AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation

Abstract

The invention discloses an AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation, and the method comprises the steps: S1, data bits group a plurality of subcarriers of AFDM, and each group comprises a plurality of subcarriers; s2, dividing the total information bit into a plurality of parallel bit streams, and further dividing the bit streams into index bits and data bits; s3, determining a pre-chirp parameter corresponding to each subcarrier of the target group; s4, modulating the data bits in each bit stream into data symbols; s5, modulating the signal, carrying out serialization processing, and sending the signal to a time-frequency double-scattering channel; and S6, enabling the signal to pass through the time-frequency double-scattering channel, carrying out FFT (Fast Fourier Transform) on the received signal after cyclic prefix at one position, and then returning to the frequency domain. According to the AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation, different pre-chirp parameters are allocated to each subcarrier, the ADFM waveform is further optimized, and the spectrum efficiency and the energy efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the field of AFDM waveform modulation, and in particular to an AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation. Background Art

[0002] In related technologies, B5G and 6G communication technologies, in high-speed mobile scenarios, because the wireless channels will experience time-frequency dual selective fading, the multipath effect causes interference between data symbols and Doppler frequency shift. Therefore, most of them use orthogonal time-frequency space and orthogonal linear frequency modulation wavelength division multiplexing technology for waveform modulation to combat multipath fading. The special 2D structure of the orthogonal time-frequency space makes the pilot overhead large, thereby reducing the resources available for data transmission and reducing the spectrum efficiency; the diversity order of orthogonal linear frequency modulation wavelength division multiplexing cannot reach the optimal diversity order because it depends on the delay-Doppler distribution of the channel, which may lead to an increase in the transmission error rate in channels with severe fading, reducing the reliability of data transmission. Summary of the Invention

[0003] The purpose of the present invention is to provide an AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation to solve the technical problems in related technologies such as low spectrum efficiency and inability to achieve optimal diversity order, which in turn affects the data transmission rate.

[0004] To achieve the above objectives, the present invention provides an AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation, comprising:

[0005] S1, data bits group multiple subcarriers of AFDM, each group contains multiple subcarriers;

[0006] S2, the total information bits are divided into multiple parallel bit streams, and each parallel bit stream is further divided into index bits and data bits;

[0007] S3. Determine the pre-chirp parameter corresponding to each subcarrier of the target group according to the preset mapping relationship table and the index bit;

[0008] S4, modulating the data bits in each bit stream into data symbols;

[0009] S5. Modulate the signal, then serialize the symbols, add a cyclic prefix, and send it to the time-frequency double scattering channel;

[0010] S6. The signal passes through the time-frequency double scattering channel, removes the cyclic prefix from the received signal, performs FFT, and then returns to the frequency domain.

[0011] Preferably, step S3 includes:

[0012] S31. Determine a symbol set according to the number of subcarriers in each group and the number of pre-chirp parameters;

[0013] S32. For each subcarrier, determine a preset mapping relationship table according to the character set, the number of subcarriers in the target group, and the number of pre-chirp parameters in the character set;

[0014] S33. According to a preset mapping relationship table, the index bit is mapped to select the corresponding pre-chirp parameter to determine the number of additional information bits that can be implicitly transmitted in each group;

[0015] S34: Determine a pre-chirp parameter corresponding to each subcarrier of the target group.

[0016] Preferably, the preset mapping relationship table in step S32 represents the mapping relationship between the index bit, the subcarrier and the pre-chirp parameter, and S32 includes:

[0017] S321: Determine, based on the number of subcarriers in the target group and the number of pre-chirp parameters in the character set, an implicitly transmitted index bit in a preset mapping relationship table, specifically including:

[0018]

[0019] Where b2 is the number of additional information bits implicitly transmitted by the permutation of the pre-chirp parameters for each group of subcarriers; Indicates that from max(λ,N c ) select min(λ,N c ) The number of combinations of elements; N c is the number of subcarriers in each group, λ is the number of pre-chirp parameters in the symbol set;

[0020] S322. Map each index value to a pre-chirp pattern in a preset mapping relationship table according to the value of b2;

[0021] S323: Generate a signal according to the multiple pre-chirp parameters in the character set. There are three kinds of arrangement methods, and each index value corresponds to a unique arrangement method.

