Abstract:
An apparatus and method for saving a battery of a paging receiver. The apparatus includes a paging terminal for sequentially assigning time slots by the unit of a POCSAG code, and generating the first batch following a preamble as a header batch with respect to each POCSAG code, and the paging receiver for receiving the POCSAG code transmitted from the paging terminal to detect the header batch, and turning off a power source of a radio frequency unit when time slot information contained in the header batch does not correspond to the time slot of the paging receiver.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to paging receivers and, more particularly, to an apparatus and method for saving battery power of a paging receiver when receiving messages. 
     2. Description of the Related Art 
     A Post Office Code Standardization Advisory Group (POCSAG) system, which is one of the current protocols used for paging receivers, transmits data asynchronously. Another currently used protocol is the FLEX™ Paging Protocol by Motorola, which employs a high speed paging system that transmits data synchronously. Referring to FIG. 1A, a diagram of a prior art POCSAG protocol signal used in a paging receiver is shown. The transmission of POCSAG is of a digital format and begins with preamble data of 576 bits followed by a plurality of batch data (generally 30 to 60 batches) which consists of address and message codewords. Particularly, one batch begins with a 32-bit synchronization codeword (“word sync”) followed by 8 frames each having 64 bits. Each frame has a duration equivalent to two codewords, i.e., a 32-bit address codeword and a 32-bit message codeword. Therefore, one batch consists of 544 bits of data, seventeen words of 32 bits. 
     Referring now to FIG. 1B, a structure of a combined channel with POCSAG and FLEX system having collapse information equal to 4, as well as an operating waveform BS of a conventional paging receiver at that channel is shown. 
     Generally, a conventional paging receiver of a paging system includes a radio frequency (RF) circuit which is repeatedly turned on and off at regular intervals in order to detect the presence or absence of a signal such as preamble data, for example, to detect an incoming message or call. Hence, the RF circuit of the paging receiver is energized irrespective of whether or not the paging receiver is receiving its corresponding signal. Consequently, power is unnecessarily expended thereby reducing the life of the battery of the paging receiver. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a system and method for conserving the power consumed from a battery during call reception in a paging receiver. 
     It is another object of the present invention to provide a system and method for minimizing the power consumed from a battery while detecting a self signal of a paging receiver in a POCSAG paging signaling system. 
     It is still another object of the present invention to provide a system and method for minimizing the power consumed from a battery while detecting a self signal of a POCSAG paging receiver at a combined channel using the POCSAG system and a FLEX system. 
     In one aspect of the present invention, an apparatus for saving battery power of a paging receiver having a radio frequency unit comprises a paging terminal for receiving a paging message, generating a POCSAG code in accordance with the paging message and sequentially assigning a corresponding time slot for transmission of the POCSAG, the POCSAG code having preamble data and a first batch as a head batch following the preamble, the header batch having time slot information associated with the paging receiver, whereby the paging receiver receives the POCSAG code transmitted from the paging terminal and detects the header batch, the paging receiver controlling the battery power of the radio frequency unit in accordance with the time slot information contained in the header batch. 
     In another aspect of the present invention, a method for saving a battery in a paging receiver having a decoder for decoding frame data to an original paging message, determining whether a data batch is POCSAG data based on a time slot number contained in a header batch, and means for communicating with a paging terminal through a combined channel, comprises the steps of: supplying a power source to a radio frequency unit, and assigning a header address for receiving the header batch and a data address for receiving the data batch to the decoder; determining whether one of the header address and the data address is detected; holding the decoder and setting a time of a decoder hold timer if only the header address is detected; and checking the time of the decoder hold timer, and if the setting time of the decoder hold timer elapses, releasing a hold state of the decoder and returning to the determining step. 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a diagram illustrating the structure of a prior art POCSAG protocol code used in a paging receiver; 
