A high-sensitivity satellite navigation signal tracking method

Abstract

The invention belongs to the technical field of satellite positioning, and specifically relates to a high-sensitivity satellite navigation signal tracking method, comprising: building an improved signal tracking algorithm based on FFT spectrum line mapping of double-sideband signals; and performing double-sideband joint tracking on satellite navigation signals by using the tracking scheme. The invention builds an improved signal tracking algorithm based on FFT spectrum line mapping of double-sideband signals, and the scheme of FFT spectrum line mapping can eliminate the influence of spectrum line offset of upper and lower sidebands of double-sideband signals after FFT caused by the Doppler effect, and realizes the upper and lower sideband joint tracking of multiple-channel composite modulation signals such as AltBOC and ACEBOC. Therefore, the invention can effectively reduce the influence of the Doppler effect on the double-sideband signal tracking, make full use of the energy of the double-sideband, and realize the high-sensitivity tracking of the satellite navigation signals of the multiple-channel composite modulation.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite positioning, and in particular relates to a high-sensitivity satellite navigation signal tracking method. Background Art

[0002] With the continuous advancement of science and technology, the importance of space resources has gradually become prominent. In addition to being widely used in low-Earth orbit services, GNSS (Global Navigation Satellite System) has also been gradually applied in higher orbits. As a key step in deep space exploration, the lunar exploration mission also has a deeper strategic significance. When processing satellite navigation signals of lunar orbit receivers, it is necessary to consider the special effects of fewer visible satellites, low-power sidelobe signals, and the geometric distribution of visible satellites. These factors increase the difficulty of the receiver to receive signals. The carrier tracking algorithm in satellite navigation receivers has always been one of the core algorithms that has received much attention and has long been the focus of many researchers.

[0003] Traditional double-sideband tracking algorithms include BPSK-like and dual-loop estimation tracking. The BPSK-like tracking algorithm tracks the double-sideband signals as BPSK signals separately, but does not fully utilize the advantages of double-sideband signals. The phase detector used in the algorithm will bring additional noise and poor tracking stability. Dual-loop estimation tracking usually uses carrier loop and code loop for tracking. However, under the conditions of Earth-Moon navigation, the distance between the receiver and the satellite can reach more than 300,000 kilometers, resulting in an extremely low received signal-to-noise ratio. Traditional carrier loop and code loop are difficult to cope with such scenarios. The advantage of the FFT estimation algorithm is that it uses FFT calculation instead of the frequency detector and loop filter, effectively solving the problems of the carrier loop and code loop. However, the traditional FFT estimation algorithm has defects in the application of double-sideband signals: when subcarriers exist, the Doppler frequency shift will cause the correlation peak of the double-sideband signal to shift, affecting the joint processing of the double-sideband signal and reducing the tracking performance of the satellite navigation receiver in complex environments such as high orbit and Earth-Moon navigation orbit. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a high-sensitivity satellite navigation signal tracking method, comprising:

[0005] S1: Building an improved signal tracking algorithm based on FFT spectrum line mapping of double-sideband signals;

[0006] An improved signal tracking algorithm is built based on FFT spectrum line mapping of double-sideband signals, including:

[0007] S11: Capture the double-sideband navigation signal through the satellite navigation signal receiver to obtain the carrier frequency and code frequency, and configure the carrier NCO and code NCO of the local reproduction signal;

[0008] S12: using the local reproduction signal to perform short-time correlation calculation on the double-sideband navigation signal that has completed the down-conversion processing, to obtain a coherent integration result, and store it in a plurality of coherent integration arrays;

[0009] S13: executing FFT spectrum line mapping with a set coefficient ratio, performing FFT mapping processing on the double-sideband navigation signal after the coherent integration is completed, and adding spectrum lines of corresponding frequency points of the double-sideband navigation signal after the FFT mapping processing to achieve energy accumulation of the double-sideband navigation signal;

[0010] S14: Find the peak of the spectrum line, make a threshold decision, output the tracking result according to the position of the peak of the spectrum line, and update the tracking loop according to the carrier NCO and code NCO of the local reproduced signal;

[0011] S15: through steps S11-S14, complete the tracking of the P branch correlator branch in the local reproduced signal, and repeat the operations of steps S11-S14 to track the E and L branch correlators in the local reproduced signal;

[0012] S2: Using the improved signal tracking algorithm to perform double-sideband joint tracking on the satellite navigation signal to improve tracking sensitivity.