[0022] Preferably, in step S34, each subcarrier is assigned a unique c2 value from a limited alphabet of λ legal pre-chirp parameter implementations, indexed by the b2 bit according to the index bit stream and the value from P c N selected from c The pre-chirp parameter corresponding to each subcarrier is determined based on the predefined relationship between the arrangements of the elements, so that the pre-chirp parameter is applied to the corresponding subcarrier.

[0023] Preferably, step S4 includes:

[0024] The data bits in each bit stream are modulated into data symbols using an M-ary PSK modulation scheme.

[0025] Preferably, step S5 includes:

[0026] S51, after all groups are mapped, generate a time domain transmission signal through N-point IDAFT;

[0027] S52: Send the time domain signal to a time-frequency double scattering channel.

[0028] Preferably, before step S52, the method further includes:

[0029] A linear frequency modulation period prefix is ​​added to the modulated signal, and parallel-to-serial conversion is performed.

[0030] Preferably, the post-chirp parameters corresponding to each subcarrier in the target group are the same and are Where N is the total number of subcarriers in AFDM, α max is the maximum value of the normalized Doppler shift.

[0031] Preferably, step S6 includes:

[0032] S61: After receiving the signal, the receiving end removes the linear frequency modulation period prefix and performs serial-to-parallel conversion;

[0033] S62, removing post-chirp parameters of the signal;

[0034] S63, converting the signal from the time domain to the frequency domain through fast Fourier transform to obtain a frequency domain signal;

[0035] S64. Remove the influence of the previous chirp parameter by combining the chirp parameter character set; and restore the complete bit stream by demapping the index bits and demodulating the data bits in combination with M-ary PSK.

[0036] This invention combines PIM with AFDM, dividing multiple bit streams into index bits and data bits. The index bits are mapped to the corresponding pre-chirp parameter c2, while the data bits are modulated using M-ary PSK to generate data symbols. Each subcarrier is then pre-processed using the selected pre-chirp parameter c2. The data symbols are then converted from the frequency domain to the time domain using IDAFT. The output signal is then post-chirped and cyclically prefixed to complete transmission.

[0037] Finally, the signal passes through a time-frequency dual-selective channel, removing the cyclic prefix and returning it to the frequency domain through DAFT. The post-chirp parameters are gradually removed from the signal, and then combined with the pre-chirp parameter alphabet to remove the pre-chirp parameters. The complete bit stream is recovered by demapping the index bits and demodulating the data bits using M-ary PSK.

[0038] The present invention optimizes the ADFM waveform by allocating different pre-chirp parameters to each subcarrier, thereby improving spectrum efficiency and energy efficiency, thereby improving data transmission efficiency and reducing communication energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 1 is a flow chart of an AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the structure of AFDM-PIM according to an embodiment of the present invention;

[0042] Figure 3 1 is a performance comparison diagram of AFDM-PIM and AFDM at different spectral efficiencies according to an embodiment of the present invention;

[0043] Figure 4 FIG. 4 is a performance comparison diagram of AFDM-PIM and AFDM-IM at different spectrum efficiencies according to an embodiment of the present invention. DETAILED DESCRIPTION

[0044] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0045] The development of B5G and 6G communication technologies is expected to provide ultra-high reliability, high data rates, and low-latency communications in high-speed mobile scenarios. However, in high-speed mobile scenarios such as low-Earth orbit (LEO) satellites, high-speed mobile railways, unmanned aerial vehicles (UAVs), and vehicle-to-vehicle (V2V) communication technologies, wireless channels experience dual-selective fading in time and frequency. Multipath effects cause interference and Doppler shift between data symbols. Technologies such as Orthogonal Frequency Division Multiplexing (OFDM) used in 4G / 5G standards are no longer applicable. This is because Doppler shift causes the wireless channel to change within the OFDM symbol, thereby destroying the orthogonality between subcarriers. The loss of orthogonality, in turn, leads to severe inter-carrier interference, significantly degrading the performance of the OFDM system.

