A method for realizing high spectral efficiency and secure transmission

Abstract

This invention discloses a method for achieving highly spectrally efficient secure transmission. First, legitimate transceivers share chaotic sequence initial values ​​and employ the same chaotic mapping method, thereby sharing a set of chaotic sequences. Secondly, a secure mapping method is designed based on the chaotic sequences, linking information bits with constellation pattern indices and modulation symbols. Because an unauthorized eavesdropper cannot obtain the chaotic sequence initial values, and because the chaotic mapping method is sensitive to these initial values ​​and exhibits aperiodicity, even if they know the secure mapping method, they would be unable to correctly decode legitimate signals. The physical layer security technology proposed in this invention offers both high security and high spectral efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to a method for implementing high-spectrum-efficiency secure transmission. Background Art

[0002] Orthogonal Time Frequency Space (OTFS) is a multi-carrier modulation technology suitable for high-speed mobile communication scenarios. It places information symbols in the delay-Doppler (DD) domain and converts them to the time-frequency (TF) domain using a two-dimensional transform. This allows each information symbol to be expanded to the entire TF domain, obtaining the full time-frequency diversity gain of the channel. Ultimately, it achieves better error performance in high-speed mobile scenarios than the common orthogonal frequency division multiplexing (OFDM) multi-carrier modulation technology.

[0003] Index modulation (IM) is a highly spectrally efficient modulation technique that transmits information using conventional constellation symbols and the activation index of the transmitting entity. For example, index information is transmitted using the combined index of activated antennas in a multi-antenna system or the combined index of activated subcarriers in an OFDM system. For OFDM systems, since activating only some subcarriers does not fully utilize spectrum resources, academics have proposed using a permutation of n distinguishable signal constellation patterns to index n subcarriers, activating all subcarriers while also transmitting index information. This type of modulation, known as multi-mode (MM) OFDM-IM, uses a permutation rather than a combination approach to modulate subcarrier indices, with all subcarriers activated simultaneously. This allows for the transmission of more index information and conventional constellation symbol information than in classic OFDM-IM systems, resulting in higher spectral efficiency. Because the OTFS system places constellation mapping symbols on a DD-domain grid, the combination of IM modulation and the OTFS system can also utilize the combined index of the activation grid to transmit information bits.

[0004] Current research on OTFS-IM systems mainly focuses on activation entity selection, receiving complexity reduction, and reliability analysis. However, considering that IM modulation can introduce additional security in the index dimension, there is still a lack of work dedicated to using IM modulation to achieve physical layer security in OTFS systems. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention provides a highly spectrally efficient secure transmission method. First, legitimate transceivers share the initial value of a chaotic sequence and employ the same chaotic mapping method, thereby sharing a set of chaotic sequences. Secondly, a secure mapping method is designed based on the chaotic sequence to map information bits to constellation pattern indices and modulation symbols. Because an unauthorized eavesdropper cannot obtain the initial value of the chaotic sequence, and because the chaotic mapping method is sensitive to this initial value and non-periodic, even if they know the secure mapping method designed by the present invention, they would be unable to correctly decode the legitimate signal. The physical layer security technology proposed by the present invention offers both high security and high spectral efficiency.

[0006] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0007] Step 1: The transmitter processes as follows:

[0008] Step 1-1: Before security indexing, legitimate transceivers share the initial value of the chaotic sequence and use the same chaotic mapping method to share a set of chaotic sequences. The chaotic sequences are represented as d1, d2, ...;

[0009] Step 1-2: For an OTFS system with M subcarriers with a subcarrier spacing of Δf and N symbols with a symbol time of T, the total bandwidth is B = MΔf, and the signal frame duration is T f =NT; the OTFS system is critically sampled, i.e., T∆f = 1; before OTFS modulation, the MN DD domain grids are divided into g sub-blocks, each of which has a size of n = MN / g; at the same time, the m information bits to be transmitted are equally divided into g groups, each containing p = m / g bits;

[0010] Since each group of information bits is processed using the same mapping method, the bit grouping requirements for the βth group of information bits are as follows, where β∈{1,2,…,g};

[0011] The p information bits of the βth group are divided into two parts:

[0012] The first part is called the IM sequence, which consists of p1 bits and determines the index arrangement of n distinguishable signal constellation patterns. The arrangement of the w-th constellation pattern is shown as follows:

[0013]

