JPH05100007A - Diffusion symbol capturing circuit - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] A spread code acquisition circuit used for synchronously acquiring spread codes of GPS satellite radio waves, and shortening the time required for acquisition. Configuration: A shift register 20 outputs n spread code signals P1 to Pn delayed by one bit. These are sent to the detection unit 30, and the error such as the Doppler shift frequency of the spread code signal of the satellite and the satellite signal is removed by the exclusive logic of the spread code signal of the satellite, the signals NI, NQ from the numerical control oscillator 60, and the like. .. The remaining signal components are counted by the sampling clock CK and the correlation result is output. The controller determines the acquisition of the spread code of the satellite signal by searching for the largest one among them. If it cannot be captured, the control signal from the control unit 70 shifts the phase of the spread code signal PA to perform a search, and the search is repeated until it is captured. As described above, with the configuration in which the n detectors are used to perform the search at the same time, the spread code can be captured at high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread code capturing circuit for shortening the time required to capture radio waves from a plurality of GPS satellites.

[0002]

2. Description of the Related Art Using GPS satellites, the latitude of the observer,
There is a GPS receiver as a device for obtaining longitude and altitude. GP
The S receiver uses radio waves received from multiple GPS satellites,
It captures the spread code that is phase-modulating the carrier wave, performs tracking based on the capture, demodulates and decodes the navigation data, and calculates the receiving position of the observer. As described above, when the carrier wave is captured from the satellite signal, a means for predicting the carrier wave frequency of the satellite signal based on the orbit information peculiar to each satellite and performing the acquisition in a shorter time is adopted. Spread code is GP
It is a code unique to the S satellite and is a code string composed of 1023 chips. In order to capture the spread code of the GPS satellite, first, the same spread code as the spread code formed on the satellite signal is generated by the spread code generator of the GPS receiver. Then, the correlation process between the generated spread code and the spread code of the satellite signal is performed, and the phase search process that both spread codes temporally match and the correlation value becomes maximum, that is, the process of capturing the spread code is performed. It is being appreciated. This spread code acquisition is performed by performing correlation processing while shifting the phase of the spread code generated by the spread code generator by 1/2 chip at regular intervals with respect to the spread code of the satellite signal. It is repeated up to 2045 times until the value is obtained, that is, the spread code of the satellite signal is acquired.

[0003]

However, the above-mentioned conventional configuration has a problem that it takes a long time to capture the spread code of the satellite signal.

The present invention solves the above-mentioned problems of the prior art, and an object of the present invention is to provide a spread code acquisition circuit which can shorten the time required to acquire the spread code of a satellite signal and which can be simply constructed. And

[0005]

In order to achieve this object, the present invention converts the frequency of the radio wave from the GPS satellite into an intermediate frequency when capturing the spread code included in the radio wave from the GPS satellite. A digitizing circuit that outputs a digitized signal by sampling the binarized signal obtained by binarizing 1 to 1 bit, and a spreading circuit that generates the same spreading code as the spreading code included in the radio wave from the GPS satellite. A code generator, a shift register that simultaneously outputs n spread code signals obtained by phase-shifting the spread code signals generated by the spread code generator bit by bit, a signal transmitted at a specified frequency, and a 90-degree phase shift Of the output signals from the shift register and the spread code included in the satellite signal input via the digitizing circuit. Process performs a detecting unit to obtain a result signal from the output of the numerically controlled oscillator, is provided with a control unit for sending a capture control signal to enter capture control results from the detecting unit.

[0006]

According to the present invention, the correlation value between the spread code of the satellite signal and the spread code generated by the n number of detecting means for performing the parallel search in the search for capturing the spread code of the satellite signal. , The phase of the generated spreading code is shifted by n bits, and the correlation processing is performed to search for the maximum point of the correlation value. Here, 1 bit is a bit obtained in a clock cycle of 1-bit sampling, and n bits form one chip of a spread code. As a result, the time required to capture the spread code of the satellite signal can be shortened, and the circuit can be easily constructed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a spread code capturing circuit according to an embodiment of the present invention. In FIG. 1, 10 is G
A digitizing circuit that receives radio waves from the PS satellite via the antenna 6 and converts them into a digital signal, 50 is a spread code generator that generates the same spread code as the spread code of the satellite signal,
Reference numeral 20 is a shift register for shifting the spread code generated by the spread code generator 50 bit by bit and simultaneously outputting n spread codes each shifted by 1 bit, and 30 is a n detector 30-1 to 30. -N to detect the correlation between the spread code and the spread signal of the satellite signal, 40 is a control unit that feeds back the correlation result to the detection unit 30, and 60
Is a numerical control oscillator that outputs an in-phase signal of a specified frequency and its quadrature signal. 5 is a digitizing circuit 10,
A sampling clock generator that generates a timing clock for the shift register 20, the spread code generator 50, and the detection unit 30.

