Frequency-code joint index modulation method

Abstract

The invention provides a frequency-code joint index modulation method, and relates to the technical field of wireless communication. Based on an index modulation technology and a frequency-code combined index modulation technology, code index modulation and subcarrier index modulation are combined, modulation and demodulation methods are researched at a sending end and a receiving end of a signal, and mapping selection and cyclic shift operations are performed on a spread spectrum sequence at the sending end of the signal, so that the modulation and demodulation efficiency of the signal is improved. Different spread spectrum sequences are selected to carry out spread spectrum processing on the subcarrier index modulation signals so as to improve the spectrum efficiency; at a signal receiving end, aiming at index information of different resources in a frequency code joint index modulation signal, a receiving framework combining step-by-step detection and feedback detection is designed, and the bit error rate performance of a communication system is improved while a target of a global optimal solution is changed into local optimum.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and in particular to a frequency-code combined index modulation method. Background Art

[0002] Due to its characteristics of significantly improving data transmission rate and capacity under limited bandwidth and power constraints, index modulation technology has attracted much attention and developed rapidly in recent years. Compared with traditional modulation methods, index modulation carries information through the index of resources, getting rid of the dependence on symbol amplitude and phase, and significantly improving spectral efficiency. However, current research mainly focuses on index modulation of a single resource (such as the frequency domain, code domain, or spatial domain). Although it performs excellently in certain specific scenarios, its single-dimensional resource utilization method is difficult to meet the requirements for higher performance in complex communication environments.

[0003] To solve this problem, joint index modulation technology has emerged. It transmits information bits by jointly indexing multiple resource dimensions (such as the frequency domain, code domain, or spatial domain), enhancing the robustness and flexibility of the system while improving spectral efficiency. However, existing joint index modulation methods often lead to a significant increase in the bit error rate while improving spectral efficiency, and the improvement of spectral efficiency is still limited, making it difficult to fully meet the requirements of future communication systems for high-speed and reliable transmission. Therefore, designing an efficient joint index modulation scheme, optimizing resource allocation, improving system capacity, and reducing system complexity have important scientific value and practical significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a frequency-code combined index modulation method for the deficiencies of the above-mentioned existing technologies. At the signal sending end, through mapping selection and cyclic shift operation of the spreading sequence, different spreading sequences are used to spread the subcarrier index modulation signal to improve spectral efficiency; at the signal receiving end, for the index information of different resources in the frequency-code combined index modulation signal, a receiving framework combining step-by-step detection and feedback detection is designed. While changing the goal of the global optimal solution to a local optimal one, the bit error performance of the communication system is improved.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is:

[0006] The present invention provides a frequency-code combined index modulation method, including the following steps:

[0007] Step 1: Obtain the input information generated by the information source, divide the input information generated by the information source into several groups through serial-to-parallel conversion, and generate the same number of OFDM sub-blocks. Each group of information is divided into multiple parts for parallel transmission; the multiple parts include modulation information, spreading sequence index information, spreading sequence phase index information, and subcarrier index information;

[0008] Obtain the mg-bit input information generated by the information source. Divide the mg-bit input information generated by the information source into g groups through an information splitter and generate g OFDM sub-blocks. Each group of information is m bits, and the information modulation method within each group is the same. Then divide the m-bit information within each group into 4 parts and perform parallel transmission using different transmission methods. Among them, the first part of the information is the modulated information D1(a) of m1 bits, the second part of the information is the spreading sequence index information D2(b) of m2 bits, the third part of the information is the spreading sequence phase index information D3(d) of m3 bits, and the fourth part of the information is the subcarrier index information D4(e) of m4 bits. Here, a is the index of the discrete time sequence, b is the spreading sequence index, d is the spreading sequence phase index, and e is the subcarrier index. a, b, d, and e are used to represent the values of each part of the information at specific time points or sample points;

[0009] Perform parallel transmission on each part of the information within each group using different transmission methods. Among them, the modulated information D1(a) is transmitted through M-ary modulation, the spreading sequence index information D2(b) and the spreading sequence phase index information D3(d) are transmitted through the spreading sequence index, and the subcarrier index information D4(e) is transmitted through the subcarrier index;

[0010] Step 2: Set the alternative spreading sequence set of the OFDM sub-block. Select a spreading sequence from the alternative spreading sequence set using the spreading sequence index information, and perform a phase shift on the selected spreading sequence using the spreading sequence phase index information to obtain the phase-shifted spreading sequence;

[0011] Set the alternative spreading sequence set C of the OFDM sub-block, including G mutually orthogonal spreading sequences c1, c2, … c G , as shown in the following formula (1):

[0012] C = [c1, c2, … c G (1)

[0013] The l-th (l ∈ G) spreading sequence c l is shown in the following formula (2):

[0014] c l = [v1, v2, v3, …, v p (2)

[0015] where v1, …, v p are the code elements of the spreading sequence c l with a period of p;

[0016] The condition that the relationship between the number G of spreading sequences in the alternative spreading sequence set C and the number of bits m2 of the spreading sequence index information D2(b) needs to satisfy is shown in the following formula (3):

[0017]

[0018] Among them, C h (G, 1) is the number of combinations of selecting 1 spreading sequence from G spreading sequences;

[0019] Select the spreading sequence of the i-th OFDM sub-block (where i ∈ {1, 2, 3,..., g}) from the set of candidate spreading sequences by using the spreading sequence index information D2(b). And use the spreading code phase index information D3(d) to perform phase shift on the spreading sequence of the i-th OFDM sub-block to obtain the shifted spreading sequence. The specific method is as follows:

[0020] Perform radix conversion processing on the spreading sequence index information D2(b) and the spreading sequence phase index information D3(d) as shown in the following formulas (4) and (5):

[0021] L = bin2dec[D2(b)] (4)

[0022] J1 = bin2dec[D3(d)] (5)

[0023] Among them, bin2dec[·] is the binary-to-decimal operation, L is the decimal representation of the spreading sequence index information D2(b), and J1 is the decimal representation of the spreading sequence phase index information D3(d);

[0024] Select the L-th spreading sequence c in the set of candidate spreading sequences C according to the decimal representation L of the spreading sequence index information D2(b) L as the spreading sequence of the i-th OFDM sub-block. According to the decimal representation J1 of the spreading sequence phase index information D3(d), perform circular shift processing on the spreading sequence of the i-th OFDM sub-block to obtain the shifted spreading sequence of the i-th OFDM sub-block. As shown in the following formula (6):

[0025]

[0026] Among them, is the operation of circular right shift by J1 bits;

[0027] Step 3: Perform spreading processing on the modulation information;

[0028] Perform M-ary modulation on the m1-bit binary information in the modulation information D1(a) of the i-th OFDM sub-block to obtain symbol data d. i, as shown in formula (7) below:

[0029] d i = a i + jb i (7)

[0030] where a i is the real component of the symbol data d i and b i is the imaginary component of the symbol data d i ;

[0031] In the i-th OFDM sub-block, using the spreading sequence and the shifted spreading sequence to perform spreading processing on the real component a i and the imaginary component b i of the symbol data d i respectively, to obtain the spread symbol data d i ′, as shown in formula (8) below:

[0032]

[0033] where a i ′ is the real component of the spread symbol data d i ′, and b i ′ is the imaginary component of the spread symbol data d i ′;

[0034] Step 4: Activate some subcarriers in the communication bandwidth and modulate the spread symbol data onto the activated subcarriers;

[0035] Divide N subcarriers equally into g subcarrier blocks, each subcarrier block contains n′ subcarriers, i.e., N = g * n′, each subcarrier block corresponds to an OFDM sub-block, and map the subcarriers of the subcarrier block to the corresponding OFDM sub-block; for each OFDM sub-block, use the subcarrier index information D4(e) containing m4 bits of information to perform mapping selection on different combinations of activated subcarriers, select k activated subcarriers from n′ subcarriers, and the total number of index combinations of the selected subcarriers needs to satisfy the condition as shown in formula (9) below:

[0036]

[0037] where C h (n′, k) is the number of combinations of selecting k activated subcarriers from n′ subcarriers;

[0038] Use k combinations of numbers weighted and represented as shown in formula (10) below:

[0039]

[0040] Among them, w k is the k-th selected active subcarrier;

[0041] Generate a decreasing sequence D weighted and represented according to k combination numbers s , as shown in the following formula (11):

[0042] D s = (w k , w k-1 , …, w1), w k > w k-1 >... > w1 (11)

[0043] Generate the active subcarrier combination of the i-th OFDM sub-block according to the subcarriers corresponding to the decreasing sequence D s i Modulate the symbol data d i ' after spreading processing onto the active subcarriers to obtain the active subcarrier signal S i,q (t) of the i-th OFDM sub-block, as shown in the following formula (12):

[0044]

[0045] Among them, q is the q-th active subcarrier, and f i,q is the q-th subcarrier activated in the i-th subcarrier block;

[0046] Step 5: Based on the active subcarrier signal, introduce idle carriers to obtain a frequency-code joint index modulation signal, complete the frequency-code joint index modulation, and the frequency-code joint index modulation signal is transmitted to the receiving end through the channel after carrier modulation;

[0047] Step 6: The receiving end receives the frequency-code joint index modulation signal after carrier modulation and performs preprocessing on it, including matched filtering, sampling, and FFT processing, to obtain the OFDM symbols of each OFDM sub-block;

[0048] The receiving end receives the frequency-code joint index modulation signal after carrier modulation and performs preprocessing on it, including matched filtering, sampling, and FFT processing, to obtain the OFDM symbol y of each OFDM sub-block, as shown in the following formula (13):

[0049]

[0050] Among them, s is all the channel transmission symbols of each OFDM symbol, s(1), …, s(N) are the transmission symbols of subcarriers 1, …, N, n is additive white Gaussian noise, n(1), …, n(α), …, n(N) are the additive white Gaussian noise of subcarriers 1, …, α, …, N, n(α) follows a Gaussian distribution CN(0, N0), H is the channel matrix, h(1), …, h(α), …, h(N) are the Rayleigh fading channel coefficients of subcarriers 1, …, α, …, N, h(α) follows a complex Gaussian distribution CN(0, 1), E s is the average transmit power of the constellation modulation symbols, γ is the signal-to-noise ratio of each active subcarrier, is the power allocation coefficient, N0 is the noise power spectral density;

[0051] Channel state estimation information is added to the Rayleigh fading channel coefficients, as shown in the following formula (14):

[0052] h * (α) = h′(α) + e(α) (14)

[0053] Among them, h′(α) is the estimated value of the Rayleigh fading channel coefficient of subcarrier α, which follows CN(0, 1 - ε 2 ), e(α) is the channel state information estimation error, which follows a Gaussian distribution CN(0, ε 2 ), ε 2 is the variance of the channel state information estimation error;

[0054] The estimated signal of the received signal is calculated using the maximum likelihood detection method, as shown in the following formula (15):

[0055] s′ = argmin s ||y - H′s|| 2 (15)

[0056] Among them, s′ is the estimated signal of the received signal obtained by the maximum likelihood detection method, which is used to parse the index information and constellation modulation information, H′ is the transpose matrix of the channel matrix, and ||·|| is the norm operation;

[0057] Step 7: Parse the OFDM symbols of each sub-block step by step to obtain the input information sent by the transmitting end;

[0058] Step 7.1: Parse the subcarrier index information D4(e);

[0059] Calculate the signal power of the entire subcarrier set θ = {θ1, θ2,..., θ n′} included in each OFDM sub-block, and sort them in descending order according to the signal power of each subcarrier to obtain the set θ′ of the top k active subcarriers, as shown in the following formula (16):

[0060] θ′ = {θ1, θ2, ..., θ k} (16)

[0061] where k is the number of active subcarriers in each sub - block, and θ′ is the set of active subcarriers;

[0062] Analyze the symbol data d i ′ and sub - carrier index information D4(e) transmitted by the active subcarriers in the i - th OFDM sub - block by combining the permutation and combination method;

[0063] Optionally, according to the actual situation of computing resources, choose whether to perform feedback detection on the sub - carrier index information D4(e). If the computing resources are insufficient, no feedback detection is performed. If the computing resources are sufficient, feedback detection is performed on the sub - carrier index information D4(e). The specific method is as follows:

[0064] When the computing resources are sufficient, perform feedback detection by using the spreading sequence c l and the received signal. Set all spreading sequences in the spreading sequence set to zero at all possible positions of the idle carriers to obtain a new sequence set C l ′, as shown in the following formula (17):

[0065]

[0066] where is the l th new spreading sequence in the new sequence set C ′;

[0067] Perform inner - product operations on all sequences in the new sequence set C l ′ with the in - phase component of the received signal, as shown in the following formula (18):

[0068] cor i,l = c l ′ · a i ′ (18)

[0069] where cor i,l represents the result of the inner - product operation of the th spreading sequence c l ′ and the received data in the i - th sub - block;

[0070] Compare to obtain the maximum result and its corresponding sequence c l ′ and the decreasing sequence D s ′ representing the positions of the active subcarriers, and analyze the feedback detection information of the sub - carrier index information D4(e) by combining the permutation and combination method;

[0071] Step 7.2: Analyze the M - ary modulation information D1(a);

[0072] Combined with the method for generating joint index modulation signals, the symbol data d after spreading processing i ′ is spread using different spreading sequences for the real and imaginary parts of the transmission, and the symbol data d after separated spreading processing i ′, the real part Re(d i ′) and the imaginary part Im(d i ′) data are as shown in the following formula |(19):

[0073]

[0074] where a i ′ is the set of the real parts of the symbol data d after spreading processing in the i-th OFDM sub-block, and b i ′ is the set of the imaginary parts of the symbol data d after spreading processing in the i-th OFDM sub-block; Fourier transforms are respectively performed on a i ′ and b i ′, and correlation operations are performed with the l-th alternative spreading sequence in the set of alternative spreading sequences. The correlation operation results h i and h′ i are as shown in the following formula (20): i,l and h′ i,l are as shown in the following formula (20):

