CN108254767B - BOC signal capturing method and baseband synchronous receiver - Google Patents

BOC signal capturing method and baseband synchronous receiver Download PDF

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CN108254767B
CN108254767B CN201810001874.7A CN201810001874A CN108254767B CN 108254767 B CN108254767 B CN 108254767B CN 201810001874 A CN201810001874 A CN 201810001874A CN 108254767 B CN108254767 B CN 108254767B
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code
boc
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CN108254767A (en
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符强
陈孝倩
孙希延
纪元法
程雷
雷正强
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Guilin University of Electronic Technology
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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
    • G01S19/29—Acquisition or tracking or demodulation of signals transmitted by the system carrier including Doppler, related
    • 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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Abstract

The invention is suitable for the technical field of satellite navigation positioning, and provides a BOC signal capturing method and a baseband synchronous receiver. The method comprises the following steps: receiving a BOC intermediate frequency signal; mixing the BOC intermediate frequency signal with a local carrier in an orthogonal demodulation mode to strip the carrier to obtain a baseband BOC signal; performing signal decomposition on pseudo-random noise PRN codes generated by a local pseudo-code generator according to the modulation order N of a baseband BOC signal to obtain N sub PRN codes; and taking out the first sub PRN code and the Nth sub PRN code, dividing the first sub PRN code and the Nth sub PRN code into two paths, respectively correlating with the baseband BOC signal branch to obtain sub cross-correlation branches, reconstructing the sub cross-correlation branches, and performing non-coherent integration to obtain a capture result. The BOC signal self-correlation side peak eliminating device is simple in structure, low in error capturing rate and higher in sensitivity, can complete rapid capture of BOC, can basically eliminate the self-correlation side peak of the BOC signal, and keeps the narrow correlation characteristic of the BOC signal.

Description

BOC signal capturing method and baseband synchronous receiver
Technical Field
The invention belongs to the technical field of satellite navigation positioning, and particularly relates to a BOC signal capturing method and a baseband synchronous receiver.
Background
With the birth and development of various global navigation systems and the application of different aspects such as military and civilian, navigation signals of different modulation modes need to share the same frequency band; in the development of urban buildings, navigation signals are required to have certain multipath effect resistance so as to ensure positioning accuracy. Because the signal energy of the BOC (Binary Offset Carrier) modulated signal is mainly distributed on both sides of the center frequency, it can be well compatible with BPSK (Binary Phase Shift Keying) signals, and the main peak of the BOC's correlation peak is steeper than the BPSK signal, and has better anti-multipath performance and higher tracking accuracy. Therefore, each large Navigation System adopts BOC signals as a new GNSS (Global Navigation Satellite System) signal.
The baseband signal processing part of the baseband synchronous receiver mainly comprises acquisition and tracking, and aims to complete baseband synchronization of intermediate frequency navigation signals. However, due to the multi-peaked nature of the BOC correlation function, both its acquisition and tracking are ambiguous, i.e., may be incorrectly synchronized to the side peaks of the correlation function. As shown in fig. 1, a baseband synchronous receiver in the prior art mainly includes a mixer, n correlators, n integrate-clear, a carrier phase detector, a PRN code phase detector, a loop filter, a carrier NCO (digitally controlled oscillator), a pseudo code NCO, a pseudo code generator, and a delay unit. The traditional baseband synchronous receiver has a simple structure, is easy to capture and lose lock of BOC system signals in a weak signal environment, and is not suitable for a novel satellite navigation system any more. In the prior art, a receiver for eliminating the synchronization ambiguity of the BOC signal by using the spectral characteristics of the BOC signal is processed after approximating the BOC signal to a BPSK signal and shifting the BPSK signal up and down in a frequency domain. Such as BPSK-like method, but the correlation peak width obtained by this method is similar to that of BPSK signal, and the advantage of narrow correlation property of BOC signal is sacrificed.
Disclosure of Invention
The invention aims to provide a BOC signal capturing method, a computer readable storage medium and a baseband synchronous receiver, aiming at solving the problem that the prior art can eliminate the synchronization ambiguity of the BOC signal, but sacrifice the advantage of narrow correlation characteristic of the BOC signal.
