Orthogonal index modulation OTFS communication method based on spread spectrum

Abstract

The invention discloses an orthogonal index modulation OTFS communication method based on spread spectrum, and belongs to the technical field of information and communication. The invention aims to solve the problem of low spectrum utilization rate of the existing S-OFDM-IM system. Comprising the following steps: dividing bit streams into a plurality of groups at a sending end; each group of bit signals is divided into two parts, one part of bits are used for constellation modulation, and the other part of bits are used for controlling indexes of subcarriers; generating a DD domain signal from each group of modulated signals through an OTFS block generator, and performing spectrum spreading, inverse Fourier transform, Heisenberg transform, cyclic prefix addition, parallel-serial conversion and digital-to-analog conversion to obtain a sending signal; and at a receiving end, carrying out analog-to-digital conversion and serial-to-parallel conversion on a received signal, removing a cyclic prefix to obtain a one-dimensional time domain received signal, carrying out Wigner transformation, Schmidt Fourier transformation and de-spread spectrum, then carrying out de-mapping and demodulation, and obtaining a bit stream of the receiving end through a bit synthesizer. The invention is used for modulation of communication signals.

Description

Technical Field

[0001] The invention relates to an orthogonal index modulation (OTFS) communication method based on spread spectrum, and belongs to the technical field of information and communication. Background Art

[0002] Low-Earth orbit satellite communications have advantages such as global coverage and flexible deployment, but the high mobility of satellites will lead to severe Doppler effects, and traditional modulation technologies are difficult to meet communication requirements. OTFS (Orthogonal Time-Frequency-Space) is a modulation technology that processes signals in the delay-Doppler domain, which can effectively counteract the time-varying and frequency-varying characteristics of the channel and improve the performance of the communication system in high-speed mobile scenarios.

[0003] The newly proposed precoded OFDM-IM (S-OFDM-IM) uses precoding matrices such as WH and ZC to expand the non-zero data symbols and their indexes of the activated subcarriers, and then compresses them to all available subcarriers, thereby increasing the transmit diversity by using multipath and index diversity, and can better cope with multipath fading channels and improve the reliability of the system. Due to the introduction of index modulation and spread spectrum operations, although the reliability and anti-interference ability of the system are improved to a certain extent, it also leads to a decrease in spectrum efficiency.

[0004] In time-varying channel environments such as high-speed mobile, OTFS can transform fast time-varying channels into two-dimensional time-invariant channels in the delay-Doppler (DD) domain, so that all symbols on the transmission frame can obtain the same channel gain. Index-based OTFS modulation inherits the above advantages of OTFS. On the basis of index modulation, it further enhances the resistance to Doppler frequency deviation, making the transmission of index information and data information more stable and reliable in high-dynamic scenarios, reducing index errors and data errors caused by frequency deviation. OTFS-IM (OTFS-index modulation) is a new modulation technology developed on the basis of OTFS.

[0005] In OTFS technology, traditional modulation methods such as PSK (phase shift keying) and QAM (quadrature amplitude modulation) mainly perform symbol mapping in the time-frequency domain. OTFS-IM uses the idea of ​​index modulation. In addition to the traditional symbol-carrying information, it also uses the bit splitter and sub-block divider to flexibly adjust the length of the index bit and symbol bit according to its own characteristics, thereby realizing the dynamic configuration of the index bit and symbol bit. Compared with the relatively fixed bit allocation method in the index-based OFDM modulation, it can make full use of limited resources to transmit more information and improve spectrum utilization. At the same time, it can use index information to convey part of the data, reducing the energy demand for symbol transmission and improving energy efficiency while ensuring the information transmission rate.

[0006] OTFS-IM introduces an additional information dimension through index modulation, making it more difficult for interference signals to destroy all useful information. When there is interference in the channel, even if some symbols are interfered with, the receiver can still use the index information and uninterrupted symbols to recover the data to enhance the anti-interference capability. Summary of the invention

[0007] Aiming at the problem of low spectrum utilization rate of the existing S-OFDM-IM system, the present invention provides an orthogonal index modulation (OTFS) communication method based on spread spectrum.

