Flexible-configuration time delay Doppler domain OTFS index modulation method, system and program product

Abstract

The invention discloses a flexibly configured time delay Doppler domain OTFS index modulation method, system and program product. The system comprises a transmitting end and a receiving end, wherein the transmitting end comprises an IQ mapping module capable of dynamically configuring grid activation ratio and modulation order. At a transmitting end, binary sequences of in-phase components and quadrature components are mapped respectively, the in-phase components and the quadrature components of sub-blocks are constructed, and sub-block level dynamic grid activation ratio and modulation order configuration are obtained. At a receiving end, an improved message passing detection algorithm is adopted to obtain an activated time delay Doppler domain grid position and a modulation symbol. According to the invention, through dynamic subcarrier activation and modulation order configuration, changing channel conditions and transmission requirements can be adapted; an information bit sequence is reasonably mapped into sub-blocks of in-phase and orthogonal components, so that effective information transmission under different configurations is ensured, and meanwhile, relatively low mapping complexity is maintained; the detection complexity is reduced by an improved messaging detector while maintaining good BER performance.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and more specifically, to a flexible configuration delay-Doppler domain OTFS index modulation method, system and program product. Background Art

[0002] Index modulation technology has made important progress in the field of wireless communications, especially in orthogonal frequency division multiplexing (OFDM) systems. The introduction of index modulation OFDM (OFDM-IM) and its many derivative technologies represents an important milestone in the application of index modulation. However, these technologies still have limitations in high-speed mobile communication scenarios, especially when facing significant Doppler shift. The inter-symbol interference (ICI) caused by Doppler shift seriously affects the performance of OFDM systems, limiting their reliability and spectrum efficiency in high-mobility environments.

[0003] To address this challenge, OTFS (Orthogonal Time Frequency Space Modulation), as an emerging modulation technology, has attracted much attention due to its robustness in high Doppler environments. Furthermore, OTFS index modulation (OTFS-IM) technology has emerged, providing a new path for high-speed mobile communications. OTFS-IM implements index modulation in the delay-Doppler (DD) domain and uses the unactivated DD domain grid as a protection symbol to combat signal interference in high Doppler frequency shift scenarios, significantly improving communication reliability under high Doppler frequency shift conditions. Compared with traditional OFDM-IM, its performance advantage in resisting Doppler frequency shift and time-varying channel conditions is more obvious.

[0004] However, the existing OTFS-IM technology still has shortcomings, mainly reflected in the use of a fixed-ratio grid activation strategy for different sub-blocks within the entire OTFS frame, and the activated grid can only carry signals with fixed modulation orders, which to a certain extent inhibits its potential in spectrum efficiency and system flexibility. In addition, the mapping mechanism of information bits to index modes and modulation symbols, as well as the corresponding signal detection complexity, are also key factors restricting the widespread application of existing OTFS-IM technology. Therefore, how to introduce more degrees of freedom in the delay-Doppler domain, simplify the detection process, and improve spectrum efficiency and system flexibility has become an urgent problem to be solved. In particular, for high-mobility scenarios such as high-speed trains and aviation communications, it is particularly urgent to develop an index modulation technology that can adapt to a wide range of mobile speed requirements and can effectively deal with the effects of multipath effects and Doppler frequency shift. Summary of the invention

[0005] Due to the above-mentioned defects in the prior art, the present invention is committed to proposing a method, system and program product of flexibly configurable delay-Doppler domain OTFS index modulation (abbreviated as E-OTFS-IM-IQ), aiming to solve the problems of fixed activation subcarrier ratio, single modulation order and information mapping and detection complexity in the existing OTFS-IM technology. The enhanced delay-Doppler domain index modulation technology enables different sub-blocks in the OTFS frame to adopt different grid activation ratios, and allows the activated grids to carry modulation symbols of different modulation orders. At the same time, decoupling the in-phase branch and the orthogonal branch adds another degree of freedom to the system, thereby greatly improving the system flexibility, spectrum efficiency and reliability.

[0006] To achieve the above object, on the one hand, the present invention provides a flexible configuration of delay-Doppler domain OTFS index modulation method, characterized in that: a system including an IQ mapping module and a receiving end that can dynamically configure a grid activation ratio and a modulation order performs:

[0007] In the IQ mapping module capable of dynamically configuring the grid activation ratio and the modulation order, the input bit stream is divided into several groups by a bit splitter, and each group of bits is passed through an IQ bit segmentation module to obtain a binary sequence of an in-phase component and an orthogonal component; the binary sequences of the in-phase component and the orthogonal component are mapped respectively to construct the in-phase component and the orthogonal component of the sub-block, and the dynamic grid activation ratio and the modulation order configuration at the sub-block level are obtained; all the sub-blocks are spliced ​​together to generate an OTFS symbol block, which is transmitted to a fast time-varying channel for transmission after OTFS modulation;

[0008] At the receiving end, the time domain received signal is demodulated by OTFS to obtain the received signal in the delay-Doppler domain, and the activated delay-Doppler domain grid position and modulation symbol are obtained by using an improved message passing detection algorithm.