     FIG. 1B is a diagram illustrating a structure of a combined channel of a POCSAG and FLEX system having collapse information equal to 4, and an operating waveform of a conventional paging receiver at that channel; 
     FIG. 2 is a block diagram of a conventional paging signaling system in which the present invention may be implemented; 
     FIG. 3 is a block diagram of a paging terminal illustrated in FIG. 2; 
     FIG. 4 is a block diagram of a paging receiver in accordance with an embodiment of the present invention; 
     FIG. 5 is a flow diagram illustrating an operating process of a paging terminal in accordance with the present invention; 
     FIG. 6 is a flow diagram illustrating a paging message immediate transmission routine shown in FIG. 5; 
     FIG. 7 is a flow diagram illustrates an operation of a paging receiver in accordance with the present invention; 
     FIGS. 8A to  8 C are timing diagrams illustrating a battery saving state of a paging receiver for one time slot in accordance with the present invention; 
     FIGS. 9A to  9 C are timing diagrams illustrating a battery saving state of a paging receiver for a plurality of time slots in accordance with the present invention; 
     FIGS. 10A to  10 C illustrate a structure of a time slot in accordance with an embodiment of the present invention; 
     FIG. 11 illustrates a form of a POCSAG code of a battery saving type at a FLEX combined channel according to an embodiment of the present invention; 
     FIG. 12 illustrates a structure of a header batch in the POCSAG code shown in FIG. 11; 
     FIG. 13 illustrates a plurality of forms for receiving data of first to fifth FLEX combined channels; 
     FIG. 14 illustrates waveform charts of battery saving signals of a POCSAG paging receiver at FLEX combined channels in accordance with an embodiment of the present invention; and 
     FIG. 15 is a flow diagram of a battery saving method of a paging receiver in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following description of preferred embodiments, specific details are set forth to provide a more thorough understanding of the present invention. It is to be understood, however, that a detailed description of functions or constructions related to the present invention which are known by those of ordinary skill in the art will not be provided where such description would obscure the subject matter of the present invention. 
     Referring now to FIG. 2, a block diagram of a conventional paging signaling system in which the present invention may be implemented is shown. When a user requests to transmit a paging message through, e.g., a telephone  300  or a facsimile  400 , the paging message is transmitted to a paging terminal  32  through a switching system or a public switched telephone network (PSTN)  200 . The paging terminal  32  call-signaling-protocols the paging message. If the call-signaling-protocol message is a POCSAG signal, the paging terminal  32  determines an accurate time slot for transmission of the POCSAG signal by using information received from a Global Positioning System (GPS)  500  and transmits the POCSAG signal to a corresponding one of a plurality of paging receivers  52  through  56  via one or more of a plurality of base station units  22  through  24  during the determined time slot. The GPS  500  is an automatic positioning system which receives time and position data from 24 satellites and computes the current 3-dimensional position and time by using the principle of triangulation. 
     Referring to FIG. 3, a block diagram of the paging terminal  32  of FIG. 2 is shown. A controller  30  controls the reception and transmission of the paging message received through the PSTN  200 . A memory  31  is connected to the controller  30  for storing information about the paging receivers of the paging system such as an address of the paging receiver, a message type (voice, numeric or alphanumeric), and time slot group information. The time slot group information is previously designated by the paging system and is based on the address of the paging receiver. Referring again to FIG. 1A, the 32 bit address codeword consists of one address/data identification bit (bit  1 ), an 18-bit address portion (bits  2 - 19 ), a 2-bit address multiplier portion (bits  20  and  21 ), a 10-bit parity portion (bits  22 - 31 ), one block check bit (bit  32 ). The time slot group information is determined by using information of the address portion, i.e, whether the information value of the address portion is an even or odd number. Alternatively, the time slot group information may be determined on the basis of a remainder obtained by dividing the information value of the address portion by 2 or more. 
