Abstract:
A method of scheduling cell search activity in a mobile communication user terminal ( 28 ) during transmission gap sequencing in burst mode, the method comprising the steps of:
       maintaining ( 404 ) a table ( 62 ) of regular periodic patterns of discreet cell search commands for execution during the transmission gap sequences, wherein the commands are ordered by the desired execution times; and   sequentially executing commands ( 408 - 414 ) in the table at the desired execution time.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the scheduling of cell search operations in a mobile communications user terminal, and in particular to the scheduling of cell search operations during transmission gap sequences in burst mode. The present invention is suitable for use in scheduling cell search operations during transmission gap Sequences in compressed mode in mobile W-CDMA systems, and it will be convenient to describe the invention in relation to that exemplary application. It is to be appreciated however, that the invention is not limited to use in that application only. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Mobile phone systems are required to use a scheme that allows the mobile station to find and analyze radio signals from one or more base stations, often on different radio frequencies. The process of searching for different base stations is called cell search. During the cell search process, the mobile station identifies all base stations and determines which of them are the most suitable for “camping”. Camping on the cell means starting to monitor whether there is an incoming call or allow the user to make an outgoing call. The cell search has to be performed Periodically because when the moving station is moving, the cell that has been identified as the best may have a reduced Signal quality whilst the radio signal from another cell may have improved. Based upon repeated cell searching, the mobile station keeps a periodically updated list of all available cells. When the signal quality from the currently used cell has dropped below a certain threshold, the mobile station stops monitoring the current cell and camps on a new cell, that is to say, the mobile station performs reselection. 
         [0003]    In most mobile systems, such as W-CDMA, a periodic cell search has to be performed even when there is a call in Progress so that the handover from one cell to the next can be performed and the call in progress is not dropped if the signal from the currently used cell diminishes in quality whilst there is another cell available with better signal quality. 
         [0004]    Moreover, in mobile systems which rely upon spread spectrum, such as W-CDMA, the transmission and reception protocol is often designed in such a way to allow for a mobile station to temporarily stop transmitting and receiving, and to perform a cell search on a different radio channel. The momentary interruption of transmission and reception does not cause any data loss, because both the mobile station and the base station compensate by temporally increasing the data transmission speed so as to maintain an overall average data transmission speed. In some mobile W-CDMA system, such as UMTS, this feature is called compressed mode. The compressed mode is typically controlled by a telecommunications network. Prior to activation of a sequence of transmission Pauses or gaps, the network communicates the exact timing of the gaps to the mobile terminal using a control channel. The mobile terminal is then expected to use the provided transmission gap sequences to perform cell search and measurements on frequencies different than the current nominal frequency. This is referred to as inter-frequency cell search or measurement, or inter-frequency activity. 
         [0005]    For mobile terminals that support multiple radio access technologies, such as a dual W-CDMA and GSM terminal, the network can provide compressed mode gap sequences for performing neighbor cell search activity on radio access technology, different from the one the mobile terminal is currently connected to. This is omen called inter-system activity. The network can provide several different compressed mode gap sequences at the same time, for example some gap sequences for inter-frequency activity and some gap sequences for inter-system activity. 
         [0006]    In some mobile W-CDMA systems, such as UMTS, the cell search activities can have “bursty” characteristics involving temporary Pausing and resuming Of activity, in scenarios other than activation of compressed mode. For example, in forward access state, the terminal may be performing cell search on one radio channel, whilst being Camped on a cell on a different radio channel at the same time. In this case, the cell search must be paused during those occasions when the terminal is transmitting bursts of data on the forward access channel. On other occasions, the mobile terminal may be idle (not in connection) but is periodically activated for short time durations, to perform monitoring of the paging channel and carry out a burst of cell search activity on one nominal channel frequency followed by another burst on a different radio frequency. Such a case is similar to performing compressed mode intra-frequency and inter-frequency activity. 
         [0007]    It would be advantageous to provide a method for performing cell search activity during one or more different types of bursty activity. It would be particularly advantageous to provide a generic method of scheduling cell search activity able to be used by a mobile terminal regardless of the type of bursty activity involved. It would also be advantageous to provide a generic scheduling method that is simple to develop, test and/or implement when compared to current scheduling methods involving dedicated methods and techniques for each type of bursty activity. Moreover, it would be advantageous to Provide a cell search activity scheduling method able to be efficiently implemented in a mobile terminal. 