[0009] The present invention not only adopts independent activation of in-phase / quadrature components: decomposing the two-dimensional modulation symbols in each sub-block into in-phase and quadrature components, activating the sub-carriers independently, increasing the system's degree of freedom and information transmission capacity, but also proposes an innovative sub-block-level dynamic sub-carrier activation and modulation order configuration strategy, allowing the number of activated sub-carriers in each sub-block and their corresponding modulation orders to be dynamically adjusted according to actual transmission requirements to adapt to changing channel conditions and transmission requirements. In addition, the present invention designs a computationally efficient coding mapping method to reasonably map the information bit sequence to the sub-blocks of in-phase and quadrature components, ensuring effective information transmission under different configurations while maintaining low mapping complexity. Aiming at the balance between the detection complexity and the bit error rate (BER) performance at the receiving end, an improved message passing detection algorithm is designed, which can effectively process sub-carriers with different activation modes and modulation orders, reduce the detection complexity while maintaining good BER performance.

[0010] Furthermore, in the IQ mapping module that can be dynamically configured with a grid activation ratio and a modulation order, the binary bit information first obtains a binary sequence of an in-phase component and an orthogonal component according to preset parameter information; then, the two binary sequences are respectively transmitted to a bit mapper to determine an indication parameter, and bit segmentation is performed; and then, the segmented binary sequences are respectively transmitted to an index selection module and a modulation symbol mapping module in combination with a compensation value; at the receiving end, an improved message passing detection is used to detect the activation grid index and modulation symbol of the in-phase and orthogonal components, and then the original information bits are restored.

[0011] Furthermore, the working process of the IQ mapping module that can be dynamically configured with a grid activation ratio and a modulation order specifically includes: dividing the transmitted binary bit information into several groups according to a bit splitter, and first obtaining a binary sequence of an in-phase component and an orthogonal component for each group of bits according to preset parameter information; then respectively transmitting the two binary sequences into a bit mapper, determining an indication parameter, performing bit segmentation, and then respectively transmitting the segmented binary sequences into an index selection module and a modulation symbol mapping module in combination with a compensation value; then respectively obtaining the in-phase and orthogonal components and then combining them into sub-blocks; after obtaining all the sub-blocks, splicing the sub-blocks together to generate an OTFS symbol block, and the generated delay Doppler domain signal is transformed by an ISFFT, and then transformed into a time domain signal by a Heisenberg transform module, and finally, after parallel-to-serial conversion, adding a cyclic prefix, and digital-to-analog conversion, it is input into a fast time-varying channel for transmission.

[0012] Furthermore, for the g-th sub-block, the information bit sequence b with a length of b is mapped to the sub-block x g The steps are as follows:

[0013] Step 1: Convert the information bit sequence b into a decimal number Z, Z∈[0,2 b -1];

[0014] Step 2: Calculate the parameters according to the following formula:

[0015]

[0016] Step 3: Place the Z I Convert to length The binary sequence And Z Q Convert to length The binary sequence

[0017] Step 4: Mapping and Construct the in-phase components separately and the orthogonal components Then the sub-block to be transmitted is obtained arrive and arrive The mapping process is the same as arrive The mapping process is as follows:

[0018] Step 4.1: Convert to decimal Determine the indicated parameter according to the following formula:

[0019]

[0020] Calculate the number of sign bits Then the number of bits in the grid activation pattern is b1=b-b2; the first b1 bits of the information bit sequence b are recorded as b1, and the remaining b2 bits are recorded as b2;

[0021] Step 4.2: If r = 1, set the compensation value Z c =0; if r≠1, Convert to length The binary sequence and will The first b1 bits are converted to the decimal compensation value Z c ;

[0022] Step 4.3: Convert b1 to decimal Z1 and then subtract Z from Z1 c ; According to the difference Z1-Z c , determines the index of the active grid Every element in I satisfies the following conditions:

[0023]

[0024] in, is satisfied The largest integer, is satisfied The maximum integer of, and so on, and for a<b, it is considered

[0025] Step 4.4: Get k from b2 r From the constellation map The modulation symbol of

