Patent Publication Number: US-2006014557-A1

Title: Method and system for determining a power level for communication in a wireless network

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY  
      The present invention is related to that disclosed in U.S. Provisional Patent No. 60/588,809, filed Jul. 16, 2004, entitled “Technique to Efficiently Deploy the CDMA2000 Networks.” U.S. Provisional Patent No. 60/588,809 is assigned to the assignee of the present application. The subject matter disclosed in U.S. Provisional Patent No. 60/588,809 is hereby incorporated by reference into the present disclosure as if fully set forth herein. The present application hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent No. 60/588,809.  
    
    
     TECHNICAL FIELD OF THE INVENTION  
      The present invention relates generally to wireless networks and, more specifically, to a method and system for determining a power level for communication in a wireless network.  
     BACKGROUND OF THE INVENTION  
      The use of cellular telephones and wireless networks has become increasingly widespread. Mobile stations, such as cellular telephones, perform system access procedures to access the wireless network for services, such as call origination, page response, registration, data burst request or response, order request or response, and the like. Basically, the mobile station enters the system access state whenever it has to send a message to a base station in the wireless network while it is not on a traffic channel.  
      An attempt by a mobile station to transmit the message over the air is referred to as an access probe. Each message the mobile station is sending over the access channel fits within one access probe. A collection of access probes sent at increasing power levels is referred to as an access probe sequence. The entire process of the mobile station sending a message on the access channel and receiving or failing to receive a response from the base station is referred to as an access attempt, which is made up of several access probe sequences.  
      The access attempt ends with either a layer 2 acknowledgement to the transmitted message being received within a certain amount of time or a time-out based on not receiving an acknowledgement to a maximum number of access probe sequences. When the acknowledgement is received from the base station, the service requested by the mobile station is generally provided.  
      However, in conventional wireless networks, when the mobile station subsequently wants to request another service, the entire process is started again from the beginning with neither the base station nor the mobile station making any use of information from the previous access attempt. In addition, information related to the access attempt that may be helpful for the base station to provide better service for mobile stations in its coverage area is not made available to the base station.  
      Therefore, there is a need in the art for improved wireless networks that more efficiently facilitate access attempts and that provide information useful to the base stations based on the access attempts. In particular, there is a need for a wireless network that is able to provide mobile stations capable of informing the base stations of a power level and also a number of access attempts in a successful access probe that may be used by the base stations to determine coverage holes, to resolve link imbalance, to implement intelligent power control, and to set up calls more quickly.  
     SUMMARY OF THE INVENTION  
      In accordance with the present invention, a method and system for determining a power level for communication in a wireless network are provided that substantially eliminate or reduce disadvantages and problems associated with conventional methods and systems.  
      To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a method for determining a power level for communication in a wireless network. According to an advantageous embodiment of the present invention, the method comprises generating a probe message comprising a power level indicator. The power level indicator corresponds to a particular power level of transmission for the probe message. The probe message is operable to request a base station to provide system access for a mobile station. The probe message is sent to the base station at the particular power level.  
      According to one embodiment of the present invention, an access parameter message comprising an initial power level and a power level increment is received from the base station.  
      According to another embodiment of the present invention, the power level indicator comprises a probe number for the probe message and the access parameter message further comprises a maximum probe number.  
      According to still another embodiment of the present invention, a response to the probe message is received from the base station and communication with the base station is provided based on the particular power level.  
      According to yet another embodiment of the present invention, the probe message comprises an Automatic Repeat Request message.  
      According to a further embodiment of the present invention, the probe message is sent to a plurality of base stations.  
      According to a still further embodiment of the present invention, the power level indicator comprises a probe number for the probe message.  
      According to yet a further embodiment of the present invention, the probe message further comprises a coverage area indicator.  
      According to an even further embodiment of the present invention, the coverage area indicator comprises an access sequence number that is operable to identify an access sequence associated with the probe message.  
      Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the term “each” means every one of at least a subset of the identified items; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:  
       FIG. 1  illustrates an exemplary wireless network that is capable of providing power level determination for communication according to the principles of the present invention;  
       FIG. 2  illustrates an exemplary base station that is capable of identifying a power level for communication with a mobile station according to the principles of the present invention;  
       FIG. 3  is a flow diagram illustrating a method for determining a power level for communication in the wireless network of  FIG. 1  from the perspective of the base station of  FIG. 2  according to the principles of the present invention;  
       FIG. 4  illustrates an exemplary mobile station that is capable of controlling power levels for communication with a base station according to the principles of the present invention; and  
       FIG. 5  is a flow diagram illustrating a method for determining a power level for communication in the wireless network of  FIG. 1  from the perspective of the mobile station of  FIG. 4  according to the principles of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 1 through 5 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged wireless network.  
       FIG. 1  illustrates an exemplary wireless network  100  that is capable of providing power level determination for communication according to the principles of the present invention. Wireless network  100  comprises a plurality of cell sites  121 - 123 , each containing one of the base stations, BS  101 , BS  102 , or BS  103 . Base stations  101 - 103  communicate with a plurality of mobile stations (MS)  111 - 114  over code division multiple access (CDMA) channels according to, for example, the IS-2000 standard (i.e., CDMA2000). In an advantageous embodiment of the present invention, mobile stations  111 - 114  are capable of receiving data traffic and/or voice traffic on two or more CDMA channels simultaneously. Mobile stations  111 - 114  may be any suitable wireless devices (e.g., conventional cell phones, PCS handsets, personal digital assistant (PDA) handsets, portable computers, telemetry devices) that are capable of communicating with base stations  101 - 103  via wireless links.  
      The present invention is not limited to mobile devices. The present invention also encompasses other types of wireless access terminals, including fixed wireless terminals. For the sake of simplicity, only mobile stations are shown and discussed hereafter. However, it should be understood that the use of the term “mobile station” in the claims and in the description below is intended to encompass both truly mobile devices (e.g., cell phones, wireless laptops) and stationary wireless terminals (e.g., a machine monitor with wireless capability).  
      Dotted lines show the approximate boundaries of cell sites  121 - 123  in which base stations  101 - 103  are located. The cell sites are shown approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the cell sites may have other irregular shapes, depending on the cell configuration selected and natural and man-made obstructions.  
      As is well known in the art, each of cell sites  121 - 123  is comprised of a plurality of sectors, where a directional antenna coupled to the base station illuminates each sector. The embodiment of  FIG. 1  illustrates the base station in the center of the cell. Alternate embodiments may position the directional antennas in corners of the sectors. The system of the present invention is not limited to any particular cell site configuration.  
      In one embodiment of the present invention, each of BS  101 , BS  102  and BS  103  comprises a base station controller (BSC) and one or more base transceiver subsystem(s) (BTS). Base station controllers and base transceiver subsystems are well known to those skilled in the art. A base station controller is a device that manages wireless communications resources, including the base transceiver subsystems, for specified cells within a wireless communications network. A base transceiver subsystem comprises the RF transceivers, antennas, and other electrical equipment located in each cell site. This equipment may include air conditioning units, heating units, electrical supplies, telephone line interfaces and RF transmitters and RF receivers. For the purpose of simplicity and clarity in explaining the operation of the present invention, the base transceiver subsystems in each of cells  121 ,  122  and  123  and the base station controller associated with each base transceiver subsystem are collectively represented by BS  101 , BS  102  and BS  103 , respectively.  
      BS  101 , BS  102  and BS  103  transfer voice and data signals between each other and the public switched telephone network (PSTN) (not shown) via communication line  131  and mobile switching center (MSC)  140 . BS  101 , BS  102  and BS  103  also transfer data signals, such as packet data, with the Internet (not shown) via communication line  131  and packet data server node (PDSN)  150 . Packet control function (PCF) unit  190  controls the flow of data packets between base stations  101 - 103  and PDSN  150 . PCF unit  190  may be implemented as part of PDSN  150 , as part of MSC  140 , or as a stand-alone device that communicates with PDSN  150 , as shown in  FIG. 1 . Line  131  also provides the connection path for control signals transmitted between MSC  140  and BS  101 , BS  102  and BS  103  that establish connections for voice and data circuits between MSC  140  and BS  101 , BS  102  and BS  103 .  
