# Patent

## Title
Pre-allocated random access identifiers

## Abstract

Systems and methods of pre-allocating identifiers to wireless devices for use in requesting resources over a random access channel are described. A wireless communication system includes a random access channel over which wireless devices can anonymously send requests for resources. The base stations receiving and processing the anonymous requests reduces the probability of random access channel collisions and conserves the resources needed to support the anonymous requests by pre-allocating one or more codes to select wireless devices. The wireless devices having the pre-allocated codes can transmit a particular code over the random access channel as a request for resources that uniquely identifies the requester.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. patent application Ser. No. 11/469,794, filed Sep. 1, 2006, which is incorporated by reference as if fully set forth.


BACKGROUND
Wireless communication systems may support discontinuous transmission in which the various parties to a communication link use resources only as needed. Limiting the allocation and consumption of resources to those devices actively engaged in communications increases the capacity of a wireless communication system. However, each device may need to request an allocation of resources before it is granted the opportunity to communicate. The request and grant of communication resources can itself consume a large amount of resources that otherwise could be used to support additional users or provide increased bandwidth to active users.
It is desirable to minimize the amount of resources consumed in requesting and allocating resources for discontinuous communications. However, there remains the need to maximize the flexibility in generating access requests and allocating the resources associated with the access requests.
BRIEF SUMMARY
Systems and methods of pre-allocating identifiers to wireless devices for use in requesting resources over a random access channel are described herein. A wireless communication system includes a random access channel over which wireless devices can anonymously send requests for resources. The base station receiving and processing the anonymous requests reduces the probability of random access channel collisions and conserves the resources needed to support the anonymous requests by pre-allocating one or more codes to select wireless devices. The wireless devices having the pre-allocated codes can transmit a particular code over the random access channel as a request for resources that uniquely identifies the requester.
Aspects of the present disclosure include a method of processing random access identifiers. The method includes determining a set of random access codes, designating at least a subset of the random access codes as allocatable codes, selecting a first code from the subset of random access codes, and assigning the first code to the subscriber station as a first identifier in a random access channel.
Aspects of the present disclosure include a method of processing random access identifiers. The method includes receiving a code value over a random access channel, determining whether the code corresponds to a pre-allocated code, determining an identity of a subscriber station to which the code is allocated, and determining a request from the subscriber station based at least in part on the value of the code.
Aspects of the present disclosure include an apparatus for processing random access identifiers in a wireless communication system that includes a receiver configured to receive information from a subscriber station, a configuration module coupled to the receiver and configured to select at least one allocatable code from a set of random access codes and configured to allocate the at least one code to the subscriber station, and a transmitter configured to transmit to the subscriber station at least one message pre-allocating the at least one allocatable code to the subscriber station.
Aspects of the present disclosure include an apparatus for processing random access identifiers in a wireless communication system that includes a receiver configured to receive a random access code from a subscriber station during a random access channel opportunity and a random access code processor coupled to the receiver and configured to determine if the random access code corresponds to a pre-allocated code, determining an identity of the subscriber station if the random access code is determined to be pre-allocated and determine a response, based at least in part on the random access code.
Aspects of the present disclosure include a method of processing random access identifiers. The method includes receiving at least one random access code allocation from a base station, determining a triggering event for accessing a random access channel, determining whether any of the allocated at least one random access codes corresponds to a request type for the triggering event, selecting a first code of the allocated at least one random access codes corresponding to the request type, and transmitting the first code to the base station over a random access channel.
Aspects of the present disclosure include an apparatus for processing random access identifiers in a wireless communication system that includes a receiver configured to receive at least one allocated random access code from a base station, a storage device coupled to the receiver and configured to store the random access code assignment, a message generator coupled to the storage device and configured to generate a random access channel message having a first access code from the at least one allocated random access code, and a transmitter coupled to the message generator and configured to transmit the random access channel message to the base station over a random access channel.



BRIEF DESCRIPTION OF THE DRAWINGS
The features, objects, and advantages of embodiments of the disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like elements bear like reference numerals.
FIG. 1 is a simplified functional block diagram of an embodiment of a wireless communication system.
FIG. 2 is a simplified functional block diagram of an embodiment of a base station implementing pre-allocated random access identifiers.
FIG. 3 is a simplified functional block diagram of an embodiment of a subscriber station implementing pre-allocated random access identifiers.
FIG. 4 is a simplified flowchart of an embodiment of allocating random access identifiers.
FIG. 5 is a simplified flowchart of an embodiment of processing pre-allocated random access identifiers.
FIG. 6 is a simplified flowchart of an embodiment of implementing pre-allocated random access identifiers.



DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Methods and apparatus are described for allocating one or more codes to specific subscriber stations and attaching a specific semantic for each distinct code. The use of pre-allocated codes avoids the collision probability associated with random subscriber selected access codes as each subscriber station can potentially be assigned a distinct set of codes. The use of pre-allocated codes allows a base station to react faster to a subscriber station request because it knows more information about the specific request.
The descriptions contained herein generally focus on Orthogonal Frequency Division Multiple Access (OFDMA) wireless communication systems, and particularly are directed towards IEEE 802.16 wireless communication systems. However, the implementation of pre-allocated codes in an IEEE 802.16 system is used merely as an example. The use of pre-allocated random access identifiers in a wireless communication system can be implemented in virtually any type of wireless communication system.
FIG. 1 is a simplified functional block diagram of an embodiment of a wireless communication system 100. The wireless communication system 100 includes a plurality of base stations 110a, 110b, each supporting a corresponding service or coverage area 112a, 112b, Each base station 110a and 110b can be coupled to a network (not shown) such as a wired network, and can be configured to allow wireless communication with devices on the wired network.
A base station, for example 110a, can communicate with wireless devices within its coverage area 112a. For example, the first base station 110a can wirelessly communicate with a first subscriber station 130a and a second subscriber station 130b within the coverage area 112a. In another example, the first subscriber station 130a can communicate with a remote device (not shown) via the first base station 110a. In another example, the first subscriber station 130a can communicate with the second subscriber station 130b via the first base station 110a. 
The base stations, 110a and 110b, can be part of the same communication network or can be part of distinct communications networks. The base stations 110a and 110b can be in communication with each other, either through a direct communication link or via an intermediary network. Alternatively, where the base stations 110a and 110b are in distinct networks, a first base station 110a may have no knowledge regarding the operation of the second base station 110b. 
There may be any number of base stations 110a and 110b within a wireless communication system 100, although FIG. 1 depicts only two base stations 110a and 110b. The base stations 110a and 110b alternatively can be referred to as access points or nodes.
Although only two subscriber stations 130a and 130b are shown in the wireless communication system 100, the system can be configured to support virtually any number of subscriber stations. The subscriber stations 130a and 130b can be mobile stations or stationary stations. The subscriber stations 130a and 130b alternatively can be referred to, for example, as mobile stations, mobile units, or wireless terminals.
A mobile station can be, for example, a wireless handheld device, a vehicle mounted portable device, or a relocatable portable device. A mobile subscriber station can take the form of, for example, a handheld computer, a notebook computer, a wireless telephone, or some other type of mobile device.
In one example, the wireless communication system 100 is configured for Orthogonal Frequency Division Multiple Access (OFDMA) communications. For example, the wireless communication system 100 can be configured to substantially comply with a standard system specification, such as IEEE 802.16 or some other wireless standard. The wireless communication system 100 can support the pre-allocated access identifiers described herein as an extension to the system standard or as part of a system standard.
The wireless communication system 100 is not limited to an OFDMA system, and use of the pre-allocated access identifiers described herein is not limited to application in OFDMA systems. The description is offered for the purposes of providing a particular example of the operation of a pre-allocated access identifiers in a wireless communication environment.
The base stations 110a and 110b are configured to transmit data packets to the subscriber stations 130a and 130b organized in frames using one or more slots. The term “downlink” is used to refer to the direction of communication from the base station, e.g. 110a, to a subscriber station, e.g. 110a. Each slot can include a predetermined number of Orthogonal Frequency Division Multiplex (OFDM) subcarriers, symbols, or a combination of subcarriers and symbols.
Each base station, for example 110a, can supervise and control the communications within its respective coverage area 112a. Each active subscriber station, for example 130a, registers with the base station 110a upon entry into the coverage area 112a. The subscriber station 130a can notify the base station 110a of its presence upon entry into the coverage area 112a, and the base station 110a can interrogate the subscriber station 130a to determine the capabilities of the subscriber station 130a. 
The base station 110a assigns a temporary identifier to the subscriber station 130a for use identifying the subscriber station 130a to the base station 110a. The temporary identifier can be referred to as a Connection Identifier (CID). The system can allocate a predetermined range for the CID, and reserves a number of bits necessary to support the maximum CID value in each message requiring a CID value.
In a packet based wireless communication system 100, it may be advantageous for the system to allocate resources as needed, rather than maintaining an active channel assignment for each subscriber station 130a or 130b having an established communication session with a base station 110a or 110b. The base station 110a can allocate resources to the subscriber station 130a on an as needed basis. For example, in an OFDM system, the base station 110a can allocate time and frequency resources to each subscriber station 130a when the subscriber station 130a has information to send to the base station 110a. 
The communication link from the subscriber station 130a to the base station 110a is typically referred to as the “uplink.” The base station 110a can allocate uplink resources to the subscriber station 130a to avoid collisions that may occur if the subscriber stations 130a or 130b are allowed random access to the resources. The base station 110a can allocate the uplink resources in units of frames and OFDM subcarriers. Additionally, the base station 110a can specify a modulation format, an encoding rate, Forward Error Correction (FEC), and the like, or some combination thereof in the resource allocation messages.
The subscriber stations 130a and 130b can notify the serving base station, for example, 110a, when the subscriber stations 130a and 130b are reporting information to the base station 110a or when the subscriber stations 130a and 130b request uplink resources. Each base station, for example 110a, can allocate some resources to support a random access channel (RAC) used by the subscriber stations 130a and 130b to report or request resources. The base station 110a can periodically allocate resources to support the random access channel. In one embodiment, the base station 110a can support a random access channel in each uplink frame. For example, a base station 110a can allocate a portion of the uplink to a random access channel. The base station 110a can allocate, for example, a time, duration, and number of OFDM subcarriers on the uplink portion for the random access channel. Each of the random access channel parameters may be static or may be dynamic. The base station 110a can include the random access channel allocation information in a downlink portion that is broadcast across its associated coverage area 112a. 
The information bandwidth of the random access channel may be limited due to, for example, a limited duration or limited number of subcarriers allocated to supporting the channel. Thus, each subscriber station, for example 130a, can notify the base station 110a by transmitting an identifier on the random access channel. The base station 110a can respond to the information it receives over the random access channel.
The subscriber stations 130a and 130b can use virtually any identifier in a request over the random access channel. However, wireless communication standards typically specify the types of identifiers and methods of communicating information over a random access channel.
The IEEE 802.16 wireless communication standard specifies 256 distinct pseudorandom codes and four corresponding usage types for conveying information over a random access channel. The four usage types include initial ranging, periodic ranging, bandwidth request, and handover. Each base station, for example 110a, can support a distinct set of 256 pseudorandom codes. A subscriber station 130a can generate the set of pseudorandom codes associated with a particular base station 110a based on a base station 110a identifier or sector identifier and a predetermined generator polynomial.
The base station 110a can define groups or ranges of pseudorandom codes, also referred to as Code Division Multiple Access (CDMA) codes or merely codes, for each usage type. A subscriber station 130a having a need to communicate information with the base station 110a can randomly select a code from the available group of codes corresponding to a usage type. The subscriber station 130a sends the randomly selected code corresponding to the usage type to the base station 110a over the random access channel. The subscriber station 130a can modulate the subcarriers of the random access channel with the selected code using a predetermined modulation type, for example, BPSK.
For example, if the subscriber station 130a needs to send a bandwidth request to a serving base station, 110a, the subscriber station 130a selects a code from the group of codes associated with bandwidth requests assigned by the base station 110a. The subscriber station 130a transmits the code to the base station 110a and the base station 110a responds by granting a typically small amount of bandwidth to allow the subscriber station 130a to transmit the specific request.
The base station 110a receiving the code over the random access channel does not yet know the identity of the transmitting subscriber station 130a. The base station 110a can only identify the purpose of the request, based on the group in which the code belongs. The subscriber station 130a sends the code to notify the base station 110a of a pending request. The base station 110a grants a small portion of bandwidth, based on the usage type indicated by the code, to allow the subscriber station 130a to transmit details of the request. This multiple stage access has a large associated latency and is rather cumbersome for many transactions.