[0075]

[0076] where is the Fourier operation, is the inverse Fourier operation, conj is the conjugate operation, and c l is the l-th alternative spreading sequence in the set of alternative spreading sequences;

[0077] The maximum peak-to-average ratio is calculated for the correlation operation results h i,l and h′ i,l to obtain the result matrices PA i and PA′ i of the correlation operations of the G alternative spreading sequences in the set of alternative spreading sequences with a′ i,l and b′ i,l respectively, as shown in the following formula (21):

[0078]

[0079] where PARR(·) is the maximum peak-to-average ratio operation;

[0080] For each OFDM sub-block, the same analysis method is adopted to obtain the in-phase component a i ′ and the quadrature component b iThe result of performing a correlation operation on the spreading sequence used and G alternative spreading sequences in the set of alternative spreading sequences is as shown in the following formula (22):

[0081]

[0082] Select PA i and PA i ′, the maximum values PA i,l and PA′ i,l and their corresponding spreading sequences c l and c′ l , perform inner product operations on the spreading sequences c l and c′ l with a i ′ and b i ′ respectively, as shown in the following formula (23):

[0083]

[0084] Obtain the M-ary modulation symbol of the i-th OFDM sub-block, and complete the parsing of the M-ary modulation information D1(a);

[0085] Step 7.3: Parse the spreading sequence index information D2(b) and the spreading code phase index information D3(d);

[0086] Extract the positions corresponding to the maximum peaks, denoted as pos1 and pos2 respectively, and convert the decimal representation L of D2(b) and the peak position difference into binary, as shown in the following formula (24):

[0087]

[0088] Complete the parsing of the spreading sequence index information D2(b) and the spreading code phase index information D3(d);

[0089] Step 7.4: Perform a parallel-to-serial conversion on the parsed D1(a), D2(b), D3(d), and D4(e) to obtain the output information.

[0090] The beneficial effects of adopting the above technical solutions are as follows: A frequency-code combined index modulation method provided by the present invention, based on the index modulation technology and the frequency-code combined index modulation technology, introduces the generation mechanism of MC-CDMA signals, combines code index modulation and subcarrier index modulation, and studies its modulation and demodulation methods at the signal transmitting end and receiving end. At the signal transmitting end, through operations such as mapping selection and cyclic shift of the spreading sequence, different spreading sequences are selected to perform spreading processing on the subcarrier index modulation signal to improve the spectral efficiency; at the signal receiving end, for the index information of different resources in the frequency-code combined index modulation signal, a receiving framework combining step-by-step detection and feedback detection is designed. While changing the goal of the global optimal solution to a local optimal one, the bit error performance of the communication system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 It is the overall framework diagram of the frequency-code combined index modulation method provided by the embodiment of the present invention;

[0092] Figure 2 It is the schematic diagram of the generation process of the frequency-code combined index modulation signal provided by the embodiment of the present invention;

[0093] Figure 3 It is the schematic diagram of the receiving process of the frequency-code combined index modulation signal provided by the embodiment of the present invention;

[0094] Figure 4 It is the comparison diagram of the spectral efficiency change of each method under different conditions provided by the embodiment of the present invention;

[0095] Figure 5 It is the comparison diagram of the influence of the number of subcarriers on the spectral efficiency provided by the embodiment of the present invention;

[0096] Figure 6 It is the comparison diagram of the influence of the total number of spreading sequences on the receiving complexity provided by the embodiment of the present invention;

[0097] Figure 7 It is the comparison diagram of the complexity of each method at different modulation orders provided by the embodiment of the present invention. Among them, (a) is the complexity of each method at different modulation orders M, and (b) is the enlarged view of the change trend of the NGD method;

[0098] Figure 8 It is the receiving result of each method under the condition of perfect CSI estimation provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0099] The following combines the drawings and embodiments to further describe in detail the specific embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0100] A frequency-code combined index modulation method according to this embodiment is as follows Figure 1 shown, and includes the following steps:

[0101] Step 1: Obtain the input information generated by the information source, divide the input information generated by the information source into several groups through serial-to-parallel conversion, and generate the same number of OFDM sub-blocks. Divide each group of information into multiple parts for parallel transmission; the multiple parts include modulation information, spreading sequence index information, spreading sequence phase index information, and subcarrier index information;

[0102] Obtain mg-bit input information generated by the information source. Divide the mg-bit input information generated by the information source into g groups through an information splitter and generate g OFDM sub-blocks. Each group of information is m bits, and the information modulation method within the group is the same; then divide the m-bit information within each group into 4 parts and perform parallel transmission using different transmission methods. Among them, the first part of the information is m1-bit modulation information D1(a), the second part of the information is m2-bit spreading sequence index information D2(b), the third part of the information is m3-bit spreading sequence phase index information D3(d), and the fourth part of the information is m4-bit subcarrier index information D4(e), where a is the index of the discrete time sequence, b is the spreading sequence index, d is the spreading sequence phase index, and e is the subcarrier index. a, b, d, and e are used to represent the values of each part of the information at a specific time point or sample point;

[0103] Perform parallel transmission on each part of the information within each group using different transmission methods. Among them, the modulation information D1(a) is transmitted through M-ary modulation, the spreading sequence index information D2(b) and the spreading sequence phase index information D3(d) are transmitted through spreading sequence index, and the subcarrier index information D4(e) is transmitted through subcarrier index;

[0104] Step 2: Set an alternative spreading sequence set for the OFDM sub-block, select a spreading sequence from the alternative spreading sequence set using the spreading sequence index information, and perform a phase shift on the selected spreading sequence using the spreading sequence phase index information to obtain a phase-shifted spreading sequence;

[0105] Set an alternative spreading sequence set C for the OFDM sub-block, including G mutually orthogonal spreading sequences c1, c2, … c G , as shown in the following formula (1):

[0106] C = [c1, c2, … c G (1)

[0107] The l-th ∈ G spreading sequence c l is as shown in the following formula (2):

[0108] c l = [v1, v2, v3, …, vp ] (2)

[0109] Among them, v1,…,v p is the spreading sequence c l The code element with a period of p in ;

[0110] The relationship between the number G of spreading sequences in the candidate spreading sequence set C and the number m2 of bits of the spreading sequence index information D2(b) must satisfy the following condition as shown in formula (3):

[0111]

[0112] Among them, C h (G,1) is the number of combinations for selecting one spreading sequence from G spreading sequences;

[0113] Use the spreading sequence index information D2(b) to select the spreading sequence of the i∈{1,2,3,...,g}th OFDM sub-block from the candidate spreading sequence set And use the spreading code phase index information D3(d) to spread the spectrum sequence of the i-th OFDM sub-block Perform phase shift to obtain the shifted spread spectrum sequence The specific method is:

[0114] The spreading sequence index information D2(b) and the spreading sequence phase index information D3(d) are converted into binary system, as shown in the following formula (4) and formula (5):

[0115] L=bin2dec[D2(b)] (4)

[0116] J1=bin2dec[D3(d)] (5)