[0008] The present invention provides an orthogonal index modulation (OTFS) communication method based on spread spectrum, comprising:

[0009] At the transmitting end, the bit stream is divided into multiple groups; each group of bit signals is divided into two parts, one part of the bits is used for constellation modulation, and the other part of the bits is used to control the index of the subcarrier; each group of modulated signals generates a DD domain signal through an OTFS block generator; the DD domain signal is spread based on the Walsh-Hadamard matrix or the Zadoff-Chu matrix to obtain a spread DD domain signal, the spread DD domain signal is converted into a time-frequency domain signal through an inverse sigmoid Fourier transform, and then converted into a time domain signal through a Heisenberg transform, and a cyclic prefix is ​​added and parallel-to-serial conversion and digital-to-analog conversion are performed to obtain a transmission signal;

[0010] At the receiving end, the received signal is converted from analog to digital and from serial to parallel, and the cyclic prefix is ​​removed to obtain a one-dimensional time domain received signal; the one-dimensional time domain received signal is subjected to Wigner transform to obtain a two-dimensional signal in the time-frequency domain, and then subjected to sigmoid Fourier transform to obtain a DD domain received signal; the DD domain received signal is despread and redivided into multiple subgroups, and the part of each subgroup received signal corresponding to the transmitting end is demapped and demodulated, and then the receiving end bit stream is obtained through a bit synthesizer.

[0011] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, at the transmitting end, the bit stream is divided into g groups by a bit splitter, and the number of bits of each group of bit signals is p a , where the number of bits used to control the subcarrier index is p1, and the number of bits used for constellation modulation is p2;

[0012] Assume that the OTFS frame size output by the OTFS block generator is M×N, where M is the number of subcarriers and N is the number of symbols; divide the total number of grids MN into g subblocks, each subblock size is m×n, where m is the number of subcarriers in the subblock and n is the number of symbols in the subblock; then:

[0013]

[0014] Where k is the number of sub-block subcarrier activations, C(mn,k) is the number of activation index bit combinations, and M mod is the modulation order.

[0015] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, for the β-th sub-block, β=1, 2, 3, ..., g, the activation index I of the β-th sub-block is β It is expressed as:

[0016] I β ={i β,1 ,…,i β, k},

[0017] where i β,γ ∈{1,2,…,n},β={1,2,…,g},γ={1,…,k};

[0018] The constellation mapping S of the βth sub-block β It is expressed as:

[0019] S β ={s β (1),…,s β (k)},

[0020] where s β (γ)∈Λ,β={1,2,…,g},γ={1,2,…,k}, Λ represents the set of constellation modulation symbols;

[0021] Then the bit signal x of the βth sub-block is β for:

[0022] x β = {I β ,S β},β={0,…,g}.

[0023] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, the DD domain signal generated by the OTFS block generator is represented by X DD :

[0024]

[0025] In the formula κ=0,...,N-1, ι=1,...,M-1, M mod Constellation diagram of 1-order constellation modulation.

[0026] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, the DD domain signal is spread spectrum based on the Walsh-Hadamard matrix or the Zadoff-Chu matrix, and the DD domain signal after spread spectrum is expressed as sDD :

[0027]

[0028] Where τ is the time delay, v is the Doppler frequency shift, and w ij is the i-th row index information set w of the spread spectrum matrix W i The jth index information of , τ0 is the reference delay, v0 is the reference Doppler frequency shift, {x j} is a DD domain signal, indicating X DD The modulation symbol sequence.

[0029] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, the DD domain signal s after spread spectrum DD Convert to time-frequency domain signal X through inverse sigmoid Fourier transform FT :

[0030]

[0031] Where F M is the M-dimensional discrete Fourier matrix, is the N-dimensional discrete Fourier matrix F N The conjugate transposed matrix of ;

[0032] Time-frequency domain signal X FT Converted to time domain signal X through Heisenberg transform T :

[0033]

[0034] In the formula is the M-dimensional discrete Fourier matrix F M The conjugate transposed matrix of .

