An estimation method for physical layer quadrature scrambling code sequences in low-Earth orbit satellite communication systems

Abstract

This invention discloses a method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems, belonging to the field of satellite communication technology. The method includes: selecting a target signal subjected to four-phase physical layer complex scrambling based on inter-frame BPSK modulation and intra-frame QPSK modulation criteria to obtain an equivalent sequence; analyzing the periodicity of the equivalent sequence to obtain an estimated equivalent sequence, then performing polynomial matching to obtain the generator polynomial of the estimated equivalent sequence, further analyzing to obtain the equivalent sequence generation rule and generating a local equivalent sequence; traversing according to the equivalent sequence generation rule to generate candidate adjoint sequences, combining them with the estimated equivalent sequence to obtain a candidate scrambling code sequence; descrambling the target signal according to the candidate scrambling code sequence, and if the descrambled target signal meets the decision condition, outputting the candidate scrambling code sequence as the scrambling code sequence. This invention solves the problem in blind signal demodulation where the sample phase transformation caused by the four-phase physical layer complex scrambling of the original signal prevents effective demodulation of the target signal.

Description

Technical Field

[0001] This invention relates to a method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems, belonging to the field of satellite communication technology. Background Technology

[0002] With the rapid development of technology, low-Earth orbit (LEO) satellite communication systems are playing an increasingly important role in modern communications. LEO satellite communication boasts significant advantages such as wide coverage, low transmission latency, and minimal path loss, enabling it to overcome geographical limitations and achieve seamless global communication coverage. In the military and defense sectors, LEO satellite communication systems are critical infrastructure for ensuring the stable operation of remote command and control, intelligence transmission, and military communication networks. They play an irreplaceable role in enhancing the combat effectiveness, strategic deployment capabilities, and emergency response speed of the armed forces. In the civilian sector, they are widely used in communications in remote areas, aviation and maritime communications, emergency rescue communications, and IoT data transmission, greatly promoting global information interconnection, driving socio-economic development and progress, and improving the quality of life and productivity. Therefore, the importance of LEO satellite communication is self-evident.

[0003] While low-Earth orbit satellite communication systems employ encryption measures to prevent third parties from obtaining additional information from intercepted signals, these problems are primarily caused by the four-phase complex scrambling technique used at the physical layer. This technique leads to sample phase transformations, making it impossible to effectively demodulate the target signal. In traditional network protection systems, encryption measures are often limited to the link layer, exposing the entire physical layer. When a third party successfully intercepts a signal, they can demodulate it by extracting signal parameters and estimating its modulation scheme, and even recover the transmitted bit sequence through processes such as inverse channel coding. However, in the DVB-S2 standard, although it employs I and Q-channel complex scrambling encryption at the physical layer, theoretically, if the interceptor cannot descramble, demodulation is difficult to perform. In reality, however, most existing scrambling sequence recovery algorithms focus on link-layer scrambling and are not applicable to the complex scrambling codes used at the physical layer, especially the sample phase transformation problem caused by four-phase complex scrambling, which becomes a major obstacle to effective demodulation. Summary of the Invention

[0004] The purpose of this invention is to provide an estimation method for the physical layer four-phase complex scrambling code sequence of a low-Earth orbit satellite communication system. The scrambling code sequence is obtained by inverse analysis of the target signal, and the target signal is blindly descrambled to solve the problem in the prior art that the sample point phase transformation caused by the use of four-phase physical layer complex scrambling cannot effectively demodulate the target signal.

[0005] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution.

[0006] This invention provides a method for estimating the physical layer quadrature scrambling code sequence for low-Earth orbit satellite communication systems, comprising:

[0007] From the target low-Earth orbit satellite communication system frame dataset, target frame data capable of performing four-phase complex scrambling code sequence estimation is selected according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria.

[0008] Assuming the target frame data is a sequence of consecutive zeros before modulation, the equivalent sequence is estimated according to the four-phase complex scrambling code scrambling rules, and the estimated equivalent sequence is obtained.

[0009] The time-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; otherwise, no action is taken.

[0010] The generating polynomial of the estimated equivalent sequence is estimated using a polynomial matching search algorithm, and the generation rules of the estimated equivalent sequence are analyzed.

