Abstract:
A truncated asynchronous paging method is a hybrid of synchronous paging and asynchronous paging modes. A time slot  106  of paging messages ( 140 - 163 ) is formatted into N paging message groups of M paging messages per group. The paging messages ( 140 - 163 ) are then transmitted in order to maximize the throughput of paging messages while providing the highest resistance to loss of data due to fading.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention pertains to paging and more particularly for arrangements for paging messages.  
           [0002]    Generally, there are two paging modes. The synchronous mode and the asynchronous mode. The current CDMA (Code Division Multiple Access) paging channel supports both of these paging modes.  
           [0003]    The current asynchronous paging mode provides a relatively high throughput, but at an unacceptably high loss rate. This paging mode trades a relatively high throughput for a lack of immunity to page losses due to fading of over-the-air transmissions. For a fade situation in the asynchronous mode, many pages are lost. High page loss rates cause missed call terminations, resulting in missed revenue and dissatisfied customers.  
           [0004]    On the other hand, synchronous paging provides relatively low loss rate due to fading, however, the amount of paging messages that may be transmitted in the synchronous paging mode is considerably less than the asynchronous paging mode. Low paging capacity of a system provides inherent inefficiencies and is costly for system operators since more paging equipment is required to achieve the same paging throughput.  
           [0005]    Since the RF (Radio Frequency) spectrum is the most valuable resource in a communication system, more transmission equipment as required by synchronous paging would be more costly to paging system operators thereby driving up the price of paging services.  
           [0006]    Accordingly, it would be highly desirable to provide a paging method having more paging throughput with low paging loss due to fading. Furthermore, it would be highly advantageous to provide such a paging method using less transmission equipment, power and bandwidth. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0007]    [0007]FIG. 1 is a layout diagram of a synchronous paging mode stream.  
         [0008]    [0008]FIG. 2 is a layout diagram of an asynchronous paging mode stream.  
         [0009]    [0009]FIG. 3 is a block diagram of a communication system interfacing with users in accordance with the present invention.  
         [0010]    [0010]FIG. 4 is a layout of a Truncated Asynchronous Paging stream in accordance with the present invention.  
         [0011]    [0011]FIG. 5 is a layout diagram of a truncated asynchronous paging stream in accordance with the present invention.  
         [0012]    [0012]FIG. 6 is a plot of loss rate versus pages per slot for the present invention in comparison with prior art methods. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    [0013]FIG. 1 depicts a layout of an 80 millisecond (ms) timeslot  100  of a CDMA paging frame. This frame arrangement is useful for IS95 and CDMA 2000 systems. Timeslot  100  includes four pages, page  1  through page  4 . The paging mode shown is the synchronous paging mode. In the synchronous paging mode the pages, page  1  through page  4 , are spread out in time from each other and start on a 20 ms time boundary. The synchronous paging mode has the advantage of resistance to possible fading. A one millisecond fade will wipe out typically only one page but will not affect the transmission or reception of the next page because of the time-spaced separation. In the synchronous paging mode, the next page begins at the start of the next time slot so that a time spacing is created. However, due to the time separation, synchronous paging is wasteful of unused information bits. This is due to the fact that each new page must begin on a specified time boundary. Therefore, the synchronous mode of paging provides very good resistance to fading, however, the throughput of paging information is substantially diminished.  
         [0014]    [0014]FIG. 2 depicts a layout of a paging slot  101  of a paging frame in the asynchronous paging mode. Paging slot  101  is an 80 millisecond slot which includes seven pages, page  1  through page  7 . Page  1  through page  7  are aligned end to end without any bit breaks until the end of the paging slot  101 .  
         [0015]    It can be observed from a comparison of the asynchronous paging mode of FIG. 2 with the synchronous paging mode of FIG. 1, that the throughput of the asynchronous mode is greatly increased. That is seven pages may be put through in an 80 millisecond paging slot in the asynchronous mode while only four pages may be put through in an 80 millisecond slot in the synchronous mode.  
         [0016]    Since the paging timeslot  101  is transmitted over the air, the timeslot is subject to wireless interference or fading during transmission. The successful reception over the air by a paging unit requires the successful reception of all the pages before it up through the 80 millisecond paging slot  101 . One occurrence of a fade for as little as one millisecond will compromise the information of all the pages during and after the page. In the worst case, if the fade occurred during page one, all pages, page one through page  7 , of the asynchronous paging slot will be lost. Although the asynchronous paging slot arrangement includes a higher throughput, it is subject to loss of many pages with a single incidence of fading.  
         [0017]    Referring to FIG. 3, a simplified paging system is shown. Paging communication system  10  transmits a synchronous paging frame or asynchronous paging frame  15  to mobile paging devices  20  and  30 . As these pages are transmitted over the air, they are subject to noise distortion, atmospheric distortion and various other forms of distortion, all individually or collectively termed fading. In the asynchronous paging mode shown in FIG. 2, for example, if a prior paging slot to  101  were subjected to fading then pages  2  and  3  which, for example, where intended for paging units  20  and  30  would be compromised and unreceivable by paging units  20  and  30 .  
