3D-OFDM system working method based on dual-mode index modulation

Abstract

The invention relates to a 3D-OFDM (Three Dimensional Orthogonal Frequency Division Multiplexing) system working method based on dual-mode index modulation, which comprises the following steps of: firstly, dividing information bits of a sending end into G groups through a serial-parallel conversion bit splitter, further dividing each group of information bits into three parts, respectively selecting a subcarrier activation mode and two constellation mapping symbols, and combining through an OFDM block generator to generate a frequency domain transmission signal matrix; secondly, performing N-point 2D inverse fast Fourier transform on the frequency domain transmission signal matrix, converting the frequency domain transmission signal matrix into a time domain signal, adding a cyclic prefix to the time domain signal by a sending end, performing parallel-serial conversion, and transmitting the time domain signal to a receiving end through a Rayleigh fading channel; and finally, a receiving end carries out N-point 2D fast Fourier transform on the time domain signal to obtain a frequency domain receiving signal, carries out log-likelihood ratio detection based on greedy detection, carries out de-mapping and demodulation, and recovers corresponding sending information bits. According to the method, the detection complexity is greatly reduced, and meanwhile, the bit error rate performance approximate to an ML algorithm is obtained.

Description

Technical Field

[0001] The invention relates to a 3D-OFDM system working method based on dual-mode index modulation, belonging to the technical field of wireless communication transmission. Background Art

[0002] Orthogonal frequency division multiplexing index modulation (OFDM-IM) is an index modulation technology applied to the carrier frequency domain. OFDM improves anti-fading capability by converting serial data into multiple low-rate parallel data streams, and OFDM-IM can further improve the spectrum efficiency of traditional OFDM. It can activate some subcarriers in the frequency domain for implicit transmission of additional information without providing additional overhead, thereby improving system transmission efficiency under certain bit error rate performance. On the other hand, for three-dimensional orthogonal frequency division multiplexing (3D-OFDM) systems, by increasing its dimension, more signal constellation points can be obtained without reducing the minimum Euclidean distance between modulated signals, thereby improving transmission efficiency. At the same time, the minimum Euclidean distance of modulated signals can be increased under the same constellation dimension, thereby reducing the system bit error rate and improving transmission reliability.

[0003] WZJin et al. (see WZJin, et al., "Energy-Efficient and Fading-Resistant Multi-Mode OFDM-IM With High Dimensional Mapping", IEEE Transactions on Wireless Communications, 2023, 22(8): 5005-17.) proposed a new wireless transmission scheme called high-dimensional multi-mode orthogonal frequency division multiplexing and index modulation (MM-HD-OFDM-IM). By introducing a rotating signal constellation and designing a high-dimensional multi-mode constellation mapper, they aim to solve the problem of the decrease of the minimum Euclidean distance in the traditional MM-OFDM-IM scheme as the constellation dimension increases, and obtain a closed-form solution for the bit error rate of the system in a Rayleigh fading channel. Simulations show that the MM-HM-OFDM-IM scheme has better BER performance than traditional MM-OFDM-IM and other OFDM-IM schemes in Rayleigh fading channels. Although the above scheme improves the system energy efficiency, the spectrum efficiency is limited because the number of activated subcarriers in each subblock is small. Summary of the invention

[0004] Based on the existing technology and solution design, the present invention proposes a 3D-OFDM system working method based on dual-mode index modulation, and proposes a low-complexity log-likelihood ratio detection algorithm based on greedy detection, which effectively improves the system spectrum efficiency, reduces the average bit error probability, and ensures the reliable transmission of information.