     A page queue  34 , which is connected to the controller  30 , temporarily stores the paging message in a standby state when received through the PSTN  200 . An area is divided in the page queue  34  so as to store the time slot corresponding to the time slot group information. A data encoder  33  converts the paging message in the page queue  34  into the POCSAG signal which can be transmitted to the corresponding paging receiver  52 - 56  through a corresponding one of the base station units  22 - 24 . A timing unit  35  controls timing necessary for the operation of the paging terminal  32 . 
     Referring now to FIG. 4, a block diagram of a paging receiver in accordance with an embodiment of the present invention is shown. An RF unit  41  receives paging information and performs functions such as frequency conversion, demodulation and waveform shaping, and then outputs digitally converted paging information. A pattern detector  52  detects the preamble data from the digital signal output from the RF unit  41 . An address/message detector  54  detects an address or a message of the digital signal output from the RF unit  41 . A battery saving controller  42  turns on or off a power source (not shown) of the RF unit  41  under the control of a controller  44 . 
     A decoder  56  sets an operating mode of the paging receiver under the control of the controller  44 . In an idle mode, the decoder  56  controls the power supplied to the RF unit  41  so that the pattern detector  52  can detect the preamble data. In a batch mode, the decoder  56  controls the power supplied to the RF unit  41  so that the address/message detector  54  may detect word sync data and frame data. Further, the decoder  56  decodes the detected frame data into its original data form. A second clock generator  58  controls the operation timing of the decoder  56 . 
     The controller  44  receives and processes the decoded data provided from the decoder  56 , and controls operation of an alarm unit  43 . In addition, the controller  44  generates a decoder hold signal DH which causes the decoder  56  to turn off the power source of the RF unit  41  via the battery saving controller  42 . The alarm unit  43  may be any conventional vibrator or a buzzer. In response to an alarm control signal received from the controller  44 , the alarm unit  43  generates an alarm signal (e.g., a tone signal or a vibration signal) to indicate that a call is received. A display unit  45  displays a message from the caller, as well as status information of the paging receiver, by a display control signal generated from the controller  44 . A memory  46  stores data such as the unique address information assigned to the paging receiver, frame information and received messages. 
     A first clock generator  47  supplies clock signals to the controller  44  which are necessary for the operation of the paging receiver. A timer  60  of the controller  44  is used to sense the state of the time slot repeated with a constant time length. A key input unit  48 , which is user interface means, has a plurality of keys which are used to set one of a plurality of modes of the paging receiver as well as to confirm the paging message. 
     Referring now to FIG. 5, a flow diagram illustrating an operation of the paging terminal  32  in accordance with the present invention is shown. In FIG. 5, it is assumed that a paging request generated at any time slot is immediately transmitted at that time slot or the paging request is transmitted at the next time slot. The flow chart of FIG. 5 is divided into an operation at an n-th time slot, a current time slot, and an operation at an (n+1)-th time slot, the next time slot (where n is an even number). 
     The paging terminal  32  shown in FIGS. 2 and 3 checks whether a paging message is received through the PSTN  200  (step  5   a ). As discussed above, the paging message is inputted by the user through, e.g., a telephone or facsimile and transmitted to the paging terminal  32  through the PSTN  200 . When the paging message is received, it is classified with reference to information stored in memory  31  and the timing unit  35  (step  5   b ). Specifically, a CAP (Code Assignment Plan) code corresponding to the paging receiver (which is contained in the paging message) is calculated to check whether the called paging receiver belongs to an odd or even-numbered time slot group. Since the paging terminal  32  only processes a subscriber call having an even CAP code number during an even-numbered time slot and a subscriber call having an odd CAP code number during an odd-numbered time slot, the paging receivers are classified into an even or odd-numbered time slot group depending on the designated time slot. 
