Estimation method for physical layer four-phase complex scrambling code sequence of low earth orbit satellite communication system

Abstract

The invention discloses an estimation method for a physical layer four-phase complex scrambling code sequence of a low earth orbit satellite communication system, which belongs to the technical field of satellite communication and comprises the following steps: screening target signals adopting four-phase physical layer complex scrambling to obtain an equivalent sequence according to an inter-frame BPSK modulation intra-frame QPSK modulation criterion; analyzing the periodicity of the equivalent sequence to obtain an estimated equivalent sequence, performing polynomial matching to obtain a generator polynomial of the estimated equivalent sequence, analyzing to obtain an equivalent sequence generation rule, and generating a local equivalent sequence; traversing according to an equivalent sequence generation rule, generating a candidate adjoint sequence and combining the candidate adjoint sequence with the estimated equivalent sequence to obtain a candidate scrambling code sequence; and descrambling the target signal according to the candidate scrambling code sequence, and if the descrambled target signal meets a judgment condition, outputting the candidate scrambling code sequence as a scrambling code sequence. According to the invention, the problem that the target signal cannot be effectively demodulated due to sampling point phase transformation caused by the fact that the original signal adopts four-phase physical layer complex scrambling in signal blind demodulation is solved.

Description

Technical Field

[0001] The invention relates to an estimation method for a physical layer four-phase complex scrambling code sequence of a low-orbit satellite communication system, and belongs to the technical field of satellite communications. Background Art

[0002] With the rapid development of science and technology, low-orbit satellite communication systems have occupied an increasingly important position in the field of modern communications. Low-orbit satellite communications have significant advantages such as wide coverage, low transmission delay, and low path loss. They can break through the limitations of geographical conditions and achieve seamless communication coverage around the world. In the field of military and national defense, low-orbit satellite communication systems are key infrastructure to ensure the stable operation of remote combat command, intelligence transmission, and military communication networks. They play an irreplaceable role in improving the combat effectiveness, strategic deployment capabilities, and emergency response speed of the military. In the civilian field, they are widely used in remote area communications, aviation and navigation communications, emergency rescue communications, and Internet of Things data transmission. They have greatly promoted the interconnection of global information, promoted social and economic development and progress, and improved human quality of life and production efficiency. Therefore, the importance of low-orbit satellite communication scenarios is self-evident.

[0003] Although encryption measures are used in low-orbit satellite communication systems to prevent third parties from obtaining additional information from intercepted signals, these problems are mainly caused by the four-phase complex scrambling technology used in the physical layer, which causes the phase change of the sample points, making it impossible to effectively demodulate the target signal. In traditional network protection systems, encryption measures are often limited to the link layer, which exposes the information of the entire physical layer. When a third party successfully intercepts a signal, they can demodulate it by extracting signal parameters and estimating its modulation method, and even recover the transmitted bit sequence through processes such as inverse channel coding. However, in the DVB-S2 standard, although the I and Q two-way complex scrambling code encryption method implemented at the physical layer is adopted, in theory, if the intercepting party cannot descramble, the demodulation work will be difficult to carry out. But the reality is that most of the existing scrambling code sequence recovery algorithms focus on the scrambling code of the link layer, which is not applicable to the complex code used in the physical layer, especially the problem of sample point phase change caused by four-phase complex scrambling, which has become a major obstacle to effective demodulation. Summary of the invention

[0004] The purpose of the present invention is to provide an estimation method for a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system. The scrambling code sequence is obtained by reversely analyzing a target signal, and the target signal is blindly descrambled to solve the problem in the prior art that the target signal cannot be effectively demodulated due to the phase change of the sample points caused by the use of four-phase physical layer complex scrambling.

[0005] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions.

[0006] The present invention provides a method for estimating a physical layer four-phase scrambling code sequence for a low-orbit satellite communication system, comprising:

[0007] From the target low-orbit satellite communication system frame data set, according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria, the target frame data that can be used for four-phase complex scrambling code sequence estimation is screened out;

[0008] Assuming that the target frame data is a continuous zero sequence before modulation, the equivalent sequence is estimated according to the scrambling rule of the four-phase complex scrambling code to obtain an estimated equivalent sequence;

[0009] The delayed autocorrelation method is used to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated. If periodicity does not exist, no processing is performed.

