JP2001177438A - Initial synchronization acquisition circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an initial synchronization acquisition circuit that can realize high-speed initial synchronization acquisition almost without increasing the scale of hardware. SOLUTION: A shift register 11 shifts a reception spread code 101. A local spread code generating circuit 14 generates a local spread code. A register 13 latches the local spread code generated from the local spread code generating circuit 14. An exclusive NOR circuit 12 detects whether or not the received spread code shifted by the shift register 11 is coincident with the local spread code latched by the register 13. A full adder circuit 15 calculates number of coincident codes detected by the exclusive NOR circuit 12. Changing a sampling frequency used for analog/digital conversion, number of stages of the shift registers 11 and an operating frequency S into a multiple of n (n is a positive integer being 2 or over), outputs of the shift register 11 are extracted at an interval of (n-1) and number of coincidence between the extracted outputs and the outputs of the register is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an initial synchronization acquisition circuit, and more particularly to acquisition of initial synchronization for performing despreading of a spectrum in a communication system using a spread spectrum communication system [in particular, a direct sequence system (Direct Sequence system)]. And a circuit that performs

[0002]

2. Description of the Related Art Conventionally, in a spread spectrum communication system, in particular, a direct spread system, an A / D (analog / digital) conversion is performed on a received spread signal received by a receiver on the receiving side, and the A / D conversion is performed. Despreading of the spectrum is performed using a spreading code (hereinafter referred to as a reception spreading code) and a copy of the spreading code used for performing the spectrum spreading on the transmission side.

In order to perform despreading, it is necessary to first acquire initial synchronization. This acquisition is performed by using a received spreading code and a spreading code obtained by a spreading code generation circuit provided on the receiving side (hereinafter referred to as a local spreading code). This is performed by taking a cross-correlation with the above and detecting a synchronization position based on the correlation.

Although the cross-correlation is obtained in the initial synchronization for the above-mentioned reason, when the received spread code is A / D-converted at the same sampling frequency as the frequency of the local spread code, the A / D conversion is performed every time the maximum value is obtained. Since the D conversion cannot be performed, a loss may occur.

[0005] Usually, in order to reduce this loss, A / D conversion is performed at a sampling frequency twice or more the frequency of the local spreading code. However, when a spreading code having a spreading factor of several thousand times is used, a correlator (which is constituted by a shift register or the like) used to obtain this cross-correlation by increasing the sampling frequency to reduce loss. Hardware size) will increase fatally.

This can be avoided by repeatedly using a correlator operating at the same sampling frequency as the conventional local spreading code several times, but in this case, the processing time, that is, the initial synchronization acquisition time is increased. This is a problem in communication, especially in burst communication requiring high speed.

[0007]

In the above-described conventional direct spreading method, when the sampling frequency is increased in order to reduce the loss in capturing the initial synchronization, the cross-correlation is performed by repeatedly using the conventional correlator several times. Has taken. However, this has a problem that the acquisition time of the initial synchronization is increased in burst communication requiring high speed.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an initial synchronization acquisition circuit capable of realizing a high-speed initial synchronization acquisition without substantially increasing the hardware scale.

[0009]

According to the present invention, there is provided an initial synchronization acquisition circuit which is used in a spread spectrum communication system and takes a cross-correlation between a spread code as a periodic code and a local spread code for one cycle, An integration circuit that integrates a correlation value output from the correlation circuit, and an initial synchronization acquisition circuit that performs synchronization acquisition from the correlation of all correlation values obtained by the integration circuit, provided in the correlation circuit and having a high speed. A means for enabling initial synchronization acquisition; and a control means for performing timing control on the correlation circuit and the integrating circuit.

That is, the initial synchronization acquisition circuit of the present invention comprises:
Means for cross-correlating the received spreading code and the local spreading code received by the receiver (hereinafter referred to as a correlator)
Means for integrating the correlation value obtained from the correlator,
It has means for controlling the timing of the correlator and the integrating circuit, and a memory for storing the correlation value.