Additionally, there is a finite probability of code collision, where two distinct subscriber stations 130a and 130b select the same code for transmission in the same instance of the random access channel. The wireless communication system 100 can define a random backoff, using a random backoff algorithm implemented in each subscriber station 130a and 130b, to address the possibility of collisions. However, collisions increase the latency from the time of the initial request to the time of servicing the request.
The wireless communication system 100 can alleviate at least some of the latency by pre-allocating one or more codes to each subscriber station 130a and 130b. A base station 110a can pre-allocate one or more codes to each subscriber station 130a and 130b that is registered within its coverage area 112a. Each pre-allocated code can also have an associated semantic. The base station 110a can reserve some codes for use by subscriber stations not having a pre-allocated code for a particular usage type or instance.
FIG. 2 is a simplified functional block diagram of an embodiment of a base station 200 configured to perform assignment and processing of pre-allocated codes. The base station 200 can be, for example, one of the base stations in the wireless communication system of FIG. 1.
The base station 200 is configured to pre-allocate one or more codes to a subscriber station registering in the coverage area. The base station 200 supports communicating random access channel messages using pre-allocated codes as well as random access channel messages using subscriber station selected codes. The base station 200 pre-allocates one or more codes to registered subscriber stations that support pre-allocated codes. The base station 200 tracks the code allocation such that each of the allocatable codes are allocated to at most one subscriber station at a time. The subscriber station having pre-allocated codes releases the pre-allocated codes when it de-registers with the base station 200.
In another embodiment, a plurality of base stations 200 may share a pool of codes for allocation to subscriber stations. A base station 200 can pre-allocate a code to a particular subscriber station and the subscriber station can use the pre-allocated code for communicating with a plurality of base stations, for example, the plurality of base stations participating in a communication handoff. In another embodiment, a base station 200 can pre-allocate a code to a particular subscriber station and the subscriber station may use the pre-allocated code for communicating with any base station belonging to a predetermined group of base stations, such as a system wide group of base stations.
The base station 200 includes an antenna 202 that can be coupled to a receiver 210 and transmitter 280 within the base station 200. Although FIG. 2 illustrates a single antenna 202, the antenna 202 can be one or more antenna configured to support the transmit and receive operating bands. If the base station 200 supports frequency division multiplexing of the transmit and receive bands, the base station 200 can include a duplexor (not shown) to isolate the transmit signals from the receiver 210. The receiver 210 and transmitter 280 can be distinct or can be part of a transceiver.
Code Pre-Allocation
The receiver 210 is configured to receive the uplink transmissions broadcast by the subscriber stations (not shown). Initially, a subscriber station can synchronize and register with a base station 200 once the subscriber station enters a coverage area of the base station 200 or upon waking up from a sleep or idle state.
The subscriber station transmits an initial ranging signal over a ranging channel defined by the base station 200. The ranging channel can be, for example, the random access channel.
The receiver 210 receives the initial transmissions from the subscriber station and couples them to a configuration module 220. The configuration module 220 operates to register the subscriber station in a manner set forth in a wireless standard. For example, the configuration module 220 can assign and track a connection identifier assigned to the subscriber station.
The configuration module 220 can track the set of codes that may be used in the random access channel in conjunction with a random access code mapper 240. The random access code mapper 240 is configured to track the complete list of random access codes, their designation as open codes or allocatable codes, the usage type groups, and their status as allocated or available for allocation.
In one embodiment, the random access code mapper 240 can be configured to generate the entire set of available codes and store the set in memory. The random access code mapper 240 can associate usage types with subsets of the codes. For example, the random access code mapper 240 can associate a distinct subset of codes with each of four usage types, where the usage types include initial ranging, periodic ranging, bandwidth request, and handover.
The random access code mapper 240 can similarly designate a first portion of codes as allocatable codes and a distinct second portion of codes as open codes, where an open code refers to a code that will not be assigned to any particular subscriber station but can be randomly selected by subscriber stations for use in a random access channel message. The random access code mapper 240 can designate the first and second portions in such a manner that the union of the two portions includes the entire group of codes. For example, the random access code mapper 240 can define five distinct code groups from N possible codes, one for each of four usage types and one for allocatable codes. The first group (0 through i) can be assigned to initial ranging, the second group ((i+1) though p) can be assigned to periodic ranging, the third group ((p+1) through b) can be assigned to bandwidth requests, the fourth group ((b+1) through h) can be assigned to handoffs, and the fifth group ((h+1) through N) can be assigned as allocatable codes. Further, the allocatable codes can be divided by purpose or function. The random access code mapper 240 thus allows the base station 200 to support both pre-allocated codes as well as codes that are randomly selected by subscriber stations.
If the configuration module 220 determines that the registering subscriber station is capable of supporting pre-allocated codes, such as via a capabilities negotiation phase of the registration process, the configuration module 220 can examine the code map in the random access code mapper 240 to determine which of the allocatable codes are available.
The configuration module 220 can be configured to allocate one or more codes to a particular subscriber station based on a variety of factors. Although the description provided herein focuses on allocating codes as part of the registration process, the configuration module 220 is not limited to allocating codes as a result of, or during, registration of the subscriber station. In some embodiments, the configuration module 220 operates to allocate codes to a subscriber station independent of any registration process, and independent of a capabilities negotiation that occurs during a registration process.
The configuration module 220 can be configured to monitor, either directly or indirectly, mobility of a subscriber station and can be configured to allocate one or more codes based on a measure of the mobility. Additionally, the configuration module 220 can be configured to determine characteristics of communications with a subscriber station and allocate one or more codes based on the characteristics of the communications. For example, the base station 200 can communicate with a subscriber station over a link characterized as a “best effort” level of connection. The configuration module 220 can be configured to allocate one or more codes to the subscriber station based on the base station 200 supporting a “best effort” communication link with the subscriber station. Similarly, the subscriber station may communicate real time traffic such as voice or real time video via the base station 200. Real time traffic may be more sensitive to latency and the latency requirements may not support a request for retransmission of erased or otherwise corrupted information. The configuration module 220 can determine if a communication link to a subscriber station is in support of real time traffic and can allocate one or more codes to the subscriber station based on the base station 200 supporting a real time traffic communication link with the subscriber station.
The configuration module 220 can utilize other factors and parameters in determining whether to allocate one or more codes to a subscriber station. The examples described herein are illustrative of the types of factors that the configuration module 220 may consider and are not intended as limitations on the operation of code pre-allocation.
The configuration module 220 can select one or more allocatable codes and pre-allocate them to a registering subscriber station. The configuration module 220 can pre-allocate multiple codes to a single subscriber station for any of a variety of reasons. The configuration module 220 can pre-allocate a distinct code for each of a plurality of usage types. The configuration module 220 can also pre-allocate multiple codes within the same usage type with each distinct code attached to a distinct semantic. For example, the configuration module 220 can allocate two distinct codes within the bandwidth request usage type. A first code can represent a first bandwidth request and a second code can represent a distinct bandwidth request. In another example, the configuration module 220 can allocate two distinct codes within the bandwidth request usage type, where each of the codes can represent a different requested class of service.
Once the configuration module 220 selects an allocatable code from the code map, the random access code mapper 240 identifies the code as allocated and no longer available for allocation. The base station 200 can pre-allocate each code for an indefinite duration or for a predetermined duration. The base station 200 can pre-allocate some codes for an indefinite duration while pre-allocating other codes to the same subscriber station for a predetermined duration.
In one embodiment, the base station 200, via the configuration module 220, pre-allocates codes for an indefinite duration. The subscriber station releases one or more pre-allocated codes upon a predetermined event. For example, a subscriber station releases any pre-allocated codes when it de-registers with the base station 200 such as when leaving the base station coverage area or when transitioning to an unregistered state such as sleep or idle. As another example, a subscriber station can be given a pre-allocated code for use in a handoff to communicate with the plurality of base stations participating in the handoff, and the subscriber station can release the pre-allocated code upon completion of the handoff. In another embodiment, the configuration module 220 pre-allocates one or more codes for a predetermined duration. The pre-allocated code can expire and be released at the end of the predetermined duration. Alternatively, the pre-allocated code can conditionally expire at the end of the duration based on some event. For example, a pre-allocated code may expire unless the subscriber station takes some explicit action to renew the pre-allocated code. In yet another embodiment, the configuration module 220 can revoke or otherwise terminate a pre-allocated code assignment The configuration module 220 and random access code mapper 240 can determine the release or termination of pre-allocated codes and can update the code map accordingly.
