Abstract:
A TDMA voice information reading apparatus is constituted by two shift registers, a synchronous detection circuit, a selector, an AND gate, a TCH data read window generation circuit, and a clock signal generation circuit. The apparatus includes a processing circuit unit for, when reception data based on time division multiple access is received with a pull-out, delaying the reception data with the pull-out and detecting synchronization before the data is read out, and then reading out voice data and outputting the voice data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a time division multiple access (TDMA) voice information reading apparatus for reading out voice data from data received by TDMA and, more particularly, to a TDMA voice information reading apparatus which delays voice data until synchronous detection even upon receipt of out of frame reception data (e.g., a pull-out of reception data) in a transmission line such as a radio channel, thereby normally reading out the voice data and outputting it. 
     2. Description of the Prior Art 
     Conventionally, a TDMA voice information reading apparatus of this type is applied to, e.g., a portable telephone. In this case, the timing of reception data sometimes shifts from the original timing due to the distance from a cell base station connected via a radio channel or multiple radio wave propagation (multipath) at an obstacle at the moving position. That is, voice data out of phase may be received. 
     A “bit synchronization circuit” disclosed in Japanese Unexamined Patent Publication No. 4-10725 is known as a measure against such reception data out of phase. In this prior art, when a pull-out occurs, erroneous data is not read out from the FIFO memory. That is, the data out of phase is discarded. 
     FIG. 1 is a block diagram showing the arrangement of main part (TCH (Traffic Channel) read circuit) of a conventional TDMA voice information reading apparatus. Referring to FIG. 1, the TCH read circuit has a TCH data read window generation circuit  13  for generating TCH data read window data S 1  of high level at a free-running timing. The TCH read circuit also has an AND gate  12  for receiving the TCH data read window data Si and reception data S 2  and outputting voice output data S 14  to a digital signal processor (DSP) (not shown) for processing speech communication voice data, and a synchronous detection circuit  5  for detecting synchronization from the reception data S 2  and sending bit shift data S 8  representing the shift of the reception data S 2  from the prescribed timing to the TCH data read window generation circuit  13 . 
     FIGS. 2A to  2 C are process timing charts showing the operation of the conventional TDMA voice information reading apparatus. In FIGS. 1 and 2A to  2 C, the standards of a digital mobile telephone system to which the TCH read circuit in the TDMA voice information reading apparatus is applied are defined on the basis of “RCR-27D”. In this system, a synchronization code word for synchronous detection is set in a reception slot, as shown in FIG.  2 A. 
     The TCH data read window data S 1  of high level is generated by the TCH data read window generation circuit  13  at a free-running timing as shown in FIG.  2 B and input to one input terminal of the AND gate  12 . The reception data S 2  is input to the other input terminal of the AND gate  12  and the synchronous detection circuit  5 . The synchronous detection circuit  5  detects the bit shift data S 8  representing the shift of the reception data  52  from the prescribed timing and outputs the bit shift data S 8  to the TCH data read window generation circuit  13 . 
     When the synchronous detection circuit  5  detects the bit shift, an erroneous data portion in the reception data has already been output from the AND gate  12  to the DSP as TCH data or the voice output data S 14 . In this case, the DSP cannot perform normal voice data processing. As a result, the TCH data of the current slot cannot be processed as normal voice data although the synchronous timing of the next slot can be calculated from the bit shift data obtained from the current slot. Therefore, the channel quality degrades. 
     As described above, in the conventional TDMA voice information reading apparatus, TCH data of the current slot cannot be processed as normal voice data although the synchronous timing of the next slot can be calculated from the bit shift data obtained from the current slot. Therefore, the channel quality degrades to result in a low transmission efficiency and low reliability of data transmission. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above situation of the prior art, and has as its object to provide a TDMA voice information reading apparatus which can normally output TCH data of a current slot as voice data even when data based on time division multiple access is received with a pull-out due to degradation in channel quality, thereby largely improving the transmission efficiency and reliability of transmission. 