[0046] Related technologies use Orthogonal Time Frequency Space (OTFS) and Orthogonal Chirp Division Multiplexing (OCDM) technologies for waveform modulation. OTFS is a two-dimensional modulation method that uses sigmoid finite Fourier transform to map information symbols into the delay-Doppler domain. OCDM is based on discrete Fresnel transform and uses a set of orthogonal chirped signals whose frequencies vary with time to modulate information. However, the special 2D structure of OTFS results in a large pilot overhead, which reduces the resources available for data transmission and reduces spectrum efficiency. The diversity order of OCDM cannot reach the optimal diversity order because it depends on the delay-Doppler distribution of the channel, which may lead to an increase in the transmission error rate in channels with severe fading, reducing the reliability of information transmission.

[0047] In addition, Index Modulation (IM) technology can be considered a solution for optimizing AFDM systems. IM utilizes the indices of the components in the communication system to transmit additional information bits, thereby improving spectral and energy efficiency. Unlike traditional digital modulation schemes that transmit information solely by modulating the amplitude, phase, or frequency of a sinusoidal carrier signal, IM schemes can also map information bits by changing the on / off state of its transmission units, where these units include the transmitting antenna, subcarrier, relay, and modulation type.

[0048] Affine Frequency Division Multiplexing (AFDM) is primarily based on the Discrete Affine Fourier Transform (DAFT), which uses two parameters that can be adjusted based on the delay-Doppler spread of a dual-fading channel. Furthermore, under specific parameter settings, AFDM can achieve full diversity. Because AFDM only requires a one-dimensional transform, its implementation complexity is relatively low.

[0049] Given this, combining AFDM and IM can improve spectral and energy efficiency. Information bits are transmitted without energy consumption through the activation pattern of subsymbols in the DAFT domain, and it has been verified that index bits have stronger diversity protection capabilities than modulation bits. There are also multi-carrier systems that use the activation pattern of AFDM chirped subcarriers as an index, demonstrating that IM-assisted AFDM can improve bit error rate and energy efficiency. However, these related technologies focus only on the post-chirp parameters in AFDM and do not consider the flexibility and freedom of the pre-chirp parameters.

[0050] Based on this, an embodiment of the present invention provides an AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that here.

[0051] like Figure 1 As shown in FIG, a method for optimizing AFDM waveform based on pre-chirp frequency modulation parameter index modulation is proposed. Based on pre-chirp index modulation (PIM), AFDM (Affine Frequency Division Multiplexing) and pre-chirp index modulation are combined. Figure 2 As shown in FIG, the AFDM-PIM structure is referred to as the AFDM-PIM structure, which assigns different pre-chirp parameters to each subcarrier and embeds extra bits into the index pattern of the pre-chirp parameter assignment to improve spectrum efficiency and energy efficiency.

[0052] The process includes the following steps:

[0053] S1. Divide the data to be transmitted into multiple bit streams, and divide each bit stream into index bits and data bits.

[0054] The transmitted bit stream is initially mapped onto a symbol vector, which can be represented as:

[0055]

[0056] Among them, x A [j] represents the frequency domain symbol modulated on the j-th subcarrier, generated using M-ary phase shift keying, with the sequence j ranging from 0 to N-1. The total information bits corresponding to the data to be transmitted are B, which are divided into G parallel bit streams, each containing b bits:

[0057] b=B / G.

[0058] Secondly, each bit stream is further divided into b1 bit symbol stream and b2 index bit stream, data bits:

[0059] b=b1+b2.

