JPS6343025B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a clock synchronization system in a digital communication system that transmits burst signals and receives the burst signals at appropriate time intervals.

(Background Art) Time division multiple access (TDMA) is a typical communication system that uses burst-like digital modulation signals that are temporally divided and transmitted from a transmitting station at appropriate intervals. Time division multiple access (TDMA) where clocks are not phase synchronized between bursts
Conventionally, this method regenerated the clock for each burst. FIG. 1 shows a typical frame structure of this conventional method. 501 to 504 are bursts that are divided in time and transmitted. 51 to 55 indicate the contents of each burst, 51 is a guard time, 52 is a carrier recovery code, 53 is a clock recovery code, 54 is a synchronization word, and 55 is information to be communicated. This conventional method regenerates the clock for each burst, so
A clock reproduction code 53 is attached to the beginning of the burst, but in order to reproduce a clock with a small phase error, a code length that is somewhat long is required due to the circuit pull-in time. Therefore, the conventional system has the drawback of reduced transmission efficiency. In order to compensate for this drawback of reduced transmission efficiency, an invention disclosed in Japanese Patent Application Laid-Open No. 57-57054 (Synchronization Signal Generation Circuit) has been made in the past. Its contents include storing the clock frequency information and phase information of the previous burst signal, and using the clock frequency information and phase information of the previous burst signal as initial values when reproducing the clock of the next burst signal, thereby shortening the time required for clock reproduction. It is something to do.

In addition, in order to increase the transmission efficiency in the TDMA system, there is a conventional method of lengthening the frame period. In addition, there is a drawback that the signal transmission delay time increases due to writing/reading of burst signals into a buffer memory in order to convert them into a continuous signal train. These effects become more pronounced especially in TDMA systems with lower transmission speeds (low-speed TDMA systems). In general, in the case of the TDMA system, if the frame period is shortened in order to shorten the transmission delay time, the length of the information signal to be transmitted in one frame will be shortened. Since the length does not change, the preamble length occupies a relatively high proportion of the burst signal, and the transmission efficiency deteriorates. This rate of deterioration is greater in the low-speed TDMA method than in the high-speed TDMA method.

When considering communication serviceability first, reducing transmission delay time must be prioritized over increasing transmission efficiency, and low-speed TDMA
The burst signal length naturally becomes shorter as the method increases, and the preamble occupies a larger proportion of the burst. Considering such a low-speed TDMA system, the invention disclosed in Japanese Patent Application Laid-Open No. 57-57054 does not allow the clock regeneration circuit to start up sufficiently (that is, the clock regeneration circuit has a large thermal noise and has sufficiently low jitter. (cannot be reproduced), the burst signal will disappear before long, and there will be cases where a sufficiently clear clock cannot be reproduced from the previous burst signal alone. If an attempt is made to reproduce a sufficiently clear clock, the ratio of the clock reproduction code to the burst length becomes larger and larger, and the utilization efficiency of the transmission path, which is already poor, further deteriorates. As described above, the conventional methods have been insufficient to improve transmission efficiency even for the low-speed TDMA method.

(Problem to be solved by the invention) The present invention provides a synchronous relationship between the clock frequency and phase between bursts transmitted by the same station, and in order to demodulate an arbitrary burst signal transmitted by this station, the burst signal is The clock is characterized in that a clock recovered from one or more burst signals transmitted from the same station that precedes the signal is used as an identification clock for the burst signal, and the purpose is that even in the low-speed TDMA system, by using the above system. The purpose of this method is to eliminate the clock recovery code that was conventionally attached to the beginning of a burst to improve transmission efficiency.

(Structure and operation of the invention) FIG. 2 shows one or more burst signals transmitted from the same station preceding the burst signal when demodulating an arbitrary burst signal digitally modulated and transmitted from a certain station using the TDMA method. This is an embodiment in which a signal is identified using a clock reproduced from the signal.