[0011] All possible candidate adjoint sequences are generated by iterating through the estimated equivalent sequence generation rules, and the candidate adjoint sequences are combined with the estimated equivalent sequences to form a candidate scrambling sequence.

[0012] Candidate scrambling code sequences are used to descramble the frame data of the target low-Earth orbit satellite communication system. If the descrambled data meets the characteristics that the frame header / tail data has periodicity or the pilot symbols have consistent phase, then the candidate scrambling code sequence is output as the scrambling code sequence.

[0013] Furthermore, from the target low-Earth orbit satellite communication system frame dataset, target frame data suitable for four-phase complex scrambling code sequence estimation is selected based on the intra-frame QPSK modulation and inter-frame BPSK modulation criteria. The four-phase complex scrambling code sequence is represented as:

[0014] ;

[0015] In the formula, This represents a four-phase complex scrambling code sequence. Indicates the intra-frame index. The frame length.

[0016] Furthermore, the four-phase complex scrambling code sequence is defined using equivalent sequences and adjoint sequences, wherein the four-phase complex scrambling code sequence is defined as:

[0017] ;

[0018] in, This represents a four-phase complex scrambling code sequence. For equivalent sequences, For the companion sequence, there is an arbitrary four-phase complex scrambling code sequence. Both can be derived from a set of equivalent sequences and accompanying sequences The only certainty.

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

[0020] ;

[0021] In the formula, This represents the pseudo-random sequence generating polynomial. To generate polynomial order, To generate the linear feedback shift register corresponding to the polynomial, the first... 1 register value, of which x i ∈ [ x 1 , x 2 ,..., x L ] , For the first The tap coefficients of each register, where... c i ∈ [ c 1 , c 2 ,..., c L ] ;

[0022] Wherein, if the equivalent sequence is For a pseudo-random sequence of order 1, the equivalent sequence has the following properties:

[0023] ;

[0024] In the formula, This represents an equivalent sequence.

[0025] Furthermore, the target low-Earth orbit satellite communication system frame dataset is represented as follows:

[0026] ;

[0027] In the formula, This represents the target low-Earth orbit satellite communication system frame dataset. Indicates the number of frames in the dataset. Represents the first frame in the dataset Frame data, Indicates the intra-frame index. Indicates the frame length. Assuming the target low-Earth orbit satellite communication system uses physical layer quadrature scrambling at the transmitting end, let the frame data before scrambling be... The scrambled frame data is represented as:

[0028] ;

[0029] In the formula, This represents the scrambled frame data. Represents an exponential function. The imaginary unit;

[0030] The target low-Earth orbit satellite communication system frame dataset Represented as:

[0031] ;

[0032] in, Indicates the first Data before frame scrambling Represents an exponential function. It is the imaginary unit.

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

[0034] Before scrambling the frame data When BPSK modulation is used, the signal samples within the same frame exhibit a QPSK modulation pattern;

[0035] Before scrambling the frame data When using BPSK modulation, signal samples at the same intra-frame position between different frames exhibit the BPSK modulation pattern.

[0036] Furthermore, assuming the target frame data is a sequence of consecutive zeros before modulation, the equivalent sequence is estimated according to the four-phase complex scrambling code scrambling rules, resulting in the estimated equivalent sequence, which is expressed as:

[0037] ;

[0038] In the formula, To estimate the equivalent sequence, It is a modulo function. It is the arctangent function. For target frame data, This is the set of frame indices for the target frame data.

[0039] Furthermore, the time-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; otherwise, no processing is performed. The time-delayed autocorrelation function is used to estimate the internal periodicity of the equivalent sequence, and this function is expressed as:

[0040] ;

[0041] in, It is a time-delayed autocorrelation function. This represents the estimated equivalent sequence. Indicates the number of delay samples. For intra-frame indexing, The frame length.

[0042] Furthermore, a polynomial matching search algorithm is used to estimate the generator polynomial of the estimated equivalent sequence, and the generation rules of the estimated equivalent sequence are analyzed. The homogeneous linear equation system 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, Indicates the order of the generator polynomial. This represents the dimension of the homogeneous linear system of equations. Describes the estimated equivalent sequence, where, .

