Abstract:
A method and apparatus for accessing a telecommunications system. A channel having a plurality of data rates and a plurality of frame sizes is utilized by a mobile station to gain access to the system. If channel conditions allow, a faster data rate of the available data rates and a smaller frame size of the available frame sizes may be used to request access over the channel. By dynamically determining the data rate based on channel conditions, overall access delays for mobile stations using packet data services and making many access attempts may be reduced.

Description:
FIELD OF THE INVENTION 
     This invention relates to telecommunications systems and, more particularly, to a method and apparatus for accessing a system utilizing an access channel providing reduced access delay in a telecommunications system. 
     BACKGROUND OF THE INVENTION 
     Major cellular telecommunications systems types include those operating according to the Global Services for Mobile (GSM) Standard, the TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual Mode Wide Band Spread Spectrum Cellular Systems (IS-95A, currently being updated as IS-95B in the document TIA/EIA SP-3693), the TIA/EINIS-136 Mobile Station-Base Station Compatibility Standard (IS-136), and the TIA/EIA 553 Analog Standard (AMPS/TACS). Other major cellular systems include those operating in the personal communications system (PCS) band according to the IS-95 based ANSI-J-STD-008 1.8-2.0 GHz standard or those operating according to the GSM-based PCS 1900/1910 MHz frequency range standard. Currently, each of the major cellular system standards bodies is implementing packet data services into its digital cellular specifications. A packet data specification has been finalized for GSM and IS-95A. Packet data specifications compatible with the IS-136 and IS-95B standards are also being prepared. 
     In a typical cellular system a call establishment begins either by a base station transmitting a paging message to a mobile station on a paging channel and then the mobile station transmitting a paging response message to the base station on an access channel, or by a mobile station accessing the system on an access channel by transmitting an origination message to a base station. In either of these call establishment cases, the mobile station must access the system on an access channel, and information unique to the particular call establishment must be exchanged between the mobile station and base station over the access channel or other channels of the system air interface. The paging response message and origination message typically carry a large portion of the information. The information unique to the particular call establishment could include called number data, mobile station identification and capability related data, authentication information, etc. After receiving this information, the system must then use the information to set up the different layers of communication necessary in the system to implement the call. 
     In packet data applications, a mobile station establishes a connection with the base station when it has one or more data packets in the buffer of the mobile station to send or when it is paged by a base station having data packets to send. The mobile station accesses the system for a channel connection and transmits until it is determined that no data exists in the buffer for transmission. Since data may be received from a data server at the mobile or base station intermittently, it may be necessary to release the channel connection in order to maximize the use of the channel by other mobile stations. This means that the mobile station will be making multiple access attempts to establish a channel connection, each access attempt being made when the mobile or base station has enough data to transmit. Each access attempt may in itself involve more than one access attempt if initial access attempts are unsuccessful. In the current packet data system for GSM, IS-95A, IS-95B and IS-136, the access channel has a fixed frame size and data rate. For example, the IS-95B packet data access channel is the same channel used to originate regular calls. The IS-95B access channel has a frame size of 20 msec and a data rate of 4.8 kbps. 
     As third generation systems which will replace GSM, IS-136 and IS-95B are developed and packet data usage becomes more common, solutions must be found to handle packet data service delays that may be caused by the delays incurred when requesting access to the system each time packet data is to be sent. If many packet data users are in the system competing for channels, there will be a need to release access channels as often as possible and a need to perform new accesses following release of the accessed channel if new data is accumulated for transmission. An improved access procedure will be required for packet data services in these systems. 
     OBJECTS OF THE INVENTION 
     It is, therefore, an object of this invention to provide an improved method and apparatus for accessing a telecommunications system that overcomes the foregoing and other problems. 
     Another object of this invention is to provide a method and apparatus for accessing a telecommunications system using a channel providing reduced access delay. 
     Another object of this invention is to provide a method and apparatus for accessing a telecommunications system using a channel having variable data rates and frame sizes for access. 
     A further object of this invention is to provide a method and apparatus for accessing a telecommunications system using a channel having variable data rates and frame sizes assignable to a mobile station based on channel conditions and service type required. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved method and apparatus for accessing a telecommunications system. The method and apparatus utilizes a channel having variable data rates and frame sizes. In the method and apparatus, access to the system may be requested via at least one channel having variable data rates. Each of the available data rates is associated with at least one transmission frame size of a plurality of frame sizes. If channel conditions allow, a higher data rate of the available data rates may be used to request access over the channel. The method and apparatus has an advantage for use in packet data services. By dynamically determining the data rate based on channel conditions, overall access delays for mobile stations using packet data services and making many access attempts may be reduced. 
