Patent Document

RELATED APPLICATIONS 
   This application is a Divisional Application from U.S. patent application Ser. No. 09/756,066 filed on Jan. 8, 2001 now U.S. Pat. No. 6,816,736. U.S. patent application Ser. No. 09/756,384 and U.S. patent application Ser. No. 09/756,370 were filed on Jan. 8, 2001. 

   TECHNICAL FIELD 
   This invention relates to wireless communications systems and, more particularly, to wireless communications between wireless terminals and base stations. 
   BACKGROUND OF THE INVENTION 
   In wireless communications systems, wireless terminals (WTs) are paged, i.e., have special messages—so-called paging messages—sent to them, by associated base stations (BSs) to initiate communications. In order to realize this, the base stations typically have a channel on the downlink called the paging channel. In prior known paging arrangements, the paging channel is subdivided into a plurality of paging time slots. A group of wireless terminals is typically allocated a paging time slot of a prescribed periodicity for receiving paging messages from associated base stations. As shown in  FIG. 1 , wireless terminals  1  to N are allocated to time slot  1 , wireless terminals N+1 to Y are allocated to time slot  2 , and so on. Each wireless terminal is expected to monitor for paging messages from an associated base station during these paging time slots. To this end, the periodicity of the paging time slots is made sufficiently long that each of the wireless terminals can effectively turn off most of its circuitry between two of its designated paging time slots and, thus, save energy. This is referred to as the wireless terminal entering a so-called “sleep” mode. The wireless terminal, even though in the sleep mode, still has to keep track of the received paging time slots. The wireless terminal is caused to “wake up” prior to the arrival of its designated paging time slot, tunes to the downlink channel, and achieves carrier, timer and frame synchronization. Then, the wireless terminal decodes the paging time slot, and if its identifier is included in the wireless terminal&#39;s designated paging time slot, it knows that the paging message is meant for it. The wireless terminal then takes the appropriate action indicated in the paging message. If the paging message is not meant for the wireless terminal, it returns to the sleep mode, and monitors the next received paging time slot designated for it. 
   A disadvantage of this prior paging arrangement is that the wireless terminal has to decode the entire paging message in order to determine if the message is meant for it. When many wireless terminals share the paging time slot, it is quite likely that the paging message is not meant for that particular wireless terminal. This can cause the wireless terminal to expend power and reduce its battery life unnecessarily. 
   SUMMARY OF THE INVENTION 
   Problems and limitations of prior wireless paging arrangements are overcome by employing a unique paging time slot format. In the unique paging time slot format, each of the allocated paging time slots occurs periodically and is split into several prescribed paging time slots including at least one first type paging time slot having a relatively short duration and at least one second type paging time slot having a longer duration. The at least one first type paging time slot is of relatively short duration and transports an indication whether a particular associated wireless terminal was paged. The second type paging time slot is of longer duration than the first type time slot and transports the entire paging message. 
   Specifically, a base station periodically transmits paging time slots intended to transport paging messages to one or more wireless terminals that are normally in a standby mode. Each individual paging time slot includes one or more of the first type paging time slots and at least one associated second type paging time slot. The first type paging time slot includes fewer bits than its associated second paging time slot and is intended to transport an indication that a particular one of the wireless terminals has been paged. The second type paging time slot being intended to transport a complete paging message for a paged wireless terminal. 
   A technical advantage of this unique two type time slot format is that only a small number of bits need to be transmitted from a base terminal and, then, decoded by a receiving wireless terminal from its designated first type time slot to determine if the paging message in the second type time slot is meant for it. As a result, the wireless terminal does not have to perform as much “work” for paging messages not intended for it, and consequently conserves power and extends battery life. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a graphic representation of a prior known paging time slot format; 
       FIG. 2  shows, in simplified block diagram form, details of a base station and a plurality of wireless terminals in which the invention may be employed; 
       FIG. 3  graphically illustrates applicants&#39; unique paging time slot format, in accordance with the invention; 
       FIG. 4  is a flow chart illustrating the steps in the process of a base station transmitting paging messages; and 
       FIG. 5  is a flow chart illustrating the steps in the process of a wireless terminal processing the wireless terminal paging messages. 
   