     Next, a determination is made as to whether a current time slot is identical to the time slot of the called paging receiver (step  5   c ). If the time slot assigned to the called paging receiver is an even-numbered time slot, the paging message may be immediately transmitted under the state that messages for other called paging receivers belonging to the even-numbered time slot group have been processed. In particular, whether the paging message is immediately transmitted at a corresponding time slot depends on factors such as the number of other paging messages to be transmitted at the same frame and the length of each message. If the paging message can not be transmitted at a current time slot, it should be placed in a standby state until the next even-numbered time slot. Then the paging message should be stored in a memory (queue). As stated above, for purposes of the following description of preferred embodiments, these circumstances are disregarded and it is assumed that the paging message is immediately transmitted. Accordingly, referring back to FIG. 5, if the time slot of the called paging receiver is not identical to an n-th time slot (negative result in step  5   c ), the paging message is stored in an odd-numbered time slot standby queue (step  5   e ). If the time slot is identical to the n-th time slot (affirmative result at step  5   c ), a paging message immediate transmission routine is executed (step  5   d ). 
     Next, a determination is made as to whether it is time to transmit the paging message for a new time slot (step  5   f ). This determination is made even if the paging message is not received (negative result in step  5   a ). If it is determined that it is not time to transmit the paging message for the new time slot (negative result in step  5   f ), process returns to step  5   a.  If it determined that it is time to transmit the paging message for the new time slot (affirmative result in step  5   f ), the paging message of the standby state (at step  5   e ) is transmitted. Like the even (n-th) time slot, the paging message request may be sensed at the odd ((n+1)-th) time slot. However, only an operation for processing the paging message stored in the odd-numbered time slot standby queue at the odd-numbered time slot will be described in detail. 
     Next, the preamble and word sync is transmitted (step  5   g ). A header batch is then formed (step  5   h ). In this instance, the state of a traffic bit should be 1. Next, the paging message stored in the odd-numbered time slot standby queue is searched (step  5   i ). A data batch consisting of a data address and a data message is formed (step  5   j ) and the data batch is transmitted (step  5   k ). 
     Referring now to FIG. 6, a flow diagram of the paging message immediate transmission routine (of step  5   d ) of FIG. 5 is shown. The paging terminal  32  checks whether the header batch has been transmitted at a corresponding time slot (step  6   a ). If the header batch has been transmitted (affirmative result in step  6   a ), a determination is made as to whether the traffic bit contained the header batch is logic  0  or logic  1 . If the traffic bit is logic  0 , the paging receiver will turn off the power source (described in detail below with reference to FIG.  7 ). On the other hand, if the traffic bit is logic  1 , the power source is not turned off. If the header batch having a traffic bit of logic  0  is transmitted, there is no use to transmit the paging message. Therefore, if it is determined that the traffic bit is logic  0  (negative result in step  6   b ), the paging message is stored in an even-numbered time slot standby queue (step  6   c ). The stored paging message will then be transmitted at the next even-numbered time slot. 
     On the other hand, if the header batch has not been transmitted (negative result in step  6   a ) (i.e., if it is time to start to transmit the preamble or if the preamble is being transmitted) a header batch having a traffic bit of logic  1  is formed and transmitted (step  6   d ) after the preamble has been transmitted. Next, a data batch consisting of the data address and the data message is formed (step  6   e ) and the data batch is transmitted (step  6   f ). 
     Referring now to FIG. 7, a flow diagram of an operation of a paging receiver in accordance with the present invention is shown. In a standby state, the controller  44  of the paging receiver supplies a power source to the RF unit  41  (step  7   a ), and then performs an initialization operation (step  7   b ). During initialization, a normal operating timer (which can normally operate the decoder  56 ) is set to approximately 15 seconds. In addition, a decoder hold timer (which prevents the decoder  56  from operation for a corresponding time) is released. Next, a header/data address (or CAP code) is assigned to the decoder  56  (step  7   c ) so that the header batch and the data batch can be extracted from a signal received by the RF unit  41 . 