[0014] in represents the index of the αth constellation pattern, where there are n! permutations of n distinguishable signal constellation patterns, corresponding to the value range of w;

[0015] For the n grids of the βth group, n different constellation modes are used, which are expressed as follows:

[0016]

[0017] in, That is, different grids adopt different constellation modes; therefore, for the arrangement of n different constellation modes, it is required

[0018] The second part is called the data symbol modulation DSM sequence, which includes p2 bits and determines n constellation mapping symbols, as shown below:

[0019]

[0020] in represents the symbol corresponding to the αth constellation mode; for n distinguishable constellation modes, all are Q-order modulation, p2 = nlog2 Q;

[0021] From the above, we can see that the total number of information bits should satisfy:

[0022]

[0023] Step 1-3: Based on the chaotic sequence and grouping bits obtained in steps 1-1 and 1-2, secure mapping is performed between information bits based on the chaotic sequence and constellation mode index and modulation symbols;

[0024] The security mapping method for the βth group of information bits is as follows:

[0025] First, a secure mapping between information bits based on the chaotic sequence and constellation pattern index is performed, and n chaotic values ​​are extracted from the chaotic sequence, which are expressed as follows:

[0026]

[0027] Rearrange them from large to small in value, as shown below:

[0028]

[0029] in, represents the jth largest chaos value, The elements in The elements in correspond to each other. The element number in is the basis, Corresponds to a set of element number indexes; all bit patterns of the IM sequence correspond to I β A constellation pattern arrangement; according to the IM bit sequence of the βth group, find the corresponding I β The constellation pattern is arranged, thereby determining the distinguishable signal constellation pattern adopted by the n grids of the β-th sub-block corresponding to the β-th group of bits;

[0030] Secondly, a secure mapping between information bits and modulation symbols based on the chaotic sequence is performed. After the constellation pattern of the n grids of the β-th sub-block is determined, constellation mapping of the n grids is performed according to the DSM sequence. For any constellation pattern, each constellation mapping symbol corresponds to a unique bit arrangement. The random shift Gray mapping method is used to extract n chaotic values ​​from the chaotic sequence, which are expressed as follows:

[0031]

[0032] Rearrange them from large to small, as shown below:

[0033]

[0034] in, represents the jth largest chaos value, The elements in The elements in correspond to each other. The element number in is the basis, It also corresponds to a set of element indices; after determining the random shift Gray mapping table corresponding to each grid, the constellation mapping of n grids can be performed according to the DSM sequence, and then the constellation mapping symbols of the n grids can be determined;

[0035] After the g groups of information bits are securely mapped to the information bits, mode indexes, and modulation symbols based on chaotic sequences, the DD domain grid symbols of the OTFS system are Sure;

[0036] Steps 1-4: OTFS System DD Domain Grid Symbol X DD The corresponding column vector is Satisfy x=vec(X DD ), where vec(·) refers to the column-wise vectorized operation; for X DD Use the inverse symplectic Fourier transform (ISFFT) to convert the symbolic matrix X into the TF domain. TF , X TF It is expressed as follows:

[0037]

[0038] Among them, F, F H They represent the discrete Fourier transform matrix and the discrete inverse Fourier transform matrix respectively;

[0039] Steps 1-5: Assuming typical rectangular pulse shaping, transform the TF domain symbol matrix X into TF Convert to time domain signal It is expressed as follows:

[0040]

[0041] Then, the length N cp The CP is added to the beginning of s to obtain the baseband signal s cp , where N cp ≥L, L is the maximum delay spread of the channel;

[0042] Step 1-6: Baseband signal s cp Perform digital up-conversion, digital-to-analog conversion, RF up-conversion, and finally transmit to the antenna for transmission;

[0043] Step 2: The receiving end processing flow is as follows:

[0044] Step 2-1: Perform RF down-conversion, analog-to-digital conversion, and digital down-conversion on the received signal to obtain the baseband signal r cp ,

[0045] Step 2-2: Baseband signal r cp Remove the CP operation and get r,

[0046] Step 2-3: Perform discrete Wigner transform on r and convert it to TF domain, which is expressed as follows:

[0047] Y TF =F M R

[0048] Where R = unvec M,N (r) represents the matrix R with M rows and N columns arranged in columns;

[0049] Step 2-4: Perform sigmoid Fourier transform (SFFT) on the TF domain signal matrix R, which is expressed as follows:

[0050]

[0051] in Receive signals for the DD domain;