     A TDMA voice information reading apparatus of the present invention comprises processing means for, in a pull-out of reception data based on time division multiple access, delaying the reception data pulling out synchronization and detecting synchronization before the reception data is read out, and then reading out voice data and outputting the voice data in order to normally read out and output the voice data. 
     In the TDMA voice information reading apparatus of the present invention, a delay time until the reception data is read out is a minimum time for synchronous detection. 
     In the present invention, phase matching of a read signal associated with a timing at which the voice data in the reception data is read out is adjusted by delaying the read signal or reception data in units of bits. 
     In order to achieve the above object, according to the first aspect of the present invention, there is provided a TDMA voice information reading apparatus comprising: 
     (a) a first shift register for storing, in units of bits, window data used to read out the voice data in the reception data, reading out the window data, and outputting the window data; 
     (b) a second shift register for storing reception data of a slot in units of bits and outputting the reception data with a timing shift of several bits before or after a synchronization code word stored in a reception slot on the basis of the reception data received at a prescribed timing; 
     (c) a synchronous detection circuit for comparing, in units of slots, a reception timing of the synchronization code word in the reception data with a free-running pulse internally generated at a prescribed timing and outputting bit shift data representing a phase shift of the timing; 
     (d) an AND gate for sending voice output data obtained by ANDing read window data phase-matching the voice data in the reception data and reception data delayed until establishment of synchronization, which is output from the second shift register; 
     (e) a selector for selecting the read window data and outputting the read window data phase-matching the voice data in the reception data on the basis of the bit shift data representing the position and the number of bits shifted from the prescribed timing, which is output from the synchronous detection circuit after reception of the synchronization code word in the slot; and 
     (f) a voice data read window generation circuit for generating the read window data at a free-running timing allowing reception of a synchronization code word in the next slot after reception of the synchronization code word in the preceding slot. 
     In order to achieve the above object, according to the second aspect of the present invention, there is provided a TDMA voice information reading apparatus comprising: 
     (a) a voice data read window generation circuit for generating read window data at a free-running timing allowing reception of a synchronization code word in the next slot after reception of a synchronization code word in a preceding slot; 
     (b) a first shift register for delaying the read window data from the voice data read window generation circuit in units of bits and outputting the read window data; 
     (c) a second shift register for storing reception data in units of bits and outputting delayed reception data; 
     (d) a synchronous detection circuit for comparing, in units of slots, a reception timing of the synchronization code word in the reception data with a free-running pulse internally generated at a prescribed timing and outputting bit shift data representing a phase shift of the timing; 
     (e) a selector for selecting the read window data from the second shift register, which is delayed by the second shift register, on the basis of the bit shift data representing the position and the number of bits shifted from the prescribed timing, which is output from the synchronous detection circuit after reception of the synchronization code word in the slot, and outputting the reception data; and 
     (f) an AND gate for sending voice output data obtained by ANDing read window data phase-matching the voice data in the reception data and reception data delayed until establishment of synchronization, which is output from the first shift register. 
     As is apparent from the above-described arrangements, the TDMA voice information reading apparatus of the present invention can output normal voice data from the current slot even when the reception data based on time division multiple access pulls out synchronization due to degradation in channel quality, so the transmission efficiency and reliability of transmission are largely improved. 
    
    
     The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principles of the present invention are shown by way of illustrative examples. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the arrangement of main part (TCH read circuit) of a conventional TDMA voice information reading apparatus; 
     FIGS. 2A to  2 C are process timing charts associated with the operation of the prior art; 
     FIG. 3 is a block diagram showing the arrangement of main part (TCH read circuit) of a TDMA voice information reading apparatus according to an embodiment of the present invention; 
     FIGS. 4A to  4 F are timing charts showing data processing associated with the operation of the embodiment shown in FIG. 3; and 
     FIG. 5 is a block diagram showing the arrangement of main part (TCH read circuit) of a TDMA voice information reading apparatus according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 
     FIG. 3 is a block diagram showing the circuit arrangement of a TDMA voice information reading apparatus according to an embodiment of the present invention. The TDMA voice information reading apparatus shown in FIG. 3 has a shift register  3  serving as a FIFO buffer operated by a reception clock signal CLK. The shift register  3  stores TCH data read window data Si in units of bits, which is set at high level only in correspondence with the timing of TCH data, i.e., a voice data portion in reception data S 2 , and outputs TCH data read window data S 6 . 