     Next, a determination is made as to whether the header address is detected (step  7   d ). If the header address is detected (affirmative result at step  7   d ), the header message is analyzed (step  7   e ) to determine if the current time slot corresponds to the time slot designated for the paging receiver (“receiver time slot”). If the current time slot corresponds to the receiver time slot, the state of the traffic bit is checked (step  7   f ). It is assumed that a traffic bit of logic  0  represents that there is no data batch to be transmitted whereas a traffic bit of logic  1  represents that there is a data batch to be transmitted. Accordingly, if it is determined that the traffic bit is logic  0  (negative result in step  7   f ), the decoder hold signal DH is generated and the decoder hold time is set to a corresponding time slot (step  7   g ), thereby turning off the power source of the RF unit  41  during that time. Next, the decoder hold timer is checked to determine if the time set for the decoder hold timer has elapsed (step  7   h ). If the setting time has elapsed (affirmative result in step  7   h ), the decoder hold signal DH is prevented from being generated (step  7   i ) so as to supply a normal power source. The normal operating timer is then set (step  7   j ) and execution returns to step  7   d.    
     If, on the other hand, the traffic bit is logic  1  (affirmative result at step  7   f ), a determination is made as to whether the data address is detected (step  7   k ). If the data address is detected (affirmative result at step  7   k ), the data message is received from the decoder (step  7   l ). The received data message is processed and stored (step  7   m ). The received data message is displayed through the display unit  45  and aurally transmitted through the alarm unit  43  (step  7   n ). Next, a determination is made as to whether the setting time of the normal operating timer has elapsed (step  7   o ). Moreover, even if the data address is not detected (negative result at step  7   k ), the setting time of the normal operating timer is checked to see if it has elapsed (step  7   o ). If the setting time has not elapsed (negative result in step  7   o ), execution returns to step  7   k.  The elapse of the time set in the normal operating timer corresponds to the point at which the time permitted to a self time slot elapses. That is, if the self time slot is an even-numbered time slot, the fact that the time permitted to the self time slot elapses represents that it is time to start a new odd-numbered time slot. By driving the decoder hold timer in accordance with the setting time, the decoder  56  will not be operated during the next time slot except the self time slot. 
     Next, if the header address is not detected (negative result at step  7   d ), it is determined if the data address is detected (step  7   k ). This is done because a situation may arise during a normal operation that the data address is detected even though the header address is missed without any reason. 
     Referring now to FIGS. 8A through 8C, timing diagrams illustrating a battery saving state of a paging receiver for one time slot in accordance with the present invention are shown. In particular, FIG. 8A illustrates a structure of one time slot with a constant time length. FIG. 8B illustrates that the power source is normally supplied to the RF unit during a data batch stream when a current time slot is determined as the receiver time slot by detecting the preamble and checking the header batch. FIG. 8C illustrates that the power supplied to the RF unit is cut off during the data batch stream when the current time slot is not the receiver time slot. In this situation, the paging receiver does not receive the data batch information during the current time slot and does not operate as the receiver by a decoder holding operation. 
     FIGS. 9A to  9 C are timing diagrams illustrating a battery saving state of the paging receiver for a plurality of time slots. In particular, FIG. 9A illustrates a the form of the transmission of the time slots with each time slot having constant time length. FIG. 9B shows a battery consuming state when the time slot of the paging receiver is an odd-numbered time slot. FIG. 9C shows a battery consuming state when the time slot of the paging receiver is an even-numbered time slot. In the inventive control method, only about 50% of the conventional power is consumed (assuming of course that power consumption of the conventional paging receiver is 100%). In addition, if the traffic bit is 0, only the preamble is detected and the RF unit  41  is turned off until the corresponding data batch and the next time slot. Then only about 3.33% of the conventional power is consumed (again assuming that the power consumption of the conventional paging receiver is 100%). 
     As shown, when the time slots with constant time length are transmitted, the paging receiver checks the preamble and the header batch. If the current time slot is not the receiver time slot, the RF unit  41  is turned off. On the other hand, if the current time slot is the receiver time slot, the RF unit  41  is turned on. It is to be appreciated that, since the RF unit  41  is only turned on if the current time slot is the receiver time slot, there is no consumption of the battery when the current time slot is not the self time slot and, therefore, the power is saved. 