      Communication line  131  may be any suitable connection means, including a T1 line, a T3 line, a fiber optic link, a network packet data backbone connection, or any other type of data connection. Line  131  links each vocoder in the BSC with switch elements in MSC  140 . The connections on line  131  may transmit analog voice signals or digital voice signals in pulse code modulated (PCM) format, Internet Protocol (IP) format, asynchronous transfer mode (ATM) format, or the like.  
      MSC  140  is a switching device that provides services and coordination between the subscribers in a wireless network and external networks, such as the PSTN or Internet. MSC  140  is well known to those skilled in the art. In some embodiments of the present invention, communications line  131  may be several different data links where each data link couples one of BS  101 , BS  102 , or BS  103  to MSC  140 .  
      In the exemplary wireless network  100 , MS  111  is located in cell site  121  and is in communication with BS  101 . MS  113  is located in cell site  122  and is in communication with BS  102 . MS  114  is located in cell site  123  and is in communication with BS  103 . MS  112  is also located close to the edge of cell site  123  and is moving in the direction of cell site  123 , as indicated by the direction arrow proximate MS  112 . At some point, as MS  112  moves into cell site  123  and out of cell site  121 , a hand-off will occur.  
      In accordance with an advantageous embodiment of the present invention, one or more of mobile stations  111 - 114  are able to provide access probe and access sequence number information to base stations  101 - 103 . When a mobile station, such as mobile station  111 , performs a system access procedure to access wireless network  100  for services, such as call origination, page response, registration, data burst request or response, order request or response, and the like, mobile station  111  transmits a probe message in an access probe to base station  101 . It will be understood that mobile station  111  may also transmit a probe message to one or more other base stations, such as base stations  102 - 103 , without departing from the scope of the present invention.  
      If the probe message is not acknowledged within a specified period of time, mobile station  111  increases the power level associated with the access probe and sends another probe message. If the power level reaches a maximum value, mobile station  111  begins a new access sequence by sending the probe message at the initial power level again. Mobile station  111  continues until a maximum number of access sequences is reached or until an acknowledgement is received from base station  101 .  
      In generating the probe message for each access probe, mobile station  111  includes a power level indicator and may include a coverage area indicator within the probe message. For example, mobile station  111  may include in the probe message both a probe number to identify the current probe within the current access sequence and an access sequence number to identify the current access sequence. For one embodiment, the probe message may comprise an Automatic Repeat Request (ARQ) message.  
      Based on the initial power level used by mobile station  111  in transmitting the access probe and based on the value of the increment used to increase the power level in each successive access probe, base station  101  is able to determine the power level at which mobile station  111  transmitted the successful access probe from the probe number. In addition, base station  101  may use the access sequence number to determine locations of coverage holes, to resolve link imbalance, and to set up calls more quickly.  
       FIG. 2  illustrates base station (BS)  101  in greater detail according to the principles of the present invention. BS  101  comprises base station controller (BSC)  210  and at least one base transceiver subsystem (BTS)  220 , as previously described in connection with  FIG. 1 . Base station controller  210  manages the resources in cell site  121 , including base transceiver subsystem  220 . According to one embodiment, base transceiver subsystem  220  comprises base transceiver subsystem (BTS) controller  225 , channel controller  235  (which may comprise at least one channel element  240 ), transceiver interface (IF)  245 , radiofrequency (RF) transceiver unit  250 , antenna array  255 , and power level identifier  260 .  
      BTS controller  225  may comprise processing circuitry and memory capable of executing an operating program that controls the overall operation of base transceiver subsystem  220  and communicates with base station controller  210 . Under normal conditions, BTS controller  225  directs the operation of channel controller  235 , which may comprise a number of channel elements, such as channel element  240 , that are each operable to perform bidirectional communication in the forward channel and the reverse channel. A “forward channel” refers to outbound signals from the base station  101  to mobile stations  111  and  112  and a “reverse channel” refers to inbound signals from mobile stations  111  and  112  to base station  101 . Transceiver IF  245  transfers bidirectional channel signals between channel controller  240  and RF transceiver unit  250 .  