In a first aspect, the present invention provides a BOC signal capturing method, including:
receiving a binary offset carrier BOC intermediate frequency signal;
mixing the BOC intermediate frequency signal with a local carrier in an orthogonal demodulation mode to strip the carrier to obtain a baseband BOC signal;
performing signal decomposition on pseudo-random noise (PRN) codes generated by a local pseudo-code generator according to the modulation order N of a baseband BOC signal to obtain N sub-PRN codes, wherein N is a natural number greater than or equal to 2;
taking out a first sub PRN code and an Nth sub PRN code, dividing the first sub PRN code and the Nth sub PRN code into two paths, respectively correlating with a baseband BOC signal branch to obtain sub cross-correlation branches, and reconstructing the sub cross-correlation branches to obtain a capture result;
and judging whether the capturing is successful according to whether the capturing result is larger than a preset capturing threshold.
In a second aspect, the present invention provides a computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the BOC signal acquisition method as described above.
In a third aspect, the present invention provides a baseband synchronization receiver, including: a processor, a memory, and one or more computer programs, wherein the one or more computer programs are stored in the memory and configured to be executed by the one or more processors, the processor implementing the steps of the BOC signal capture method as described above when executing the computer programs.
In a fourth aspect, the present invention provides a tracking method for a baseband synchronous receiver, the method including:
taking the capture result obtained by the BOC signal capture method as the initial value of the tracking loop;
the carrier NCO generates a local carrier according to the Doppler initial value, the local carrier is mixed with an intermediate frequency signal input by the baseband synchronous receiver, a pseudo code is stripped after the mixing result is related to a local code, and the carrier NCO is adjusted through a carrier phase discriminator after integration-clearing;
the pseudo code NCO generates a local pseudo code according to an initial value of a code phase, and generates an advance branch and a delay branch which advance and delay a preset code phase with a current instant branch through a delayer according to a modulation order of a received BOC signal;
the method comprises the steps that a leading branch, an instant branch and a delay branch decompose a local pseudo code into N sub PRN codes through a signal decomposer according to the modulation order of a BOC signal;
the method comprises the steps that a leading branch, an instant branch and a delay branch respectively take out a first sub PRN code and an Nth sub PRN code, the first sub PRN code and the Nth sub PRN code are correlated with a mixing output to obtain sub cross-correlation branches, and reconstruction results obtained by the sub cross-correlation branches are reconstructed;
carrying out integration-clearing on reconstruction results obtained by the leading branch and the delay branch, and continuously adjusting a pseudo code NCO through a PRN code phase discriminator;
and locking the received signal to obtain the Doppler frequency, the pseudo code and the square wave subcarrier of the received signal, and demodulating navigation data by using the obtained Doppler frequency, the pseudo code and the square wave subcarrier to complete the baseband synchronization of the BOC signal.
In the invention, according to the modulation order N of the baseband BOC signal, the PRN code generated by a local pseudo code generator is subjected to signal decomposition to obtain N sub PRN codes, the first sub PRN code and the Nth sub PRN code are taken out and divided into two paths which are respectively related to the baseband BOC signal branch to obtain sub cross-correlation branches, and the capturing result is obtained by reconstructing the sub cross-correlation branches. Compared with other capturing technologies in the prior art, the BOC capturing device is simple in structure, low in error capturing rate and higher in sensitivity, and can complete rapid capturing of BOC. The invention can basically eliminate the side peak of the BOC signal autocorrelation, keep the narrow correlation characteristic of the BOC signal, is suitable for all BOC (kn, n) signals, is also suitable for TMBOC (6, 1, 4/33) signals and CBOC (6, 1, 1/11) signals, meets the BOC modulation signals of various large satellite navigation systems, and has the advantages of strong universality, short baseband synchronization time and high precision compared with other receivers.
Drawings
Fig. 1 is a block diagram of a prior art baseband synchronous receiver.
Fig. 2 is a flowchart of a BOC signal capturing method according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a BOC (n, n) signal capture result obtained by the BOC signal capture method according to the embodiment of the present invention when the snr is 20 dB.
Fig. 4 is a schematic diagram of two-dimensional results of BOC (n, n) signal capturing method, BPSK-like signal and ASPeCT signal capturing method according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of two-dimensional results of BOC (2n, n) signal capturing method, BPSK-like signal and ASPeCT signal capturing method according to an embodiment of the present invention.
