JPS6037663B2 - Synchronization method for demodulating wideband signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION One of the methods for performing good code transmission on a transmission line where interference exists is a code transmission method using a wideband signal.

A wideband signal is a signal having a bandwidth wider than the required bandwidth of the information to be transmitted, and is known as a binary or multivalued pseudorandom signal, a linear FM signal, a frequency pattern signal, etc. To demodulate these wideband signals, the same wideband signal as that on the transmitting side is generated as a local signal, and processing is performed to correlate this with the receiving input. In this case, the wideband signal used as the local signal must have a waveform whose timing matches the receiving input. The present invention relates to a synchronization method for demodulating such a wideband signal. In demodulating a wideband signal, if the timings of the local signal and the received wideband signal are not made to match, the level of the correlation output will decrease and the S/N of the correlation output will deteriorate. The process of adjusting this timing is synchronization. Furthermore, at the start of transmission, it is unclear where in one cycle of the wideband signal the difference in timing between the received input and the local signal is. The procedure for obtaining synchronization is divided into two: search mode and tracking mode. Among these, in search mode, the difference in timing between the local signal and the received input is approximately 1/2 chip length (a chip refers to each signal element of a wideband signal; for example, in Figure 3, there are 7 chips and 1 piece of information of length T). (This is an example in which the timing difference is within about 1/2 chip.) Taking advantage of the fact that the level of the correlation output is small unless it is within 1/2 chip, the level of the correlation output is used to determine whether the timing difference is within about 1/2 chip.
If there is a difference, change the timing of the local signal by half, for example.
Control is performed to shift the timing difference by an appropriate value, such as chip length to 1 chip length, to bring the timing difference within a range that allows synchronization in the tracking mode. Next, in the tracking mode, timing differences are detected more precisely, and a phase-locked loop or the like is used to control the timing differences to zero. Known methods include a delay lock loop and a dither loop. By the way, in the search mode, conventionally, the timing is shifted in one direction by a certain amount (for example, 1/2 to 1 times the chip length) and the judgment is repeated, so a relatively long synchronization acquisition time is required. Unable to demodulate.

Therefore, when performing half-duplex communication using press talk, there is a problem in that it is necessary to wait a certain period of time each time a press is made before starting to speak. Furthermore, since the chip speed of a wideband signal is often relatively fast, even if the signal is interrupted for a short time, a timing difference that exceeds the controllable range of the tracking mode is likely to occur. If the timing difference is such that it cannot be retracted in tracking mode, it will return to search mode, but
In a conventional shift in one direction, if the timing is shifted in the opposite direction to the shift direction, the same time as the initial retraction is required for retraction. These are major drawbacks. The present invention was made to eliminate the above-mentioned drawbacks, and it measures the time during which the signal is interrupted and limits the range of timing shift in search mode to the range of the maximum expected timing difference. This feature is characterized by shortening the re-drawing time and making bit misalignment less likely to occur, which will be explained in more detail below.

First, the principle of code transmission using wideband signals will be explained.

Figure 1 is an example of the circuit configuration of a modulator for a wideband signal, Figure 2 is an example of the circuit configuration of a demodulator, and Figure 3 is an example of a circuit configuration when a 7-bit binary pseudorandom code is used as the wideband signal. 1 and 2; FIG. In the modulator shown in Fig. 1, the pseudo-random signal b generated by the pseudo-random signal generator 4 based on the input from the clock generator 3 is output as is if the signal a of the input data 1 is a mark, or as a polarity if it is a space. The carrier input from the carrier oscillator 7 is then balanced modulated by the balanced modulator 6 using the output c of the sign inverting circuit 5 to obtain the transmission signal 2.

