Spatial modulation and space-time code assisted signal recovery method

Abstract

The invention discloses a signal recovery method assisted by spatial modulation and space-time codes, which comprises the following steps of: 1, performing spatial modulation on information bit stream groups according to the number of time slots and the number of carriers to obtain spatial modulation symbols; 2, mapping the spatial modulation symbols into a space-time coding structure; 3, performing orthogonal time-frequency-space multi-carrier modulation on the spatial modulation symbols with the same transmission period, and transmitting the data symbols on a plurality of transmitting antennas respectively; and step 4, carrying out signal detection recovery on the transmission data symbols obtained in the step 3 based on the special sparsity of the signal structure. The method is used for recovering various source end signals which cannot be directly measured, high transmission rate and high diversity gain are realized, and the problems of poor signal detection performance and relatively high calculation complexity in the signal recovery process of a multi-antenna multi-carrier system are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of communication device signal transmission system and signal processing, and particularly relates to a space modulation and space-time code assisted signal recovery method based on channel sparsity. BACKGROUND

[0002] Signal detection is one of the key parts of a communication system receiver, and the accuracy of signal detection determines the performance of the system, which has a crucial influence on the system performance. The existing signal detection algorithms are difficult to balance high performance and low complexity. At present, the research focus of signal detection algorithm involves linear detection algorithm, nonlinear signal detection algorithm, and cascaded detection algorithm. Linear detection algorithm mainly includes traditional maximum likelihood algorithm, minimum mean square error detection algorithm, maximum ratio combining detection and its modified and derived signal detection algorithm. Linear detection algorithm is simple to operate, but involves matrix inversion multiplication and other operations, which has extremely high complexity. Nonlinear detection algorithm mainly includes message passing type signal detection algorithm, Bayesian detection algorithm, and deep learning combined algorithm, etc. Nonlinear detection algorithm involves various iterations and has good performance but is complex to implement. The cascaded detection algorithm combines the advantages of the two algorithms, which further improves the performance at the cost of complexity.

[0003] In addition, the joint design of multiple antennas and waveforms brings higher spectrum efficiency and performance gain, and therefore has very necessary research value. However, with the introduction of multiple antenna technology, signal detection is further difficult, and the complexity is further improved, and the difficulty of signal detection is further expanded. At present, the research on the joint design of multiple antennas and waveforms is still in the initial stage, and the research on signal detection algorithm balancing high performance and low complexity needs to be further carried out. SUMMARY

[0004] To solve the above technical problems, the application provides a space modulation and space-time code assisted signal recovery method, which is used for recovering various source signals that cannot be directly measured, realizes fast transmission rate and high diversity gain, and solves the problems of poor signal detection performance and high calculation complexity in the signal recovery process of a multiple antenna and multiple carrier system.

[0005] The purpose of the application is realized by the following technical scheme, a space modulation and space-time code assisted signal recovery method, comprising the following steps:

[0006] Step 1, spatial modulation is performed on the information bit stream grouping according to the number of time slots and the number of carriers, to obtain spatial modulation symbols;

[0007] Step 2, mapping the spatial modulation symbols into a space-time coding structure;

[0008] Step 3: Take spatial modulation symbols with the same transmission period and perform orthogonal time-frequency space-carrier modulation, and transmit data symbols on multiple transmitting antennas respectively;

[0009] Step 4: Based on the sparsity of the signal structure, perform signal detection and recovery on the transmitted data symbols obtained in Step 3.

[0010] Preferably, in step 1, the specific method for spatially modulating the information bit stream groups according to the number of time slots and the number of carriers is as follows:

[0011] Suppose the system has N t Root transmitting antenna, N r Root receiving antenna, N a = 1 active antenna, and the system transmits a total of M subcarriers and N symbols, dividing the information bits into M×N groups, where B(k,l)=b1+b2 represents the bit information transmitted by the l-th subcarrier in the k-th time slot;

[0012]

[0013] b1 is used to select the active antenna, where Indicates the number of effective antenna combinations. b1 represents the floor function; b2 is used to generate a constellation mapping symbol s, where L represents the order of the constellation mapping. The spatial modulation symbol of the l-th subcarrier in the k-th time slot can then be represented as:

[0014] x(k,l)=[…,0,s q ,0,…] T k∈[1,N], l∈[1,M]

[0015] In the formula, q represents the index of the activated antenna, and s q This represents the corresponding constellation mapping symbol.

