A method for unambiguous tracking of B1C signals based on pseudo-exponential function

Abstract

Aiming at the tracking ambiguity problem of the Beidou B1C pilot channel QMBOC (6,1,4 / 33) signal, the present invention proposes and designs a B1C signal unambiguous tracking method based on a pseudo-exponential function, comprising the following steps: (1) performing carrier stripping and code correlation processing on the pilot channel QMBOC (6,1,4 / 33) signal; (2) sending the correlation value to the exponential function module for processing; (3) a discriminator processes the output value of the exponential function module; (4) the discriminator result is processed by a loop filter to control the code ring NCO, adjust the local code phase, and form a closed loop. The present invention can effectively eliminate the secondary peak of the correlation curve, eliminate the false lock point output by the discriminator, and process the correlation result between the received signal and the local signal using the pseudo-exponential function module, thereby realizing unambiguous tracking of the QMBOC (6,1,4 / 33) signal. At the same time, compared with the traditional BPSK-like method, SCPC method and ASPeCT method, the B1C signal unambiguous tracking method based on the pseudo-exponential function of the present invention has better anti-multipath performance.

Description

Technical Field

[0001] The present invention relates to the technical field of signal unambiguous tracking methods, and in particular to a B1C signal unambiguous tracking method based on a pseudo-exponential function. Background Art

[0002] The B1C frequency of the BeiDou-3 navigation system is 1572.42 MHz. The pilot channel utilizes quadrature multiplexed binary offset carrier (QMBOC) modulation. This, along with GPS's time-multiplexed binary offset carrier (TMBOC) modulation and Galileo's composite binary offset carrier (CBOC) modulation, is a derivative of the binary offset carrier (BOC) and is known as the "new system navigation signal." While QMBOC signals bear some similarities to TMBOC and CBOC signals, their time-domain implementation is more complex, making their research more challenging. Compared to traditional BPSK modulation signals, BOC-derived modulation signals offer advantages such as greater compatibility, wider bandwidth, and improved anti-interference capabilities. These signals not only effectively alleviate GNSS frequency band congestion but also improve the ranging accuracy and anti-interference capabilities of navigation systems. However, the spread spectrum code modulated by BOC will have tracking ambiguity problems, resulting in positioning errors of tens or even hundreds of meters in the satellite positioning results. In addition, the tracking error of the code tracking loop will affect the carrier phase tracking accuracy. Therefore, solving the QMBOC signal tracking ambiguity problem is a problem that needs to be faced during the B1C signal synchronization process.

[0003] Currently, ambiguity-free tracking techniques are mainly categorized into the following: Bump-Jumping (BJ), Sideband Processing (B&F), and Side-peaks Cancellation (SC). The BJ method uses additional far-leading and far-lagging correlators to determine whether the instantaneous branch is correctly locked to the main peak. This method is only applicable to low-order BOC signals, and the increased number of correlators makes the hardware structure more complex. B&F methods are divided into single-sided and double-sided B&F. The most representative of these methods is the BPSK-Like method, which converts the BOC signal into one or two BPSK signals through filtering and other means to avoid ambiguity in the BOC subcarrier band. This method results in energy loss and loses the inherent advantages of the BOC signal, such as high tracking accuracy and strong multipath immunity. SC methods include the Auto-Correlation Side Peak Cancellation Technique (ASPeCT) and Subcarrier Phase Cancellation (SCPC). The ASPeCT method uses a locally regenerated correlation function to replace the correlation function of the BOC signal, retaining the BOC signal modulation characteristics; Reference [8] Chae K, Seong R. An unambiguous correlation function for generic sine-phased binary offset carrier signal tracking [J]. Computers and Electrical Engineering, 2016, 49 (10): 161-172. The subcarrier is divided into multiple rectangular pulses and then correlated with the received signal respectively, and then the tracking ambiguity problem is solved by recombining the new correlation function; Reference [9] Qian Sujuan, Yin Xinfu. Research on BOC modulation signal capture and tracking based on ASPeCT [J]. Modern Electronic Technology, 2016, 39 (21): 65-69. ASPeCT is applied to the receiver capture and tracking module to further verify the effectiveness of the method. The SCPC method eliminates the BOC signal ambiguity problem through subcarriers. The shape of its autocorrelation function is similar to that of the BPSK-like method, and therefore has the same shortcomings. The PCF method designs two local code vectors that are correlated with the received signal separately and then synthesized to generate a correlation function without side peaks, thereby achieving the purpose of unambiguous tracking. This method can retain the characteristics of BOC signal tracking with high accuracy and strong anti-multipath capability.In addition, the literature