[0010] Using a polynomial matching search algorithm to estimate the generating polynomial of the estimated equivalent sequence, and analyzing the generating rule of the estimated equivalent sequence;

[0011] All possible candidate companion sequences are traversed and generated according to the estimated equivalent sequence generation rule, and the candidate companion sequences and the equivalent sequences are combined into candidate scrambling code sequences;

[0012] The target low-orbit satellite communication system frame data is descrambled using the candidate scrambling code sequence. If the descrambled data meets the characteristics that the frame header / frame tail data has periodicity or the pilot symbol phase is consistent, the candidate scrambling code sequence is output as the scrambling code sequence.

[0013] Further, from the target low-orbit satellite communication system frame data set, according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria, the target frame data capable of estimating the four-phase scrambling code sequence is screened out, wherein the four-phase scrambling code sequence is expressed as:

[0014] ;

[0015] In the formula, Represents the four-phase scrambling code sequence represents the intra-frame index, is the frame length.

[0016] Further, the four-phase complex scrambling code sequence is defined by using an equivalent sequence and a companion sequence, wherein the four-phase complex scrambling code sequence is defined as:

[0017] ;

[0018] in, represents the four-phase scrambling code sequence, is an equivalent sequence, is the companion sequence, where any four-phase scrambling sequence can be represented by a set of equivalent sequences and the adjoint sequence The only certainty.

[0019] Furthermore, the equivalent sequence and the adjoint sequence share the same generating polynomial. The pseudo-random sequence is a pseudo-random sequence of order, wherein the pseudo-random sequence generating polynomial is expressed as:

[0020] ;

[0021] In the formula, represents the pseudo-random sequence generating polynomial, is the generating polynomial order, The first linear feedback shift register in the generator polynomial register values, where x i ∈ [ x 1 , x 2 ,..., x L ] , For the The tap coefficients of the registers, where c i ∈ [ c 1 , c 2 ,..., c L ] ;

[0022] Wherein, if the equivalent sequence is If the pseudo-random sequence of order is , then the equivalent sequence has the following properties:

[0023] ;

[0024] In the formula, Represents an equivalent sequence.

[0025] Furthermore, the target low-orbit satellite communication system frame data set is expressed as:

[0026] ;

[0027] In the formula, represents the target low-orbit satellite communication system frame dataset, represents the number of frames in the dataset, Indicates the frame data set Frame data, represents the intra-frame index, represents the frame length. Assuming that the target low-orbit satellite communication system uses physical layer four-phase multiplexing scrambling at the transmitting end, the frame data before scrambling is , the scrambled frame data is expressed as:

[0028] ;

[0029] In the formula, Indicates the scrambled frame data. represents the exponential function, is an imaginary unit;

[0030] The target low-orbit satellite communication system frame data set It is expressed as:

[0031] ;

[0032] in, Indicates the data before scrambling of the frame. represents the exponential function, Is an imaginary unit.

[0033] Furthermore, the intra-frame QPSK modulation and inter-frame BPSK modulation criteria include:

[0034] When the frame data before scrambling When BPSK modulation is used, the signal samples in the same frame present a QPSK modulation pattern;

[0035] When the frame data before scrambling When BPSK modulation is used, signal samples at the same position within different frames present a BPSK modulation pattern.

[0036] Furthermore, assuming that the target frame data is a continuous zero sequence before modulation, an equivalent sequence is estimated according to the scrambling rule of the four-phase complex scrambling code to obtain an estimated equivalent sequence, wherein the estimated equivalent sequence is expressed as:

[0037] ;

[0038] In the formula, To estimate the scrambling code equivalent sequence, is the remainder function, is the inverse tangent function, is the target frame data, It is the frame index set of the target frame data.

[0039] Furthermore, the time-delay autocorrelation method is used to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated, and if periodicity does not exist, no processing is performed, wherein the time-delay autocorrelation function is used to estimate the internal periodicity of the equivalent sequence. The time-delay autocorrelation function is expressed as:

[0040] ;

[0041] in, is the delayed autocorrelation function, represents the estimated equivalent sequence, Indicates the number of delayed samples, is the intra-frame index, is the frame length.