[0026] Step 4.5: Construct the in-phase component of the sub-block by combining the obtained trellis activation pattern and modulation symbol

[0027] Step 5: Combine the in-phase component and the orthogonal component to obtain the g-th sub-block x g The vector form of is:

[0028]

[0029] Furthermore, the working process of the receiving end specifically includes:

[0030] After being affected by the fast time-varying channel and noise, the received time domain signal is subjected to analog-to-digital conversion, cyclic prefix removal and serial-to-parallel conversion; then, the DD domain received signal is obtained through Wigner transform and SFFT transform; for the DD domain received signal, an improved message passing detection algorithm is used to obtain the activation grid index and modulation symbols of the in-phase and orthogonal components, and then the detection results are demapped to restore the original information bits.

[0031] Furthermore, the steps of the improved message passing detection algorithm in the tth iteration are described as follows:

[0032] Step 1: Distractions The mean and variance As a message from the observation node y′[d] passed to the variable node can be approximated as a Gaussian random variable, written as:

[0033]

[0034] The mean of is:

[0035]

[0036] The variance is:

[0037]

[0038] The probability of the variable node x[c] is calculated according to the following formula:

[0039]

[0040] The variable node x′[c] is passed to the observation node The actual message is the probability mass function The elements in can be calculated by the following formula:

[0041]

[0042] in:

[0043]

[0044] A damping factor Δ∈(0,1] is introduced in the probability update to control the convergence speed to improve the performance; Δ can be obtained through Monte Carlo simulation;

[0045] Step 2: Calculate the convergence index:

[0046]

[0047] In the formula, is an indicator function whose value is 1 if the expression in the brackets is true, otherwise it is 0; the posterior probability of the transmitted symbol is expressed as:

[0048]

[0049] If γ (t) >γ (t-1) , the probability of transmitting symbols is updated as:

[0050]

[0051] Repeat the above steps until γ is reached. (t) = 1 or the maximum number of iterations t max .

[0052] Step 3: Once the stopping criteria are met, the log-likelihood ratio (LLR) of each grid is calculated according to the following formula:

[0053]

[0054] Then calculate the processed LLR:

[0055]

[0056] Where H0(·) represents the Heaviside step function; and They are used to obtain the index positions of the in-phase component and the orthogonal component activation of the g-th sub-block respectively; similar to the index position of obtaining the orthogonal component activation, from The process of obtaining the index position of the in-phase component activation is as follows:

[0057] Sure The Hamming distance between each legal grid activation pattern and find the minimum Hamming distance d min The relevant possible legal grid activation mode set is denoted as P; make the following judgments:

[0058] If d min =0, judge Activate the pattern for the estimated legal grid;

[0059] If d min >1, then The elements with the smallest LLR value in are reversed to reduce the minimum Hamming distance until d min =1;

[0060] If d min =1, find The positions in P that are different from all the elements in P are found, and the elements with the smallest LLR amplitude are reversed to obtain the activated index position;

[0061] Step 4: Determine the modulation symbols on the activated grid based on the following metrics:

[0062]

[0063]

[0064] in and Represents the set of activated grids detected by the in-phase component and the orthogonal component respectively; then demaps each sub-block one by one, that is, implements the reverse process of coding mapping to restore the original information bits.

[0065] On the other hand, the present invention provides a flexibly configurable delay-Doppler domain OTFS index modulation system, characterized in that it includes a transmitting end and a receiving end as described above, wherein the transmitting end includes an IQ mapping module that can dynamically configure the grid activation ratio and the modulation order, and is used to execute the above-mentioned flexibly configurable delay-Doppler domain OTFS index modulation method.

[0066] On the other hand, the present invention provides a computer program product, characterized in that when the computer program product is run on a computer, the computer is enabled to execute the above-mentioned flexibly configurable delay-Doppler domain OTFS index modulation method.

[0067] Compared with the prior art, the beneficial effects of the present invention are:

[0068] (1) Improve spectrum efficiency: By dynamically configuring the subcarrier activation ratio and modulation order, information transmission is optimized according to channel conditions, significantly improving the efficiency of spectrum resource utilization.

[0069] (2) Enhanced system flexibility: Adapts to a wider range of application scenarios and can achieve optimal performance by adjusting configuration, whether it is low mobility or high mobility.

[0070] (3) Optimizing detection performance: A low-complexity improved message passing detector is proposed, which reduces the system complexity while ensuring decoding accuracy, which is conducive to practical deployment.

[0071] (4) Improve system reliability: Through flexible resource configuration and efficient information mapping, the transmission reliability in high Doppler frequency shift scenarios is enhanced.