[0117] Wherein, bin2dec[·] is a binary-to-decimal conversion operation, L is the decimal representation of the spreading sequence index information D2(b), and J1 is the decimal representation of the spreading sequence phase index information D3(d);

[0118] According to the decimal representation L of the spreading sequence index information D2(b), select the Lth spreading sequence c in the candidate spreading sequence set C. L As the spreading sequence of the i-th OFDM sub-block According to the decimal representation J1 of the spreading sequence phase index information D3(d), the spreading sequence of the i-th OFDM sub-block is Perform cyclic shift processing to obtain the spread spectrum sequence of the i-th OFDM sub-block after shifting As shown in the following formula (6):

[0119]

[0120] Among them, is an operation of circular right shift by J1 bits;

[0121] Step 3: Perform spreading processing on the modulation information;

[0122] Perform M-ary modulation on the m1-bit binary information in the modulation information D1(a) of the i-th OFDM sub-block to obtain symbol data d i , as shown in the following formula (7):

[0123] d i = a i +jb i (7)

[0124] Among them, a i is the real part component of the symbol data d i , b i is the imaginary part component of the symbol data d i ;

[0125] In the i-th OFDM sub-block, use the spreading sequence and the shifted spreading sequence to perform spreading processing on the real part component a i and the imaginary part component b i of the symbol data d i respectively, to obtain the spread symbol data d i ′, as shown in the following formula (8):

[0126]

[0127] Among them, a i ′ is the real part component of the spread symbol data d i ′, b i ′ is the imaginary part component of the spread symbol data d i ′;

[0128] Step 4: Activate some subcarriers in the communication bandwidth and modulate the spread symbol data onto the activated subcarriers;

[0129] Divide the N subcarriers equally into g subcarrier blocks, each subcarrier block contains n′ subcarriers, that is, N = g * n′, each subcarrier block corresponds to an OFDM sub-block, and map the subcarriers of the subcarrier block to the corresponding OFDM sub-block; for each OFDM sub-block, use the subcarrier index information D4(e) containing m4 bits of information to perform mapping selection on different activated subcarrier combinations, select k activated subcarriers from n′ subcarriers, and the total number of index combinations of the selected subcarriers needs to meet the following conditions as shown in formula (9):

[0130]

[0131] Among them, C h (n′, k) is the number of combinations of selecting k active subcarriers from n′ subcarriers;

[0132] The weighted representation using k numbers of combinations is shown in the following formula (10):

[0133]

[0134] Among them, w k is the k-th selected active subcarrier;

[0135] According to the weighted representation using k numbers of combinations generate a decreasing sequence D s , as shown in the following formula (11):

[0136] D s =(w k , w k-1 , …, w1), w k > w k-1 >...> w1 (11)

[0137] According to the decreasing sequence D s generate the active subcarrier combination of the i-th OFDM sub-block for the subcarriers corresponding to the frequencies Modulate the symbol data d i ′ after spreading processing onto the active subcarriers to obtain the active subcarrier signal S i,q (t) of the i-th OFDM sub-block, as shown in the following formula (12):

[0138]

[0139] Among them, q is the q-th active subcarrier, and f i,q is the q-th subcarrier activated in the i-th subcarrier block;

[0140] Step 5: Based on the active subcarrier signal, introduce idle carriers to obtain a frequency-code joint index modulation signal, complete the frequency-code joint index modulation, and the frequency-code joint index modulation signal is transmitted to the receiving end through the channel after carrier modulation;

[0141] The generation process of the frequency-code joint index modulation signal is as Figure 2 shown;

[0142] Step 6: The receiving end receives the frequency-code joint index modulation signal after carrier modulation and performs preprocessing on it, including matched filtering, sampling, and FFT processing, to obtain the OFDM symbols of each OFDM sub-block;

[0143] The receiving end receives the frequency-code joint index modulation signal after carrier modulation and performs preprocessing on it, including matched filtering, sampling, and FFT processing, to obtain the OFDM symbol y of each OFDM sub-block, as shown in the following formula (13):

[0144]

[0145] where s is all the channel transmission symbols of each OFDM symbol, s(1), …, s(N) are the transmission symbols of subcarriers 1, …, N, n is the additive white Gaussian noise, n(1), …, n(α), …, n(N) are the additive white Gaussian noises of subcarriers 1, …, α, …, N, n(α) follows a Gaussian distribution CN(0, N0), H is the channel matrix, h(1), …, h(α), …, h(N) are the Rayleigh fading channel coefficients of subcarriers 1, …, α, …, N, h(α) follows a complex Gaussian distribution CN(0, 1), E s is the average transmission power of the constellation modulation symbols, γ is the signal-to-noise ratio of each active subcarrier, is the power allocation coefficient, N0 is the noise power spectral density;

[0146] Considering that the receiving end in the actual system cannot perfectly estimate the channel state information, therefore, in this embodiment, the channel state estimation information is added to the Rayleigh fading channel coefficient, as shown in the following formula (14):

[0147] h * (α) = h′(α) + e(α) (14)

[0148] where h′(α) is the estimated value of the Rayleigh fading channel coefficient of subcarrier α, following CN(0, 1 - ε 2 ), e(α) is the channel state information estimation error, following a Gaussian distribution CN(0, ε 2 ), ε 2 is the variance of the channel state information estimation error;

[0149] The maximum likelihood detection method is used to calculate the estimated signal of the received signal, as shown in the following formula (15):

[0150] s′ = argmin s ||y - H′s|| 2 (15)

[0151] where s′ is the estimated signal of the received signal obtained by the maximum likelihood detection method, used to analyze the index information and constellation modulation information, H′ is the transpose matrix of the channel matrix, and ||·|| is the norm operation;

[0152] Step 7: Analyze the OFDM symbols of each sub-block step by step to obtain the input information sent by the sending end;

[0153] Due to the exponential growth of the number of likelihood probability calculations caused by the transmission of index information, and the actual computing resources are difficult to meet the requirements. On this basis, the idea of step-by-step parsing and greedy detection is introduced to reduce the computational amount;

[0154] Step 7.1: Parse the subcarrier index information D4(e);

[0155] Calculate the signal power of the entire subcarrier set θ = {θ1, θ2,..., θ n′} included in each OFDM sub-block, and sort them in descending order according to the signal power of each subcarrier to obtain the set θ′ of the top k active subcarriers, as shown in the following formula (16):

[0156] θ′ = {θ1, θ2,..., θ k} (16)

[0157] Where k is the number of active subcarriers in each sub-block, and θ′ is the set of active subcarriers;

[0158] Combine the permutation and combination method to parse the symbol data d i ′ transmitted by the active subcarriers in the i-th OFDM sub-block and the subcarrier index information D4(e);

[0159] The permutation and combination method is a way of data transmission or encoding by arranging or selecting certain elements. First, calculate the permutation and combination number of the transmission information and perform weighted processing on it; then, find the positions of the corresponding subcarriers according to the obtained permutation and combination number; during the signal reception process, combine formula (10) and formula (16) to obtain the information corresponding to the combination according to the mapping rule, and convert it into a binary data stream as the demodulated index bit information;