[0060] S2. Group multiple AFDM subcarriers, where each group includes multiple subcarriers; the number of bit streams is the same as the number of subcarrier groups.

[0061] The total number of AFDM subcarriers is N, and the N subcarriers are divided into G groups, each group includes N c Subcarriers:

[0062] N c =N / G.

[0063] It should be noted that the number of bit streams is the same as the number of subcarrier groups, both of which are G.

[0064] S3. Each subcarrier confirms a unique pre-chirp parameter from a preset symbol set.

[0065] It should be noted that the target group is any group in group G. The embodiment of the present invention only takes one group as an example for description, and the same applies to the other groups.

[0066] Step S3 specifically includes:

[0067] S31, determining a character set; the character set includes a plurality of pre-chirp parameters;

[0068] Among them, the character set Can be a pre-set character set The pre-chirp parameters are included

[0069]

[0070] S32, according to the character set, the number of subcarriers in the target group, and the number of pre-chirp parameters in the character set, determine a preset mapping relationship table. The pre-chirp pattern of the target group is indexed by the b2 bit according to the index bit stream and the N selected fromc The arrangement of the elements is determined by the predefined relationship between them.

[0071] The preset mapping relationship table represents the mapping relationship between index bits, subcarriers and pre-chirp parameters.

[0072] The index bit list in the preset mapping table covers all values ​​of the target index bit, and the target index bit is any index bit in the G bit streams. For example, assuming that each group has 4 subcarriers and 4 pre-chirp parameter values, then the index bits in the preset mapping table are 2 from 0000 to 1111. 4 combinations.

[0073] At this time, the index bit in each bit stream can be compared with the preset mapping relationship table to find the pre-chirp pattern matching it in the index bit list, and obtain the pre-chirp parameter of each corresponding subcarrier.

[0074] Step S32 further includes:

[0075] S321: Determine the number of bits of each index bit in the preset mapping relationship table according to the number of subcarriers in the target group and the number of pre-chirp parameters in the character set, specifically including:

[0076]

[0077] Wherein, b2 is the number of bits of each index bit in the preset mapping relationship table, N c is the number of subcarriers in each group, and λ is the number of pre-chirp parameters in the symbol set.

[0078] The number of bits b2 of each index bit in the index bit list of the preset mapping relationship table is the number of subcarriers N in the target group. c , character set The number of pre-chirp parameters λ is determined.

[0079] Therefore, by determining the number of bits b2 of each index bit, we have a basis for splitting each bit stream.

[0080] In an optional implementation, additional information bits may be embedded in the index bits of each bit stream to reduce energy loss.

[0081] S322, generate a list of index bits in the preset mapping relationship table according to the size of the values. Each index bit corresponds to multiple subcarriers of the target group and a pre-chirp parameter of each subcarrier.

[0082] For example, as shown in Table 1, assuming Nc =4 and λ=4, each row corresponds to an index bit. Indicates the rounding operation of the integer part, b2 can be calculated as:

[0083]

[0084] Wherein, b2 is the number of additional information bits implicitly transmitted by the arrangement of the pre-chirp parameters (c2 value) of each group of subcarriers. Indicates that from max(λ,N c ) select min(λ,N c ) elements. N c is the number of subcarriers in each group, and λ is the number of pre-chirp parameters in the symbol set.

[0085] N c Substituting λ=4 and λ=4 into the formula, we can get b2=4. At this time, each group of subcarriers in the preset mapping relationship table can implicitly transmit 4 bits of additional information through the arrangement of c2 values.

[0086] Table 1

[0087]

[0088]

[0089] S323: Generate a signal according to the multiple pre-chirp parameters in the character set. There are three kinds of arrangement methods, and each index value corresponds to a unique arrangement method.

[0090] The embodiment of the present invention performs index modulation on the pre-chirp parameter c2, and each subcarrier obtains a unique c2 value from a limited set of symbols, which is determined by the system parameter N c and λ are determined.

