CN103869341B - Catch method and the device of L2C signal in GPS - Google Patents

Abstract

The invention discloses a global positioning system L2C signal capture and device, S1, A/D sampling is performed on the intermediate frequency signal processed by the front end of the receiver according to the sampling rate; S2, the digital down-conversion of the signal sampled by S1 to the search Carrier frequency grid; S3, the signal obtained by S2 is summed with two L2C chip lengths as a period to obtain the received signal; S4, according to the phase range of the code to be searched, according to the CM code rate in L2C to generate a local pseudo code; S5, Correlate the local pseudocode generated by S4 with the received signal obtained by S3; S6, if the correlation value obtained by S5 is greater than the capture threshold, then according to the code phase corresponding to the correlation value, the code corresponding to the sampling point when S3 is summed The phases are detected separately to remove the code phase ambiguity caused by the summation operation of S3; S7, if the correlation value obtained by S5 is not greater than the capture threshold, then slide the received signal to search for the next code phase, or adjust the digital down-conversion unit to search for the next carrier frequency grid until the entire code phase and carrier frequency space is searched.

Description

Method and device for capturing L2C signal in GPS

technical field

The present invention relates to the field of global positioning system (GPS), in particular to a method and device for capturing L2C signals in GPS.

Background technique

In the process of modernization of the Global Positioning System (GPS), in order to improve signal acquisition and tracking capabilities and improve user performance under weak signal conditions, a new type of civilian signal, namely L2C (English full name: L2civil, where L2 means its Signal frequency point in GPS) signal. The spreading sequence adopted by this signal is significantly different from the widely used C/A code signal. It mixes medium-length pseudocodes (called CM codes) and long-period pseudocodes (called CL codes) through a time-division multiplexing technique. After adopting this technology, the navigation message only modulates the CM code, not the CL code. Adjust the CM code with the navigation message as the data channel to provide the receiving device with the navigation message. The CL code of the unmodulated navigation message is used as a pilot channel, so that the receiving device does not need to consider the influence of the navigation message when processing the navigation signal, and can obtain better acquisition and tracking performance through long-term pre-detection integration.

Capturing the L2C signal is a prerequisite for the work of the L2C receiving terminal, but the existing capturing method takes a long time to capture.

Contents of the invention

Embodiments of the present invention provide a method and device for capturing L2C signals in GPS. By reducing the complexity of correlation operations between local signals and received signals, it reduces the difficulty of capturing pseudo-codes of L2C signals and improves the speed of pseudo-code search, thereby shortening the capture of pseudo-codes. time.

The embodiment of the present invention adopts following technical scheme:

A method for capturing L2C signals in GPS, comprising:

S1. Perform A/D sampling according to the sampling rate for the intermediate frequency signal processed by the front end of the receiver;

S2. Digitally down-convert the signal sampled by S1 to the carrier frequency grid to be searched;

S3. Perform a summation process on the signal obtained in S2 with the period of two L2C chip lengths as a period to obtain a received signal;

S4. According to the phase range of the code to be searched, a local pseudocode is generated according to the CM code rate in the L2C;

S5, correlating the local pseudocode generated by S4 with the received signal obtained by S3;

S6. If the correlation value obtained in S5 is greater than the capture threshold, then according to the code phase corresponding to the correlation value, the code phases corresponding to the sampling points during the S3 summation are respectively detected to remove the code phase caused by the S3 summation operation Vague;

S7. If the correlation value obtained in S5 is not greater than the capture threshold, then slide the received signal to search for the next code phase, or adjust the digital down-conversion unit to search for the next carrier frequency grid until the entire code phase and carrier frequency space is searched.

Optionally, performing A/D sampling according to the sampling rate in S1 includes:

A/D sampling is carried out according to the sampling rate M times of the L2C pseudo-code rate, and M is the ratio of the sampling rate to the L2C pseudo-code rate.

Optionally, the rate of receiving signals in S3 is 0.5115 MHz.

Optionally, the CM code rate in S4 is 0.5115MHz.