The base station 200 pre-allocates the codes to a subscriber station by generating a pre-allocation message to the subscriber station including the codes identified by the configuration module 220. The base station 200 can generate a downlink message to the subscriber station having the pre-allocation message. The base station 200 can support virtually any type of pre-allocation message, and the specific manner in which a code is pre-allocated to a subscriber station is not limited to any particular format or message.
For example, the configuration module 220 can generate a type-length-value (TLV) triplet to the subscriber station with the pre-allocated code. The base station 200 can transmit the TLV triplet in a TLV exchange occurring during the capability negotiation phase with the subscriber station. The configuration module 220 can generate a distinct TLV triplet for each pre-allocated code. In another embodiment, the configuration module 220 can generate a dedicated message to the subscriber station including the pre-allocated codes that is transmitted in the downlink. In yet another embodiment, the configuration module 220 can generate a code allocation message to a specific subscriber station and can include the pre-allocation message in an extended sub-header portion of a MAC Payload Data Unit (PDU) directed to the subscriber station, where the MAC is the unique MAC address corresponding to the subscriber station.
The configuration module 220 generates a pre-allocation message and couples the message to the downlink processor 270. Alternatively, the configuration module 220 can provide the pre-allocated codes, associated semantics, and the identify of the subscriber station to the downlink processor 270, and the downlink processor 270 can generate the pre-allocated code message.
In one embodiment, the downlink processor 270 maps the pre-allocated message to one or more subcarriers of one or more OFDM symbols. The downlink processor 270 couples the OFDM symbols to the transmitter 280 where the OFDM symbols are filtered, amplified, and frequency converted to a desired operating band, where they are transmitted across the coverage area via the antenna 280.
Once the subscriber station receives the pre-allocated code assignment, the subscriber station can transmit one or more codes to the base station 200 over the random access channel. The subscriber station can select the code, whether pre-allocated or random, based in part on the usage type of the request.
Random Access Channel Code Processing
The base station 200 can periodically allocate a random access channel in the uplink. The uplink scheduler 260 can determine the timing and uplink resources to allocate to supporting a random access channel. For example, the uplink scheduler 260 can allocate to the random access channel a predetermined number of subcarriers out of a predetermined number of symbols in an uplink frame. The uplink scheduler 260 can generate an Uplink-Map (UL-MAP) that is coupled to the downlink signal processor 270 for inclusion in the downlink symbols. The transmitter 280 transmits the UL-MAP as part of the downlink frame.
The subscriber stations in the base station 200 coverage area receive the UL-MAP and can determine the resource allocation for the random access channel. The subscriber stations can each generate a code for transmission to the base station 200 over the random access channel.
The base station 200 receives the uplink transmissions, including the one or more OFDM symbols including the random access channel. The receiver 210 processes the uplink OFDM symbols to recover the underlying data and information. There may be many channels supported in any given received OFDM symbol, and the receiver 210 can extract and recover the data for each of the channels.
The receiver 210 can, for example, amplify, filter, and downconvert the received OFDM symbols to baseband OFDM symbols. The receiver 210 can extract the information carried in the symbols by transforming the time domain samples to the corresponding OFDM frequency domain subcarriers. The receiver 210 can demodulate each of the subcarriers in a manner that is dependent, at least in part, on the channel to which the subcarrier is assigned. For example, the receiver 210 can be configured to BPSK demodulate the subcarriers assigned to the random access channel to recover the data. The receiver 210 can map the demodulated subcarrier data to the respective channels to recover the underlying data.
The receiver 210 couples the codes recovered from the random access channel to a random access code processor 230. The random access code processor 230 compares the received codes to the random access code map from the random access code mapper 240 to determine the corresponding usage type and to determine if the code corresponds to a pre-allocated code.
If the random access code processor 230 determines that the received code has not been pre-allocated to a specific subscriber station, the random access code processor 230 signals the UL scheduler 230 based on the usage type of the received code. The UL scheduler 260 may allocate some uplink bandwidth for the subscriber station to provide additional information depending on the usage type associated with the received code.
However, if the random access code processor 230 determines that the received code has been pre-allocated to a specific subscriber station, the random access code processor 230 communicates with the configuration module 220 to determine the identity of the subscriber station. The random access code processor 230 can, for example, compare the received code to a look up table or relational database in the configuration module 240 and determine the associated subscriber station. The random access code processor 230 can also determine if the code has a defined semantic distinct from the usage type. For example, the random access code processor 230 can determine that the code corresponds to a bandwidth request of a specific number of bytes.
The random access code processor 230 couples the subscriber station identity and the specific resource request to the UL scheduler 260 to allow the UL scheduler 260 to allocate the requested resources to the subscriber station in the UL-MAP. For example, if the received code corresponds to a specific bandwidth request, the UL scheduler 260 can grant the resource allocation in the UL-MAP. Without the pre-allocated code, the base station 200 would need to initially grant a small amount of bandwidth to the source of the code in order to identify the subscriber station transmitting the code and to identify the amount of bandwidth requested.
The random access code processor 230 can also notify the feedback processor 250 when the base station 200 receives a pre-allocated code. The feedback processor 250 can be configured to monitor the signals received by the receiver 210. The feedback processor 250 can monitor, for example, receive signal parameters that are corrected in closed loop control. The feedback processor 250 can monitor, for example, the power of the received signals, the timing of the received signals, and the frequency of the received signals. For each monitored parameter, the feedback processor can generate feedback data or a feedback message directed to the originating subscriber station.
The feedback processor 250 can monitor the received power using a detector, using a processor to calculate a power of a digital representation of the received signal, and the like, or some other manner of determining the received power. The power can be averaged over some predetermined time duration. The feedback processor 250 determines the power of the received signal corresponding to each of the distinct signal sources. The feedback processor 250 can be configured to generate a feedback signal that is used in a power control loop that controls the transmit power of the subscriber station. For example, the feedback processor 250 can generate a control signal or message to instruct a subscriber station to increase or decrease the transmit signal power and that may provide some indication of the magnitude of the change.
Similarly, the feedback processor 250 can monitor timing of the received signal. In an OFDM system, the base station 200 can allocate uplink resources to a subscriber station by allocating subcarriers and the time or OFDM symbols in which those subcarriers are allocated. The feedback processor 250 can monitor the received signal to determine the timing of the received signal from a particular subscriber station relative to its allocated time. The feedback processor 250 can generate a feedback control signal or message to instruct the subscriber station to advance or delay its transmission time, in order to better align with the system timing.
The feedback processor 250 can also monitor the frequency of the received signal to determine if there is a frequency offset from an ideal received frequency. The feedback processor 250 can generate a feedback control signal or message to instruct the subscriber station to increase or decrease its transmit frequency and can provide some indication of the magnitude of the change. Alternatively, the feedback processor 250 can generate a feedback control signal or message that is indicative of the frequency offset relative to a desired receive frequency.
The feedback processor 250 couples the various control signals or feedback messages to the downlink signal processor, where they are configured in a downlink message that is directed to the particular subscriber station. The feedback processor 250 can concurrently monitor the receive signal from several subscriber stations, and the downlink signal processor 270 can be configured to generate a downlink signal to each of the subscriber stations having the relevant feedback information.
If the random access code processor 230 determines that the code received in the random access channel is a pre-allocated code, the feedback processor can associate the signal received over the random access channel with the originating subscriber station. The knowledge of the identity of the subscriber station originating the random access channel code allows the feedback processor 250 to generate a feedback message that is relevant to the originating subscriber station.
In the condition where the code received over the random access channel is not a pre-allocated code, the feedback processor 250 has no knowledge of the identity of the originating subscriber station and therefore, does not have the ability to associate the feedback information to a particular subscriber station. Any correction determined based on an anonymous code is broadcast across the coverage area to ensure receipt by the originating subscriber station.
Subscriber Station
FIG. 3 is a simplified functional block diagram of an embodiment of a subscriber station 300. The subscriber station 300 is configured to utilize pre-allocated codes assigned by a base station, such as the base station of FIG. 2. The subscriber station 300 can be, for example, a subscriber station of the wireless communication system of FIG. 1.