[0035] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, the time domain signal X T After adding a cyclic prefix and performing parallel-to-serial conversion and digital-to-analog conversion, the transmitted signal X is obtained.

[0036] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, the received signal X transmitted through the channel to the receiving end is represented as Y, the received signal Y is converted into analog to digital and serial to parallel, and then the cyclic prefix is ​​removed to obtain a one-dimensional time domain received signal Y T ;

[0037] The signal Y is received in one-dimensional time domain T The two-dimensional signal in the time-frequency domain obtained after Wigner transformation is expressed as Y FT :

[0038] Y FT =FM Y T .

[0039] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, a two-dimensional signal Y in the time-frequency domain is FT The received signal in the DD domain is represented by Y DD :

[0040]

[0041] According to the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention, the DD domain received signal Y is quantized by using the MMSE algorithm. DD Conduct testing and obtain

[0042]

[0043] Where H is the channel matrix, I MN is the identity matrix, ρ snr is the average signal-to-noise ratio;

[0044] Will Rearrange and transform into a two-dimensional signal in the delay-Doppler domain

[0045]

[0046] In the formula Represents a collection;

[0047] For two-dimensional signals After despreading, the signals are divided into multiple subgroups again, and the part of the received signal of each subgroup corresponding to the transmitting end is demapped and demodulated, and then the receiving end bit stream is obtained through the bit synthesizer.

[0048] Beneficial effects of the invention: The method of the invention performs orthogonal index modulation on the signal based on spread spectrum, solving the problems of low spectrum utilization and high bit error rate of the S-OFDM-IM system. In order to further improve the system diversity gain and anti-fading capability in complex channel environments, waveform modulation is performed based on the precoding matrix of OTFS-IM.

[0049] The method of the present invention is based on OTFS-IM. After expansion of different spread spectrum matrices, the signal effectively resists multipath interference or evenly distributes the signal energy in the entire frequency domain, so that the system can transmit more information within the same bandwidth, thereby improving the spectrum efficiency of the system. A more uniform power spectrum density means that the frequency band resources are more fully utilized.

[0050] The method of the present invention is based on OTFS-IM. After passing through the ZC or WH matrix, the signal performance is improved, which is better than the channel performance of the S-OFDM-IM system, and the bit error rate is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the principle of the transmitting end of the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention; W in the figure represents spread spectrum;

[0052] Figure 2 It is a schematic diagram of the frame structure design of the method of the present invention based on OTFS-IM;

[0053] Figure 3 It is a schematic diagram of the receiving end principle of the orthogonal index modulation OTFS communication method based on spread spectrum of the present invention;

[0054] Figure 4 It is a schematic diagram of the comparison of the WH and ZC precoding channel performances of the S-OTFS-IM system based on the method of the present invention and the existing S-OFDM-IM; in the figure, BER represents the bit error rate, and Es / No represents the signal-to-noise ratio;

[0055] Figure 5 It is a schematic diagram of channel performance comparison of the S-OTFS-IM system based on the method of the present invention. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0058] The present invention will be further described below in conjunction with the accompanying drawings, but is not intended to be a limitation of the present invention.