[0072] (5) Optimizing BER performance: Through adaptive modulation order and efficient detection algorithm, the bit error rate can be maintained at a low level even in high mobility environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The present invention and its features and advantages will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings, which are not drawn entirely to scale, emphasis being placed on illustrating the subject matter of the present invention.

[0074] Figure 1 It is a block diagram of a transmitting end of a delay-Doppler domain OTFS index modulation system with flexible configuration in one embodiment of the present invention;

[0075] Figure 2 It is a block diagram of an in-phase / quadrature bit mapping module of a flexibly configured delay-Doppler domain OTFS index modulation system in one embodiment of the present invention;

[0076] Figure 3 It is a schematic diagram of a bit error rate performance curve of a flexibly configured delay-Doppler domain OTFS index modulation system in an embodiment of the present invention. DETAILED DESCRIPTION

[0077] To further help understand the technical solution of the present invention, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. It should be understood that all of these exemplary embodiments described are only partial embodiments and examples of the present invention, rather than all of them. On the contrary, these exemplary embodiments are provided so that those skilled in the art can more thoroughly understand the present invention and can more completely convey the technical content of the present invention to those skilled in the art.

[0078] Example

[0079] This embodiment provides a flexible configuration delay-Doppler domain OTFS index modulation system and method. The proposed flexible configuration delay-Doppler domain OTFS index modulation system transmitter block diagram is as follows: Figure 1 As shown. Consider an OTFS system with M subcarriers and N time slots, where the subcarrier spacing and symbol duration are Δf and T respectively. Assume that an OTFS frame needs to transmit B bits. These B bits are divided into G groups, each group containing b = B / G bits. Each group of b bits is mapped to an OTFS subblock of size n = MN / G in the DD domain. For the in-phase component and the orthogonal component, the number of grids allowed to be activated in each subblock is k1,...,k R (0<k1<k2<...<k R ≤n). Two Pulse Amplitude Modulation (PAM) constellation diagrams and Represents a 2D amplitude-phase constellation diagram S i The real and imaginary parts of i The activation pattern of the in-phase component and the orthogonal component of X, where i = 1, 2, ..., R. Let X I and X Q are the sets of all possible realizations of the in-phase component and the quadrature component, respectively. The total number of possible grid activation patterns for both the in-phase component and the quadrature component is here, represents the binomial coefficient. Therefore, the number of all possible sub-block realizations of the in-phase component and the orthogonal component are:

[0080]

[0081] and

[0082]

[0083] Then the total number of possible sub-block realizations for transmission can be calculated as:

[0084] |X|=|X I |·|X Q |

[0085] Therefore, the flexibly configurable delay-Doppler domain OTFS index modulation system can be realized by using a constant length of The bidirectional mapping between the information bits and |X| sub-blocks is realized, so that the spectral efficiency of the flexibly configured delay-Doppler domain OTFS index modulation system is:

[0086]

[0087] For the sake of clarity, the spectral efficiency of the present invention and OTFS-IM is compared in Table 1, and the subblock lengths of the two systems involved in the comparison are set to n=4, 8. The parameters of the flexibly configured delay-Doppler domain OTFS index modulation system are R=2, k1=1, k2=2; the OTFS-IM system involved in the comparison contains two active subcarriers in each subcarrier block. It can be observed that under the same modulation order, the flexibly configured delay-Doppler domain OTFS index modulation can achieve a spectral efficiency that is more than twice that of OTFS-IM. Even in the case of equivalent information transmission (2PAM modulation and QPSK modulation of IQ two-way), the flexibly configured delay-Doppler domain OTFS index modulation also produces spectral gains of 66.7% and 75% respectively.

[0088] Table 1 Comparison of spectrum efficiency of different schemes

[0089]

[0090] For the g-th sub-block, map the information bit sequence b of length b to sub-block x g The specific steps are as follows:

[0091] Step 1: Convert the information bit sequence b into a decimal number Z, Z∈[0,2 b -1].

[0092] Step 2: Calculate the parameters according to the following formula:

[0093]

[0094] Step 3: Place the Z I Convert to length The binary sequence And Z Q Convert to length The binary sequence

[0095] Step 4: Figure 2 As shown, the mapping and Construct the in-phase components separately and the orthogonal components Then the sub-block to be transmitted is obtained because arrive and arrive The mapping process is the same as that of arrive The mapping process is as follows:

[0096] Step 4.1: Convert to decimal Determine the indicated parameter according to the following formula:

[0097]

[0098] Calculate the number of sign bits Then the number of grid activation mode bits is b1=b-b2. The first b1 bits are denoted as b1, and the remaining b2 bits are denoted as b2.