     The TDMA voice information reading apparatus also has a shift register  4  serving as a FIFO buffer operated by the reception clock signal CLK generated from the reception data S 2 . The shift register  4  stores the reception data S 2  of one slot in units of bits, as needed, and outputs reception data S 7  whose timing is shifted by several bits before or after a synchronization code word stored in a reception slot on the basis of the reception data S 2  received at a prescribed timing (20 mS in RCR-27D). 
     This TDMA voice information reading apparatus also has a synchronous detection circuit  5  which compares, in units of slots, the reception timing of the synchronization code word in the reception data S 2  with the free-running pulse internally generated at a prescribed timing and outputs bit shift data S 8  representing that the reception data S 2  is shifted in units of bits, and an AND gate  12  for sending, to a digital signal processor (DSP) for processing speech communication voice data, voice output data S 11  containing only a normal TCH data portion extracted by ANDing TCH data read window data S 10  phase-matching the TCH data in the reception data S 2  and the reception data S 7  from the shift register  4 , which is delayed until establishment of synchronization. 
     The TDMA voice information reading apparatus also has a selector  9  which selects TCH data read window data S 6  from the shift register  3  on the basis of the bit shift data S 8  representing the position and the number of bits shifted from the prescribed timing, which is output from the synchronous detection circuit  5  after reception of the synchronization code word in the slot, and outputs the TCH data read window data S 10  phase-matching the TCH data in the reception data S 2 . 
     The TDMA voice information reading apparatus also has a TCH data read window generation circuit  13  for generating the TCH data read window data Si at a free-running timing allowing reception of the synchronization code word in the next slot after 20 mS from reception of the synchronization code word in the preceding slot, and a clock signal generation circuit  14  for sending the reception clock signal CLK generated from the reception data S 2  to various portions. 
     The operation of this embodiment will be described next. 
     FIGS. 4A to  4 F are timing charts of data processing in the operation of this embodiment. In FIGS. 3 and 4A to  4 F, the reception data S 2  is input to the shift register  4 . The shift register  4  serves as a FIFO buffer operated by the reception clock signal CLK generated from the reception data S 2  and stores the reception data S 2  of a slot in units of bits, as needed. The shift register  4  outputs the reception data with a shift of several bits forward or backward on the basis of the reception data S 2  received at the prescribed timing (20 mS in RCR-27D). This output is made after reception of the synchronization code word stored in the reception slot. 
     The shift register  3  serves as a FIFO buffer operated by the reception clock signal CLK and stores the TCH data read window data S 1  generated by the TCH data read window generation circuit  13  at a timing shown in FIG. 4B in units of bits. This TCH data read window data S 1  is data of high level, which is internally generated at a free-running timing. The TCH data read window data S 1  of high level, which corresponds to only the timing of the TCH data, i.e., the voice data portion in the reception data S 2 , is output to the AND gate  12  together with the reception data S 2  passing through the shift register  4 . 
     The voice output data S 11  shown in FIG. 4F is sent from the AND gate  12  to a DSP (not shown) for processing speech communication voice data as serial data. The timing at which the TCH data read window data Si of high level is output from the TCH data read window generation circuit  13  in correspondence with TCH data is calculated on the basis of the bit shift data S 8  representing a shift from the prescribed timing of the preceding output, which is output from the synchronous detection circuit  5  at a timing shown in FIG.  4 C. 
