High-security ranging code design method based on pseudo-satellite system

Abstract

The invention discloses a high-security ranging code design method based on a pseudo-satellite system, and the method comprises the steps: employing a Legendre polynomial sequence based on a quadratic residue theory, introducing an interception point parameter and a phase difference parameter, and generating a Weil code through a shift XOR operation; and generating a ranging code main code sequence from the generated Weil code sequence through cyclic interception and truncation operation, and introducing a periodic code changing scheme to further enhance the security of the code sequence. According to the method disclosed by the invention, the security performance of the ranging code is further improved on the premise of basically not influencing the correlation, so that the ranging code is more suitable for being used in a scene with high requirements on confidentiality and correlation.

Description

Technical Field

[0001] The invention belongs to the field of navigation technology, and in particular relates to a high-security ranging code design method based on a pseudo-satellite system. Background Art

[0002] The Global Navigation Satellite System (GNSS) is widely used in all walks of life due to its powerful functions, but as a space-based radio navigation system, it still has many inherent defects. Since GNSS satellites are about 20,000 kilometers away from the earth's surface, the navigation signal is very weak when it reaches the receiver, and the signal is easily affected by various interferences during the propagation process. Its service performance is significantly reduced in complex environments such as tunnels, indoors, cities and canyons. For this reason, various alternative and enhanced auxiliary systems are being developed at an accelerated pace, among which the ground-based pseudo-satellite navigation and positioning system (Pseudolite, PL) has become one of the research focuses.

[0003] A pseudo-satellite is a device used to generate and send GNSS-like signals. It can not only serve as an augmentation system for GNSS in complex environments, but also provide independent navigation and positioning services in GNSS-denied environments. Compared with GNSS satellites, pseudo-satellites are very close to user receivers, usually within a range of several hundred meters to several kilometers from users. At the same time, the location of pseudo-satellite base stations is also fixed and is often set on the ground or in low altitudes, so there is no need to consider the impact of ionospheric delay. The principle of the pseudo-satellite system is similar to that of the GNSS system. It also requires at least four base stations to provide navigation and positioning services. The base station sends out navigation signals, and the user receiver receives the signals to calculate the distance between the user receiver and the base station. To ensure the effectiveness and reliability of the system, the ranging code used by the current pseudo-satellite system is basically the same as that of the existing navigation system, that is, most of them use Gold code sequences to form ranging codes.

[0004] Gold code is generated by modulo-2 sum of m-sequences generated by two linear feedback shift registers. Its generation method is relatively simple and has better correlation performance and security performance than m-sequence. Therefore, Gold code sequence is widely used in pseudo-satellite systems. However, Gold code is difficult to meet the needs in some scenarios with higher requirements for confidentiality and correlation. Therefore, the idea of ​​using Weil code sequence to form ranging code has become one of the research focuses. Compared with Gold code, Weil code is generated differently. It is generated by two Legendre sequences (Legendre) through cyclic shift and then modulo-2 sum. This generation method makes it have better correlation performance and security performance than Gold code, so it is more suitable for use in navigation systems with high confidentiality and high correlation requirements. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a high-security ranging code design method based on a pseudo-satellite system, using a Legendre polynomial sequence based on quadratic residue theory, wherein interception point parameters and phase difference parameters are introduced, and Weil codes are generated by shift XOR operations; the generated Weil code sequence is then used to generate a ranging code main code sequence through cyclic interception and truncation operations, and a periodic code switching scheme is introduced to further enhance the security of the code sequence. The method of the present invention further improves the security performance of the ranging code without substantially affecting the correlation, making it more suitable for use in scenarios with high confidentiality and correlation requirements.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] Step 1: Generate Legendre sequence L(k):

[0008]

[0009] The value range of k is 0 to (N-1), generating a Legendre sequence of length N; the value of x in the formula is 1 to (N-1);

[0010] Step 2: Compare and screen the interception point parameters p and phase difference parameters w of the code sequences corresponding to different PRN numbers, and select a1 groups of different code sequences; the range of the interception point parameters p and phase difference parameters w specified in the Weil code generation process is

[0011] Step 3: Calculate and generate the Weil code sequence after cyclic truncation;

[0012]

[0013] Replace the parameter k in the formula with (n+p-1) mod N, and finally calculate the Weil code sequence with a total length of N after cyclic truncation;

[0014] Step 4: Take the first m bits of the Weil code sequence obtained in step 3 to obtain a final ranging code sequence of length m;

[0015] Step 5: Repeat steps 1 to 4 to generate multiple different Weil code sequence sets.