[0013] Preferably, the set coefficient ratio of the FFT spectral line mapping includes:

[0014]

[0015] in, Indicates the set coefficient ratio of FFT spectrum line mapping, represents the upper sideband mapping coefficient, represents the lower sideband mapping coefficient, Indicates the subcarrier frequency of the satellite navigation signal, Indicates the center frequency of the satellite navigation signal.

[0016] Preferably, performing FFT spectrum line mapping with a set coefficient ratio, and performing FFT mapping processing on the double-sideband navigation signal after completing the coherent integration, comprises:

[0017]

[0018] in, Indicates the spectral line position of the correlation peak after FFT of the upper sideband signal, Indicates the spectral line position of the correlation peak after FFT of the lower sideband signal, Indicates the set coefficient ratio of FFT spectrum line mapping, represents the upper sideband mapping coefficient, Represents the lower sideband mapping coefficient, and round() means rounding.

[0019] Preferably, updating the tracking loop according to the carrier NCO and the code NCO of the local reproduced signal includes:

[0020] Assume that the peak position of the spectrum line exceeding the threshold is x, and the number of FFT points is FFT num , the coherent integration time of each segment input to FFT is T seconds, and the baseband sampling rate of the double-sideband navigation signal is f s Hz, the intermediate frequency is f0 Hz, then the carrier NCO update formula is: Carrier NCO = f 0 + x / η 2 T ⋅ FFT num ] / f s ;

[0021] According to the peak position x of the spectrum line that exceeds the threshold, complete the upper and lower side energy combination of the E path and the upper and lower sideband energy combination of the L path: add the xth spectrum line of the upper sideband of the E path to the xth spectrum line of the lower sideband of the E path. On the root spectrum line, the energy combination Enew of the E path is formed, which makes the upper sideband of the L path The root line is added to the lower sideband of the L path. On the root spectrum line, an energy combination Lnew of the L path is formed. According to the energy combination Enew of the E path and the energy combination Lnew of the L path, the phase detection result of the code loop phase detector is ;

[0022] The phase detection result is sent to the code loop filter to complete the update of the code NCO.

[0023] Beneficial effects of the present invention:

[0024] The present invention builds an improved signal tracking algorithm based on FFT spectral line mapping of double-sideband signals. The scheme of FFT spectral line mapping can eliminate the influence of spectral line deviation of double-sideband signals directly after FFT caused by the Doppler effect, and realize joint tracking of multi-channel composite modulated signals. Therefore, the present invention can effectively reduce the influence of the Doppler effect on double-sideband signal tracking, and realize high-sensitivity joint tracking of double-sideband satellite navigation signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the tracking algorithm structure of a high-sensitivity satellite navigation signal tracking method of the present invention;

[0026] Figure 2 A schematic diagram of the spectrum of Galileo E5a and E5b signals after coherent integration and FFT calculation respectively provided in an embodiment of the present invention;

[0027] Figure 3This is a diagram showing the direct addition result of the corresponding spectrum lines of the double-sideband signal FFT of the present invention;

[0028] Figure 4 A schematic diagram of the double-sideband joint addition result after FFT spectrum line mapping provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Embodiment 1:

[0031] This embodiment discloses a high-sensitivity satellite navigation signal tracking method, such as Figure 1 As shown, the following steps are included:

[0032] An improved signal tracking algorithm is built based on FFT spectrum line mapping of double-sideband signals;

[0033] The improved signal tracking algorithm is used to perform double-sideband joint tracking on the satellite navigation signal to obtain a tracking result.