[0160] Optionally, according to the actual situation of the computing resources, select whether to perform feedback detection on the subcarrier index information D4(e). If the computing resources are insufficient, no feedback detection is performed. If the computing resources are sufficient, feedback detection is performed on the subcarrier index information D4(e). The specific method is as follows:

[0161] When the computing resources are sufficient, perform feedback detection through the spreading sequence c l and the received signal. Set all spreading sequences in the spreading sequence set to zero at all possible positions of the idle carriers to obtain a new sequence set C l ′, as shown in the following formula (17):

[0162]

[0163] Where is the new sequence set C l ′ in A new spreading sequence;

[0164] Since there are possibilities for the positions where zero values are assigned, the new sequence set C l ′ contains new spreading sequences, with serial numbers

[0165] For all sequences in the new sequence set C l ′, perform inner product operations with the in-phase component of the received signal respectively, as shown in the following formula (18):

[0166] cor i,l = c l ′·a i ′ (18)

[0167] where cor i,l represents the result of the inner product operation between the th spreading sequence c l ′ in the i-th sub-block and the received data;

[0168] Compare to obtain the maximum result and its corresponding sequence c l ′ and the decreasing sequence D s ′ representing the positions of the active subcarriers, and combine the permutation and combination method to analyze the feedback detection information of the subcarrier index signal D4(e);

[0169] Step 7.2: Analyze the M-ary modulation information D1(a);

[0170] Combined with the method for generating joint index modulation signals, different spreading sequences are used for spreading the real and imaginary parts of the symbol data d i ′ after spreading processing. Separate the real part Re(d i ′) and the imaginary part Im(d i ′) of the symbol data d i ′ after spreading processing, as shown in the following formula (19):

[0171]

[0172] where a i ′ is the set of the real parts of the symbol data d i ′ after spreading processing in the i-th OFDM sub-block, and b i ′ is the set of the imaginary parts of the symbol data d i ′ after spreading processing in the i-th OFDM sub-block; Perform Fourier transforms on a i ′ and b i ′ respectively, and perform correlation operations with the i,land h′ i,l As shown in the following formula (20):

[0173]

[0174] in, is the Fourier operation, is the Fourier inverse operation, conj is the conjugate operation, c l is the lth candidate spreading sequence in the candidate spreading sequence set;

[0175] For the relevant operation result h i,l and h′ i,l Perform the maximum peak-to-average ratio calculation to obtain the G candidate spreading sequences in the candidate spreading sequence set and a′ i and b′ i The result matrix PA of the correlation operation i,l and PA′ i,l , as shown in the following formula (21):

[0176]

[0177] Wherein, PARR(·) is the maximum peak-to-average ratio calculation;

[0178] The same analytical method is used for each OFDM sub-block to obtain the carrier in-phase component a in the i-th OFDM sub-block. i ′ and the orthogonal component b i The result of correlation operation between the spreading sequence used by ′ and the G candidate spreading sequences in the candidate spreading sequence set is shown in the following formula (22):

[0179]

[0180] Select PA respectively i and PA′ i The maximum value PA i,l and PA′ i,l and its corresponding spreading sequence c l and c′ l , for the spreading sequence c l and c′ l For a i ′ and b i ′ performs inner product operation, as shown in the following formula (23):

[0181]

[0182] Get the M-ary modulation symbol of the i-th OFDM sub-block and complete the parsing of the M-ary modulation information D1(a);

[0183] Step 7.3: Parse the spreading sequence index information D2(b) and the spreading code phase index information D3(d);

[0184] Extract the positions corresponding to the maximum peaks, denoted as pos1 and pos2 respectively, and convert the decimal representation L of D2(b) and the peak position difference into binary, as shown in the following formula (24):

[0185]

[0186] Complete the parsing of the spreading sequence index information D2(b) and the spreading code phase index information D3(d);

[0187] Step 7.4: Perform a parallel-to-serial conversion on the parsed D1(a), D2(b), D3(d), and D4(e) to obtain the output information.

[0188] The receiving process of the frequency-code combined index modulation signal in this embodiment is as Figure 3 shown.

[0189] In this embodiment, to explore the performance superiority of the frequency-code combined index modulation signal, the proposed combined index modulation method is subjected to simulation testing and analysis, and the combined index modulation signal is compared and analyzed with MC-CDMA, MC-DS-CDMA, and PCSS-OFDM signals in terms of spectral efficiency, index resources, complexity, and bit error rate to verify the superiority of the proposed method compared with other methods. The basic parameters of the simulation are shown in Table 1.

[0190] Table 1 Simulation parameter settings

[0191]

[0192] In terms of spectral efficiency, the combined index modulation signal is compared and analyzed with MC-CDMA, MC-DS-CDMA, and PCSS-OFDM signals. In a multi-carrier communication system for spread-spectrum communication, the spectral efficiency is defined as the ratio of the information rate R b of the system to the system bandwidth B: η = R b / B. If it is assumed that the number of sub-carriers N is large enough, the system bandwidth can be expressed as B = N * △f, and the information rate R b is the ratio of the number of original information bits m included in each symbol to T s : R b = m / T s . Also, because △f = 1 / T s , so η = m / N. For the FCIM system of frequency-code combined index modulation, under the same conditions, the amount of information m FCIM carried by each symbol and the number of sub-carriers N FCIM are as shown in the following formula:

[0193]

[0194] Among them, p′ is the number of unactivated subcarriers;

[0195] Spectral efficiency Γ PCSS-OFDM The calculation process is shown in the following formula:

[0196]

[0197] To compare the spectral efficiencies of MC-CDMA, MC-DS-CDMA, PCSS-OFDM, and FCIM-OFDM systems, assume that the modulation method is QPSK for all, and a spreading code with a period of 1023 is used as the spreading sequence, that is: p = 1023. Thus, the spectral efficiencies under different total numbers G of spreading sequences, numbers r of spreading sequences used, and numbers p′ of unactivated subcarriers are as Figure 4 shown.

[0198] From Figure 4 it can be seen that the spectral efficiencies of MC-CDMA and MC-DS-CDMA systems are theoretically the same. In contrast, PCSS-OFDM improves the index information transmission rate by increasing the number r of spreading sequences and expanding the PN code selection combination number, but the effect is limited. While FCIM, under the same conditions, further improves the spectral efficiency through the spreading code phase offset and activated subcarriers. When p′ increases to 3, the spectral efficiency can be increased to more than 0.04, showing the flexibility of FCIM in improving the spectral efficiency.

[0199] Through the above analysis, the ability of PCSS-OFDM and FCIM systems to improve the spectral efficiency is verified. However, compared with MC-CDMA and MC-DS-CDMA, PCSS-OFDM and FCIM have higher requirements for index resources, and the number of index resources of spreading codes and subcarriers directly affects the data transmission rate.

[0200] Therefore, to analyze the influence of limited resources on the spectral efficiency, a comparative analysis of the spectral efficiencies of MC-CDMA, MC-DS-CDMA, PCSS-OFDM, and FCIM systems under certain index resource conditions is carried out, as shown in Table 2.