The operation of the spreading code acquisition circuit configured as described above will be described with reference to the time chart shown in FIG.

First, the spread code generator 50 generates a signal PD in which a spread code unique to a satellite signal is formed. Then, the spread code signal PD and the clock signal CK (FIG. 2A)
Are input to the shift register 20, and the spread code signal PD is sequentially shifted to the subsequent stage according to the timing of the clock signal CK. Therefore, in the shift register 20, the spread code signals P1 to Pn delayed by 1 bit are provided.
(FIG. 2C) is output. And the spread code signal P1
To Pn are output corresponding to the detectors 30-1 to 30-n, respectively. In the detector 30, each detector 30-1
.About.30-n are transmitted from the digitizing circuit 10 to the satellite spread code signal (FIG. 2B) and spread code signals P1 to P
Phase comparison is performed with n by exclusive OR, and the spread code component is removed. As a result, a frequency component of about the error between the Doppler shift frequency of the satellite signal and the internal clock frequency remains.

Then, an in-phase signal N from the numerical control oscillator 50 in which a frequency similar to the remaining frequency is designated.
I and the quadrature signal NQ (FIGS. 2 (d) and (e)) are phase-compared by exclusive OR of the remaining frequency components to output signals DI1 to DIn and DQ1 to DQn, and then the counter 31 1 to 31-n count the sampling clock CK and count the correlation code for one period, and then the correlation result is calculated as in-phase components I1 to In and quadrature component Q1.
~ Output as Qn. The counting is performed by a method that maximizes the correlation result when both phases match.

In the control unit 70, R1 = I1 + Q1 to Rn =
Calculate In + Qn. When the spread code included in the satellite signal and one of the spread code signals P1 to Pn output from the shift register 20 match in phase, the sum of the count values becomes maximum due to the property of the spread code. Therefore, conversely, the spreading code of the satellite signal can be captured by searching for the maximum value among the above-mentioned R1, R2, ... Rn.

If it is determined from the calculated R1 to Rn that none of the spread code signals P1 to Pn temporally matches the spread code included in the satellite signal, the spread code generator 50 outputs the same. The phase of the spread code signal PA is shifted by one chip (= n bits) of the spread code, and the spread code of the satellite signal is searched again in the same manner. At this time, the spread code selection, frequency and phase control, etc. are performed by a control signal from the control unit 70, and the control signal is output until the spread code of the satellite signal is captured.

As described above, according to this embodiment, the spread code can be captured at high speed by providing the structure for simultaneously searching the spread code included in the satellite signal by using the n detectors.

[0015]

As described above, according to the present invention, the spread code signal generated by the spread code generator is converted into n spread code signals which are phase-shifted bit by bit, and the phase-shifted n spread code signals are converted. By providing a shift register and n detectors that simultaneously output the signal, the spread code included in the satellite signal can be acquired in a short time, and an excellent spread code acquisition circuit can be realized with a simple circuit.

[Brief description of drawings]

FIG. 1 is a block connection diagram of a spread code capturing circuit according to an embodiment of the present invention.

FIG. 2 is a time chart of a main part of a spread code capturing circuit according to the same embodiment.

[Explanation of symbols]

 5 Sampling Clock Generator 6 Antenna 10 Digitizing Circuit 20 Shift Register 30 Detector 30-1 to 30-n Detector 50 Spreading Code Generator 60 Numerical Control Oscillator 70 Controller

Claims (1)

[Claims] 1. When a spread code included in a radio wave from a GPS satellite is captured, the frequency of the radio wave from the GPS satellite is converted into an intermediate frequency, and the binarized signal obtained by binarizing the frequency is converted into 1 bit. A digitizing circuit that outputs a digitized signal by sampling, a spreading code generator that generates the same spreading code as the spreading code included in the radio wave from the GPS satellite, and a spreading code generated by the spreading code generator. A shift register for simultaneously outputting n spread code signals in which signals are phase-shifted bit by bit, a numerical control oscillator for outputting a signal phase-shifted by 90 degrees with a signal transmitted at a specified frequency, and the shift register From the output of the numerical control oscillator, while performing the correlation processing between the respective output signals of and the spread code included in the satellite signal input through the digitizing circuit. A detecting unit to obtain a result signal, the spreading code acquisition circuit, characterized in that a control unit for sending a capture control signal to enter capture control results from the detecting unit.