[0034] The improved signal tracking algorithm specifically comprises the following steps:

[0035] S1: According to the carrier frequency and code frequency captured by the satellite navigation signal receiver, the carrier NCO and code NCO of the local reproduction signal are configured; according to the satellite number captured by the receiver, the satellite secondary code of the code generator is configured;

[0036] S2: using the local recurrence signal to perform short-time correlation calculation on the double-sideband navigation signal that has completed the down-conversion processing, to obtain a coherent integration result, and to store it in a plurality of coherent integration arrays;

[0037] S3: Execute FFT spectrum line mapping with a set coefficient ratio, perform FFT mapping processing on the double-sideband navigation signal after the coherent integration, and add the spectrum lines of the double-sideband navigation signal with corresponding frequency points after the FFT mapping processing to achieve energy accumulation of the double-sideband hacking signal;

[0038] S4: Find the peak of the spectrum line, make a threshold decision, output the tracking result according to the position of the peak of the spectrum line, and update the tracking loop according to the carrier NCO and code NCO of the local reproduced signal;

[0039] S5: Through steps S1-S4, complete the tracking of the P branch correlator branch in the local reproduced signal, and repeat the operations of steps S1-S4 to track the E and L branch correlators in the local reproduced signal.

[0040] The pre-configured local recurrence signal specifically includes:

[0041] The carrier NCO and code NCO of the local recurrence signal are configured according to the carrier frequency and code frequency captured and searched by the satellite navigation signal receiver, thereby completing the pre-configuration of the local recurrence signal.

[0042] The local recurrence signal is used to perform short-time correlation calculation on the double-sideband navigation signal that has completed the down-conversion processing to obtain the coherent integration result, which specifically includes:

[0043] The E, P, and L correlator branches in the local reproduced signal are coherently integrated to achieve parallel integration of the three code phases, and the integration results are stored in an array. After completing multi-segment integration accumulation, FFT calculations are performed on the three branches respectively.

[0044] Taking the Galileo E5 signal as an example, the signal adopts a four-way constant envelope AltBOC modulation method. The center frequencies of the E5a and E5b signals are 1176.45 MHz and 1207.14 MHz respectively. It contains four signal components: E5a-I, E5a-Q, E5b-I, and E5b-Q. The intermediate frequency E5 signal can be expressed as:

[0045] s E 5 t ={[ D E 5 a - I ( t ) ⋅ C E 5 a - I ( t )+ j D E 5 a - Q ( t ) ⋅ C E 5 a - Q ( t )] ⋅ e - j 2 π f sc t +[ D E 5 b - I ( t ) ⋅ C E 5 b - I ( t )+ j D E 5 b - Q ( t ) ⋅ C E 5 b - Q ( t )] ⋅ e j 2 π f sc t } e j 2 π f 0 t (1)

[0046] Wherein, D represents the navigation message of the signal component, C represents the spread spectrum code of the signal component, represents the imaginary unit, t represents the time;

[0047] For the E5 signal containing Doppler frequency received by the receiver, the Doppler frequency includes code Doppler frequency, subcarrier Doppler frequency and carrier Doppler frequency. When the relative speed between the satellite and the receiver is v, the code Doppler frequency , c is the speed of light, f c is the spreading code frequency, subcarrier Doppler , f sc is the subcarrier frequency, carrier Doppler , f RF is the RF frequency, f0 is the intermediate frequency. When it is E5 signal, f c =10.23MHz, f sc =15.345MHz, f RF =1191.795MHz.

[0048] Substituting Doppler into the above expression for the E5 signal yields:

[0049] s E5 (t)={[ C E5a - I (( f c + f dc )t)+j C E5a - Q (( f c + f dc )t)] ⋅ e - j2π( f sc + f dsc )t +[ C E5b - I (( f c + f dc )t)+j C E5b - Q (( f c + f dc )t)] ⋅ e j2π( f sc + f dsc )t } ⋅ e j2π( f 0 + f d )t (2)

[0050] If the carrier Doppler frequency of the local configuration signal is , the corresponding subcarrier Doppler frequency is , the code Doppler frequency is , down-converted to The E5 signal is short-term correlated.