[0201] Table 2 Comparison of index resources of MC-CDMA, MC-DS-CDMA, PCSS-OFDM, and FCIM

[0202]

[0203] From the data in Comparison Table 2, it can be seen that the spectral efficiency of MC-CDMA and MC-DS-CDMA is the lowest and cannot be improved by increasing resources. When using 1024 subcarriers and 16 spreading sequences, under the condition that both FCIM and PCSS-OFDM use one spreading sequence for spreading, the spectral efficiency of FCIM is 0.0244, which is much higher than 0.0098 of PCSS-OFDM. Although when choosing to use 5 spreading sequences for spreading processing, the PCSS-OFDM scheme can achieve a spectral efficiency of 0.293 with a smaller number of local spreading sequences, FCIM can increase the frequency band utilization to 0.332 by adding 1 subcarrier. Compared with the PCSS-OFDM which depends on the increase in the number of spreading sequences, the FCIM scheme can also improve the spectral efficiency by increasing the number of subcarriers.

[0204] When the number of active subcarriers remains unchanged, as Figure 5 shown, since the increase in the total number of subcarriers has no effect on the transmission rate of index information in the PCSS-OFDM scheme, it leads to a slight decrease in its spectral efficiency. For the FCIM scheme, the increase in subcarriers will bring more activation methods, thus increasing the transmission rate of subcarrier index information and improving the spectral efficiency.

[0205] In addition, the number of spreading codes used in the PCSS-OFDM scheme is limited by the spreading sequence resources, resulting in a lower upper limit for improving its spectral efficiency. To prove this more intuitively, under the condition that the number of subcarriers is 2048 and the number of spreading sequences is 16, the spectral efficiencies of each method are shown in Table 3.

[0206] Table 3 Comparison of Index Resources of MC-CDMA, MC-DS-CDMA, PCSS-OFDM and FCIM

[0207]

[0208] According to the spectral efficiency calculation formula, under the condition of 2048 subcarriers and 16 spreading sequences, when r = 1 and p' = 0, PCSS-OFDM can obtain the highest spectral efficiency of 0.0449, while the spectral efficiency of FCIM can reach 1.0044. It can be seen that the spectral efficiencies of MC-CDMA, MC-DS-CDMA and PCSS-OFDM are much lower than that of FCIM. This is because although PCSS-OFDM can improve the spectral efficiency by expanding the set of alternative spreading sequences, the improvement efficiency is low, while FCIM can flexibly coordinate the two index resources of spreading sequences and subcarriers to improve the spectral efficiency and is less affected by resource limitations.

[0209] To compare the receiving complexity of the FCIM and PCSS-OFDM methods, in this embodiment, the parsing process of the frequency-code joint index modulation signal is analyzed, including calculation steps such as correlation detection and maximum likelihood detection. Maximum likelihood detection needs to calculate the likelihood probabilities of all possible transmitted signals and the received signal, and find the signal with the maximum probability. Although this method improves the spectral efficiency, it needs to calculate the likelihood probability multiple times when receiving signals, and the computational complexity increases in a multiplicative manner. In contrast, the NML method uses step-by-step reception. First, the subcarrier index and constellation modulation information are parsed through maximum likelihood detection, and then the spread spectrum sequence index and spread spectrum code phase index information are parsed through correlation operations, making the complexity increase in an additive manner, thus reducing the computational complexity. The near-greedy detection proposed in this embodiment further uses step-by-step reception on the basis of NML, dividing the process of receiving signals and parsing information into four steps, reducing the number of calculations and complexity.

[0210] To effectively compare the complexity, the number of floating-point operations per subcarrier is used as the complexity measurement index. Under the conditions of modulation order M, number of spread spectrum codes G, spread spectrum code period p, and number of subcarriers n, the complexity calculation formulas for each OFDM sub-block in various methods are shown in Table 4.

[0211] Table 4 Complexity of Different Detection Methods

[0212]

[0213] As can be seen from Table 4, PCSS-OFDM and FCIM improve the spectral efficiency by increasing the index information transmission rate, and their receiving complexity is affected by the total number of spread spectrum sequences G and the spread spectrum code period p. Increasing the number of spread spectrum sequences r will increase the receiving complexity of PCSS-OFDM, but it has no effect on the FCIM method. For different receiving methods of FCIM signals, greedy detection avoids the high complexity of calculating the likelihood probability for each subcarrier, but additional power calculation is required. Overall, compared with NML, greedy detection reduces the receiving complexity and eliminates the influence of the modulation order on the signal receiving complexity. The NGDFB receiving method slightly increases the complexity in an additive form due to the feedback adjustment mechanism.

[0214] Based on the above analysis, under the conditions of Table 1, the complexity of various methods is compared, and the common logarithm of the number of floating-point operations Flops is used as the index, as Figure 6As shown, the index information transmitted by FCIM leads to a relatively high complexity of the ML and NML receiving methods. Although the NGD and NGDFB receiving methods effectively reduce the complexity, it is still higher than that of the PCSS-OFDM method. In addition, the increase in the total number G of spreading sequences affects the complexity of both PCSS-OFDM and FCIM, but has a more significant impact on PCSS-OFDM signals. Combining Table 2, it can be seen that the increase in the number r of spreading sequences further increases the complexity of PCSS-OFDM, while having no effect on FCIM. This results in the complexity of PCSS-OFDM gradually approaching that of FCIM as G and r increase. When r is 5 and G is 32, the complexity ratio of the two decreases to 0.4 dB, as Figure 7 shown. (a) shows the complexity of each method for different modulation orders M, and (b) is an enlarged view of the change trend of the NGD method.

[0215] As Figure 7 can be seen, with the increase in the modulation order, the number of floating-point calculations per OFDM sub-block in the ML and NML detection schemes increases. As shown in Table 1, under the same conditions, the complexity of NML is significantly lower than that of ML. Although the proposed NGDFB receiving method has a higher complexity than NML, it is much lower than the ML detection method. When no feedback detection is performed, its complexity is lower than that of the NML receiving method.

[0216] Under the parameter settings in Table 1, the BER results of different receiving methods for PCSS-OFDM, MC-CDMA, and FCIM systems are as Figure 8 .

[0217] As Figure 8 can be seen, although the frequency-domain spread PCSS-OFDM system improves the spectral efficiency, its performance is poor, and the BER is higher than that of MC-CDMA. When the signal-to-noise ratio is relatively large, the BER performance of the PCSS-OFDM system gradually improves, but it still does not exceed that of the MC-CDMA system. As r increases from 1 to 3, although the spectral efficiency is increased to 0.0235, the BER further decreases accordingly. For FCIM under the condition of a spectral efficiency of 0.0244, if the NML method is used for reception, the system performance is better when the signal-to-noise ratio is lower than 7 dB. After the signal-to-noise ratio is higher than 7 dB, its BER is higher than that of the MC-CDMA and PCSS-OFDM systems. However, when received by the proposed NGDFB method in this paper, the BER performance is lower than that of the NML detection method when the signal-to-noise ratio is above -8 dB. And when the target of reducing the bit error rate to 0.01 is achieved, the signal-to-noise ratio required by the NGDFB receiving method is reduced by 14 dB compared with the approximate likelihood detection.

