JPS60213145A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To increase the change of detection of correlation on the receiving side and to shorten a synchronization confirmation time by applying redundancy to a false noise code of the longest code string at a degree preventing the randam property of a transmission side from damage. CONSTITUTION:On the transmission side, a false noise code generating circuit 3 forms a false noise code in the longest code string and a code string 30 obtained by shifting the former code by 1/2 at its phase and an exclusive OR23 switches said codes successively in each code period to form a code string 31 having the period of twice the original code period and transmit data as a spread spectrum wave SS on the basis of the code string 31. On the receiving side, the same false noise code 32 as that of the transmission side and a code string 23 phase-shifted by 1/2 the code period are inputted to two delay circuits 28, i.e. 1/2-bit and 1-bit delay circuits, and two code strings each of which consists of three kinds of codes are outputted from the circuits 28, properly selected by a switch circuit 29 and sent to three correlators 7-9. A synchronization detecting circuit 26 detects respective correlator output signals and also controls a clock signal control circuit 19 and a code string switching circuit 29 on the basis of output signals from pattern detectors 21, 25 outputting certain patterns in each code string period of a false noise code generating circuit 20.

Description

[Detailed Description of the Invention] The technical field to which the invention pertains is that the synchronization detection probability is high at the initial stage and at the time of recapture.
The present invention also relates to a spread spectrum communication system that requires shortening of synchronization establishment time.

Description of the Prior Art In a spread spectrum communication system, when a modulated wave whose spectrum is spread by a pseudo-noise code on the transmitter side is despread demodulated using a pseudo-noise code on the receiver side, is it necessary to accurately code-synchronize both the transmitting and receiving codes? It is desirable to ensure synchronization detection and shorten synchronization establishment time.

Conventionally, on the transmitting side, as shown in FIG. 1(a), a clock signal from a p-c oscillator 2 is supplied to a pseudo-noise code generation circuit 3 composed of a multi-stage shift register and an exclusive OR circuit. The generated pseudo-noise code and the information signal DATA
The clock signal is combined with the signal reclocked by the flip-flop circuit 1 using exclusive OR 4, and the output signal of the carrier wave oscillator 6 is modulated by the modulator 5 with this combined signal to generate a spread spectrum wave SS. Send.

On the receiving side, as shown in FIG.
A pseudo noise code generation circuit 20 having the same structure as the transmitting side
supplied to the After the generated pseudo-noise code is phase-shifted by the % bit and 1-bit delay circuit 13,
These three types of code sequences are spread spectrum received waves 8
S is despread by three correlators 7 to -9, and correlation is detected by a narrow band pass filter 10-12. The correlation detection output of 3al is used in the synchronization detection circuit 14 to determine synchronization detection, and together with the output of the pattern detector 21 which detects a constant pattern every code sequence period, the phase of the code sequence is periodically changed until synchronization occurs. The clock signal control circuit 19 is controlled to cause the clock signal to slip by a very small amount. If synchronization is detected, the search process is stopped and the correlation discriminator 16 is used to maintain synchronization.
, a loop filter 17 and a voltage controlled oscillator 18 to operate a delay locked loop. The output of the narrow band pass filter IO is demodulated by the baseband demodulator 15, and the received information signal DATA is regenerated. In order to reduce the probability, the search speed is slowed9, and in the synchronization detection circuit 14, the detection threshold level is set high to avoid false detection due to cross-correlation with other types of code sequences. If the code period is particularly long, there is a drawback that it takes a long time to establish synchronization.

Purpose of the Invention This invention 8A was made based on the above consideration, and therefore, the purpose of the present invention is to provide a new spread spectrum communication system that can increase the synchronization detection probability and shorten the synchronization time. I am going to do something.