[0051] Using the upper sideband E5a-Q signal for short-time correlation, we can get:

[0052] s E5a - Q ' (t)=r(t) ⋅ {[j C E5a - Q (( f c + f dc ' )t)] ⋅ e - j2π( f sc + f dsc ' )t ⋅ e j2π( f 0 + f d ' )t } * (3)

[0053] Where r(t)=S E5 (t)+n(t), n(t) represents noise, It means to find the conjugate inside {}.

[0054] Using the lower sideband E5b-Q signal for short-time correlation, we can get:

[0055] s E5b - Q ' (t)=r(t) ⋅ {[j C E5b - Q (( f c + f dc ' )t)] ⋅ e j2π( f sc + f dsc ' )t ⋅ e j2π( f 0 + f d ' )t } * (4)

[0056] For the E5 signal with Doppler frequency received by the receiver, taking the E5a-Q signal as an example, when the Doppler offsets of the received signal and the local configuration signal are and When the carrier frequency of the received signal is , the code frequency is .

[0057] Assuming that the spreading codes are aligned, the upper sideband complex carrier obtained by multiplying the received signal by the conjugate of the local reproduced signal is:

[0058] e j2π[ ∆ f - ∆ f ' - ∆ f f RF f SC - ∆ f ' f RF f SC ] t = e j2π[ ∆ f - ∆ f ' 1- f SC f RF ] t (5)

[0059] in, Indicates the subcarrier frequency of the satellite navigation signal, Indicates the center frequency of the satellite navigation signal.

[0060] Assuming that the spreading codes are aligned, the lower sideband complex carrier obtained by multiplying the received signal by the conjugate of the local reproduced signal is:

[0061] e j2π[ ∆ f - ∆ f ' 1+ f SC f RF ] t (6)

[0062] In formula (5), the frequency of the n1th spectral line is calculated as:

[0063] (7)

[0064] In formula (6), the frequency of the n2th spectral line is calculated as:

[0065] (8)

[0066] Combining (7) and (8), we have:

[0067]

[0068] Right now:

[0069]

[0070] make:

[0071] ,

[0072] Taking E5 signal as an example, f sc =1.5×10.23MHz, f RF =116.5×10.23MHz, ;

[0073] Taking E5 signal as an example, f sc =1.5×10.23MHz, f RF=116.5×10.23MHz, ;

[0074] Here it is called are the coefficients of the proportional mapping:

[0075]

[0076]

[0077]

[0078] Therefore, when the upper and lower sidebands are captured, the spectral lines corresponding to their frequency domain peaks are deviated. If the correlation peak of the upper sideband is on the n1th spectral line, the correlation peak of the lower sideband is on the n2th spectral line. Therefore, when the upper and lower sidebands are jointly captured, it is necessary to map the spectral line of the upper sideband correlation peak to the lower sideband signal, and then add the upper and lower sideband spectral lines, that is, through the mapping of the corresponding proportional coefficient, the spectral line where the upper sideband peak is located is mapped. By mapping, we can find the spectrum line at the corresponding position of the lower sideband and realize the peak accumulation of the double sideband. For example, when n1=100, n2=round(100×118 / 115)=103, that is, we need to add the 100th spectrum line of the upper sideband to the 103rd spectrum line of the lower sideband.