[0016] Preferably, in step 1, the spatial modulation symbol of the l-th subcarrier in the k-th time slot can also be represented as:

[0017]

[0018] Preferably, in step 2, Almouti coding is used to map spatial modulation symbols to a space-time coding structure.

[0019] Preferably, in step 2, the method of mapping spatial modulation symbols to a space-time coding structure using Almouti coding is as follows:

[0020] The Almouti structure calls spatial modulation symbols, and in the t-th transmission period, B t (k,l)=b1 t +b2 tInformation bits are transmitted, in which:

[0021]

[0022] b1 is used to carry antenna index information, and b2 is used to generate two LQAM constellation mapping symbols s. The transmission matrix of all transmission periods in the k-th time slot and the l-th subcarrier is a codebook, which can be expressed as:

[0023]

[0024] Among them, I k = (k1,k2) represents the set of indices of the active antennas, S k = (S1, S2) represents the set of corresponding constellation mapping symbols.

[0025] Preferably, in step 3, symbols with the same transmission period are used for orthogonal time-frequency space-time multicarrier (OTFS) modulation, and data symbols are transmitted on multiple transmit antennas respectively.

[0026] Preferably, in step 3, the specific methods for modulation and demodulation are as follows:

[0027] The symbol on the i-th antenna during the t-th transmission cycle That is, the signal in each column of the codebook matrix is ​​re-represented as an S×N dimensional symbol matrix as follows:

[0028]

[0029] Transmitted signals at the transmitting end OTFS modulation is performed, and the received signal is obtained by OTFS demodulation at the receiving end through a time-delay Doppler channel. The overall input-output transformation relationship is as follows:

[0030]

[0031] Where H is the bi-dispersive channel matrix, N is the equivalent channel noise, and F N Let I be the Nth order Fourier transform matrix. M It is an M-order identity matrix. Let be the inverse of the Nth-order Fourier transform matrix. Then the equivalent channel matrix of the system is:

[0032]

[0033] Preferably, in step 4, the specific method for signal detection and recovery of transmitted data symbols is as follows:

[0034] Treating a codebook as a detection unit, for a transmitted signal, the signal from all transmit antennas in the t-th transmission period (t∈[1,T]), k-th time slot (k∈[1,N]), and l-th subcarrier (l∈[1,M]) for the transmitted signal is treated as a single transmitted signal unit symbol, as follows:

[0035]

[0036] For the received signal, the signal transmitted from all receiving antennas in the t-th transmission period (t∈[1,T]), m-th time slot (m∈[1,N]), and n-th subcarrier (n∈[1,M]) is treated as a single received signal unit symbol, represented as:

[0037]

[0038] For the channel matrix, the channel coefficients of all transmit antennas transmitting from the m-th time slot (n-th subcarrier) in the t-th transmission period (m-th time slot, n-th time slot, M-th time slot) to all receive antennas transmitting from the k-th time slot (l-th subcarrier) in the k-th time slot (l-th time slot, M-th time slot) form a block channel matrix as follows:

[0039]

[0040] Where: a = (n-1) × N + m, b = (k-1) × N + l ∈ [1, MN];

[0041] Define the transmit signal block as The received signal block is After being divided into blocks, the overall input-output relationship of the SM-STBC-OTFS system is as follows:

[0042]

[0043] Suppose I(i) and J(j) are the sets of indices of the non-zero blocks in the i-th row and j-th column, respectively, and the probability density function of the codebook is p. i,j ={p i,j (a q )|q=1,…,Q,a q ∈Λ}, where Q is the number of codebook types and Λ is the codebook set;

[0044] From the observation node y i The mean and variance of i∈[1,MN] are passed to message node x. j ,j∈I(i), the interference part Treat it as a Gaussian random variable:

[0045]

[0046] From the observation node y iThe mean and variance information of i∈[1,MN] are transmitted to the message node x. j For j∈I(i), the mean and variance of the interference component are as follows:

[0047]

[0048] probability density From variable node x j The j∈[1,MN] values ​​are passed to the message node y. i ,i∈J(j), can be represented as:

[0049]

[0050] Using probability density in message node x j and variable node y i The updates and iterations are performed between each iteration. The relationship between the probability density of the nth iteration and the probability density of the (n-1)th iteration is as follows:

[0051]

[0052] Where α∈(0,1] represents the convergence factor, used to change the convergence speed and improve performance, and c is the normalization constant, expressed as follows:

[0053]

[0054] Once the required number of iterations is met, the corresponding codebook symbol can be detected.

