Improved satellite navigation authorization signal real-time estimation device

Abstract

The invention discloses an improved satellite navigation authorization signal real-time estimation device, which comprises a public signal tracking module used for tracking a public pseudo code of a satellite navigation signal in real time and outputting the public pseudo code of the satellite signal, a navigation message, baseband data after carrier stripping and a chip synchronization signal; the authorization signal purification module is used for estimating a pseudo code of the authorization signal in real time; and the public signal tracking module is connected with the authorization signal purification module. According to the method, the navigation message and the public pseudo code information of each code period are demodulated firstly, and then pseudo code estimation of M baseband constellations is improved into pseudo code estimation of M / 2 baseband constellations under the assistance of the navigation message and the public pseudo code, so that the bit error rate of authorized pseudo code estimation is reduced, and the accuracy of pseudo code estimation is improved. And the high gain requirement of the satellite navigation authorization signal estimation device on the receiving antenna is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite navigation signal processing, and more specifically, to an improved satellite navigation authorization signal real-time estimation device. Background Art

[0002] At present, the pseudo code estimation technology of satellite navigation authorization signal is widely used in the field of navigation warfare and navigation signal analysis. The estimation of the authorization signal pseudo code is based on the assistance of the public pseudo code. In short, by tracking the public pseudo code of the navigation signal, the carrier frequency, carrier phase, pseudo code frequency and pseudo code phase information of the authorization signal can be obtained, and then the baseband data stripped of the carrier is integrated within the code chip. The integration result is correlated with M modulation constellations to obtain the baseband constellation corresponding to the maximum value of the correlation result. The corresponding modulation sequence is the estimated authorization pseudo code, where M is the number of constellation points of the baseband modulation. For QPSK modulation signals, M is 4. Since the navigation signal is a weak signal, the conventional 1MHz code rate navigation signal input signal-to-noise ratio is -17dB (navigation signal power -130dBm, thermal noise power -113dBm). Using such a low signal-to-noise ratio for authorization signal estimation has a very high bit error rate. If the pseudo code estimation error is set to 10 -3 , the required input signal-to-noise ratio is 7dB, and the required receiving gain is as high as 24dB. Therefore, most of the high-gain parabolic antennas or large-scale array antennas are currently used for digital beamforming, so that the signal-to-noise ratio is increased to about 7dB. For parabolic antennas, the diameter is about 1.6m, and for array antennas, the number of arrays is about 256. It can be seen that their sizes are relatively large and the cost is high. The bit error rate of the authorized pseudo code estimation is related to the input signal-to-noise ratio and the number of baseband constellation points. Under certain input signal-to-noise ratio conditions, the fewer the number of baseband constellation points, the lower the bit error rate. Therefore, if the number of related constellation points can be reduced, the bit error rate can be further reduced, or in other words, while keeping the bit error rate unchanged, the input signal signal-to-noise ratio requirements can be reduced, and the antenna receiving gain requirements can be reduced, so the size of the parabolic antenna can be reduced, and the number of array elements of the array antenna can be reduced. If the navigation message and public pseudo code information of each code period are obtained first, the pseudo code estimation of M constellations can be improved to the pseudo code estimation of M / 2 constellations, thereby reducing the error rate of the authorization pseudo code estimation, reducing the size of the parabolic antenna, and reducing the number of array elements of the array antenna. Based on this, an improved satellite navigation authorization signal real-time estimation device can be developed. Summary of the invention

[0003] The purpose of the present invention is to provide an improved satellite navigation authorization signal real-time estimation device to overcome the defects of the prior art.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] An improved satellite navigation authorization signal real-time estimation device, comprising:

[0006] The public signal tracking module is used to track the public pseudo code of the satellite navigation signal in real time, and output the public pseudo code of the satellite signal, the navigation message, the baseband data after stripping the carrier, and the chip synchronization signal;

[0007] An authorization signal purification module, used for estimating the pseudo code of the authorization signal in real time;

[0008] The public signal tracking module is connected to the authorized signal purification module.

