel due to the probability α; while the access point may transmit at a lower power due to the probability 1-alpha. Therefore, since α is 0.5, the access point has half the time to broadcast the channel acknowledgement. On the other hand, by choosing α to be 0.5, the access point is forced to broadcast the channel confirmation less frequently, but this results in increased transmission power and increased overall collision probability for the remaining time.

Fig. 6 is a diagram illustrating weighted partitioning 600 based on quantized CQI values. Instead of dividing the region into a plurality of regions of uniform space, the division is made according to weighted quantized CQI values. By weighting these regions, the probability that an access terminal is in a region is greater (i.e., a higher clustering function), and additional preamble sequences are available in such regions. For example, regions 604, 608, and 612 are larger regions that may correspond to a larger number of available access sequences. In contrast, regions 616 and 620 are smaller regions, meaning that there are a smaller number of users and therefore fewer available access sequences. Thus, the area can be subdivided with respect to the allocation of C/I or received power within a particular range in a given cell being known in advance. It is contemplated that the geographic region does not always represent an area of concentrated users within a given CQI range. Conversely, a graphical representation of non-uniform spacing is used to give a non-uniform distribution of access sequences across a given cell region.

In one embodiment, the probability distribution of access terminals within a cell may be dynamically varied according to the distribution of access terminals over time. Thus, certain partitioned regions may become larger or smaller depending on whether or not there are access terminals at a given time of day, or may be adjusted depending on how concentrated the access terminals are present in a given CQI region.

Thus, the sequence available for initial access is divided into N partitions. The access terminal determines a partition for an access attempt based at least on the observed pilot power and the buffer level. It is contemplated that the partition may also be determined based on other factors, such as packet size, traffic type, bandwidth requirements, or quality of service. Once the partition is determined, the access terminal selects the sequence ID with a uniform probability over the partition. Among the sequences available for access, one subsequence is reserved for active set operation, while another subsequence may be used for initial access. In one embodiment, reserved sequences 0,1, and 2 are used for active set operation, while sequence 3 of all access sequences may be used for initial access.

The size of each partition depends on the access sequence partition in the system information block. This is typically part of the sector parameters. The particular partition number N includes sequence identifiers ranging from a low threshold (partition N lower bound) to a high threshold (partition N upper bound). Both thresholds are determined by using partition sizes, which are given in part in table 1 below:

thus, in this embodiment the access terminal selects a pilot level based on the ratio (expressed in decibels) of the acquired pilot power for the sector in which the access attempt is located to the total power received in the acquisition channel slot. The pilot threshold value is determined based on the pilot strength field in the system information message.

Various embodiments describe a technique whereby the access sequence space is partitioned according to statistics of quantized CQI. More specifically, the present invention is described in detail,

p＝[p₁p₂…p_M]

is a probability clustering function (mass function) of the quantized CQI value, wherein

Pr(CQI＝1)＝p₁，Pr(CQI＝2)＝p₂，…，Pr(CQI＝M)＝p_M).

Then, the access sequence space is divided, so as to obtain similar probability cluster functions. That is, the ratio of the number of access sequences to the total number of access sequences in each set should be proportional, and thus,

p＝[p₁p₂…p_M](i.e. the)

Wherein N is_kIs the number of access sequences in the set K e 1, 2, …, M.

In an example describing a two-stage CQI quantization function, the following equation results:

pr (m (cqi) ═ 1 ═ α and Pr (m (cqi) ═ 2) ═ 1- α

Thus, the number of access sequences in each set is (α) N and (1- α) N, respectively. The resulting collision probability is:

which is the smallest probability of collision possible.

For a more general setup, with M possible CQI levels and U simultaneous attempts, the analytical expression for the collision probability would be more complex.

In another example, consider M6, U8 and N1024. It is assumed that the CQI values are quantized in steps of 4-5 db. The CQI value is given by [ -3, 1, 5, 10, 15, 20] decibels with the following probability quality function [0.05, 0.25, 0.25, 0.20, 0.15, 0.10 ]. That is, the user will have 5% of the time to report a CQI value below-3 db, 25% of the time to report a CQI value between-3 and 1 db, and so on. The access point may then adjust the power of the acknowledgement channel based on the reported CQI value.