[0055]

[0056] By finding the index, the corresponding detection unit can be found in the codebook set, thus determining which codebook to select. Based on the correspondence between the codebook symbols and the bit stream, the corresponding bit information can be found by converting the index.

[0057] Compared with the prior art, the present invention has the following advantages:

[0058] This invention provides a spatial modulation and space-time code-assisted signal recovery method, and designs a spatial modulation and space-time code-assisted OTFS system. Compared with commonly used MIMO-OFDM systems, it simultaneously utilizes the time domain, frequency domain, spatial domain, and code domain to transmit data symbols, achieving high spectral efficiency and high diversity gain. The signal detection algorithm designed for this system, by setting up transmit signal units, receive signal units, and a channel block matrix, utilizes the block sparsity of the system channel equivalent matrix to perform detection using the codebook as the unit. This achieves significantly better bit error rate performance than other detection algorithms without sacrificing spectral efficiency, and with much lower computational complexity. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the signal recovery method using spatial modulation and space-time code assistance in an embodiment of the present invention.

[0060] Figure 2 This is a schematic diagram of the detection algorithm for the spatial modulation and space-time code-assisted signal recovery method in an embodiment of the present invention.

[0061] Figure 3 This is a schematic diagram showing the comparison between the bit error rate in this embodiment of the invention and the bit error rate in the traditional scheme;

[0062] Figure 4 This is a flowchart of the signal recovery method using spatial modulation and space-time code assistance in an embodiment of the present invention. Detailed Implementation

[0063] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0064] To address the above problems, the present invention provides a signal recovery method assisted by spatial modulation and space-time code, comprising the following steps:

[0065] Step 1: Spatial modulation is performed on the information bit stream groups according to the number of time slots and the number of carriers to obtain spatial modulation symbols:

[0066] Suppose the system has N t Root transmitting antenna, N r Root receiving antenna, N a = 1 active antenna, and the system transmits a total of M subcarriers and N symbols, dividing the information bits into M×N groups, where B(k,l)=b1+b2 represents the bit information transmitted by the l-th subcarrier in the k-th time slot;

[0067]

[0068] b1 is used to select the active antenna, where Indicates the number of effective antenna combinations. b1 represents the floor function; b2 is used to generate a constellation mapping symbol s, where L represents the order of the constellation mapping. The spatial modulation symbol of the l-th subcarrier in the k-th time slot can then be represented as:

[0069] x(k,l)=[…,0,s q ,0,…] T k∈[1,N], l∈[1,M]

[0070] In the formula, q represents the index of the activated antenna, and s q This represents the corresponding constellation mapping symbol.

[0071] For simplicity, the SM symbol is reformulated based on the different transmission antennas from which the signal is transmitted:

[0072]

[0073] Step 2: Map the spatial modulation symbols to a space-time coding structure:

[0074] The Almouti structure calls spatial modulation symbols, and in the t-th transmission period, B t (k,l)=b1 t +b2 t Information bits are transmitted, in which:

[0075]

[0076] b1 is used to carry antenna index information, and b2 is used to generate two LQAM constellation mapping symbols. The transmission matrix of the l-th subcarrier in the k-th time slot for all transmission periods is a codebook, which can be expressed as:

[0077]

[0078] Among them, I k = (k1,k2) represents the set of indices of the active antennas, S k = (s1, s2) represents the set of corresponding constellation mapping symbols.

[0079] Each row of the codebook matrix corresponds to the symbol set of the k-th time slot and the l-th subcarrier in each transmission cycle, and each column corresponds to the transmission signal set transmitted by each transmit antenna. The symbol transmitted in the t-th transmission cycle, i.e., the t-th row of the codebook matrix, can also be rewritten based on transmission from different antennas as follows:

[0080]

[0081] Step 3: Modulation and demodulation. Spatial modulation symbols with the same transmission period are modulated and transmitted on multiple transmit antennas respectively.