[0009] Furthermore, the input intermediate frequency signal r(n) of the public signal tracking module is expressed as:

[0010] r(n)=A*c(k)*exp(j 2πf i nt s +θ0)+w(n)

[0011] Where n is the sample sequence of the intermediate frequency signal r(n), A is the signal amplitude, j is the imaginary number sign, and t s is the sampling interval, τ is the unknown signal delay, f i is the unknown carrier frequency, θ0 is the unknown initial phase of the carrier, w(n) is the thermal noise, and exp() is the exponential function. is the pseudo code sequence index, is the rounded down symbol, c(k) is the modulated pseudo code, including two branches, IQ, which is a complex signal, and the expression of c(k) is:

[0012] c(k)=d nav *(c I (k)+jc Q (k))

[0013] Where, d nav is the unknown navigation message before demodulation, c I (k) is the public pseudo code, located in the I branch, c Q (k) is an unknown authorization pseudo code located in the Q branch.

[0014] Further, the public signal tracking module includes a carrier tracking unit, a mixing tracking unit, a pseudo code tracking unit and a tracking accumulation unit;

[0015] The tracking carrier unit is used to generate a local carrier signal s that is in the same frequency and phase as the satellite signal. c (n), its expression is:

[0016] s c (n) = exp(-j 2πfl nt s -θ l )

[0017] In the formula, f l is the local carrier frequency, θ l is the local carrier phase. After stable tracking (i.e., the carrier phase detector output error value is less than the threshold value, i.e., the loop is determined to be locked), f l ≈f i ,θ l ≈θ0;

[0018] The tracking mixer unit is used to strip the carrier from the input intermediate frequency signal r(n) and output a baseband signal b(n), which is expressed as:

[0019]

[0020] Where w1(n) is the thermal noise in the baseband signal, Δf is the carrier frequency error, Δθ is the carrier phase error, and Δf = f i -f l ≈0, Δθ=θ0-θ l ≈0;

[0021] The tracking pseudo code unit is used to generate a local public pseudo code for chip alignment τ l is the local pseudo code delay. After stable tracking, τ l ≈τ, and at the same time output the chip alignment pulse to mark the starting position of the chip;

[0022] The tracking accumulation unit is used to realize the coherent accumulation of the local pseudo code and the baseband signal, and output the IQ branch accumulation values ​​of the early code, the late code, and the instant code, wherein the positive and negative signs of the accumulation value IP of the instant code I branch represent the value of the navigation message modulated in the code period, and the expression of the accumulation value IP of the instant code I branch is:

[0023]

[0024] real() is a real part operation. If the IP value is negative, the navigation message d modulated by the code period is nav is 1, otherwise the navigation message d nav = -1, the tracking accumulation unit outputs the navigation message d at the end of each code cycle nav .

[0025] Further, the authorization signal purification module includes a purification cache unit, a purification accumulation unit, a purification correlation unit and a purification decision unit;

[0026] The purification buffer unit is used to buffer the baseband data, public pseudo code, and chip overflow flag of a complete code period, and output the buffered baseband data, public pseudo code, chip overflow flag, and navigation message after obtaining the navigation message modulated by the code period;

[0027] The purification accumulation unit is used to accumulate the baseband data within the code chip and output the accumulated baseband constellation data b c (k), its expression is:

[0028] b c (k)=Σb(n)

[0029] =A c *c(k)+w c (k)

[0030] =A c *(c I (k)+jc Q (k))+w c (k)

[0031] Where b(n) is the baseband data after stripping the carrier, A c is the signal amplitude of the accumulated value, c(k) is the binary complex chip symbol, in complex form, c I (k) is the public pseudo code of branch I, c Q (k) is the authorization pseudo code of Q branch, k is the chip index, w c (k) is the accumulated thermal noise;

[0032] The purification correlation unit is used to realize the accumulated baseband constellation data b c (k) Correlation with M / 2 baseband constellation data, outputting M / 2 correlation values;

[0033] The purification decision unit is used to compare the magnitudes of M / 2 correlation values, and the authorization pseudo code modulated by the baseband constellation corresponding to the maximum correlation value is the estimated authorization pseudo code c Q (k).

