Abstract:
A method and apparatus for reducing call setup latency for a wireless device in a cellular network where the wireless device receives, stores, and analyzes base station overhead information to reduce the need to perform initialization after a call session terminates.

Description:
REFERENCE TO RELATED APPLICATIONS—CLAIM OF PRIORITY  
       [0001]    This invention is related and claims priority under 35 USC 119 to U.S. Provisional Application No. 60/379,375, filed May 8, 2002, Attorney Docket Number 02-0534/PR, and entitled “Fast Traffic Channel Reconnection with Base Station Assistance”, the contents of which are hereby incorporated in their entirety by reference. 
     
    
     
       BACKGROUND  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to methods and apparatus for wirelessly communicating data and voice signals between a base station and a mobile unit, and more particularly, to a method and apparatus for reducing call setup latency.  
           [0004]    2. Description of Related Art  
           [0005]    In cellular networks a mobile unit or wireless device conducts calls via a base station. The wireless device must interact with the base station using predetermined protocols that are commonly standardized. The interaction protocol standards may evolve but the base station must be able to support different generations of protocol standards. In some systems, the base station standardization compatibility requirements disadvantageously increases call setup latency. For example, the Code Division Multiple Access (“CDMA”) IS2000A standard dictates that a wireless unit performs base station connection initialization after each call terminates. This requirement increases the call setup latency for such wireless devices. The increased latency is unacceptable for many data calls.  
           [0006]    Therefore, a need exists for a cellular system and method that reduce call setup latency. The present invention provides such a cellular system and method.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention relates to a system, wireless device, method, and article of manufacture for communicating data signals using a cellular network, the cellular network including a plurality of base stations coupled to the cellular network.  
           [0008]    In one exemplary embodiment the invention receives and stores base station overhead information. The invention processes the received base station overhead information to determine whether the received base station overhead information is current for one of the plurality of base stations after a call session is completed. The wireless device may have an active base station set that includes a sub-set of the plurality of base stations. In this embodiment, when a call session ends with the at least one of the plurality of base stations, the invention receives overhead information related to each base station in the active base station set. In an exemplary embodiment the cellular network is a CDMA based network and the base station overhead parameters includes at least one of the following parameters: Pseudorandom Noise Offset, CDMA channel number, CDMA Band Class, Station Identifier, Network Identifier pair, Protocol Revision, BCCH code channel, BCCH data rate, BCCH coding rate, PCH code channel, and PCH data rate. In this embodiment, the invention may determine whether the BCCH parameters for a base station are current. The invention may also determine whether the PCH parameters for a base station are current.  
           [0009]    Reduced call setup latency is achieved using the fast traffic channel reconnection system and method of the present invention. Using the present inventive fast traffic channel reconnection techniques and apparatus, a mobile station can access traffic channels in much less time than was heretofore available using the prior art techniques. For example, using the fast traffic channel reconnection methods and apparatus of the present invention, a mobile station accesses the traffic channel approximately one hundred times faster than what was heretofore possible using the prior art approaches. This reduction in traffic channel access time significantly reduces call setup latencies when placing packet data calls.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:  
         [0011]    [0011]FIG. 1 is an illustration of a wireless device in a cellular system comprising a plurality of base stations.  
         [0012]    [0012]FIG. 2 is an illustration of a wireless device state diagram used in prior art devices.  
         [0013]    [0013]FIG. 3 is an illustration of a wireless device state diagram where the cellular system does not employ fast channel reconnection techniques.  
         [0014]    [0014]FIG. 4 is an illustration of a wireless device state diagram where the cellular system employs fast channel reconnection techniques in accordance with an embodiment of the present invention.  
         [0015]    [0015]FIG. 5 is a block diagram of an exemplary wireless device that may be used to practice the present invention.  
         [0016]    [0016]FIG. 6 is a block diagram of an exemplary base station that may be used to practice the present invention.  
         [0017]    [0017]FIG. 7 is a flowchart of an exemplary fast channel reconnection method for use in a wireless device in accordance with the present invention.  
         [0018]    [0018]FIG. 8 is a flowchart of another exemplary fast channel reconnection method that works in conjunction with the method shown in FIG. 9.  
         [0019]    [0019]FIG. 9 is a flowchart of a base station fast channel reconnection method that works in conjunction with the method shown in FIG. 8.  
     
    
     DETAILED DESCRIPTION  
       [0020]    Throughout this description, embodiments and variations are described for the purpose of illustrating uses and implementations of the invention. The illustrative description should be understood as presenting examples of the invention, rather than as limiting the scope of the invention.  