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

[0046] ;

[0047] in, Candidate scrambling sequence, Candidate companion sequences, To estimate the equivalent sequence.

[0048] Furthermore, candidate scrambling code sequences are used to descramble the frame data of the target low-Earth orbit satellite communication system. If the descrambled data conforms to the characteristics of periodicity in the frame header / tail data or phase consistency of pilot symbols, then the candidate scrambling code sequence is output as the scrambling code. The descrambling process is represented as follows:

[0049] ;

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

[0051] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0052] 1. The four-phase complex scrambling code sequence estimation method employed in this invention can estimate the physical layer complex scrambling code of an unknown system when prior information is insufficient, thereby cracking its physical layer encryption and advancing demodulation, and further conducting signal analysis at the link layer. In practical work, the method proposed in this invention has successfully reverse-engineered the physical layer complex scrambling code of a foreign low-Earth orbit satellite communication system, solving the problem in existing technologies where the use of four-phase physical layer complex scrambling leads to sample phase transformation and prevents effective demodulation of the target signal.

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

[0054] 3. This invention proposes that if the descrambled data meets the criteria of periodicity in the frame header / tail data or phase consistency of the pilot symbols, then the descrambling is considered successful. This solves the problem of how to prove the success of descrambling in non-cooperative communication. The three criteria proposed, namely, periodicity in the frame header / tail data or phase consistency of the pilot symbols, are all of practical significance in engineering. Attached Figure Description

[0055] Figure 1 The diagram shown is a schematic representation of an estimation method for a physical layer quadrature scrambling code sequence for a low-Earth orbit satellite communication system provided by an embodiment of the present invention.

[0056] Figure 2 The diagram shown is a schematic diagram of the target signal filtering provided in an embodiment of the present invention;

[0057] Figure 3 The diagram shown is a schematic diagram of using the time-delay autocorrelation function to perform sequence periodicity analysis on an equivalent sequence whose sequence length exceeds a threshold, according to an embodiment of the present invention.

[0058] Figure 4 The diagram shown is a schematic diagram of polynomial matching of the estimated equivalent sequence provided in an embodiment of the present invention;

[0059] Figure 5 The diagram shown is a schematic diagram of the equivalent sequence generation rule analysis provided in an embodiment of the present invention;

[0060] Figure 6 The figure shown is a comparison of the pilot symbols of the target signal before and after descrambling of the satellite system's actual signal obtained according to an embodiment of the present invention;

[0061] Figure 7 The diagram shown is a comparison of the autocorrelation of the frame header synchronization symbols of the target signal before and after descrambling of the satellite system's actual acquired signal according to an embodiment of the present invention.

[0062] Figure 8 The figure shown is a comparison of the time-domain signals of the target signal frame tail before and after descrambling of the satellite system's actual signal acquisition provided in an embodiment of the present invention. Detailed Implementation

[0063] The technical solution of the present invention will be described in detail below with reference to 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 thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0064] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0065] Example 1

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

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

[0068] This invention selects frame data suitable for four-phase complex scrambling sequence estimation from the frame dataset of the target low-Earth orbit satellite communication system. The selection is based on the criterion of using QPSK modulation within the frame and BPSK modulation between frames. This facilitates the scrambling sequence estimation in subsequent steps, reduces the amount of data processed, improves the efficiency of subsequent steps, and ensures that the selected data is suitable for the estimation of four-phase complex scrambling sequences.

[0069] Step 2: Assuming the target frame data is a sequence of consecutive zeros before modulation, estimate the equivalent sequence according to the four-phase complex scrambling code scrambling rules to obtain the estimated equivalent sequence.

[0070] This invention simplifies the problem by assuming that the target frame data is a sequence of consecutive zeros before modulation and estimating the equivalent sequence according to the four-phase complex scrambling code scrambling rules, thus obtaining an equivalent sequence that has a specific relationship with the original scrambling code sequence.

[0071] Step 3: Use the time-delayed autocorrelation method to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, truncate the estimated equivalent sequence; otherwise, do not perform any processing.

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

[0073] A generator polynomial is a mathematical representation that describes the rules for generating sequences. It can be used to generate sequences with the same properties as the estimated equivalent sequences.

