JPS6412140B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for synchronizing received signals in a spread spectrum receiver.

Generally, in a spread spectrum receiver, in the process of demodulating a received signal, it is desired to establish synchronization of an internally generated local pseudo-noise signal with respect to the received signal at a high synchronization detection rate and in a short time. Conventionally, this type of synchronization circuit generates a local pseudo-noise signal, periodically slips the phase of this signal by a certain minute amount, and captures a received signal by correlation detection. Also,
Tracking circuitry is also added to maintain synchronization after synchronization is acquired.

In such a conventional example, as seen in FIG. Ru. The pseudo-noise code is generated by feeding back the final stage output of the n-stage shift register 15 and a specific inter-stage output to the first stage via the exclusive OR circuit 16. 1-bit adjacent outputs of n-stage shift register 15 and 1/2-bit shift register 1
1, three types of code sequences d, e, and f whose phase relationships are shifted by a fixed amount are obtained. These codes are obtained by despreading the spread spectrum received signal RXSS by three correlators 1 to 3, and detecting the correlation by envelope detectors 4 to 6. The detected three types of correlation outputs a, b, and c are used in the synchronization detection circuit 14 to determine synchronization detection, and the clock control circuit 13 is controlled to slip the phase of the local code until synchronization occurs. is detected,
Stop the search operation. After synchronization acquisition, the correlation detection outputs a and c are sent to the correlation discrimination circuit 8 and loop filter 9 of the delay lock loop in order to maintain synchronization.
is applied to the voltage controlled oscillator 10 through the oscillator, where the phase of the oscillation output is controlled. Further, the output of the correlator 1 is sent to the output side as a despread signal DESS via a bandpass filter 7 in order to demodulate the baseband of the information signal obtained by inverting the polarity of the pseudo-noise code. .

However, according to this method, the opportunity for synchronization detection is only once per period of the pseudo-noise code, and especially when the code period is long, detection errors may occur during the process of searching by phase shifting all codes. The problem was that it took a long time to establish synchronization.

The purpose of this invention is to eliminate the above-mentioned conventional drawbacks,
An object of the present invention is to provide a synchronization method for a spread spectrum receiver that has a high probability of synchronization detection and can establish synchronization in a short time.

According to the present invention, in a receiver for a spread spectrum signal modulated by a pseudo-noise code of the longest linear sequence converted into information, a pseudo-noise code of the longest linear sequence and a code obtained by phase-shifting the pseudo-noise code of the longest linear sequence are combined. means for generating a plurality of code sequences that phase shift the original code sequence by a different amount by calculating the sum modulo , and means for selecting each code sequence obtained from the generating means. and making each output selected by the selection means correspond to a plurality of correlators provided for demodulating the information signal and delay lock loop, and detecting the correlation of the spread spectrum signals applied to these correlators. A synchronization method for a spread spectrum receiver is obtained.

Next, a synchronization method for a spread spectrum receiver according to the present invention will be described in detail by giving examples and referring to the drawings.

FIG. 2 is a block diagram showing the structure of an embodiment according to the present invention. In this figure, the clock signal from the voltage controlled oscillator 10 is clocked by the clock signal control circuit 1 of the local pseudo-noise code generation circuit 17.
8 and is supplied to the n-stage shift register 20. Generally, the longest code sequence with the maximum autocorrelation function is selected as a spread spectrum pseudo-noise code, but this is done by exclusive ORing the final stage output of the n-stage shift register 20 and a specific interstage output. It is obtained by returning to the first stage via. Additionally, the pseudo-noise code with the longest code sequence has the property that the exclusive OR of the phase-shifted code and the original code becomes a third code that is the original code phase-shifted by a different amount. , it can be set to generate a code whose phase is shifted by any desired amount. Therefore, by selecting specific outputs from the n-stage shift register 20 and obtaining outputs by exclusive ORs 22 and 23, the phases are shifted by about 1/3 from each other for one period of the pseudo-noise code. Three sets of code outputs are obtained. These outputs are then applied to a data selector 24 that includes a 1-bit shift register.