[0052] Step 2-5: Determine g receiving sub-blocks according to the sub-block division in step 1-2; for the β-th sub-block, the original information bits are recovered as follows, where β∈{1,2,…,g};

[0053] For the βth sub-block, demapping is performed between the information bits based on the chaotic sequence and the constellation mode index and the modulation symbol respectively;

[0054] First, for the βth sub-block, the constellation mode adopted by each grid is determined according to the received symbol situation of its n grids, and a constellation mode index of length n is obtained; according to the chaotic sequence shared in step 1-1 and the security mapping rule between the information bits based on the chaotic sequence and the constellation mode index in step 1-3, a table with a length of n is obtained. IM sequence;

[0055] Secondly, for the βth sub-block, based on the chaotic sequence shared in step 1-1 and the secure mapping rules between information bits, constellation mode indexes, and modulation symbols based on the chaotic sequence in step 1-3, the randomly shifted Gray mapping tables corresponding to the n grids are obtained. Then, referring to the corresponding randomly shifted Gray mapping tables, the constellation symbols of the n grids are demapped respectively, and a QDSM sequence of length p2 = nlog2 is recovered.

[0056] After demapping the information bits based on the chaotic sequence and the constellation pattern index and modulation symbols in the g sub-blocks respectively, the legal receiving end has recovered the m information bits transmitted.

[0057] Preferably, the constellation mapping adopts Gray mapping.

[0058] The beneficial effects of the present invention are as follows:

[0059] (1) The first advantage is that the physical layer security technology proposed in the present invention is highly secure. On the one hand, the present invention utilizes an index constellation pattern to transmit index information. On the other hand, the bit mapping relationship based on constellation symbol transmission is pseudo-random. If an eavesdropper does not know the chaotic initial value shared by the legitimate transceiver and the security mapping method designed by the present invention, even if the OTFS symbol is correctly detected, it will not be possible to obtain the index information and correctly restore the modulation information before constellation mapping. Moreover, the pseudo-random Gray mapping method designed by the present invention will not degrade the system's bit error performance.

[0060] (2) A second advantage is the high spectral efficiency of the physical layer security technology proposed in this invention. While implementing physical layer security for the OTFS system based on the index dimension of IM modulation, this invention also transmits index information, thereby improving the spectral efficiency of the OTFS system. Furthermore, this invention employs a distinguishable signal constellation pattern for security indexing, activating all grids within the OTFS sub-block. This results in higher spectral efficiency than conventional IM modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a block diagram of the MM-OFDM-IM system of the present invention.

[0062] Figure 2 This is a schematic diagram of determining a constellation mode index in an embodiment of the present invention, taking n=4 as an example.

[0063] Figure 3 This is a schematic diagram of generating a random shift Gray mapping table, taking n=4 as an example in an embodiment of the present invention.

[0064] Figure 4 This is a schematic diagram of OTFS sub-block division in an embodiment of the present invention, taking M=4, N=2, and g=2 as an example.

[0065] Figure 5 FIG. 4 is a schematic diagram of four distinguishable constellation patterns obtained by rotating QPSK constellation points according to an embodiment of the present invention. DETAILED DESCRIPTION

[0066] The present invention will be further described below with reference to the accompanying drawings and examples.

[0067] To achieve physical layer security for the OTFS system, the present invention provides a physical layer security implementation technology for the OTFS system based on IM modulation. To achieve higher spectral efficiency, the present invention utilizes the arrangement of distinguishable signal constellation patterns for security indexing. This method first shares the initial values ​​of chaotic sequences at legitimate transceivers, employing the same chaotic mapping method to further share a set of chaotic sequences. Secondly, a secure mapping method is designed based on the chaotic sequence to map information bits to constellation pattern indices and modulation symbols. Because an unauthorized eavesdropper cannot obtain the initial values ​​of the chaotic sequence, and because the chaotic mapping method is sensitive to and aperiodic to the initial values, even if an unauthorized eavesdropper knows the security mapping method designed by the present invention, they would be unable to correctly decode the legitimate signal.