[0091] The limited character set depends on the predefined links. Each index b2 corresponds to a row in the character set. The predefined character set is mainly based on N c The index bits map the input bits to corresponding parameter combinations, which are used in signal modulation or transmission.

[0092] The example continues, as shown in Table 1, assuming that in the g-th group (1≤g≤G), corresponding to 2 4 The λ=4 chirp parameters in the character set are arranged by index bits to obtain 2 4 There are permutations, each of which corresponds to an index bit, and the permutations are the pre-chirp parameters corresponding to the four subcarriers in group g, and each pre-chirp parameter value is unique.

[0093] Taking the g-th group as an example, the pre-chirping pattern (PCP) corresponding to the subcarriers of the g-th group can be expressed as:

[0094]

[0095] in, express The set matrix of all pre-chirp parameters in the arrangement, c 2,m represents the pre-chirp parameter of the mth subcarrier, and m∈N c (g-1), N c (g-1)+1,…,N c g-1; complex field Indicates a dimension of N c ×1 complex column vector.

[0096] Then the PCP of all groups can be expressed as This set can be defined as PCPG, and all possible PCPGs can be combined into a set

[0097] S33: Determine, according to a preset mapping relationship table, an ordering relationship of multiple pre-chirp parameters corresponding to the target index bit among multiple subcarriers in the target group.

[0098] S33. Determine a pre-chirp parameter corresponding to each subcarrier of the target group according to the sorting relationship.

[0099] S4. Modulate the data bits in each bit stream into data symbols.

[0100] In an optional implementation, the data bits in each bit stream may be modulated into data symbols using an M-ary PSK modulation scheme.

[0101] Taking the gth group (1≤g≤G) as an example, b1=N c The sign bit of log2(M) is represented by N c M-ary symbols are transmitted, then the data bits of the g-th group can be expressed as:

[0102]

[0103] Among them, x g represents the frequency domain symbol vector of the g-th subcarrier group, x g [i] represents the modulation result of the i-th subcarrier in the g-th group, and the sequence i ranges from 0 to N c -1.

[0104] S5. Convert the data symbols from the frequency domain to the time domain, obtain a multi-carrier signal in the time domain, and send it to the receiving end.

[0105] After all groups are modulated into corresponding data symbols, the data symbols are converted from the frequency domain to the time domain to obtain a multi-carrier signal, which is then transmitted to the receiving end.

[0106] In an optional embodiment, step S5 includes:

[0107] S51. After all groups are mapped, the time domain transmission signal can be generated by N-point IDAFT, which is expressed as

[0108]

[0109] Where n and m represent the indices of the time domain and DAFT domain (i.e., frequency domain), respectively, and m, n∈{0,1,…,N-1}, c1 is the DAFT post-chirp parameter, c2 is the DAFT pre-chirp parameter, N is the total number of AFDM subcarriers, and x[m] represents the frequency domain symbol modulated on the mth subcarrier. Let the pre-chirp diagonal matrix and the post-chirp diagonal matrix be and The matrix form of the transmitted signal is expressed as The multi-carrier signal in the time domain is post-chirped and a linear frequency modulation period prefix is ​​added.

[0110] The multi-carrier signal in the time domain is post-chirped and a linear frequency modulation period prefix is ​​added.

[0111] Specifically, a cyclic prefix needs to be added to the AFDM system to solve the multipath problem. Considering that there is periodicity in DAFT, a cyclic prefix with a length of L can be added. cp The chirp-periodic prefix (CPP) of the linear frequency modulation.

[0112] At the same time, in order to reduce the impact of multipath effects, the length of CPP should be greater than the maximum delay spread of the channel.

[0113] S52: Send the time domain signal to a time-frequency dual-selective channel.

[0114] In addition, during the AFDM modulation process, after applying different pre-chirp parameters to different subcarriers, their orthogonality can still be guaranteed.