[0005] The technical solution of the present invention is as follows:

[0006] A working method of a 3D-OFDM system based on dual-mode index modulation, the system includes a transmitter, a channel, and a receiver: wherein the transmitter includes a serial-to-parallel conversion bit splitter, a subcarrier index selector, a constellation mapper, an OFDM block generator, and an OFDM modulation module; the receiver includes a serial-to-parallel conversion receiving signal splitter, an OFDM demodulation module, a signal detection module, a demapping and demodulation module; it is assumed that the links between the transmitting and receiving antennas of the 3D-OFDM modulation system experience independent Rayleigh fading, the noise is additive white Gaussian noise, the receiving end has known perfect channel state information, the transmitting end OFDM symbol includes N subcarriers, each OFDM block is divided into G OFDM subblocks, and each OFDM subblock includes n subcarriers; including:

[0007] First, the information bit stream at the transmitting end is divided into G groups by the serial-to-parallel conversion bit splitter, corresponding to G OFDM sub-blocks. Each group of information bits is divided into three parts. The first part is used to determine the activated subcarrier index for sending dual-mode modulation signals, and the other two parts are subjected to dual-mode 3D constellation mapping to obtain the corresponding OFDM sub-block modulation symbols; then, the OFDM block generator merges the modulation symbols of each sub-block to obtain a 3×N-dimensional frequency domain transmission signal matrix X;

[0008] Secondly, the frequency domain transmission signal matrix X enters the OFDM modulation module and performs N-point 2D inverse fast Fourier transform (2D-IFFT) to transform it into a time domain signal X′. The transmitter adds a cyclic prefix to the time domain signal X′, performs parallel-to-serial conversion, and transmits the time domain signal X′ to the receiver via a Rayleigh fading channel.

[0009] Finally, the receiving end receives the time domain signal Y′ and performs an N-point 2D fast Fourier transform (2D-FFT) on it to obtain the frequency domain received signal Y. Then, the signal detection module performs greedy detection-based log-likelihood ratio (GD-LLR) detection on Y, and demaps and demodulates it in the demapping and demodulation module to recover the corresponding transmitted information bits.

[0010] Preferably, at the transmitting end, the information bit stream m is converted into a G×P-dimensional binary matrix B by a serial-to-parallel conversion bit splitter, and the binary matrix B is split into G groups by row, and sent to the subcarrier index selector and the constellation mapper, the constellation mapper includes a 3D constellation mapper A and a 3D constellation mapper B; the modulation orders of the 3D constellation mapper A and the 3D constellation mapper B are M respectively. A and M B ; The number of information bits contained in each group is:

[0011]

[0012] Among them, (ii ) represents the binomial coefficient, Indicates rounding down;

[0013] Item 1 After bits enter the subcarrier index selector, k=k1+k2 activated subcarriers are selected, k≤n, where k1 and k2 represent the number of subcarriers activated by 3D constellation mapper A and 3D constellation mapper B, respectively, and the corresponding subcarrier activation modes are recorded as i A and i B ;

[0014] The second term K2=k1 log2M A bits enter the 3D constellation mapper A and select M A Order modulation constellation symbol, denoted by S A ;

[0015] The third term K3=k2log2M B bits enter the 3D constellation mapper B and select M B Order modulation constellation symbol, denoted by S B ;

[0016] For the g-th OFDM subblock, its subcarrier activation mode is and They refer to the subsets consisting of k1 and k2 activated subcarrier indices respectively, Indicates the activated subcarrier index for sending 3D constellation symbols, Λ=A,B; the generated modulation symbol is and express Corresponding to the transmitted 3D constellation mapping symbol;

[0017] Will and Combine to get the frequency domain transmission signal on the g-th OFDM sub-block in represents a 3-row n-column complex matrix, Indicates The modulated signal transmitted on subcarriers; and Respectively represent the components of the corresponding modulation signal on the x, y and z axes;

[0018] All sub-blocks are combined by the OFDM block generator to construct a 3×N-dimensional frequency domain transmission signal matrix X=[x(1)x(2)…x(N)], where x(δ)=[s x (δ)s y (δ)s z (δ)]T ∈{0,S} represents the signal transmitted on the δth subcarrier, 0 represents the all-zero matrix, S represents the 3D constellation point set, δ=1,2,…,N; s x (δ)s y (δ)s z (δ) represent the components of the OFDM block modulation symbol on the x, y and z axes respectively.