[0042] Furthermore, a polynomial matching search algorithm is used to estimate the generating polynomial of the estimated equivalent sequence, and the generating rule of the estimated equivalent sequence is analyzed, wherein the homogeneous linear equation group corresponding to the polynomial matching search algorithm is expressed as:

[0043] [ Z ^ u ( 1 ) Z ^ u ( 2 ) ⋯ Z ^ u ( L ) Z ^ u ( L + 1 ) Z ^ u ( 2 ) Z ^ u ( 3 ) ⋯ Z ^ u ( L + 1 ) Z ^ u ( L + 2 ) ⋮ ⋮ ⋱ ⋮ ⋮ Z ^ u ( D ) Z ^ u ( D + 1 ) ⋯ Z ^ u ( L + D − 1 ) Z ^ u ( L + D ) ] ⋅ [ 1 c 1 ⋮ c L − 1 c L ] = 0 ;

[0044] in, represents the order of the generating polynomial, represents the dimension of the homogeneous linear system, represents the estimated scrambling code equivalent sequence, where .

[0045] Furthermore, the candidate scrambling code sequence expression is:

[0046] ;

[0047] in, is the candidate scrambling code sequence, is a candidate adjoint sequence, To estimate the scrambling code equivalent sequence.

[0048] Furthermore, the target low-orbit satellite communication system frame data is descrambled using the candidate scrambling code sequence. If the descrambled data meets the characteristics that the frame header / frame tail data has periodicity or the pilot symbol phase is consistent, the candidate scrambling code sequence is output as the scrambling code, wherein the descrambling process is expressed as:

[0049] ;

[0050] In the formula, represents the target low-orbit satellite communication system frame dataset, Represents the descrambled frame data signal, represents the exponential function, Is an imaginary unit.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. The four-phase scrambling code sequence estimation method adopted by the present invention can estimate the physical layer scrambling code of an unknown system in the absence of sufficient prior information, crack its physical layer encryption to promote demodulation, and further carry out signal analysis at the link layer. In actual work, the method proposed by the present invention has successfully reversed the physical layer scrambling code of a foreign low-orbit satellite communication system, solving the problem in the prior art that the sample point phase change caused by the use of four-phase physical layer scrambling cannot effectively demodulate the target signal.

[0053] 2. The present invention transforms the problem of scrambling code sequence estimation into the problem of equivalent sequence estimation and adjoint sequence estimation, providing ideas and breakthroughs for scrambling code sequence estimation.

[0054] 3. The present invention proposes that if the descrambled data meets the periodicity of the frame header / frame tail data or the consistency of the pilot symbol phase, the descrambling is judged to be successful, which solves the problem of how to prove the success of descrambling in the context of non-cooperative communication. The three criteria of periodicity of the frame header / frame tail data or the consistency of the pilot symbol phase are all of practical significance in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 FIG. 1 is a schematic diagram of a method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system provided by an embodiment of the present invention;

[0056] Figure 2 Shown is a schematic diagram of screening target signals provided by an embodiment of the present invention;

[0057] Figure 3 It is a schematic diagram of performing sequence periodicity analysis on an equivalent sequence whose sequence length exceeds a threshold value by using a delayed autocorrelation function provided by an embodiment of the present invention;

[0058] Figure 4 FIG. 1 is a schematic diagram of performing polynomial matching on an estimated equivalent sequence provided by an embodiment of the present invention;

[0059] Figure 5 The figure is a schematic diagram of an analysis of equivalent sequence generation rules provided by an embodiment of the present invention;

[0060] Figure 6 The figure shows a comparison diagram of pilot symbols of a target signal before and after descrambling of a real-acquired signal of a satellite system provided by an embodiment of the present invention;

[0061] Figure 7 The figure is a schematic diagram of comparing the autocorrelations of the frame header synchronization symbols of the target signal before and after descrambling of the actual signal collected by the satellite system provided by an embodiment of the present invention;

[0062] Figure 8 The figure shows a time domain signal comparison diagram of the target signal frame tail before and after descrambling of the actual signal collected by the satellite system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. The embodiments of the present invention and the technical features in the embodiments may be combined with each other unless there is a conflict.