[0079] The tracking loop is updated according to the carrier NCO and code NCO of the local reproduced signal, including:

[0080] Assume that the peak position of the spectrum line exceeding the threshold is x, and the number of FFT points is FFT num , the coherent integration time of each segment input to FFT is T seconds, and the baseband sampling rate of the double-sideband navigation signal is f s Hz, the intermediate frequency is f0 Hz, then the carrier NCO update formula is: Carrier NCO = f 0 + x / η 2 T ⋅ FFT num ] / f s ;

[0081] According to the peak position x of the spectrum line that exceeds the threshold, complete the upper and lower side energy combination of the E path and the upper and lower sideband energy combination of the L path: add the xth spectrum line of the upper sideband of the E path to the xth spectrum line of the lower sideband of the E path. On the root spectrum line, the energy combination Enew of the E path is formed, which makes the upper sideband of the L path The root line is added to the lower sideband of the L path. On the root spectrum line, an energy combination Lnew of the L path is formed. According to the energy combination Enew of the E path and the energy combination Lnew of the L path, the phase detection result of the code loop phase detector is ;

[0082] The phase detection result is sent to the code loop filter to complete the update of the code NCO.

[0083] Embodiment 2:

[0084] On the basis of Example 1, this Example 2 further discloses a tracking algorithm simulation solution based on Example 1;

[0085] Specifically:

[0086] In this embodiment, the capture scheme is to obtain the capture integration result of the navigation signal receiver, compensate the FFT spectrum line of the coherent integration matrix according to the Doppler shift, and finally perform incoherent integration to obtain the two-dimensional capture result of the signal.

[0087] Specifically, the work process of capturing the algorithm structure includes:

[0088] Step 1: First, configure the carrier NCO and code NCO of the local signal according to the carrier frequency and code frequency of the satellite navigation signal, configure the satellite secondary code of the code generator according to the satellite number searched by the satellite navigation signal receiver, and start Figure 1 The trace structure flow shown.

[0089] Step 2: Get the coherent integration result. In this example, the main code length of the signal is 10230 chips. The coherent integration time can be selected as 1s, and the number of short-time segments is 1000, that is, 1ms integration time is 1 segment.

[0090] Step 3: Perform FFT and spectral line shifting of the corresponding proportional coefficients on the double-sideband data after the coherent integration to achieve energy accumulation of the double-sideband signal.

[0091] Step 4: Make a threshold decision and update the tracking loop when the threshold is exceeded.

[0092] In a specific embodiment of the present application, the tracking scheme proposed in Example 1 is experimentally verified by simulating navigation signal data. In this experiment, the data sampling rate is 151MHz, the spread spectrum code rate is 10.23MHz, and the Doppler frequency deviation between the local recurrence signal and the received signal is 200Hz. First, the spectrum lines of the E5a and E5b signals are estimated by directly generating signals. Figure 2 The spectral lines are represented after coherent integration of E5a and E5b signals respectively.

[0093] According to formula (5), the upper sideband peak position can be calculated to be 200×(1-3 / 233)=197. Figure 2The peak position of the E5a spectrum line is located at 197. According to formula (6), the peak position of the lower sideband can be calculated to be 200×(1+3 / 233)=203. Figure 2 The peak position of the E5b spectral line is located at 203, and the simulation is consistent with the theoretical value.

[0094] Because of the difference in the correlation peak spectral lines, the double-sideband signals cannot be directly added for joint tracking. When using the traditional FFT estimation algorithm for double-sideband joint tracking, if the corresponding spectral lines of the two signals are directly added, the result is Figure 3 In the result diagram, since the peaks are not on the same spectral line, peak superposition cannot be achieved, and it can be seen that there are two peaks.

[0095] The calculation method in Example 1 is used to perform spectrum mapping of the corresponding proportional coefficient on the FFT result of the E5a signal, and the peak value is Figure 2 The 197th spectral line of E5a is mapped to the 203rd spectral line, completing the mapping of E5a signal to E5b signal. Figure 4 This is the result of double-sideband joint addition after FFT spectrum line mapping. It can be seen that after FFT spectrum line mapping with corresponding scale coefficients, Figure 4 An obvious single spectral line peak appears in the signal, which can realize the corresponding addition of the energy of the upper and lower sidebands. Therefore, the proposed algorithm can realize the joint tracking of the AltBOC double-sideband signal, thereby achieving high-sensitivity tracking of the satellite navigation receiver under the condition of low carrier-to-noise ratio.