[0019] According to the preferred embodiment of the present invention, the frequency domain transmission signal matrix X enters the OFDM modulation module for OFDM modulation, that is, the time domain OFDM transmission symbol is generated by N-point 2D-IFFT transformation in, is the IFFT matrix.

[0020] The tail of the transmission signal X′ is copied to be no less than the maximum multipath delay, and is added to the front of the transmission signal X′ as a cyclic prefix. After parallel-to-serial conversion, the transmission signal is sent from the transmitting antenna to the receiving end via the Rayleigh fading channel.

[0021] Preferably, according to the present invention, at the receiving end, the opposite operation of the transmitting end is performed on the time domain received signal Y′, first, the cyclic prefix of the time domain signal Y′ is removed, and then N-point 2D-FFT is performed, and G 3×n-dimensional frequency domain received signal matrices Y are obtained through a serial-to-parallel conversion received signal splitter;

[0022] For the g-th OFDM sub-block, the frequency domain signal matrix in, Indicates the multiplication of corresponding elements in the matrix, Y g =[y(1)y(2)…y(n)], y(φ)=[y x (φ)y y (φ)y z (φ)] T represents the transmission signal corresponding to the φth subcarrier received in the gth OFDM subblock, y x (φ)y y (φ)y z (φ) represents the components of y(φ) in the x, y, and z axes, respectively; represents the transmit signal matrix of the g-th OFDM sub-block, represents the channel matrix corresponding to the g-th OFDM sub-block, whose elements are independent and obey a complex Gaussian random distribution with a mean of 0 and a variance of 1. represents the additive white Gaussian noise matrix of the g-th OFDM sub-block, whose elements obey the complex Gaussian distribution with mean 0 and variance N0.

[0023] Preferably, according to the present invention, a signal detection module performs log-likelihood ratio detection based on greedy detection on the frequency domain received signal matrix Y, and a demapping and demodulation module performs demapping and demodulation; including:

[0024] Step 1: Based on the idea of ​​step-by-step selection of the optimal local solution based on greedy detection, the subcarrier activation pattern in the OFDM subblock is estimated block by block;

[0025] Step 2: Use the LLR detection algorithm to estimate two different constellation modes of the modulation signal on the activated subcarrier, that is, estimate the selected 3D constellation mapper by judging the log-likelihood ratio of the constellation symbol on the activated subcarrier under the two constellation mode symbols.

[0026] Step 3: Estimate the corresponding 3D constellation symbols based on the maximum likelihood criterion.

[0027] Preferably, according to the present invention, based on the idea of ​​step-by-step selection of the optimal local solution of greedy detection, the subcarrier activation mode in the OFDM subblock is estimated in blocks; comprising:

[0028] Calculate the received signal matrix Y of the g-th OFDM sub-block g Power in y(n) represents the received signal carrying the φth subcarrier index information;

[0029] right Arrange the elements in descending order to get the corresponding subcarrier index Among them, u1 and u n They are The index of the largest and smallest elements in , desc(·) is a descending function; select the first k indexes and estimate the first k indexes as the activated subcarrier indexes Among them, asc(·) is an ascending function; at the same time, the corresponding activated subcarrier signal matrix is ​​obtained

[0030] Preferably, according to the present invention, an LLR detection algorithm is used to estimate two different constellation modes of the modulation signal on the activated subcarrier, that is, the selected 3D constellation mapper is estimated by judging the log-likelihood ratio of the constellation symbol on the activated subcarrier under the two constellation mode symbols; comprising:

[0031] Suppose the probability that the αth activated subcarrier in the gth OFDM subblock transmits a symbol using the 3D constellation mapper A is in, and denote the symbol probabilities of activating subcarriers to transmit 3D constellation mapper A and 3D constellation mapper B, respectively, α=1,2,…,k; Denote the transmitted signals mapped by 3D constellation mappers A and B respectively; γ is converted into α Simplify to get The subcarrier activation modes corresponding to 3D constellation mapper A and 3D constellation mapper B are obtained by calculation. and