[0016] Step 6: A periodic code change strategy is adopted for the generated ranging code sequence, that is, the intercept point parameter p and the phase difference parameter w of the Weil code are changed at regular intervals, so as to achieve the goal of changing the Weil code sequence to improve security; the specific operations are as follows:

[0017] Step 6-1: Determine the code hopping interval parameter period, take "hour" as the code hopping interval unit, set period = h to indicate that the code hopping interval is once every h hours, and record the current time with parameter t;

[0018] Step 6-2: Set the parameter addnum of the intercept point and phase difference change value, and set its initial value to 1; adjust the addnum value according to the current time information, and the adjustment principle is: addnum (n) =addnum (n-1) +t (n) , the upper right corner superscript represents the serial number information;

[0019] Step 6-3: Specify the tth (n) The code sequence phase difference parameter w and intercept point parameter p at time PRN number s are

[0020] Step 6-4: Use modulus operation to limit the range of the phase difference w and the intercept point p to ensure that the range of the phase difference parameter w is within The intercept point parameter p varies between the range [1, N]; when When using the modulus operation, Complete the setting of the phase difference parameters at this moment; similarly, set the intercept point parameters. When using the modulus operation, Complete the setting of the intercept point parameter p at this moment;

[0021] Step 6-5: Generate different Weil code sequence sets that change at any time.

[0022] Preferably, a1=63.

[0023] The beneficial effects of the present invention are as follows:

[0024] The present invention uses the Weil code sequence to form the ranging code, because the Legendre sequence itself has the characteristics of orthogonality and low cross-correlation, and the Weil code is generated by the Legendre sequence shift XOR, which increases the orthogonality and anti-interference performance of the generated Weil code sequence, so it has better autocorrelation and cross-correlation performance than the Gold code sequence; and from the values ​​of the phase difference parameter w and the intercept point parameter p, it can be seen that the Weil code has Different code sequence combinations make the Weil code more secure. At the same time, a periodic code switching strategy is adopted in the design, which stipulates that the phase difference parameters and interception point parameters of the Weil code sequence change over time, thereby generating different sets of Weil code sequences at different times. This strategy further improves the security performance of the ranging code without basically affecting the correlation, making it more suitable for use in scenarios with high confidentiality and correlation requirements, such as controlling navigation systems, including aircraft positioning and navigation systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of a method for generating a high-security ranging code in the present invention;

[0026] Figure 2 This is a comparison chart of the correlation between Weil code and Gold code between PRN numbers 1 and 2.

[0027] Figure 3 Figure 2 is the cross-correlation performance diagram of the Weil codes with PRN numbers 1 and 2 after the 1st and 6th code hopping. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0029] Code length and code rate are important parameters of ranging codes. The two are closely related and have a significant impact on the resolution, bandwidth and transmission characteristics of the signal.

[0030] The code length and code rate are usually represented by m and Rc respectively, and their relationship with the code period T can be expressed as:

[0031]

[0032] The code rate determines the time resolution of the signal. A higher code rate corresponds to a shorter code chip time, which can provide higher time resolution, thereby allowing the receiver to measure the arrival time of the signal more accurately.

[0033] The code length will affect the system's anti-interference performance and ranging accuracy. Longer code sequences have better correlation characteristics, which helps to improve the ranging accuracy of the code sequence and the anti-interference performance of the signal.

[0034] Considering the ranging accuracy and anti-interference performance of the ranging code, the code rate R is specified. c It is 10.23Mcps.

[0035] Since the length of the Legendre sequence must be a prime number, a Legendre sequence of N=10243 is generated here to generate a Weil code sequence with a code length of 10243, and then the code sequence with a length of m=10230 bits before the original sequence is taken to generate a ranging code sequence.

[0036] According to the formula, the corresponding ranging code period is 1ms.

[0037] Finally, the number of base stations p to be selected is determined, and p groups of different ranging codes are selected from the preferred sequence. Generally, the value of p is 5 to 8. In the embodiment, 6 groups of code sequences are selected, and the PRN numbers are 1, 2, 8, 9, 11, and 12 respectively. The specific parameters are shown in Table 1.

[0038] Table 1

[0039]

[0040]

[0041] The ranges of the phase difference parameter (w) and the interception point parameter (p) are: w∈[1,5121], p∈[1,10243]; at this time, there are a total of w*p=52454403 code family capacities. Preferably, 20 groups are selected, that is, a1=20.

[0042] The parameter for periodic code hopping is specified as period=3, that is, the code hopping operation is performed every 3 hours.

[0043] like Figure 1 As shown, the specific steps of the embodiment are:

[0044] Step 1: First generate the Legendre sequence L(k) according to the formula:

[0045]

[0046] The value range of k is 0 to 10242, generating a Legendre sequence of length N; the value of x in the formula is 1 to 10242;

[0047] Step 2: Compare and screen the code sequence interception point parameters (p) and phase difference parameters (w) corresponding to different PRN numbers, and select and generate 20 groups of different code sequences.

[0048] The value ranges of these two parameters in the Weil code generation process are specified as w∈[1,5121], p∈[1,10243];

[0049] Step 3: Calculate and generate the initial Weil code sequence after cyclic truncation;

[0050]

[0051] In this step, the parameter k in the formula is replaced by (n+p-1) mod 10243. Finally, the Weil code sequence after cyclic truncation can be calculated;

[0052] Step 4: Take the first m=10230 bits of each group of truncated sequences obtained in step 3, and finally obtain a ranging code sequence with a length of 10230.