[13] Hodgart M, Blunt P, Unwin M. Double estimator a new receiver principle for tracing BOC signals. Inside GNSS, 2008: 26-36. proposed a dual-loop tracking method, which tracks the spread spectrum code and subcarrier separately and combines the tracking results to eliminate the tracking ambiguity. However, simply combining the two tracking results cannot improve the anti-multipath capability; the literature

[14] Yao Z, Lu MQ, Unambiguous sine-phased binary offset carrier modulated signal acquisition technique. IEEE Transactions on Wireless Communications, 2010, 9(2): 577-580. proposed a GRASS method, which is only applicable to sinusoidal BOC signals and is complex to implement. The current unambiguous tracking technology cannot achieve both the tracking ambiguity elimination effect and the hardware implementation complexity. The algorithm with the best tracking ambiguity elimination effect is often more complex to implement. Therefore, an unambiguous tracking method that takes into account both the tracking ambiguity elimination effect and the implementation complexity needs further research. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in order to solve the problems existing in the above-mentioned background technology, an improved B1C signal unambiguous tracking method based on a pseudo-exponential function is provided. By adding an exponential function module at the previous stage of the discriminator, the curve properties of the exponential function and the fact that the secondary peak of the autocorrelation function of the QMBOC signal (6, 1, 4 / 33) is negative are utilized to limit the secondary peak of the QMBOC signal autocorrelation, thereby eliminating the secondary peak and achieving unambiguous tracking.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a B1C signal unambiguous tracking method based on a pseudo-exponential function, the steps are as follows:

[0006] Step 1: Carrier stripping and code correlation processing are performed on the pilot channel QMBOC (6, 1, 4 / 33) signal;

[0007] Step 2: Send the relevant value to the exponential function module for processing;

[0008] Step 3: The discriminator processes the output value of the exponential function module;

[0009] Step 4: The discriminator result is processed by the loop filter to control the code loop NCO, adjust the local code phase, and form a closed loop.

[0010] The specific step 1 is: the method of performing carrier stripping and code correlation processing on the pilot channel QMBOC (6, 1, 4 / 33) signal is as follows:

[0011] The receiver receives the B1C signal and feeds the pilot channel QMBOC (6,1,4 / 33) signal into the tracking loop. After mixing the local in-phase and quadrature carriers, the signal carrier is stripped off to obtain the I and Q branches. This is then correlated with the leading, immediate, and lagging local codes to obtain six correlation values: IE, IP, IL, QE, QP, and QL.

[0012] The specific method of step 2 is: sending the correlation value to the exponential function module for processing is as follows:

[0013] Modify the exponential function and obtain an expression that meets the requirements:

[0014] y=a x -1(a>1)

[0015] Normalize the above formula and make it pass through (0,0) and (1,1) to get the pseudo-exponential function expression:

[0016]

[0017] As the value of a increases, the secondary peak elimination effect is more ideal and the remaining main peak is narrower. When a = 100, the secondary peak is completely eliminated, and the purpose of unambiguous tracking can be achieved. Further processing, the autocorrelation function can be obtained from the exponential function as follows:

[0018]

[0019] The specific step three is: the discriminator processes the output value of the exponential function module as follows:

[0020] The discriminator uses a non-coherent advance-minus-lag power phase detector with a correlator interval of 1 / 16 code chip. Under infinite bandwidth processing, the discriminator output is processed by SCPC, ASPeCT, BPSK-like and pseudo-exponential function (a=100) methods.

[0021] The beneficial effects of the present invention are:

[0022] (1) The unambiguous tracking method of the B1C signal based on the pseudo-exponential function of the present invention can effectively eliminate the secondary peak of the correlation curve and the false lock point output by the discriminator, thereby realizing unambiguous tracking of the QMBOC (6, 1, 4 / 33) signal;

[0023] (2) Compared with the traditional BPSK-like method, SCPC method and ASPeCT method, the pseudo-exponential function method described in this paper has better anti-multipath performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and examples.