The simplified functional block diagram of FIG. 3 is limited to those functional blocks related to the processing of random access channel codes and the associated information. The functional blocks relating to other aspects of the subscriber station 300 are omitted for the sake of clarity.
The subscriber station 300 includes an antenna 302 for interfacing with the wireless channel. The subscriber station 300 includes a receiver 310 coupled to the antenna to receive and process the received signals that originate from base stations. Additionally, the subscriber station 300 includes a transmitter 370 to process signals for transmission to a base station via the antenna 302.
A subscriber station 300 registers with a base station upon entry into the coverage area and may re-register upon waking from a sleep or idle state. The subscriber station 300 can initially receive overhead information that indicates general parameters, such as the identity of the base station, the date, and other overhead information, and engages in a capabilities negotiation with the base station, in part, using the overhead information. For example, the base station may broadcast an Uplink Channel Descriptor (UCD) that includes a usage type map for the random access codes. The base station can also transmit a UL-MAP that provides the random access channel allocation in the uplink.
The subscriber station 300 receives the overhead information in one or more OFDM symbols. The receiver 310 processes the received symbols to extract the overhead information and couples the base station cell identification to a random access code generator 330. In other embodiments, the receiver 310 couples a base station sector identification to the random access code generator if the base station supports a sectorized coverage area. The random access code generator 330 uses the base station cell identification in conjunction with a predetermined generator function to generate all possible random access codes supported by the base station. The random access code generator 330 can store the codes in a storage device 340, which can include one or more memory devices.
The subscriber station 300 also receives the UCD information from the base station and couples the UCD information to a code assignment module 320. The UCD information includes the usage type map for the random access codes. The code assignment module 320 can associate the usage types to the codes stored in the storage device. In some instances, the usage type map received from the base station may not map all of the codes. The code assignment module 320 can presume that those codes absent from the usage type map represent codes reserved for pre-allocation, and that the reserved codes are not to be randomly selected for a random access channel request and can indicate in the storage device that the codes are reserved or can otherwise indicate that the codes are not available for selection. In another embodiment, the usage type map can explicitly label a group of one or more codes reserved for pre-allocation.
A random access channel message generator 350 can generate an initial ranging message by selecting an initial ranging code from the list of available codes in the storage device. The random access channel message generator 350 couples the selected initial ranging code or the initial ranging message that is generated using the selected initial ranging code to the transmitter 370. The transmitter 370 is configured to generate the OFDM symbols having the initial ranging message, for example, by BPSK modulating the selected initial ranging code onto a plurality of subcarriers allocated to the random access channel. The transmitter 370 transmits the message to the base station during a ranging opportunity, where the ranging opportunity occurs over a combination of time and frequency resources allocated to the random access channel.
The subscriber station 300 and base station can engage in a capabilities negotiation phase that is part of the registration process. During the capabilities negotiation phase, the subscriber station and base station can exchange their capabilities. The capabilities exchange may be direct, where each party to the communication submits its capabilities or queries the other party as to its capabilities. The capabilities exchange may also be indirect, where each party reveals its capabilities or learns of the other party's capabilities through examination or query of a parameter that indirectly refers to the capabilities. For example, in a subscriber station, a manufacturer model number or a software version associated with a baseband processor may indirectly indicate the capabilities of the subscriber station. Some capabilities may be exchanged directly while others are exchanged indirectly.
As a result of the capabilities negotiation phase, the subscriber station 300 will indicate its ability to support the pre-allocated codes. The subscriber station 300 can then receive one or more pre-allocated codes to which it is assigned. The subscriber station 300 can also receive a usage type and a semantic associated with each pre-allocated code.
The pre-allocated codes and their corresponding usage types or semantics can be received by the subscriber station 300 in a Type, Length, Value (TLV) exchange with the base station. Alternatively, the subscriber station 300 can receive the pre-allocated codes and associated information in one or more dedicated messages, extended subheaders, or some other manner of conveying information to the subscriber station 300.
The receiver 310 couples the pre-allocated code information to the code assignment module 320. The code assignment module 320 can update the code values stored in the storage device 340 to indicate the pre-allocated codes and the associated information, such as usage type and semantic.
After the subscriber station 300 has completed registration and remains registered with the base station, the subscriber station 300 can communicate over the random access channel using the pre-allocated codes. The subscriber station 300 can include a number of modules that are configured to monitor for events that create the need to transmit a request to the base station over the random access channel.
The subscriber station 300 can include a handoff module 362, a ranging module 364, and a bandwidth request module 366 that monitor the performance and activities of the subscriber station 300 and determine when it is desirable to transmit a code over the random access channel to the base station. The handoff module 362 can be configured to monitor the link with the serving base station, and can be configured to monitor the strength of candidate base stations. The handoff module 362 can direct the subscriber station 300 to initiate a handoff when the conditions warrant.
The ranging module 364 can be configured to support the initial ranging with the base station that can be used to synchronize with the system. Additionally, the ranging module 364 can be configured to monitor and support periodic ranging that may need to be performed by the subscriber station 300. During periodic ranging, the subscriber station 300 can transmit a ranging code over the random access channel and the base station may correct the timing offset and power control in a feedback message to the subscriber station 300.
A bandwidth request module 366 can track the uplink information generated or otherwise received at the subscriber station 300 and available for transmission over an uplink channel. The bandwidth request module 366 can be configured to initiate a bandwidth request to request an allocation of uplink resources. The bandwidth request module 366 can monitor, for example, the type of information to be transmitted on the uplink. For example, voice information may be relatively low density, but may have constraints regarding the latency. Likewise, there may be data intensive transmissions that have less stringent latency requirements.
When any of the modules determines a need to transmit a code over the random access channel, the relevant module, for example the bandwidth request module 366, indicates the event to the random access channel message generator 350. The random access channel message generator 350 determines the usage type associated with the request, which in this example is a bandwidth request. The random access channel message generator 350 examines the codes stored in the storage device 340 to determine whether the subscriber station has been pre-allocated one or more codes for bandwidth requests.
If the random access channel message generator 350 determines that there are no pre-allocated codes for the particular usage type, the random access channel message generator 350 selects a code randomly from the available codes of the desired usage type. The random access channel message generator 350 assembles the message and couples it to the transmitter 370 for transmission over the random access channel.
If the random access channel message generator 350 determines that there is at least one pre-allocated code of the desired usage type, the random access channel message generator 350 determines whether any of the pre-allocated codes has a semantic that supports the event indicated by the bandwidth request module. For example, the subscriber station 300 can be allocated a number of bandwidth request codes, each with a different semantic attached. A first semantic attached to a first pre-allocated code can indicate a particular bandwidth request, such as a first number of bytes, while a second semantic attached to a second pre-allocated code can indicate a second bandwidth request having a second number of bytes distinct from the first number of bytes.
The random access channel message generator 350 selects the pre-allocated code having the desired semantic and assembles a random access control message using the code. If no pre-allocated codes have the desired semantic, but there exists a pre-allocated code having no semantic attached, the random access channel message generator 350 selects the pre-allocated code having no semantic attached. If there is no pre-allocated code with no semantic attached, the random access channel message generator 350 randomly selects a code just as in the case where the subscriber station 300 has no pre-allocated codes.
The subscriber station 300 can receive a ranging correction message in response to any request using a pre-allocated code. The receiver 310 receives the correction message, which can be a feedback control message, and couples the message to a feedback control processor 380. The feedback control processor 380 can process the feedback control message and can adjust the operating parameters of the transmitter 370. For example, the feedback control processor 380 can direct the transmitter 370 to increase the transmit power or to adjust a timing offset.
Process Descriptions
FIG. 4 is a simplified flowchart of an embodiment of a method 400 of allocating random access identifiers. The random access identifiers can be, for example, the CDMA codes used in the random access channel of a IEEE 802.16 wireless communication system. The method 400 can be implemented, for example, by a base station of FIG. 1 or the base station of FIG. 2.