         [0008]    With this in mind, one aspect of the invention provides a method of scheduling cell search activity in a mobile communication user terminal during transmission gap sequencing in burst mode, the method comprising the steps of: 
         [0009]    maintaining a table of regular periodic patterns of discreet cell search commands for execution during the transmission gap sequences, wherein the commands are ordered by the desired execution times; and 
         [0010]    sequentially executing commands in the table at the desired execution time. 
         [0011]    The cell search commands may include pause and resume commands for pausing and resuming any two or mops of intra-frequency, inter-frequency or inter-system cell search activity. Burst mode may include W-COMA compressed mode. 
       SUMMARY OF THE INVENTION 
       [0012]    The method may further include the step of calculating the table of regular periodic patterns of discreet cell search commands under one or more predefined conditions. 
         [0013]    The predefined conditions may include when burst mode is required and there is a need to interleave separate cell search activities. 
         [0014]    The predefined conditions may further include when cell search activities are required to be performed and a final command from the table has been executed. 
         [0015]    The predefined conditions may further include when new patterns of discreet cell search commands are received from a communications network while cell search activities are currently being executed. 
         [0016]    The method may further includes the step of calculating the table of regular periodic patterns of discreet cell search commands by: 
         [0017]    decomposing all active burst mode patterns into regular periodic patterns of discreet commands; 
         [0018]    storing discreet commands and command execution time in the table; and 
         [0019]    sorting the commands in the table according to desired execution time. 
         [0020]    The following description refers in more detail to the various features of the cell search activity scheduling method of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawings where the invention is illustrated in a preferred embodiment. It is to be understood however, that the invention is not limited to the preferred embodiment illustrated in the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic diagram illustrating a multiple radio access network; 
           [0022]      FIG. 2  is a schematic diagram of selected functional elements of a mobile station forming part of the multiple radio access technology network shown in  FIG. 1 ; 
           [0023]      FIG. 3  is a now chan showing various cell search activities undertaken during intra-frequency, inter-frequency and inter-system cell search activities; 
           [0024]      FIG. 4  is a timing diagram showing sequences of operations performed by the mobile station illustrated in  FIG. 2  during intra-frequency cell search activity and inter-frequency cell search activity; 
           [0025]      FIG. 5  is a timing diagram illustrating operation of the mobile station shown in  FIG. 2  during intra-frequency, inter-frequency and inter-system cell search activity; 
           [0026]      FIG. 6  is a timing diagram illustrating the decomposition of active burst mode patterns carried out in the mobile terminal shown in  FIG. 2 ; 
           [0027]      FIG. 7  is a flow chart illustrating the steps performed by the mobile station shown in  FIG. 2  during cell search activity scheduling; and 
           [0028]      FIG. 8  is a schematic diagram illustrating the sorting of commands maintained in a temporary table during one step of the cell search activity scheduling illustrated in  FIG. 7 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    Referring now to  FIG. 1 , there is shown generally a wireless communications system  10  including a W-CDMA network  12  and base stations  14 ,  16  and  18 . The wireless communications system  10  also includes a second radio access network, in this case a GSM network  20 , and base stations  22 ,  24  and  26 . A mobile station  28  is adapted to receive a number of radio signals transmitted from cells served by the base stations  14 ,  16  and  18 , and also from the base stations  22  to  26 , depending upon the radio access technology currently selected by the mobile station  28 . It will be appreciated that whilst the events will be described in relation to radio access technologies only, namely W-CDMA and GSM, the present invention is applicable to other multiple radio access technologies in which a mobile station is adapted to communicate with multiple radio networks. 