[0053] It is stipulated that the length of the truncated sequence should be as consistent as possible with the length of the original Weil code sequence to minimize the impact on the correlation of the code sequence;

[0054] Step 5: Repeat steps 1 to 4 to generate multiple sets of different Weil code sequences. Here, steps 1 to 4 need to be performed 20 times to generate 20 sets of sequences.

[0055] Step 6: A periodic code switching strategy is adopted for the generated sequence, that is, the intercept point parameter (p) and phase difference parameter (w) of the Weil code are changed at regular intervals, so as to achieve the goal of changing the Weil code sequence to improve security.

[0056] The specific steps for implementing the strategy are as follows:

[0057] Step 6-1: Determine the code hopping interval parameter period, with "hour" as the code hopping interval unit, set period = 3 to indicate that the code hopping interval is once every 3 hours, and record the current time with parameter t;

[0058] Step 6-2: Set the parameter addnum of the interception point and phase difference change value, set its initial value to 1, and then adjust the addnum value according to the current time information (the upper right corner subscript represents the serial number information). The adjustment principle is: addnum (n) =addnum (n-1) +t (n) ;

[0059] Step 6-3: Specify the tth (n) The code sequence phase difference parameter w and intercept point parameter p at time PRN number s are

[0060] Step 6-4: Use the modulus operation to limit the variation range of the phase difference parameter w and the intercept point parameter p. It is necessary to ensure that the variation range of the phase difference parameter w is between [1,5121] and the intercept point parameter p is between [1,10243].

[0061] When tn When (s)≥5121, use the modulus operation to make Complete the phase difference parameter setting at this moment. Similarly, set the intercept point parameters. When using the modulus operation, Complete the setting of the intercept point parameter p at this moment;

[0062] After step 6 is implemented, different Weil code sequence sets that change at any time can be generated.

[0063] In this embodiment, starting from the hour, the value of t is 0, 3, 6, 9, 12, 15, 18, 21, a total of 8 times, and the value of the change parameter addnum after the end of different times is 1, 4, 10, 19, 31, 46, 64, 85 respectively.

[0064] Figure 2 The comparison chart of the correlation between Weil code and Gold code between PRN No. 1 and 2 is shown. It can be seen from the figure that the cross-correlation distribution of Weil code is compact and clustered, with a smaller coverage range and a lower noise floor;

[0065] Figure 3 The cross-correlation performance diagram of Weil codes with PRN numbers 1 and 2 after the 1st and 6th code hopping is shown. By calculation, the maximum correlation sidelobe energy after code hopping is 32.0327dB and 31.6025dB respectively.

Claims

1. A high-security ranging code design method based on a pseudo-satellite system, characterized in that: The steps include: Step 1: Generate Legendre sequence L(k): The value range of k is 0 to (N-1), generating a Legendre sequence of length N; the value of x in the formula is 1 to (N-1); Step 2: Compare and screen the interception point parameters p and phase difference parameters w of the code sequences corresponding to different PRN numbers, and select a1 groups of different code sequences; the range of the interception point parameters p and phase difference parameters w specified in the Weil code generation process is p∈[1,N]; Step 3: Calculate and generate the Weil code sequence after cyclic truncation; W(k;w)=L(k)⊕L((k+w)modN) Replace the parameter k in the formula with (n+p-1) mod N, and finally calculate the Weil code sequence with a total length of N after cyclic truncation; Step 4: Take the first m bits of the Weil code sequence obtained in step 3 to obtain a final ranging code sequence of length m; Step 5: Repeat steps 1 to 4 to generate multiple sets of different Weil code sequence sets; Step 6: A periodic code change strategy is adopted for the generated ranging code sequence, that is, the intercept point parameter p and the phase difference parameter w of the Weil code are changed at regular intervals, so as to achieve the goal of changing the Weil code sequence to improve security; the specific operations are as follows: Step 6-1: Determine the code hopping interval parameter period, take "hour" as the code hopping interval unit, set period = h to indicate that the code hopping interval is once every h hours, and record the current time with parameter t; Step 6-2: Set the parameter addnum of the intercept point and phase difference change value, and set its initial value to 1; adjust the addnum value according to the current time information, and the adjustment principle is: addnum (n) =addnum (n-1) +t (n) , the upper right corner superscript represents the serial number information; Step 6-3: Specify the tth (n) The code sequence phase difference parameter w and intercept point parameter p at time PRN number s are Step 6-4: Use modulus operation to limit the range of the phase difference w and the intercept point p to ensure that the range of the phase difference parameter w is within The intercept point parameter p varies between the range [1, N]; when When using the modulus operation, Complete the setting of the phase difference parameters at this moment; similarly, set the intercept point parameters. When using the modulus operation, Complete the setting of the intercept point parameter p at this moment; Step 6-5: Generate different Weil code sequence sets that change at any time.

2. A method for designing a high-security ranging code based on a pseudo-satellite system according to claim 1, characterized in that: a1＝63。

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