The method 400 begins at block 410, where the base station generates a list of all the available random access codes supported by the base station. The base station can generate the list using, for example a generator polynomial and a cell identification value. The base station need not generate the codes every time that they are needed, but rather, may generate or otherwise be provided the codes one time and may store the list of codes in a memory as a look up table, database, or some other record.
The base station proceeds to block 420 and maps the codes to specific usage types. The base station can support a predetermined number of usage types, such as initial ranging, periodic ranging, bandwidth request, and handover. The base station can, for example, select a range of codes that corresponds to each of the usage types. The base station can identify each code with its associated usage type in the look up table having the list of codes.
The base station proceeds to block 430 and maps the codes to one or the other set of open or allocatable codes. The base station can configure the codes such that it supports only open codes, only allocatable codes, or a combination of open and allocatable codes. The base station identifies each code in the look up table as either open or allocatable. The term “open” refers to a code that will not be allocated to a particular subscriber station, but instead, remains open for random selection by a subscriber station. In contrast, the term “allocatable” refers to those codes that the base station can select for pre-allocation to a particular subscriber station.
The base station proceeds to block 440 and receives a registration request from a subscriber station. The base station may limit active communication sessions to those subscriber stations registered with the base station. Typically, each subscriber station registers with the serving base station upon entry into the coverage area. Alternatively, the base station may receive a subscriber basic capability request from the subscriber station.
The base station proceeds to block 450 and determines the subscriber station capabilities based on the subscriber station basic capability request or the registration request or other direct or indirect information. For example, the base station can enter a capabilities negotiation with the subscriber station. The base station proceeds to decision block 460 and determines, based on the capabilities negotiation, whether the subscriber station supports pre-allocated codes.
If the base station determines that the subscriber station does not support pre-allocated codes, the base station proceeds from decision block 460 to block 480 and is done. However, if the base station determines that the subscriber station supports pre-allocated codes, the base station proceeds from decision block 460 to block 470 and pre-allocates one or more random access codes to the subscriber station.
In one embodiment, the base station can determine the usage types and associated semantics for which to pre-allocate a code based on one or more parameters associated with the subscriber station. The base station may have a limited number of codes which can be pre-allocated, and may preferentially allocate codes to subscriber stations based on some subscriber station parameter. For example, the base station can perform preferential pre-allocation of codes to those subscriber stations identified as mobile devices.
The base station can pre-allocate a distinct code for each of a plurality of bandwidth requests, classes of service, or some other factor based in part on the results of the capabilities negotiation. For example, the base station may pre-allocate a plurality of bandwidth request usage types to the same subscriber station and each bandwidth request code may be attached to a distinct semantic that indicates the size of the bandwidth request. Then, if the base station receives the pre-allocated code in the random access channel, the base station knows both the identity of the subscriber station as well as the size of the bandwidth request. The base station can immediately allocate the resources to the subscriber station in a UL-MAP.
The base station can communicate the pre-allocated codes and associated usage types and semantics in any of a variety of ways. For example, the base station may communicate pre-allocated codes and usage types to a subscriber station using a TLV triplet transmitted on an extended subheader. Similarly, a base station can communicate pre-allocated codes having a usage type and specific semantic using a dedicated message. The base station may use other techniques as well.
The base station can allocate codes for an indefinite period of time or for a defined period of time. The base station can associate a duration with a pre-allocated code based on a characteristic transmitted with the code, based on a usage type, or based on some other factor or combination of factors. An indefinite allocation may remain until it is released by the subscriber station, such as when the subscriber station deregisters with the base station. A temporary allocation can be time or event based. For example, a time based allocation may expire after a predetermined time. An event based allocation may expire upon the occurrence or lack of occurrence of one or more events.
In some instances, the base station may have the ability to allocate codes that remain active so long as the subscriber station continues to use them or otherwise conveys an interest in renewing the allocation. In such a case, the code may remain valid indefinitely.
After pre-allocating one or more random access codes, the base station proceeds to block 480 and is done.
FIG. 5 is a simplified flowchart of an embodiment of a method 500 of processing pre-allocated random access identifiers. The method 500 can be performed, for example, by a base station of the wireless communication system of FIG. 1 or the base station of FIG. 2.
The method 500 begins at block 510 when the base station receives a random access code over the random access channel. For example, the base station can allocate an uplink random access channel having a predetermined number of OFDM subcarriers in a predetermined number of symbols occurring at a predetermined time in an uplink frame. The base station can monitor the random access channel for the presence of a random access code. The base station can determine the presence of a random access code, for example, by correlating the information received over the random access channel with each of the possible random access codes. The base station can perform the method 500 for each random access code identified in the random access channel.
After receiving a code, the base station proceeds to decision block 520 and determines whether the received code corresponds to a pre-allocated code. The base station can, for example, compare the received code to code values in a look up table having the codes and the associated characteristics.
If the base station determines that the code does not correspond to a pre-allocated code, the base station proceeds from decision block 520 to block 530 and processes the code as a request per the standard response techniques. For example, the base station can allocate a small amount of bandwidth to whichever subscriber station transmitted a bandwidth request code so that the subscriber station can identify itself and provide the details of the request. The base station proceeds from block 530 to block 580 and is done.
If the base station, at decision block 520 determines that the received code corresponds to a pre-allocated code, the base station proceeds to block 540 and determines the source associated with the code. In one embodiment, the base station examines a code map to determine the identity of the subscriber station to which the code is allocated. The base station can, for example, store the connection identifier (CID) of the subscriber station with the pre-allocated code in a look up table or a database.
After determining the identity of the subscriber station associated with the code, the base station proceeds to block 550 and determines the request corresponding to the pre-allocated code. In one embodiment, the base station can determine the request by examining a look up table to determine the usage type associated with the pre-allocated code. In another embodiment, the base station can examine a look up table to determine both a usage type and a semantic attached to the pre-allocated code. The semantic can indicate, for example, a particular class of service requested by the subscriber station. In another example, the pre-allocated code can indicate a number of bytes requested in an uplink allocation.
After determining the nature of the request, the base station proceeds to block 560 and processes the request per the code map. The base station can allocate to the subscriber station, for example, the number of bytes requested by the pre-allocated code. In another example, the base station can perform some other action requested by the pre-allocated code.
The base station proceeds to block 570 and performs control loop processing on the received code. The base station can monitor, for example, the power of the received code signal, the timing of the received signal relative to system time, and the frequency of the received signal relative to a desired receive frequency. The base station can generate one or more feedback messages to transmit to the originating subscriber station in order to provide feedback for a closed loop correction performed by the subscriber station. The base station can advantageously monitor the control loop parameters on the received code and can determine a timely feedback message based on the pre-allocated code.
After performing closed loop processing on the received signal, the base station proceeds to block 580 and is done. The base station can repeat the method 500 for each received code.
FIG. 6 is a simplified flowchart of an embodiment of method 600 of implementing pre-allocated random access identifiers. The method 600 can be performed, for example, by a subscriber station of the wireless communication system of FIG. 1 or the subscriber station of FIG. 3.
The method 600 begins at block 610 when the subscriber station registers with a base station. The base station may support pre-allocated codes for registered subscriber stations and may have alternative support for unregistered subscriber stations. Additionally, the subscriber station is typically unable to support an active communication session with the base station unless it is registered with the base station.
During the registration process, the subscriber station determines the set of codes corresponding to the base station or base station sector. The subscriber station also receives from the base station the mapping of the random access codes in the associated code set. For example, the subscriber station can receive a code map that indicates the range of codes associated with initial ranging, periodic ranging, bandwidth requests, and the range of codes reserved for pre-allocation.