[0115] Define the mth subcarrier as φ n (m), the inner product between two subcarriers of AFDM is defined as and The two subcarriers have the same post-chirp parameter c1 and different pre-chirp parameter c2. m1 and m2 are any two subcarriers among the m subcarriers.

[0116] Therefore, we can know that:

[0117]

[0118] When the current chirp parameter c2 has different values, the subcarriers of AFDM remain orthogonal, indicating that the flexibility of c2 allocation can be used not only to achieve independent transmission between subcarriers but also to transmit additional information bits, thereby significantly improving the system's spectral efficiency and energy efficiency without increasing energy consumption, thereby improving the efficiency of subsequent data transmission.

[0119] The embodiments of the present invention improve spectrum efficiency and energy efficiency by adopting non-fixed pre-chirp parameters determined from a predefined symbol set and transmitting additional bits through the index of a specific pre-chirp parameter value on a subcarrier.

[0120] In an optional embodiment, the post-chirp parameters corresponding to each subcarrier in the target group are the same and are Where N is the total number of subcarriers in AFDM, max is the maximum value of the normalized Doppler shift.

[0121] Specifically, by properly setting the value of the post-chirp parameter c1, it is possible to ensure that no interference or overlap occurs between the components of the transmitted data on different paths, thereby achieving full diversity performance under the channel. When , the full diversity order can be obtained in a double-dispersion channel.

[0122] S6. The signal passes through the time-frequency double scattering channel, removes the cyclic prefix from the received signal, performs FFT, and then returns to the frequency domain.

[0123] S61. After receiving the signal, the receiving end removes the linear frequency modulation period prefix and performs serial-to-parallel conversion.

[0124] In high mobility scenarios, due to severe Doppler shift and multipath effects, transmitted data will experience severe time-frequency dual-selective fading channels. Considering a channel with P paths, it can be modeled as:

[0125]

[0126] in, represents the channel coefficient of the pth path, v p and τ p represent the Doppler shift and delay of the p-th path respectively.

[0127] Therefore, the normalized delay and Doppler shift can be expressed as τ p Δf and NTv p, where Δf is the subcarrier spacing of AFDM, T is the sampling interval, and N is the total number of subcarriers of AFDM. The normalized delay and Doppler shift are d p =τ p Δf and At the same time p ∈[0,d max ]、α p ∈[-α max ,α max ], d max and α max Represent the maximum delay and maximum Doppler shift respectively. After removing the CPP at the receiving end, the time domain signal is recorded as

[0128]

[0129] After DAFT operation, the signal in DAFT domain is expressed as

[0130]

[0131] Use H eff represents the effective channel matrix, then the signal can also be expressed as

[0132]

[0133] Among them, the diagonal matrix represents the Doppler effect, A is the DAFT matrix, w is the noise vector, is the N×N matrix of CPP, the forward cyclic shift matrix is represented as follows:

[0134]

[0135] Upon receiving y A After that, a maximum likelihood detector can be applied to detect the transmitted signal.

[0136] The time-frequency double scattering channel can be estimated by the pilot-assisted channel estimation algorithm, and the maximum likelihood data detection can be formulated as the following optimization problem:

[0137]

[0138] S62, removing post-chirp parameters of the signal;

[0139] S63, converting the signal from the time domain to the frequency domain through fast Fourier transform to obtain a frequency domain signal;

[0140] S64. Remove the influence of the previous chirp parameter by combining the chirp parameter character set; and restore the complete bit stream by demapping the index bits and demodulating the data bits in combination with M-ary PSK.