      Antenna array  255  transmits forward channel signals received from RF transceiver unit  250  to mobile stations in the coverage area of base station  101 . Antenna array  255  is also operable to send to RF transceiver unit  250  reverse channel signals received from mobile stations in the coverage area of the base station  101 . According to one embodiment of the present invention, antenna array  255  comprises a multi-sector antenna, such as a three-sector antenna in which each antenna sector is responsible for transmitting and receiving in a coverage area corresponding to an arc of approximately 120°. Additionally, RF transceiver unit  250  may comprise an antenna selection unit to select among different antennas in antenna array  255  during both transmit and receive operations.  
      For the illustrated embodiment, power level identifier  260  is operable to extract a power level indicator and a coverage area indicator from a probe message received from a mobile station, such as mobile station  111 . For example, power level identifier  260  may be able to extract a probe number and an access sequence number from the probe message. For one embodiment, the probe message may comprise an Automatic Repeat Request (ARQ) message.  
      Power level identifier  260  has access to the initial power level used by mobile station  111  in transmitting the access probe and to the value of the increment used to increase the power level in each successive access probe, which are both provided to mobile station  111  by base station  101  in an access parameter message. In addition, the access parameter message may comprise a maximum probe number and/or a maximum access sequence number. For another embodiment, however, the maximum probe number and/or the maximum access sequence number may be predetermined. For a particular embodiment, for example, both maximum numbers may be 16.  
      Based on the initial power level and the value of the increment used to increase the power level in successive probes and based on the probe number extracted from the probe message, power level identifier  260  is able to determine the power level at which mobile station  111  transmitted the successful access probe. In addition, power level identifier  260  may use the extracted access sequence number to determine locations of coverage holes, to resolve link imbalance, and to set up calls more quickly.  
       FIG. 3  is a flow diagram illustrating a method  300  for determining a power level for communication in wireless network  100  from the perspective of base station  101  according to the principles of the present invention. For the purposes of simplicity and clarity in explaining the operation of the present invention, it shall be assumed in the following example that base station (BS)  101  of wireless network  100  provides service for mobile station (MS)  111 . However, the descriptions that follow also apply to the remaining base stations and mobile stations in wireless network  100 .  
      Initially, BS  101  sends an access parameter message (APM) to MS  111  in a paging channel (process step  305 ). The access parameter message comprises information for MS  111  to use in attempting to access BS  101  to request services. For example, the access parameter message may comprise an initial power level for MS  111  to use in an initial probe, as well as a power level increment by which to increase the power level with each subsequent probe in a particular access sequence. The access parameter message may also comprise a maximum probe number and/or a maximum access sequence number.  
      At a later time, BS  101  receives a probe comprising a probe message from MS  111  (process step  310 ). For one embodiment, the probe message may comprise an Automatic Repeat Request (ARQ) message. Based on information within the probe message, power level identifier  260  of BS  101  identifies the power level at which the probe was transmitted from MS  111  (process step  315 ). For example, power level identifier  260  may extract a probe number and an access sequence number from the probe. Using the initial power level and the power increment information previously provided by BS  101  to MS  111  in the access parameter message, power level identifier  260  is able to calculate the transmission power level for the received probe. BS  101  may also be able to determine information about the coverage area based on the access sequence number.  
      BS  101  then begins communication with MS  111  at the identified power level (process step  320 ). BS  101  may also send an updated access parameter message to MS  111  based on the identified power level (process step  325 ). For example, BS  101  may change the initial power level for use by MS  111  in future probes to correspond to the identified power level to increase the chances of a successful probe earlier in the access sequence. In addition, BS  101  may make adjustments to the maximum probe number and/or maximum access sequence number. For example, BS  101  may reduce the maximum probe number such that the final power level before beginning a new access sequence remains the same.  
       FIG. 4  illustrates mobile station  111  in greater detail according to one embodiment of the present invention. Mobile station (MS)  111  is illustrated by way of example only. However, it will be understood that the components illustrated and described with respect to MS  111  are also part of mobile stations  112 - 114 . MS  111  comprises antenna  405 , radio frequency (RF) transceiver  410 , transmit (TX) processing circuitry  415 , microphone  420 , receive (RX) processing circuitry  425 , and speaker  430 . MS  111  also comprises main processor  440 , input/output (I/O) interface (IF)  445 , keypad  450 , display  455 , lagging feature (LF) button  458 , and memory  460 .  