[0074] This invention employs a polynomial matching search algorithm to estimate the generator polynomial of the estimated equivalent sequence, revealing the generation rules of the estimated equivalent sequence. This provides a basis for the generation of candidate adjoint sequences in subsequent steps, and also improves the accuracy and reliability of scrambling sequence estimation.

[0075] Step 5: Generate all possible candidate adjoint sequences according to the estimated equivalent sequence generation rules, and combine the candidate adjoint sequences with the estimated equivalent sequences to form a candidate scrambling sequence.

[0076] This invention generates all possible candidate companion sequences based on the estimated equivalent sequence generation rules, and combines the candidate companion sequences with the estimated equivalent sequences to form candidate scrambling sequences, thus generating multiple possible scrambling sequences. This increases the chance of finding the correct scrambling sequence. By generating the sequence through a traversal process, the integrity and diversity of the candidate scrambling sequences are ensured.

[0077] Step 6: Descramble the target low-Earth orbit satellite communication system frame data using candidate scrambling code sequences. If the descrambled data conforms to the characteristics of periodicity in the frame header / tail data or phase consistency of pilot symbols, then the candidate scrambling code sequence is output as the scrambling code sequence.

[0078] This invention proposes that the criteria for determining successful descrambling are that the descrambled data conforms to the periodicity of the frame header / frame tail data or the phase consistency of the pilot symbols. At the same time, through the verification step, it ensures 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 Embodiment 1, this embodiment introduces the specific implementation steps of an estimation method for physical layer quadrature complex scrambling code sequences for low-Earth orbit satellite communication systems, including:

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

[0082] In this embodiment, the target low-Earth orbit satellite communication system frame dataset is represented as follows:

[0083] ;

[0084] In the formula, This represents the target low-Earth orbit satellite communication system frame dataset. Indicates the number of frames in the dataset. Represents the first frame in the dataset Frame data, Indicates the intra-frame index. Indicates the frame length. Assuming the target low-Earth orbit satellite communication system uses physical layer quadrature scrambling at the transmitting end, let the frame data before scrambling be... The scrambled frame data is represented as:

[0085] ;

[0086] In the formula, This represents the scrambled frame data. Represents an exponential function. The imaginary unit;

[0087] The target low-Earth orbit satellite communication system frame dataset Represented as:

[0088] ;

[0089] in, Indicates the first Data before frame scrambling Represents an exponential function. It is the imaginary unit.

[0090] In this embodiment, target frame data suitable for four-phase complex scrambling code sequence estimation is selected from the target low-Earth orbit satellite communication system frame dataset according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria. The four-phase complex scrambling code sequence is represented as follows:

[0091] ;

[0092] In the formula, This represents a four-phase complex scrambling code sequence. Indicates the intra-frame index. The frame length.

[0093] This 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] Before scrambling the frame data When BPSK modulation is used, the signal samples within the same frame exhibit a QPSK modulation pattern;

[0095] Before scrambling the frame data When using BPSK modulation, signal samples at the same intra-frame position between different frames exhibit the BPSK modulation pattern.

[0096] In this embodiment, when When using BPSK modulation, for signal samples within the same frame, due to the four-phase complex scrambling sequence... After scrambling, The phase of 0, , , The rotation of the signal results in a QPSK modulation pattern within the final frame; when When using BPSK modulation, for signal samples at the same intraframe position across different frames, the scrambling sequence used at the same position varies. The same result leads to the final inter-frame signal It still exhibits BPSK modulation. Let the set of frame indices for the target frame data after filtering be... .