[0141] It should be added that the input-output relationship of AFDM-PIM is expressed as:

[0142]

[0143] The input-output relationship can be expressed as a matrix:

[0144]

[0145] loc in the above formula p =(α p +2Bc1d p ) N , indicating that for the two chirp parameters of AFDM-PIM, only the post-chirp parameter is determined by loc p Determine the matrix H p The position of the non-zero elements in H has an impact on this, which has nothing to do with the pre-chirp parameters. Therefore, similar to AFDM, H can be avoided by adjusting c1. i and H j The overlap of non-zero elements of (i≠j) and the proposed AFDM-PIM When , the full diversity order can be obtained in a double-dispersion channel.

[0146] Finally, the AFDM-PIM solution of the embodiment of the present invention is compared with the AFDM solution and AFDM-IM solution in the related art.

[0147] like Figure 3 As shown in Figure 2, the BER performance of the AFDM-PIM scheme and the AFDM scheme under the same dual-dispersion channel when P = 4. To ensure the same spectrum efficiency, AFDM-PIM uses BPSK and QPSK to achieve a spectrum efficiency of 2 and 3 bit / s / Hz respectively. Other parameters are set as (N, G, λ, d max ,α max )=(8,2,4,2,2), and AFDM sets the number of subcarriers to 8, using QPSK and 8-PSK, respectively. It can be seen that AFDM-PIM has a signal-to-noise ratio gain of approximately 2dB compared to the classic AFDM scheme. This is because AFDM-PIM allows the same spectral efficiency as AFDM to be achieved with a lower-order constellation diagram, indicating that AFDM-PIM provides a viable alternative for communications in dual-dispersion channels.

[0148] like Figure 4 As shown in Figure 2, the bit error rate performance of the AFDM-PIM scheme and the AFDM-IM scheme in a dual-dispersion channel with path P = 3 is analyzed for the spectrum efficiency of 2 and 3 bit / s / Hz respectively. The parameters of AFDM-PIM are set to (N, G, λ, dmax ,α max )=(8,2,4,2,2). In the AFDM-IM scheme, each group contains n subcarriers, and only a subcarriers are activated for each transmission. To ensure that AFDM-IM and AFDM-PIM have the same spectrum efficiency, the AFDM-IM parameters (n,a)=(4,2) and (n,a)=(8,7), and 8-PSK is used. Although neither meets the conditions for full diversity order, it can be seen that AFDM-PIM has better BER performance than AFDM, especially when the BER is 10 -3 The AFDM-PIM scheme proposed in the present invention can achieve the same spectrum efficiency as AFDM-IM through a lower-order constellation diagram, thereby improving the BER performance.

[0149] In this embodiment, the transmitting end of the AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation mentioned above includes:

[0150] The data bit carrier grouping module is used to group multiple subcarriers of AFDM, where each group includes multiple subcarriers; the number of bit streams is the same as the number of subcarrier groups;

[0151] The bit stream segmentation module divides each bit stream into data bits and index bits.

[0152] Index mapping module, index bits select corresponding pre-chirp parameters through mapping, and data bits generate data symbols through M-ary PSK modulation.

[0153] The modulation module performs pre-chirp, inverse fast Fourier transform and post-chirp operations on the subcarrier.

[0154] The post-processing module converts the signal into parallel and serial signals, adds a cyclic prefix to the modulated signal, and sends it to the time-frequency double scattering channel.

[0155] This embodiment also includes a receiving end applied to the above-mentioned AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation, including:

[0156] A data receiving module is used to receive a multi-carrier signal in the time domain from a transmitting end through a time-frequency dual-selective channel;

[0157] Receive signal processing module, removes the cyclic prefix of the received signal and performs serial-to-parallel conversion

[0158] The demodulation module removes the post-chirp parameters of the received signal, performs a fast Fourier transform, and removes the pre-chirp parameters.

[0159] The demapping module is used to restore the data bits through M-ary PSK demodulation and restore the index bits through de-mapping to obtain the complete transmission data.

[0160] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0161] The transmitting end and the receiving end in the embodiment of the present invention are presented in the form of functional units, where the units refer to ASIC (Application Specific Integrated Circuit) circuits, processors and memories that execute one or more software or fixed programs, and / or other devices that can provide the above functions.