[0218] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope defined by the claims of the present invention.

Claims

1. A frequency-code combined index modulation method, characterized in that: It includes the following steps: Step 1: Obtain the input information generated by the information source, divide the input information generated by the information source into several groups through serial-to-parallel conversion, generate the same number of OFDM sub-blocks, and divide each group of information into multiple parts for parallel transmission; the multiple parts include modulation information, spreading sequence index information, spreading sequence phase index information, and sub-carrier index information; Step 2: Set an alternative spreading sequence set for the OFDM sub-blocks, select a spreading sequence from the alternative spreading sequence set using the spreading sequence index information, and perform a phase shift on the selected spreading sequence using the spreading sequence phase index information to obtain a phase-shifted spreading sequence; Step 3: Perform spreading processing on the modulation information; Step 4: Activate some of the sub-carriers in the communication bandwidth, and modulate the spread processed symbol data onto the activated sub-carriers; Step 5: Based on the activated sub-carrier signal, introduce idle carriers to obtain a frequency-code joint index modulation signal, complete the frequency-code joint index modulation, and the frequency-code joint index modulation signal is transmitted to the receiving end through the channel after carrier modulation; Step 6: The receiving end receives the frequency-code joint index modulation signal after carrier modulation and performs pre-processing on it, including matched filtering, sampling, and FFT processing, to obtain the OFDM symbols of each OFDM sub-block; Step 7: Analyze the OFDM symbols of each sub-block step by step to obtain the input information transmitted by the transmitting end.

2. The index modulation method combining frequency codes according to claim 1, wherein: The specific method of Step 1 is as follows: Obtain the mg-bit input information generated by the information source, divide the mg-bit input information generated by the information source into g groups through an information splitter and generate g OFDM sub-blocks. Each group of information is m bits, and the information modulation method within the group is the same; then divide the m-bit information within each group into 4 parts and perform parallel transmission using different transmission methods. Among them, the first part of the information is the m1-bit modulation information D1(a), the second part of the information is the m2-bit spreading sequence index information D2(b), the third part of the information is the m3-bit spreading sequence phase index information D3(d), and the fourth part of the information is the m4-bit sub-carrier index information D4(e), where a is the index of the discrete time sequence, b is the spreading sequence index, d is the spreading sequence phase index, e is the sub-carrier index, and a, b, d, e are used to represent the values of each part of the information at a specific time point or sample point; Perform parallel transmission on each part of the information within each group using different transmission methods. Among them, the modulation information D1(a) is transmitted through M-ary modulation, the spreading sequence index information D2(b) and the spreading sequence phase index information D3(d) are transmitted through spreading sequence index, and the sub-carrier index information D4(e) is transmitted through sub-carrier index.

3. The index modulation method combining frequency and code according to claim 2, wherein: The specific method of Step 2 is as follows: Set an alternative spreading sequence set C for the OFDM sub-blocks, including G mutually orthogonal spreading sequences c1, c2, … c G , as shown in the following formula (1): C = [c1, c2, … c G (1) The l-th spreading sequence c where l ∈ G l is as shown in the following formula (2): c l = [v1, v2, v3, …, v p (2) where, v1, …, v p are the chips of the spreading sequence c l with period p; The relationship between the number G of spreading sequences in the alternative spreading sequence set C and the number m2 of bits of the spreading sequence index information D2(b) needs to satisfy the condition shown in the following formula (3): Among them, C h (G, 1) is the number of combinations of selecting 1 spreading sequence from G spreading sequences; Select the spreading sequence of the \(i^{th}\) OFDM sub - block (\(i\in\{1,2,3,\cdots,g\}\)) from the set of alternative spreading sequences using the spreading sequence index information \(D2(b)\). And perform a phase shift on the spreading sequence of the \(i^{th}\) OFDM sub - block using the spreading code phase index information \(D3(d)\). To obtain the shifted spreading sequence. The specific method is as follows: Perform radix conversion processing on the spreading sequence index information D2(b) and the spreading sequence phase index information D3(d), as shown in the following formula (4) and formula (5): L = bin2dec[D2(b)] (4) J1 = bin2dec[D3(d)] (5) where, bin2dec[·] is the binary-to-decimal operation, L is the decimal representation of the spreading sequence index information D2(b), and J1 is the decimal representation of the spreading sequence phase index information D3(d); Select the $L$-th spreading sequence $c$ in the alternative spreading sequence set $C$ according to the decimal representation $L$ of the spreading sequence index information $D2(b)$ L as the spreading sequence of the $i$-th OFDM sub-block According to the decimal representation $J1$ of the spreading sequence phase index information $D3(d)$, for the spreading sequence of the $i$-th OFDM sub-block perform a cyclic shift operation to obtain the shifted spreading sequence of the $i$-th OFDM sub-block as shown in the following formula (6): Among them, is an operation of circularly shifting right by J1 bits.

4. A frequency-code combined index modulation method according to claim 3, characterized in that: The specific method of step 3 is as follows: Perform M-ary modulation on the m1-bit binary information in the modulation information D1(a) of the i-th OFDM sub-block to obtain symbol data d i , as shown in the following formula (7): d i = a i + jb i (7) Among them, a i is the real part component of the symbol data d i and b i is the imaginary part component of the symbol data d i ; In the i-th OFDM sub-block, the spreading sequence and the shifted spreading sequence are used to spread the real part component a i and the imaginary part component b i of the symbol data d i respectively, to obtain the spread symbol data d′ i , as shown in the following formula (8): where a′ i is the real component of the spread-spectrum processed symbol data d′ i and b′ i is the imaginary component of the spread-spectrum processed symbol data d′ i .

5. The index modulation method combining frequency and code according to claim 4, wherein: The specific method of step 4 is as follows: Divide N subcarriers into g subcarrier blocks equally, each subcarrier block contains n' subcarriers, that is, N = g * n', each subcarrier block corresponds to an OFDM sub-block, and map the subcarriers of the subcarrier block to the corresponding OFDM sub-block; for each OFDM sub-block, use the subcarrier index information D4(e) containing m4-bit information to perform mapping selection on different active subcarrier combinations, select k active subcarriers from n' subcarriers, and the total number of index combinations of the selected subcarriers needs to meet the conditions shown in the following formula (9): Among them, C h (n′, k) is the number of combinations of selecting k active subcarriers from n′ subcarriers; Weighted representation using the number of k combinations As shown in the following formula (10): where, w k is the k-th selected active subcarrier; Weighted representation according to the number of k combinations Generate a decreasing sequence D s , as shown in the following formula (11): D s =(w k ,w k-1 ,…,w1), w k >w k-1 >...>w1 (11) According to the decreasing sequence D s Generate the active subcarrier combination of the i-th OFDM sub-block for subcarriers of corresponding frequencies For the symbol data d′ after spreading processing i Modulate it onto the active subcarriers to obtain the active subcarrier signal S of the i-th OFDM sub-block i,q (t), as shown in the following formula (12): where q is the q-th activated subcarrier, and f i,q is the q-th activated subcarrier in the i-th subcarrier block.