Fig. 6 is a relationship curve of acquisition probability and carrier-to-noise ratio of the BOC (n, n) acquisition by the BPSK-like and ASPeCT and the BOC signal acquisition method according to the embodiment of the present invention.
Fig. 7 is a block diagram of a baseband synchronous receiver according to a third embodiment of the present invention.
Fig. 8 is a flowchart of a tracking method of a baseband synchronous receiver according to a fourth embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to explain the technical means of the present invention, the following description will be given by way of specific examples.
The first embodiment is as follows:
referring to fig. 2, a BOC signal capturing method according to an embodiment of the present invention includes the following steps: it should be noted that, if the results are substantially the same, the BOC signal capturing method of the present invention is not limited to the flow sequence shown in fig. 2.
S101, receiving a BOC intermediate frequency signal.
BOC intermediate frequency signal rIF(t) can be expressed as:
Figure BDA0001537052260000041
wherein,
Figure BDA0001537052260000042
d (t) is the navigation message with the level value of + -1, fIFAt intermediate frequency, theta is the initial phase of the carrier, tau is the phase of the delayed code, NnMean value is zero and variance is sigma2White Gaussian noise, SBOC(t) is a BOC code, which represents the product of the pseudo code and the square wave subcarrier, namely:
sBOC(t)＝c(t)*sign(sin(2πfsct))
s102, mixing the BOC intermediate frequency signal with a local carrier in an orthogonal demodulation mode to strip the carrier, and obtaining a baseband BOC signal.
The baseband BOC signal r (t) can be expressed as:
Figure BDA0001537052260000051
where Δ f is the carrier frequency estimation error.
S103, according to the modulation order N of the baseband BOC signal, performing signal decomposition on a PRN (pseudo-random noise) code generated by a local pseudo-code generator to obtain N sub-PRN codes, wherein N is a natural number greater than or equal to 2.
In the first embodiment of the present invention, S103 may specifically include the following steps:
the expression of the time domain of the modulated signal output by the baseband synchronous receiver is as follows:
sBOC(kn,n)(t)＝A*d(t)*c(t)*sign(sin(2πfsct))
where A is the signal amplitude, d (t) is the navigation data, c (t) is the spread spectrum PRN code, sign (sin (2 π f)sct)) denotes a subcarrier, denoted by f01.023MHz is a reference frequency, BOC (kn, n) represents the frequency f of c (t)c＝nf0Sub-carrier frequency fsc＝knf0N2 kn/N2 k is defined as the modulation order of BOC (kn, N), the product of PRN and subcarrier is defined as BOC code, and s is usedBOC(t) is expressed as:
sBOC(t)＝c(t)*sign(sin(2πfsct))
basebandCross correlation function R of BOC signal and PRNB/P(τ) can be expressed as:
Figure BDA0001537052260000052
wherein τ is the code phase delay, N is the modulation order of the baseband BOC signal,
Figure BDA0001537052260000053
indicates a peak value at
Figure BDA0001537052260000054
Correlation peak of (1), Tc＝1/fcIndicates one PRN code period;
the BOC code sBOC(t) is expressed in the form of rectangular pulses:
Figure BDA0001537052260000055
wherein p isi(t) represents a pulse signal, and the expression is:
Figure BDA0001537052260000061
the PRN code can be expressed using a rectangular pulse as:
Figure BDA0001537052260000062
will sc,i(t) is defined as the ith sub-PRN code, i.e., each PRN chip is divided into N segments, only the ith PRN chip value is retained, and the PRN chip values of the other segments are set to 0.
S104, a first sub-PRN code and an Nth sub-PRN code are taken out, the first sub-PRN code and the Nth sub-PRN code are divided into two paths which are respectively related to a baseband BOC signal branch circuit to obtain a sub-cross-correlation branch circuit, and a capturing result is obtained by reconstructing the sub-cross-correlation branch circuit.
In the first embodiment of the present invention, the sub cross correlation function corresponding to the sub cross correlation branch is generated by:
defining a sub-cross-correlation function as a cross-correlation function of a BOC code and an ith sub-PRN code with coherent integration time Tcoh, and using RB/Pi(τ) is expressed as:
Figure BDA0001537052260000063
therefore, the locally generated sub PRN code is used for being correlated with the baseband BOC signal after the carrier wave is stripped by the baseband synchronous receiver to obtain a sub cross-correlation branch.