         [0030]      FIG. 2  is a schematic diagram showing selected elements of the mobile station  28 . The mobile station  28  includes an antenna  40 , a demodulator  42  for down conversion of received radio signals to a base band frequency, and an analogue to digital converter  44  for digitizing the down converted and demodulated signals. The mobile station  28  further includes a W-CDMA branch, including a W-CDMA cell searcher block  46  for search for a cell served by one of the base stations  14 ,  16  and  18  and determining the down link scrambling code and frame synchronization for that cell. A W-CDMA demodulator block  48  demodulates the code output from the W-CDMA cell searcher block  46  with detected spread codes, whilst a W-CDMA decoder block  50  acts to decode the demodulated signals output by the W-CDMA demodulator block  48 . Similarly, the mobile station  28  includes a GSM arm, including a GSM cell searcher block  52 , a GSM demodulator block  54  and a GSM decoder block  56 , having functionality similar to the corresponding blocks in the W-CDMA arm of the mobile station  28 . Selective operation of the cell searcher blocks  46  and  52  is controlled by a system controller  58 . A first memory device  60  is provided for storing a series of program instructions controlling operation of the system controller  58 , and a second volatile memory device  62  is provided for the temporary storage of data for use by the system controller  58  in performing cell Search operations. 
         [0031]    A typical scenario in which cell search activities are undertaken by the mobile station  28  is illustrated in  FIG. 1 . At step  70  the W-CDMA network  12  sends a request to the mobile station  28  to perform intra-frequency cell search activities. The commands to be performed during intra-frequency cell search, and the timing of those commands, are maintained in the volatile memory  62  of the mobile station  28 . At step  72 , the mobile station  28  carries out that intra-frequency cell search activity. 
         [0032]    At step  74  however the W-CDMA network  12  sends a request to the mobile station  28  to conduct inter-frequency cell search activity. In other words, rather than conduct an intra-frequency cell search in which the cell having the strongest signal transmitted on the same frequency as the signal currently being received by the mobile station  28 , a search is conducted for cells served by base stations forming part of the W-CDMA network  12  on other frequencies. The inter-frequency compressed mode pattern timing is transmitted to the mobile terminal  28  from the W-CDMA network  12  at step  76 . The pattern timing is stored in the volatile memory  62  of the mobile station  28 . At a time determined by the data maintained in the volatile memory  62 , the inter-frequency pattern becomes active at step  78 . At step  80 , both intra-frequency and inter-frequency cell search activities are operative, so that the two cell search functions are required to be interleaved. At step  82 , the mobile station  28  reports back to the W-CDMA network  12  the results of the intra-frequency and inter-frequency cell search activities. 
         [0033]    As step  84 , the W-CDMA network  12  may request that the mobile station  28  carry out inter-system cell search activities. That is, rather than performing cell search activities in the W-CDMA network  12 , the mobile station may undertake cell search activities in the GSM network  20 . The inter-system compressed mode pattern timing is also transmitted to the mobile station  28  in step  84 . At step  86 , the intra-frequency, inter-frequency and inter-system cell search activities are interleaved. 
         [0034]    The system controller  58  causes selective operation of the cell searcher blocks  46  and  42  of the mobile station  28  in order to allow for temporary pausing of processing of each of the cell search activities at an exactly specified time, and 
         [0000]    allow later resumption, at an exactly specified time of that same cell searching activity. Storage of intermediate results of that cell search activity is provided for in the volatile memory  62 , so that any two or more of the intra-frequency, inter-frequency and inter-system cell search activities can be interleaved. 
         [0035]    An example of the sequence of operations undertaken in such interleaved cell search activities is illustrated in  FIG. 4 . In this figure, the system controller  58  issues an intra-frequency cell search request  101  to the W-CDMA cell searcher block  46 . This request contains the exact starting time of an intra-frequency burst. The cell searcher block  46  starts the cell search activity at a start time  102 . Preferably, the timing of the operations controlled by the system controller  58  is implemented in hardware, enabling precise timing of the cell search activities via a system clock cycle. Immediately after the cell searcher block  46  commences intra-frequency cell search operations  103 , an acknowledgement  104  is sent to the system controller  58 . The system controller then determines that the next required cell search activity is a pause of intra-frequency searching at an exact time  106 , and accordingly sends to the cell searcher block  46  a request  105  for this pause. After the cell searcher block  46  pauses, an acknowledgement  107  is returned from the cell searcher block  46  to the system controller  58 . 