         [0018]    In addition, if there were many paging users, the synchronous mode of paging depicted in FIG. 1 would be inefficient to provide paging services to each of the many paging devices. Additionally, a satellite paging transmitter  40  may formulate and transmit the paging slots to mobile paging units  20  and  30  similar to paging communication system  10 .  
         [0019]    Fading loss is of critical importance. Paging systems should exhibit no more than two percent dropped calls in total and more specifically, dropped calls due to fading should be minimized to one percent or less. Many paging systems typically make two delivery attempts for a given page. Therefore, a ten percent page message loss due to fading causes one percent of all calls to be dropped given two successive page attempts. Likewise, a fifteen percent page message loss causes 2.25% of calls to be dropped and a 25% loss due to fading causes 6.25% of calls to be dropped. Therefore, referring to FIG. 2 again, if a one millisecond fade occurs prior to slot  101  all seven pages would be lost and the loss rate would be at an unacceptably high level.  
         [0020]    Referring to FIG. 4, an embodiment of the present invention is depicted in layout form. The 80 millisecond paging slot  105  is shown to include 20 pages,  110  through  129 . These pages are grouped in groups of five to comprise four groups  130  through  133 . Paging group  130  includes pages  110  through  114 ; group  131  includes pages  115  through  119 ; group  132  includes pages  120  through  124 ; and group  133  includes pages  125  through  129 . Each group is separated in time from the next group by 260 microseconds approximately and is aligned so that each group of messages begins on a frame boundary.  
         [0021]    This page message ordering arrangement of time slot  105  is called Truncated Asynchronous Paging or TAP. This Truncated Asynchronous Paging arrangement delivers 20 pages per 80 millisecond timeslot with breaks in between each group  130 - 133  of five pages. This arrangement of page messages is termed a truncated asynchronous paging of length N=5, 20 pages per slot. M which is the number of pages in a group is equal to five for this example.  
         [0022]    Referring to FIG. 5, a preferred embodiment of this invention is shown. Paging slot  106  has eight ( 170 - 177 ), three message groups of pages,  140  through  163 . That is, there is a total of 24 paging messages grouped in an 80 millisecond paging slot  106 . The first paging group  170  includes paging messages  140 - 142 . The grouping of three paging messages per group and eight groups of pages was found to be the best compromise between throughput of paging messages and providing for low loss rates due to fading.  
         [0023]    Referring again to FIG. 3, paging communication system  10  or satellite  40  formats the grouping of paging messages as shown in FIG. 5 and transmit this paging slot over the air to paging devices  20  and  30 . Paging devices  20  and  30  would receive their appropriate pages and decode the message. That is, the communication system  10  or satellite  40  formulates the paging message shown in FIG. 5 and transmits this paging slot over the air to devices  20  and  30 . Devices  20  and  30  receive the appropriate paging message in the paging slot and decode this message for receiving their information via the paging message.  
         [0024]    [0024]FIG. 6 shows a plot of the number of pages per slot versus the loss rate for the various paging systems described. FIG. 6 depicts the paging loss rate assuming one millisecond fade durations occurring randomly with an average interval of 150 milliseconds, points of the number of pages per slot versus the loss rate percentage for those paging messages for the various paging modes. For the synchronous system, point  180  of the plot indicates a maximum of 16 paging messages per 80 millisecond slot and an approximate loss rate of three to four percent. This is an acceptable loss rate, however, the throughput of paging messages is very low. That is, the number of paging messages transmitted through the paging slot is limited to 16.  
         [0025]    For the asynchronous paging method, point  181  of the plot depicts a number of pages per slot of 24 and a loss rate of 26 to 27 percent. This is an unacceptable loss rate. Modern telecommunication systems for paging may not operate with such an excessive loss rate. Therefore, the asynchronous mode is unusable for paging.  
         [0026]    For the Truncated Asynchronous Paging method as shown in FIG. 5, with the message length per group of three point  182  of the plot indicates that there are a maximum of 24 paging messages per 80 millisecond timeslot with a loss rate of slightly less that 5% for three paging messages per group. Therefore, the truncated asynchronous paging with a paging message length of three provides the best combination of maximum messages per slot with the lowest loss rate due to fading.  
         [0027]    The Truncated Asynchronous Paging arrangement shown above increases the paging message capacity of each paging slot by 50% over use of the synchronous Paging mode. Furthermore, the Truncated Asynchronous paging mode retains the high resistance to fade loss of the synchronous paging mode. Use of the truncated asynchronous paging mode eliminates the need for operating companies to add extra forward common control channels or from using precious traffic channels to achieve higher paging message throughput.  
         [0028]    Although the preferred embodiment of the invention has been illustrated, and that form described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the present invention or from the scope of the appended claims.