[0068] The physical layer security implementation technology of the OTFS system based on IM modulation provided by the present invention includes the following steps in the transmitting end processing:

[0069] Step 1: Before the security index is established, the legitimate transceivers share the initial value of the chaotic sequence and use the same chaotic mapping method to share a set of chaotic sequences. The chaotic sequence can be represented as d1, d2, ...;

[0070] Step 2: Without loss of generality, consider an OTFS system with M subcarriers with a subcarrier spacing of Δf and N symbols with a symbol time of T, a total bandwidth of B = MΔf, and a signal frame duration of T f = NT. Furthermore, consider the OTFS system to be critically sampled, i.e., T∆f = 1. Before OTFS modulation, the MN DD domain grids are divided into g sub-blocks, each of size n = MN / g. Simultaneously, the m information bits to be transmitted are equally divided into g groups, each containing p = m / g bits. Since each group of information bits is processed using the same mapping method, for simplicity, the bit grouping requirements are illustrated using the βth group of information bits, where β∈{1,2,…,g}.

[0071] The p information bits of the βth group are divided into two parts. The first part is called the IM sequence, which includes p1 bits and is used to determine the index arrangement of n differentiable signal constellation patterns. The arrangement of the wth constellation pattern is shown as follows:

[0072]

[0073] in Represents the index of the αth constellation mode. There are n! permutations of n distinguishable signal constellation modes, corresponding to the value range of w. For the n grids of the βth group, n different constellation modes are used, which are expressed as follows:

[0074]

[0075] in, That is, different grids adopt different constellation modes. Therefore, for the arrangement of n different constellation modes, it is required

[0076] The second part is called the data symbol modulation (DSM) sequence, which consists of p2 bits and determines n constellation mapping symbols, as shown below:

[0077]

[0078] in Denotes the symbol corresponding to the αth constellation mode. Considering that all n distinguishable constellation modes are Q-order modulation, p2 = nlog2 Q.

[0079] From the above, we can see that the total number of information bits should satisfy:

[0080]

[0081] Step 3: Perform a secure mapping between the information bits based on the chaotic sequence and the constellation pattern index and modulation symbol according to the chaotic sequence and grouped bits obtained in steps 1 and 2. The secure mapping method designed by the present invention is still described using the βth group of bits as an example.

[0082] First, a secure mapping between information bits based on the chaotic sequence and constellation pattern index is performed. n chaotic values ​​are extracted from the chaotic sequence, which are expressed as follows:

[0083]

[0084] Rearrange them from large to small in value, as shown below:

[0085]

[0086] in, represents the jth largest chaos value. The elements in The elements in correspond to each other. The element number in is the basis, Corresponds to a set of element serial number indexes. Figure 2 , taking n=4 as an example, the IM sequence includes p1=log24!=4 bits. The corresponding index is [2,1,3,4], so the bit pattern of the IM sequence starts from [2,1,3,4], that is, the first bit pattern of the IM sequence [0,0,0,0] corresponds to I β The constellation pattern arrangement of [2,1,3,4], the next bit pattern [0,0,0,1] corresponds to I β The constellation pattern arrangement of [2,1,4,3] in the IM sequence is repeated until all bit patterns of the IM sequence correspond to I β Then, according to the IM bit sequence of group β, find the corresponding I β The constellation pattern is arranged, and the distinguishable signal constellation patterns adopted by the n grids of the β-th sub-block corresponding to the β-th group of bits are determined.

[0087] Secondly, a secure mapping between information bits and modulation symbols based on a chaotic sequence is performed. After the constellation pattern of the n grids of the βth sub-block is determined, constellation mapping of the n grids can be performed according to the DSM sequence. Constellation mapping generally adopts the common Gray mapping. For any constellation pattern, each constellation mapping symbol corresponds to a unique bit arrangement. If the mapping relationship between the bit arrangement and the constellation symbol is arbitrarily disrupted, it will lead to a decrease in bit error performance. Therefore, the present invention proposes a random shift Gray mapping method. Then, n chaotic values ​​are extracted from the chaotic sequence, which are expressed as follows:

[0088]

[0089] Rearrange them from large to small, as shown below:

[0090]

[0091] in, represents the jth largest chaos value. The elements in The elements in correspond to each other. The element number in is the basis, Also corresponds to a set of element indices. Figure 3 , taking n=4 as an example, if The corresponding indexes are [4, 3, 1, 2]. According to the random shift Gray mapping method proposed in this invention, a Gray mapping scheme is assigned as a benchmark for each of the four distinguishable constellation patterns. The Gray mapping benchmark table corresponding to the four grids in the βth group is then cyclically shifted by 4, 3, 1, and 2 times, respectively, to obtain four random shift Gray mapping tables. After determining the random shift Gray mapping table corresponding to each grid, constellation mapping can be performed on n grids based on the DSM sequence, thereby determining the constellation mapping symbols for the n grids.