     In an embodiment of the invention, a plurality of access channel data rates and frame durations are available for use by a mobile station requesting access. The data rates and frame durations may be set so that the number of data bits per frame is constant for ease of processing. A mobile station accessing the system selects a data rate and associated frame duration based on channel conditions, mobile station power conditions or the type of service required. Packet data service users requiring shorter access delay may select a higher data rate and associated frame duration for a particular type of service under certain channel conditions, subject to transmission power requirements. Since a higher data rate requires a higher transmitted power to achieve a comparable Eb/No as at a lower data rate, transmission power of the mobile station at the higher rate must be increased compared to that at the lower rate without exceeding the maximum allowable transmitted power for the mobile station so the frame error rate (FER) and bit error rate (BER) remain within acceptable limits. 
     Transmission power requirements may be determined on the basis of a desired Eb/No to be received at the base station antenna for access attempts by the mobile station. The mobile station determines whether an estimated path loss is less than a maximum allowable path loss for a desired data rate for access. If the estimated path loss is less than the maximum allowable path loss at the desired data rate for access and the mobile station transmission power necessary to achieve the desired Eb/No does not exceed the maximum allowed power the mobile station is limited to for acceptable system performance, the desired data rate is selected. If the estimated path loss is greater than the maximum allowable path loss for the desired data rate for access or the necessary mobile station transmission power exceeds the allowable maximum for the mobile station, a lower data rate having a maximum allowable path loss greater than the estimated path loss and/or greater than the maximum allowed power for the mobile station is selected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read in conjunction with the accompanying drawings wherein: 
     FIG. 1 illustrates a block diagram of a telecommunications system constructed according to an embodiment of the present invention; 
     FIG. 2 is a block diagram of portions of a mobile station of the embodiment of the invention shown in FIG. 1; 
     FIG. 3 is a block diagram of portions of a base station of the embodiment of the invention shown in FIG. 1; 
     FIGS. 4A and 4B are illustrations of an access probe transmission and access probe sequence, respectively, according to an embodiment of the invention; and 
     FIG. 5 is a flow diagram illustrating process steps performed when accessing a system according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a block diagram of a telecommunications system  100  constructed according to an embodiment of the present invention. System  100  comprises mobile station  114 , and an infrastructure comprising system controller and switch  112  and base stations  102 ,  104 ,  106 ,  108  and  110 . A subscriber who subscribes to service provided by the operator of cellular system  100  may use mobile station  114  to make and receive phone calls over a radio interface, such as shown by radio interface  118  between mobile station  114  and base station  108 , as the subscriber moves throughout the coverage area of cellular system  100 . The subscriber also may use mobile station  114  to make and receive packet switched data calls over the radio interface  118 . During a packet data call, mobile station  114  may function as a data terminal for transmitting or receiving data. As such, mobile station  114  may be connected to a portable computer or fax machine. Each of base stations  102 ,  104 ,  106 ,  108  and  110  provides coverage over a separate area of system  100 , shown as cell A, cell B, cell C, cell D and cell E, respectively, in FIG.  1 . Base stations  102 ,  104 ,  106 ,  108  and  110  are connected to system controller and switch  112  by connections as in a conventional cellular system. System controller and switch  112  may be connected to a public switched telephone network to allow subscribers of cellular system  100  to make and receive phone calls from the landline public network. In the embodiment of FIG. 1, cell A, cell B, cell C and cell D are shown to be of about the same size and may be the size of what is commonly called a “microcell” or a cell of about 500 meters in width. A micro cell of system  100  may require a maximum mobile station transmission power level of approximately 200 mw. Cell E of system  100  is shown to be contained within the coverage area of cell C and may be the size of what is commonly called a “picocell” or a cell of about 100 meters in width. A picocell of system  100  may require a maximum mobile station transmission power level of approximately 20 mw. The embodiment of the invention has particular application to packet data users operating in a microcell or picocell environment. In this type of environment, signal path loss between the mobile station  114  and base stations  102 - 108  may be small, allowing necessary transmission power increases by mobile station  114  required for faster data rate and small frame access attempts. However, the embodiment has application to cellular systems having all sizes of cells. In the embodiment of FIG. 1, cellular system  100  may operate according to the Code Division Multiple Access (CDMA) cellular system standard specified in the document, “The CDMA 2000 ITU-R RTT Candidate Submission,” published by the Telecommunications Industry Association, TR45.5 Subcommittee, Apr. 2, 1998 (CDMA 2000). The method and apparatus of the invention has application to all types of telecommunications systems that use similar access principles, such as, for example, time division multiple access (TDMA) systems. 