         [0036]    After receiving the acknowledgement  107 , the system controller  58  then determines that the next command to be issued is a resume of inter-frequency cell searching  110  to be initiated at an exact point in time  109 . Accordingly, the system controller  58  sends a corresponding request  108  to the W-CDMA cell search block  46  to initiate the inter-frequency cell search activity  110 . Immediately after the cell block  46  commences the inter-frequency cell search activity, an acknowledgement  111  is returned to the system controller  58 . The system controller  58  determines that the required operation is a pause of the inter-frequency search at an exact time  113 , and so sends a request  112  to the cell searcher  46  for this pause. After the cell searcher pauses the inter-frequency search activity  110 , an acknowledgement  114  is returned to the system controller  58 . 
         [0037]      FIG. 5  illustrates an example of the mobile station  28  performing not only intra-frequency cell search activities and inter-frequency cell search activities but also inter-system cell search activities. The mobile terminal  28  schedules the different cell search activities to that inter-frequency measurements are performed within a compressed mode pattern  201 , inter-system measurements are performed within a different compressed mode pattern  202  and intra-frequency measurements are performed outside of any compressed mode patterns  203 . Intra-frequency activity bursts  205  are interleaved with inter-frequency bursts  207  and inter-system bursts  210 . 
         [0038]    The W-CDMA cell searcher block  46  is controlled using the above described request/acknowledgment mechanism, for example using request  204  and acknowledgement  206  in relation to the intra-frequency activity burst  205 . The inter-frequency activity bursts  207  occur during repetitive transmission sequence gaps  208  provided in the inter-frequency pattern  201  whilst the inter-frequency activity bursts  210  are scheduled to occur during transmission gap sequences  209  in the inter-system pattern  202 . The mobile station  28  performs the above specified process by issuing pause and resume commands to the cell searcher block  46  so that the pause and resume times corresponds to the edges of the compressed mode patterns represented in  FIG. 5 . 
         [0039]    The mobile station  28  acts to determine whether a pause or resume command for intra-frequency cell search activity, inter-frequency cell search activity or inter-system cell search activity by retrieving commands from a pre-calculated temporary table maintained in the volatile memory  62 . Each command is retrieved from the table in sequence and executed by the system controller  58 . Advantageously, the use of a pre-calculated table in this way results in a simple and fast process, requiring minimum use of processing and energy resources in the mobile station, since looking up a command from a pre-calculated table is all that is required for executing of two or more interleaved cell search processes. 
         [0040]    The table of pause and resume commands is calculated, in this exemplary embodiment as follows. Initially all actively compressed mode gap patterns are decomposed to regular periodic patterns of discreet pause and resume commands. It is to be understood that whilst compressed mode gap patterns, or any other patterns of burst mode activity, to regular periodic patterns of discreet pause and resume commands. This is made possible due to the fact that the element 3GPP standard specifies burst mode gaps in such a way that the gaps consist of periodically repeated groups of individual gaps. 
         [0041]    For example, in  FIG. 6 , an inter-frequency compressed mode gap pattern  301  is represented as including two regularly occurring compressed mode transmission gaps  303  and  304 . A standard transmission gap pattern period  302  separates each of the compressed mode transmission  303  from each other as well as each of the compressed mode transmission gaps  304  from each other. The generated sequences of commands corresponding to the compressed mode edges are called gap start times and gap end times. As shown in  FIG. 6 , the inter-frequency compressed mode gap pattern  301  can be decomposed into regular periodic gap patterns  305 ,  306 ,  307  and  308 . The gap start and gap end times for each of the compressed mode transmission gaps  303  and  304  are separated by the same standard transmission gap period  302 . 
         [0042]    Other types of bursty activity, such as measurements aligned with paging occasions or measurements aligned with forward access channel measurement occasions can similarly be decomposed into regular periodic patterns of commands in the same fashion. The above-described decomposition step is dependent on what type of bursty measurement is being performed, however the rest of the scheduling process described is generic to all types of bursty activity. 