[0092] After the g groups of information bits are securely mapped to the information bits, mode indexes, and modulation symbols based on chaotic sequences, the DD domain grid symbols of the OTFS system are Sure.

[0093] Step 4: OTFS System DD Domain Grid Symbol X DD The corresponding column vector is Satisfy x=vec(X DD ), where vec(·) refers to the column-wise vectorized operation. DD Use the Inverse Symplectic FastFourier Transform (ISFFT) to transform the symbolic matrix X into the TF domain TF .X TF It is expressed as follows:

[0094]

[0095] Among them, F, F H They represent the discrete Fourier transform matrix and the discrete inverse Fourier transform matrix respectively.

[0096] Step 5: Assuming typical rectangular pulse shaping, transform the TF domain symbol matrix X into TF Convert to time domain signal s represents the following:

[0097]

[0098] Then, the length N cp The CP is added to the beginning of s to obtain the baseband signal s cp , where N cp ≥L, where L is the maximum delay spread of the channel.

[0099] Step 6: Baseband signal s cp Perform digital up-conversion, digital-to-analog conversion, RF up-conversion, and finally transmit to the antenna for transmission.

[0100] The receiving end processing flow is as follows:

[0101] Step 7: Perform RF down-conversion, analog-to-digital conversion, and digital down-conversion on the received signal to obtain the baseband signal r cp .in

[0102] Step 8: Baseband signal r cp Perform the CP removal operation to obtain r.

[0103] Step 9: Perform discrete Wigner transform on r and convert it to TF domain, which is expressed as follows:

[0104] Y TF =F M R

[0105] Where R = unvec M,N (r) represents the matrix R with r arranged into M rows and N columns.

[0106] Step 10: Perform a symplectic fast fourier transform (SFFT) on the TF domain signal matrix R, which is expressed as follows:

[0107]

[0108] in Receives signals for the DD domain.

[0109] Step 11: Determine g receive subblocks based on the subblock division in Step 2. Since each subblock is processed using the same demapping method, for simplicity, the βth subblock is used as an example to illustrate the original information bit recovery operation, where β∈{1,2,…,g}. For the βth subblock, demapping is performed between the information bits and the constellation index and modulation symbol based on the chaotic sequence.

[0110] First, for the βth sub-block, the constellation mode adopted by each grid can be determined according to the received symbols of its n grids, and the constellation mode index of length n can be obtained. According to the chaotic sequence shared in step 1 and the security mapping rule between the information bits based on the chaotic sequence and the constellation mode index in step 3, the length of IM sequence.

[0111] Next, for the βth sub-block, the randomly shifted Gray mapping tables corresponding to the n grids are obtained based on the chaotic sequence shared in step 1 and the secure mapping rules between information bits, constellation mode indices, and modulation symbols based on the chaotic sequence in step 3. The constellation symbols of the n grids are then demapped using the corresponding randomly shifted Gray mapping tables, recovering a QDSM sequence of length p2 = nlog2.

[0112] After demapping the information bits based on the chaotic sequence and the constellation pattern index and modulation symbols in the g sub-blocks respectively, the legal receiving end has recovered the m information bits transmitted.

[0113] Example:

[0114] According to the MM-OTFS-IM physical layer security technology proposed in the present invention, it is assumed that the number of OTFS modulation subcarriers M = 4, the number of time slots N = 2, the number of subblocks g = 2, the subblock size n = MN / g = 4, and the CP length N cp = 2. Sender Alice and legitimate receiver Bob use the Cubic chaotic mapping method, with a chaotic factor of ρ = 2.8 and a chaotic initial value of d0 = 0.51. Alice uses rotated QPSK to obtain four distinguishable signal constellation patterns, so the modulation order Q = 4. Furthermore, assume that the eavesdropper Eve is unaware of the secure mapping method and chaotic initial value designed in this invention.

[0115] Step 1: Before the security index is generated, the legal transceiver shares the initial value of the chaotic sequence d0 = 0.51 and uses the Cubic chaotic mapping method. The Cubic chaotic mapping method is expressed as follows:

[0116]

[0117] The chaotic factor ρ = 2.8. A set of chaotic sequences is obtained, which is expressed as follows (only the first 16 bits are shown):

[0118]

[0119] Step 2: See attached Figure 4 , the 8 DD domain grids of the OTFS system are divided into 2 sub-blocks. The size of each sub-block is 4, and the corresponding IM sequence length is bits, the DSM sequence length is p2=4log24=8. Therefore, the total number of information bits to be transmitted is m=(p1+p2)g=24.