A device for capturing L2C signals in GPS, comprising:

The A/D module is used for digitally sampling the analog intermediate frequency signal;

A digital down-conversion module, which is used to digitally lower the frequency of the sampled signal to the carrier frequency grid to be searched;

The two-chip summation module is used to sum the received signals with the period of two L2C chip lengths to obtain a received signal with a rate of 0.5115MHz;

The local CM code generator is used to generate the local CM code according to the CM code rate in L2C, namely 0.5115MHz, according to the phase range of the code to be searched;

The correlation module is used to correlate the received signal of 0.5115MHz with the local CM code of 0.5115MHz to obtain a correlation value;

A threshold comparison module is used to compare the relevant value with a preset capture threshold;

The deambiguity module is used to detect the code phases of the received signals corresponding to the summing process when the correlation value is greater than the threshold, and remove the code phase ambiguity caused by the summation.

Based on the above technical solution, the embodiment of the present invention performs summation processing on the received signals according to the length of every two L2C chips, and reduces the signal correlation rate from the sampling rate to the CM code rate, which can greatly save the amount of calculation, improve the pseudo code search speed, Shorten capture time.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a flowchart of a method for capturing L2C signals in GPS provided by an embodiment of the present invention;

Fig. 2 is a structural diagram of an apparatus for capturing L2C signals in GPS provided by an embodiment of the present invention.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are the Some, but not all, embodiments are invented. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The embodiments of the present invention reduce the complexity of correlation calculations between local signals and received signals, reduce the difficulty of capturing pseudo-codes of L2C signals, increase the speed of pseudo-code search, shorten the time for capturing pseudo-codes, and shorten the time for the first positioning of L2C navigation equipment.

As shown in Figure 1, an embodiment of the present invention provides a method for capturing L2C signals in GPS, including:

S1. Perform A/D sampling according to the sampling rate for the intermediate frequency signal processed by the front end of the receiver;

S2. Digitally down-convert the signal sampled by S1 to the carrier frequency grid to be searched;

S3. Perform a summation process on the signal obtained in S2 with the period of two L2C chip lengths as a period to obtain a received signal;

S4. According to the phase range of the code to be searched, a local pseudocode is generated according to the CM code rate in the L2C;

S5, correlating the local pseudocode generated by S4 with the received signal obtained by S3;

S6. If the correlation value obtained in S5 is greater than the capture threshold, then according to the code phase corresponding to the correlation value, the code phases corresponding to the sampling points during the S3 summation are respectively detected to remove the code phase caused by the S3 summation operation Vague;

S7. If the correlation value obtained in S5 is not greater than the capture threshold, then slide the received signal to search for the next code phase, or adjust the digital down-conversion unit to search for the next carrier frequency grid until the entire code phase and carrier frequency space is searched.

Optionally, performing A/D sampling according to the sampling rate in S1 includes:

A/D sampling is carried out according to the sampling rate M times of the L2C pseudo-code rate, and M is the ratio of the sampling rate to the L2C pseudo-code rate.

Optionally, the rate of receiving signals in S3 is 0.5115 MHz.

Optionally, the CM code rate in S4 is 0.5115MHz.

Here, specific parameters are used as an example to describe the implementation steps of the method. The implementation of the method is not limited to these specific parameters and can be flexibly selected. The implementation steps are as follows:

1. For the intermediate frequency signal processed by the front end of the receiver, A/D sampling is performed at a sampling rate of 5.115MHz, which is 5 times the L2C signal code rate;

2. Digitally down-convert the signal sampled in step 1 to the first carrier frequency grid to be searched;

3. Take the received signal in step 2 as a group of 10 sampling points, and perform summation processing to obtain a received signal with a sampling rate of 0.5115MHz;

4. Generate a local CM code sequence according to the CM code rate of 0.5115MHz;

5. Correlating the local CM code sequence generated in step 4 with the received signal obtained in step 3;

6. If the correlation value obtained in step 5 is greater than the preset capture threshold, the code phases corresponding to the 10 sampling points during the summation in step 3 are detected respectively to remove the code phase ambiguity caused by the summation;

7. If the correlation value obtained in step 5 is not greater than the preset acquisition threshold, then slide the received signal to search for the next code phase, or adjust the digital down-conversion unit to search for the next carrier frequency grid until the entire code phase and carrier frequency space is searched.

