Incoherent index modulation method and system based on fluid antenna

Abstract

The invention discloses an incoherent index modulation method and system based on a fluid antenna, and belongs to the field of wireless communication. A plurality of fluid antenna transmitting modes are preset for a fluid antenna wireless communication system, and a beam forming vector corresponding to each transmitting mode is optimized by using a closed expression of a fluid antenna space coding gain, so that a transmitter can transmit a phase shift keying modulation symbol while transmitting the phase shift keying modulation symbol; spatial bit information can be implicitly transmitted through a cyclic shift value of a fluid antenna emission mode index value, and the whole communication process does not need to depend on channel state information, so that the multiple-input-multiple-output communication method for fluid antenna energization without channel estimation is realized.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and particularly to a non - coherent index modulation method and system based on a fluid antenna. Background Art

[0002] With the rapid development of wireless communication technologies, multiple - input multiple - output (MIMO) technologies have emerged. By utilizing the spatial degrees of freedom provided by multiple antennas, the channel capacity and spectral efficiency have been significantly improved. In recent years, new electromagnetic devices such as radio frequency lenses and reconfigurable intelligent surfaces (RIS) have been introduced, further enhancing the performance of MIMO systems. However, these technologies mostly rely on fixed - position antennas and lack the ability to be flexibly adjusted after deployment, resulting in limited effects in dynamic environments.

[0003] The emergence of fluid antenna (FA) technology has brought new breakthroughs to wireless communication. FAs use the movement of liquids or gases to dynamically adjust the antenna position, providing spatial degrees of freedom for MIMO systems without additional radio frequency links, and having advantages such as software controllability, structural reconfigurability, and hardware miniaturization. It performs well in improving the signal - to - interference - plus - noise ratio, supporting more user capacity, reducing the probability of network interruption, etc., and can also adapt to emerging application scenarios such as integrated sensing and communication, simultaneous wireless information and power transfer, and secure communication.

[0004] Index modulation (IM), as an important means to improve the spectral efficiency of MIMO systems, transmits additional information by using the index of communication resources, achieving high spectral efficiency and high energy efficiency while maintaining low hardware complexity. Early IM forms such as spatial modulation (SM) avoid inter - carrier interference (ICI) and multi - antenna synchronization problems by activating a single antenna, while FA - IM schemes transmit information by leveraging the mobility of FAs. Nevertheless, existing coherent modulation schemes mostly rely on channel state information (CSI), and non - coherent modulation schemes such as differential spatial modulation still have deficiencies in spatial - time resource utilization and decoding complexity, and there is no non - coherent modulation scheme for FA systems yet.

[0005] In FA - MIMO systems, the pilot overhead for channel estimation is large, and inaccurate CSI will significantly reduce the detection performance. To address these challenges, there is an urgent need for a non - coherent modulation scheme that does not rely on CSI and is suitable for FA systems to fully utilize the additional degrees of freedom provided by FAs, achieve higher diversity and multiplexing gains, while reducing the decoding complexity and improving the overall system performance. Summary of the Invention

[0006] The present invention provides a non - coherent index modulation method and system based on a fluid antenna. Aiming at the limitation that it is difficult to obtain the channel state information of FA - MIMO mentioned in the background technology, as well as the urgent need and requirements for a new non - coherent index modulation method, the present invention optimizes the beamforming vector corresponding to each transmission mode by using the closed - form expression of the spatial coding gain of the fluid antenna, implicitly transmits additional spatial bit information through the cyclic shift value of the transmission mode index value of the fluid antenna, and the entire communication process does not rely on the channel state information.

[0007] The first - aspect embodiment of the present invention provides a non - coherent index modulation method based on a fluid antenna, including the following steps:

[0008] Step 1: Deploy a fluid antenna and a traditional fixed - type antenna at the transmitter and the receiver respectively;

[0009] Step 2: Preset and optimize K transmission modes of the communication system, and assign a corresponding weight vector to each transmission mode;

[0010] Step 3: Construct information mapping and modulation, and use the shift selection of PSK modulation symbols and FA weight vectors to transmit communication information;

[0011] Step 4: Perform non - coherent modulation on the baseband signal at the transmitter to achieve signal transmission;

[0012] Step 5: At the receiver, use the maximum - likelihood detection algorithm and the multi - stage decoding algorithm to decode the signal and recover the original binary bit information.