[0082] Symbols with the same transmission period are selected and modulated using OTFS, and then transmitted on multiple transmit antennas. Specifically, the symbol on the i-th antenna during the t-th transmission period is... That is, the signal in each column of the codebook matrix is ​​re-represented as an M×N dimensional symbol matrix:

[0083]

[0084] Transmitted signals at the transmitting end OTFS modulation is performed, and the received signal is obtained by OTFS demodulation at the receiving end through a time-delay Doppler channel. The overall input-output transformation relationship is as follows:

[0085]

[0086] Where H is the bi-dispersive channel matrix, N is the equivalent channel noise, and F N Let I be the Nth order Fourier transform matrix. M It is an M-order identity matrix. Let be the inverse of the Nth-order Fourier transform matrix. Then the equivalent channel matrix of the system is:

[0087]

[0088] Step 4: Perform signal detection and recovery on the transmitted data symbols obtained in Step 3:

[0089] Treating a codebook as a detection unit, for a transmitted signal, the signal from all transmit antennas in the t-th transmission period (t∈[1,T]), k-th time slot (k∈[1,N]), and l-th subcarrier (l∈[1,M]) for the transmitted signal is treated as a single transmitted signal unit symbol, as follows:

[0090]

[0091] For the received signal, the signal transmitted from all receiving antennas in the t-th transmission period (t∈[1,T]), m-th time slot (m∈[1,N]), and n-th subcarrier (n∈[1,M]) is treated as a single received signal unit symbol, represented as:

[0092]

[0093] For the channel matrix, the channel coefficients of all transmit antennas transmitting from the m-th time slot (n-th subcarrier) in the t-th transmission period (m-th time slot, n-th time slot, M-th time slot) to all receive antennas transmitting from the k-th time slot (l-th subcarrier) in the k-th time slot (l-th time slot, M-th time slot) form a block channel matrix as follows:

[0094]

[0095] Where: a = (n-1) × N + m, b = (k-1) × M + l ∈ [1, MN];

[0096] Define the transmit signal block as The received signal block is After being divided into blocks, the overall input-output relationship of the SM-STBC-OTFS system is as follows:

[0097]

[0098] The channel matrix exhibits strong sparsity, containing many blocks of all zeros. Assume I(i) and J(j) are the sets of indices of the non-all-zero blocks in the i-th row and j-th column, respectively, and that the probability density function of the codebook is p. i,j ={p i,j (a q )|q=1,…,Q,a q ∈Λ}, where Q is the number of codebook types and Λ is the codebook set;

[0099] From the observation node y i The mean and variance of i∈[1,MN] are passed to message node x. j ,j∈I(i), the interference part Treat it as a Gaussian random variable:

[0100]

[0101] From the observation node y i The mean and variance information of i∈[1,MN] are transmitted to the message node x. j For j∈I(i), the mean and variance of the interference component are as follows:

[0102]

[0103] Conversely, probability density From variable node x j The j∈[1,MN] values ​​are passed to the message node y. i ,i∈J(j), can be represented as:

[0104]

[0105] Using probability density in message node x j and variable node y i The updates and iterations are performed between each iteration. The relationship between the probability density of the nth iteration and the probability density of the (n-1)th iteration is as follows:

[0106]

[0107] Where α∈(0,1] represents the convergence factor, used to change the convergence speed and improve performance, and c is the normalization constant, expressed as follows:

[0108]

[0109] Once the required number of iterations is met, the corresponding codebook symbol can be detected.

[0110]

[0111] Finally, by finding the index, the corresponding detection unit is located in the codebook set, thus determining which codebook to select. Based on the correspondence between the codebook symbols and the bit stream, the corresponding bit information can be found by converting the index.