With this proposed access sequence partitioning technique, the resulting collision probability is approximately 2.5%. In contrast, the collision power with uniform access sequence partitioning is 3.3%. However, when uniform access sequence division is used, in order to obtain similar collision power, the total number of sequences needs to be increased by 25% to reach 1280. Therefore, the large number of access sequences to be searched translates directly into high complexity and high false alarm probability.

This partitioning strategy can also be used to send other information such as packet size, traffic type and bandwidth request to access channels. This strategy is particularly useful when the access channel (preamble portion) is used as a means for users to go back into the system or request resources. If statistical information about the information to be transmitted is known (e.g., the percentage of time a certain traffic connection (http, ftp, SMS) is requested or the bandwidth typically required, etc.), this information can be used to determine the partition of the access preamble sequence space.

Fig. 7 shows a table 700 stored in memory that divides a set of access sequences into sub-sets of access sequences based on different factors. These factors include CQI range, buffer level, quality of service, packet size, frequency bandwidth request, or other factors. The number of access sequences in a given subgroup may initially depend on statistics of past concentration of users within a given cell, which statistics are made based on factors considered. Thus, each cell may have a predetermined cluster distribution of access sequences for a combination of various factors. In this way, the probability of collision for multiple users selecting the same access sequence is minimized.

In one embodiment, the number of access sequences assigned to a combination of factors may be dynamically changed according to changes in the composition of the user's needs. Thus, if a certain area to which a large number of users move has a CQI within a given range and a certain amount of buffer level and other various factors, the area may be allocated an additional access sequence. Thus, dynamically allocating access sequences simulates an optimal scenario that minimizes the probability of collisions.

Fig. 8 shows a process 800. An initial partition is set (804), whereby a plurality of access sequences are divided into a plurality of sets of access sequences. These groups may be based on a range of CQI values. In one embodiment, the initial setting may be based on a uniform distribution of access sequences. In another embodiment, the initial partition size may be based on historical data. A counter 808 counts the access attempts in each subset. The counter may track access attempts over time to determine if there is a usage or heavy or light changing pattern. Based on this access attempt over time, the expected value of the access attempt in the given subset is updated (812). The expected value can be expressed by the following formula;

E_m：＝(1-β)E_m+βα_m(α_m-1)

wherein E is_mIs the expected value; a is_mRepresenting the number of access sequences in a given subset, and β is a forgetting factor. The forgetting factor recursively calculates an average value that will be comparedA large weight gives newer data and a smaller weight gives older data.

Based on the new expected value, a new subset size is determined (816). In one embodiment, the subset size is determined by the following equation:

wherein N is_mIs a new subset size, E_kIs the "old" expected value for the kth subset, and M is a given subset of the total of M subsets.

A determination is made as to whether the newly determined subset size is significantly different from the previously set subset size (820). The threshold for determining whether to "significantly differ" is configurable. If the newly determined subset size is determined to be significantly different (824), the subset size is reset. Otherwise (828), the current subset size is maintained (832).

Various aspects and features of the present invention have been described above with reference to specific embodiments. To the extent that the term "includes," "including," or other words are used in this application, they are not to be construed as including only the elements or limitations that follow the term. Thus, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, but may also include other elements not expressly listed or inherent to the claim.

Although the invention is described herein with reference to specific embodiments, it should be understood that these embodiments are exemplary and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention as described in the following claims.

Claims (45)

1. In a wireless communication system, a method for determining a channel quality indicator, the method comprising:

determining a metric of the observed transmission;

determining an estimate of channel quality based at least on the measure of the observed transmission;

randomly selecting one access sequence from one of a plurality of sets of access sequences, wherein the plurality of sets of access sequences correspond to different ranges of channel quality values, and wherein the selected access sequence is from a set of access sequences of the plurality of sets of access sequences that corresponds to the determined channel quality estimate; and

the selected access sequence is transmitted.

2. The method of claim 1, wherein determining the metric further comprises:

the power of the observed pilot signal is determined.

3. The method of claim 1, wherein determining the channel quality estimate further comprises:

a ratio of received pilot power to noise is determined.

4. The method of claim 1, wherein determining the channel quality estimate further comprises:

a ratio of the received pilot power to a sum of the received pilot power and the noise is determined.

5. The method of claim 1, wherein a plurality of access sequences in the plurality of sets of access sequences are non-uniformly distributed.

6. The method of claim 1, wherein the sending further comprises:

the transmission is performed according to a Frequency Division Multiplexing (FDM) scheme.