[0025] Figure 1 This is the overall flow chart of the unambiguous tracking method described in the present invention.

[0026] Figure 2 is the autocorrelation curve of QMBOC(6,1,4 / 33).

[0027] Figure 3 This is the QMBOC (6,1,4 / 33) phase-locked detection curve.

[0028] Figure 4 It is a pseudo-exponential function curve.

[0029] Figure 5 These are the correlation curves after processing with different methods.

[0030] Figure 6 These are the correlation curves after the pseudo-exponential function method uses different parameters a.

[0031] Figure 7 Output curves of the discriminator for different methods.

[0032] Figure 8 The phase discrimination curves after being processed with different parameters a using the pseudo-exponential function method.

[0033] Figure 9 is the multipath error with different parameters a of the pseudo-exponential function method.

[0034] Figure 10 is the average multipath error of the pseudo-exponential function method with different parameters a.

[0035] Figure 11 is the multipath error of different methods.

[0036] Figure 12 is the average multipath error of different methods. DETAILED DESCRIPTION

[0037] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0038] like Figure 1 The steps of the present invention are as follows:

[0039] Step 1: Carrier stripping and code correlation processing are performed on the pilot channel QMBOC (6, 1, 4 / 33) signal.

[0040] Step 2: Send the relevant value to the exponential function module for processing.

[0041] Step 3: The discriminator processes the output value of the exponential function module.

[0042] Step 4: The discriminator result is processed by the loop filter to control the code loop NCO, adjust the local code phase, and form a closed loop.

[0043] The present invention takes the BeiDou-3 B1C pilot channel QMBOC (6, 1, 4 / 33) signal as the object to perform anti-multipath performance analysis, and compares it with the SCPC method, ASPeCT, and BPSKlike method to explain the specific processing process of the present invention in detail.

[0044] In step 1, for ease of processing, only one multipath signal consisting of positive and negative phase multipath error envelopes is processed, the multipath-direct signal energy ratio is 0.5, and the correlator interval is 0.1 chip; the QMBOC (6, 1, 4 / 33) autocorrelation curve is as follows: Figure 2 As shown, the curve contains two secondary peaks in addition to the main peak. It is precisely because of these two secondary peaks that the tracking ambiguity problem occurs. The QMBOC (6, 1, 4 / 33) phase detection curve is shown in Figure 3 As shown in the figure, the signal phase detection curve crosses the zero phase five times, and there are two false lock points. During the tracking phase, due to noise, dynamic stress, short-term loss of lock caused by occlusion, etc., the tracking loop may deviate to the false lock point, resulting in tracking ambiguity.

[0045] In step 2, the pseudo-exponential function curve is as follows Figure 4 As shown, the autocorrelation function image after pseudo-exponential function processing is as follows Figure 5 As shown in Figure 2, when a=100, the side peaks on both sides of the QMBOC (6, 1, 4 / 33) correlation image are eliminated after processing by this method. Compared with SCPC, ASPeCT, and BPSK-like methods, this method has no residual side peaks and has a narrower correlation peak, resulting in higher tracking accuracy. The correlation curves of the pseudo-exponential function method after processing with different parameters a are shown in Figure 2. Figure 6 As shown in Figure 1, as the value of a increases, the secondary peak elimination effect is more ideal and the remaining main peak is narrower. When a = 100, the secondary peak is completely eliminated, and the purpose of unambiguous tracking can be achieved.

[0046] In step 3, under infinite bandwidth processing, the discriminator outputs after SCPC, ASPeCT, BPSK-like and pseudo-exponential function (a=100) processing, and the phase discrimination results after processing when the pseudo-exponential function parameter a is 5, 20, and 100 respectively are as follows: Figure 7 、 8As shown in FIG, the pseudo-exponential function method phase discrimination result completely eliminates the false lock point, and can achieve the purpose of unambiguous tracking; the multipath error and average multipath error after the QMBOC (6,1,4 / 33) signal is processed by the pseudo-exponential function method of the present invention are shown in FIG. Figure 9 and Figure 10 As shown in Figure 1, as the parameter a increases, the code loop multipath envelope area gradually becomes smaller, and the average multipath error becomes smaller. That is, the larger the parameter a is, the better the anti-multipath performance is and the higher the code loop tracking accuracy is. Under 8MHz bandwidth processing, the multipath envelope error and average multipath error of the QMBOC (6, 1, 4 / 33) signal after being processed by ASPeCT, BPSK-like, SCPC and pseudo-exponential function (a=100) are shown in Figure 1. Figure 11 and Figure 12 As shown in the figure, for the QMBOC (6, 1, 4 / 33) signal, the code loop multipath envelope area, i.e., the multipath error, and the average multipath error after processing by the pseudo-exponential function method of the present invention are smaller than those of the traditional BPSK-like method, SCPC method, and ASPeCT method. That is, the pseudo-exponential function method has better anti-multipath performance and higher code loop tracking accuracy.