[0032] According to the preferred embodiment of the present invention, the corresponding 3D constellation symbol is estimated based on the maximum likelihood criterion

[0033] The beneficial effects of the present invention are:

[0034] The present invention combines dual-mode index modulation and 3D-OFDM technology, utilizes the implicit extra information bits carried by dual-mode index modulation to improve the effectiveness of signal transmission, utilizes 3D-OFDM technology to increase the Euclidean distance between symbols, ensures the transmission reliability of the system, and proposes a log-likelihood ratio detection algorithm based on greedy detection. Simulation results show that compared with the optimal ML detector, the present invention greatly reduces the detection complexity while obtaining an error performance similar to that of the ML algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flowchart of a 3D-OFDM system working method based on dual-mode index modulation of the present invention;

[0036] Figure 2 The comparison of the average bit error probability of DM-IM-3D-OFDM, 3D-OFDM-IM and DM-3D-OFDM systems under different modulation orders under the conditions of n=8, k=4 and k1=2;

[0037] Figure 3 It is a simulation comparison chart of the average bit error probability performance of the maximum likelihood detection (ML) of the DM-IM-3D-OFDM scheme under different modulation orders and the GD-LLR detection algorithm proposed in the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments, but is not limited thereto.

[0039] Example 1

[0040] A working method of a 3D-OFDM system based on dual-mode index modulation, the system includes a transmitter, a channel, and a receiver, wherein the transmitter includes a serial-to-parallel conversion bit splitter, a subcarrier index selector, a constellation mapper, an OFDM block generator, and an OFDM modulation module; the receiver includes a serial-to-parallel conversion receiving signal splitter, an OFDM demodulation module, a signal detection module, a demapping and demodulation module; it is assumed that the links between the transmitting and receiving antennas of the 3D-OFDM modulation system experience independent Rayleigh fading, the noise is additive white Gaussian noise, the receiver has known perfect channel state information, the transmitter OFDM symbol includes N subcarriers, each OFDM block is divided into G OFDM subblocks, and each OFDM subblock includes n subcarriers; as Figure 1 As shown, including:

[0041] First, the information bit stream at the transmitting end is divided into G groups by the serial-to-parallel conversion bit splitter, corresponding to G OFDM sub-blocks. Each group of information bits is divided into three parts. The first part is used to determine the activated subcarrier index for sending dual-mode modulation signals, and the other two parts are subjected to dual-mode 3D constellation mapping to obtain the corresponding OFDM sub-block modulation symbols. Then, the OFDM block generator combines the modulation symbols of each sub-block to obtain a 3×N-dimensional frequency domain transmission signal matrix X.

[0042] Secondly, the frequency domain transmission signal matrix X enters the OFDM modulation module, performs N-point 2D inverse fast Fourier transform (2D-IFFT), and transforms the frequency domain transmission signal matrix X into a time domain signal X′. The transmitter adds a cyclic prefix to the time domain signal X′, performs parallel-to-serial conversion, and transmits the time domain signal X′ to the receiver through the Rayleigh fading channel.

[0043] Finally, the receiving end receives the time domain signal Y′ and performs an N-point 2D fast Fourier transform (2D-FFT) on it to obtain the frequency domain received signal Y. Then, the signal detection module performs greedy detection-based log-likelihood ratio (GD-LLR) detection on Y, and demaps and demodulates it in the demapping and demodulation module to recover the corresponding transmitted information bits.