No matter what value N takes, RB/P1(τ) and RB/PNEach of (τ) has a nonzero value only in the vicinity of the (0, 0) point, and there is a relationship of being rotated by 180 ° around the (0, 0) point. Thus making use of RB/P1(τ) and RB/PNThe product of (tau) is inverted to obtain a correlation function R having a main positive peak and two side negative peaksMExpressed as:
RM＝-RB/P1*RB/PN
considering that the detection quantity of the capture output is generally | · or | · ceiling2In the form of reconstructing the correlation function to obtain R for further removing secondary peaks and increasing the peak value of the main peakRSCThe expression is as follows:
RRSC＝|RM+|RM||＝||RB/P1*RB/PN|-RB/P1*RB/PN|
in the first embodiment of the present invention, the sub cross-correlation branch is reconstructed by the following method:
the 1 st sub-PRN code sc,1(t) and Nth sub-PRN code sc,N(t), multiplying by r (t) and coherently integrating to obtain:
S1＝Ad(t)RB/P1(τ)sinc(πΔfTcoh)+N1＝S1(τ,Δf)+N1
SN＝Ad(t)RB/PN(τ)sinc(πΔfTcoh)+NN＝SN(τ,Δf)+NN
wherein, A is the signal amplitude after coherent integration, d (t) is the navigation message with the level value of +/-1τ is the delayed code phase and Δ f is the carrier frequency estimation error. N is a radical of1、NNIs a mean of zero and a variance of σ2White gaussian noise.
The reconstruction rule is that1And SNMultiply to obtain SMIn the pair SMAdding its absolute value to obtain the final captured output V1, which is expressed as:
V1＝|SM+|SM||＝||S1*S|-S*SN|
if the number of non-coherent integrations is NncThe reconstructed and integrated-cleared capture output is V2:
Figure BDA0001537052260000071
and S105, judging whether the acquisition is successful or not according to whether the acquisition result is larger than a preset acquisition threshold or not, changing the number of the acquired satellite if the acquisition of the current satellite is failed, and returning to the step S103 until the acquisition is successful.
Fig. 3 shows a BOC signal acquisition method provided in an embodiment of the present invention for a sampling frequency f at a signal-to-noise ratio SNR of-20 dBS40.920MHz, Doppler shift fd1500Hz and 800 (sample points) code phase, results for BOC (n, n) signal acquisition.
Fig. 4 and fig. 5 are two-dimensional graphs of the BOC signal capturing method and the BOC (n, n) and BOC (2n, n) signals captured by the existing BPSK-like and ASPeCT methods according to the first embodiment of the present invention, respectively, and the obtained normalized correlation peak value changes with the code phase. When the BOC (n, n) signal is captured, although the BPSK-like and the ASPeCT can remove ambiguity, the main peak width of the BPSK-like is consistent with that of a traditional GNSS signal, and the narrow correlation characteristic of the BOC modulation signal is sacrificed. The ASPeCT has a secondary peak with the amplitude of 0.1673 when the code phase is +/-0.375 Tc, and the secondary peak with the peak value of 0.04948 exists at the position where the code phase is-0.475 Tc in the first embodiment of the invention, so that the BOC signal capturing method provided by the first embodiment of the invention not only can obtain a narrower main correlation peak, but also has the false capturing rate of the side peak of the BOC (n, n) signal which is only 1.946% of the ASPeCT; when the BOC (2n, n) is captured, BPSK-like obtains a correlation peak value similar to that of the BOC (n, n); aspecct is now unable to remove ambiguity over BOC signal capture; the BOC signal capturing method provided by the embodiment of the invention can still remove the ambiguity of the BOC signal, and correspondingly improve the narrow correlation characteristic of the main peak along with the improvement of the BOC modulation order.
Fig. 6 is a detection probability-carrier-to-noise ratio relationship curve obtained by capturing BOC (n, n) by the BOC signal capturing method and the existing BPSK-like and ASPeCT methods according to an embodiment of the present invention. When coherent integration time Tcoh is 1ms, incoherent accumulation frequency Nnc is 10, constant false alarm probability Pfa is 10-6, and detection probability of 90% is the standard, the acquisition sensitivity of the BOC signal acquisition method provided by the embodiment of the present invention is improved by about 3.1dB and 2.8dB respectively compared with BPSK-like and ASPeCT, so that acquisition can be completed more quickly.