[0034] Compared with the prior art, the advantages of the present invention are: the present invention first demodulates the navigation message and public pseudo code information of each code period, and then, with the assistance of the navigation message and the public pseudo code, improves the pseudo code estimation of M baseband constellations into the pseudo code estimation of M / 2 baseband constellations, thereby reducing the error rate of the authorized pseudo code estimation and the high gain requirement of the receiving antenna. Taking M=4 as an example, the present application can improve the authorized pseudo code estimation of QPSK into the authorized pseudo code estimation similar to BPSK. When the error rate requirement is 10 -3The required signal-to-noise ratio before the improvement is 7dB, and the required signal-to-noise ratio after the improvement is about 5dB, obtaining a signal-to-noise ratio margin of about 2dB. For small-aperture antennas, the aperture is reduced from 1.6m to 1.3m, and for array antennas, the number of array elements is reduced from 256 to 164, thereby reducing the high-gain requirements for the receiving antenna, reducing the size of the parabolic antenna, and reducing the number of array elements in the array antenna. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a schematic diagram of the improved satellite navigation authorization signal real-time estimation device of the present invention.

[0037] Figure 2 It is a timing diagram of the tracking pseudo code unit in the present invention.

[0038] Figure 3 It is the baseband constellation required for the maximum decision before the improvement in this embodiment.

[0039] Figure 4 It is the baseband constellation required for the maximum decision after improvement in this embodiment. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0041] See also Figure 1 As shown, this embodiment discloses an improved satellite navigation authorization signal real-time estimation device, including a public signal tracking module 1, which is used to track the public pseudo code of the satellite navigation signal in real time, and output the public pseudo code of the satellite signal, the navigation message, the baseband data after stripping the carrier, and the code chip synchronization signal; the authorization signal purification module 2 is used to correlate the accumulated value in the code chip of the baseband signal with M / 2 baseband constellation data, and output the estimated value of the authorization pseudo code after taking the larger judgment, where M is the number of baseband constellation points; the public signal tracking module and the authorization signal purification module are connected.

[0042] In this embodiment, it is assumed that the navigation signal pseudo code rate is 1MHz, the pseudo code period is 1ms, the QPSK modulation mode is adopted, the I branch modulates the public pseudo code, the Q branch modulates the authorized pseudo code, the sampling rate is 40MHz, and the required authorized pseudo code estimated bit error rate is ≤10 -3 .

[0043] In this embodiment, the public signal tracking module 1 includes a carrier tracking unit 11 , a frequency mixing tracking unit 12 , a pseudo code tracking unit 13 and a tracking accumulation unit 14 .

[0044] The input intermediate frequency signal r(n) of the public signal tracking module is expressed as:

[0045] r(n)=A*c(k)*exp(j 2πf i nt s +θ0)+w(n)

[0046] Where n is the sample sequence of the intermediate frequency signal r(n), A is the signal amplitude, j is the imaginary number sign, and t s is the sampling interval, τ is the unknown signal delay, f i is the unknown carrier frequency, θ0 is the unknown initial phase of the carrier, w(n) is the thermal noise, and exp() is the exponential function. is the pseudo code sequence index, is the rounded down symbol, c(k) is the modulated pseudo code, including two branches, IQ, which is a complex signal, and the expression of c(k) is:

[0047] c(k)=d nav *(c I (k)+jc Q (k))

[0048] Where, d nav is the unknown navigation message before demodulation, c I (k) is the public pseudo code, located in the I branch, c Q (k) is an unknown authorization pseudo code located in the Q branch.

[0049] The tracking carrier unit 11 is used to generate a local carrier signal s that is in the same frequency and phase as the satellite signal. c (n), its expression is:

[0050] s c (n) = exp(-j 2πf l nt s -θ l )

[0051] In the formula, f l is the local carrier frequency, θ lis the local carrier phase. After stable tracking (i.e., the carrier phase detector output error value is less than the threshold value, i.e., the loop is determined to be locked), f l ≈f i ,θ l ≈θ0.

[0052] The tracking mixer unit 12 is used to remove the carrier from the input intermediate frequency signal r(n) and output a baseband signal b(n), which is expressed as:

[0053]

[0054] Where w1(n) is the thermal noise in the baseband signal, Δf is the carrier frequency error, Δθ is the carrier phase error, and Δf = f i -f l ≈0, Δθ=θ0-θ l ≈0.

[0055] The tracking pseudo code unit 13 is used to generate a local public pseudo code for chip alignment τ l is the local pseudo code delay. After stable tracking, τ l ≈τ, and at the same time output the chip alignment pulse to mark the starting position of the chip, such as Figure 2 shown.