   DETAILED DESCRIPTION  
     FIG. 2  shows, in simplified block diagram form, a wireless multiple access communications system in which the invention may be advantageously employed. It should be noted that although applicants&#39; unique invention will be described in the context of a mobile wireless communications system, it has equal application to non-mobile, e.g. fixed, wireless communications systems. One such mobile wireless communications system is the Orthogonal Frequency Division Multiplexed (OFDM) based spread spectrum multiple access system. 
   Specifically, shown in  FIG. 2  is a multiple access wireless communications system  200 . System  200  includes base station  201  including antenna  202  and one or more remote wireless terminals, i.e., wireless terminals  203 - 1  through  203 -M including associated antennas  204 - 1  through  204 -M, respectively. Transmission of signals is from and to base station  201 , to and from remote wireless terminals  203 . All of wireless terminals  203  share the transmission spectrum in a dynamic fashion. 
   In this example, base station  201  includes transmitter  205 , receiver  207  and controller  206  for transmitting and receiving wireless messages via antenna  202 . Controller  206  is employed to control operation of transmitter  205  and receiver  207 , in accordance with the invention. Similarly, in this example, each of wireless terminals  203 - 1  through  203 -M includes transmitter  208 , receiver  210  and controller  209  for transmitting and receiving wireless messages via antenna  204 . Controller  209  is employed to control operation of transmitter  208  and receiver  210 , in accordance with the invention. 
   In accordance with the invention, base station  201  generates and transmits paging messages in applicants&#39; unique format shown in  FIG. 3  and described below to wireless terminals  203 . Typically, wireless terminals  203  when not in use are in a standby mode commonly referred to as a “sleep” mode. In the sleep mode, most of the circuitry in the wireless terminals  203  is turned off in order to conserve energy and, thereby, extend battery life. In order for each of the wireless terminals  203  to detect whether there is a paging message intended for it, the particular wireless terminal  203  must come out of the sleep mode, i.e., wake up, and monitor its incoming dedicated periodically occurring time slots for an indication that a paging message has been received for the particular wireless terminal  203 , as described below in relationship to  FIG. 3 . 
     FIG. 3  graphically illustrates applicants&#39; unique paging time slot format. The format includes a plurality of periodically occurring paging time slots each including at least one relatively short first type paging time slot, referred to as a type “A” paging time slot, that transports an indication whether an associated wireless terminal has been paged and a second type paging time slot, referred to as a type “B” paging time slot, that transports an entire paging message for a particular paged wireless terminal  203 , in accordance with the invention. Shown in  FIG. 3  is paging time slot  301 - 1  that is divided, in this example, into type A paging time slots  302 - 1  and a type B paging time slot  303 - 1 . The type A paging time slots include relatively short duration time slots  302 - 1 - 1 ,  302 - 1 - 2 , etc. that transport only an indication of whether an assigned wireless terminal  203  has been paged, while type B paging time slot  303 - 1  includes the complete paging message for the paged wireless terminals  203  that are indicated as being paged in the type A paging time slots  302 - 1 . Thus, in this example, type A paging time slot  302 - 1 - 1  has a subgroup including wireless terminals  203 - 1  through  203 -X assigned to it, type A paging time slot  302 - 1 - 2  has a subgroup including wireless terminals  203 -X+1 through  203 -Z assigned to it and so on through wireless terminal  203 -N. Also, in this example, type B paging time slot  303 - 1  transports the complete paging messages for assigned wireless terminals  203 - 1  through  203 -N. The remaining ones of wireless terminals  203  are assigned to other periodically occurring paging time slots in the format. 
   Thus, wireless terminal  203 - 1  only decodes its assigned type A paging time slot  302 - 1 - 1  to determine whether there is a received paging message for it. Since the type A type paging time slot only transports relatively few bits of information as compared to the complete paging message transported by the type B paging time slot, it is relatively easy to decode. It should be noted that the number of bits used for a type A paging time slot is dependent on the number of wireless terminals assigned to each type A time slot and is left to the implementer. Consequently, there is a significant computational saving in the monitoring process for determining whether or not a particular wireless terminal has been paged with a corresponding saving in battery energy expended. 
     FIG. 4  is a flow chart illustrating the steps in the process of a base station  201  transmitting a paging message for a particular wireless terminal  203  using applicants&#39; unique format. In step  401  a page indication for a particular wireless terminal  203  arrives. Step  402  causes an indication that the particular wireless terminal  203 , for example  203 - 1 , has been paged to be transmitted in the assigned type A paging time slot, in this example, type A paging time slot  302 - 1 - 1 . Then, in step  403 , a paging message is caused to be transmitted in a type B paging time slot  303 - 1  associated with type A paging time slot  203 - 1 . Finally, in step  404  base station  201  moves to the next state in the paging operation or the transmitting and receiving operation of base station  201 . 
     FIG. 5  is a flow chart illustrating the steps in the process of a wireless terminal  203  processing the wireless terminal paging messages. Initially, the wireless terminal  203 , for example wireless terminal  203 - 1 , is in the so-called sleep mode, i.e., standby mode, as indicated in step  501 . In step  502 , wireless terminal  203 - 1  periodically wakes up to monitor a type A paging time slot, in this example,  302 - 1 - 1 , that is assigned to it in order to determine whether or not it has been paged. Note that only a few bits need to be decoded by wireless terminal  203 - 1  depending on the number of additional wireless terminals  203  that have been assigned to the type A paging time slot  302 - 1 - 1 . If only one wireless terminal is assigned to each type A paging time slot  302 - 1  then a simple logical 1 or logical 0 only need be transported, as will be apparent to those skilled in the art. If no valid message is detected in step  502 , control is returned to step  501  and wireless terminal  203 - 1  returns to the sleep mode. If a valid message, i.e., an indication that wireless terminal  203 - 1  has been paged, is detected in step  502 , step  503  causes the associated type B time slot  303 - 1  to be monitored. If no valid message for the paged wireless terminal  203 - 1  assigned to type A paging time slot  302 - 1 - 1  is detected in step  503  control is returned to step  501  and wireless terminal  203 - 1  returns to the sleep mode. If a valid message is detected in step  503  for wireless terminal  203 - 1 , step  504  causes wireless terminal to move to its next step in the paging and/or receiving and transmitting process. For example, the wireless terminal  203 - 1  may execute any action set forth in the paging message. Again, it should be noted that if only one wireless terminal is assigned to a type A paging time slot  302  additional information may have to be included in the paging message transported in its associated type B paging time slot  303  in order to relate the message to the appropriate wireless terminal being paged. 
   The above-described embodiments are, of course, merely illustrative of the principles of the invention. Indeed, numerous other methods or apparatus may be devised by those skilled in the art without departing from the spirit and scope of the invention. Moreover, the invention may be implemented as hardware, as an integrated circuit, via programming on a microprocessor, on a digital signal processor or the like.

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