[0064] The term "and / or" is only a description of the association relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " generally indicates that the related objects are in an "or" relationship.

[0065] Example 1

[0066] like Figure 1 As shown, this embodiment introduces a method for estimating a physical layer four-phase scrambling code sequence for a low-orbit satellite communication system, including:

[0067] Step 1: From the target low-orbit satellite communication system frame data set, according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria, select the target frame data that can be used for four-phase complex scrambling code sequence estimation.

[0068] The present invention screens out frame data that can be used for estimating a four-phase complex scrambling code sequence from a frame data set of a target low-orbit satellite communication system, and screens according to the criterion of using QPSK modulation within a frame and using BPSK modulation between frames, which is helpful for estimating the scrambling code sequence in subsequent steps, reduces the amount of data to be processed, improves the efficiency of subsequent steps, and ensures that the screened data is suitable for estimating the four-phase complex scrambling code sequence.

[0069] Step 2: Assuming that the target frame data is a continuous zero sequence before modulation, estimate the equivalent sequence according to the scrambling rule of the four-phase complex scrambling code to obtain an estimated equivalent sequence.

[0070] The present invention simplifies the problem by assuming that the target frame data is a continuous zero sequence before modulation and estimating an equivalent sequence according to a four-phase complex scrambling code scrambling rule, thereby obtaining an equivalent sequence having a specific relationship with the original scrambling code sequence.

[0071] Step 3: Use the delayed autocorrelation method to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated. If there is no periodicity, no processing is performed.

[0072] Step 4: Use a polynomial matching search algorithm to estimate the generating polynomial of the estimated equivalent sequence, and analyze the generating rules of the estimated equivalent sequence.

[0073] A generating polynomial is a mathematical representation of a sequence generation rule, which can be used to generate a sequence with the same properties as an estimated equivalent sequence.

[0074] The present invention adopts a polynomial matching search algorithm to estimate the generating polynomial of the estimated equivalent sequence, reveals the generating rule of the estimated equivalent sequence, provides a basis for generating the candidate accompanying sequence in the subsequent steps, and also improves the accuracy and reliability of the scrambling code sequence estimation.

[0075] Step 5: All possible candidate companion sequences are traversed and generated according to the estimated equivalent sequence generation rule, and the candidate companion sequences and the estimated equivalent sequences are combined into candidate scrambling code sequences.

[0076] The present invention traverses and generates all possible candidate companion sequences according to the estimated equivalent sequence generation rule, combines the candidate companion sequences with the estimated equivalent sequences into candidate scrambling code sequences, generates multiple possible scrambling code sequences, increases the chance of finding the correct scrambling code sequence, and ensures the integrity and diversity of the candidate scrambling code sequences through traversal generation.

[0077] Step 6: Use the candidate scrambling code sequence to descramble the target low-orbit satellite communication system frame data. If the descrambled data meets the characteristics of periodicity of the frame header / frame tail data or consistent phase of the pilot symbol, the candidate scrambling code sequence is output as the scrambling code sequence.

[0078] The present invention proposes that the basis for judging the success of descrambling is that the descrambled data meets the periodicity of the frame header / frame tail data or the phase consistency of the pilot symbol, and at the same time, through the verification step, it is ensured that the output scrambling code sequence is correct and effective, thereby improving the reliability and performance of the communication system.

[0079] Example 2

[0080] Based on the same inventive concept as Example 1, this embodiment introduces specific implementation steps of a method for estimating a physical layer four-phase scrambling code sequence for a low-orbit satellite communication system, including:

[0081] Step 1: From the target low-orbit satellite communication system frame data set, according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria, select the target frame data that can be used for four-phase complex scrambling code sequence estimation.

[0082] In this embodiment, the target low-orbit satellite communication system frame data set is expressed as:

[0083] ;

[0084] In the formula, represents the target low-orbit satellite communication system frame dataset, represents the number of frames in the dataset, Indicates the frame data set Frame data, represents the intra-frame index, represents the frame length. Assuming that the target low-orbit satellite communication system uses physical layer four-phase multiplexing scrambling at the transmitting end, the frame data before scrambling is , the scrambled frame data is expressed as:

[0085] ;

[0086] In the formula, Indicates the scrambled frame data. represents the exponential function, is an imaginary unit;

[0087] The target low-orbit satellite communication system frame data set It is expressed as:

[0088] ;

[0089] in, Indicates the data before scrambling of the frame. represents the exponential function, Is an imaginary unit.