         [0021]    [0021]FIG. 1 is a block diagram of a cellular system segment  10  in which the present invention may be employed. In this segment  10 , there are a plurality of base stations  22 ,  24 ,  26 ,  42 , and  44  that are geographically separated and a wireless device  30 . The wireless device may be any wireless apparatus that includes a cellular Modulator/Demodulator (“modem”) that may communicate with a base station  22 ,  24 ,  26 ,  42 , or  46 . For example, the wireless device may be a cellular telephone, personal data assistant (“PDA”), or computer. In one embodiment, each base station may communicate with the wireless device when the signal strength of the wireless device, as received at a base station, is sufficiently strong. In one invention embodiment, the base stations support the same wireless communication protocol standard (such as the IS2000A standard). In another embodiment of the invention, the base stations may support different or multiple communication protocol standards. In addition, the wireless device  30  may support a single or multiple communication protocol standards, e.g., the device  30  may support a CDMA standard, an Advanced Mobile Phone Service (“AMPS”) standard, a Time Division Multiple Access (“TDMA”) standard, and a Groupe Spécial Mobile (“GSM”) standard. In the example shown in FIG. 1, the wireless device  30  is capable of communicating with all of the base stations  22 ,  24 ,  26 ,  44 , or  46  using a CDMA standard.  
         [0022]    [0022]FIG. 2 (Prior Art) is an illustration of a wireless device state diagram based on the CDMA IS2000A standard. More specifically, FIG. 2 (Prior Art) shows how a wireless device functions under Release 0 of the CDMA IS2000 standard without BCCH. After the wireless device  30  is powered up (state  52 ), the device is initialized (and control is passed to the initialization state  54 ). Under the CDMA IS2000A standard, for example, the device  30  acquires a pilot signal from a base station. The device  30  must then acquire the synchronization channel, system time, and any overhead messages. Control then passes to the idle state  56 . During this state, the wireless device monitors overhead messages to maintain pilot signal acquisition. When a call is initiated (incoming or outgoing) a base station grants, or the wireless device  30  requests, access to a traffic channel (access state  58 ). When a base station grants a traffic channel to the wireless device  30  the wireless device conducts the call (traffic channel state  62 ). In the CDMA IS2000A standard, when a call is complete, the wireless device must perform initialization again (i.e., return to the initialization state  54 ).  
         [0023]    When the call is used to communicate (transmit and/or receive) packet data, the actual time spent by the wireless device in the traffic channel state may be shorter than the time spent in the initialization  54 , idle  56 , and access  58  states. This is an inefficient use of bandwidth and reduces the potential upload or download packet data rate of the wireless device. FIG. 3 is another illustration of a wireless device state diagram that may occur in a cellular system using the CDMA IS2000A standard. More specifically, FIG. 3 shows how the wireless device functions in accordance with the CDMA IS2000 Release A with BCCH. In this state diagram  70 , the wireless device  30  starts at the initialization state  72  and transitions to the idle state  74  based on a pilot signal that is acquired from a base station transmitting on Freq. 1. A base station may then direct the wireless device to a different CDMA channel that is transmitted on another frequency, with a Non-TD BCCH (wherein “TD” stands for “Transmit Diversity”) transmitted on Freq. 2 (i.e., state  84 ) or a TD BCCH pilot signal transmitted on Freq. 3 (i.e., state  94 ). In any of these idle states  74 ,  84 , or  94 , after completing a call (from a traffic state  76 ,  86 , or  96 , respectively), the wireless device is directed to acquire a pilot signal on Freq. 1 (initialization state  72  versus initialization states  82  or  92 ). In one embodiment of the present invention, after completion of a call, the wireless device returns to its most recent idle state  74 ,  84 , or  94 , as shown in FIG. 4.  
         [0024]    [0024]FIG. 4 is an illustration of a wireless device state diagram that may occur in a cellular system using a modified CDMA IS2000A standard in accordance with an embodiment of the present invention. As shown in FIG. 4, control ideally passes from a traffic channel state  76 ,  86 , and  96  to the corresponding idle state  74 ,  84 , and  94 , respectively. FIG. 7 illustrates an exemplary wireless device fast channel reconnection method  140  in accordance with the present invention shown in flowchart format. The method  140  reduces the likelihood that initialization will be required after a call session is complete so control may therefore return directly to an idle state after a traffic session state. The method  140  directs the wireless device  30  to perform initialization at a step  142  (go to initialization state) upon startup. The method then gathers overhead information from each base station it visits (step  144 ) (such as, for example, the base stations  22 ,  24 ,  26  of FIG. 1). The method  140  then stores the overhead information (step  146 ). The method  140  ideally gathers and stores all of the overhead information that is necessary to achieve an idle state with the base station. In a CDMA based system, for example, the method  140  may gather and store the following overhead information: Pseudorandom Noise (“PN”) Offset, CDMA channel number, CDMA Band Class, Station Identifier (“SID”), Network Identifier (“NID”) pair, Protocol Revision (“P_REV”), BCCH code channel, BCCH data rate, BCCH coding rate, PCH code channel, and PCH data rate.  