      RF transceiver  410  receives from antenna  405  an incoming RF signal transmitted by BS  101 . RF transceiver  410  down-converts the incoming RF signal to produce an intermediate frequency (IF) or a baseband signal. The IF or baseband signal may be sent to receiver processing circuitry  425 , which produces a processed baseband signal by filtering, decoding, and/or digitizing the baseband or IF signal. Receiver processing circuitry  425  is also operable to transmit the processed baseband signal to speaker  430  (e.g., when the processed baseband signal comprises voice data) or to main processor  440  for further processing (e.g., when the processed baseband signal relates to web browsing).  
      Transmitter processing circuitry  415  receives, analog or digital voice data from microphone  420  or other outgoing baseband data (e.g., web data, e-mail, interactive video game data and the like) from main processor  440 . Transmitter processing circuitry  415  encodes, multiplexes and/or digitizes the outgoing baseband data to produce a processed baseband or IF signal. RF transceiver  410  receives the outgoing processed baseband or IF signal from transmitter processing circuitry  415 . RF transceiver  410  up-converts the baseband or IF signal to an RF signal that may be transmitted via antenna  405 .  
      According to one embodiment, main processor  440  may comprise a microprocessor or microcontroller. Memory  460 , which is coupled to main processor  440 , may comprise a random access memory (RAM) and/or a read-only memory (ROM). Main processor  440  executes basic operating system program  465  stored in memory  460  in order to control the overall operation of mobile station  111 . In one such operation, main processor  440  controls the reception of forward channel signals and the transmission of reverse channel signals by RF transceiver  410 , receiver processing circuitry  425 , and transmitter processing circuitry  415 . Main processor  440  may also execute other processes and programs resident in memory  460 . Main processor  440  may move data into or out of memory  460 , as required by an executing process.  
      Memory  460  further comprises a power level controller  470  and a probe message controller  475 . Although illustrated separately, it will be understood that power level controller  470  and probe message controller  475  may be implemented together in a single application without departing from the scope of the present invention.  
      Power level controller  470  is operable to make adjustments to the power level used by mobile station  111  to transmit messages. For example, power level controller  470  is operable to determine an initial power level for sending a probe to base station  101  based on an access parameter message previously received from base station  101 . In addition, power level controller  470  is operable to determine a power level increment based on the access parameter message. Power level controller  470  is also operable to increase the power level of subsequent probes within an access sequence by the power level increment.  
      Probe message controller  475  is operable to provide a power level indicator and a coverage area indicator to base station  101 . When mobile station  111  performs a system access procedure to access wireless network  100  for services, such as call origination, page response, registration, data burst request or response, order request or response, and the like, probe message controller  475  generates a probe message comprising a probe number as a power level indicator and an access sequence number as a coverage area indicator. For one embodiment, the probe message may comprise an Automatic Repeat Request (ARQ) message. For a particular embodiment, the ARQ message may comprise a four-bit field for the probe number and a four-bit field for the access sequence number.  
      Mobile station  111  transmits the probe message in an access probe to base station  101 . It will be understood that mobile station  111  may also transmit the probe message to one or more other base stations, such as base stations  102 - 103 , without departing from the scope of the present invention.  
      If mobile station  111  does not receive an acknowledgement of the probe message within a specified period of time, power level controller  470  is operable to increase the power level associated with the access probe. In addition, probe message controller  475  is operable to generate an updated probe message that comprises the updated probe number and access sequence number. Mobile station  111  may then send the updated probe message to base station  101 .  
      Power level controller  470  is also operable to determine that the power level has reached a maximum value based on a maximum number of probes being sent in a particular access sequence, at which point mobile station  111  may begin a new access sequence. For one embodiment, the maximum probe number may be provided by base station  101  in the access parameter message or other suitable communication. For another embodiment, the maximum probe number may be predetermined.  
      To begin a new access sequence, power level controller  470  adjusts the power level back down to the initial power level and sends the corresponding probe message generated by probe message controller  475  at the initial power level. Mobile station  111  continues until a maximum number of access sequences is reached or until an acknowledgement is received from base station  101 . As with the maximum number of probes, the maximum access sequence number may be provided by base station  101  in the access parameter message or other suitable communication. For another embodiment, the maximum access sequence number may be predetermined.  
