Abstract:
In a method and an apparatus for reducing the power consumption of a battery operated transceiver in standby mode, particularly a mobile telephone station, in which the receiver of the transceiver is adapted to receive successive word blocks on a forward control channel, each word block consisting of a predetermined number of bits forming a dotting sequence, a word synchronization sequence and a predetermined number of word repeats, a switching device is adapted to switch off the receiver after a word repeat in a word block has been validly received, and to switch on the receiver to receive a word repeat in the next successive word block.

Description:
TECHNICAL FIELD 
     This invention relates to a method and an apparatus for reducing the power consumption of a battery operated transceiver in standby mode, particularly a mobile telephone station, wherein successive word blocks are received by the receiver of the transceiver on a forward control channel, each word block consisting of a predetermined number of bits forming a dotting sequence, a word synchronization sequence and a predetermined number of word repeats. 
     BACKGROUND 
     A mobile telephone station in standby mode must monitor the appropriate control channel of the system in which it is located in a manner such that the mobile telephone station receives all system control messages addressed to it. This necessarily requires that the mobile telephone station monitors the control channel during any time periods within which control messages directed to that mobile telephone station could possibly be transmitted. 
     In systems such as the EIA/TIA-553 system (AMPS), the Total Acccess Communications System (TACS), and the D-AMPS IS-136 system, a mobile telephone station in standby mode, receives successive word blocks on a forward control channel (FOCC). Each word block consists of a 10-bit dotting sequence, an 11-bit word synchronization sequence, and ten word repeats each containing 40 bits. The word repeats are separated into two time-multiplexed data streams, the A stream and the B stream, each consisting of five word repeats. Depending on the last digit of the subscriber number, a mobile telephone station in standby mode listens to either the A stream or the B stream. 
     In the above systems, when the mobile telephone station monitors the forward control channel, the receiver is constantly on in that all five repeats of a word within a word block, are received, whereupon a majority decision is made, and BCH (Bose-Chaudhuri-Hocquenqhem) decode operations and parity check operations are performed. Thus, battery power is consumed in a mobile telephone station also in the standby mode. Moreover, this power consumption of the receiver of the mobile telephone station, when the mobile telephone station is monitoring the forward control channel, is a significant percentage of the total power consumption of the mobile telephone station. 
     SUMMARY 
     The object of the invention is to bring about a method and an apparatus for reducing the power consumption of a mobile telephone station in standby mode. 
     This is attained by the method according to the invention in that the receiver is switched off after a word repeat in a word block has been validly received, and the receiver is switched on to receive a word repeat in the next successive word block. 
     According to the invented method, the receiver is switched on in that time pulses are generated, said time pulses corresponding to bits that should have been received, had the receiver not been switched off, that said time pulses are counted, and that the receiver is switched on when the number of time pulses counted corresponds to the number of bits between the end of a word repeat in one word block and the beginning of a word repeat in the next word block. 
     According to the invented method, said time pulses are generated by a clock generator in a free-running mode, said clock generator being brought into said free-running mode from a tracking mode, in which the clock generator tracks the bits received, when the receiver is switched off. 
     According to the invented method the receiver is switched off after a word repeat in a word block has been validly received, and the receiver is switched on again to receive the same word repeat in the next word block. 
     According to the invented method, the receiver is switched off after the first word repeat in a word block has been validly received, and the receiver is switched on again to receive the first word repeat in the next word block. 
     According to the invented method, valid reception of a word repeat is determined by performing a parity check of its parity field. 
     The above object is also attained by the apparatus according to the invention in that a switching means is adapted to switch off the receiver after a word repeat in a word block has been validly received, and to switch on the receiver to receive a word repeat in the next successive word block. 
     According to the invented apparatus, said switching means is adapted to switch on said receiver upon receipt of a control signal from a counting means, said counting means being adapted to count time pulses corresponding to bits that should have been received,-had the receiver not been switched off, and to generate the control signal when the number of time pulses counted corresponds to the number of bits between the end of a word repeat in one word block and the beginning of a word repeat in the next word block. 
     According to the invented apparatus, a clock generator is adapted, in a free running mode, to generate said time pulses corresponding to bits that should have been received, had the receiver not been switched off, and, in a tracking mode, to track the bits received by the receiver, said clock generator being brought into said free running mode from said tracking mode by said switching means when the receiver is switched off. 
     According to the invented apparatus, said switching means is adapted to switch off the receiver after a word repeat in a word block has been validly received, and to switch on the receiver to receive the same word repeat in the next word block. 
     According to the invented apparatus, said switching means is adapted to switch off the receiver after the first word repeat in a word block has been validly received, and to switch on the receiver to receive the first word repeat in the next word block. 
     According to the invented apparatus, said switching means is adapted to determine valid reception of a word repeat in a word block by performing a parity check of the parity field of the word repeat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described more in detail below with reference to the appended drawings, in which 
     FIG. 1 illustrates A and B data streams transmitted on an analog forward control channel in a D-AMPS, AMPS or TACS system, 
     FIG. 2 is a schematic block diagram of the receiver of a mobile telephone station, which operates according to the invention, 
     FIG. 3 is a flow diagram which illustrates steps performed according to the invention in the receiver according to FIG. 2, and 
     FIGS. 4 a  and  4   b  are time diagrams illustrating the on and off periods of a receiver in a mobile telephone station listening to the A data stream and the B data stream, respectively. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a complete word block  1  and part of a successive word block  2 , received in standby mode by the receiver of a transceiver, particularly a mobile telephone station, in a D-AMPS, AMPS or TACS system. 