[0044] Example 2

[0045] The 3D-OFDM system working method based on dual-mode index modulation according to Embodiment 1 is different in that:

[0046] At the transmitting end, the information bit stream m is converted into a G×P dimensional binary matrix B by a serial-to-parallel conversion bit splitter, and the binary matrix B is split into G groups by row and sent to the subcarrier index selector and the constellation mapper. The constellation mapper includes a 3D constellation mapper A and a 3D constellation mapper B. The modulation orders of the 3D constellation mapper A and the 3D constellation mapper B are M and M, respectively. A and M B ; The number of information bits contained in each group is:

[0047]

[0048] Among them, (i i ) represents the binomial coefficient, Indicates rounding down;

[0049] Item 1 After bits enter the subcarrier index selector, k=k1+k2 activated subcarriers are selected, k≤n, where k1 and k2 represent the number of subcarriers activated by 3D constellation mapper A and 3D constellation mapper B, respectively, and the corresponding subcarrier activation modes are recorded as i A and i B ;

[0050] The second term K2=k1 log2M A bits enter the 3D constellation mapper A and select M A Order modulation constellation symbol, denoted by S A ;

[0051] The third term K3=k2log2M B bits enter the 3D constellation mapper B and select M B Order modulation constellation symbol, denoted by S B ;

[0052] For the g-th OFDM subblock, its subcarrier activation mode is and They refer to the subsets consisting of k1 and k2 activated subcarrier indices respectively, Indicates the activated subcarrier index for sending 3D constellation symbols, Λ=A,B; the generated modulation symbol is and express Corresponding 3D constellation symbols;

[0053] Will and Combine to get the frequency domain transmission signal on the g-th OFDM sub-block in represents a 3-row n-column complex matrix, Indicates The modulated signal transmitted on subcarriers; and Respectively represent the components of the corresponding modulation signal on the x, y and z axes;

[0054] All sub-blocks are combined by the OFDM block generator to construct a 3×N-dimensional frequency domain transmission signal matrix X=[x(1)x(2)…x(N)], where x(δ)=[sx (δ)s y (δ)s z (δ)] T ∈{0,S} represents the signal transmitted on the δth subcarrier, 0 represents the all-zero matrix, S represents the 3D constellation point set, δ=1,2,…,N; s x (δ)s y (δ)s z (δ) represent the components of the OFDM block modulation symbol on the x, y and z axes respectively.

[0055] The frequency domain transmission signal matrix X enters the OFDM modulation module for OFDM modulation, that is, the time domain OFDM transmission symbol is generated through N-point 2D-IFFT transformation in, is the IFFT matrix;

[0056] The tail of the transmission signal X′ that is equal to or longer than the maximum multipath delay is copied and added to the front of X′ as a protection interval cyclic prefix. The modulated parallel symbol bits are converted into serial symbol bits with a cyclic prefix added. After parallel-to-serial conversion, they are sent from the transmitting antenna to the receiving end via the Rayleigh fading channel.

[0057] At the receiving end, the opposite operation of the transmitting end is performed on the time domain received signal Y′. First, the cyclic prefix of the time domain signal Y′ is removed, and then an N-point 2D-FFT is performed. After the serial-to-parallel conversion received signal splitter, G 3×n-dimensional frequency domain received signal matrices Y are obtained;

[0058] For the g-th OFDM sub-block, the frequency domain signal matrix in, Indicates the multiplication of corresponding elements in the matrix, Y g =[y(1)y(2)…y(n)], y(φ)=[y x (φ)y y (φ)y z (φ)] T represents the transmission signal corresponding to the φth subcarrier received in the gth OFDM subblock, y x (φ)y y (φ)y z (φ) represents the components of y(φ) in the x, y, and z axes, respectively; represents the transmit signal matrix of the g-th OFDM sub-block, represents the channel matrix corresponding to the g-th OFDM sub-block, whose elements are independent and obey a complex Gaussian random distribution with a mean of 0 and a variance of 1. represents the additive white Gaussian noise matrix of the g-th OFDM sub-block, whose elements obey the complex Gaussian distribution with mean 0 and variance N0.