[0059] Specific implementation method 1. Combination Figures 1 to 3 As shown, the present invention provides an orthogonal index modulation OTFS communication method based on spread spectrum, comprising:

[0060] At the transmitting end, the bit stream is divided into multiple groups; each group of bit signals is divided into two parts, one part of the bits is used for constellation modulation, and the other part of the bits is used to control the index of the subcarrier; each group of modulated signals generates a DD domain signal through an OTFS block generator; the DD domain signal is spread based on the Walsh-Hadamard matrix or the Zadoff-Chu matrix to obtain a spread DD domain signal, the spread DD domain signal is converted into a time-frequency domain signal through an inverse sigmoid Fourier transform, and then converted into a time domain signal through a Heisenberg transform, a cyclic prefix (CP) is added, and parallel-to-serial conversion and digital-to-analog (P / S module) conversion are performed to obtain a transmission signal that is sent to the channel for transmission;

[0061] At the receiving end, the received signal is converted into analog-to-digital (S / P module) and serial-to-parallel, and then the cyclic prefix (CP) is removed to obtain a one-dimensional time domain received signal; the one-dimensional time domain received signal is subjected to Wigner transform to obtain a two-dimensional signal in the time-frequency domain, and then subjected to sigmoid Fourier transform to obtain a DD domain received signal; the DD domain received signal is despread and redivided into multiple subgroups, and the part of each subgroup received signal corresponding to the transmitting end is demapped and demodulated, and then the receiving end bit stream is obtained through a bit synthesizer.

[0062] After the DD domain signal in the transmitting end is expanded by the Zadoff-Chu sequence, the sequences generated by different root sequence numbers have an ideal cross-correlation characteristic during cyclic shift, thereby effectively resisting multipath interference.

[0063] After the DD domain signal in the transmitting end is expanded by the Walsh-Hadamard matrix, the signal energy is evenly distributed in the entire frequency domain, so that the system can transmit more information within the same bandwidth, thereby improving the spectrum efficiency of the system.

[0064] In high-speed mobile scenarios, the OTFS-IM system will be affected by the Doppler effect, causing the frequency of the received signal to shift. This frequency shift will destroy the orthogonality of the signal, thereby generating inter-carrier interference (ICI). Multipath propagation is a ubiquitous phenomenon that causes multiple different delays in the received signal, resulting in inter-symbol interference (ISI). At the same time, the signal energy may be concentrated in certain specific delay-Doppler regions, resulting in the waste of some frequency band resources. After the Zadoff-Chu sequence expansion, the sequences generated by different root numbers have ideal cross-correlation characteristics when cyclically shifted, that is, the cross-correlation of two different Zadoff-Chu sequences is zero or close to zero. This effectively resists multipath interference. After the signal is expanded by the Walsh-Hadamard matrix, the signal energy is evenly distributed throughout the frequency domain, allowing the system to transmit more information within the same bandwidth, thereby improving the system's spectrum efficiency. A more uniform power spectrum density means that frequency band resources are more fully utilized.

[0065] Walsh-Hadamard and Zadoff-Chu sequences are square and reversible, and have the following two key features: (i) the complex numbers of the two matrices have the same size. Therefore, each non-zero data symbol is evenly distributed on N subcarriers, which can enable S-OTFS-IM to achieve significant diversity gain over existing OTFS-IM schemes; (ii) the two matrices are orthogonal, i.e., G -1 =G H , which aims to achieve interference-free transmission, so that the Euclidean distance between any pair of signals before and after spread spectrum remains unchanged.

[0066] The present invention uses the Walsh-Hadamard matrix to spread the OTFS-IM system to improve the spectrum efficiency of the system, and uses the Zadoff-Chu sequence to spread the OTFS-IM system to resist multipath interference.

[0067] A.Walsh-Hadamard Matrix Theory:

[0068] The WH matrix recursively becomes:

[0069]

[0070] The size of the WH matrix is ​​N = 2 k Since all elements are real-valued, this matrix is ​​particularly suitable for low-complexity implementation.

[0071] B.Zadoff-Chu (ZC) matrix theory:

[0072] Construct the ZC root sequence as follows:

[0073]

[0074] Where q is an integer, m is any integer relative to N, and n = 1, 2, ..., N. The ZC matrix is ​​represented by f1 = [c1, ..., c N ] T , as its first column, and the other columns are cyclic shifts of f1. For example, when N=4, m=1 and q=0. f1=[-j,-1,-j,1] T . Construct an orthogonal matrix and let -j be a, then the above formula can be obtained as f1 = [a, -1, a, 1] T .calculate Here Then the ZC matrix is ​​as follows:

[0075]

[0076] The parameters are We can get ||W||2 =1.