1 is an input signal, 2 is a clock extraction circuit, 3 is a recovered clock, 4 is an identification circuit, 5 is a demodulated signal, 12
13 is a clock frequency information and phase information holding circuit; 13 is a clock frequency information and phase information; 8 is a timing control signal generation circuit; 9 is a readout control signal; 14 is an identification clock generation circuit;
5 is an identification clock, 10 is a reference timing, 11
is a control signal for holding, 16 is a control circuit,
17 is reception burst position information. The operation of this circuit will be explained below. First, as a transmission clock,
A stable transmitting clock is used in which the frequency difference and phase difference between the transmitting clocks between frames can be ignored. That is, between adjacent burst signals transmitted from the same transmitting station, the frequency and phase of the clocks are synchronized.

The clock extraction circuit 2 uses a tank limiter, a PLL circuit, etc. as in the above circuit, and extracts the clock from the input signal 1 and outputs it as a reproduced clock 3.

It is sufficient for this regenerated clock to have no phase error from the optimum phase in the latter half of the burst. 12 extracts the frequency information and phase information of the clock 3 extracted in 2 for each transmitting station by the control signal from the timing control signal generation circuit 8 in the latter half of the burst where the phase error of the clock 3 disappears, and The average of the information up to that point is taken, and this is held as the clock frequency information and phase information for that burst. Reference numeral 11 is a control signal for holding information in this case in 12. 8
is the position information 1 of the received burst from the control circuit 16
7 and the reference timing 10 for the TDMA signal received from the outside, and this timing 1.
0 and the reception burst position information 17, the reception timing of the burst signal sent from each transmitting station, that is, the reception timing synchronized with the beginning of the burst, is created, and the clock frequency and clock frequency for the burst received at this reception timing are determined. A control signal 9 for reading out the phase is given to 12. 1
The timing for issuing the control signal 1 is also created from the reference timing 10. 12 reads out the corresponding frequency information and phase information 13 according to the control signal 9 and supplies it to 14. Information 13 read from 12 is information obtained from signals up to the burst before the burst signal to be demodulated at this point. 14
uses this information 13 to generate an identification clock 15 for demodulating the received burst signal, uses this identification clock 15 to identify the burst signal by 4, and obtains demodulated data 5.

(Effects of the Invention) As described in detail above, in the present invention, the identification clock is a clock generated using averaged clock frequency information and phase information extracted from the reproduced clock up to the previous burst. Since this identification clock can be extracted from the data portion of each preceding burst, there is no need for a clock recovery code. Therefore, transmission efficiency can be improved.

[Brief explanation of the drawing]

Figure 1 is a typical frame configuration diagram of the conventional TDMA system in which the clock phase is not synchronized between bursts. Figure 2 is a demodulation of an arbitrary burst signal digitally modulated and transmitted from a certain station using the TDMA system. precedes the burst signal when
Furthermore, this is an embodiment in which signals are identified using clocks recovered from one or more preceding burst signals transmitted from the same transmitting station. 501 to 504... Burst transmitted in temporal divisions, 51... Guard time, 52... Carrier recovery code, 53... Clock recovery code, 54... Synchronization word, 55... Information to be communicated, 1... Input signal, 2
...Clock extraction circuit, 3. Regenerated clock, 4. Identification circuit, 5. Demodulation signal, 8. Control circuit, 9. Read control signal, 10. Reference timing, 11. Control signal for holding, 12. Frequency information and phase information holding circuit, 13... Clock frequency and phase information, 14... Identification clock generation circuit, 15... Identification clock, 16... Control circuit, 17... Reception burst position information.

Claims (1)

[Claims] 1. In a digital communication system in which a transmitting side transmits a temporally intermittent modulated burst signal and a receiving side receives the burst signal at appropriate time intervals, adjacent signals transmitted from the same transmitting station In order to demodulate an arbitrary burst signal by establishing a synchronization relationship in clock frequency and phase between the burst signals, one or more preceding burst signals that precede the burst signal and are transmitted from the same transmitting station are used. A clock synchronization method characterized in that a reproduced clock is used as an identification clock for the burst signal.