Example two:
the second embodiment of the present invention provides a computer-readable storage medium, where a computer program is stored, and when the computer program is executed by a processor, the steps of the BOC signal capture method provided in the first embodiment of the present invention are implemented.
Example three:
fig. 7 shows a specific structure block diagram of a baseband synchronous receiver according to a third embodiment of the present invention, where a baseband synchronous receiver 100 includes: a processor 101, a memory 102, and one or more computer programs, wherein the processor 101 and the memory 102 are connected by a bus, the one or more computer programs are stored in the memory 102 and configured to be executed by the one or more processors 101, and the steps of the BOC signal capture method provided in the first embodiment of the present invention are implemented when the computer programs are executed by the processors 101.
Example four:
referring to fig. 8, a tracking method of a baseband synchronous receiver according to a fourth embodiment of the present invention includes the following steps:
s201, taking a capture result obtained by the BOC signal capture method provided by the first embodiment of the invention as an initial value of a tracking loop.
S202, the carrier NCO generates a local carrier according to the Doppler initial value, the local carrier is mixed with an intermediate frequency signal input by the baseband synchronous receiver, a pseudo code is stripped after the mixing result is related to the local code, and the carrier NCO is adjusted through the carrier phase discriminator after integration-clearing, so that the carrier of the input signal is accurately tracked.
S203, the pseudo code NCO generates a local pseudo code according to the initial value of the code phase, and generates an advance branch and a delay branch which advance and delay the current instant branch by a preset code phase through a delayer according to the modulation order of the received BOC signal.
And S204, the advance branch, the prompt branch and the delay branch decompose the local pseudo code into N sub-PRN codes through a signal decomposer according to the modulation order of the BOC signal.
In the fourth embodiment of the present invention, S204 may specifically be:
the PRN code can be expressed using a rectangular pulse as:
Figure BDA0001537052260000091
where c (t) is a spreading PRN code, pi(t) represents a pulse signal, and the expression is:
Figure BDA0001537052260000092
Tc＝1/fcdenotes a PRN code period, and s isc,i(t) is defined as the ith sub-PRN code, i.e., each PRN chip is divided into N segments, only the ith PRN chip value is retained, and the PRN chip values of the other segments are set to 0.
S205, the advance branch, the prompt branch and the delay branch respectively take out a first sub-PRN code and an Nth sub-PRN code, the first sub-PRN code and the Nth sub-PRN code are correlated with the mixing output to obtain sub-cross-correlation branches, and reconstruction results obtained by the sub-cross-correlation branches are reconstructed.
In the fourth embodiment of the present invention, the sub cross correlation function corresponding to the sub cross correlation branch is generated by the following method:
defining a sub-cross-correlation function as a cross-correlation function of a BOC code and an ith sub-PRN code with coherent integration time Tcoh, and using RB/Pi(τ) is expressed as:
Figure BDA0001537052260000093
in the fourth embodiment of the present invention, the sub cross-correlation branch is reconstructed by the following method:
the 1 st sub-PRN code sc,1(t) and Nth sub-PRN code sc,N(t), multiplying by r (t) and coherently integrating to obtain:
S1＝Ad(t)RB/P1(τ)sinc(πΔfTcoh)+N1＝S1(τ,Δf)+N1
SN＝Ad(t)RB/PN(τ)sinc(πΔfTcoh)+NN＝SN(τ,Δf)+NN
wherein, a is the signal amplitude after coherent integration, d (t) is the navigation message with level value of ± 1, τ is the delay code phase, and Δ f is the carrier frequency estimation error. N is a radical of1、NNIs a mean of zero and a variance of σ2White gaussian noise.
The reconstruction result V3 obtained through the sub-cross-correlation reconstruction is as follows: v3 | | S1*S|-S*SN|
S206, integrating and clearing reconstruction results obtained by the leading branch and the delay branch, and continuously adjusting the pseudo code NCO through the PRN code phase discriminator so as to accurately track the pseudo code phase of the input signal, and returning to recapture and track if the phase is unlocked.
