CN112731476A - GPS satellite M code signal demodulation method based on short code de-spreading and timing recovery combination - Google Patents
GPS satellite M code signal demodulation method based on short code de-spreading and timing recovery combination Download PDFInfo
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- CN112731476A CN112731476A CN202011149741.8A CN202011149741A CN112731476A CN 112731476 A CN112731476 A CN 112731476A CN 202011149741 A CN202011149741 A CN 202011149741A CN 112731476 A CN112731476 A CN 112731476A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention provides a GPS satellite M code signal demodulation method based on short code de-spreading and timing recovery, which utilizes the mutual promotion relationship of short code de-spreading and timing recovery to effectively reduce the signal-to-noise ratio threshold of demodulation, equivalently reduce the aperture of an antenna and save the construction cost. Firstly, acquiring a carrier frequency and a carrier phase of a GPS satellite navigation signal by a typical carrier estimation method, carrying out carrier recovery and IQ separation, and further realizing the extraction of a GPS M code signal by band-pass filtering; and then short code decoding is carried out on the GPS M code signal to obtain coding gain, timing synchronization is carried out by adopting blind processing for the first time on the basis, the M code stream containing the information of the M code signal is obtained after judgment, the information is fed back to the front end to carry out timing synchronization operation on the signal again, and the timing synchronization precision can be improved.
Description
Technical Field
The invention belongs to the technical field of satellite system monitoring and maintenance, and particularly relates to a GPS satellite M code signal demodulation method based on short code despreading and timing recovery combination.
Background
With the modernization of the GPS satellite, the GPS satellite navigation system M code has already preliminarily completed global networking, and the corresponding M code navigation receiver has also been put into use successively. Because an M-code signal in a GPS signal is mixed with a C/a code and a P code, a local M-code signal is mainly constructed by a GPS signal blind demodulation method to construct a GPS M-code receiving device at present under the condition that a code pattern and an encryption mode of the M code cannot be acquired. When blind demodulation is performed on an M code signal, a large-caliber high-gain antenna is mainly adopted to receive a GPS satellite navigation signal so as to ensure demodulation performance. However, the existing large-aperture antenna has high construction and maintenance cost, needs a demodulation technology of a low signal-to-noise ratio GPS signal, reduces the signal-to-noise ratio threshold of demodulation, equivalently reduces the aperture of the antenna, and saves the construction cost.
Disclosure of Invention
In order to solve the technical problems, the invention provides a GPS satellite M code signal demodulation method based on short code de-spreading and timing recovery combination, which utilizes the mutual promotion relationship of short code de-spreading and timing recovery to effectively reduce the signal-to-noise ratio threshold of demodulation, equivalently reduce the antenna aperture and save the construction cost.
In order to achieve the above purpose, the invention provides a GPS satellite M code signal demodulation method based on short code de-spreading and timing recovery combination, comprising the following steps:
step 2, timing synchronization is carried out on the M code oversampling signals by adopting a blind processing mode to obtain M code soft symbols;
step 3, judging the current M code soft symbol to obtain an M code stream;
step 4, reconstructing an M code oversampling signal by using the M code stream obtained in the step 3 to obtain a pseudo reference signal, and performing timing synchronization again on the M code oversampling signal obtained in the step 1 by using the pseudo reference signal to obtain an M code soft symbol;
and 5, repeating the steps 3-4, and stopping operation to finish demodulation when the M code stream obtained by judgment is not changed any more.
In step 1, the specific manner of obtaining the M-code oversampled signal is as follows:
carrying out data rate conversion on the GPS satellite M code signal to obtain a BOC modulation M code signal with 4 times of oversampling rate;
and performing serial-to-parallel conversion on the BOC modulation M code signal to obtain 4 paths of signal subsequences, and performing weighted combination on the 4 paths of signal subsequences by respectively using +1, -1, +1 and-1 by using known M code BOC modulation information to obtain 1 path of M code oversampled signals.
In step 1, the acquisition mode of the M-code signal of the GPS satellite is:
sampling GPS satellite navigation signals; and C/A code signal stripping and P code signal stripping are carried out on the sampled GPS satellite navigation signals to obtain GPS satellite M code signals.