With the above configuration, when the number of stages of the conventional shift register and that of the register are the same,
While the shift register can be shifted only in units of one chip, the shift register can be shifted in units of half a chip, and the calculation time of the total cross-correlation output can be reduced.

Regarding the hardware scale, the initial synchronization acquisition time can be shortened only by expanding the shift register without changing the scale of the local spreading code generating circuit and the register holding the local spreading code. Therefore, high-speed initial synchronization acquisition can be realized without increasing the hardware scale.

[0013]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an initial synchronization acquisition circuit according to one embodiment of the present invention. Referring to FIG. 1, an initial synchronization acquisition circuit according to one embodiment of the present invention includes an A / D converter 1, a correlator 2, a control circuit 3, an integration circuit 4, and a correlation value storage memory 5. I have.

The A / D converter 1 performs A / D conversion on the spread signal 100 to perform despreading of the spectrum of the spread signal 100 received by a receiver (not shown). The correlator 2 calculates the cross-correlation between the received spread code (received input) 101 obtained by A / D conversion and the local spread code.

The integrating circuit 4 integrates the correlation values obtained from the correlator 2. The control circuit 3 performs timing control on the correlator 2 and the integrating circuit 4. The correlation value storage memory 5 stores the correlation value integrated by the integration circuit 4.

FIG. 2 is a block diagram showing a detailed configuration of the correlator 2 of FIG. In FIG. 2, the coarse phase shifter 2 includes a shift register 11, an exclusive NOR (ExNOR) circuit 12, a register 13, a local spreading code generation circuit 14, and a full addition circuit 15.

The shift register 11 has a reception spread code 101
Shift. The local spreading code generation circuit 14 generates a local spreading code. The register 13 holds the local spreading code generated by the local spreading code generating circuit 14. The exclusive NOR circuit 12 is a shift register 1
A match between the received spread code shifted by 1 and the local spread code held in the register 13 is detected. The full adder 15 calculates the number of matches detected by the exclusive NOR circuit 12.

The operation of the initial synchronization acquisition circuit according to one embodiment of the present invention will be described with reference to FIGS. What is important in the operation of the initial synchronization acquisition circuit according to the embodiment of the present invention is the correlator 2 for calculating the cross-correlation. Here, the correlator 2 will be specifically described with reference to FIG.

Generally, a spread code used in a spread spectrum communication system is a periodic code, and synchronization is acquired by obtaining a correlation of all correlation values obtained by taking a cross-correlation between a local spread code and a received spread code for one period. Is detected from.

In FIG. 2, the cross-correlation output at a certain time is represented by the output of a register 13 holding the local spread code output from the local spread code generation circuit 14 and the reception input 10.
It can be obtained by calculating the number of matches with the output of the shift register 11 that shifts one, giving the total correlation value,
That is, the correlation value for one cycle can be obtained by shifting the reception input 101 by one cycle.

Conventionally, the shift register 11
And the register 13 have the same number of stages and operate at the same clock frequency. Therefore, one chip (a chip is
It can be shifted only in units of a basic pulse in a spreading code), and in order to increase the sampling frequency and reduce the loss due to A / D conversion, the correlator 2 is repeatedly used several times to obtain a correlation output. Or the same correlator 2 must be prepared several times to obtain a correlation output.

In the former case, the initial synchronization acquisition time increases, and in the latter case, the initial synchronization acquisition time does not change.
A problem arises in that the circuit becomes larger in proportion to the increase of the sampling frequency.

In the present invention, the number of stages of the shift register 11 for shifting the reception input is set to n times (n
Is a positive integer of 2 or more), and the sampling frequency used for A / D conversion and the operating frequency S of the shift register 11 are set to n times the frequency of the local spreading code.
The output of 1 is taken every (n-1) and the number of matches between this output and the output of register 13 is calculated. In FIG. 2, since the number of stages of the shift register 11 is twice as large as that of the register 13, the output of the shift register 11 is taken every other one (in the case of three times, every two outputs).