         [0025]    Those skilled in the wireless communications arts shall recognize that none, any one of, or all of the overhead information parameters given above may be gathered or stored by the method  140 . For example, in one embodiment, the method  140  may gather and store only one of the overhead information parameters given above. In another exemplary embodiment, the method  140  may gather and store two or more of the parameters, while in yet another exemplary embodiment, the method  140  may gather and store all of the overhead information parameters. The scope of the present invention is intended to encompass all of these embodiments. In an embodiment where the wireless device supports different cellular networks using differing standards, the wireless device may gather and store overhead information from base stations for each supported cellular network.  
         [0026]    When the wireless device  30  moves geographically, it may gather and store overhead information from other base stations (such as the base stations  42  and  44  shown in FIG. 1). In an exemplary embodiment, while the wireless device is in an idle state, base stations may determine when the signal strength of the wireless device  30  is sufficiently strong for a future call session. In this embodiment, the method  140  may only gather and store overhead information from base stations that indicate that the signal strength of the device is sufficiently strong. The method  140  continues to gather and store base station overhead information until a call is initiated (step  148 ). After the call is conducted and completed (steps  152  and  154 ), the method  140  searches for a base station having sufficient signal strength for a future call session (step  155 ). The method  140  then determines whether stored overhead information (if any is present) for the located base station is current (steps  156  and  158  in one embodiment). When the information is current the method returns to the idle state, whereat the wireless device gathers and stores base station overhead information until another call is initiated. There may be other base stations that have a sufficiently strong signal for a future call session (i.e., base stations in the active set of the wireless device). In an exemplary embodiment, the method checks the stored overhead information related to all such base stations (steps  156 ,  158 , and  159 ) until a current set is located in steps  156  or  158 .  
         [0027]    Otherwise, the method  140  performs a full initialization procedure (step  142 ). In an embodiment wherein the wireless device supports different cellular networks, the wireless device may analyze base stations in another supported cellular network before returning to an initialization state (step  142 ). In the exemplary CDMA network, the method  140  determines whether the stored BCCH overhead information (if any is present) for the base station being analyzed (step  156 ) is current. When the BCCH information is current, control returns to the idle state (steps  144 ,  146 ). Otherwise, the method determines whether the stored PCH overhead information (if any) for the base station being analyzed (step  158 ) is current. When the PCH information is current, control returns to the idle state (steps  144 ,  146 ). When the wireless device  30  is fairly stationary during a call (traffic channel state) the method  140  should be able to return the wireless device  30  to an idle state. When the wireless device  30  moves during a call (traffic channel state), or some overhead information changes for a base station during a call session, the method  140  may not be able to return the wireless device  30  to an idle state without first performing initialization (step  142 ).  
         [0028]    [0028]FIG. 8 illustrates another exemplary wireless device fast channel reconnection method  190  that works in conjunction with the method  160  shown in FIG. 9. This method further reduces the likelihood that initialization is needed after termination of a call session. FIG. 9 illustrates a base station fast channel reconnection method  160  that works in conjunction with the method  190  shown in FIG. 8 in accordance with the present invention. The method  190  is similar to the method  140  (FIG. 7) in that the method also gathers and stores overhead information from base stations in the active set of the wireless device during idle states until a call is initiated (steps  174 ,  176 ,  178 ,  182 , and  184 ). However, unlike the method  140 , the method  190  receives updated overhead information for base stations in the active set of the wireless device after a call session is completed (step  186 ). The wireless device  30  receives the updated overhead information from the base station that is conducting/completing the call session (step  168  of FIG. 9).  
         [0029]    In a CDMA-based system, the base station method  160  sends the wireless device  30  updated overhead parameters including the following overhead parameters: the Pseudorandom Noise (“PN”) Offset, CDMA channel number, CDMA Band Class, Station Identifier (“SID”), Network Identifier (“NID”) pair, BCCH code channel, BCCH data rate, BCCH coding rate, PCH code channel, and PCH data rate for each base station in the active set of the wireless device. Similar to the wireless device fast channel reconnection method  140  described above with reference to FIG. 7, those skilled in the wireless communications arts shall recognize that none, any one of, or all of the overhead parameters given above may be sent to the wireless device using the base station method  160 . For example, in one embodiment, the base station method  160  may send only one of the overhead parameters given above. In another exemplary embodiment, the base station method  160  send two or more of the overhead parameters, while in yet another exemplary embodiment, the method  160  may send all of the overhead information parameters. The scope of the present invention is intended to encompass all of these embodiments.  