The specific mode of carrying out C/A code signal stripping on the sampled GPS satellite navigation signal is as follows:
the carrier frequency and the carrier phase of the GPS satellite navigation signal are obtained, the carrier recovery of the GPS satellite navigation signal is completed by utilizing the carrier frequency and the carrier phase, the separation of the orthogonal component and the in-phase component of the signal is completed through orthogonal processing, the C/A code signal is stripped, and the P code branch signal and the M code branch signal are obtained.
And stripping the P code signals in the P code and M code branch signals through band-pass filtering to obtain the M code signals of the GPS satellite.
The specific method for sampling the GPS satellite navigation signal is as follows:
and receiving the GPS satellite navigation signal by using the antenna, converting the GPS satellite navigation signal into an intermediate frequency, and then carrying out AD sampling.
Has the advantages that:
according to the invention, the mutual promotion relationship of short code de-spreading and timing recovery is utilized, firstly, the short code de-spreading is carried out on an oversampled M code signal, on the basis of obtaining coding gain, the blind processing is firstly adopted to carry out timing synchronization on the M code signal, and the M code stream is obtained after judgment, wherein the M code stream contains the innovation of the M code signal, so that the system performance under the low signal-to-noise ratio can be improved; by adopting an iteration processing mode, the innovation obtained by demodulating the M code signal is fed back to the front end, and the innovation is fed back to the front end to be used as an auxiliary for carrying out timing synchronization operation on the signal again, so that the timing synchronization precision can be improved, the demodulation quality of the GPS M code signal can be effectively improved, the signal-to-noise ratio threshold can be effectively reduced under the condition of obtaining the same demodulation error rate, the aperture of a receiving antenna is reduced, and the system construction and maintenance cost is saved.
Drawings
FIG. 1 is a schematic diagram of an implementation process of a GPS M-code signal demodulation method based on short code despreading and timing recovery joint processing according to the present invention;
FIG. 2 is a block diagram of a short code despreading and timing recovery based joint process of the present invention;
FIG. 3 is a schematic diagram of the BOC modulated M-code oversampled signal with 4 times oversampling rate obtained in step 4 of the present invention;
FIG. 4 is a schematic diagram of the signal subsequences before and after weighted combination in step 5 of the present invention;
fig. 5 is a block diagram of a typical prior art blind demodulation of an M-code signal.
Detailed Description
The present invention will be described in detail below with reference to examples.
Considering the relevance of each step of the M-code signal demodulation processing, i.e. the relevance of different stages of the signal demodulation processing, the different processing stages of information recovery using the received data obviously affect each other, for example, the quality of the timing synchronization performance directly affects the rear-end decoding effect and the final symbol decision result. Comprehensive consideration and combined treatment are carried out on the treatment processes, and better system performance can be obtained.
The invention obtains the carrier frequency and the carrier phase of the GPS satellite navigation signal by a typical carrier estimation technology, carries out carrier recovery and IQ separation, further realizes the extraction of the GPS satellite M code signal by band-pass filtering, then carries out short code decoding on the GPS satellite M code signal to obtain coding gain, carries out timing synchronization and M code judgment on the basis, realizes the extraction of the M code stream, and is different from the traditional demodulation method of timing synchronization and BOC decoding (figure 5). Based on the short code despreading and timing recovery combination, the invention firstly carries out short code decoding on the over-sampled BOC modulation signal to obtain coding gain, carries out subsequent processing on the basis, and can improve the system performance under low signal-to-noise ratio, and concretely comprises the following steps:
step 2, timing synchronization is carried out on the M code oversampling signals by adopting a blind processing mode to obtain M code soft symbols;
step 3, judging the current M code soft symbol to obtain an M code stream;
step 4, reconstructing an M code oversampling signal by using the M code stream obtained in the step 3 to obtain a pseudo reference signal, and performing timing synchronization again on the M code oversampling signal obtained in the step 1 by using the pseudo reference signal to obtain an M code soft symbol;
and 5, repeating the steps 3-4, and stopping operation to finish demodulation when the M code stream obtained by judgment is not changed any more.