[0099] Step 4.2: If r = 1, set the compensation value Z c =0. If r≠1, Convert to length The binary sequence and will The first b1 bits are converted to the decimal compensation value Z c .

[0100] Step 4.3: Convert b1 to decimal Z1 and then subtract Z from Z1 c . According to the difference Z1-Z c , determines the index of the active grid Every element in I satisfies the following conditions:

[0101]

[0102] in, is satisfied The largest integer, is satisfied The maximum integer of, and so on, and for a<b, it is considered

[0103] Step 4.4: Get k from b2 r From the constellation map modulation symbol.

[0104] Step 4.5: Construct the in-phase component of the sub-block by combining the obtained trellis activation pattern and modulation symbol

[0105] Step 5: Combine the in-phase component and the orthogonal component to obtain the g-th sub-block x g The vector form of

[0106]

[0107] After getting all G sub-blocks, these G sub-blocks are spliced ​​together to generate OTFS symbol blocks The subsequent process is the same as the traditional OTFS modulation transmission process, that is, the generated delay Doppler domain signal is transformed by the inverse symplectic finite Fourier transform (ISFFT), and then transformed into a time domain signal by the Heisenberg transform module, and finally input into the fast time-varying channel for transmission after parallel-to-serial conversion, adding a cyclic prefix, and digital-to-analog conversion.

[0108] Here we use an example to illustrate the above mapping method. Assume that the parameters n = 4, k1 = 1, k2 = 3, and All are 2PAM modulation {-1,1}. Assume that the information bit sequence is b = [1010101101]. Without loss of generality, we take the g-th sub-block for illustration. It can be seen that |X I |=|X Q |=40,

[0109] First, b is converted into a decimal number Z = 685. The decimal numbers representing the in-phase component information and the orthogonal component information of the sub-block are calculated as and Z Q =mod(Z,|X Q |)=mod(685,40)=5. Next, Z I =17 and Z Q =5 are converted into 6-bit binary sequences and

[0110] Then, is used for mapping the in-phase components of the sub-blocks. I =17, and the indicated parameter r=2 and the compensation value Z are obtained. c = 1. The first three bits Convert to Z1=2, according to Z1-Z c = 1 to obtain the index of the activated grid I = {1, 2, 4}. The last three bits Modulated into three 2PAM symbols The in-phase component of the sub-block is constructed as

[0111] same, is used for mapping the orthogonal components of the sub-blocks. Q =5, we get r=1 and compensation value Z c = 0. The first five bits The index used to obtain the activated grid is I={3}, the last bit Modulated to The orthogonal components of the sub-blocks are constructed as The sub-block used for transmission is

[0112] At the receiving end, after being affected by the fast time-varying channel and noise, the received time domain signal is converted to digital, the cyclic prefix is ​​removed, and the serial-to-parallel conversion is performed; then the DD domain received signal is obtained by Wigner transformation and SFFT transformation; for the DD domain received signal, an improved message passing detection algorithm is used to obtain the activation grid index and modulation symbol of the in-phase and orthogonal components, and then the detection results are demapped to restore the original information bits. The use of the improved message passing detection algorithm with lower complexity can accurately identify the activated position information and restore the original information bits. The input and output relationship of the DD domain is abbreviated as:

[0113] y=Hx+w

[0114] in, is the receiving signal, is the DD domain channel matrix, is the signal sent, is the noise vector.

[0115] The input-output relation can be rewritten in the real-valued domain as:

[0116]

[0117] In the formula, Among the MN elements in each row and column of H, only L elements are non-zero. It can be seen that there are 2L elements in each row and column of H' that are non-zero. and denote the index set of non-zero elements in the dth row and cth column of H′, respectively. The system can be modeled as a sparsely connected factor graph. In this factor graph, each observation node y′[d] is connected to a set of 2L variable nodes Similarly, each variable node x′[c] is connected to a set of 2L observation nodes

[0118] make and For the improved message passing detection algorithm, its steps in the tth iteration are described as follows:

[0119] Step 1: Distractions The mean and variance As a message from the observation node y′[d] passed to the variable node can be approximated as a Gaussian random variable, written as:

[0120]

[0121] The mean of is:

[0122]

[0123] The variance is:

[0124]

[0125] The probability of the variable node x[c] is calculated according to the following formula:

[0126]

[0127] The variable node x′[c] is passed to the observation node The actual message is the probability mass function The elements in can be calculated by the following formula:

[0128]

[0129] in,

[0130]

[0131] In order to achieve a trade-off between convergence speed and performance, a damping factor Δ∈(0,1] is introduced in the probability update to control the convergence speed to improve the performance. Δ can be obtained through Monte Carlo simulation.