[0162] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. An AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation, characterized in that: The following steps are involved: S1, data bits group multiple subcarriers of AFDM, each group contains multiple subcarriers; S2, the total information bits are divided into multiple parallel bit streams, and each parallel bit stream is further divided into index bits and data bits; S3. Determine the pre-chirp parameter corresponding to each subcarrier of the target group according to the preset mapping relationship table and the index bit; S4, modulating the data bits in each bit stream into data symbols; S5. Modulate the signal, then serialize the symbols, add a cyclic prefix, and send it to the time-frequency double scattering channel; S6. The signal passes through the time-frequency double scattering channel, removes the cyclic prefix from the received signal, performs FFT, and then returns to the frequency domain.

2. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 1, characterized in that: Step S3 includes: S31. Determine a symbol set according to the number of subcarriers in each group and the number of pre-chirp parameters; S32. For each subcarrier, determine a preset mapping relationship table according to the character set, the number of subcarriers in the target group, and the number of pre-chirp parameters in the character set; S33. According to a preset mapping relationship table, the index bit is mapped to select the corresponding pre-chirp parameter to determine the number of additional information bits that can be implicitly transmitted in each group; S34: Determine a pre-chirp parameter corresponding to each subcarrier of the target group.

3. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 2, characterized in that: The preset mapping relationship table in step S32 represents the mapping relationship between the index bit, the subcarrier and the pre-chirp parameter. S32 includes: S321: Determine, based on the number of subcarriers in the target group and the number of pre-chirp parameters in the character set, an implicitly transmitted index bit in a preset mapping relationship table, specifically including: Where b2 is the number of additional information bits implicitly transmitted by the permutation of the pre-chirp parameters for each group of subcarriers; Indicates that from max(λ,N c ) select min(λ,N c ) The number of combinations of elements; N c is the number of subcarriers in each group, λ is the number of pre-chirp parameters in the symbol set; S322. Map each index value to a pre-chirp pattern in a preset mapping relationship table according to the value of b2; S323: Generate a signal according to the multiple pre-chirp parameters in the character set. There are three kinds of arrangement methods, and each index value corresponds to a unique arrangement method.

4. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 3, characterized in that: In step S34, each subcarrier is assigned a unique c2 value from a finite alphabet of λ legal pre-chirp parameter implementations, indexed by the b2 bit according to the index bit stream and the P c N selected from c The pre-chirp parameter corresponding to each subcarrier is determined based on the predefined relationship between the arrangements of the elements, so that the pre-chirp parameter is applied to the corresponding subcarrier.

5. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 1, characterized in that: Step S4 includes: The data bits in each bit stream are modulated into data symbols using an M-ary PSK modulation scheme.

6. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 1, characterized in that: Step S5 includes: S51, after all groups are mapped, generate a time domain transmission signal through N-point IDAFT; S52: Send the time domain signal to a time-frequency double scattering channel.

7. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 5, characterized in that: Before step S52, the method further includes: A linear frequency modulation period prefix is ​​added to the modulated signal, and parallel-to-serial conversion is performed.

8. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 1, characterized in that: The post-chirp parameters corresponding to each subcarrier in the target group are the same and are Where N is the total number of subcarriers in AFDM, α max is the maximum value of the normalized Doppler shift.

9. The AFDM waveform optimization method based on pre-chirp frequency modulation parameter index modulation according to claim 1, characterized in that: Step S6 includes: S61: After receiving the signal, the receiving end removes the linear frequency modulation period prefix and performs serial-to-parallel conversion; S62, removing post-chirp parameters of the signal; S63, converting the signal from the time domain to the frequency domain through fast Fourier transform to obtain a frequency domain signal; S64. Remove the influence of the previous chirp parameter by combining the chirp parameter character set; and restore the complete bit stream by demapping the index bits and demodulating the data bits in combination with M-ary PSK.

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