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

[0098] This invention analyzes the signal characteristics that meet the screening conditions in step 1, and provides the results from the filtered frame data. Equivalent sequence estimation was performed, and the following correspondence was found between the binary equivalent sequence and the quaternary scrambling sequence:

[0099] ;

[0100] therefore, In this embodiment, the constellation diagram drawn according to the frame index dimension from approximately 80 selected frames of data is as follows: Figure 2 As shown, this group of frame data exhibits BPSK modulation at the same intra-frame index, while exhibiting QPSK modulation across different intra-frame indices due to phase differences. This conforms to the characteristics of inter-frame BPSK modulation and intra-frame QPSK modulation. Therefore, the filtered signal is represented as:

[0101] ;

[0102] According to the screening criteria, BPSK modulation is used, therefore for any ,whether Scrambling sequence values They always appear in pairs in the form of {0, 2} or {1, 3}, therefore it is assumed that the signal is filtered before transmission. ,so:

[0103] ;

[0104] In this embodiment, it is assumed that the target frame data is a sequence of consecutive zeros before modulation. The equivalent sequence is estimated according to the four-phase complex scrambling code scrambling rule, and the estimated equivalent sequence is obtained. The estimated equivalent sequence is expressed as:

[0105] ;

[0106] In the formula, To estimate the equivalent sequence, It is a modulo function. It is the arctangent function. For target frame data, Let be the set of frame indices for the target frame data. Therefore, the estimated length of the equivalent sequence is 307020.

[0107] This embodiment uses equivalent sequences and adjoint sequences to define the four-phase complex scrambling code sequence, wherein the four-phase complex scrambling code sequence is defined as:

[0108] ;

[0109] in, This represents a four-phase complex scrambling code sequence. For equivalent sequences, For the companion sequence, there is an arbitrary four-phase complex scrambling code sequence. Both can be derived from a set of equivalent sequences and accompanying sequences The only certainty.

[0110] Step 3: Use the time-delayed autocorrelation method to analyze and estimate the internal periodicity of the equivalent sequence. If periodicity exists, truncate the estimated equivalent sequence; otherwise, do not perform any processing.

[0111] Since the estimated equivalent sequence length of 307020 is a very large number, directly analyzing such a long sequence is extremely difficult and impractical. Therefore, this embodiment uses the time-delayed autocorrelation method to analyze the internal periodicity of the estimated equivalent sequence. If periodicity exists, the estimated equivalent sequence is truncated; otherwise, no processing is performed. Specifically, the time-delayed autocorrelation function is used to estimate the internal periodicity of the equivalent sequence. The time-delayed autocorrelation function is expressed as:

[0112] ;

[0113] in, It is a time-delayed autocorrelation function. This represents the estimated equivalent sequence. Indicates the number of delay samples. For intra-frame indexing, Given the frame length. Estimate the equivalent sequence. The results of the time-delay autocorrelation function are as follows Figure 3 As shown, the estimated equivalent sequence exhibits a periodicity of 32767. Therefore, the equivalent sequence is truncated to obtain the intra-frame index. .

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

[0115] Step 4: Use a polynomial matching search algorithm to estimate the generator polynomial of the estimated equivalent sequence and analyze the generation rules 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 rules of the estimated equivalent sequence. The homogeneous linear equation system corresponding to the polynomial matching search algorithm is expressed as follows:

[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, Indicates the order of the generator polynomial. This represents the dimension of the homogeneous linear system of equations. Describes the estimated equivalent sequence, where, Iterate through all possible combinations of binary tap coefficients. When the number of zeros in the homogeneous linear equation system exceeds a threshold, it is considered a successful match.

[0119] In this embodiment, let , Suppose that the number of equations in the system that result in zero is greater than... When the time is right, it is considered a successful match, and a polynomial matching diagram is generated as shown below. Figure 4 As shown, when the generator polynomial is represented in decimal as 8193, 2970 out of 3000 equations result in zero, indicating that the generator polynomial is successfully matched.

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

[0121] ;

[0122] In the formula, This represents the pseudo-random sequence generating polynomial. To generate polynomial order, To generate the linear feedback shift register corresponding to the polynomial, the first... 1 register value, of which x i ∈ [ x 1 , x 2 ,..., x L ] , For the first The tap coefficients of each register, where... c i ∈ [ c 1 , c 2 ,..., c L ] ;

[0123] Wherein, if the equivalent sequence is For a pseudo-random sequence of order 1, the equivalent sequence has the following properties:

[0124] ;

[0125] In the formula, This represents an equivalent sequence.