In step 1, the specific manner of obtaining the M-code oversampled signal is as follows:
carrying out data rate conversion on the GPS satellite M code signal to obtain a BOC modulation M code signal (figure 3) with 4 times of oversampling rate, wherein the sampling rate is 81.84MHz in the embodiment;
performing serial-to-parallel conversion on the obtained BOC modulation M code signal according to the diagram shown in FIG. 4 to obtain 4 paths of signal subsequences with the sampling rate of 20.46MHz, and performing weighted combination on the 4 paths of subsequences by respectively using +1, -1, +1 and-1 by using known M code BOC modulation information to obtain 1 path of M code oversampled signals;
the acquisition mode of the GPS satellite M code signal is as follows:
receiving and digitally sampling GPS satellite navigation signals;
carrier frequency and carrier phase estimation are carried out on the sampled GPS satellite navigation signals; completing GPS satellite navigation signal carrier recovery by utilizing the obtained carrier frequency and carrier phase, completing IQ separation of C/A code signals and P code and M code signals, and obtaining P code and M code branch signals; performing band-pass filtering on the obtained P code branch signals and M code branch signals, and stripping the P code signals to obtain GPS satellite M code signals;
wherein, the rate of the M code stream obtained by judging the M code soft symbol obtained after the primary timing synchronization is 5.115 Mbps; and the sampling rate of the M code signal reconstructed by the obtained M code stream is 20.46 MHz.
In the embodiment, the antenna is used for receiving a GPS satellite navigation radio frequency signal, the central frequency point of the signal is 1575.42MHz, and the radio frequency signal is converted to an intermediate frequency and then subjected to AD sampling.
The separation of the quadrature component and the in-phase component of the signal (IQ separation) is accomplished by quadrature processing, stripping the C/a code signal.
And designing a band-pass filter according to the difference of the P code and the M code on the frequency spectrum, and stripping the P code signal.
The present invention is capable of other embodiments, and various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention.
Claims (6)
1. A GPS satellite M code signal demodulation method based on short code despreading and timing recovery is characterized by comprising the following steps:
step 1, short code decoding is carried out on a GPS satellite M code signal to obtain coding gain, and an M code oversampling signal is obtained;
step 2, timing synchronization is carried out on the M code oversampling signals by adopting a blind processing mode to obtain M code soft symbols;
step 3, judging the current M code soft symbol to obtain an M code stream;
step 4, reconstructing an M code oversampling signal by using the M code stream obtained in the step 3 to obtain a pseudo reference signal, and performing timing synchronization again on the M code oversampling signal obtained in the step 1 by using the pseudo reference signal to obtain an M code soft symbol;
and 5, repeating the steps 3-4, and stopping operation to finish demodulation when the M code stream obtained by judgment is not changed any more.
2. The method for demodulating M-code signals of GPS satellites based on short code despreading and timing recovery combination according to claim 1, wherein the specific way to obtain M-code oversampled signals in step 1 is:
carrying out data rate conversion on the GPS satellite M code signal to obtain a BOC modulation M code signal with 4 times of oversampling rate;
and performing serial-to-parallel conversion on the BOC modulation M code signal to obtain 4 paths of signal subsequences, and performing weighted combination on the 4 paths of signal subsequences by respectively using +1, -1, +1 and-1 by using known M code BOC modulation information to obtain 1 path of M code oversampled signals.
3. The method as claimed in claim 1, wherein the GPS satellite M-code signal demodulation method based on short code despreading and timing recovery combination comprises, in step 1, the acquisition mode of the GPS satellite M-code signal:
sampling GPS satellite navigation signals; and C/A code signal stripping and P code signal stripping are carried out on the sampled GPS satellite navigation signals to obtain GPS satellite M code signals.
4. The method for demodulating M-code signals of GPS satellites based on the combination of short code despreading and timing recovery as claimed in claim 3, wherein the C/A code signal stripping is performed on the sampled GPS satellite navigation signals by:
the carrier frequency and the carrier phase of the GPS satellite navigation signal are obtained, the carrier recovery of the GPS satellite navigation signal is completed by utilizing the carrier frequency and the carrier phase, the separation of the orthogonal component and the in-phase component of the signal is completed through orthogonal processing, the C/A code signal is stripped, and the P code branch signal and the M code branch signal are obtained.
5. The GPS satellite M-code signal demodulation method based on short code despreading and timing recovery combination as claimed in claim 4, wherein the GPS satellite M-code signal is obtained by band-pass filtering to strip off the P-code signal in the P-code and M-code branch signals.
6. The method for demodulating GPS satellite M-code signal based on short code despreading and timing recovery combination as claimed in claim 3, wherein the GPS satellite navigation signal is sampled by:
and receiving the GPS satellite navigation signal by using the antenna, converting the GPS satellite navigation signal into an intermediate frequency, and then carrying out AD sampling.
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