The subscriber station selects a code from the set of codes mapped to initial ranging and transmits the code in an instance of the random access channel. The base station receives the initial ranging code during a random access channel ranging opportunity and assigns some resources to the subscriber station that transmitted the initial ranging code during the ranging opportunity to allow the subscriber station to communicate additional information in a dedicated link.
The subscriber station transmits its Medium Access Code (MAC) address to the base station over the assigned resources. The base station responds by assigning a Connection Identifier (CID) to the subscriber station.
The subscriber station uses its CID value to identify itself in communications with the base station. For example, the subscriber station can transmit one or more Subscriber Basic Capability message to the base station that communicates some of the capabilities of the subscriber station. The subscriber station can, for example, communicate the ability to support pre-allocated codes.
The base station can process the Subscriber Basic Capability message and determine the ability of the subscriber station to support pre-allocated codes. The base station can allocate one or more codes to the subscriber station at this point of the registration process.
Additionally, the subscriber station can transmit one or more registration request message to the base station that communicates the capabilities of the subscriber station, including its ability to support pre-allocated codes. The base station can process the registration request message and determine the ability of the subscriber station to support pre-allocated codes. The base station can allocate one or more codes to the subscriber station at this point of the registration process.
The subscriber station proceeds to block 620 and receives at least one pre-allocated code assignment from the base station. Although block 620 is shown as distinct from block 610 illustrating registering with the base station, the subscriber station can receive the one or more pre-allocated code assignment from the base station during the course of registering with the base station. For example, the subscriber station can receive one or more pre-allocated code assignments in response to the Subscriber Basic Capability message. Alternatively, the subscriber station can receive one or more pre-allocated code assignments in response to the registration request message or after the subscriber station registers with the base station. The subscriber station proceeds to block 630 and receives from the base station a usage type corresponding to each pre-allocated code. The subscriber station can also receive a semantic associated with one or more of the pre-allocated codes. The semantic can associate additional information with the pre-allocated access code distinct from the usage type.
After receiving the pre-allocated codes and the associated definitions, the subscriber station proceeds to block 640 and determines that it needs to access the random access channel and transmit a code to the base station. The need to access the random access channel can be any triggering event that results in accessing the random access channel. The subscriber station can determine, for example, that it needs to transmit a periodic ranging code, a bandwidth request, or some other request that can be conveyed over the random access channel.
The subscriber station proceeds to decision block 650 and determines if the subscriber station has a pre-allocated code corresponding to the specific request type. The subscriber station can determine whether any of the pre-allocated codes corresponds to a request that services the triggering event that caused the need to access the random access channel. For example, the subscriber station may have information to transmit on the uplink as the triggering event and need to transmit a bandwidth request. The subscriber station examines the pre-allocated codes to determine if one is associated with bandwidth requests.
If the subscriber station determines that it does not have a corresponding pre-allocated code, the subscriber station proceeds to block 690 and randomly selects a code from the group of codes associated with a desired usage type. The subscriber station then proceeds to block 670, described below.
If the subscriber station determines at decision block 650 that it does have a corresponding pre-allocated code, the subscriber station proceeds to block 660 and selects the desired pre-allocated code from memory, for example from a look up table of pre-allocated codes. The subscriber station proceeds to block 670.
At block 670, the subscriber station generates or otherwise assembles a message using the selected code, regardless of whether the code was selected from a pre-allocated code or randomly selected from a group of codes having the desired usage type. The subscriber station proceeds to block 680 to process the message and transmit the message to the base station over the random access channel.
Applications and Variations
The base station may allocate several codes to a subscriber station, with each code having a different meaning. For example, each distinct pre-allocated code can represent a distinct class of service. In another example, each distinct code can imply a number of pending bytes that the subscriber station has to transmit, operating similar to an incremental bandwidth request. The base station can allocate bandwidth more intelligently since it knows the source of the request and the class of service or number of pending bytes corresponding to each pre-allocated code.
As an example, a subscriber station may have the ability to determine an indication of its level of mobility. A subscriber station can determine its mobility in a variety of ways, such as through examination of a change in its location in time determined using a Global Positioning System (GPS) receiver or some other position location process, such as time of arrival of one reference signals. The subscriber station can report the indication of its mobility to the serving base station.
Alternatively, the base station may have the ability to determine an indication of the mobility of the subscriber station, for example, using time of arrival of a time stamped subscriber station signal or some other means. The base station can determine that a mobile station is highly mobile based on the indication of mobility and can allocate a code to the highly mobile subscriber station. The subscriber station can transmit the allocated code to allow the base station to characterize the power, timing, and frequency of the subscriber station.
In a mobile environment the power, timing, and frequency of the subscriber station needs to be adjusted over time. By allocating a specific code such as a CDMA code to a subscriber station, it is possible for the base station to efficiently estimate the power, timing, and frequency change over time and take appropriate corrective action on both the downlink as well as the uplink. In particular, allocating unique CDMA codes to highly mobile subscriber stations allows for them to transmit in frequent, if not every, ranging opportunity without the worry of colliding. These pre-allocated codes will be decoded at the base station and acted upon with priority in order to provide for quick correction.
The base station can implement a bias or filter mechanism that favor metrics received for a subscriber station. These metrics can be determined from a pre-allocated CDMA code received in the random access channel. Alternatively, the metrics can be determined by the base station from the received information in a scheduled data allocation provided data is being received from mobile station. This information can then be used to potentially calculate timing, power and frequency adjustments more accurately.
A mobile subscriber station can transition from a coverage area supported by a first base station to a coverage area supported by a second base station. In such a scenario, the communication link from the subscriber station is handed over from the first or serving base station to the second base station, referred to as a target base station. In a handover condition, the serving base station or the target base station can allocate a code to the subscriber station for use during the handover.
During a handover condition, the target base station allocates a non-contention initial ranging opportunity using a pre-allocated CDMA code. The target base station assigning a pre-allocated code to a subscriber station for the initial ranging may be advantageous as pre-allocation of an initial ranging code uses fewer resources than allocating an uplink opportunity, especially if the subscriber station in handover does not show up in the target base station for some reason, such as returning to the coverage area of the serving base station.
As another example, a subscriber station can have the ability to establish different types of communication links with a base station. For example, a subscriber station can establish a “best effort” communication link with a base station. The subscriber can establish a communication link with a base station to communicate real time traffic. The link established for real time traffic can be more sensitive to latency compared to the best effort communication link.
The base station can allocate a code to the subscriber station engaged in a link carrying real time traffic. The code can be, for example, used for uplink bandwidth requests and can indicate that the subscriber station is requesting bandwidth in support of real time traffic. The base station receiving the allocated code from the subscriber station will know the identity of the subscriber station and will know that the request is in support of real time traffic. The base station can then prioritize the bandwidth request over a bandwidth request from a subscriber station supporting a best effort link.
Apparatus and methods have been described herein for pre-allocating identifiers, such as CDMA codes, to a subscriber station for use in a random access channel. The base station pre-allocation of codes allows additional information to be conveyed through use of the code and decreases the latency and resources required to service an anonymous resource request over the random access channel.
As used herein, the term coupled or connected is used to mean an indirect coupling as well as a direct coupling or connection. Where two or more blocks, modules, devices, or apparatus are coupled, there may be one or more intervening blocks between the two coupled blocks.
The steps of a method, process, or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The various steps or acts in a method or process may be performed in the order shown, or may be performed in another order. Additionally, one or more process or method steps may be omitted or one or more process or method steps may be added to the methods and processes. An additional step, block, or action may be added in the beginning, end, or intervening existing elements of the methods and processes.
The above description of the disclosed embodiments is provided to enable any person of ordinary skill in the art to make or use the disclosure. Various modifications to these embodiments will be readily apparent to those of ordinary skill in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the disclosure.