7. The method of claim 1, wherein the sending further comprises:

the transmission is performed according to a Code Division Multiplexing (CDM) scheme.

8. The method of claim 1, wherein the sending further comprises:

the transmission is performed according to an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.

9. The method of claim 1, wherein selecting further comprises:

information indicating the needs of the access terminal is selected.

10. The method of claim 9, wherein the selection information further comprises:

information buffer level requirements, quality of service requirements, forward link channel quality indicators are selected.

11. In a wireless communication system, an apparatus for determining a channel quality indicator, the apparatus comprising:

a receiver for receiving observed transmissions;

a processor configured to determine a metric of the observed transmission and to determine a channel quality estimate based at least on the metric of the observed transmission;

a storage unit configured to store a plurality of sets of access sequences, wherein the plurality of sets of access sequences correspond to different ranges of channel quality values;

a selector for randomly selecting an access sequence from one of the groups of access sequences, the group of access sequences corresponding to the determined channel quality value; and

a transmitter for transmitting the selected access sequence.

12. The apparatus of claim 11, the processor further comprising:

a received pilot power to noise ratio is determined.

13. The apparatus of claim 11, a plurality of access sequences in the plurality of sets of access sequences are non-uniformly distributed.

14. The apparatus of claim 11, wherein the transmitter is further configured to transmit in accordance with a Frequency Division Multiplexing (FDM) scheme.

15. The apparatus of claim 11, wherein the transmitter is further configured to transmit in accordance with a Code Division Multiplexing (CDM) scheme.

16. The apparatus of claim 11, wherein the transmitter is further configured to transmit in accordance with an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.

17. The apparatus of claim 11, wherein the selector is further configured to select information indicative of access terminal requirements.

18. The apparatus of claim 17, wherein the information indicative of access terminal requirements comprises buffer level, quality of service requirements, forward link channel quality indicator.

19. In a wireless communication system, an apparatus for determining a channel quality indicator, comprising:

a power level determination module to determine a power level of an observed transmission;

a CQI value determination module for determining a CQI value based on the observed power level of the transmission;

an access sequence selection module to randomly select an access sequence from one of a plurality of sets of access sequences, wherein the plurality of sets of access sequences correspond to different ranges of CQI values, and wherein the selected access sequence is from a set of access sequences of the plurality of sets of access sequences that corresponds to the determined CQI value; and

means for transmitting the selected access sequence.

20. The apparatus of claim 19, wherein the power level determination module further comprises:

means for determining a power level of an observed pilot signal.

21. The apparatus of claim 19, wherein a plurality of access sequences in the plurality of sets of access sequences are non-uniformly distributed.

22. The apparatus of claim 19, wherein means for transmitting further comprises means for transmitting in accordance with a Frequency Division Multiplexing (FDM) scheme.

23. The apparatus of claim 19, wherein means for transmitting further comprises means for transmitting according to a Code Division Multiplexing (CDM) scheme.

24. The apparatus of claim 19, wherein means for transmitting further comprises means for transmitting in accordance with an Orthogonal Frequency Division Multiplexing (OFDM) scheme.

25. The apparatus of claim 19, wherein the means for transmitting further comprises means for transmitting in accordance with an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.

26. The apparatus of claim 19, wherein the access sequence selection module further comprises:

means for selecting information indicative of access terminal requirements.

27. The apparatus of claim 26, wherein the means for selecting information further comprises selecting information regarding buffer level requirements, quality of service requirements, and/or forward link channel quality indicators.

28. In a wireless communication system, a method for transmitting information regarding access terminal requirements, the method comprising:

determining a received power level of an observed pilot signal;

determining a CQI value according to the received power level;

randomly selecting one access sequence from one of a plurality of sets of access sequences, wherein the plurality of sets of access sequences correspond to a plurality of predetermined factors, the predetermined factors including a plurality of ranges of CQI values; and

the selected access sequence is transmitted.

29. The method of claim 28, wherein the predetermined factors further include one or more of: range of buffer levels, packet size, traffic type, frequency bandwidth requirements, and range of quality of service indicators.