[0126] Simply finding the generator polynomial of the estimated equivalent sequence is insufficient to independently generate a local equivalent sequence; it is also necessary to find the generation rule for the estimated equivalent sequence. A pseudo-random sequence can be uniquely determined by the generator polynomial and the initial state. By traversing all possible initial states and comparing them with the estimated equivalent sequence, the generation rule for the equivalent sequence can be found. The generation rule for the estimated equivalent sequence needs to be analyzed on a case-by-case basis. In this embodiment, a pseudo-random sequence is generated by traversing all initial states corresponding to the generator polynomial estimated in step 4. The pseudo-random sequence is then compared with the estimated equivalent sequence. A diagram illustrating the number of identical bits between them is shown below. Figure 5 As shown, the traversal process of the generating polynomial is equivalent to the cyclic shift process of the pseudo-random sequence. From Figure 5 As can be seen from this, the estimated equivalent sequence Since the pseudo-random sequences with cyclic shifts of 15858 and 16878 times have a large number of identical bits, the estimated equivalent sequence generation rules are obtained.

[0127] Step 5: Generate all possible candidate adjoint sequences according to the estimated equivalent sequence generation rules, and combine the candidate adjoint sequences with the estimated equivalent sequences to form a candidate scrambling sequence.

[0128] Based on the estimated equivalent sequence generation rule, candidate adjoint sequences are generated by traversing all initial states. .

[0129] In this embodiment, the candidate adjoint sequence is combined with the estimated equivalent sequence to form a candidate scrambling sequence, the expression of which is:

[0130] ;

[0131] in, Candidate scrambling sequence, Candidate companion sequences, To estimate the equivalent sequence.

[0132] Step 6: Descramble the target low-Earth orbit satellite communication system frame data using candidate scrambling code sequences. If the descrambled data conforms to the characteristics of periodicity in the frame header / tail data or phase consistency of pilot symbols, then the candidate scrambling code sequence is output as the scrambling code sequence.

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

[0134] ;

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

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

[0137] In summary, the four-phase complex scrambling code sequence estimation method employed in this invention can estimate the physical layer complex scrambling code of an unknown system when prior information is insufficient, thereby cracking its physical layer encryption and advancing demodulation, and further conducting signal analysis at the link layer. In practical work, the method proposed in this invention has successfully reverse-engineered the physical layer complex scrambling code of a foreign low-Earth orbit satellite communication system, solving the problem in existing technologies where the sample phase transformation caused by the use of four-phase physical layer complex scrambling prevents effective demodulation of the target signal. This invention transforms the problem of scrambling code sequence estimation into the problem of equivalent sequence estimation and adjoint sequence estimation, providing a new approach and breakthrough for scrambling code sequence estimation. This invention proposes that if the descrambled data conforms to the condition that the frame header / tail data has periodicity or the pilot symbols have consistent phase, it determines that descrambling is successful, solving the problem of how to prove successful descrambling in non-cooperative communication. The three criteria proposed—that the frame header / tail data has periodicity or the pilot symbols have consistent phase—are all of practical significance in engineering.

[0138] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied 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] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0140] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0141] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0142] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems, characterized in that, include: From the target low-Earth orbit satellite communication system frame dataset, target frame data capable of performing four-phase complex scrambling code sequence estimation is selected according to the intra-frame QPSK modulation and inter-frame BPSK modulation criteria. Assuming the target frame data is a sequence of consecutive zeros before modulation, the equivalent sequence is estimated according to the four-phase complex scrambling code scrambling rules, and the estimated equivalent sequence is obtained. The time-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; otherwise, no action is taken. The generating polynomial of the estimated equivalent sequence is estimated using a polynomial matching search algorithm, and the generation rules of the estimated equivalent sequence are analyzed. All possible candidate adjoint sequences are generated by iterating through the estimated equivalent sequence generation rules, and the candidate adjoint sequences are combined with the estimated equivalent sequences to form a candidate scrambling sequence. Candidate scrambling code sequences are used to descramble the frame data of the target low-Earth orbit satellite communication system. If the descrambled data meets the characteristics that the frame header / tail data has periodicity or the pilot symbols have consistent phase, then the candidate scrambling code sequence is output as the scrambling code sequence.