[0090] In this embodiment, from the target low-orbit satellite communication system frame data set, according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria, the target frame data capable of estimating the four-phase scrambling code sequence is screened out, wherein the four-phase scrambling code sequence is expressed as:

[0091] ;

[0092] In the formula, Represents the four-phase scrambling code sequence represents the intra-frame index, is the frame length.

[0093] The present invention proposes intra-frame QPSK modulation and inter-frame BPSK modulation criteria by summarizing and analyzing the scrambling characteristics of four-phase complex scrambling codes, including:

[0094] When the frame data before scrambling When BPSK modulation is used, the signal samples in the same frame present a QPSK modulation pattern;

[0095] When the frame data before scrambling When BPSK modulation is used, signal samples at the same position within different frames present a BPSK modulation pattern.

[0096] In this embodiment, when When BPSK modulation is used, for the signal samples in the same frame, due to the four-phase complex scrambling sequence After scrambling, The phase occurs 0, , , The rotation of the final frame signal presents a QPSK modulation pattern; when When BPSK modulation is used, for the signal samples at the same position in different frames, the scrambling sequence used at the same position in different frames is Same, resulting in the final inter-frame signal It still presents the BPSK modulation style. Suppose after filtering, the frame index set of the target frame data is .

[0097] Step 2: Assuming that the target frame data is a continuous zero sequence before modulation, estimate the equivalent sequence according to the scrambling rule of the four-phase complex scrambling code to obtain the estimated equivalent sequence.

[0098] The present invention analyzes the signal characteristics that meet the screening conditions in step 1 to obtain the frame data after screening. The equivalent sequence is estimated in , and the corresponding relationship between the binary equivalent sequence and the quaternary scrambling sequence is obtained as follows:

[0099] ;

[0100] therefore, In this embodiment, about 80 frames of data are screened out, and the constellation diagram drawn according to the frame index dimension is as follows Figure 2 As shown, it can be seen that the frame data presents BPSK modulation at the same intra-frame index, while the indexes in different frames generally present QPSK modulation due to different phases, which conforms to the characteristics of inter-frame BPSK modulation and intra-frame QPSK modulation. Therefore, the filtered signal is expressed as:

[0101] ;

[0102] According to the screening criteria BPSK modulation is used, so for any ,whether , scrambling code sequence value It always appears in pairs in the form of {0, 2} or {1, 3}, so it is assumed that the signal after filtering before sending ,so:

[0103] ;

[0104] In this embodiment, it is assumed that the target frame data is a continuous zero sequence before modulation, and an equivalent sequence is estimated according to the scrambling rule of the four-phase complex scrambling code to obtain an estimated equivalent sequence, wherein the estimated equivalent sequence is expressed as:

[0105] ;

[0106] In the formula, To estimate the scrambling code equivalent sequence, is the remainder function, is the inverse tangent function, is the target frame data, is the frame index set of the target frame data. Thus, the length of the estimated equivalent sequence is 307020.

[0107] In this embodiment, the four-phase complex scrambling code sequence is defined by using an equivalent sequence and a companion sequence, wherein the four-phase complex scrambling code sequence is defined as:

[0108] ;

[0109] in, represents the four-phase scrambling code sequence, is an equivalent sequence, is the companion sequence, where any four-phase scrambling sequence can be represented by a set of equivalent sequences and the adjoint sequence The only certainty.

[0110] Step 3: Use the delayed autocorrelation method to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated. If there is no periodicity, no processing is performed.

[0111] Since the length of the estimated equivalent sequence is 307020, which is a very large number, it is very difficult and unrealistic to directly analyze such a long sequence. Therefore, this embodiment uses the delayed autocorrelation method to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated. If periodicity does not exist, no processing is performed. The delayed autocorrelation function is used to estimate the internal periodicity of the equivalent sequence. The delayed autocorrelation function is expressed as:

[0112] ;

[0113] in, is the delayed autocorrelation function, represents the estimated equivalent sequence, Indicates the number of delayed samples, is the intra-frame index, is the frame length. Estimate the equivalent sequence The delayed autocorrelation function result is as follows Figure 3 As shown, it can be seen that the estimated equivalent sequence has a period of 32767, so the equivalent sequence is truncated, so that the intra-frame index .