[0112] like Figure 1 The diagram shown is a modulation schematic provided by an embodiment of the present invention using Almouti coding and BPSK constellation mapping. Figure 2 This is a schematic diagram of the detection algorithm provided in an embodiment of the present invention, where each observation node y i Connect to P variable nodes x j ,j∈I(i), and similarly, each variable node x j Connect to P observation nodes y i ,i∈J(j), where P is the number of paths. By continuously passing and exchanging messages between observation nodes and variable nodes on the factor graph model, the posterior marginal probability density function of the transmitted signal is further approximated, thereby achieving the purpose of signal detection. Figure 3 This paper compares the bit error rate performance of the detection algorithm provided in this embodiment of the invention with that of traditional schemes. The parameter is set to N. t =4,N r =4, M=16, N=16, P=4 and lmax max Both utilize BPSK constellation mapping. Figure 4 The algorithm flowchart provided for the implementation of this invention.

[0113] The following specific example further illustrates the spatial modulation and space-time code-assisted signal recovery method provided in this invention. Figures 1 to 4 As shown, the signal recovery method provided in this embodiment with spatial modulation and space-time code assistance includes the following steps:

[0114] Step 1, Spatial Modulation

[0115] Specifically, such as Figure 1 As shown, if the STBC encoding uses Almouti encoding, the number of transmit antennas N in the multi-antenna OTFS system... t =4, Number of receiving antennas N r =4, number of active antennas N a =2, using BPSK mapping, with M=16 subcarriers and N=16 time slots.

[0116] The transmitted bitstream is divided into MN = 256 groups. In each transmission cycle, a total of four bitstreams are transmitted; the bitstream required to select two antennas from the four antennas is... The bitstream is configured such that 00 indicates the selection of the first and second antennas, 10 indicates the selection of the second and third antennas, 01 indicates the selection of the third and fourth antennas, and 11 indicates the selection of the first and fourth antennas; the remaining two bits... It is used to generate two BPSK constellation mapping symbols, which are transmitted by two selected antennas respectively.

[0117] Therefore, for bitstream 0000, the first two bits 00 indicate the selection of the first and second antennas, and the last two bits 00 are mapped to the symbol [-1, -1] via BPSK. Thus, the symbols transmitted to the four antennas are (antennas that do not transmit bitstream symbols can default to transmitting a symbol of 0):

[0118] [-1,-1,0,0]

[0119] This yields a set of SM symbols:

[0120] x(k,l)=[-1,-1,0,0],k∈[1,16],l∈[1,16].

[0121] Step 2: Map the spatial modulation symbols into a space-time coding structure.

[0122] With a transmission period T = 2, if the symbol transmitted in the first transmission period is [-1, -1, 0, 0], then in the second transmission period, the first symbol is negatively conjugate to the second symbol of the first transmission period, and the second symbol of the second transmission period is conjugate to the first symbol of the first transmission period. Therefore, the codebook symbols are:

[0123]

[0124] Different column symbols correspond to different antennas for transmission, i.e. Transmitted to the first antenna, Transmitted to the second antenna, The data is transmitted to the third and fourth antennas respectively (as above, antennas that do not transmit bit stream symbols transmit 0 symbols by default). Different rows correspond to different transmission cycles, that is, the first row of the codebook symbol is transmitted in the first transmission cycle, and the second row of the codebook symbol is transmitted in the second transmission cycle.

[0125] Step 3: Modulation and Demodulation

[0126] After spatial modulation and space-time block coding, a total of MN = 256 codebook symbols x(k,l), k∈[1,16], l∈[1,16] are obtained. These symbols are transmitted on the i-th transmit antenna over the t-th cycle. It is transformed into a data symbol with a length of mN = 256.

[0127] First, transform the symbol into a data matrix form x[k,l] in the M×N dimension time-delay Doppler domain.

[0128]

[0129] At the transmitting end, the signal is mapped to the time-frequency domain after ISFFT transformation, becoming a time-frequency domain signal. After adding a transmission window, it undergoes Heisenberg transformation to become a time-domain transmitted signal, which is then transmitted through a multipath time-varying wireless channel. At the receiving end, the reverse process is executed: the time-domain received signal is first subjected to Wigner transformation, then SFFT transformation after adding a receive window, ultimately obtaining the time-delay Doppler domain data received symbol.

[0130]

[0131] Step 4: Signal Detection and Recovery

[0132] The transmitted signal unit symbol is defined as the signal from all transmit antennas in the t-th transmission period (t∈[1,2]), k-th time slot (k∈[1,16]), and l-th subcarrier (l∈[1,16]).