[0120] The total information bits are divided equally into two groups, each containing 12 bits. Taking the first group as an example, the first four bits are selected as the IM sequence and the last eight bits are selected as the DSM sequence. The IM sequence is used to determine the index arrangement of the four distinguishable signal constellation patterns. The wth constellation pattern arrangement is shown as follows:

[0121]

[0122] in Represents the index of the αth constellation mode. There are 24 permutations of the four distinguishable signal constellation modes, corresponding to the value range of w. Four different constellation modes are used for the four grids in the first group, as shown below:

[0123]

[0124] in, That is, different grids adopt different constellation modes. Figure 5 ,This example obtains four distinguishable constellation patterns by rotating the QPSK constellation ,symbols 3 times.

[0125] The DSM sequence determines four constellation mapping symbols, which are expressed as follows:

[0126]

[0127] in Denotes the symbol corresponding to the αth constellation mode. Consider the four distinguishable constellation modes, all of which are QPSK modulations, with only different rotation angles.

[0128] Step 3: Perform a secure mapping between the information bits based on the chaotic sequence and the constellation pattern index and modulation symbol according to the chaotic sequence and grouped bits obtained in steps 1 and 2. The secure mapping method designed by the present invention is still described using the first group of bits as an example.

[0129] First, a secure mapping between information bits and constellation pattern indices based on the chaotic sequence is performed. The chaotic values ​​numbered 1 to 4 are extracted from the chaotic sequence and expressed as follows:

[0130]

[0131] Rearrange them from large to small in value, as shown below:

[0132]

[0133] The elements in The elements in correspond to each other. The element number in is the basis, Corresponding to a set of element indexes [2,1,3,4]. Figure 2 , that is, the first bit pattern of the IM sequence [0,0,0,0] corresponds to I 1 The constellation pattern arrangement of [2,1,3,4], the next bit pattern [0,0,0,1] corresponds to I 1 The constellation pattern arrangement of [2,1,4,3] in the IM sequence is repeated until all bit patterns of the IM sequence correspond to I 1 Then, according to the IM bit sequence of group 1, find the corresponding I 1 The constellation pattern is arranged, thereby determining the distinguishable signal constellation patterns adopted by the four grids of the first sub-block corresponding to the first group of bits.

[0134] Secondly, a secure mapping between information bits and modulation symbols based on the chaotic sequence is performed. After the constellation pattern of the four grids of the first sub-block is determined, the constellation mapping of the four grids can be performed according to the DSM sequence. The chaotic values ​​numbered 5 to 8 are then extracted from the chaotic sequence and expressed as follows:

[0135]

[0136] Rearrange them from large to small, as shown below:

[0137]

[0138] The elements in The elements in correspond to each other. The element number in is the basis, Corresponding to a set of element indexes [4,3,1,2]. Figure 3 According to the random shift Gray mapping method proposed in this invention, a Gray mapping scheme is assigned as a reference for each of the four distinguishable constellation patterns. The Gray mapping reference table corresponding to the four grids in the first group is then cyclically shifted by 4, 3, 1, and 2 times, respectively, to obtain four random shift Gray mapping tables. After determining the random shift Gray mapping table corresponding to each grid, constellation mapping is performed on the four grids based on the DSM sequence, thereby determining the constellation mapping symbols for the four grids.

[0139] After the two groups of information bits are securely mapped with the chaotic sequence-based information bits, pattern indexes, and modulation symbols, the DD domain grid symbols of the OTFS system are Sure.

[0140] Step 4: OTFS System DD Domain Grid Symbol X DD The corresponding column vector is Satisfy x=vec(X DD ), where vec(·) refers to the column-wise vectorized operation. DD Use ISFFT to convert the symbolic matrix X into the TF domain TF .X TF It is expressed as follows:

[0141]

[0142] Among them, F, F H They represent the discrete Fourier transform matrix and the discrete inverse Fourier transform matrix respectively.

[0143] Step 5: Assuming typical rectangular pulse shaping, transform the TF domain symbol matrix X into TF Convert to time domain signal s represents the following:

[0144]

[0145] Then, a CP of length 2 is added to the beginning of s to obtain the baseband signal s cp , where N cp ≥L, where L is the maximum delay spread of the channel.