[0059] In the signal detection module, the frequency domain received signal matrix Y is subjected to log-likelihood ratio detection based on greedy detection, and demapping and demodulation are performed in the demapping and demodulation module; including:

[0060] Step 1: Based on the idea of ​​step-by-step selection of the optimal local solution based on greedy detection, the subcarrier activation pattern in the OFDM subblock is estimated block by block;

[0061] Step 2: Use the LLR detection algorithm to estimate two different constellation modes of the modulation signal on the activated subcarrier, that is, estimate the selected 3D constellation mapper by judging the log-likelihood ratio of the constellation symbol on the activated subcarrier under the two constellation mode symbols.

[0062] Step 3: Estimate the corresponding 3D constellation symbols based on the maximum likelihood criterion.

[0063] Based on the idea of ​​step-by-step selection of the optimal local solution of greedy detection, the subcarrier activation mode in the OFDM subblock is estimated in blocks; including:

[0064] Calculate the received signal matrix Y of the g-th OFDM sub-block g Power in y(n) represents the received signal carrying the φth subcarrier index information;

[0065] right Arrange the elements in descending order to get the corresponding subcarrier index Among them, u1 and u n They are The index of the largest and smallest elements in , desc(·) is a descending function; select the first k indexes and estimate the first k indexes as the activated subcarrier indexes Among them, asc(·) is an ascending function; at the same time, the corresponding activated subcarrier signal matrix is ​​obtained

[0066] An LLR detection algorithm is used to estimate two different constellation modes of the modulation signal on the activated subcarrier, that is, the selected 3D constellation mapper is estimated by judging the log likelihood ratio of the constellation symbol on the activated subcarrier under the two constellation mode symbols; including:

[0067] Suppose the probability that the αth activated subcarrier in the gth OFDM subblock transmits a symbol using the 3D constellation mapper A is in, and denote the symbol probabilities of transmitting 3D constellation mapper A and 3D constellation mapper B on the activated subcarriers, α=1,2,…,k; denote the modulation symbols of 3D constellation mappers A and B respectively; γ is converted intoα Simplify to get The subcarrier activation modes corresponding to 3D constellation mapper A and 3D constellation mapper B are obtained by calculation. and

[0068] The corresponding 3D constellation symbols are estimated based on the maximum likelihood criterion

[0069] Figure 2 The comparison of the average bit error probability of DM-3D-OFDM-IM, 3D-OFDM-IM and DM-3D-OFDM systems under different modulation orders under the conditions of n=8, k=4 and k1=2. The horizontal axis represents the system signal-to-noise ratio, and the vertical axis represents the system average bit error probability. Figure 2 It can be seen that when the total modulation order is the same, the average bit error probability of the DM-3D-OFDM-IM working method proposed in the present invention is significantly better than that of the traditional DM-3D-OFDM and 3D-OFDM-IM working methods.

[0070] Figure 3 The figure is a comparison chart of the average bit error probability performance simulation of the maximum likelihood detection (ML) of the DM-3D-OFDM-IM scheme under different modulation orders and the GD-LLR detection algorithm proposed in the present invention. The horizontal axis represents the system signal-to-noise ratio, the vertical axis represents the system average bit error probability, and the modulation orders of the proposed scheme are M A =M B =M=2 and M A =M B =M=4. Figure 3 It can be seen that under the same system configuration, the average bit error probability performance of the GD-LLR detection algorithm is close to that of the ML detection algorithm, but the GD-LLR detection algorithm has lower computational complexity.