     Referring now to FIGS. 10 a  through  10   c,  a structure of a time slot in accordance with the present invention is shown. In particular, FIG. 10 a  illustrates one time slot group (TSG) consisting of 4 time slots. In FIG. 10 a,  reference symbols OTS 1  and OTS 2  designate odd-numbered time slots; ETS 2  and ETS 4  represent even-numbered time slots; B 1 -B 31  refer to data batches; PR refers to the preamble data; and HDB refers to the header batch. Assuming that each time slot has a duration of 15 seconds, one TSG has a duration of one minute. 
     FIG. 10B illustrates a construction of the header batch (HDB) contained in the odd-numbered time slot (OTS) and FIG. 10 c  illustrates a construction of the header batch contained in the even-numbered time slot (ETS). Referring to FIG. 10 b,  2 time slot information bits S 0  and S 1  are assigned to the message data constituting any one frame of the header batch of the odd-numbered time slot. Preferably, the time slot group (TSG) consists of 4 time slots because there are 4 numbers, for example, 1, 2, 3 and 4, designated by the 2 bits. Although the fundamental construction shown in FIGS. 10 b  and  10   c  are similar, the frame having information is determined depending on whether the time slot is an even or odd-numbered time slot within one time slot group. In other words, the first frame in FIG. 10 b  has address data A 1  and message data M 1  since OTS 1  is an odd-numbered time slot, whereas the second frame has no data (designated by X X). The first frame in FIG. 10 c  has no data since ETS 4  is an even-numbered time slot, whereas the second frame has address data A 2  and message data M 2 . The traffic information T is one bit. Since the transmission of data is reduced in the night, the paging terminal transmits only the preamble and the header batch when there is no data transmission. Therefore, the consumption of the battery can be reduced. For example, the traffic information bit of 0 means that there is no data batch. Hence, the paging receiver turns off the RF unit  41 . Since the traffic information bit of 1 means that there is the data batch, the paging receiver turns on the RF until  41 . The AM/PM information is one bit, hour information is 4 bits, 10-minute information is 4 bits, one-minute information is 4 bits, and a checksum bit is 4 bits. The checksum bit is used to determine whether header information data of 16 bits, that is, the slot, traffic and AM/PM information, hour information, 10-minute information and 1-minute information, has an error. If a value added by the unit of 4 bits (nibble) is over 16, that value is discarded, and only a value between 0 to 15 is transmitted. The paging receiver determines whether the information is effective by comparing the 16 most significant bits with a checksum value. 
     Referring now to FIG. 11, a form of a POCSAG code of a battery saving type at a FLEX combined channel according to an embodiment of the present invention is shown. The first batch following the preamble is the header batch which consists of a synchronization code (SC) and 8 frames. Each frame consists of 2 codewords. Each batch consists of 17 codewords. The remainder of the batches following the header batch are the data batches. 
     Referring now to FIG. 12, a structure of the header batch in the POCSAG code of FIG. 11 is shown. It is assumed that one minute (32 frames) is one period and the length of one time slot is 15 seconds and 4 time slots forms one time slot group. Each time slot has the header batch as shown in FIG.  12 . There are two slot information bits that are assigned to the message data constituting the frame of the header batch. For example, if the slot information bits S 0  of 1 and S 1  of 0 are assigned to message data M 1  constituting the first frame of the header batch of the first time slot, it will be appreciated that the transmitted data belongs to the first time slot. 
     In addition to the slot information, the AM/PM information consists of one bit, the hour information consists of 4 bits, the 10-minute information consists of 4 bits, the one-minute information consists of 4 bits, and the collapse information consists of 4 bits. There are bits assigned to the hours, minutes and seconds in order to transmit accurate time information because a FLEX paging system uses the GPS information. The collapse bits are characteristic of a FLEX form of operation. Consequently, a paging receiver at the FLEX combined channel detects the time slot number and the collapse bits from the header batch following the preamble and previously senses the transmission time of FLEX data. Therefore, the paging receiver can turn the RF unit  41  off while the FLEX data is transmitted. 
     The following Table 1 and Table 2 show the state and contents of the collapse bits and time slots. 
     