Structure of the Invention In order to achieve the above object, the spread spectrum communication system according to the present invention spread-modulates a carrier wave with an information signal and a pseudo-noise code and transmits the signal, and the receiving side uses a code having the same structure as the transmitting side. In a spread spectrum communication system that despreads and demodulates a received wave to reproduce an information signal, the transmitting side switches between a pseudo-noise code having the longest code sequence and a code sequence obtained by optimally shifting the phase of the pseudo-noise code at each code period. The device includes means for generating a third code sequence, and means for providing a plurality of pattern detectors on the receiving side corresponding to the phase-shifted code sequence on the transmitting side, and detects correlation in a search process by phase shift control. The present invention is characterized in that the synchronization establishment time is shortened based on the signal and information from the pattern detector.

3. Detailed Description of the Invention Next, a preferred embodiment of the present invention will be specifically described with reference to the drawings.

Fig. 2 (a), (b) Vi is a block configuration diagram showing an embodiment of the present invention, and shows the case of a new code sequence in which a pseudo-noise code is combined with a code whose phase is shifted by % of the code period. ing. The operating principle will be explained in detail below.

On the transmitting side of FIG. 2(a), reference number 22 indicates a pattern detector, 23 exclusive ORs, 24 indicates a code sequence switching circuit, and the same reference numbers as in FIG. 1(a) indicate the first The same elements as in Figure (a) are shown. Here, the clock signal from the clock oscillator 2 is input to a pseudo-noise code generation circuit 3, which generates a pseudo-noise code.

Generally, the longest code sequence with excellent autocorrelation is adopted as the pseudo-noise code, but if the code in this case is the longest sequence, two or more appropriate multi-stage shift registers constituting the pseudo-noise code generation circuit 3 are used. By taking the exclusive OR 23 of the output stage of 0, a second code sequence 31 having a phase shift of approximately A in the code period from the first code sequence 30 is obtained. is sequentially switched for each code period by a code sequence switching circuit 24 according to the output signal of a pattern detection circuit 22 that detects a certain pattern in the original code sequence. However, in view of the balance of the code sequence, it is better to have the polarity of the inner code sequence reversed. The new code sequence obtained in this way is a code sequence 31 that is inverted by shifting the code period by about % following the code sequence 30 generated by the pseudo-noise code generation circuit 3, and the code period is the same as the original code sequence. It is twice the sign. The information signal DATA is re-clocked by the above-mentioned clock signal in a flip-flop 1 circuit 1, and then synthesized with the new code sequence by an exclusive OR 4.The output signal of the n1 carrier wave oscillator 6 is modulated by a modulator 5 to generate a spectrum. It is transmitted as a spread wave SS.

2), reference numbers 21 and 25 are pattern detectors, 26 is a synchronization detection circuit, 27 is an exclusive OR, 28 is a % bit and 1 bit delay circuit, and 29 is a code sequence switching circuit. 1v! Shows the same elements as J(b).

On the receiving side, the clock output signal of the voltage controlled oscillator 18 is supplied through a clock signal control circuit 19 to a pseudo-noise code generator [20] having the same structure as the transmitting side.

The generated pseudo-noise code 32 and the code sequence 33I' whose phase is shifted by about % of the code period obtained in the same way as on the transmitting side.
i is connected via an exclusive OR 27 to two sets of % bit and 1 bit delay circuits 28, respectively. The code sequences of each of the two sets of three woodcutters delayed by the delay circuit 28 are transferred to the code sequence switching circuit 2.
9, the selection is made at the appropriate time to create three new code sequences, each of which corresponds to three correlators 7 to 9, receives one spread spectrum wave SS and despreads it one time, and passes through the narrow band pass filters lO to 1.
Correlation is detected in step 2. The synchronization detection circuit 26 performs 2-modulo-hull [8 detection] on each correlation detection output signal, and performs pattern detection to detect a pattern corresponding to the code sequence 32 for each code sequence period of the pseudo-noise code generation circuit 2o. vessel 21 and h
The clock signal control circuit 19 is activated by the output signal of the pattern detector 25 corresponding to the code sequence 33 whose periodic phase has been shifted.
and controls the code sequence switching circuit 29.