     Referring now to FIG. 2, therein is a block diagram of portions of mobile station  114  of the embodiment of the invention shown in FIG.  1 . Mobile station  114  comprises antenna  200 , duplexer  202 , transmit power amplifier  204 , analog receiver  206 , transmit power controller  208 , searcher receiver  210 , digital data receiver  212 , digital data receiver  214 , diversity combiner/decoder  216 , control processor  218 , user digital vocoder  220 , transmit modulator  222  and user interface  224 . 
     Antenna  200  is coupled to analog receiver  206  through duplexer  202 . Signals received at antenna  200  are input to analog receiver  206  through duplexer  202 . The received signals are then converted to an IF frequency and then filtered and digitized in analog receiver  206  for input to digital data receiver  212 , digital data receiver  214  and searcher receiver  210 . The digitized IF signal input to digital data receiver  212 , digital data receiver  214  and searcher receiver  210  may include signals from many ongoing calls, together with the pilot carriers transmitted by the base station of the cell site in which the mobile station is currently located, plus the pilot carriers transmitted by the base stations in all neighboring cell sites. Digital data receiver  212  and digital data receiver  214  perform correlation on the IF signal with a pseudo random noise (PN) sequence of a desired received signal. The output of digital data receivers  212  and  214  is a sequence of encoded data signals from two independent paths. Searcher receiver  210  scans the time domain around the nominal time of a received pilot signal of a base station for other multi-path pilot signals from the same base station and for other signals transmitted from different base stations. Searcher receiver  210  measures the strength of any desired waveform at times other than the nominal time. Searcher receiver  210  generates signals to control processor  218  indicating the strengths of the measured signals to control processor  218 . 
     The encoded data signals output from digital data receiver  212  and digital data receiver  214  are input to diversity combiner/decoder  216 . In diversity combiner/decoder  216  the encoded data signals are aligned and combined, and the resultant data signal is then decoded using error correction and input to digital vocoder  220 . Digital vocoder  220  then outputs information signals to the user interface  224 . User interface may be a handset with a keypad or another type of user interface, such as a laptop computer monitor and keyboard. 
     For transmission of signals from mobile station  114 , a signal received at user interface  224  is input to user digital vocoder  220  in digital form as, for example, data or voice that has been converted to digital form at user interface  224 . In digital vocoder  220  the signal is encoded and output to transmit modulator  222 . Transmit modulator  222  Walsh encodes the signal and then modulates the Walsh encoded signal onto a PN carrier signal, with the PN carrier sequence being the PN carrier sequence of the CDMA channel to which the mobile station is assigned. The PN carrier information is transmitted to mobile station  114  from the system  100  and transferred to control processor  218  from digital data receivers  212  and  214  after being received from the system. Control processor  218  sends the PN carrier information to transmit modulator  222 . The PN modulated signal is then output from transmit modulator  222  to transmit power controller  208 . Transmit power controller  208  sets the level of the transmission power of mobile station  114  according to commands received from control processor  218 . In the embodiment of the invention, the transmission power is dependent on the data rate and frame size used for access. Control processor  218  also generates commands that set the transmission data rate and frame sizes used for access. The power control commands may be generated by control processor  218  according to commands received from the system or may be generated by software of control processor  218 , according to the embodiment of the invention, in response to data received from th e system through digital data receivers  212  and  214 . 
     The modulated signal is then output from transmit power controller  208  to transmit power amplifier  204  where the signal is amplified and converted to an IF frequency signal. The IF frequency signal is then output from power amplifier  204  to duplexer  20   2  and transmitted from antenna  200 . 