This data selector 24 is combined with the 1/2 bit shift register 11 to output each of the three sets of codes independently, or to select only one set of codes and output 1/2
Three bit phase-shifted codes d', e' and
Output f′. These codes are processed by three correlators 1~
3 despread the received signals RXSS, and envelope detectors 4 to 6 perform correlation detection. Correlation detection outputs a', b' and c' are synchronization detection circuit 1 with data selection function.
9 is used for determining synchronization detection. For initial acquisition and reacquisition, the three sets of codes d', e' and f' are 1/3
All codes are searched by periodically shifting the phase by a small amount. When correlation is detected by any one of the three codes, the synchronization detection circuit 19 supplies the detected correlation signal to the data selector 24 for the delay lock loop.
The data selector 24 is controlled to select the code corresponding to the signal. As a result of this control, when synchronization is detected, the clock control circuit 18 is controlled to stop the search operation and the synchronization state is maintained.

According to this embodiment, in the case of initial acquisition and reacquisition, the phase of the pseudo-noise code received at any time among the three divisions shifted by 1/3 period from each other is independently correlated with each other. Since it is useful for detection, the detection chances are tripled compared to the conventional method, and the search time for pseudo noise codes is reduced to one-third. However, since the correlation of pseudo-noise codes is narrow between two bits, the judgment timing for synchronization detection is performed by a 1/2-bit search to prevent a high probability of detection errors caused by the conventional 1-bit search.
Even so, overall, the probability of synchronization detection is higher than in the past, and the time required to establish synchronization is shortened. 3A and 3B are time charts showing a comparison of correlation detection by the conventional method shown in FIG. 1 and the embodiment shown in FIG. 2, respectively. As can be seen from this figure, in the conventional method, the timing of determination is a 1-bit search, and correlation is detected only at one point in one cycle, but in the method of the embodiment, the timing of determination is 1/2.
This is a bit shift search, and detection opportunities are obtained at three locations in one cycle. Furthermore, when compared for the same time T, it will be seen that in the method of the embodiment, the chances of correlation detection are twice as large as in the conventional method.

As is clear from the above description, according to the present invention, there are provided a plurality of code sequence generation means for phase-shifting the original code sequence by a different amount, and means for selecting each code sequence obtained from the means. By providing this, when receiving spread spectrum signals, it is possible to increase the correlation detection rate and greatly reduce the time required to establish synchronization, improving the performance and reliability of the spread spectrum receiver. The effects that can be achieved are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a configuration example of a conventional synchronization method in a spread spectrum receiver, FIG. 2 is a block diagram showing a configuration of an embodiment according to the present invention, and FIGS. 2 is a time chart for comparatively explaining the correlation detection operation in the conventional example and the embodiment of FIG. 2. In the figure, 1 to 3 are correlators, 4 to 6 are envelope detectors, 7 is a band pass filter, 8 is a correlation discrimination circuit, 9 is a loop filter, 10 is a voltage controlled oscillator, and 11 is a 1/2 bit shift register. ,12,1
7 is a local pseudo-noise code generation circuit; 13 and 18 are clock signal control circuits; 14 and 19 are synchronization detection circuits; 15 and 20 are n-stage shift registers;
1, 22, and 23 are exclusive OR circuits, and 24 is a data selector.

Claims (1)

[Claims] 1. In a receiver of a spread spectrum signal modulated by a pseudo-noise code of the longest linear sequence that has been converted into information, a sum modulo 2 of the pseudo-noise code of the longest linear sequence and a code obtained by phase-shifting the pseudo-noise code. means for generating a plurality of code sequences that phase shift the original code sequence by different amounts by taking Each output selected by the selection means is made to correspond to a plurality of correlators provided for demodulating information signals and delay lock loops, and the spread spectrum signals applied to these correlators are subjected to correlation detection. Synchronization method for spread spectrum receivers.