     Each word block consists of a 10-bit dotting sequence DS, an 11-bit word synchronization sequence WS, and five word repeats for an A mobile telephone station and five word repeats for a B mobile telephone station. Each word repeat contains 40 bits, including a parity field. Whether a mobile station is an A or a B station is determined by the last digit of the subscriber number. 
     As indicated in FIG. 1, in word block  1 , there are five repeats of word A 1  for a A mobile telephone station, and five repeats of word B 1  for a B mobile telephone station. 
     In word block  2 , only the first repeat of word A 2  and the first repeat of word B 2  are shown for the A mobile telephone station and the B mobile telephone station, respectively. 
     In FIG. 2 which is a schematic block diagram of the receiving portion of a mobile telephone station,  1  denotes a receiver having an input IN,  2  denotes a decoder for decoding the data received by the receiver  1 ,  3  denotes a word synchronization detector,  4  denotes a counter,  5  denotes a clock generator, and  6  denotes a microprocessor. 
     By means of the flow diagram in FIG.  3  and the time diagrams in FIGS. 4A and 4B, the operation of the receiving portion in FIG. 2 will now be described. 
     At Step  300  the process begins in that the power to the receiver  1  is switched on. At Step  301  the receiver  1  is tuned to a forward control channel (FOCC), and at Step  302  the clock generator  5  in FIG. 2 is set to tracking mode. This means that the rate of the time pulses generated by the clock generator  5  will track the rate of the bits of the incoming word block as decoded by the decoder  2 . 
     At Step  303  word synchronization is performed by means of the word synchronization detector  3 . The word synchronization is carried out on the word synchronization sequence WS of a word block, e.g. word block  1  in FIG.  1 . 
     At Step  304  repeat  1  of a word of a word block is received, e.g. word A 1  of word block  1  in FIG.  1 . The repeat  1  of word A 1  of word block  1  is received by the microprocessor  6  from the decoder  2  as indicated by the doubled-lined arrow in FIG.  2 . 
     At Step  305  the microprocessor  6  performs a BCH decode operation on the received repeat  1  of word A 1 . A BCH decode operation is well known in this connection and will, consequently, not be described further. At Step  306 , the parity, derived at Step  305  from the parity field of the received repeat  1 , is checked to verify a correct reception of repeat  1  of word A 1  of word block  1 . 
     If the parity as checked at Step  306 , is OK, at Step  307  the number of “sleep bytes” between the last byte in repeat  1  of word A 1  of word block  1  and the first byte in repeat  1  of word A 2  of word block  2 , is calculated. 
     At Step  308  the clock generator  5  is set to free running mode, and at the same time the receiver  1  is switched off at Step  309  by the microprocessor  6 . 
     Since the receiver  1  is now off, the time pulses gene-rated by the clock generator  5  in free running mode correspond to the bits that should have been received, had the receiver  1  not been switched off. These time pulses are counted by the counter  4  which informs the microprocessor  6  of every counted “sleep byte” at Step  310 . 
     At Step  311  the microprocessor  6  checks whether a “sleep byte” issued by counter  4  is the last “sleep byte” as calculated at Step  307 . 
     If “YES”, the microprocessor  6  turns on the receiver  1  at Step  312  and at the same time at Step  313  the clock generator  5  is set to tracking mode again to receive repeat  1  of word A 2  of word block  2 , whereupon the process goes back to Step  304  in FIG.  3 . 
     If the parity of repeat  1  of word A 2  of word block  2  is OK as checked at Step  306 , the receiver  1  will again be switched off at Step  309 . 
     Thus, as apparent from FIG. 4 a , the receiver  1  in an A mobile telephone station will be on only during repeat  1  of a word A in each word block. The same is true for a B mobile telephone station which will be on only during repeat  1  of a word B in each word block. Consequently, the power reduction effect is equal for both A and B mobile telephone stations. 
     If, at Step  306 , the parity of repeat  1  of a word in a word block, is not OK, the rest of the repeats of that word in the word block, is received at Step  314 , whereupon at Step  315  a word synchronization has to be performed again by means of the word synchronization detector  3 . 
     At Step  314 , when the rest of the repeats of the same word have been received, a majority decision is made and BCH decode operations and parity check operations are performed in a conventional manner. 
     After that the word synchronization has been performed at Step  315 , repeat  1  of a word of the successive word block is received at Step  304  and the process goes on as described above. 
     In accordance with the invention, the sleep time is prolonged over the end of a current word block and the bit and word synchronization sequences of the following word block, i.e. the receiver  1  is switched on exactly in time for receiving the first word repeat in the successive word block. Thus, the sleep time equals the maximal theoretical one between equal-numbered word repeats in two successive word blocks. 
     By means of the invention, the resynchronization to the received data stream, after tuning to a forward control channel and initial use of the word synchronization sequence, is avoided. This minimizes the risk of false word synchronization detection after the sleep periods, which could occur if the sleep time was different from the one described above. 
     At Step  304  in FIG. 3, it is not absolutely necessary to receive the first repeat of-a word of a word block and carry out the rest of the process in relation to that first repeat. In fact, it is theoretically possible to select any of the five repeats at Step  304  to be received and run through the process on the basis on that selected repeat. However, if at Step  306  it is found that the parity of the selected received repeat is not OK, too little data may be received at Step  314  to make a majority decision. Thus, in practice, the first repeat of a word of a word block should be received. 
     Also, at Step  306 , if the parity of the first word repeat is found to be not OK, at Step  314  just the second repeat could be received instead of all the repeats  2 - 5 . In that case the BCH decode operation at Step  305  would have to be performed on that second repeat. If the parity as checked at Step  306  is found to be OK for that second repeat, the process would continue at Step  307  by calculating the number of “sleep bytes” from that second repeat to the first repeat in the next successive word block.