[0133]

[0134] The received signal unit symbol is defined as the symbol transmitted from all receiving antennas in the t-th transmission period (t∈[1,2]), the m-th time slot (m∈[1,16]), and the n-th subcarrier (n∈[1,16]).

[0135]

[0136] For the channel matrix, a block channel matrix is ​​formed by the channel coefficients of all transmit antennas transmitting from the m-th time slot (t∈[1,2]th time period) to the l-th time slot (k∈[1,16]th time period) on the n-th subcarrier.

[0137]

[0138] a=(n-1)×16+m, b=(k-1)×16+l∈[1,256]

[0139] Define the transmit signal block as The received signal block is After segmentation, the overall input-output relationship of the SM-STBC-OTFS system can be observed as follows:

[0140]

[0141] Specifically, such asFigure 2 As shown, a message factor graph is constructed.

[0142] Suppose I(i) and J(j) are the index sets of non-all-zero blocks in the i-th row and j-th column, respectively, and the probability density function of the codebook is p. i,j ={p i,j (a q )|q=1,…,Q,a q ∈Λ}, where Q is the number of codebook types and Λ is the codebook set. In the first iteration, we set:

[0143]

[0144] That is, it is determined that the probability of obtaining Q codebooks is the same.

[0145] First, observe node y i The mean and variance information of i∈[1,256] are passed to message node x. j For j∈I(i), the mean and variance of this interference component can be calculated as follows:

[0146]

[0147] Conversely, this probability density is determined by the variable node x. j The values ​​j∈[1,256] are passed to message node y. i For i∈J(j), this probability density can be expressed as:

[0148]

[0149] Using probability density in message node x j and variable node y i The updates and iterations are performed between each iteration. The relationship between the probability density of the nth iteration and the probability density of the (n-1)th iteration is as follows:

[0150]

[0151] Where α∈(0,1] represents the convergence factor, used to change the convergence speed and improve performance. c is a normalization constant, expressed as follows:

[0152]

[0153] Once the required number of iterations is met, the corresponding codebook symbol can be detected.

[0154]

[0155] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A signal recovery method assisted by spatial modulation and space-time code, characterized in that: The method includes the following steps: Step 1: Spatial modulation is performed on the information bit stream groups according to the number of time slots and the number of carriers to obtain spatial modulation symbols; Step 2: Map the spatial modulation symbols to a space-time coding structure; Step 3: Take spatial modulation symbols with the same transmission period and perform orthogonal time-frequency space-carrier modulation, and transmit data symbols on multiple transmitting antennas respectively; Step 4: Based on the sparsity of the signal structure, perform signal detection and recovery on the transmitted data symbols obtained in Step 3.

2. The signal recovery method assisted by spatial modulation and space-time code as described in claim 1, characterized in that: In step 1, the specific method for spatially modulating the information bit stream groups according to the number of time slots and the number of carriers is as follows: Suppose the system has N t Root transmitting antenna, N r Root receiving antenna, N a = 1 active antenna, and the system transmits a total of M subcarriers and N symbols, dividing the information bits into M×N groups, where B(k,l)=b1+b2 represents the bit information transmitted by the l-th subcarrier in the k-th time slot; b1 is used to select the active antenna, where Indicates the number of effective antenna combinations. b1 represents the floor function; b2 is used to generate a constellation mapping symbol s, where L represents the order of the constellation mapping. The spatial modulation symbol of the l-th subcarrier in the k-th time slot can then be represented as: x(k,l)=[…,0,s q ,0,…] T ,k∈[1,N],l∈[1,M] In the formula, q represents the index of the activated antenna, and s q This represents the corresponding constellation mapping symbol.

3. The signal recovery method assisted by spatial modulation and space-time code as described in claim 2, characterized in that: In step 1, the spatial modulation symbol of the l-th subcarrier in the k-th time slot can also be represented as:

4. The signal recovery method with spatial modulation and space-time code assistance as described in claim 3, characterized in that: In step 2, Almouti coding is used to map spatial modulation symbols into a space-time coding structure.