[0013] Optionally, in an embodiment of the present invention, Step 1 specifically includes:

[0014] Configure a two - dimensional fluid antenna wide - mouth array with P t =P x ×P y units of two - dimensional rectangular plane, where P x , P y are the number of antenna elements in each row and each column of the two - dimensional rectangular plane array of the fluid antenna respectively. The element intervals on the x - axis and y - axis are and meters respectively, and place it at the base station as a downlink communication transmitter. N t radio - frequency liquid metals can instantaneously move to any N t of the P t positions to complete the rapid reconstruction of the fluid - state antenna;

[0015] Configure a two - dimensional fixed - arrangement antenna array with N r =N x ×N y units of two - dimensional rectangular plane, where N x , Ny are the number of antenna elements in each row and each column of the two-dimensional rectangular plane array of the fixed antenna of the receiver, and the element intervals on the x and y axes are respectively and meters, and are placed at the user as a downlink communication receiver;

[0016] Establish a fluid antenna channel model as an N r ×P t -dimensional equivalent channel H eff .

[0017] Optionally, in an embodiment of the present invention, step 2 specifically includes:

[0018] Configure a corresponding weight vector u for each transmission mode i , 1 ≤ i ≤ K, u i satisfies the constant power constraint of and ||u i ||0 ≤ N t the maximum sparsity constraint condition, and represent the weight vector set in matrix form U = [u1, u2,..., u K , and optimize the coding gain when transmitting M-ary phase shift keying (M-PSK) symbols c p ;

[0019] Let p and q represent the index values for selecting M-PSK symbols, and i and j represent the index values of the weight vectors. When the combination (p, i) ≠ (q, j), c p u i and c q u j The closed-form expression of the coding gain is c q is the qth symbol in the M-PSK symbol set. Traverse all combinations (p, i) ≠ (q, j) to obtain the minimum value of the coding gain of U:

[0020]

[0021] where r represents the rank of the difference matrix after the operation of (c p u i -c q u j )(c p u i -c q u j ), and λ H is (c i u p -c i u q u j )(c p ui -c q u j ) H Eigenvalue of the matrix;

[0022] Traverse all combinations and use the gradient descent method to calculate the gradient and then maximize f(U), u i Real part of and imaginary part Gradient of the gradient and are calculated respectively as:

[0023]

[0024] where, ∈ represents the gradient direction increment;

[0025] Record the historical optimal coding gain and update the historical optimal value in real time:

[0026]

[0027] where, β is the learning rate of gradient descent;

[0028] Perform gradient descent operations to continuously update all weight vectors:

[0029]

[0030] During the process of optimal design, when the increment of the coding gain is lower than t f , t f is the perturbation start threshold, introduce perturbation, randomly reconfigure the position of a non-zero element in u i and perform a random phase shift of angle ξ, that is, multiply by e jξ After the weight vector is optimized, deploy the weights to the hardware side of the fluid antenna to perform phase modulation and amplitude modulation when the antenna transmits electromagnetic wireless baseband signals.

[0031] Optionally, in an embodiment of the present invention, step 3 specifically includes:

[0032] Divide the signal frame with length W into K reference signal time slots and W - K information signal time slots;

[0033] Divide the B = B1 + B2 - bit binary information bit vector b to be transmitted into two parts, namely b1 and b2, where the dimension of b1 is B1 = log2(K), and the dimension of b2 is B2 = log2(M);

[0034] Use b1 to map to the k cs,w cyclic shift FA mode index, and its conversion relationship is In the w-th codeword time slot, according to k w = [kw-1 +k cs,w K Select the corresponding FA mode index and use the vector u4 to control the positions and weights of the FAs;

[0035] Map b2 to a symbol in the M-ary PSK (M-PSK) constellation set where represents the M-PSK symbol index of the corresponding information bit in the w-th codeword time slot; differential modulation of the M-PSK symbol is achieved by multiplying consecutive symbols, i.e., and when w ≤ K, the initial condition is c0 = 1;

[0036] Model the cyclic shift operation process of the FA mode and the differential operation process of M-PSK in the form of vectors and matrices. The non-zero positions and values on each row respectively represent the selection of the fluid antenna transmission mode and the selection of the communication modulation symbol.

[0037] Optionally, in an embodiment of the present invention, step 4 specifically includes:

[0038] The information vector x in the w-th codeword time slot w is mapped from B = B1 + B2 bits of information bits, and the specific form is:

[0039]

[0040] where the sparse information vector x w the positions and values of the only non-zero elements are respectively mapped from b1 and b2;

[0041] The mode selection vector s in the current codeword time slot w is obtained by the following method:

[0042]

[0043] where C s (·) is a shift expansion function, according to k w =[k w-1 +k cs,w K the modulo K operation, realizes the cyclic shift of the non-zero element indexes in the vector, and its definition is:

[0044] C s (s w-1 )=[s w-1 ,Cs w-1 ,C 2 s w-1 ,...,C K-1 s w-1

[0045] ​​​The shift matrix E is used to perform circular shifts of vectors, and its specific form is:

[0046]

[0047] The differential modulation iteration process of fluid antenna non - coherent index modulation is expressed as:

[0048]

[0049] where y w represents the baseband signal after sampling the received signal.

