Extended wide-narrow correlator based on GPS L1 signal / L5 signal

Abstract

An extended wide-narrow correlator based on GPS L1 signal / L5 signal includes: a first estimation unit, a second estimation unit and a third estimation unit connected in sequence, wherein: each estimation unit will give an estimation value, and the correlator outputs an estimation value of the code delay error at the previous moment after three estimations based on the code delay estimation value. The present invention realizes the combination of correlators with different intervals through the natural high and low code rate characteristics of the two signals, improves the tracking accuracy and improves the anti-multipath performance under the premise of ensuring the robustness of the system.

Description

Technical Field

[0001] The present invention relates to a technology in the field of navigation, and in particular to a correlator which utilizes multi-frequency point signals to improve the tracking accuracy, robustness and anti-multipath performance of navigation signals in urban environments. Background Art

[0002] GNSS is a satellite system that covers the world and provides autonomous geographic and spatial positioning. The code tracking loop, as an important part of signal tracking, is susceptible to signal shielding and multipath in urban environments, resulting in reduced accuracy or even loss of lock. The correlator is a component of the code tracking loop and is used to estimate the current tracking error. The traditional wide-narrow correlator is a widely used correlator. It uses a combination of a group of wide correlators and a group of narrow correlators to achieve the effect of anti-multipath, but the noise level is increased. At present, navigation signals are abundant. Many navigation constellations such as GPS, Galileo, and BDS (Beidou Satellite Navigation System) broadcast signals in multiple frequency bands. Signals in different frequency bands have differences in accuracy and robustness due to different code rates, energy, and modulation methods. At present, multi-frequency signals have been widely used in positioning solutions, but they are still independent of each other in the tracking loop. The present invention will be conducive to the fusion of the advantages of different signals and improve the accuracy and robustness of tracking through the combination of multi-frequency signals in the tracking loop. Summary of the invention

[0003] Aiming at the background that the existing tracking algorithms fail to effectively utilize the advantages of joint tracking of high and low bit rate signals, and it is difficult to balance tracking accuracy and robustness in urban environments, the present invention proposes an extended wide-narrow correlator based on GPS L1 signal / L5 signal. By taking advantage of the natural high and low bit rate characteristics of the two signals, the combination of correlators with different intervals is realized, and the tracking accuracy is improved while ensuring the robustness of the system, and the anti-multipath performance is enhanced.

[0004] The urban environment refers to an environment with complex terrain, numerous obstacles such as high-rise buildings and viaducts, frequent signal obstructions, and easy reflection of signals to form NLOS or multipath phenomena, making it difficult to ensure high accuracy and good robustness.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention relates to an extended wide-narrow correlator based on GPS L1 signal / L5 signal, comprising: a first estimation unit, a second estimation unit and a third estimation unit connected in sequence, wherein: each estimation unit will give an estimation value, and the correlator outputs an estimation value of the code delay error at the previous moment after three estimations according to the code delay estimation value.

[0007] The first estimation unit receives the code delay estimation value The first estimate of the output code delay error δτ1 and L1 signal instant branch correlation value P L1 The first estimation unit includes: an L1 correlator and a phase detector, wherein: the L1 correlator receives the code delay estimation value, with one code chip as the early and late branch interval Generate three groups of local signals, namely: early branch, instantaneous branch, and late branch; correlate the three groups of local signals with the received signal respectively, and obtain the correlation values ​​of the early, instantaneous, and late branches (E L1 , P L1 , L L1 ), where the instantaneous branch correlation value is output; the phase detector uses the Normalized Early minus Late Envelop, and the phase detector value δτ is calculated based on the early and late branch correlation values. L1 , as the first estimate δτ 1 =δτ L1 Output.

[0008] The second estimation unit receives the first estimation value δτ 1 , L1 instant branch related value P L1 and the third estimated value δτ of the code delay error at the previous N moments 3 [kl], l = 1…n (where N is the sliding average window size and k is the current time), the second estimate of the output code delay error δτ 2 The second estimation unit includes: an L1 signal carrier-to-noise ratio estimator, a window size estimator and a sliding average window, wherein: the L1 signal carrier-to-noise ratio estimator estimates the L1 carrier-to-noise ratio C / N according to the L1 instantaneous branch correlation value within 1s. 0 L1 ; The window size estimator obtains the window size N from the comparison table with the L1 carrier-to-noise ratio; the sliding average window averages the third estimation value of the previous N moments and the first estimation value of the current moment according to the window size, and outputs it as the second estimation value.

[0009] The third estimation unit receives the code delay estimation value and the second estimation value of the code delay error at the previous moment, and outputs the third estimation value of the code delay error δτ 3 The third estimation unit includes: an L5 correlator and a phase detector, wherein: the L5 correlator estimates the code delay and the second estimate of the code delay error δτ 2 difference Centered on the code chip, the early and late branch intervals are Generate three groups of local signals, namely: early branch, instantaneous branch, and late branch; correlate the three groups of local signals with the received signal respectively, and obtain the correlation values ​​of the early, instantaneous, and late branches (E L5 , PL5 , L L5 );The phase detector also uses an early-minus-late phase detector, and the phase detector value δτ is calculated based on the correlation value of the early and late branches L5 , the phase detection value is added to the second estimated value of the code delay error (δτ L5 +δτ 2 ), as the third estimate δτ 3 =δτ L5 +δτ 2 Output.