[0056] The tracking accumulation unit 14 is used to realize the coherent accumulation of the local pseudo code and the baseband signal, and output the IQ branch accumulation values ​​of the early code, the late code, and the prompt code, wherein the positive and negative signs of the accumulation value IP of the prompt code I branch represent the value of the navigation message modulated in the code period, and the expression of the accumulation value IP of the prompt code I branch is:

[0057]

[0058] real() is a real part operation. If the IP value is negative, the navigation message d modulated by the code period is nav is 1, otherwise the navigation message d nav = -1, the tracking accumulation unit outputs the navigation message d at the end of each code cycle nav .

[0059] In this embodiment, the authorization signal purification module 2 includes a purification cache unit 21 , a purification accumulation unit 22 , a purification correlation unit 23 and a purification decision unit 24 .

[0060] The purified cache unit 21 is used to cache the baseband data, public pseudo code, and code chip overflow flag of a complete code period. After obtaining the navigation message modulated by the code period, the cached baseband data, public pseudo code, code chip overflow flag and navigation message are output. The purified cache unit 21 is implemented using a dual-port BRAM with a cache depth of 80,000 samples, providing a cache depth of 2 pseudo code periods.

[0061] The purification accumulation unit 22 is used to accumulate the baseband data within the code chip and output the accumulated baseband constellation data b c (k), its expression is:

[0062] b c (k) = ∑b(n)

[0063] =A c *c(k)+w c (k)

[0064] =A c *(c I (k)+jc Q (k))+w c (k)

[0065] Where b(n) is the baseband data after stripping the carrier, A c is the signal amplitude of the accumulated value, c(k) is the binary complex chip symbol, in complex form, c I (k) is the public pseudo code of branch I, c Q (k) is the public pseudo code of the Q branch, k is the chip index, w c (k) is the accumulated thermal noise, and the purification accumulation unit 22 can be implemented by using one accumulator and one trigger.

[0066] The purification correlation unit 23 is used to realize the accumulated baseband constellation data b c (k) is correlated with M / 2 baseband constellation data, and M / 2 correlation values ​​are output. The 2 baseband constellation data are:

[0067] c1(k)=d nav *(c I (k)+j*1)

[0068] c2(k)=d nav *(c I (k)+j*-1)

[0069] d nav is the known navigation message that has been demodulated, c I (k) is the local known public pseudo code, j is the imaginary symbol, and the two related value expressions are:

[0070] p1(k)=b c (k)*c1(k)

[0071] p2(k)=b c (k)*c2(k)

[0072] The purification correlation unit 23 can be implemented by using two complex multipliers.

[0073] The purification decision unit 24 is used to compare the magnitudes of the M / 2 correlation values. The authorization pseudo code modulated by the baseband constellation corresponding to the maximum correlation value is the estimated authorization pseudo code c Q (k) The purification decision unit 24 can be implemented using a 2-input comparator.

[0074] The present invention first demodulates the navigation message and public pseudo code information of each code period, and then, with the assistance of the navigation message and the public pseudo code, can improve the authorization pseudo code estimation of QPSK into an authorization pseudo code estimation similar to BPSK. Typically, when the bit error rate is required to be 10 -3 Before the improvement, it is necessary to make a maximum decision among the four baseband constellations, such as Figure 3 As shown, the required signal-to-noise ratio is 7dB. After the improvement, since the modulation data of the I branch is known, it is only necessary to make a larger decision among the two baseband constellations, such as Figure 4 As shown, the required signal-to-noise ratio is about 5 dB. Therefore, this embodiment obtains a signal-to-noise ratio margin of about 2 dB. For a small-aperture antenna, its aperture is reduced from 1.6 m to 1.3 m, and for an array antenna, the number of array elements is reduced from 256 to 164, thereby reducing the high gain requirement for the receiving antenna, reducing the size of the parabolic antenna, and reducing the number of array elements in the array antenna.

[0075] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, various changes or modifications may be made within the scope of the appended claims. As long as they do not exceed the protection scope described in the claims of the present invention, they should be within the protection scope of the present invention.

Claims

1. An improved satellite navigation authorization signal real-time estimation device, characterized in that: include: The public signal tracking module is used to track the public pseudo code of the satellite navigation signal in real time, and output the public pseudo code of the satellite signal, the navigation message, the baseband data after stripping the carrier, and the chip synchronization signal; An authorization signal purification module, used for estimating the pseudo code of the authorization signal in real time; The public signal tracking module is connected to the authorized signal purification module.