Claims

1. A 3D-OFDM system working method based on dual-mode index modulation, characterized in that: The system includes a transmitter, a channel, and a receiver, wherein the transmitter includes a serial-to-parallel conversion bit splitter, a subcarrier index selector, a constellation mapper, an OFDM block generator, and an OFDM modulation module; the receiver includes a serial-to-parallel conversion receiving signal splitter, an OFDM demodulation module, a signal detection module, a demapping and demodulation module; it is assumed that the links between the transmitting and receiving antennas of the 3D-OFDM modulation system experience independent Rayleigh fading, the noise is additive white Gaussian noise, the receiving end has known perfect channel state information, the transmitting end OFDM symbol includes N subcarriers, each OFDM block is divided into G OFDM subblocks, and each OFDM subblock includes n subcarriers; including: First, the frequency domain information bit stream of the transmitting end is divided into G groups by the serial-to-parallel conversion bit splitter, corresponding to G OFDM sub-blocks. Each group of information bits is divided into three parts. The first part is used to determine the activated subcarrier index for sending dual-mode modulation signals, and the other two parts are subjected to dual-mode 3D constellation mapping to obtain the corresponding OFDM sub-block modulation symbols; then, the OFDM block generator merges the modulation symbols of each sub-block to obtain a 3×N-dimensional frequency domain transmission signal matrix X; Secondly, the frequency domain transmission signal matrix X enters the OFDM modulation module, performs N-point 2D inverse fast Fourier transform, and transforms the frequency domain transmission signal matrix X into the time domain signal X′. The transmitter adds a cyclic prefix to the time domain signal X′, performs parallel-to-serial conversion, and transmits the time domain signal X′ to the receiver through the Rayleigh fading channel. Finally, the receiving end receives the time domain signal Y′ and performs an N-point 2D fast Fourier transform on it to obtain the frequency domain received signal Y. Then, the signal detection module performs log-likelihood ratio detection based on greedy detection on Y, and demaps and demodulates it in the demapping and demodulation module to recover the corresponding transmitted information bits.

2. The 3D-OFDM system working method based on dual-mode index modulation according to claim 1, characterized in that: At the transmitting end, the information bit stream m is converted into a G×P dimensional binary matrix B by a serial-to-parallel conversion bit splitter, and the binary matrix B is split into G groups by row and sent to the subcarrier index selector and the constellation mapper. The constellation mapper includes a 3D constellation mapper A and a 3D constellation mapper B. The modulation orders of the 3D constellation mapper A and the 3D constellation mapper B are M and M, respectively. A and M B ; The number of information bits contained in each group is: in, represents the binomial coefficient, Indicates rounding down; Item 1 After bits enter the subcarrier index selector, k=k1+k2 activated subcarriers are selected, k≤n, where k1 and k2 represent the number of subcarriers activated by 3D constellation mapper A and 3D constellation mapper B, respectively, and the corresponding subcarrier activation modes are recorded as i A and i B ; The second term K2=k1 log2M A bits enter the 3D constellation mapper A and select M A Order modulation constellation symbol, denoted by S A ; The third term K3=k2log2M B bits enter the 3D constellation mapper B and select M B Order modulation constellation symbol, denoted by S B ; For the g-th OFDM subblock, its subcarrier activation mode is and They refer to the subsets consisting of k1 and k2 activated subcarrier indices respectively, Indicates the activated subcarrier index for sending 3D constellation symbols, Λ=A,B; the generated modulation symbol is and express Corresponding 3D constellation symbols; Will and The frequency domain transmission signal on the g-th OFDM sub-block is obtained by combining in represents a 3-row n-column complex matrix, Indicates The modulated signal transmitted on subcarriers; and Respectively represent the components of the corresponding modulation signal on the x, y and z axes; All sub-blocks are combined by the OFDM block generator to construct a 3×N-dimensional frequency domain transmission signal matrix X=[x(1)x(2)…x(N)], where x(δ)=[s x (δ)s y (δ)s z (δ)] T ∈{0,S} represents the signal transmitted on the δth subcarrier, 0 represents the all-zero matrix, S represents the 3D constellation point set, δ=1,2,…,N; s x (δ)s y (δ)s z (δ) represent the components of the OFDM block modulation symbol on the x, y and z axes respectively.

3. The 3D-OFDM system working method based on dual-mode index modulation according to claim 1, characterized in that: The frequency domain transmission signal matrix X enters the OFDM modulation module for OFDM modulation, that is, the time domain OFDM transmission symbol is generated through N-point 2D-IFFT transformation in, is the IFFT matrix; The tail of the transmission signal X′ that is equal to or longer than the maximum multipath delay is copied and added to the front of X′ as a protection interval cyclic prefix. The modulated parallel symbol bits are converted into serial symbol bits with a cyclic prefix added. After parallel-to-serial conversion, they are sent from the transmitting antenna to the receiving end via the Rayleigh fading channel.