## Claims

1. A method for handover of an existing communication link with a mobile station from a serving base station to a target base station, the method comprising:
allocating, by the target base station, a random access identifier that uniquely identifies the mobile station in a coverage area of the target base station;
obtaining, by the serving base station from the target base station, an indication of the allocated random access identifier;
transmitting, by the serving base station to the mobile station over the existing communication link, the indication of the allocated random access identifier;
receiving, by the mobile station from the serving base station over the existing communication link, the indication of the allocated random access identifier;
transmitting, by the mobile station to the target base station over a random access channel, the allocated random access identifier;
receiving, by the target base station from the mobile station over the random access channel, the allocated random access identifier;
generating, by the target base station, a feedback message comprising an adjustment based on the receiving of the allocated random access identifier by the target base station;
transmitting, by the target base station to the mobile station, the feedback message;
receiving, by the mobile station from the target base station, the feedback message; and
synchronizing the mobile station with the target base station using the adjustment in association with the handover of the existing communication link.

2. The method of claim 1, further comprising:
registering the mobile station with the target base station.

3. The method of claim 1, further comprising:
releasing the allocated random access identifier after synchronization.

4. The method of claim 1, further comprising:
the target base station receiving a registration message from the mobile station.

5. The method of claim 1, wherein the random access channel is limited to time and frequency resources within an uplink communication channel.

6. The method of claim 1, wherein the adjustment of the feedback message comprises at least one of a timing adjustment, a power adjustment, or a frequency offset.

7. The method of claim 1, wherein the random access identifier is a code division multiple access (CDMA) code.

8. The method of claim 1, wherein the allocated random access identifier received by the target base station is further usable by the target base station for bandwidth requests by the mobile station.

9. The method of claim 1, wherein the allocating, by the target base station of the random access identifier, is based on a handover condition responsive to a registration request message transmitted by the mobile station to the target base station during registration.

10. A system for handover of an existing communication link comprising:
a mobile station;
a serving base station in signal communication with the mobile station over the existing communication link; and
a target base station in signal communication with the mobile station,
wherein the target base station comprises a processor, a receiver, and a transmitter, the processor configured to allocate a random access identifier uniquely identifying the mobile station in a coverage area of the target base station in association with the handover of the existing communication link to the target base station, the receiver configured to receive the allocated random access identifier from the mobile station over a random access channel, the processor further configured to generate a feedback message comprising an adjustment based on the reception of the allocated random access identifier from the mobile station, and the transmitter configured to transmit the feedback message to the mobile station for synchronizing the mobile station with the target base station,
wherein the serving base station comprises a module configured to receive an indication of the allocated random access identifier from the target base station, and a transmitter configured to transmit the received indication of the allocated random access identifier to the mobile station over the existing communication link, and
wherein the mobile station comprises a receiver configured to receive the indication of the allocated random access identifier from the serving base station over the existing communication link, a transmitter configured to transmit the allocated random access identifier to the target base station over the random access channel, and a processor configured to synchronize the mobile station with the target base station using the adjustment.

11. The system of claim 10, wherein the receiver of the target base station is further configured to receive a registration message from the mobile station.

12. The system of claim 10, wherein the allocated random access identifier is released after synchronization.

13. The system of claim 10, wherein the random access channel is limited to time and frequency resources within an uplink communication channel.

14. The system of claim 10, wherein the adjustment of the feedback message comprises at least one of a timing adjustment, a power adjustment, or a frequency offset.

15. The system of claim 10, wherein the random access identifier is a code division multiple access (CDMA) code.

16. A system for handover of an existing communication link comprising:
a mobile station; and
a serving base station in signal communication with the mobile station over the existing communication link,
wherein the serving base station comprises a module configured to receive an indication of an allocated random access identifier uniquely identifying the mobile station in a coverage area of another base station in association with the handover of the existing communication link to the other base station, and a transmitter configured to transmit the received indication of the allocated random access identifier to the mobile station over the existing communication link, and
wherein the mobile station comprises a receiver configured to receive the indication of the allocated random access identifier from the serving base station over the existing communication link, a transmitter configured to transmit the allocated random access identifier to the other base station over a random access channel, and a processor configured to synchronize the mobile station with the other base station using an adjustment comprised by a feedback message received from the other base station.

17. The system of claim 16, wherein the random access channel is limited to time and frequency resources within an uplink communication channel.

18. The system of claim 16, wherein the adjustment of the feedback message comprises at least one of a timing adjustment, a power adjustment, or a frequency offset.

19. The system of claim 16, wherein the random access identifier is a code division multiple access (CDMA) code.

20. A system for handover of an existing communication link comprising:
a mobile station; and
a target base station in signal communication with the mobile station,
wherein the target base station comprises a processor, a receiver, and a transmitter, the processor configured to allocate a random access identifier uniquely identifying the mobile station in a coverage area of the target base station in association with the handover of the existing communication link to the target base station, the receiver configured to receive the allocated random access identifier from the mobile station over a random access channel, the processor further configured to generate a feedback message comprising an adjustment based on the reception of the random access identifier from the mobile station, and the transmitter configured to transmit the feedback message to the mobile station for synchronizing the mobile station with the target base station, and
wherein the mobile station comprises a receiver configured to receive an indication of the allocated random access identifier from the target base station via another base station over the existing communication link, a transmitter configured to transmit the allocated random access identifier to the target base station over the random access channel, and a processor configured to synchronize the mobile station with the target base station using the adjustment.

21. The system of claim 20, wherein the random access channel is limited to time and frequency resources within an uplink communication channel.

22. The system of claim 20, wherein the adjustment of the feedback message comprises at least one of a timing adjustment, a power adjustment, or a frequency offset.

23. The system of claim 20, wherein the random access identifier is a code division multiple access (CDMA) code.

24. The system of claim 20, wherein the receiver of the target base station is further configured to receive a registration message from the mobile station.

25. The system of claim 20, wherein the processor of the target base station is further configured to release the allocated random access identifier after synchronization.