S207, locking the received signal, accurately obtaining the Doppler frequency, the pseudo code and the square wave subcarrier of the received signal, demodulating navigation data by using the obtained Doppler frequency, the pseudo code and the square wave subcarrier, completing the baseband synchronization of the BOC signal, and returning to recapture and tracking if the BOC signal is unlocked.
According to the modulation order N of a baseband BOC signal, the PRN code generated by a local pseudo code generator is subjected to signal decomposition to obtain N sub PRN codes, the first sub PRN code and the Nth sub PRN code are taken out and divided into two paths to be respectively related to the baseband BOC signal branch to obtain sub cross-correlation branches, and the sub cross-correlation branches are reconstructed and subjected to non-coherent integration to obtain a capture result. Compared with other capturing technologies in the prior art, the method has the advantages of simple structure, low false capturing rate and higher sensitivity, and can complete the rapid capture of the BOC. The invention can basically eliminate the side peak of the BOC signal autocorrelation, keep the narrow correlation characteristic of the BOC signal, is suitable for all BOC (kn, n) signals, is also suitable for TMBOC (6, 1, 4/33) signals and CBOC (6, 1, 1/11) signals, meets the BOC modulation signals of various large satellite navigation systems, and has the advantages of strong universality, short baseband synchronization time and high precision compared with other receivers.
Those skilled in the art will appreciate that all or part of the steps in the methods of the above embodiments may be implemented by associated hardware instructed by a program, which may be stored in a computer-readable storage medium, and the storage medium may include: read Only Memory (ROM), Random Access Memory (RAM), magnetic or optical disks, and the like.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (7)

1. A BOC signal acquisition method, the method comprising:
receiving a binary offset carrier BOC intermediate frequency signal;
mixing the BOC intermediate frequency signal with a local carrier in an orthogonal demodulation mode to strip the carrier to obtain a baseband BOC signal;
performing signal decomposition on pseudo-random noise (PRN) codes generated by a local pseudo-code generator according to the modulation order N of a baseband BOC signal to obtain N sub-PRN codes, wherein N is a natural number greater than or equal to 2;
taking out a first sub PRN code and an Nth sub PRN code, dividing the first sub PRN code and the Nth sub PRN code into two paths, respectively correlating with a baseband BOC signal branch to obtain sub cross-correlation branches, and reconstructing the sub cross-correlation branches to obtain a capture result;
judging whether the capturing is successful or not according to whether the capturing result is larger than a preset capturing threshold or not;
the method for decomposing the pseudo random noise PRN code generated by the local pseudo code generator according to the modulation order N of the baseband BOC signal to obtain N sub PRN codes specifically comprises the following steps:
the PRN code is represented by a rectangular pulse as:
Figure FDA0003033921180000011
where c (t) is a spreading PRN code, pi(t) represents a pulse signal, and the expression is:
Figure FDA0003033921180000012
Tc＝1/fcdenotes a PRN code period, and s isc,i(t) defining the ith sub-PRN code, i.e., dividing each PRN chip into N segments, retaining only the ith PRN chip value, and setting the PRN chip values of other segments to 0;
the sub cross-correlation function corresponding to the sub cross-correlation branch is generated by:
defining a sub-cross-correlation function as a cross-correlation function of a BOC code and an ith sub-PRN code with coherent integration time Tcoh, and using RB/Pi(τ) is expressed as:
Figure FDA0003033921180000013
wherein s isBOC(t) is the BOC code, τ is the delayed code phase;
reconstructing the sub-cross-correlation branch by:
the 1 st sub-PRN code sc,1(t) and Nth sub-PRN code sc,N(t) multiplying the baseband BOC signal r (t) and then performing coherent integration to obtain:
S1＝Ad(t)RB/P1(τ)sinc(π△fTcoh)+N1＝S1(τ,△f)+N1
SN＝Ad(t)RB/PN(τ)sinc(π△fTcoh)+NN＝SN(τ,△f)+NN
wherein, A is the signal amplitude after coherent integration, d (t) is the navigation message with the level value of +/-1, tau is the delay code phase, Deltaf is the carrier frequency estimation error, N1、NNIs a mean of zero and a variance of σ2White gaussian noise of (1);
the reconstruction rule is that1And SNMultiply to obtain SMIn the pair SMAdding its absolute value to obtain the final captured output V1, which is expressed as:
V1＝|SM+|SM||＝||S1*SN|-S1*SN|
if the number of non-coherent integrations is NncThe reconstructed and integrated-cleared capture output is V2:
Figure FDA0003033921180000021
2. the method of claim 1 wherein if the current satellite acquisition fails, the acquisition satellite number is changed, and then the method returns to the step of performing signal decomposition on the PRN code generated by the local pseudo code generator to obtain N sub-PRN codes according to the modulation order N of the baseband BOC signal until the acquisition is successful.
3. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the steps of the BOC signal acquisition method according to claim 1 or 2.
4. A baseband synchronous receiver comprising: a processor, a memory, and one or more computer programs, wherein the one or more computer programs are stored in the memory and configured to be executed by the one or more processors, wherein the steps of the BOC signal acquisition method according to claim 1 or 2 are implemented when the computer programs are executed by the processors.
5. A tracking method for a baseband synchronous receiver, the method comprising:
taking the acquisition result obtained by the BOC signal acquisition method of claim 1 or 2 as an initial value of a tracking loop;
the carrier NCO generates a local carrier according to the Doppler initial value, the local carrier is mixed with an intermediate frequency signal input by the baseband synchronous receiver, a pseudo code is stripped after the mixing result is related to a local code, and the carrier NCO is adjusted through a carrier phase discriminator after integration-clearing;
the pseudo code NCO generates a local pseudo code according to an initial value of a code phase, and generates an advance branch and a delay branch which advance and delay a preset code phase with a current instant branch through a delayer according to a modulation order of a received BOC signal;
the method comprises the steps that a leading branch, an instant branch and a delay branch decompose a local pseudo code into N sub PRN codes through a signal decomposer according to the modulation order of a BOC signal;
the method comprises the steps that a leading branch, an instant branch and a delay branch respectively take out a first sub PRN code and an Nth sub PRN code, the first sub PRN code and the Nth sub PRN code are correlated with a mixing output to obtain sub cross-correlation branches, and reconstruction results obtained by the sub cross-correlation branches are reconstructed;
carrying out integration-clearing on reconstruction results obtained by the leading branch and the delay branch, and continuously adjusting a pseudo code NCO through a PRN code phase discriminator;
and locking the received signal to obtain the Doppler frequency, the pseudo code and the square wave subcarrier of the received signal, and demodulating navigation data by using the obtained Doppler frequency, the pseudo code and the square wave subcarrier to complete the baseband synchronization of the BOC signal.
6. The method as claimed in claim 5, wherein the decomposing of the local pseudo code by the signal decomposer into N sub-PRN codes by the advance branch, the prompt branch and the delay branch simultaneously according to the modulation order of the BOC signal is embodied as:
the PRN code is represented by a rectangular pulse as:
Figure FDA0003033921180000031
where c (t) is a spreading PRN code, pi(t) represents a pulse signal, and the expression is:
Figure FDA0003033921180000032
Tc＝1/fcdenotes a PRN code period, and s isc,i(t) is defined as the ith sub-PRN code, i.e., each PRN chip is divided into N segments, only the ith PRN chip value is retained, and the PRN chip values of the other segments are set to 0.
7. The method of claim 6, wherein the sub cross correlation function corresponding to a sub cross correlation branch is generated by:
defining a sub-cross-correlation function as a cross-correlation function of a BOC code and an ith sub-PRN code with coherent integration time Tcoh, and using RB/Pi(τ) is expressed as:
Figure FDA0003033921180000041
wherein s isBOC(t) is the BOC code, τ is the delayed code phase;
reconstructing the sub-cross-correlation branch by:
the 1 st sub-PRN code sc,1(t) and Nth sub-PRN code sc,N(t) multiplication by the baseband BOC signal r (t) and coherent integrationObtaining:
S1＝Ad(t)RB/P1(τ)sinc(π△fTcoh)+N1＝S1(τ,△f)+N1
SN＝Ad(t)RB/PN(τ)sinc(π△fTcoh)+NN＝SN(τ,△f)+NN
wherein, A is the signal amplitude after coherent integration, d (t) is the navigation message with the level value of +/-1, tau is the delay code phase, Deltaf is the carrier frequency estimation error, N1、NNIs a mean of zero and a variance of σ2White gaussian noise of (1);
the reconstruction result V3 obtained through the sub-cross-correlation reconstruction is as follows: v3 | | S1*SN|-S1*SN|。
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