[0146] Step 6: Baseband signal s cp Perform digital up-conversion, digital-to-analog conversion, RF up-conversion, and finally transmit to the antenna for transmission.

[0147] The receiving end processing flow is as follows:

[0148] Step 7: Perform RF down-conversion, analog-to-digital conversion, and digital down-conversion on the received signal to obtain the baseband signal r cp .in

[0149] Step 8: Baseband signal r cp Perform the CP operation of removing the length of 2 to obtain r.

[0150] Step 9: Perform discrete Wigner transform on r and convert it to TF domain, which is expressed as follows:

[0151] Y TF =F M R

[0152] Where R = unvec M,N (r) represents the matrix R with r arranged into M rows and N columns.

[0153] Step 10: Perform SFFT transformation on the TF domain signal matrix R, which is expressed as follows:

[0154]

[0155] in For the DD domain signal, the eavesdropper Eve is unaware of the secure mapping method and chaotic initial value used in the present invention. Therefore, even if she obtains the transmitted DD domain symbol matrix Y, she cannot perform the decoding index information and constellation demapping operations in step 11.

[0156] Step 11: Determine two receive subblocks based on the subblock division in Step 2. Since each subblock is processed using the same demapping method, for simplicity, the first subblock is used as an example to illustrate the original information bit recovery operation. For the first subblock, demapping is performed between the information bits and the constellation index and modulation symbol based on the chaotic sequence.

[0157] First, for the first subblock, the constellation mode adopted by each grid is determined based on the received symbols of its four grids, resulting in a constellation mode index of length 4. Based on the chaotic sequence shared in step 1 and the secure mapping rule between information bits based on the chaotic sequence and constellation mode index in step 3, a table lookup is used to obtain a length-4 IM sequence.

[0158] Next, for the first sub-block, the randomly shifted Gray mapping tables corresponding to the four grids are derived based on the chaotic sequence shared in step 1 and the secure mapping rules between information bits, constellation mode indices, and modulation symbols based on the chaotic sequence in step 3. The constellation symbols of the four grids are then demapped using the corresponding randomly shifted Gray mapping tables to recover the DSM sequences of length 8.

[0159] After the two sub-blocks perform demapping between information bits based on chaotic sequences and constellation pattern indexes and modulation symbols, the legal receiving end has recovered the 24 transmitted information bits.