         [0043]    In some embodiments of the invention, it will be advantageous to generate additional commands in order to handle various physical limitations of the mobile terminal  28 . For example, a typical combination of a cell search device and receiver control circuitry may require time to switch from intra-frequency measurements to inter-frequency measurements and vice versa. For this reason, it may be necessary to generate an additional command for each compressed mode edge. As shown in  FIG. 6 , the command for start of the inter-frequency gap  309  may be required to be preceded by a pause command  310  following the same mechanism, the command patterns  311 ,  312 ,  313  and  314  may be generated from the command patterns  305 ,  306 ,  307  and  308 . Accordingly, the compressed mode pattern  301  has been decomposed by the system controller  58  into eight patterns of commands  305  to  314 , whereby each pattern is regular and periodic. This decomposition step is referenced  402  in  FIG. 7 . 
         [0044]    Commands from all regular command patterns are then stored in a temporary table in the volatile memory  62  at step  404 . For each command, the command type and the exact time when the command should be executed by the system controller  58  are stored. At this stage the order of storage of the commands is unimportant and it is preferable to store commands from each of the patterns  305  to  314  consecutively, without regard to the command times at this stage. For example, referring once again to  FIG. 6 , the command pattern  305  may be stored in the memory fully, before proceeding to command pattern  306 . Commands may be progressively added to the temporary table through all existing patterns or until the temporary table is full. This processing step of adding commands into a temporary memory table may advantageously by optimized in an implementation of the invention involving a digital signal processor that enables fast execution Of repetitive memory operations. 
         [0045]    An exemplary illustration of the arrangement of the commands in the Temporary table at this stage is denoted  501  in  FIG. 8 . From this figure, it can be seen that the command names ( 5   a ,  5   b , etc) corresponds to the command names represented in  FIG. 6 . The representative example is illustrative Only, showing only two periods of compressed mode gap groups. In reality, the number of repetitions is likely to be large and therefore the benefit from optimizing the method of generating the command table is optimized. The number of repetitions is referred to as the “transmission gap repetition count” in the 3GPP standards documents. 
         [0046]    At step  406 , all commands in the temporary table are sorted by the system controller  58  in ascending order according to desired execution time. The step is reference  502  in  FIG. 8 . Advantageously, the sorting algorithm used by the system controller  58  is a “Shell Sort” algorithm, namely a fast general purpose sorting algorithm not requiring recursion. Alternately, if no severe memory restraints are imposed upon the System controller  58 , an optimized solution is the recursive algorithm “Quick Sort”. As a result of this step, the temporary table of commands is now ordered according to desired execution time. The final arrangement of the commands in the table is referenced  503  in  FIG. 8 . Once again, the command names ( 5   a ,  5   b  etc) correspond to the command names referenced in  FIG. 6 . Optionally, the sorted table can now be checked for incorrect specified patterns, such as overlapping gaps or gaps that are to close to each other and violate physical limitations of the mobile terminal  28 . 
         [0047]    The table of pause and resume commands maintained in the volatile memory  62  is calculated by the system controller  58  when the system controller  58  determines that burst mode cell search activity is required, namely that there is a new need to interleave two or more of inter-frequency, intra-frequency or inter-system measurements. The table is also calculated when cell search activities are already being performed and the final command from the temporary table has been issued, so that the table needs to be re-filled. Further, the table is calculated when new command patters are provided by the network  12  to the mobile station  28  while cell search activity is already in progress. The provision of new patterns may require the addition of patterns, deletion of patterns or modification of currently active patterns by the system controller  58 . 
         [0048]    Referring once again  FIG. 7 , the mobile terminal  58  commences cell search activity by sequentially executing the commands from the table stored in the volatile memory  62  by initially determining at step  408  if the end of the table has been reached. If this is the case, then a new table of pause and resume commands is calculated at step  410 . The decomposition storage and sorting steps referenced  402  to  406  are then subsequently performed. 
         [0049]    Alternatively, if the end of the table has not been reached, then the next command is obtained from the temporary table by the system controller at step  410  for execution. At step  412 , the hardware in the mobile station  28  that is required to execute that command is programmed by the system controller  58  so that that command is executed at the desired command time. At step  414 , the system controller  58  waits until the hardware has executed that current command, and then repeats steps  408  to  412  until all commands have been executed. 
         [0050]    Finally, it is to be understood that various modifications and/or additions may be made to the cell search scheduling method without departing from the spirit or ambit of the present invention.