     Referring now to FIG. 3, therein is a block diagram of portions of a base station  110  of the embodiment of the invention shown in FIG.  1 . The block diagrams of any of the other base stations  102 ,  104 ,  106 , and  108  of FIG. 1 may be equivalent to that shown in FIG. 3 for base station  110 . Base station  110  includes a first receiver section  332 , a second receiver section  334 , control processor  322 , diversity combiner/decoder  324 , transmit power controller  326 , digital link  328 , input/out I/O  336 , transmit modulator  330 , control channel transmitter/modulator  320 , transmit power amplifier  310 , and antenna  304 . First receiver section  332  comprises antenna  300 , analog receiver  306 , searcher receiver  312  and digital data receiver  314 . Second receiver section  334  comprises antenna  302 , analog receiver  308 , searcher receiver  316  and digital data receiver  318 . 
     First receiver section  332  and second receiver section  334  provide space diversity for a single signal that may be received at both antennas  300  and  302 . The signals received at antenna  300  are input to analog receiver  306  where the signal is filtered, converted to an IF frequency and digitized to generate a digital signal. The digital signal is then output from analog receiver  306  to searcher receiver  312  and digital data receiver  314 . Searcher receiver  312  scans the time domain around the received signal to verify that digital data receiver  314  tracks the correct signal. Control processor  322  generates the control signals for digital data receiver  314  according to a signal received from the searcher receiver  312 , so that the correct signal is received at digital data receiver  314 . Digital data receiver  314  generates the proper PN sequence necessary to decode the digital signal received from analog receiver  306  and generates weighted output symbols for input to diversity combiner/decoder  324 . Antenna  302 , analog receiver  308 , searcher receiver  316  and digital data receiver  318  of second receiver section  334  function identically to the components of first receiver section  332  to generate a second set of weighted output symbols. The weighted symbols from digital data receiver  314  and digital data receiver  318  are then combined and decoded in diversity combiner/decoder  324  to generate received digital data which is then output through digital link  328  and I/O  336  to system controller and switch  112  of FIG.  1 . 
     When data received from system controller and switch  112  is to be transmitted from base station  110  on a traffic channel, the data is received at digital link  328  over I/O  336  and sent to transmit modulator  330 . Transmit modulator  330  then modulates the data using the appropriate Walsh function assigned to the mobile station to which the base station is transmitting. The Walsh modulated data is then spread by a voice channel PN sequence having the appropriate time shift and input to transmit power controller  326 . Transmit power controller  326  controls the transmission power in response to control signals received from control processor  322 . The power control commands may be generated by software in control processor  322 . The signal output from power controller  326  is input to transmit power amplifier  310  and then transmitted from antenna  304 . Base station  100  may have multiple transmit modulator and transmit power controllers for transmitting to multiple mobile stations. 
     In system  100 , a pilot channel that may be used for handoff measurements is generated by each base station. The pilot channel generated for each base station of system  100  is unique, with each pilot identified by the time shift (or phase) of the PN sequence transmitted from the particular base station rather than by a unique PN sequence. The pilot channel for base station  110  may be generated in control channel transmitter/modulator  320  in response to control signals generated by control processor  322 . The pilot channel signal may be generated by using a Walsh code sequence of all zeros and multiplying the Walsh code sequence by the system PN sequence to generate a pilot channel signal having the appropriate phase for the base station  110 . System  100  also utilizes at least one reverse pilot channel and at least one access channel from mobile station  114  to base station  108 . Each access channel is associated with a reverse pilot channel that is generated by using a Walsh code sequence of all zeros. The reverse pilot channel and access channel are used to obtain access to the system. 
     Referring now to FIGS. 4A and 4B, therein are illustrated the access channel structure and an access probe sequence, respectively, of an embodiment of the invention. In FIG. 4A the system time is shown as a series of consecutive access channel frames  402  on the system time access. The access probe transmission  400  comprises a preamble and a message capsule. The access probe transmission  400  has a duration of M×X msec preamble frames transmitted on the reverse pilot channel plus N×L msec message capsule frames transmitted on the access channel, where L and X are variable lengths. The value of X, M and N may be system constants. In the embodiment, the N×L msec message capsule frames may be of duration 20 msec, 10 msec or 5 msec with data rates of 38.4 kbps, 19.2 kbps and 9.6 kbps, respectively. The data rates and frame sizes are set so that the number of data bits per frame is constant for ease of processing. It is not required that each data rate be fixed to a specific frame size. For example, in an alternative of the embodiment, each data rate may be used with multiple frame sizes of 20 msec, 10 msec or 5 msec. For normal voice of circuit switched operations, the message capsule frames are typically 20 msec in duration. For packet switched applications, the message capsule frame duration is variable. 