      Main processor  440  is also coupled to the I/O interface  445 . I/O interface  445  provides mobile station  111  with the ability to connect to other devices, such as laptop computers, handheld computers and the like. I/O interface  445  provides a communication path between these accessories and main controller  440 . Main processor  440  is also coupled to keypad  450  and display unit  455 . The operator of mobile station  111  may use keypad  450  to enter data into mobile station  111 . Display  455  may comprise a liquid crystal display capable of rendering text and/or graphics from websites. It will be understood that additional embodiments may use other types of displays.  
       FIG. 5  is a flow diagram illustrating a method  500  for determining a power level for communication in wireless network  100  from the perspective of mobile station  111  according to the principles of the present invention. For the purposes of simplicity and clarity in explaining the operation of the present invention, it shall be assumed in the following example that base station (BS)  101  of wireless network  100  provides service for mobile station (MS)  111 . However, the descriptions that follow also apply to the remaining base stations and mobile stations in wireless network  100 .  
      Initially, MS  111  receives an access parameter message (APM) from BS  101  in a paging channel (process step  505 ). The access parameter message comprises information for MS  111  to use in attempting to access BS  101  to request services. For example, the access parameter message may comprise an initial power level for MS  111  to use in an initial probe, as well as a power level increment by which to increase the power level with each subsequent probe in a particular access sequence. The access parameter message may also comprise a maximum probe number and/or a maximum access sequence number.  
      At a later time, MS  111  decides to communicate with BS  101  and prepares to send a probe to BS  101  based on the access parameter message (process step  510 ). MS  111  initiates a first access sequence (process step  515 ). Probe message controller  475  of MS  111  then generates a first probe message that includes the probe number and the access sequence number (process step  520 ). For one embodiment, the probe message may comprise an Automatic Repeat Request (ARQ) message. For a particular embodiment, the ARQ message may comprise a four-bit field for the probe number and a four-bit field for the access sequence number. MS  111  sends the probe message to BS  101  in a first probe (process step  525 ).  
      If no response to the probe is received from BS  101  within a specified period of time (process step  530 ), power level controller  470  of MS  111  determines whether or not the probe number has reached a maximum (process step  535 ). The maximum probe number may be predetermined, may be provided by BS  101  in the access parameter message, or may be otherwise suitably determined. For a particular embodiment, the maximum probe number may be 16.  
      If the maximum probe number has not yet been reached (process step  535 ), power level controller  470  increments the power level for transmission of probes by MS  111  based on the power level increment provided by BS  101  in the access parameter message (process step  540 ). Probe message controller  475  also increments the probe number (process step  545 ) before generating another probe message based on the updated probe number (process step  520 ).  
      If the maximum probe number has been reached (process step  535 ), power level controller  470  determines whether or not the access sequence number has reached a maximum (process step  550 ). The maximum access sequence number may be predetermined, may be provided by BS  101  in the access parameter message, or may be otherwise suitably determined. For a particular embodiment, the maximum access sequence number may be 16.  
      If the maximum access sequence number has not yet been reached (process step  550 ), probe message controller  475  increments the access sequence number (process step  555 ) before initiating another access sequence (process step  515 ). However, if the maximum access sequence number has been reached (process step  550 ), the access attempt by MS  111  has failed and the method comes to an end.  
      If a response to the probe is received from BS  101  within the specified period of time (process step  530 ), MS  111  then begins communication with BS  101  at the same power level used in transmitting the successful probe (process step  560 ). MS  111  may also receive an updated access parameter message from BS  101  based on the power level of the successful probe (process step  565 ), after which the method comes to an end. For example, BS  101  may change the initial power level for use by MS  111  in future probes to correspond to the power level of the successful probe to increase the chances of a successful probe earlier in the access sequence. In addition, BS  101  may make adjustments to the maximum probe number and/or maximum access sequence number. For example, BS  101  may reduce the maximum probe number such that the final power level before beginning a new access sequence remains the same.  
      Although the present invention has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.