JPH10313289A - Spread spectrum code timing synchronization device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a frequency division ratio of a frequency divider means in response to a correlation value between a local spread code and a spread code of a received spectrum signal. SOLUTION: An input spread spectrum signal is converted into a base band spread spectrum signal by a local carrier from a generator 13, for example, a local carrier of 322.5 MHz is frequency-divided into, e.g. 1/32 or 1/32.5 at a variable frequency divider 31 and a spread code generating section 21 is operated by a frequency division output. When a matched filter 19 detects a code, the generating section 21 starts its operation and the spread spectrum signal is inversely spread by an inverse spread section 22 based on the local spread code and a control section 32 selects a frequency division ratio when the absolute value of the correlation value is more than a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention synchronizes a local spread code for despreading with a spread code of a spread spectrum signal (hereinafter, referred to as a carrier spread spectrum signal) carried on a carrier wave such as radio waves and light. The present invention relates to an apparatus for maintaining timing.

[0002]

2. Description of the Related Art FIG. 2A shows a conventional apparatus. Input terminal 1
The carrier spread signal from 1 is multiplied by the local carrier signal from the carrier generator 13 in the multiplier 12 and quasi-synchronous detection is performed to obtain a baseband spread signal.
The local carrier signal is frequency-divided by the frequency divider 14, the frequency of the frequency-divided output is compared with the reference signal from the reference oscillator 15 by the comparator 16, and the comparison output is transmitted to the carrier generator 13 through the loop filter 17. The carrier frequency of the local carrier signal is stably maintained by the phase locked loop.

The baseband spread spectrum signal from the multiplier 12 is converted to a digital signal by an AD converter 18,
This digital baseband spread spectrum signal is input to the matched filter 19 and when it matches the spread code,
The spreading code generator 21 is activated by the output pulse,
The digital baseband spread spectrum signal is despread by the despreading unit by the local spreading code from the spreading code generation unit 21. This despread output is output as reproduced data, and the cross-correlation value in the despread output is separately processed by a low-pass filter 23. The output controls the voltage controlled oscillator 24, and the output of the voltage controlled oscillator 24 is output. It is supplied to the spreading code generator 21 as an operation clock signal.
When this clock signal deviates from the timing of the input baseband spread spectrum signal, the output of the filter 23 increases or decreases in accordance with the direction and magnitude of the deviation, and the frequency of the voltage controlled oscillator 24 is controlled. Is returned, and the synchronization state is maintained.

[0004] Alternatively, as shown in FIG.
When the local spreading code deviates from the timing of the input spreading code after the spreading code generator 21 starts operating by the pulse from the matched filter 19, the polarity corresponding to the deviation and the correlation value of the magnitude are changed. Appears from the despreading unit 22, which is detected by the control unit 27, and the spreading code generation unit 21 shifts the generation position by チ ッ プ chip cycle
The local spreading code is controlled so that its timing matches the input spreading code, that is, the timing difference is returned, and the synchronization state is maintained. Note that the sample period of the digital baseband spread spectrum signal is, for example, の of the chip period of the spread code, and the local spread code from the spread code generator 21 also outputs two data in one chip period. I do.

[0005]

In the prior art (VCO method) shown in FIG. 2A, a stable synchronization tracking can be obtained. It is difficult to properly adjust the balance of conditions such as the range, and it is particularly difficult to design when the input signal is a burst-like (intermittent) signal. The control of the voltage controlled oscillator 24 is an analog control, and has a difficulty in digitizing.

The conventional technique (step type) shown in FIG. 2B can be digitized relatively easily, but since the control step width (depending on the clock frequency used) cannot be made fine, the stability (quality) of the signal during tracking is low. ) Gets worse. In order to reduce the control step width in order to improve the signal quality, a high-speed clock generator 26 must be used or a special component such as a variable delay device must be used. Type features are lost.

[0007]

According to the present invention, a local carrier signal used to convert an input spread spectrum signal into a baseband spread spectrum signal is divided by a frequency dividing means, and the divided output is spread. It is supplied to the code generation means as an operation clock signal, and the frequency division ratio of the frequency division means is controlled in accordance with the despread output, that is, the correlation value between the local spread code and the spread code of the input spread spectrum signal.

[0008]

FIG. 1 shows an embodiment of the present invention by assigning the same reference numerals to parts corresponding to those in FIG. In this embodiment, the local carrier signal from the carrier generator 13 is branched and supplied to the variable frequency divider 31, and the divided output is supplied to the spread code generator 21 as an operation clock. Despreading unit 22
, That is, the correlation value between the local spreading code from the spreading code generator 21 and the baseband spread spectrum signal is input to the controller 32. When the absolute value of the input correlation value becomes larger than a predetermined value, the control unit 32 switches the frequency division ratio of the variable frequency division unit 31 according to the polarity of the correlation value.

As the variable frequency dividing section 31, for example, 1/32
A digitally switchable one of the frequency division ratios of 1 / 32.5 and 1 / 32.5 can use a commercially available one for generating a carrier signal. Assuming that the frequency of the operation clock signal of the spreading code generator 21 is 10 MHz, the frequency of the divided output clock signal is 9.923... MHz (1/3) if the frequency of the local carrier signal is 322.5 MHz.
2.5) and 10.078... MHz (1/32). The frequency accuracy of these divided outputs is 10 MHz,
When the control unit 32 determines that the phase shift of the local spreading code with respect to the spreading code of the input baseband spread spectrum signal exceeds 1% of one chip, for example, based on the input correlation value, the accuracy is as high as 1% or less. , So that the frequency division ratio of the variable frequency division unit 31 is switched.

[0010]

The frequency of the local carrier signal is adjusted by the reference
5. For example, the local carrier signal is held at a high accuracy stably with the accuracy of the crystal oscillator, and the spread code generator 21
The frequency of the set operation clock signal can be obtained, and the divided output that is extremely close to the high and low sides of the set operation clock signal with high accuracy can be obtained stably. When the phase difference between the spread signal and the spread code exceeds, for example, 1%, the frequency difference is switched to reduce the phase difference.
%, And by repeating such switching, the phase difference can be maintained at a small value over a long period of time, so that a high decoding quality can be obtained. Since the filter can be easily and easily configured, and the filter is not provided in the control system, the stability is very good even for burst waves. As a result, the synchronization is maintained by switching the frequency division ratio, and the tracking performance is good.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a functional configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a functional configuration of a conventional spread spectrum signal timing synchronizer.

Claims (1)

[Claims] 1. An input carrier spread spectrum signal is quasi-synchronously detected by a local carrier signal and converted into a baseband spread code signal. The baseband spread code is despread by a local spread code from a spread code generating means by a despreading means. In the apparatus for despreading and controlling the spread code generating means by the despread output to maintain the timing in which the local spread code is synchronized with the baseband spread spectrum code signal, the local carrier signal is frequency-divided. Frequency dividing means for supplying a frequency divided output as an operation clock signal of the spread code generating means; and control means for controlling the frequency division ratio of the frequency dividing means by switching according to the despread output. Spread spectrum code timing synchronizer.