[0096] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-sensitivity satellite navigation signal tracking method, characterized in that: include: S1: Building an improved signal tracking algorithm based on FFT spectrum line mapping of double-sideband signals; An improved signal tracking algorithm is built based on FFT spectrum line mapping of double-sideband signals, including: S11: Capture the double-sideband navigation signal through the satellite navigation signal receiver to obtain the carrier frequency and code frequency, and configure the carrier NCO and code NCO of the local reproduction signal; S12: using the local reproduction signal to perform short-time correlation calculation on the double-sideband navigation signal that has completed the down-conversion processing, to obtain a coherent integration result, and store it in a plurality of coherent integration arrays; S13: executing FFT spectrum line mapping with a set coefficient ratio, performing FFT mapping processing on the double-sideband navigation signal after the coherent integration is completed, and adding spectrum lines of corresponding frequency points of the double-sideband navigation signal after the FFT mapping processing to achieve energy accumulation of the double-sideband navigation signal; S14: Find the peak of the spectrum line, make a threshold decision, output the tracking result according to the position of the peak of the spectrum line, and update the tracking loop according to the carrier NCO and code NCO of the local reproduced signal; S15: through steps S11-S14, complete the tracking of the P branch correlator branch in the local reproduced signal, and repeat the operations of steps S11-S14 to track the E and L branch correlators in the local reproduced signal; S2: Using the improved signal tracking algorithm to perform double-sideband joint tracking on the satellite navigation signal to obtain a tracking result.

2. A high-sensitivity satellite navigation signal tracking method according to claim 1, characterized in that: The set coefficient ratio of the FFT spectrum line mapping includes: Among them, ε represents the set coefficient ratio of FFT spectrum line mapping, η1 represents the upper sideband mapping coefficient, η2 represents the lower sideband mapping coefficient, and f sc Indicates the subcarrier frequency of the satellite navigation signal, f RF Indicates the center frequency of the satellite navigation signal.

3. A high-sensitivity satellite navigation signal tracking method according to claim 1, characterized in that: Execute FFT spectrum line mapping with a set coefficient ratio, and perform FFT mapping processing on the double-sideband navigation signal after the coherent integration is completed, including: Among them, n1 represents the spectral line position of the correlation peak after the upper sideband signal is subjected to FFT, n2 represents the spectral line position of the correlation peak after the lower sideband signal is subjected to FFT, ε represents the set coefficient ratio of the FFT spectral line mapping, η1 represents the upper sideband mapping coefficient, η2 represents the lower sideband mapping coefficient, and round() represents rounding.

4. A high-sensitivity satellite navigation signal tracking method according to claim 1, characterized in that: The tracking loop is updated according to the carrier NCO and code NCO of the local reproduced signal, including: Assume that the peak position of the spectrum line exceeding the threshold is x, and the number of FFT points is FFT num , the coherent integration time of each segment input to FFT is T seconds, and the baseband sampling rate of the double-sideband navigation signal is f s Hz, the intermediate frequency is f0 Hz, then the carrier NCO update formula is: Wherein, η2 represents the lower sideband mapping coefficient; According to the peak position x of the spectrum line that exceeds the threshold, the upper and lower sideband energy combination of E and the upper and lower sideband energy combination of L are completed: the xth spectrum line of the upper sideband of E is added to the x / εth spectrum line of the lower sideband of E to form the energy combination Enew of E, and the xth spectrum line of the upper sideband of L is added to the x / εth spectrum line of the lower sideband of L to form the energy combination Lnew of L. According to the phase detection result of the energy combination Enew of E and the energy combination Lnew of L, the phase detection result of the code loop phase detector is Among them, ε represents the set coefficient ratio of FFT spectrum line mapping; The phase detection result is sent to the code loop filter to complete the update of the code NCO.

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