[0132] Step 2: Calculate the convergence index:

[0133]

[0134] In the formula, is an indicator function whose value is 1 if the expression in brackets is true and 0 otherwise. The posterior probability of the transmitted symbol is expressed as:

[0135]

[0136] If γ (t) >γ (t-1) , the probability of transmitting symbols is updated as:

[0137]

[0138] Repeat the above steps until γ is reached. (t) = 1 or the maximum number of iterations t max .

[0139] Step 3: Once the stopping criteria are met, the log-likelihood ratio (LLR) for each grid is calculated according to the following formula:

[0140]

[0141] Then calculate the processed LLR:

[0142]

[0143] where H0(·) represents the Heaviside step function. and They are used to obtain the index positions of the in-phase component and the orthogonal component activation of the g-th sub-block. Since the process is the same, here we only show how to get Get the index position of the in-phase component activation as follows:

[0144] Sure The Hamming distance between each legal grid activation pattern and find the minimum Hamming distance d min The relevant possible legal grid activation mode set is denoted as P. Make the following judgments:

[0145] If d min =0, judge is the estimated legal grid activation pattern.

[0146] If d min >1, then The elements with the smallest LLR value in are reversed to reduce the minimum Hamming distance until d min =1.

[0147] If d min =1, find The positions in P that are different from all elements in P are found, and the elements with the smallest LLR amplitude are reversed to obtain the activated index position.

[0148] Step 4: Determine the modulation symbols on the activated grid based on the following metrics:

[0149]

[0150]

[0151] in and Represents the set of activated grids detected by the in-phase component and the orthogonal component respectively. Then, demapping is performed sub-block by sub-block, that is, the reverse process of coding mapping is implemented to restore the original information bits.

[0152] Table 2 Delay power relationship of extended vehicle A model

[0153]

[0154] Referring to Table 2, the present invention uses the extended vehicle A (EVA) model to simulate the delay-power relationship of the channel, and a simulation result shows the excellent technical effect of the E-OTFS-IM-IQ system of the present invention. In the embodiment of the present invention, the number of subcarriers of an OTFS signal is M=32, the time slot is set to N=32, the carrier frequency is set to 4GHz, and the subcarrier spacing is Δf=15kHz. The user speed is 500kmph, and the maximum path Doppler shift v max =2315Hz. The Doppler shift of the ith path is v i =v max cos(θ i ), where θ i is a uniform distribution in The parameters in the detector are set to Δ=0.4, ∈=0.01, t max =20.

[0155] The number of active grids for the in-phase and quadrature components of each sub-block of the flexible configuration delay-Doppler domain OTFS index modulation system is k1=1 and k2=3; the number of active grids for 4PAM modulation is k1=1; the number of active grids for 2PAM modulation is k2=3. The simulation results are shown in Figure 2. Figure 3 shown. Figure 3 The horizontal axis represents the signal-to-noise ratio, which is the ratio of the power of each bit of information to the noise power. The vertical axis represents the bit error rate, which is the ratio of the number of wrongly judged bits to the total number of bits. To demonstrate the advantages of this example, Figure 3 The simulation results of OTFS and OTFS index modulation (OTFS-IM) are also provided. The length of each sub-block of OTFS index modulation is 4, and each sub-block contains two active grids. Both OTFS and OTFS index modulation are modulated using 4QAM. Analysis shows that the spectral efficiency of the flexibly configured delay-Doppler domain OTFS index modulation system is 2.75 bits / s / Hz, and the spectral efficiency of the compared OTFS and OTFS index modulation is 2 bits / s / Hz. This example achieves a spectral gain of 37.5% compared to the other two systems. Moreover, at a bit error rate of 10 -3When compared with the other two systems, this example obtains gains of 4dB and 5.6dB respectively. Therefore, the present invention has better spectrum efficiency and bit error rate performance.

[0156] In summary, the present invention provides a method, system and program product for flexibly configuring delay-Doppler domain OTFS index modulation. The system includes a transmitter and a receiver including an IQ mapping module that can dynamically configure the grid activation ratio and modulation order. At the transmitter, the binary sequences of the in-phase component and the orthogonal component are mapped respectively to construct the in-phase component and the orthogonal component of the sub-block, and obtain the dynamic grid activation ratio and modulation order configuration at the sub-block level. At the receiver, an improved message passing detection algorithm is used to obtain the activated delay-Doppler domain grid position and modulation symbol. The present invention can adapt to changing channel conditions and transmission requirements through dynamic subcarrier activation and modulation order configuration; the information bit sequence is reasonably mapped into sub-blocks of in-phase and orthogonal components to ensure effective information transmission under different configurations while maintaining a low mapping complexity; the detection complexity is reduced through an improved message passing detector while maintaining good BER performance.