2. The estimation method for the physical layer four-phase complex scrambling code sequence of a low-Earth orbit satellite communication system according to claim 1, characterized in that, From the target low-Earth orbit satellite communication system frame dataset, target frame data suitable for four-phase complex scrambling code sequence estimation is selected based on the intra-frame QPSK modulation and inter-frame BPSK modulation criteria. The four-phase complex scrambling code sequence is represented as follows: ； In the formula, This represents a four-phase complex scrambling code sequence. Indicates the intra-frame index. The frame length.

3. The method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems according to claim 2, characterized in that, The four-phase complex scrambling code sequence is defined using equivalent sequences and adjoint sequences, wherein the four-phase complex scrambling code sequence is defined as: ； in, This represents a four-phase complex scrambling code sequence. For equivalent sequences, For the companion sequence, there is an arbitrary four-phase complex scrambling code sequence. Both can be derived from a set of equivalent sequences and accompanying sequences The only certainty.

4. The estimation method for the physical layer four-phase complex scrambling code sequence of a low-Earth orbit satellite communication system according to claim 3, characterized in that, The equivalent sequence and the adjoint sequence share the same generator polynomial. A pseudo-random sequence of order, wherein the generator polynomial of the pseudo-random sequence is expressed as: ； In the formula, This represents the pseudo-random sequence generating polynomial. To generate polynomial order, To generate the linear feedback shift register corresponding to the polynomial, the first... 1 register value, of which , For the first The tap coefficients of each register, where... ; Wherein, if the equivalent sequence is For a pseudo-random sequence of order 1, the equivalent sequence has the following properties: ; In the formula, This represents an equivalent sequence.

5. The estimation method for the physical layer four-phase complex scrambling code sequence of a low-Earth orbit satellite communication system according to claim 4, characterized in that, The target low-Earth orbit satellite communication system frame dataset is represented as follows: ； In the formula, This represents the target low-Earth orbit satellite communication system frame dataset. Indicates the number of frames in the dataset. Represents the first frame in the dataset Frame data, Indicates the intra-frame index. Indicates the frame length. Assuming the target low-Earth orbit satellite communication system uses physical layer quadrature scrambling at the transmitting end, let the frame data before scrambling be... The scrambled frame data is represented as: ； In the formula, This represents the scrambled frame data. Represents an exponential function. The imaginary unit; The target low-Earth orbit satellite communication system frame dataset Represented as: ； in, Indicates the first Data before frame scrambling Represents an exponential function. It is the imaginary unit.

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

7. The method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems according to claim 6, characterized in that, Assuming the target frame data is a sequence of consecutive zeros before modulation, the equivalent sequence is estimated according to the four-phase complex scrambling code scrambling rules. The estimated equivalent sequence is expressed as: ； In the formula, To estimate the equivalent sequence, It is a modulo function. It is the arctangent function. For target frame data, This is the set of frame indices for the target frame data.

8. The method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems according to claim 7, characterized in that, The time-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; otherwise, no processing is performed. The time-delayed autocorrelation function is used to estimate the internal periodicity of the equivalent sequence, and this function is expressed as: ； in, It is a time-delayed autocorrelation function. This represents the estimated equivalent sequence. Indicates the number of delay samples. For intra-frame indexing, The frame length.

9. The method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems according to claim 8, characterized in that, The generator polynomial of the estimated equivalent sequence is estimated using a polynomial matching search algorithm, and the generation rules of the estimated equivalent sequence are analyzed. The homogeneous linear equation system corresponding to the polynomial matching search algorithm is expressed as: ； in, Indicates the order of the generator polynomial. This represents the dimension of the homogeneous linear system of equations. Describes the estimated equivalent sequence, where, .

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

11. The method for estimating the physical layer four-phase complex scrambling code sequence for low-Earth orbit satellite communication systems according to claim 10, characterized in that, The target low-Earth orbit satellite communication system frame data is descrambled using candidate scrambling code sequences. If the descrambled data conforms to the characteristics of periodicity in the frame header / tail data or phase consistency of pilot symbols, then the candidate scrambling code sequence is output as the scrambling code sequence. The descrambling process is represented as follows: ； In the formula, This represents the target low-Earth orbit satellite communication system frame dataset. This represents the descrambled frame data signal. Represents an exponential function. It is the imaginary unit.

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