In the demodulator shown in FIG. 2, 8 is a received signal, 9 is demodulated data, 10 is a clock generator, 11 is a pseudorandom signal generator, 12 is a carrier oscillator, 13 is a balanced modulator, 14 is a synchronous detector, and 15 is a The phase determination circuit 16 is a synchronization determination circuit. The demodulator uses the same pseudo-random signal e(
=b is generated by the generator 11, and the carrier wave (the frequency is the same as that on the transmitting side) from the oscillation circuit 12 is balancedly modulated with this to create the local signal f. The reception input 8 is synchronously detected by the synchronous detector 14 using this local signal f, and the output g is sent to the phase determination circuit 15.
If the waveform or integration is performed at , the modulation component due to the pseudo-random signal is removed and a demodulated output 9 of information is obtained. In FIG. 2, the circuit for synchronizing the pseudo-random signals is simplified and only the synchronization determination circuit 16 is shown. Also, a circuit for carrier phase synchronization is omitted. FIG. 4 is a circuit configuration example diagram of a search mode portion of a synchronous circuit embodying the present invention, and FIG. 5 is a diagram showing an example waveform of each part in FIG. 4. In FIG. 4, reference numeral 17 is the output g of the synchronous detector 14 of FIG. 2, which is input to a level determination circuit 19) whose level is determined.
When the level is high, that is, when synchronization is achieved and the signal is being received, the determination output is sent to the shift control circuit 22 and the output to the timing shift circuit 24 is turned off.
In addition, when the level is determined to be low, such as when the input signal is interrupted, the time measurement counter 20 measures the time that the low state lasts, and a search width setting signal proportional to that time is sent from the code converter 21. Shift control circuit 2 in the form of parallel codes
Enter 2. The shift control circuit 22 generates timing control pulses corresponding to the search width, and transmits them to the clock oscillator 2.
Timing shift circuit 2 that receives the clock from 3 as input
Input to control 4. Reference numeral 18 is a drive clock j for the pseudo-random signal generator 11 in FIG.

As shown in j in FIG. 5, the waveform of the driving clock i is obtained by adding or deleting one to several pulses to a clock pulse of a constant period. By changing the number of erasing pulses and the interval, the timing of the pseudorandom code is shifted as shown in FIG. 5e. A in Figure 5e is 1
N represents a local signal with a timing that is one chip ahead, N represents a local signal with a normal timing, and D represents a local signal with a timing that is one chip behind. FIG. 5 shows an example in which a 7-bit binary pseudo-random code is used and the search is performed while shifting the code by one chip within the range of ±1 chip. Also, in this figure, 1 of the pseudorandom code
Although it is written that the timing is shifted every cycle, normally the timing is shifted every cycle of an appropriate number of clocks to reduce malfunctions caused by noise in the level determination circuit 19. If a signal is received again while the synchronization circuit is operating in such a search mode state, the input g of the level judgment circuit 19 becomes large when the timing of the local signal almost matches the received input. Then, the pull-in operation is performed by turning off the output to the timing shift circuit 24 and shifting to the tracking mode. As explained above, the effect of the present invention is that the time for re-synchronization after the reception input is interrupted is shortened, and in press talk communication, the waiting time after pressing is shortened, and errors due to fading etc. For example, the amount of time required for decoding can be shortened, and bit shifts in demodulated data are less likely to occur.

Further, in the above explanation, a binary pseudo-random signal is used as the wideband signal, but it is clear that the present invention can be applied to cases where other wideband signals are used.

[Brief explanation of the drawing]

Figure 1 is an example of the circuit configuration of a wideband signal modulator, Figure 2 is an example of the circuit configuration of a demodulator, Figure 3 is an example of waveforms for each part of Figures 1 and 2, and Figure 4 is the invention of the present invention. FIG. 5 is a diagram showing an example of the configuration of the search mode portion of the synchronous circuit in which the above is implemented, and FIG. 5 is a diagram showing an example of waveforms at each part in FIG. 1...Data input, 2...Transmission output, 3, 10, 23.
...Clock generator, 4, 11... Pseudo-random signal generator, 5... Sign inversion circuit, 6... Balanced modulator,
7, 12...Carrier oscillator, 8...Received signal input, 9...Demodulated data output, 13...Balanced modulator, 1
4... Synchronous detector, 15... Phase determination circuit, 16.
... Synchronization determination circuit, 17... Output of the synchronization detector 14,
18... Clock for driving the pseudorandom signal generator 11, 19... Level determination circuit, 20... Time measurement counter, 21... Code converter, 22... Shift control circuit, 24... Timing shift circuit. Juice l figure outside figure 2 figure spear 3 figure outside figure 4 figure soup 5 figure

Claims (1)

[Claims] 1. On the receiving and demodulating side of code transmission using a wideband signal, the input level of the received signal is determined, and the duration of the input determined to be below a certain level is measured every certain period, and The timing of the wideband signal used as the local signal for reception demodulation is changed within the time period of , the correlation with the reception input is taken, and the timing of the local signal at which the correlation output, that is, the reception signal input judgment level mentioned above, exceeds a certain value is detected. A synchronization method for demodulating a wideband signal, the method comprising: matching the timing of a local signal with a received input.