[0010] The code delay error is calculated by the Normalized Early minus Late Envelop in the first and third estimation units. Among them: E, L are the correlation values ​​of the early and late branches.

[0011] The L1 signal-to-noise ratio estimator in the second estimation unit estimates the L1 signal-to-noise ratio Where: μ, σ 2 P within 1s L1 The mean and variance of T c is the coherent integration time.

[0012] The comparison table of the second estimation unit is as follows:

[0013]

[0014] Technical Effects

[0015] The present invention combines signals of high and low difference code rates for joint tracking; uses correlation values ​​of multi-frequency point signals to estimate code delay tracking errors; and uses the phase detection result of one frequency point to pre-correct the code delay estimation of the remaining frequency points.

[0016] Compared with the prior art, the present invention ensures the robustness of the system through the phase detection result of the L1 signal, ensures the normal tracking of the L5 signal by combining the L1 signal with the time domain sliding average, and reduces the tracking error by the phase detection result of the L5 signal; the present invention realizes the fusion of the advantages of dual-frequency signals, while improving the tracking accuracy, ensuring extremely strong robustness, and has practical value in challenging urban environments with frequent signal shielding and reflection. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the present invention;

[0018] In the figure: 100 the first estimation unit of the code delay error, 101 the code delay estimation value, 102 the L1 correlator, 103 the L1 early and late branch correlation values ​​E L1 , L L1、104 L1 early-minus-late phase detector、105 The first estimate of the code delay error δτ 1 , 106 a second estimation unit for code delay error, 107 a third estimated value δτ of the code delay error at the previous N moments 3 [kl] (l = 1, 2, ..., n), 108 L1 instant branch correlation value P L1 , 109 L1 signal carrier-to-noise ratio estimator, 110 L1 signal carrier-to-noise ratio, 111 window size estimator, 112 sliding average window size N, 113 sliding average window, 114 second estimated value δτ of code delay error 2 , 115 a third estimation unit for code delay error, 116 a code delay estimation unit corrected by the second code delay error estimation 117 L5 correlator, 118 L5 early and late branch correlation peak E L5 , L L5 、119 L5 early-minus-late phase detector、120 L5 phase detector value δτ L5 、The third estimated value of 121 code delay error δτ 3 . DETAILED DESCRIPTION

[0019] like Figure 1 As shown, an extended wide-narrow correlator based on GPS L1 signal / L5 signal involved in this embodiment includes: three estimation units 100, 106 and 115.

[0020] The L1 correlator 102 of the first estimation unit 100 estimates the code delay Centered on the code chip, the early and late correlator intervals are Generate three sets of local signals (early branch Instant Branch Wanzhi Road ), specifically:

[0021]

[0022]

[0023]

[0024] Among them C L1 (·) is the L1 pseudo-random code, n represents the nth sampling point, T s is the sampling interval, is the L1 Doppler estimate, is the L1 phase estimation value. The three sets of local signals are combined with the L1 baseband signal r L1 Perform correlation and T c=10ms coherent integration, and the early, immediate and late branch correlation values ​​are obtained, which are:

[0025]

[0026]

[0027]

[0028] Among them, f s is the sampling rate, L1 signal uses complex sampling, baseband signal r L1 Expressed in plural form, so E L1 , P L1 , L L1 All are plural.

[0029] The early-minus-late phase detector 104 obtains the L1 phase detection value through the correlation value of the early and late branches. Where: ||·|| is the 2 norm. This phase detection value is used as the first estimate of the 105 code delay error δτ 1 .

[0030] In the second estimation unit 106, the L1 carrier-to-noise ratio estimator 109 calculates the L1 instantaneous branch correlation value P within 1 s. L1 L1 carrier-to-noise ratio C / N 0 L1 Make an estimate Where: μ, σ 2 P within 1s L1 The 111 window size estimator obtains the 112 window size N according to the 110 L1 carrier-to-noise ratio through the following comparison table:

[0031]

[0032] The sliding average window 113 takes the third estimate δτ of the code delay error of the first N coherent integration intervals 107 3 [kl], l = 1...n (where k represents the current kth coherent integration interval) and the first estimate δτ of the code delay error of the current coherent integration interval 105 1 [k] is averaged to obtain the second estimate of the 114 code delay error

[0033] In the third estimation unit 115, the L5 correlator 117 uses the code delay estimation corrected by the second code delay error estimation Centered on the code chip, the early and late correlator intervals are Generate three sets of local signals (early branch Instant Branch Wanzhi Road ), specifically:

[0034]

[0035]

[0036]

[0037] Where: C L5 (·) is the L5 pseudo-random code, is the L5 Doppler estimate, is the L5 phase estimation value. The three sets of local signals are combined with the L5 baseband signal r L5 Perform correlation and T c =10ms coherent integration, and the early, immediate and late branch correlation values ​​are obtained, which are:

[0038]

[0039]

[0040]

[0041] Where: f s is the sampling rate, the L5 signal uses complex sampling, and the baseband signal r L5 Expressed in plural form, so E L5 , P L5 , L L5 The early-minus-late phase detector 119 obtains the phase detection value 120L5 through the correlation value of the early and late branches 118. , using the phase detection value and the second estimated value δτ of the 114 code delay error 2 The sum is taken as the third estimate δτ of the 105 code delay error 3 =δτ L5 +δτ 2

[0042] Experiments have shown that the tracking accuracy of the extended wide and narrow correlator in the following different scenarios is increased to a level similar to that of the L5 signal, significantly exceeding that of the L1; in an occluded environment, it has stronger robustness than the L5 signal and a lower possibility of losing lock. In an open environment with strong signals, the code delay tracking error of the extended wide and narrow correlator is significantly reduced compared to the L1 signal, and slightly increased compared to the L5 signal. In a long multipath environment, the extended wide and narrow correlator can significantly reduce the code delay tracking error caused by multipath compared to the L1 signal, and the accuracy is slightly reduced compared to the L5 signal that is not affected by long multipath. In a short multipath environment, the accuracy of the extended wide and narrow correlator is slightly greater than that of L1 / L5 tracking alone.

[0043]

[0044] Compared with the existing technology, this method improves the tracking accuracy while ensuring strong robustness, and has practical value in multipath environments with frequent signal obstruction and reflection.

[0045] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. An extended wide-narrow correlator based on GPS L1 signal / L5 signal, characterized in that: include: A first estimation unit, a second estimation unit and a third estimation unit connected in sequence, wherein: each estimation unit will give an estimation value, and the correlator outputs an estimation value of the code delay error at the previous moment after three estimations based on the code delay estimation value; The first estimation unit receives the code delay estimation value The first estimated value of the output code delay error δτ1 and the instantaneous branch correlation value P of the L1 signal L1 , the first estimation unit comprises: an L1 correlator and an L1 phase detector; The second estimation unit receives the first estimation value δτ1, the L1 instant branch correlation value P L1 and the third estimated value of the code delay error δτ3[kl] at the previous N moments, l=1…n, where N is the sliding average window size, k is the current moment, and the second estimated value of the code delay error δτ2 is output. The second estimation unit includes: an L1 signal carrier-to-noise ratio estimator, a window size estimator, and a sliding average window; The third estimation unit receives the code delay estimation value at the previous moment and the second estimation value of the code delay error, and outputs the third estimation value of the code delay error δτ3. The third estimation unit includes: an L5 correlator and an L5 phase detector.

2. The extended wide-narrow correlator based on GPS L1 signal / L5 signal according to claim 1, characterized in that: The L1 correlator receives the code delay estimate value, with one chip as the early and late branch interval Generate three groups of local signals, namely: early branch, instantaneous branch, and late branch; correlate the three groups of local signals with the received signal respectively, and obtain the correlation values ​​of the early, instantaneous, and late branches (E L1 ,P L1 ,L L1 ), where the instantaneous branch correlation value is output; the L1 phase detector uses an early-minus-late phase detector, and the phase detector value δτ is calculated based on the early and late branch correlation values L1 , as the first estimate δτ1=δτ L1 Output.

3. The extended wide-narrow correlator based on GPS L1 signal / L5 signal according to claim 1, characterized in that: The L1 signal carrier-to-noise ratio estimator estimates the L1 carrier-to-noise ratio C / N0 according to the L1 instantaneous branch correlation value within 1s. L1 ; The window size estimator obtains the window size N from the comparison table with the L1 carrier-to-noise ratio; the sliding average window averages the third estimation value of the previous N moments and the first estimation value of the current moment according to the window size, and outputs it as the second estimation value.

4. The extended wide-narrow correlator based on GPS L1 signal / L5 signal according to claim 1, characterized in that: The L5 correlator estimates the code delay The difference between the second estimate of the code delay error δτ2 Centered on the code chip, the early and late branch intervals are Generate three groups of local signals, namely: early branch, instantaneous branch, and late branch; correlate the three groups of local signals with the received signal respectively, and obtain the correlation values ​​of the early, instantaneous, and late branches (E L5 ,P L5 ,L L5 ); L5 phase detector also uses the early-minus-late L5 phase detector, and the phase detector value δτ is calculated based on the correlation value of the early and late branches L5 , the phase detection value is added to the second estimated value of the code delay error (δτ L5 +δτ2), as the third estimate δτ3=δτ L5 +δτ2 output.

5. The extended wide-narrow correlator based on GPS L1 signal / L5 signal according to claim 1, characterized in that: The early-minus-late phase detectors in the first and third estimation units calculate the code delay error Among them: E, L are the correlation values ​​of the early and late branches.

6. The extended wide-narrow correlator based on GPS L1 signal / L5 signal according to claim 1, characterized in that: The L1 signal-to-noise ratio estimator in the second estimation unit estimates the L1 signal-to-noise ratio Where: μ, σ 2 P within 1s L1 The mean and variance of T c is the coherent integration time.

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