30. In a wireless communication system, a method for transmitting a Channel Quality Indicator (CQI), the method comprising:

determining a power level of an observed pilot signal;

determining a CQI value according to the power level of the observed pilot signal;

randomly selecting one access sequence from one of a plurality of sets of access sequences, wherein the plurality of sets of access sequences correspond to different CQI values;

appending the CQI value to the selected access sequence; and

transmitting the access sequence and CQI value.

31. A method for partitioning a plurality of access sequences, the method comprising:

determining a probability distribution for a plurality of access terminals located around an access point, wherein the probability distribution is a function of the plurality of access terminals, the plurality of access terminals being divided into a plurality of subgroups, wherein each subgroup is classified according to a CQI value within a predetermined range; and

allocating a plurality of sets of access sequences in proportion to the probability distribution, wherein the plurality of sets of access sequences correspond to different ranges of forward link CQI values.

32. The method of claim 31, further comprising:

reallocating access sequences according to changes in the distribution of access terminals located around the access point.

33. In a wireless communication system, an apparatus for transmitting information regarding access terminal requirements, the apparatus comprising:

a received power level determination module for determining a received power level of an observed pilot signal;

a CQI value determining module for determining a CQI value according to the received power level;

an access sequence selection module for randomly selecting an access sequence from one of a plurality of sets of access sequences, wherein the plurality of sets of access sequences correspond to a plurality of predetermined factors, wherein the predetermined factors include a plurality of ranges of CQI values; and

means for transmitting the selected access sequence.

34. The apparatus of claim 33, wherein the predetermined factors further comprise one or more of: range of buffer levels, packet size, traffic type, frequency bandwidth requirements, and range of quality of service indicators.

35. In a wireless communication system, an apparatus for transmitting a Channel Quality Indicator (CQI), the apparatus comprising:

a power level determination module for determining a power level of an observed pilot signal;

a CQI value determining module for determining a CQI value according to the power level of the observed pilot signal;

an access sequence selection module for randomly selecting an access sequence from one of a plurality of sets of access sequences, wherein the plurality of sets of access sequences correspond to different CQI values;

means for appending the CQI value to the selected access sequence; and

means for transmitting the access sequence and CQI value.

36. An apparatus for partitioning a plurality of access sequences, the apparatus comprising:

a probability distribution determination module for determining a probability distribution of a plurality of access terminals located around an access point, wherein the probability distribution is a function of the plurality of access terminals, the plurality of access terminals being divided into a plurality of subgroups, wherein each subgroup is classified according to a CQI value within a predetermined range; and

means for assigning a plurality of sets of access sequences in proportion to the probability distribution, wherein the plurality of sets of access sequences correspond to different ranges of forward link CQI values.

37. The apparatus of claim 36, further comprising:

means for reallocating access sequences based on changes in the distribution of access terminals located around the access point.

38. In a wireless communication system, a method for transmitting an acknowledgement of a detected access sequence, the method comprising:

receiving an access sequence;

determining at least one attribute of a given access terminal based on the access sequence, wherein the attribute comprises a channel quality indicator; and

transmitting an indicator of acknowledgment using an appropriate power according to the channel quality indicator.

39. The method of claim 38, wherein the attributes further comprise at least one of a buffer level indicator, a priority level indicator, and a quality of service indicator.

40. The method of claim 38, further comprising:

an indicator of acknowledgement is transmitted on a common signaling channel (SSCH).

41. The method of claim 40, wherein the indicator of the acknowledgment is included in a particular segment of a common signaling channel (SSCH), wherein the segment of the common SSCH is partitioned based on a transmit power required to successfully receive the indicator of the acknowledgment.

42. In a wireless communication system, an apparatus for transmitting an acknowledgement of a detected access sequence, the apparatus comprising:

a receiving module, configured to receive an access sequence;

a determining module for determining at least one attribute of a given access terminal based on the access sequence, the attribute comprising a channel quality indicator; and

a transmission module for transmitting an indicator of acknowledgement with an appropriate power according to the channel quality indicator.

43. The apparatus of claim 42, wherein the attributes further comprise at least one of a buffer level indicator, a priority indicator, and a quality of service indicator.

44. The apparatus of claim 42, further comprising:

means for transmitting an acknowledgement indicator on a common signaling channel (SSCH).

45. The apparatus of claim 42, wherein the acknowledgement indicator is included in a particular segment of a common signaling channel (SSCH), wherein the segment of the common SSCH is partitioned based on a transmit power required for successful reception of the acknowledgement indicator.