5. The signal recovery method assisted by spatial modulation and space-time code as described in claim 4, characterized in that: In step 2, the method of mapping spatial modulation symbols to a space-time coding structure using Almouti coding is as follows: The Almouti structure calls spatial modulation symbols, and in the t-th transmission period, B t (k,l)=b1 t +b2 t Information bits are transmitted, in which: b1 is used to carry antenna index information, and b2 is used to generate two LQAM constellation mapping symbols s. The transmission matrix of all transmission periods in the k-th time slot and the l-th subcarrier is a codebook, which can be expressed as: Among them, I k = (k1,k2) represents the set of indices of the active antennas, S k = (s1, s2) represents the set of corresponding constellation mapping symbols.

6. The signal recovery method assisted by spatial modulation and space-time code as described in claim 5, characterized in that: In step 3, symbols with the same transmission period are used for orthogonal time-frequency space-time multicarrier (OTFS) modulation, and data symbols are transmitted on multiple transmit antennas respectively.

7. The signal recovery method assisted by spatial modulation and space-time code as described in claim 6, characterized in that: In step 3, the specific methods for modulation and demodulation are as follows: The symbol on the i-th antenna during the t-th transmission cycle That is, the signal in each column of the codebook matrix is ​​re-represented as an M×N dimensional symbol matrix as follows: Transmitted signals at the transmitting end OTFS modulation is performed, and the received signal is obtained by OTFS demodulation at the receiving end through a time-delay Doppler channel. The overall input-output transformation relationship is as follows: Where H is the bi-dispersive channel matrix, N is the equivalent channel noise, and F N Let I be the Nth order Fourier transform matrix. M It is an M-order identity matrix. Let be the inverse of the Nth-order Fourier transform matrix. Then the equivalent channel matrix of the system is:

8. The signal recovery method with spatial modulation and space-time code assistance as described in claim 7, characterized in that: In step 4, the specific method for signal detection and recovery of transmitted data symbols is as follows: Treating a codebook as a detection unit, for a transmitted signal, the signal from all transmit antennas in the t-th transmission period (t∈[1,T]), k-th time slot (k∈[1,N]), and l-th subcarrier (l∈[1,M]) for the transmitted signal is treated as a single transmitted signal unit symbol, as follows: For the received signal, the signal transmitted from all receiving antennas in the t-th transmission period (t∈[1,T]), m-th time slot (m∈[1,N]), and n-th subcarrier (n∈[1,M]) is treated as a single received signal unit symbol, represented as: For the channel matrix, the channel coefficients of all transmit antennas transmitting from the m-th time slot (n-th subcarrier) in the t-th transmission period (m-th time slot, n-th time slot, n-th time slot) to all receive antennas transmitting from the l-th subcarrier in the k-th time slot (l-th time slot, M-th time slot) form a block channel matrix as follows: Where: a = (n-1) × N + m, b = (k-1) × N + l ∈ [1, MN]; Define the transmit signal block as The received signal block is After partitioning, the overall relationship between the system input and output is as follows: Suppose I(i) and J(j) are the sets of indices of the non-zero blocks in the i-th row and j-th column, respectively, and the probability density function of the codebook is p. i，j ={p i，j (a a )|q=1,…,Q,a q ∈Λ}, where Q is the number of codebook types and Λ is the codebook set; From the observation node y i The mean and variance of i∈[1,MN] are passed to message node x. j ,j∈I(i), the interference part Treat it as a Gaussian random variable: From the observation node y i The mean and variance information of i∈[1,MN] are transmitted to the message node x. j For j∈I(i), the mean and variance of the interference component are as follows: probability density From variable node x j The j∈[1,MN] values ​​are passed to the message node y. i ,i∈J(j), can be represented as: Using probability density in message node x j and variable node y i The updates and iterations are performed between each iteration. The relationship between the probability density of the nth iteration and the probability density of the (n-1)th iteration is as follows: Where α∈(0,1] represents the convergence factor, used to change the convergence speed and improve performance, and c is the normalization constant, expressed as follows: Once the required number of iterations is met, the corresponding codebook symbol can be detected. By finding the index, the corresponding detection unit can be found in the codebook set, thus determining which codebook to select. Based on the correspondence between the codebook symbols and the bit stream, the corresponding bit information can be found by converting the index.

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