[0077] The signal transmitted by the S-OTFS-IM system consists of two parts: one is the multivariate constellation modulation information carried by the activated grid points in the delay-Doppler domain, and the other is the index information implicitly transmitted by the combination of the activated grid points.

[0078] Further, at the transmitting end, the bit stream is divided into g groups by a bit splitter, and the number of bits in each group of bit signals is p a , according to its own characteristics, each group of bit signals is divided into two parts, where the number of bits used to control the subcarrier index is p1, and the number of bits used for constellation modulation is p2;

[0079] Combination Figure 2 As shown, it is assumed that the OTFS frame size output by the OTFS block generator is M×N, where M is the number of subcarriers and N is the number of symbols; Figure 1 As shown, the total number of grids MN is divided into g sub-blocks, each sub-block is m×n in size, and the number of grids is mn=M×N / g, where m is the number of sub-carriers in the sub-block and n is the number of symbols in the sub-block; then the total number of bits p in the bit stream is:

[0080]

[0081] Where k is the number of sub-block subcarrier activations, C(mn,k) is the number of activation index bit combinations, and M mod is the modulation order.

[0082] The total number of activated subcarriers is K = k × g. The p-bit information is divided into g groups, each containing p a =p / g bits, which are divided into two parts, one part of which is used for index selection and the other part is used for constellation mapping.

[0083] In this implementation, for the βth sub-block, the number of bits p1 is used for index selection, where β = 1, 2, 3, ..., g. For each sub-block, k activations are selected from the mn delay-Doppler domain grid points for transmitting data symbols. The activation index I of the βth sub-block is β It is expressed as:

[0084] I β ={i β,1 ,…,i β,k},

[0085] where i β,γ ∈{1,2,…,n},β={1,2,…,g},γ={1,…,k};

[0086] In addition, p2=k(log2(M mod)) Binary bits are used for constellation mapping, and the constellation mapping S of the βth sub-block β It is expressed as:

[0087] S β ={s β (1),…,s β (k)},

[0088] where s β (γ)∈Λ,β={1,2,…,g},γ={1,2,…,k}, Λ represents the set of constellation modulation symbols;

[0089] Thus, the data symbol x of the βth sub-block is β It can be activated by index I β and constellation mapping combination S, then the bit signal x of the βth sub-block is β for:

[0090] x β = {I β ,S β},β={0,…,g}.

[0091] The signals of each group are combined into an OTFS block of size M×N in the DD domain through the OTFS block generator to obtain the output signal X after the DD domain index modulation is completed. DD .

[0092] Similarly, the index selection and constellation mapping synthesis of all sub-blocks are completed, so that a frame of OTFS-IM signal can be expressed as:

[0093]

[0094] This implementation adopts the combination number method. When the number of subcarrier blocks is large, if the number of index resources in each sub-block is mn, and the number of activation indexes in each sub-block is k, then all activation index combinations have a total of C(mn,k). Then the maximum number of binary bits b that can be used for index mapping should satisfy:

[0095] 2 b ≤C(mn,k).

[0096] The combinatorial number theory method determines the activation index sequence J = {c k ,c k-1 ,…,c i ,…,c2,c1}, where c i Represents the index of the i-th activated index resource. Each element in J satisfies the following equation:

[0097] Z=C(c k ,k)+…+C(c k,2)+C(c k ,1),

[0098] Where n>c k >…>c1>0; Z is a decimal number whose value is in the interval [0,C(mn,k)-1].