[0050] Optionally, in an embodiment of the present invention, step 5 specifically includes:

[0051] At the receiving end, a maximum - likelihood detection algorithm and a low - complexity multi - stage algorithm are used for decoding;

[0052] The maximum - likelihood decoding process includes:

[0053] According to the probability density function of the received signal y w construct a conditional probability density function, and construct

[0054] Obtain the information vector of FA - NIM through maximum - likelihood detection:

[0055]

[0056] where, when w - 1 ≤ K, when w - 1 > K, V (1-α) and V (α) are the weight matrices of the direct differential demodulation term and the continuous decoding demodulation term respectively, and α is the forgetting factor;

[0057] The multi - stage decoding process includes:

[0058] Utilize the sparsity of the sparse matrix x w designed by the FA - NIM system and adopt a low - complexity multi - stage decoding algorithm;

[0059] In the first stage, compress the search space by calculating the vector to

[0060] In the second stage, detect the indices and modulation symbols of the non - zero elements in the sparse matrix x w .

[0061] An embodiment of the second aspect of the present invention provides a non - coherent index modulation system based on a fluid antenna for the non - coherent index modulation method based on a fluid antenna described in the above - mentioned embodiment, including:

[0062] A fluid antenna configuration module for configuring a two-dimensional fluid antenna wide-port array and a two-dimensional fixed-array antenna array, and establishing a fluid antenna channel model;

[0063] A weight vector optimization module for presetting and optimizing the transmission mode of a communication system, and assigning corresponding weight vectors to each transmission mode;

[0064] An information mapping and modulation module for splitting information bits and mapping them to corresponding signal patterns and symbols to achieve signal modulation and transmission;

[0065] A signal transmission and reception module for generating a transmission signal according to the mapped information vector and receiving the signal at the receiving end;

[0066] A decoding module for decoding the signal at the receiving end using a maximum likelihood detection algorithm and a multi-stage decoding algorithm to recover the original information bits.

[0067] Optionally, in an embodiment of the present invention, the weight vector optimization module optimizes the weight vector set through a gradient descent method and a perturbation introduction strategy.

[0068] Optionally, in an embodiment of the present invention, the information mapping and modulation module splits the information bits into two parts, which are respectively used to map the cyclic shift FA mode index and the M-PSK symbol index.

[0069] Optionally, in an embodiment of the present invention, the decoding module uses the sparsity and differential characteristics of the signal and adopts a multi-stage decoding algorithm for decoding.

[0070] The non-coherent index modulation method and system based on a fluid antenna according to the embodiments of the present invention can achieve high spectral efficiency information transmission of a fluid antenna-enabled multiple-input multiple-output wireless communication system without channel estimation, quickly optimize and configure the antenna weight vectors of the fluid antenna in each transmission mode, and implicitly transmit information through the shift amount of the index values of the weight vectors in the front and back communication codeword time slots, and can achieve better bit error rate performance in a time-varying channel compared with the existing solutions.

[0071] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0072] The above and / or additional aspects and advantages of the present invention will become apparent and be easily understood from the following description of the embodiments in conjunction with the drawings, where:

[0073] Figure 1Flow chart of a non - coherent index modulation method based on a fluid antenna according to an embodiment of the present invention;

[0074] Figure 2 Schematic diagram of a two - dimensional antenna array of a transmitter fluid antenna and a receiver fixed antenna;

[0075] Figure 3 Block diagram of a non - coherent index modulation FA - NIM communication system based on a fluid antenna proposed by the present invention;

[0076] Figure 4 BER performance results of non - coherent index modulation based on a fluid antenna proposed by the present invention in Example 2 at a spectral efficiency of 6 bpcu;

[0077] Figure 5 BER performance results of non - coherent index modulation based on a fluid antenna proposed by the present invention in Example 2 at a spectral efficiency of 8 bpcu;

[0078] Figure 6 BER performance results of non - coherent index modulation based on a fluid antenna proposed by the present invention in Example 3 under time - varying channels;

[0079] Figure 7 Schematic block diagram of a non - coherent index modulation system based on a fluid antenna according to an embodiment of the present invention. Detailed implementation manners

[0080] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described by referring to the drawings below are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0081] Figure 1 Flow chart of a non - coherent index modulation method based on a fluid antenna according to an embodiment of the present invention.