     Access probes are transmitted as shown in FIG.  4 B. An access probe sequence comprises up to 1+NUM_STEP access probes, where NUM_STEP is a system-defined parameter. The preamble is transmitted on a reverse pilot channel associated with the access channel. The reverse pilot channel space is continuously searched by the base station so mobile station access on the associated access channel can be acquired by the system. In the embodiment of the invention, searcher receivers  312  and  316 , and digital data receivers  314  and  318  are configured to search and receive access probes having multiple frame durations of 5 msec, 10 msec and 20 msec, with multiple data rates of 38.4 kbps, 14.2 kbps and 9.6 kbps. Control processor  322  generates the appropriate control signals to cause data and frame rate determination to be performed, so that an access probe is received correctly. The reverse pilot channel and channel used for access are spaced by the same long code. Each access probe begins with access probe  1  and continues up until access probe 1+NUM_STEP if no acknowledgment is received from the base station after a time-out period denoted by TA. Access probe  1  is transmitted at an initial power level, and each succeeding access probe is transmitted at a-power level incremented by PI. In the embodiment of the invention, the power levels used for access are dependent on the message capsule data rate used. The power levels for 9.6 kbps are as set for the CDMA 2000 system. The initial power level, IP, plus power increment, PI, for different access capsule data rates may be scaled such that for a rate of 19.2 kbps transmit power is 3dB above IP for 9.6 kbps, and for a rate of 38.4 kbps transmit power is 6dB above IP for 9.6 kbps. Access probes are separated by the period TA and a random probe backoff time (RT) that are system constants. If no response is received during an access probe sequence, the access probe sequence may be repeated. In an access attempt, the access probe may be repeated up to a number, MAX_SEQ, that is set by the system. 
     In the embodiment of the invention, when mobile station  114  is involved in a packet data call, mobile station  114  may utilize the variable data rate access probes of the invention to minimize the time needed to obtain access to the system. Mobile station  114  may transmit an access probe to base station  108  in response to a page received on a paging channel or autonomously when mobile station  114  has packet data to be sent. 
     Referring now to FIG. 5, therein is a flow diagram illustrating process steps performed when accessing a system using variable rate and variable length frames according to an embodiment of the invention. The process begins at step  500 . The process may begin at initial access for a packet data call or sometime during the duration of an ongoing packet data call, when a physical channel needs to be re-accessed for continued packet data transmission. This may include mobile station  114  or base station  110  initiated accesses. At step  502 , searcher receiver  210  of mobile station  114  measures the received signal strength, P pt , of the forward link pilot channel from base station  108 . Next, at step  504 , control processor  218  calculates an estimated path loss, L c . L c =P pt −P pr  where P pt  is the forward link pilot channel transmit power of base station  108 . P pt  may be fixed based upon the operating environment, cell type, etc., and the value of P pt  may be transmitted to mobile station  114  from base station  108  via message signaling. The forward link pilot channel measurements of step  502  and calculations of step  504  need not be done after access is required, as these forward link measurements and calculations may be continuously made and already available when mobile station  114  begins the process at step  500 . 
     At step  506 , a determination is made by control processor  218  as to whether or not the calculated path loss L c  is greater than a threshold path loss L 1 , where L 1  is the maximum path loss a signal transmitted from mobile station  114  can incur when transmitting at 19.2 kbps at a reference transmission power. The reference transmission power may be the maximum possible transmit power for mobile station  114 . The threshold path loss L 1  may be a system value determined based on a desired Eb/No to give a desired frame error rate (FER) and bit error rate (BER) rate. Typically, the transmitted power required to achieve a desired Eb/No at base station  118  increases with an increased data rate. Based on a desired FER and BER, then the allowable path loss for transmitting at 9.6 kbps will be greater than the maximum allowable path loss when transmitting at 19.2 kbps at a selected transmission power. 