[0099] The specific steps are summarized as follows:

[0100] Step 1: For each sub-block, convert the binary bits used for index selection into a decimal number Z;

[0101] Step 2: First determine ck, maximize ck so that C(c k ,k)≤Z, update Z, Z=ZC(c k ,k);

[0102] Step 3: Determine ck-1 so that C(c k ,k)≤Z, update Z, Z=ZC(c k ,k) And so on to get each ci;

[0103] Step 4: After iterating to the end, you can get the activation index sequence:

[0104] J={c k ,c k-1 ,…,c i ,…,c2,c1}+1.

[0105] After all sub-blocks have completed index mapping and multi-constellation modulation, the modulated information will flow into the OTFS signal frame generator. Figure 1 The frame format in the OTFS-IM system is used to obtain the two-dimensional signal in the delay-Doppler domain. The DD domain signal generated by the OTFS block generator is expressed as X DD :

[0106]

[0107] In the formula κ=0,...,N-1, ι=1,...,M-1, M mod Constellation diagram of 1-order constellation modulation.

[0108] Furthermore, the DD domain signal is spread based on the Walsh-Hadamard matrix or the Zadoff-Chu matrix, and the DD domain signal after spread is expressed as s DD :

[0109]

[0110] Where τ is the time delay, v is the Doppler frequency shift, and w ij is the i-th row index information set w of the spread spectrum matrix W i The jth index information of , τ0 is the reference delay, v0 is the reference Doppler frequency shift, {x j} is a DD domain signal, indicating X DD The modulation symbol sequence of the spreading matrix W is of dimension N×N.

[0111] DD domain signal after spread spectrum DD Convert to the time-frequency domain signal X through inverse symplectic Fourier transform (ISFFT) FT :

[0112]

[0113] Where F M is the M-dimensional discrete Fourier matrix, is the N-dimensional discrete Fourier matrix F N The conjugate transposed matrix of ;

[0114] In the time-frequency domain, the time dimension is sampled with T, and the frequency dimension is sampled with Δf to obtain a two-dimensional grid of size N×M in the time-frequency domain. The duration of a single S-OTFS-IM signal frame is NT, and the occupied frequency bandwidth is MΔf. Next, the two-dimensional time-frequency signal X is transformed using the M-point IFFT transform FT Convert it into a time domain signal to obtain the time domain expression of the system signal frame.

[0115] Time-frequency domain signal X FT Converted to time domain signal X through Heisenberg transform T :

[0116]

[0117] In the formula is the M-dimensional discrete Fourier matrix F M The conjugate transposed matrix of .

[0118] To avoid interference between signal frames, each time domain signal X T Add the cyclic prefix to get X CP After parallel-to-serial conversion and digital-to-analog conversion, the transmission signal X is obtained and sent to the wireless channel.

[0119] Going a step further, combined Figure 3 As shown, the received signal X after the transmission signal passes through the channel and reaches the receiving end is represented as Y. The received signal Y is converted into digital and serial to parallel, and then the cyclic prefix is ​​removed to obtain a one-dimensional time domain received signal Y T ;

[0120] The signal Y is received in one-dimensional time domainT The two-dimensional signal in the time-frequency domain obtained after Wigner transformation is expressed as Y FT :

[0121] Y FT =F M Y T .

[0122] In this embodiment, the two-dimensional signal Y in the time-frequency domain FT The DD domain received signal obtained by performing symplectic Fourier transform is represented as Y DD , let Y DD (τ,v) is the DD domain signal, which is obtained by sigmoid Fourier transform:

[0123]

[0124] In the S-OTFS-IM system, since each signal frame only activates part of the grid point resources for information transmission, the unactivated grid point resources remain silent. In order to recover the transmitted information, the receiver can first detect the position information of the activated grid points in each sub-block and recover the index bits of the sub-block. Then, the activated grid points are demodulated by a multi-element constellation.

[0125] The MMSE algorithm is used to calculate the received signal Y in the DD domain. DD Conduct testing and obtain

[0126]

[0127] Where H is the channel matrix, I MN is the identity matrix, ρ snr is the average signal-to-noise ratio;

[0128] Will Rearrange and transform into a two-dimensional signal in the delay-Doppler domain

[0129]

[0130] In the formula Represents a collection;

[0131] For two-dimensional signals After despreading, the signals are divided into multiple subgroups again, and the part of the received signal of each subgroup corresponding to the transmitting end is demapped and demodulated, and then the receiving end bit stream is obtained through the bit synthesizer.