       
         
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 C3 
                 C2 
                 C1 
                 C0 
                 Contents 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 0 
                 0 
                 0 
                 FLEX Combined Channel 
               
               
                   
                   
                   
                   
                   
                 0 
               
               
                   
                 0 
                 0 
                 0 
                 1 
                 FLEX Combined Channel 
               
               
                   
                   
                   
                   
                   
                 1 
               
               
                   
                 0 
                 0 
                 1 
                 0 
                 FLEX Combined Channel 
               
               
                   
                   
                   
                   
                   
                 2 
               
               
                   
                 0 
                 0 
                 1 
                 1 
                 FLEX Combined Channel 
               
               
                   
                   
                   
                   
                   
                 3 
               
               
                   
                 0 
                 1 
                 0 
                 0 
                 FLEX Combined Channel 
               
               
                   
                   
                   
                   
                   
                 4 
               
               
                   
                 . 
                 . 
                 . 
                 . 
                 Not Used 
               
               
                   
                 . 
                 . 
                 . 
                 . 
               
               
                   
                 . 
                 . 
                 . 
                 . 
               
               
                   
                 0 
                 1 
                 1 
                 1 
                 Not Used 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 S0 
                 S1 
                 Contents 
               
               
                   
               
             
             
               
                 0 
                 0 
                 Time Slot 1 
               
               
                 0 
                 1 
                 Time Slot 2 
               
               
                 1 
                 0 
                 Time Slot 3 
               
               
                 1 
                 1 
                 Time Slot 4 
               
               
                   
               
             
          
         
       
     