As shown in Figure 2, an embodiment of the present invention provides a device for capturing L2C signals in GPS, including:

The A/D module is used for digitally sampling the analog intermediate frequency signal;

A digital down-conversion module, which is used to digitally lower the frequency of the sampled signal to the carrier frequency grid to be searched;

The two-chip summation module is used to sum the received signals with the period of two L2C chip lengths to obtain a received signal with a rate of 0.5115MHz;

The local CM code generator is used to generate the local CM code according to the CM code rate in L2C, namely 0.5115MHz, according to the phase range of the code to be searched;

The correlation module is used to correlate the received signal of 0.5115MHz with the local CM code of 0.5115MHz to obtain a correlation value;

A threshold comparison module is used to compare the relevant value with a preset capture threshold;

The deambiguity module is used to detect the code phases of the received signals corresponding to the summing process when the correlation value is greater than the threshold, and remove the code phase ambiguity caused by the summation.

In the embodiment of the present invention, the local pseudo code does not need to perform additional operations such as zeroing, and only needs to generate a CM code sequence, which reduces the complexity of L2C pseudo code capture; the embodiment of the present invention calculates the received signal according to the length of every two L2C chips. And processing, the signal correlation rate is reduced from the sampling rate to the CM code rate, which can greatly save the amount of calculation, improve the pseudo code search speed, and shorten the capture time.

Those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (5)

1. catch a method for L2C signal in GPS, it is characterized in that, comprising:

S1, to the intermediate-freuqncy signal after receiver front end process, carry out A/D sampling by sampling rate;

S2, by S1 sample after signal digital downconvert to carrier frequency lattice to be searched;

S3, to S2 gained signal, with two L2C chip lengths for the cycle carry out summation process, obtain Received signal strength;

S4, according to code phase scope to be searched, generate local pseudo-code by CM bit rate in L2C;

The Received signal strength that S5, the local pseudo-code generated by S4 and S3 obtain carries out related operation;

If S6 S5 gained correlation is greater than detection threshold, then the code phase corresponding to this correlation, the code phase corresponding to sampled point when suing for peace to S3 detects respectively, fuzzy to remove the code phase that S3 sum operation causes;

If S7 S5 gained correlation is not more than detection threshold, then slip Received signal strength searches for next code phase, or the next carrier frequency lattice of adjustment Digital Down Convert unit searches, until search for complete code phase and carrier frequency space.

2. method according to claim 1, is characterized in that, carries out A/D sampling comprise in S1 by sampling rate:

The M being the pseudo-bit rate of L2C by sampling rate doubly carries out A/D sampling, and M is sampling rate and the ratio of the pseudo-bit rate of L2C.

3. method according to claim 1, is characterized in that, in S3, the speed of Received signal strength is 0.5115MHz.

4. method according to claim 1, is characterized in that, in S4, CM bit rate is 0.5115MHz.

5. catch a device for L2C signal in GPS, it is characterized in that, comprising:

A/D module, for carrying out digital sample to analog if signal;

Digital Down Converter Module, for downconverting to carrier frequency lattice to be searched by the signal digital after sampling;

Dicode sheet summation module, for two L2C chip lengths for the cycle, carry out to received signal summation process, obtain the Received signal strength that speed is 0.5115MHz;

Local CM code generator, for according to code phase scope to be searched, generates local CM code by CM bit rate and 0.5115MHz in L2C;

Correlation module, for carrying out relevant by the Received signal strength of 0.5115MHz to the local CM code of 0.5115MHz, obtains correlation;

Thresholding comparison module, for comparing correlation and default detection threshold;

Deblurring degree module, for when correlation is greater than thresholding, detects respectively to the Received signal strength code phase of corresponding summation process, removes the code phase caused because suing for peace fuzzy.