[0132] according to Figure 2 The signal frame format of the system in the delay-Doppler domain will be The proposed index detection algorithm is used to obtain the location information of the activation grid points from each word block. In order to maintain generality, the βth sub-block For example:

[0133] First, the index detection algorithm uses the input received sub-block information and the parameters m and n of the sub-block sub-part size to express each sub-part as a formula according to the signal frame format of the system in the delay-Doppler domain, where:

[0134]

[0135] Then, each sub-part is vectorized and converted into a one-dimensional vector of mn×1. Then, the grid energy of the sub-block is calculated and averaged. Then, the position information of the first k with the largest average energy is found based on the calculated average energy information. The specific operation is to use a function to find the position corresponding to the maximum value from the mn average energies.

[0136] Finally, based on the obtained position information of the activated grid points, the index mapper in the S-OTFS-IM system receiver recovers the index bits of the sub-blocks. At the same time, based on the position information of the activated grid points, the grid points at the corresponding positions of the two sub-parts are demodulated by multi-constellation to recover the corresponding modulation bits. When the index bits and modulation bits of all sub-blocks are recovered, the transmission information is recovered based on the one-to-one correspondence between the sub-blocks and the bit blocks.

[0137] The DD domain receives the signal Y DD After despreading, the signals are divided into g groups again, and then the part corresponding to the transmitting end in each subgroup is demapped and demodulated. The received signal is correlated using the same spreading code as the transmitting end to restore the original modulated data.

[0138] Finally, Matlab is used to perform simulation analysis to verify its correctness.

[0139] Combination Figure 4 As shown in the figure, based on the precoding matrix and the OTFS-IM system, the signal system performance is improved, which is better than the channel performance of the S-OFDM-IM system and the bit error rate is reduced.

[0140] Combination Figure 5 As shown in the figure, based on OTFS-IM, after the signal is expanded by the Walsh-Hadamard matrix, the signal energy is evenly distributed in the entire frequency domain, allowing the system to transmit more information within the same bandwidth, thereby improving the system's spectrum efficiency. A more uniform power spectrum density means that the frequency band resources are more fully utilized.

[0141] Based on OTFS-IM, after the signal is expanded by the Zadoff-Chu matrix, the cross-correlation of the sequence is zero or close to zero. This effectively resists multipath interference. The channel performance is improved compared to the matrix without expansion.

[0142] This confirms the correctness of the method of the present invention in improving the bit error rate performance by improving spectrum utilization, resisting multipath effects, etc.

[0143] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A spread spectrum based orthogonal index modulation OTFS communication method, characterized in that: include, At the transmitting end, the bit stream is divided into multiple groups; each group of bit signals is divided into two parts, one part of the bits is used for constellation modulation, and the other part of the bits is used to control the index of the subcarrier; each group of modulated signals generates a DD domain signal through an OTFS block generator; the DD domain signal is spread based on the Walsh-Hadamard matrix or the Zadoff-Chu matrix to obtain a spread DD domain signal, the spread DD domain signal is converted into a time-frequency domain signal through an inverse sigmoid Fourier transform, and then converted into a time domain signal through a Heisenberg transform, and a cyclic prefix is ​​added and parallel-to-serial conversion and digital-to-analog conversion are performed to obtain a transmission signal; At the receiving end, the received signal is converted into analog-to-digital and serial-to-parallel, and the cyclic prefix is ​​removed to obtain a one-dimensional time domain received signal; the one-dimensional time domain received signal is transformed by Wigner to obtain a two-dimensional signal in the time-frequency domain, and then subjected to symplectic Fourier transform to obtain a DD domain received signal; The DD domain received signal is despread and re-divided into multiple sub-groups. The part of each sub-group received signal corresponding to the transmitting end is demapped and demodulated, and then the receiving end bit stream is obtained through a bit synthesizer.

2. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 1, characterized in that: At the transmitting end, the bit stream is divided into g groups by a bit splitter, and the number of bits in each group of bit signals is p a , where the number of bits used to control the subcarrier index is p1, and the number of bits used for constellation modulation is p2; Assume that the OTFS frame size output by the OTFS block generator is M×N, where M is the number of subcarriers and N is the number of symbols; divide the total number of grids MN into g subblocks, each subblock size is m×n, where m is the number of subcarriers in the subblock and n is the number of symbols in the subblock; then: Where k is the number of sub-block subcarrier activations, C(mn,k) is the number of activation index bit combinations, and M mod is the modulation order.

3. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 2, characterized in that: For the βth sub-block, β = 1, 2, 3, ..., g, the activation index I of the βth sub-block is β It is expressed as: I β ={i β,1 ,…,i β, k}, among them β,γ ∈{1,2,…,n},β={1,2,…,g},γ={1,…,k}; The constellation mapping S of the βth sub-block β It is expressed as: S β ={s β (1),…,s β (k)}, where s β (γ)∈Λ,β={1,2,…,g},γ={1,2,…,k}, Λ represents the set of constellation modulation symbols; Then the bit signal x of the βth sub-block is β for: x β ={I β ,S β },β={0,…,g}.

4. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 3, characterized in that: The DD domain signal generated by the OTFS block generator is represented by X DD : In the formula M mod Constellation diagram of 1-order constellation modulation.

5. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 4, characterized in that: The DD domain signal is spread based on the Walsh-Hadamard matrix or the Zadoff-Chu matrix, and the DD domain signal after spread is expressed as s DD : Where τ is the time delay, v is the Doppler frequency shift, and w ij is the i-th row index information set w of the spread spectrum matrix W i The jth index information of , τ0 is the reference delay, v0 is the reference Doppler frequency shift, {x j } is a DD domain signal, indicating X DD modulation symbol sequence.

6. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 5, characterized in that: DD domain signal after spread spectrum DD Convert to time-frequency domain signal X through inverse sigmoid Fourier transform FT : Where F M is the M-dimensional discrete Fourier matrix, is the N-dimensional discrete Fourier matrix F N The conjugate transposed matrix of ; Time-frequency domain signal X FT Converted to time domain signal X through Heisenberg transform T : In the formula is the M-dimensional discrete Fourier matrix F M The conjugate transposed matrix of .

7. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 6, characterized in that: Time domain signal X T After adding a cyclic prefix and performing parallel-to-serial conversion and digital-to-analog conversion, the transmitted signal X is obtained.

8. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 7, characterized in that: The received signal X that reaches the receiving end through the channel is represented as Y. The received signal Y is converted into digital and serial to parallel, and then the cyclic prefix is ​​removed to obtain the one-dimensional time domain received signal Y. T ; The signal Y is received in one-dimensional time domain T The two-dimensional signal in the time-frequency domain obtained after Wigner transformation is expressed as Y FT : Y FT =F M Y T 。 9. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 8, characterized in that: The two-dimensional signal Y in the time-frequency domain FT The received signal in the DD domain is represented by Y DD :

10. The orthogonal index modulation (OTFS) communication method based on spread spectrum according to claim 9, characterized in that: The MMSE algorithm is used to calculate the received signal Y in the DD domain. DD Conduct testing and obtain Where H is the channel matrix, I MN is the identity matrix, ρ snr is the average signal-to-noise ratio; Will Rearrange and transform into a two-dimensional signal in the delay-Doppler domain In the formula Represents a collection; For two-dimensional signals After despreading, the signals are divided into multiple subgroups again, and the part of the received signal of each subgroup corresponding to the transmitting end is demapped and demodulated, and then the receiving end bit stream is obtained through the bit synthesizer.

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