6. A frequency-code combined index modulation method according to claim 5, characterized in that: The specific method of step 6 is as follows: The receiving end receives the frequency-code joint index modulation signal after carrier modulation and performs preprocessing on it, including matched filtering, sampling, and FFT processing, to obtain the OFDM symbol y of each OFDM sub-block, as shown in the following formula (13): Among them, s is all the channel transmission symbols of each OFDM symbol, s(1), …, s(N) are the transmission symbols of subcarriers 1, …, N, n is the additive white Gaussian noise, n(1), …, n(α), …, n(N) are the additive white Gaussian noises of subcarriers 1, …, α, …, N, n(α) follows the Gaussian distribution CN(0, N0), H is the channel matrix, h(1), …, h(α), …, h(N) are the Rayleigh fading channel coefficients of subcarriers 1, …, α, …, N, h(α) follows the complex Gaussian distribution CN(0, 1), E s is the average transmit power of the constellation modulation symbols, γ is the signal-to-noise ratio of each active subcarrier, is the power allocation coefficient, N0 is the noise power spectral density; Add channel state estimation information to the Rayleigh fading channel coefficient, as shown in the following formula (14): h * (α) = h′(α) + e(α) (14) where \(h'(\alpha)\) is the estimated value of the Rayleigh fading channel coefficient of subcarrier \(\alpha\), which follows \(\mathcal{CN}(0, 1-\varepsilon)\) 2 ), \(e(\alpha)\) is the channel state information estimation error, which follows the Gaussian distribution \(\mathcal{CN}(0,\varepsilon)\) 2 ), and \(\varepsilon\) 2 is the variance of the channel state information estimation error; Use the maximum likelihood detection method to calculate the estimated signal of the received signal, as shown in the following formula (15): s′=argmin s ||y - H′s|| 2 (15) where, s' is the estimated signal of the received signal obtained by the maximum likelihood detection method, which is used to parse the index information and constellation modulation information, H' is the transpose matrix of the channel matrix, and ||·|| is the norm operation.

7. A frequency-code combined index modulation method according to claim 6, characterized in that: Step 7 includes: Step 7.1: Parse the subcarrier index information D4(e); Calculate the signal power of the entire set of subcarriers contained in each OFDM sub-block \(\theta=\{\theta_1,\theta_2,...,\theta\}\), and sort them in descending order according to the signal power of each subcarrier to obtain the set of activated subcarriers \(\theta'\) with the top \(k\) before sorting, as shown in the following formula (16): n′} and sort them in descending order according to the signal power of each subcarrier to obtain the set of activated subcarriers \(\theta'\) with the top \(k\) before sorting, as shown in the following formula (16): θ′ = {θ1, θ2,..., θ k} (16) where, k is the number of active subcarriers in each sub-block, and θ' is the set of active subcarriers; Analyze the symbol data d' transmitted by the active subcarriers in the i-th OFDM sub-block in combination with the permutation and combination method i and the subcarrier index information D4(e); Step 7.2: Parse the M-ary modulation information D1(a); Step 7.3: Parse the spreading sequence index information D2(b) and the spreading code phase index information D3(d); Step 7.4: Perform serial-to-parallel conversion on the parsed D1(a), D2(b), D3(d), and D4(e) to obtain the output information.

8. A frequency-code combined index modulation method according to claim 7, characterized in that: Step 7.1 further includes: According to the actual situation of computing resources, select whether to perform feedback detection on the subcarrier index information D4(e). If the computing resources are insufficient, no feedback detection is performed. If the computing resources are sufficient, feedback detection is performed on the subcarrier index information D4(e). The specific method is as follows: When computing resources are sufficient, feedback detection is performed by using the spreading sequence c l and the received signal. All spreading sequences in the spreading sequence set are set to zero at all possible positions of the idle carrier to obtain a new sequence set C′ l , as shown in the following formula (17): Among them, is the new sequence set C′ l in new spreading sequences; For all sequences in the new sequence set C′ l perform an inner product operation with the in-phase component of the received signal respectively, as shown in the following formula (18): cor i,l = c' l ·a' i (18) Among them, cor i,l represents the result of the inner product operation between the th spreading sequence c' l in the i-th sub-block and the received data; Compare to obtain the maximum result and its corresponding sequence c′ l and the decreasing sequence D′ representing the positions of the active subcarriers s , and combine the permutation and combination method to analyze the feedback detection information of the subcarrier index letter D4(e).

9. A frequency-code combined index modulation method according to claim 8, characterized in that: The specific method of step 7.2 is as follows: Combined with the method for generating a joint index modulation signal, the real and imaginary parts of the symbol data d' after spreading processing i are spread using different spreading sequences, and the symbol data d' after separated spreading processing i is separated into its real part Re(d' i ) and imaginary part Im(d' i ) data, as shown in the following formula |(19): where a′ i is the set of real parts of the spread-spectrum processed symbol data d′ i in the i-th OFDM sub-block, and b′ i is the set of imaginary parts of the spread-spectrum processed symbol data d′ i in the i-th OFDM sub-block; Fourier transforms are respectively performed on a′ i and b′ i , and correlation operations are performed with the l-th alternative spread-spectrum sequence in the set of alternative spread-spectrum sequences. The correlation operation results h i,l and h′ i,l are as shown in the following formula (20): Among them, is the Fourier operation, is the inverse Fourier operation, conj is the conjugate operation, c l is the l-th alternative spreading sequence in the set of alternative spreading sequences; For the relevant operation result h i,l and h′ i,l perform the maximum peak-to-average power ratio calculation to obtain the result matrices PA i and PA′ i of the correlation operations of the G alternative spreading sequences in the alternative spreading sequence set with a′ i,l and b′ i,l respectively, as shown in the following formula (21): where, PARR(·) is the maximum peak-to-average ratio operation; The same parsing method is adopted for each OFDM sub-block to obtain the in-phase component a' of the carriers in the i-th OFDM sub-block i and the quadrature component b' i The result of performing a correlation operation between the used spreading sequence and G alternative spreading sequences in the alternative spreading sequence set is as shown in the following formula (22): Select the maximum values of PA i and PA' i respectively, which are PA i,l and PA' i,l and their corresponding spreading sequences c l and c' l , and perform inner product operations on the spreading sequences c l and c' l with a' i and b' i respectively, as shown in the following formula (23): Obtain the M-ary modulation symbol of the i-th OFDM sub-block, and complete the parsing of the M-ary modulation information D1(a).

10. A frequency-code combined index modulation method according to claim 9, characterized in that: The specific method of step 7.3 is as follows: Extract the positions corresponding to the maximum peaks, denoted as pos1 and pos2 respectively, and convert the decimal representation L of D2(b) and the peak position difference into binary, as shown in the following formula (24): Complete the parsing of the spreading sequence index information D2(b) and the spreading code phase index information D3(d).

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