2. The improved satellite navigation authorization signal real-time estimation device according to claim 1, characterized in that: The input intermediate frequency signal r(n) of the public signal tracking module is expressed as: r(n)=A*c(k)*exp(j 2πf i nt s +θ0)+w(n) Where n is the sample sequence of the intermediate frequency signal r(n), A is the signal amplitude, j is the imaginary number sign, and t s is the sampling interval, τ is the unknown signal delay, f i is the unknown carrier frequency, θ0 is the unknown initial phase of the carrier, w(n) is the thermal noise, exp() is the exponential function, is the pseudo code sequence index, is the rounded down symbol, c(k) is the modulated pseudo code, including two branches, IQ, which is a complex signal, and the expression of c(k) is: c(k)=d nav *(c I (k)+jc Q (k)) Where, d nav is the unknown navigation message before demodulation, c I (k) is the public pseudo code, located in the I branch, c Q (k) is an unknown authorization pseudo code located in the Q branch.

3. The improved satellite navigation authorization signal real-time estimation device according to claim 1, characterized in that: The public signal tracking module includes a carrier tracking unit, a frequency mixing tracking unit, a pseudo code tracking unit and a tracking accumulation unit; The tracking carrier unit is used to generate a local carrier signal sc(n) that maintains the same frequency and phase as the satellite signal, and its expression is: s c (n)=exp(-j 2πf l n.t. s -θ l ) In the formula, f l is the local carrier frequency, θ l is the local carrier phase. When the carrier phase detector output error value is less than the threshold value, f l ≈f i ,θ l ≈θ0; The tracking mixer unit is used to strip the carrier from the input intermediate frequency signal r(n) and output a baseband signal b(n), which is expressed as: Where w1(n) is the thermal noise in the baseband signal, Δf is the carrier frequency error, Δθ is the carrier phase error, and Δf = f i -f l ≈0, Δθ=θ0-θ l ≈0; The tracking pseudo code unit is used to generate a local public pseudo code for chip alignment τ l is the local pseudo code delay. After stable tracking, τ l ≈τ, and at the same time output the chip alignment pulse to mark the starting position of the chip; The tracking accumulation unit is used to realize the coherent accumulation of the local pseudo code and the baseband signal, and output the IQ branch accumulation values ​​of the early code, the late code, and the instant code, wherein the positive and negative signs of the accumulation value IP of the instant code I branch represent the value of the navigation message modulated in the code period, and the expression of the accumulation value IP of the instant code I branch is: real() is a real part operation. If the IP value is negative, the navigation message d modulated by the code period is nav is 1, otherwise the navigation message d nav = -1, the tracking accumulation unit outputs the navigation message d at the end of each code cycle nav .

4. The improved satellite navigation authorization signal real-time estimation device according to claim 1, characterized in that: Place The authorization signal purification module includes a purification cache unit, a purification accumulation unit, a purification correlation unit and a purification decision unit. ； The purification buffer unit is used to buffer the baseband data, public pseudo code, and chip overflow flag of a complete code period, and output the buffered baseband data, public pseudo code, chip overflow flag, and navigation message after obtaining the navigation message modulated by the code period; The purification accumulation unit is used to accumulate the baseband data within the code chip and output the accumulated baseband constellation data b c (k), its expression is: b c (k)=Σb(n) =A c *c(k)+w c (k) =A c *(c I (k)+jc Q (k))+w c (k) Where b(n) is the baseband data after stripping the carrier, A c is the signal amplitude of the accumulated value, c(k) is the binary complex chip symbol, in complex form, c I (k) is the public pseudo code of branch I, c Q (k) is the authorization pseudo code of Q branch, k is the chip index, w c (k) is the accumulated thermal noise; The purification correlation unit is used to realize the accumulated baseband constellation data b c (k) Correlation with M / 2 baseband constellation data, outputting M / 2 correlation values; The purification decision unit is used to compare the magnitudes of M / 2 correlation values, and the authorization pseudo code modulated by the baseband constellation corresponding to the maximum correlation value is the estimated authorization pseudo code c Q (k).

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