[0047] Simulation results show that this method can effectively eliminate the secondary peaks of the correlation curve and the false lock points of the discriminator output, achieving unambiguous tracking of the QMBOC (6, 1, 4 / 33) signal. Furthermore, compared with traditional BPSK-like, SCPC, and ASPeCT methods, the pseudo-exponential function method described in this paper has better anti-multipath performance.

[0048] In summary, the present invention addresses the tracking ambiguity problem of the Beidou B1C pilot channel QMBOC (6,1,4 / 33) signal and proposes and designs a B1C signal unambiguous tracking method based on a pseudo-exponential function. The correlation result between the received signal and the local signal is processed using a pseudo-exponential function module to achieve the purpose of unambiguous tracking. The present invention includes the following steps: (1) performing carrier stripping and code correlation processing on the pilot channel QMBOC (6,1,4 / 33) signal; (2) sending the correlation value to the exponential function module for processing; (3) the discriminator processes the output value of the exponential function module; (4) the discriminator result is processed by a loop filter to control the code loop NCO, adjust the local code phase, and form a closed loop. It has been verified that the present invention can effectively eliminate the secondary peak of the correlation curve and the false lock point output by the discriminator, thereby achieving unambiguous tracking of the QMBOC (6,1,4 / 33) signal. At the same time, compared with the traditional BPSK-like method, SCPC method and ASPeCT method, the B1C signal unambiguous tracking method based on the pseudo-exponential function of the present invention has better anti-multipath performance.

[0049] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A B1C signal unambiguous tracking method based on a pseudo-exponential function, characterized by: Here are the steps: Step 1: Carrier stripping and code correlation processing are performed on the pilot channel QMBOC (6, 1, 4 / 33) signal; Step 2: Send the relevant value to the exponential function module for processing; Step 3: The discriminator processes the output value of the exponential function module; Step 4: The discriminator result is processed by the loop filter to control the code loop NCO, adjust the local code phase, and form a closed loop; The specific method of step 2 is: sending the correlation value to the exponential function module for processing is as follows: Modify the exponential function and obtain an expression that meets the requirements: ; Normalize the above formula and make it pass through (0,0) and (1,1) to get the pseudo-exponential function expression: ; As the value of a increases, the secondary peak elimination effect is more ideal, and the remaining main peak is narrower. When a = 100, the secondary peak is completely eliminated, and the purpose of unambiguous tracking can be achieved. Further processing, the autocorrelation function can be obtained from the exponential function as follows: 。 2. The unambiguous tracking method for B1C signals based on a pseudo-exponential function according to claim 1, characterized in that: The specific step 1 is: the method of performing carrier stripping and code correlation processing on the pilot channel QMBOC (6, 1, 4 / 33) signal is as follows: The receiver receives the B1C signal and feeds the pilot channel QMBOC (6,1,4 / 33) signal into the tracking loop. After mixing the local in-phase and quadrature carriers, the signal carrier is stripped off to obtain the I and Q branches. This is then correlated with the leading, immediate, and lagging local codes to obtain six correlation values: IE, IP, IL, QE, QP, and QL.

3. The unambiguous tracking method for B1C signals based on a pseudo-exponential function according to claim 1, characterized in that: The specific step three is: the discriminator processes the output value of the exponential function module as follows: The discriminator uses a non-coherent advance-minus-lag power phase detector with a correlator interval of 1 / 16 code chip. Under infinite bandwidth processing, the discriminator output is processed by SCPC, ASPeCT, BPSK-like and pseudo-exponential function (a = 100).

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