4. The 3D-OFDM system working method based on dual-mode index modulation according to claim 1, characterized in that: At the receiving end, the opposite operation of the transmitting end is performed on the time domain received signal Y′. First, the cyclic prefix of the time domain signal Y′ is removed, and then an N-point 2D-FFT is performed. After the serial-to-parallel conversion received signal splitter, G 3×n-dimensional frequency domain received signal matrices Y are obtained; For the g-th OFDM sub-block, the frequency domain signal matrix in, Indicates the multiplication of corresponding elements in the matrix, Y g =[y(1)y(2)…y(n)], y(φ)=[y x (φ)y y (φ)y z (φ)] T represents the transmission signal corresponding to the φth subcarrier received in the gth OFDM subblock, y x (φ)y y (φ)y z (φ) represents the components of y(φ) in the x, y, and z axes, respectively; represents the transmit signal matrix of the g-th OFDM sub-block, represents the channel matrix corresponding to the g-th OFDM sub-block, whose elements are independent and obey a complex Gaussian random distribution with a mean of 0 and a variance of 1. represents the additive white Gaussian noise matrix of the g-th OFDM sub-block, whose elements obey the complex Gaussian distribution with mean 0 and variance N0.

5. The 3D-OFDM system working method based on dual-mode index modulation according to any one of claims 1 to 4, characterized in that: In the signal detection module, the frequency domain received signal matrix Y is subjected to log-likelihood ratio detection based on greedy detection, and demapping and demodulation are performed in the demapping and demodulation module; including: Step 1: Based on the idea of ​​step-by-step selection of the optimal local solution based on greedy detection, the subcarrier activation pattern in the OFDM subblock is estimated block by block; Step 2: Use the LLR detection algorithm to estimate two different constellation modes of the modulation signal on the activated subcarrier, that is, estimate the selected 3D constellation mapper by judging the log-likelihood ratio of the constellation symbol on the activated subcarrier under the two constellation mode symbols; Step 3: Estimate the corresponding 3D constellation symbols based on the maximum likelihood criterion.

6. The 3D-OFDM system working method based on dual-mode index modulation according to claim 5, characterized in that: Based on the idea of ​​step-by-step selection of the optimal local solution of greedy detection, the subcarrier activation mode in the OFDM subblock is estimated in blocks; including: Calculate the received signal matrix Y of the g-th OFDM sub-block g Power in y(n) represents the received signal carrying the φth subcarrier index information; right Arrange the elements in descending order to get the corresponding subcarrier index Among them, u1 and u n They are The index of the largest and smallest elements in , desc(·) is a descending function; select the first k indexes and estimate the first k indexes as the activated subcarrier indexes Among them, asc(·) is an ascending function; at the same time, the corresponding activated subcarrier signal matrix is ​​obtained 7. The 3D-OFDM system working method based on dual-mode index modulation according to claim 5, characterized in that: An LLR detection algorithm is used to estimate two different constellation modes of the modulation signal on the activated subcarrier, that is, the selected 3D constellation mapper is estimated by judging the log-likelihood ratio of the constellation symbol on the activated subcarrier under the two constellation mode symbols; include: Suppose the probability that the αth activated subcarrier in the gth OFDM subblock transmits a symbol using the 3D constellation mapper A is in, and denote the symbol probabilities of transmitting 3D constellation mapper A and 3D constellation mapper B on the activated subcarriers, α=1,2,…,k; denote the modulation symbols of 3D constellation mappers A and B respectively; γ is converted into α Simplify to get The subcarrier activation modes corresponding to 3D constellation mapper A and 3D constellation mapper B are obtained by calculation. and 8. The 3D-OFDM system working method based on dual-mode index modulation according to claim 7, characterized in that: The corresponding 3D constellation symbols are estimated based on the maximum likelihood criterion

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