     If, at step  506 , a determination is made that L c  is greater than L 1 , the process moves to step  508 . At step  508 , control processor  218  generates the appropriate control signals so that mobile station  114  transmits the access probes of FIGS. 4A and 4B using a message capsule with data transmitted at a rate of 9.6 kbps having a frame of 20 msec in length and initial power IP set for 9.6 kbps. The process then ends at step  510 . If, however, at step  506 , a determination is made that L c  is not greater than L 1 , the process moves to step  512 . 
     At step  512 , a determination is made by control processor  218  as to whether or not the calculated path loss L c  is less than or equal to L 1  and greater than L 2 , where L 2  is the maximum path loss a signal transmitted from mobile station  114  can suffer when transmitting at 38.4 kbps at the reference transmission power. The threshold path loss L 2  may be a value determined based on a desired FER and BER. 
     If, at step  512 , a determination is made that L c  is less than or equal to L 1  and greater than L 2 , the process moves to step  514 . At step  514 , control processor  218  then determines if the transmit power head room for transmitting at 19.2 kbps exists by determining whether the necessary transmit power for 19.2 kbps to achieve the desired Eb/No with a loss of L c  is within the maximum allowable transmit power for mobile station  114 . If a determination is made that the transmit power head room for transmitting at 19.2 kbps exists, the process moves to step  516 . At step  516 , control processor  218  generates the appropriate control signals so that mobile station  114  transmits the access probes of FIGS. 4A and 4B using a message capsule with data transmitted at a rate of 19.2 kbps having a frame of 10 msec in length and initial power IP set for 19.2 kbps. The process then ends at step  518 . If, however, at step  514 , a determination is made that the transmit power head room for transmitting at 19.2 kbps does not exist, the process moves to step  508  and transmits the access probes of FIGS. 4A and 4B using a message capsule with data transmitted at a rate of 9.6 kbps having a frame of 20 msec in length and initial power IP set for 9.6 kbps. The process then ends at step  510 . 
     If, however, at step  512 , a determination is made that L c  is not greater than L 2 , the process moves to step  520 . At step  520 , control processor  218  determines if the transmit power head room for transmitting at 38.4 kbps exists by determining whether the necessary transmit power for 38.4 kbps to achieve the desired Eb/No with a loss of L c  is within the maximum allowable transmit power for mobile station  114 . If the transmit power head room for transmitting at 38.4 kbps exists, the process moves to step  522 . At step  522 , control processor  218  generates appropriate control signals so that mobile station  114  transmits the access probes of FIGS. 4A and 4B using a message capsule with data transmitted at a rate of 38.4 kbps having a frame of 5 msec in length and initial power IP set for 38.4 kbps. The process then ends at step  524 . If, however, at step  520 , a determination is made that power head room for transmitting at 38.4 kbps does not exist, the process moves to step  514 . At step  514 , control processor  218  determines if the transmit power head room for transmitting at 19.2 kbps exists. If a determination is made that the transmit power head room for transmitting at 19.2 kbps exists, the process moves to step  516 . At step  516 , control processor  218  generates the appropriate control signals so that mobile station  114  transmits the access probes of FIGS. 4A and 4B using a message capsule with data transmitted at a rate of 19.2 kbps having a frame of 10 msec in length and initial power IP set for 19.2 kbps. The process then ends at step  518 . If, however, at step  514 , a determination is made that the transmit power head room for transmitting at 19.2 kbps does not exist, the process moves to step  508  and transmits the access probes of FIGS. 4A and 4B using a message capsule with data transmitted at a rate of 9.6 kbps having a frame of 20 msec in length and initial power IP set for 9.6 kbps. The process then ends at step  510 . 
     While the embodiment shown utilizes a set frame size for each of the different data rates that may be used for access, it is within the scope of the invention to provide multiple frame sizes for use with each possible data rate. For example, 38.4 kbps could be used with frame sizes of 5, 10 or 20 msec; 19.2 kbps could be used with frame sizes of 10 or 20 msec; and 9.6 kbps could be used with frame sizes of 20 msec. In this case, process steps  516  and  522  may involve access using varying frame sizes. Also, it is within the scope of the invention to determine the access data rate based on predetermined algorithms using parameters other than path loss or to perform the access data rate determination within other than the mobile station. For example, the access data rate may be calculated at the base station, and the appropriate information could then be transmitted to the mobile station to inform the mobile station of the data rate and frame size to use on the access channel. 
     Therefore, while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes to form and details may be made therein without departing from the spirit and scope of the invention.