In FIG. 2, since the number of stages of the shift register 11 is twice the number of stages of the register 13, the same correlation output as that obtained by shifting by half when the number of stages of the shift register is the same,
That is, it is possible to obtain a correlation output equivalent to the case where the half chip phase is shifted.

Further, since the operating frequency of the shift register 11 is also twice, shifting the shift register 11 twice makes it possible to obtain two resolutions per chip (two half-chips, two resolutions).
(Corresponding to the number of times), and the calculation time of the total cross-correlation is doubled.

As described above, in the initial synchronization acquisition circuit according to the embodiment of the present invention, when the number of stages of the conventional shift register 11 and the conventional register 13 is the same, the shift register 1
While 1 could only be shifted in units of one chip, it can be shifted in units of half a chip (or 1/3 chip if the number of stages is three times), and the calculation time of the total cross-correlation output is also reduced. be able to.

Regarding the hardware scale, the initial synchronization acquisition time can be shortened only by expanding the shift register 11 without changing the scale of the local spreading code generating circuit 14 and the register 13 holding the local spreading code. can do. Therefore, high-speed initial synchronization acquisition can be realized without increasing the hardware scale.

[0028]

As described above, according to the present invention, a correlation circuit for taking one cycle of a cross-correlation between a spread code which is a periodic code and a local spread code used in a spread spectrum communication system, and a correlation circuit An integration circuit that integrates the output correlation values, and an initial synchronization acquisition circuit that performs synchronization acquisition from the correlation of all correlation values obtained by the integration circuit.
By providing means for enabling high-speed initial synchronization acquisition in the correlation circuit and performing timing control on the correlation circuit and integration circuit, high-speed initial synchronization acquisition can be realized with almost no increase in hardware scale. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an initial synchronization acquisition circuit according to one embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of the correlator of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D converter 2 Correlator 3 Control circuit 4 Accumulation circuit 5 Correlation value storage memory 11 Shift register 12 Exclusive NOR circuit 13 Register 14 Local spreading code generation circuit 15 Full addition circuit

Claims (6)

[Claims] 1. A correlation circuit which is used in a spread spectrum communication system and takes a cross-correlation between a spread code which is a periodic code and a local spread code for one cycle, and an integrating circuit which integrates a correlation value output from the correlation circuit. An initial synchronization acquisition circuit that performs synchronization acquisition from the correlation of all correlation values obtained by the integration circuit, a means provided in the correlation circuit and enabling high-speed initial synchronization acquisition, and the correlation circuit And a control unit for performing timing control on the integration circuit and the integration circuit. 2. A correlation circuit comprising: a shift register for shifting the spreading code; and a local spreading code generating circuit for generating the local spreading code. A register for holding a local spreading code generated by the local spreading code generating circuit; a detecting means for detecting a match between the spread code shifted by the shift register and the local spreading code held in the register; And a means for enabling high-speed initial synchronization acquisition, wherein the number of stages of the shift register is n times the number of stages of the register (where n is 2).
2. The initial synchronization acquisition circuit according to claim 1, wherein the first synchronization acquisition circuit is realized by setting the above positive integer). 3. A means for realizing the high-speed initial synchronization acquisition by setting the operating frequency of the shift register to n times the frequency of the local spreading code. Initial synchronization acquisition circuit as described. 4. An analog / digital conversion circuit for analog / digital converting the spread code and outputting the spread code to the shift register, wherein the sampling frequency used for the analog / digital conversion is set to n times the frequency of the local spread code. 4. An initial synchronization acquisition circuit according to claim 2, wherein means for enabling said high-speed initial acquisition is realized. 5. The output of the shift register is (n-1)
5. The initial synchronization acquisition circuit according to claim 2, wherein an output is provided to the detection means every other time. 6. The spread spectrum communication system according to claim 1, wherein the spread spectrum communication system is a direct spread system.
The initial synchronization acquisition circuit according to any one of the above.