[0114] When the estimated equivalent sequence is too long, it is very difficult to analyze the estimated equivalent sequence. If it has a shorter periodicity, it is only necessary to truncate the estimated equivalent sequence and analyze the estimated equivalent sequence within a sub-period.

[0115] Step 4: Use a polynomial matching search algorithm to estimate the generating polynomial of the estimated equivalent sequence, and analyze the generating rule of the estimated equivalent sequence.

[0116] This embodiment uses a polynomial matching search algorithm to estimate the generator polynomial of the estimated equivalent sequence and analyzes the generation rule of the estimated equivalent sequence, wherein the homogeneous linear equation group corresponding to the polynomial matching search algorithm is expressed as:

[0117] [ Z ^ u ( 1 ) Z ^ u ( 2 ) ⋯ Z ^ u ( L ) Z ^ u ( L + 1 ) Z ^ u ( 2 ) Z ^ u ( 3 ) ⋯ Z ^ u ( L + 1 ) Z ^ u ( L + 2 ) ⋮ ⋮ ⋱ ⋮ ⋮ Z ^ u ( D ) Z ^ u ( D + 1 ) ⋯ Z ^ u ( L + D − 1 ) Z ^ u ( L + D ) ] ⋅ [ 1 c 1 ⋮ c L − 1 c L ] = 0 ;

[0118] in, represents the order of the generating polynomial, represents the dimension of the homogeneous linear system, represents the estimated scrambling code equivalent sequence, where All possible combinations of binary tap coefficients are traversed, and when the number of zeros in the homogeneous linear equation group exceeds the threshold, it is considered a successful match.

[0119] In this embodiment, , , if the number of equations in the system that have zero results is greater than When , it is considered to be matched successfully, and the polynomial matching diagram is generated as follows Figure 4 As shown, when the generating polynomial is represented as 8193 in decimal, there are 2970 sets of equations in 3000 sets of equations with the result of zero, so it can be considered that the generating polynomial matches successfully.

[0120] In this embodiment, the equivalent sequence and the adjoint sequence share the same generating polynomial. The pseudo-random sequence is a pseudo-random sequence of order, wherein the pseudo-random sequence generator polynomial is expressed as:

[0121] ;

[0122] In the formula, represents the pseudo-random sequence generating polynomial, is the generating polynomial order, The first linear feedback shift register in the generator polynomial register values, where x i ∈ [ x 1 , x 2 ,..., x L ] , For the The tap coefficients of the registers, where c i ∈ [ c 1 , c 2 ,..., c L ] ;

[0123] Wherein, if the equivalent sequence is If the pseudo-random sequence of order is , then the equivalent sequence has the following characteristics:

[0124] ;

[0125] In the formula, Represents an equivalent sequence.

[0126] Simply finding the estimated equivalent sequence generator polynomial is not enough to independently generate a local equivalent sequence. It is also necessary to find a generation rule for the estimated equivalent sequence. A pseudo-random sequence can be uniquely determined by the generator polynomial and the initial state. The generation rule of the equivalent sequence can be found by traversing all possible initial states and comparing them with the estimated equivalent sequence. The generation rule of the estimated equivalent sequence requires specific analysis of the specific situation. In this embodiment, all initial states corresponding to the generator polynomial estimated in step 4 are traversed to generate a pseudo-random sequence. The pseudo-random sequence is consistent with the estimated equivalent sequence. The schematic diagram of the number of identical bits between Figure 5 As shown, the traversal process of the generator polynomial is equivalent to the cyclic shift process of the pseudo-random sequence. Figure 5 As can be seen from the figure, the estimated equivalent sequence There are a lot of bits in common with the pseudo-random sequences with cyclic shifts of 15858 and 16878, respectively, so an estimated equivalent sequence generation rule is obtained.

[0127] Step 5: All possible candidate companion sequences are traversed and generated according to the estimated equivalent sequence generation rule, and the candidate companion sequences and the equivalent sequences are combined into candidate scrambling code sequences.