         [0030]    The base station method  160  does not transmit the Protocol Revision (“P_REV”) information because the base station software is unlikely to have been updated during the call session. In another embodiment, the method  160  may also send the Protocol Revision (“P_REV”) information so the base station may dynamically update its software. The method  190  of FIG. 8 stores these updated overhead parameters (step  188 ) and uses the updated information to perform steps  193 ,  192 ,  194 , and  195  (these steps are analogous to steps  155 ,  156 ,  158 , and  159 , respectively, of the method  140  shown in FIG. 7).  
         [0031]    In this exemplary embodiment, the base station conducting the call session with the wireless device performs the method  160  shown in FIG. 9. In accordance with the method  160 , the base station is instructed to gather overhead information related to the base stations in the active set of the wireless device (step  166 ). The method  160  transmits the updated active set overhead information to the wireless device (step  168 ). The method  190  (FIG. 8) stores the updated active set overhead information and uses this information to proceed to an idle state with a base station (steps  193 ,  192 ,  194 , and step  195 ).  
         [0032]    [0032]FIG. 5 is a block diagram of an exemplary wireless device  120  that may be used to practice the present invention. The exemplary device  120  may include a central processing unit (“CPU”)  122 , random access memory (“RAM”)  124 , read only memory (“ROM”)  126 , a display  128 , a user input device  132 , a transceiver application specific integrated circuit (“ASIC”)  134 , a microphone  138 , a speaker  142 , and an antenna  144 . The ROM  126  is coupled to the CPU  122  and stores the program instructions to be executed by the CPU  122 . The RAM  124  is coupled to the CPU  122  and stores temporary program data and gathered overhead information. The user-input device  132  may comprise an input device such as a keypad, touch pad screen, track ball or other input device that allows the user to navigate through menus in order to place calls, in addition to performing other functions. The display  128  is an output device such as a CRT, LCD or other screen display that enables the user to read received data and to place calls.  
         [0033]    The microphone  138  and speaker  142  may be incorporated in a handset that is coupled to the ASIC  134 . The microphone  138  and speaker  142  may also be separated from the handset to allow hands-free communication. In this mode, the ASIC  134  may include voice activation circuitry that may convert voice commands into data. The data is transmitted to the CPU  122  via a serial bus  136  and may include a telephone number to be dialed.  
         [0034]    The transceiver ASIC  134  includes the instruction set that is necessary to communicate data and voice signals over the cellular network  10 . In one embodiment, the transceiver ASIC  134  is a code division multiple access (“CDMA”) ASIC and the cellular network is a CDMA network that supports data and voice communication. The ASIC  134  is coupled to the antenna  144  for communicating signals with the cellular network  10 . When a data signal is received by the transceiver ASIC  134 , the data is transferred to the CPU  122  via the serial bus  136 . The data can include the base station overhead information to be stored by the wireless device in accordance with the methods described above. The ASIC  134  may perform the method  140  described above with reference to FIG. 7, or the method  190  described above with reference to FIG. 8, and it may direct the CPU  22  to store the gathered overhead information.  
         [0035]    [0035]FIG. 6 illustrates a block diagram of an exemplary base station  100  that may be used in the present invention. The exemplary base station  100  may include a CPU  102 , a RAM  104 , a ROM  106 , a storage unit  108 , a first modem/transceiver  112  and a second modem/transceiver  114 . The first modem/transceiver  112  may couple, in a well-known manner, the base station  100  to a central cellular network control center via an Internet connection or Plain Old Telephone System (“POTS”). The second modem/transceiver  114  couples the base station  100  to the cellular network  10 . The modem/transceiver  114  may be an Ethernet modem, telephone modem, wireless modem or other communication device that communicates with the cellular network  10  (FIG. 1). The CPU  102  directs communications between the first and second modem,  112  and  114 , respectively, for messages between the central network control center, Internet, or POTS, and one or more wireless devices.  
         [0036]    The ROM  106  may store program instructions to be executed by the CPU  102  including instructions necessary to implement the method  160  shown in FIG. 9. The RAM  104  may be used to store temporary program information and overhead information for other base stations in its sector (i.e., nearby base stations). The storage unit  108  may comprise any convenient form of data storage and may be used to store the overhead information.  
         [0037]    The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.  
         [0038]    While this invention has been described in terms of a best mode for achieving this invention&#39;s objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the present invention. For example, the present invention may be implemented using any combination of computer programming software, firmware or hardware. As a preparatory step to practicing the invention or constructing an apparatus according to the invention, the computer programming code (whether software or firmware) according to the invention will typically be stored in one or more machine readable storage mediums such as fixed (hard) drives, diskettes, optical disks, magnetic tape, semiconductor memories such as ROMs, PROMs, etc., thereby making an article of manufacture in accordance with the invention. The article of manufacture containing the computer programming code is used by either executing the code directly from the storage device, by copying the code from the storage device into another storage device such as a hard disk, RAM, etc., or by transmitting the code on a network for remote execution.