[0157] A person skilled in the art can understand that all or part of the steps in the flexibly configured delay-Doppler domain OTFS index modulation method of the above embodiment can be completed by instructing the relevant hardware through a program, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may include, but is not limited to, an optical disk, a CD-ROM (read-only optical disk memory), a magneto-optical disk, a ROM (read-only memory), a RAM (random access memory), an EPROM (erasable programmable read-only memory), an EEPROM (electrically erasable programmable read-only memory), a magnetic card or an optical card, a flash memory, or other types of media / machine-readable media suitable for storing machine-executable instructions. The computer-readable storage medium may be a product that is not connected to a computer device, or a component that is connected to a computer device for use.

[0158] The above describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and the devices and structures that are not described in detail should be understood to be implemented in a common manner in the art; any technician familiar with the art can use the above-disclosed methods and technical contents to make many possible changes and modifications to the technical solutions of the present invention without departing from the scope of the technical solutions of the present invention, or modify them into equivalent embodiments of equivalent changes, which does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention are still within the scope of protection of the technical solutions of the present invention.

Claims

1. A flexible configuration delay-Doppler domain OTFS index modulation method, characterized by: The system includes an IQ mapping module and a receiver that can dynamically configure the grid activation ratio and modulation order to perform: In the IQ mapping module capable of dynamically configuring the grid activation ratio and the modulation order, the input bit stream is divided into several groups by a bit splitter, and each group of bits is passed through an IQ bit segmentation module to obtain a binary sequence of an in-phase component and an orthogonal component; the binary sequences of the in-phase component and the orthogonal component are mapped respectively to construct the in-phase component and the orthogonal component of the sub-block, and the dynamic grid activation ratio and the modulation order configuration at the sub-block level are obtained; all the sub-blocks are spliced ​​together to generate an OTFS symbol block, which is transmitted to a fast time-varying channel for transmission after OTFS modulation; At the receiving end, the time domain received signal is demodulated by OTFS to obtain the received signal in the delay-Doppler domain, and the activated delay-Doppler domain grid position and modulation symbol are obtained by using an improved message passing detection algorithm.

2. The flexibly configurable delay-Doppler domain OTFS index modulation method according to claim 1, characterized in that: In the IQ mapping module that can be dynamically configured with grid activation ratio and modulation order, binary bit information first obtains binary sequences of in-phase component and orthogonal component according to preset parameter information; then the two binary sequences are respectively transmitted to the bit mapper, the indication parameters are determined, and bit segmentation is performed, and then the segmented binary sequences are respectively transmitted to the index selection module and the modulation symbol mapping module in combination with the compensation value; at the receiving end, improved message passing detection is used to detect the activation grid index and modulation symbol of the in-phase and orthogonal components, and then the original information bits are restored.

3. The flexibly configurable delay-Doppler domain OTFS index modulation method according to claim 2, characterized in that: The working process of the IQ mapping module that can be dynamically configured with a grid activation ratio and a modulation order specifically includes: dividing the transmitted binary bit information into several groups according to a bit splitter, and first obtaining a binary sequence of an in-phase component and an orthogonal component for each group of bits according to preset parameter information; then respectively transmitting the two binary sequences into a bit mapper, determining an indication parameter, performing bit segmentation, and then respectively transmitting the segmented binary sequences into an index selection module and a modulation symbol mapping module in combination with a compensation value; then respectively obtaining the in-phase and orthogonal components and then combining them into sub-blocks; after obtaining all the sub-blocks, splicing the sub-blocks together to generate an OTFS symbol block, and the generated delay Doppler domain signal is transformed by an ISFFT, and then transformed into a time domain signal by a Heisenberg transformation module, and finally input into a fast time-varying channel for transmission after parallel-to-serial conversion, adding a cyclic prefix, and digital-to-analog conversion.