     FIG. 13 illustrates data receiving forms of first to fifth FLEX combined channels. The fifth FLEX combined channel has the collapse information of 4. Assuming that one minute (32 frames) is the duration for one period, FLEX data is transmitted during the first 30 seconds (16 frames) and POCSAG data is transmitted during the next 30 seconds. The transmitted POCSAG data comprises two time slots (i.e., time slots  3  and  4  in FIG. 13) each having a duration of 15 seconds. The FLEX data is transmitted during the time corresponding to time slot  1  and time slot  2 . Therefore, with regard to the POCSAG system, the POCSAG paging receiver does not have to operate when the Flex data is being transmitted (i.e., during the time corresponding to time slot  1  and time slot  2 ). 
     The fourth FLEX combined channel has the collapse information of 3. The FLEX data is transmitted during the first 15 seconds (8 frames) and the POCSAG data is transmitted during the next 45 seconds. As shown, the POCSAG data is transmitted during time slot  2  through time slot  4 . 
     The third FLEX combined channel has the collapse information of 2. The FLEX data is transmitted during the first 7.5 seconds (4 frames) and the POCSAG data is transmitted during the next 52.5 seconds. Specifically, as shown, the POCSAG data is transmitted for 7.5 seconds during time slot  1  and during the 15 seconds for each time slot  2 ,  3 , and  4 . 
     The second FLEX combined channel has the collapse information of 1. The FLEX data is transmitted during the first 3.75 seconds (2 frames) and the POCSAG data is transmitted during the next 56.25 seconds. Specifically, the POCSAG data is transmitted during 11.25 seconds of time slot  1  and 15 seconds for each of time slots  2 ,  3 , and  4 . 
     The first FLEX combined channel has the collapse information of 0. The FLEX data is transmitted during the first 1.875 seconds (1 frame) and the POCSAG data is transmitted during the next 58.125 seconds. Specifically, the POCSAG data is transmitted during time slot  1  through time slot  4 . The time slot  1  is transmitted only during 13.125 seconds. In each of the above combined channels, the length of the FLEX data is calculated by multiplying the collapse information k by two, i.e., 2 k. In particular, the length of the FLEX data is 1, 2, 4, 8 and 16 frames. 
     Referring now to FIG. 14, waveform diagrams of battery saving signals of the POCSAG paging receiver at the FLEX combined channels are shown. The battery saving waveforms (i.e., BS 4 , BS 3 , BS 2 , BS 1 , and BS 0 ) are maintained at a low state while the FLEX data is received. In other words, while the FLEX data is received, the RF unit  41  is turned off so as to prevent the unnecessary consumption of battery power. This operation is possible by previously sensing the transmission of the FLEX data. For this, the slot information bits S 0  and S 1  contained in any frame in the header batch of FIG. 12 are detected. 
     Referring now to FIG. 15, a flow diagram of a battery saving process of the paging receiver is shown. The controller  44  of the paging receiver supplies power to the RF unit  41  (step  15   a ) and performs an initialization operation (step  15   b ). Next, the header/data address (or CAP code) is assigned to the decoder  56  so as to receive the header batch and the data batch from the signal received through the RF unit  41  (step  15   c ). The decoder  56  transmits the data message to the controller  44  by detecting the data address after the preamble is detected. The controller  44  determines whether the header address is detected (step  15   d ). If the header address is detected (affirmative result at step  15   d ), the header message is analyzed (step  15   e ). Next, a determination is made as to whether the current time slot is the final one (step  15   f ). Preferably, if the time slot number is 4 or more, the current time slot is deemed to be the final time slot. The final time slot means that the FLEX data is transmitted after the corresponding time slot. A decoder hold reservation timer is then set in order to hold the decoder  56  after a constant time (step  15   g ). The setting of the decoder hold reservation timer is done before the decoder  56  is held. 
     Next, the decoder hold reservation timer is checked to see if its setting time elapses (step  15   h ). If the time has elapsed (affirmative result at step  15   h ), the decoder hold signal DH is generated to turn off the RF unit  41  (step  15   i ). The decoder hold timer is then set (step  15   j ). A determination is then made as to whether a setting time of the decoder hold timer elapses (step  15   k ). If the setting decoder hold time elapses (affirmative result at step  15   k ), the decoder hold signal DH is stopped from being generated (step  15   l ) so as to supply a normal power source to the RF unit  41 . Thereafter, the process returns to step  15   d.  On the other hand, if the setting time of the decoder hold timer does not elapse (negative result at step  15   k ), the controller  44  continues to check the decoder hold timer until the setting time elapses. 
     Referring back to step  15   d,  if the header address is detected but the current time slot is not the final time slot (negative result at step  15   f ), process returns to step  15   d.  In this situation, the header address will not be detected (negative result in step  15   d ) because the header address has already been detected. Therefore, the data address following the header address will be detected (step  15   m ). A determination is made as to whether the data address is detected (step  15   m ). If the data address is detected (affirmative result in step  15   m ), the data message is received from the decoder (step  15   n ). The received data message is processed and stored (step  15   o ). The received data message is then visually displayed and aurally transmitted by controlling the display unit  45  and the alarm unit  43  (step  15   p ). After the message is displayed ( 15   p ), or if the data address is not detected (negative result at step  15   m ), it is determined whether the setting time of the decoder hold reservation timer elapses (step  15   h ). 
     Consequently, the POCSAG paging receiver used in the combined channel turns off the RF unit when a data type obtained by checking the preamble and the header batch is a FLEX type and turns on the RF unit only when the data type is a POCSAG type. Therefore, unnecessary power consumption can be prevented. 
     Although the illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.