[0128] According to the estimated equivalent sequence generation rule, traverse all initial states to generate candidate adjoint sequences .

[0129] In this embodiment, the candidate companion sequence and the estimated equivalent sequence are combined into a candidate scrambling code sequence, and the candidate scrambling code sequence is expressed as:

[0130] ;

[0131] in, is the candidate scrambling code sequence, is a candidate adjoint sequence, To estimate the scrambling code equivalent sequence.

[0132] Step 6: Use the candidate scrambling code sequence to descramble the target low-orbit satellite communication system frame data. If the descrambled data meets the characteristics of periodicity of the frame header / frame tail data or consistent phase of the pilot symbols, the candidate scrambling code sequence is output as the scrambling code sequence.

[0133] In this embodiment, the descrambling process is expressed as:

[0134] ;

[0135] In the formula, represents the target low-orbit satellite communication system frame dataset, Represents the descrambled frame data signal, represents the exponential function, Is an imaginary unit.

[0136] In this embodiment, the criterion for successful descrambling is set to the consistency of the phase of the pilot sample points according to the prior knowledge obtained. The constellation diagram of the pilot sample points before and after descrambling is as follows: Figure 6 As shown in FIG, the rule for determining the success of descrambling is: whether the variance of the pilot sample points in the descrambled sample points is less than the threshold. Further, when the success is determined based on the pilot signal, the descrambled data sample points reproduce the following Figure 7 The periodicity of the frame header synchronization symbol shown, and Figure 8 The periodicity of the time domain signal sample points at the end of the frame shown in FIG. 2 proves that the estimation of the scrambling code sequence of the target low-orbit satellite communication system in this embodiment is successful and correct.

[0137] In summary, the four-phase scrambling code sequence estimation method adopted by the present invention can estimate the physical layer scrambling code of an unknown system in the absence of prior information, crack its physical layer encryption to promote demodulation, and further carry out signal analysis at the link layer. In actual work, the method proposed in the present invention has successfully reversed the physical layer scrambling code of a foreign low-orbit satellite communication system, solving the problem that the sample phase change caused by the use of four-phase physical layer scrambling in the prior art cannot effectively demodulate the target signal. The present invention converts the problem of scrambling code sequence estimation into the problem of equivalent sequence estimation and accompanying sequence estimation, providing ideas and breakthroughs for scrambling code sequence estimation. The present invention proposes that if the descrambled data meets the periodicity of the frame header / frame tail data or the phase consistency of the pilot symbol, the descrambling is judged to be successful, which solves the problem of how to prove the success of descrambling in the context of non-cooperative communication. The three criteria proposed by the frame header / frame tail data are periodic or the pilot symbol phase is consistent, which are of practical significance in engineering.

[0138] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0139] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0140] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0141] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0142] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A method for estimating a four-phase scrambling code sequence at the physical layer of a low-orbit satellite communication system, characterized in that: include: From the target low-orbit satellite communication system frame data set, according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria, the target frame data that can be used for four-phase complex scrambling code sequence estimation is screened out; Assuming that the target frame data is a continuous zero sequence before modulation, the equivalent sequence is estimated according to the scrambling rule of the four-phase complex scrambling code to obtain an estimated equivalent sequence; The delayed autocorrelation method is used to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated. If periodicity does not exist, no processing is performed. Using a polynomial matching search algorithm to estimate the generating polynomial of the estimated equivalent sequence, and analyzing the generating rule of the estimated equivalent sequence; All possible candidate companion sequences are traversed and generated according to the estimated equivalent sequence generation rule, and the candidate companion sequences and the equivalent sequences are combined into candidate scrambling code sequences; The target low-orbit satellite communication system frame data is descrambled using the candidate scrambling code sequence. If the descrambled data meets the characteristics that the frame header / frame tail data has periodicity or the pilot symbol phase is consistent, the candidate scrambling code sequence is output as the scrambling code sequence.

2. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 1, characterized in that: From the target low-orbit satellite communication system frame data set, according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria, the target frame data capable of estimating the four-phase scrambling code sequence is screened out, wherein the four-phase scrambling code sequence is expressed as: ； In the formula, Represents the four-phase scrambling code sequence represents the intra-frame index, is the frame length.

3. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 2, characterized in that: The four-phase complex scrambling code sequence is defined by using an equivalent sequence and a companion sequence, wherein the four-phase complex scrambling code sequence is defined as: ； in, represents the four-phase scrambling code sequence, is an equivalent sequence, is the companion sequence, where any four-phase scrambling sequence can be represented by a set of equivalent sequences and the adjoint sequence The only certainty.

4. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 3, characterized in that: The equivalent sequence and the adjoint sequence are pseudo-random sequences of order sharing the same generator polynomial, wherein the pseudo-random sequence generator polynomial is expressed as: ； In the formula, represents the pseudo-random sequence generating polynomial, is the generating polynomial order, The first linear feedback shift register in the generator polynomial register values, where , For the The tap coefficients of the registers, where ; Wherein, if the equivalent sequence is If the pseudo-random sequence of order is , then the equivalent sequence has the following properties: ; In the formula, Represents an equivalent sequence.

5. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 4, characterized in that: The target low-orbit satellite communication system frame data set is expressed as: ； In the formula, represents the target low-orbit satellite communication system frame dataset, represents the number of frames in the dataset, Indicates the frame data set Frame data, represents the intra-frame index, represents the frame length. Assuming that the target low-orbit satellite communication system uses physical layer four-phase multiplexing scrambling at the transmitting end, the frame data before scrambling is , the scrambled frame data is expressed as: ； In the formula, Indicates the scrambled frame data. represents the exponential function, is an imaginary unit; The target low-orbit satellite communication system frame data set It is expressed as: ； in, Indicates the data before scrambling of the frame. represents the exponential function, Is an imaginary unit.

6. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 5, characterized in that: The intra-frame QPSK modulation and inter-frame BPSK modulation criteria include: When the frame data before scrambling When BPSK modulation is used, the signal samples in the same frame present a QPSK modulation pattern; When the frame data before scrambling When BPSK modulation is used, signal samples at the same position within different frames present a BPSK modulation pattern.

7. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 6, characterized in that: Assuming that the target frame data is a continuous zero sequence before modulation, the equivalent sequence is estimated according to the scrambling rule of the four-phase complex scrambling code to obtain an estimated equivalent sequence, where the estimated equivalent sequence is expressed as: ； In the formula, To estimate the scrambling code equivalent sequence, is the remainder function, is the inverse tangent function, is the target frame data, It is the frame index set of the target frame data.

8. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 7, characterized in that: The time-delay autocorrelation method is used to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated. If periodicity does not exist, no processing is performed. The time-delay autocorrelation function is used to estimate the internal periodicity of the equivalent sequence. The time-delay autocorrelation function is expressed as: ； in, is the delayed autocorrelation function, represents the estimated equivalent sequence, Indicates the number of delayed samples, is the intra-frame index, is the frame length.

9. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 8, characterized in that: A polynomial matching search algorithm is used to estimate the generating polynomial of the estimated equivalent sequence, and the generating rule of the estimated equivalent sequence is analyzed, wherein the homogeneous linear equation group corresponding to the polynomial matching search algorithm is expressed as: ； in, represents the order of the generating polynomial, represents the dimension of the homogeneous linear system, represents the estimated scrambling code equivalent sequence, where .

10. The method for estimating a physical layer four-phase complex scrambling code sequence for a low-orbit satellite communication system according to claim 9, characterized in that: The candidate scrambling code sequence expression is: ； in, is the candidate scrambling code sequence, is a candidate adjoint sequence, To estimate the scrambling code equivalent sequence.

11. The method for estimating a physical layer four-phase scrambling code sequence for a low-orbit satellite communication system according to claim 10, characterized in that: The target low-orbit satellite communication system frame data is descrambled using the candidate scrambling code sequence. If the descrambled data meets the characteristics that the frame header / frame tail data has periodicity or the pilot symbol phase is consistent, the candidate scrambling code sequence is output as the scrambling code sequence, where the descrambling process is expressed as: ； In the formula, represents the target low-orbit satellite communication system frame dataset, Represents the descrambled frame data signal, represents the exponential function, Is an imaginary unit.

Images