The synchronization establishment process will be explained below. Synchronization detection circuit 2
No. 6 detects three sets of correlation detection signals by threshold judgment, and the judgment thresholds of the second and third correlation detectors No. 11 are set as shown in Fig. 3 with respect to the search direction. do. In the case of initial and recapture, the synchronization detection circuit 26 sends the code sequence feather to the correlator corresponding to the first phase detector in the code sequence switching circuit 29, and sends the code sequence feather to the correlator corresponding to the second and third correlation detectors. Selective control is performed to connect the code sequence 32 and a new code sequence obtained by switching between the code sequence 32 and the code sequence O whose phase has been shifted by h periods. At the same time, the synchronization detection circuit 26 controls the phase shift of the code sequence generated in the clock signal control circuit 19 by using means such as changing the phase of the clock signal.

The search process continues until the synchronization detection circuit 26 detects the correlation, and when the first correlation detector detects the signal, the output signal of the pattern detector 21 or 25 at that time is checked and the code sequence is switched according to the result. The circuit 29 is selectively controlled to synchronize and stop the search process. Once synchronization is established,
Correlation discriminator 16 in the delay-locked loop to maintain synchronization
The loop filter 17 controls the phase of the clock signal of the voltage controlled oscillator 18, and the information signal DATA is output from the output of the narrow band pass filter 10 through the baseband demodulator 15.
The system according to the present invention adds redundancy to the pseudo-noise code of the longest code sequence to the extent that it does not destroy randomness on the transmitting side, and increases the chance of correlation detection on the receiving side to establish synchronization. FIG. 4 shows a comparison of the autocorrelation between the conventional method and the method according to the present invention, which shortens the time. FIG. 4(a) U The autocorrelation (longest code sequence) of the conventional method, Φ) is the autocorrelation of the method according to the present invention.

Effects of the Invention Based on the above, the present invention provides a method for optimally combining pseudo-noise code sequences into a code sequence in a spread spectrum communication system that requires high probability and high-speed synchronization establishment in initial and recapture cases. By providing redundancy, the synchronization establishment time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing the conventional spectrum spreading power equation, and (a) F! The transmitting side, Φ) indicates the receiving side, FIG. 2 is a system diagram showing the principle of this invention, (a) shows the transmitting side,
Φ) indicates the receiving side, FIG. 3 shows the correlation detection judgment threshold of the synchronization detection circuit, and FIG. 4 shows the autocorrelation characteristics in the conventional system and the system of the present invention. 1...Flip-flop circuit, 2...Clock signal oscillator, 3...Transmitting side pseudo noise code generation circuit, 4.2
7... Exclusive OR, 5... Modulator, 6... Carrier wave oscillator, 7-9... Correlator, 10-12... Narrow band pass filter, 13.28... @# and 1-bit delay circuit, 14.26...Φ synchronization detection circuit, 15.Fist/baseband demodulator, 16@...correlation discriminator, 17...loop filter, 18...voltage controlled oscillator, 19@・・・
Clock signal control circuit, 20...Receiving side pseudo-noise code generation circuit, 21° 22.25, pattern detector, 2
4.29... Code series switching circuit patent applicant NEC Corporation Agent Patent attorney Yutabe Kumagai 1 4 5 Figure 1 (0) Figure 1 (b) Figure 2 (0) Figure 2 (b) Dimensions and directions Fig. 3 (0)

Claims (1)

[Claims] In the spread spectrum communication method, a carrier wave is spread-modulated with an information signal and a pseudo-noise code and transmitted, and the receiving side despreads and demodulates the received wave using a code with the same structure as the transmitting side to reproduce the information signal. means for generating a third code sequence by switching, at each code period, a code sequence obtained by optimally shifting the phase of the pseudo-noise code of the longest code sequence and the cough pseudo-noise code on the receiving side; and a means for providing a plurality of pattern detectors corresponding to the code sequences, the synchronization establishment time being shortened based on the correlation detection signal and the information of the pattern detector in excessive search by one phase shift control. Spread spectrum communication method.