     To cope with the generated bit shift, the shift register  3  sends the TCH data read window data S 6  having a phase shift of several bits forward or backward, as shown in FIG. 4E, to the selector  9  in units of bits on the basis of reception at the prescribed timing. The synchronous detection circuit  5  compares, in units of slots, the reception timing of the synchronization code word in the reception data S 2  shown in FIG. 4A with the free-running pulse internally generated at a prescribed timing because the synchronization code word in the next slot is received after 20 mS from the reception timing of the synchronization code word in the preceding reception data S 2 , as defined in RCR-27D, and outputs the bit shift data S 8  representing the phase shift of this timing. Since the reception data S 2  is synchronized with the reception clock, the timing is phase-shifted in units of bits of the reception data S 2 . The TCH data read window generation circuit  13  generates the TCH data read window data S 1  at a free-running timing allowing reception of the synchronization code word in the next slot after 20 mS from reception of the synchronization code word in the preceding slot. The selector  9  selects the TCH data read window data S 1  and outputs the TCH data read window data S 10  phase-matching the TCH data in the reception data S 2  on the basis of the bit shift data S 8  representing the position and the number of bits shifted from the prescribed timing, which is output from the synchronous detection circuit  5  after reception of the synchronization code word in the slot. 
     The TCH data read window data S 10  phase-matching the TCH data in the reception data S 2  and the reception data S 7  from the shift register  4  shown in FIG. 2D, which is delayed until synchronization establishment, are input to the AND gate  12 . These data are ANDed, and the voice output data S 11  containing only a normal TCH data portion is output. 
     FIG. 5 is a block diagram showing the arrangement of another embodiment of the present invention. The TDMA voice information reading apparatus of this embodiment in FIG. 5 has a TCH data read window generation circuit  13  for generating TCH data read window data Si at a free-running timing allowing reception of the synchronization code word in the next slot after 20 mS from reception of the synchronization code word in the preceding slot. 
     The TDMA voice information reading apparatus also has a shift register  16  serving as a FIFO buffer operated by a reception clock signal CLK. The shift register  16  outputs TCH data read window data S 19  by delaying the TCH data read window data S 1  in units of bits. The apparatus also has a shift register  17  serving as a FIFO buffer operated by the reception clock signal CLK. The shift register  7  outputs reception data S 18  by storing and delaying reception data S 2  in units of bits. 
     The TDMA voice information reading apparatus also has a synchronous detection circuit  5  which compares, in units of slots, the reception timing of the synchronization code word in the reception data S 2  with the free-running pulse internally generated at a prescribed timing and outputs bit shift data S 8  representing the phase shift of the timing corresponding to the reception data S 2  shifted in units of bits. 
     The TDMA voice information reading apparatus also has a selector  15  which selects the reception data S 18  from the shift register  17 , which is delayed by the shift register  17 , on the basis of the bit shift data S 8  representing the direction and the number of bits shifted from the prescribed timing, which is output from the synchronous detection circuit  5  after reception of the synchronization code word in the slot, and outputs the reception data (S 2 ). 
     The TDMA voice information reading apparatus also has an AND gate  12  for sending, to a DSP for processing speech communication voice data, voice output data S 11  containing only a normal TCH data portion obtained by ANDing the TCH data read window data S 19  phase-matching the TCH data in the reception data S 2  and the reception data (S 2 ) from the shift register  17 , which is delayed until establishment of synchronization, and a clock signal generation circuit  14  for sending the reception clock signal CLK generated from the reception data S 2  to various portions. 
     The operation of this embodiment will be described next. 
     The reception data S 2  is stored in the shift register  17  in units of bits. The delayed reception data S 18  is output to the selector  15 . The selector  15  selects the reception data S 18  delayed by the shift register  17 , on the basis of the bit shift data S 8  representing a shift from the prescribed timing, which is output from the synchronous detection circuit  5  after reception of the synchronization code word, and outputs the reception data S 18  to one input terminal of the AND gate  12 . The TCH data read window data S 1  generated by the TCH data read window generation circuit  13  is input to the shift register  16  in units of bits. 
     The shift register  16  stores the TCH data read window data S 1  from the TCH data read window generation circuit  13  in units of bits. The TCH data read window data S 19  delayed and read out is output to the other input terminal of the AND gate  12 . The AND gate  12  outputs, to a DSP (not shown), the voice output data S 11  containing only a normal voice data portion obtained by ANDing the TCH data read window data S 19  from the shift register  16  and the reception data (S 2 ) selected from the delayed reception data S 18  by the selector  15 . 
     The principle and two embodiments of the present invention described above can be suitably applied to a movable terminal in a digital mobile telephone system.