Claims

1. A method for implementing high-spectral-efficiency secure transmission, characterized in that: The steps include: Step 1: The transmitter processes as follows: Step 1-1: Before security indexing, legitimate transceivers share the initial value of the chaotic sequence and use the same chaotic mapping method to share a set of chaotic sequences. The chaotic sequences are represented as d1, d2, ...; Step 1-2: For an OTFS system with M subcarriers with a subcarrier spacing of Δf and N symbols with a symbol time of T, the total bandwidth is B = MΔf, and the signal frame duration is T f =NT; the OTFS system is critically sampled, i.e., T∆f = 1; before OTFS modulation, the MN DD domain grids are divided into g sub-blocks, each of which has a size of n = MN / g; at the same time, the m information bits to be transmitted are equally divided into g groups, each containing p = m / g bits; Since each group of information bits is processed using the same mapping method, the bit grouping requirements for the βth group of information bits are as follows, where β∈{1,2,…,g}; The p information bits of group β are divided into two parts: The first part is called the IM sequence, which consists of p1 bits and determines the index arrangement of n distinguishable signal constellation patterns. The arrangement of the w-th constellation pattern is shown as follows: in represents the index of the αth constellation pattern, where there are n! permutations of n distinguishable signal constellation patterns, corresponding to the value range of w; For the n grids of the βth group, n different constellation modes are used, which are expressed as follows: in, That is, different grids adopt different constellation modes; therefore, for the arrangement of n different constellation modes, it is required The second part is called the data symbol modulation DSM sequence, which includes p2 bits and determines n constellation mapping symbols, as shown below: in Represents the symbol corresponding to the αth constellation mode; for n distinguishable constellation modes, all are Q-order modulation, p2 = nlog2 Q; From the above, we can see that the total number of information bits should satisfy: Step 1-3: Based on the chaotic sequence and grouping bits obtained in steps 1-1 and 1-2, secure mapping is performed between information bits based on the chaotic sequence and constellation mode index and modulation symbols; The security mapping method for the βth group of information bits is as follows: First, a secure mapping between information bits based on the chaotic sequence and constellation pattern index is performed, and n chaotic values ​​are extracted from the chaotic sequence, which are expressed as follows: Rearrange them from large to small in value, as shown below: in, represents the jth largest chaos value, The elements in The elements in correspond to each other. The element number in is the basis, Corresponds to a set of element number indexes; all bit patterns of the IM sequence correspond to I β A constellation pattern arrangement; according to the IM bit sequence of the βth group, find the corresponding I β The constellation pattern is arranged, thereby determining the distinguishable signal constellation pattern adopted by the n grids of the β-th sub-block corresponding to the β-th group of bits; Secondly, a secure mapping between information bits and modulation symbols based on the chaotic sequence is performed. After the constellation pattern of the n grids of the β-th sub-block is determined, constellation mapping of the n grids is performed according to the DSM sequence. For any constellation pattern, each constellation mapping symbol corresponds to a unique bit arrangement. The random shift Gray mapping method is used to extract n chaotic values ​​from the chaotic sequence, which are expressed as follows: Rearrange them from large to small, as shown below: in, represents the jth largest chaos value, The elements in The elements in correspond to each other. The element number in is the basis, It also corresponds to a set of element indices; after determining the random shift Gray mapping table corresponding to each grid, the constellation mapping of n grids can be performed according to the DSM sequence, and then the constellation mapping symbols of the n grids can be determined; After the g groups of information bits are securely mapped to the information bits, mode indexes, and modulation symbols based on chaotic sequences, the DD domain grid symbols of the OTFS system are Sure; Steps 1-4: OTFS System DD Domain Grid Symbol X DD The corresponding column vector is Satisfy x=vec(X DD ), where vec(·) refers to the column-wise vectorized operation; for X DD Use the inverse symplectic Fourier transform (ISFFT) to convert the symbolic matrix X into the TF domain. TF , X TF It is expressed as follows: Among them, F, F H They represent the discrete Fourier transform matrix and the discrete inverse Fourier transform matrix respectively; Steps 1-5: Assuming typical rectangular pulse shaping, transform the TF domain symbol matrix X into TF Convert to time domain signal It is expressed as follows: Then, the length N cp The CP is added to the beginning of s to obtain the baseband signal s cp , where N cp ≥L, L is the maximum delay spread of the channel; Step 1-6: Baseband signal s cp Perform digital up-conversion, digital-to-analog conversion, RF up-conversion, and finally transmit to the antenna for transmission; Step 2: The receiving end processing flow is as follows: Step 2-1: Perform RF down-conversion, analog-to-digital conversion, and digital down-conversion on the received signal to obtain the baseband signal r cp , Step 2-2: Baseband signal r cp Remove the CP operation and get r, Step 2-3: Perform discrete Wigner transform on r and convert it to TF domain, which is expressed as follows: Y TF =F M R Where R = unvec M,N (r) represents the matrix R with M rows and N columns arranged in columns; Step 2-4: Perform sigmoid Fourier transform (SFFT) on the TF domain signal matrix R, which is expressed as follows: in Receive signals for the DD domain; Step 2-5: Determine g receiving sub-blocks according to the sub-block division in step 1-2; for the β-th sub-block, the original information bits are recovered as follows, where β∈{1,2,…,g}; For the βth sub-block, demapping is performed between the information bits based on the chaotic sequence and the constellation mode index and the modulation symbol respectively; First, for the βth sub-block, the constellation mode adopted by each grid is determined according to the received symbol situation of its n grids, and a constellation mode index of length n is obtained; according to the chaotic sequence shared in step 1-1 and the security mapping rule between the information bits based on the chaotic sequence and the constellation mode index in step 1-3, a table with a length of n is obtained. IM sequence; Secondly, for the βth sub-block, based on the chaotic sequence shared in step 1-1 and the secure mapping rules between information bits, constellation mode indexes, and modulation symbols based on the chaotic sequence in step 1-3, the randomly shifted Gray mapping tables corresponding to the n grids are obtained. Then, referring to the corresponding randomly shifted Gray mapping tables, the constellation symbols of the n grids are demapped respectively, and a QDSM sequence of length p2 = nlog2 is recovered. After demapping the information bits based on the chaotic sequence and the constellation pattern index and modulation symbols in the g sub-blocks respectively, the legal receiving end has recovered the m information bits transmitted.

2. A method for realizing high spectral efficiency and secure transmission according to claim 1, characterized in that: The constellation mapping adopts Gray mapping.

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