4. The flexibly configurable delay-Doppler domain OTFS index modulation method according to claim 3, characterized in that: For the g-th sub-block, map the information bit sequence b of length b to sub-block x g The steps are as follows: Step 1: Convert the information bit sequence b into a decimal number Z, Z∈[0,2 b -1]; Step 2: Calculate the parameters according to the following formula: Z Q =mod(Z,|X Q |); Step 3: Place the Z I Convert to length The binary sequence And Z Q Convert to length The binary sequence Step 4: Mapping and Construct the in-phase components separately and orthogonal components Then the sub-block to be transmitted is obtained arrive and arrive The mapping process is the same as arrive The mapping process is as follows: Step 4.1: Convert to decimal Determine the indicated parameter according to the following formula: Calculate the number of sign bits Then the number of bits in the grid activation mode is b1=b-b2; the information bit sequence The first b1 bits of are denoted as b1, and the remaining b2 bits are denoted as b2; Step 4.2: If r = 1, set the compensation value Z c =0; if r≠1, Convert to length The binary sequence and will The first b1 bits are converted to the decimal compensation value Z c ; Step 4.3: Convert b1 to decimal Z1 and then subtract Z from Z1 c ; According to the difference Z1-Z c , determines the index of the active grid Every element in I satisfies the following conditions: in, is satisfied The largest integer, is satisfied The maximum integer of, and so on, and for a<b, it is considered Step 4.4: Get k from b2 r From the constellation map The modulation symbol of Step 4.5: Construct the in-phase component of the sub-block by combining the obtained trellis activation pattern and modulation symbol Step 5: Combine the in-phase component and the orthogonal component to obtain the g-th sub-block x g The vector form of is:

5. The flexibly configurable delay-Doppler domain OTFS index modulation method according to claim 3, characterized in that: The working process of the receiving end specifically includes: After being affected by the fast time-varying channel and noise, the received time domain signal is subjected to analog-to-digital conversion, cyclic prefix removal and serial-to-parallel conversion; then, the DD domain received signal is obtained through Wigner transform and SFFT transform; for the DD domain received signal, an improved message passing detection algorithm is used to obtain the activation grid index and modulation symbols of the in-phase and orthogonal components, and then the detection results are demapped to restore the original information bits.

6. The flexibly configurable delay-Doppler domain OTFS index modulation method according to claim 5, characterized in that: The steps of the improved message passing detection algorithm in the tth iteration are described as follows: Step 1: Distractions The mean and variance As a message from the observation node y′[d] passed to the variable node can be approximated as a Gaussian random variable, written as: The mean of is: The variance is: The probability of the variable node x[c] is calculated according to the following formula: The variable node x′[c] is passed to the observation node The actual message is the probability mass function The elements in can be calculated by the following formula: in: A damping factor Δ∈(0,1] is introduced in the probability update to control the convergence speed to improve the performance; Δ can be obtained through Monte Carlo simulation; Step 2: Calculate the convergence index: In the formula, is an indicator function whose value is 1 if the expression in the brackets is true, otherwise it is 0; the posterior probability of the transmitted symbol is expressed as: If γ (t) >γ (t-1) , the probability of transmitting symbols is updated as: Repeat the above steps until γ is reached. (t) = 1 or the maximum number of iterations t max . Step 3: Once the stopping criteria are met, the log-likelihood ratio (LLR) of each grid is calculated according to the following formula: Then calculate the processed LLR: Where H0(·) represents the Heaviside step function; and They are used to obtain the index positions of the in-phase component and the orthogonal component activation of the g-th sub-block respectively; similar to the index position of obtaining the orthogonal component activation, from The process of obtaining the index position of the in-phase component activation is as follows: Sure The Hamming distance between each legal grid activation pattern and find the minimum Hamming distance d min The relevant possible legal grid activation mode set is denoted as P; make the following judgments: If d min =0, judge Activate the pattern for the estimated legal grid; If d min >1, then The elements with the smallest LLR value in are reversed to reduce the minimum Hamming distance until d min =1; If d min =1, find The positions in P that are different from all the elements in P are found, and the elements with the smallest LLR amplitude are reversed to obtain the activated index position; Step 4: Determine the modulation symbols on the activated grid based on the following metrics: in and Represents the set of activated grids detected by the in-phase component and the orthogonal component respectively; then demaps each sub-block one by one, that is, implements the reverse process of coding mapping to restore the original information bits.

7. Flexible configuration of delay-Doppler domain OTFS index modulation system, characterized by: It comprises a transmitting end and a receiving end as described in any one of claims 1 to 6, wherein the transmitting end comprises an IQ mapping module capable of dynamically configuring a grid activation ratio and a modulation order, and is used to execute the flexibly configurable delay-Doppler domain OTFS index modulation method as described in any one of claims 1 to 6.

8. A computer program product, characterized in that When the computer program product is run on a computer, the computer is enabled to execute the flexibly configurable delay-Doppler domain OTFS index modulation method according to any one of claims 1 to 6.

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