[0082] As Figure 1 shown, the non - coherent index modulation method based on a fluid antenna includes the following steps:

[0083] Step 1, deploy a fluid antenna and a traditional fixed antenna at the transmitter and the receiver respectively.

[0084] Configure a two - dimensional fluid antenna wide - mouth array as Figure 2 shown to be a two - dimensional rectangular plane with P t = P x × P y cells, and the element intervals on the x - axis and y - axis are respectively and meters and placed at the base station as a downlink communication transmitter, N t radio frequency liquid metals can instantaneously move to any of the P t ports to complete the rapid reconfiguration of the fluid antenna; configure a two-dimensional fixed array antenna array with N t as an N r = N x ×N y two-dimensional rectangular plane of cells, with cell spacings on the x and y axes being and meters respectively, and placed at the user as a downlink communication receiver, and establish a fluid antenna channel model as an N r ×P t dimensional equivalent channel H eff .

[0085] Specifically, the method for establishing the fluid antenna channel model is as follows:

[0086] Let and represent the azimuth angle and elevation angle in the l t th scattering path in the environment pointed by the transmitter. The steering vector of the port array of the fluid antenna pointed to the azimuth angle can be expressed as:

[0087]

[0088] where and represent the steering vector components of the fluid antenna array on the x and y axes respectively, and are both obtained in the form of a linear uniform array:

[0089]

[0090] where represents the projection of the antenna spacing in the direction, and λ represents the carrier wavelength. The number of multipaths at the transmitting end of the communication channel is L t , corresponding to the angle of departure The transmitting end channel of the fluid antenna empowered MIMO channel model in the present invention is represented as:

[0091]

[0092] The channel modeling of the receiver fixed antenna array is similar to the design of the transmitter. The receiver array receives signals from L r paths simultaneously. When receiving signals from the l r direction, the response vector of the array is where and are from is obtained from the linear array expression of the form. The corresponding angle of arrival The receiving - end channel representation of the fluid - antenna - empowered MIMO channel model in the present invention is expressed as:

[0093]

[0094] The path response between the transmitter and the receiver is expressed as where the complex value of the \(l\) - th r row and \(l\) - th t column of this matrix represents the communication fading when the information is transmitted through the \(l\) - th t transmitting path to the \(l\) - th r receiving path. The equivalent model of the communication channel established in the present invention is expressed as:

[0095] H eff,w = G H ΩF.

[0096] Step 2: Preset and optimize \(K\) transmission modes of the communication system, and assign a corresponding weight vector to each transmission mode.

[0097] Preset and optimize \(K\) transmission modes of the communication system, and respectively configure a corresponding weight vector \(\mathbf{u}\) i , \(1\leq i\leq K\). \(\mathbf{u}\) i satisfies the constant - power constraint and \(\|\mathbf{u}\) i \|_0\leq N t the maximum - sparsity constraint. Under the condition that the weight - vector set is represented in matrix form \(U = [\mathbf{u}_1,\mathbf{u}_2,\cdots,\mathbf{u}\) K , further optimize the coding gain when transmitting the \(M\) - ary phase - shift keying (M - PSK) symbol \(\mathbf{c}\) p . Let \(p,q\) represent the index values for selecting the M - PSK symbol, and \(i,j\) represent the index values of the weight vectors. When the combination \((p,i)\neq(q,j)\), calculate the coding gain of \(\mathbf{c}\) p \(\mathbf{u}\) i and \(\mathbf{c}\) q \(\mathbf{u}\) j as Traverse all combinations \((p,i)\neq(q,j)\) and calculate the minimum value of the coding gain of \(U\):

[0098]

[0099] where \(r\) represents \((\mathbf{c}\) p \(\mathbf{u}\) i -\mathbf{c}\) q \(\mathbf{u}\) j )(\mathbf{c}\) p \(\mathbf{u}\) i -\mathbf{c}\) q \(\mathbf{u}\)j ) H The rank of the difference matrix after operation, λ i is the eigenvalue of the corresponding matrix. Traverse all combinations to find the gradient calculated using the gradient descent method and maximize f(U), where u i is the real part of and the imaginary part of the gradient and are calculated respectively as:

[0100]

[0101] where represents a very small gradient direction increment. Record the historical optimal coding gain and update the historical optimal value in real time:

[0102]

[0103] Perform gradient descent operations to continuously update all weight vectors:

[0104]

[0105] During the optimization design process, when the increment of the coding gain is lower than t f , introduce perturbations, that is, randomly reconfigure the position of a non-zero element in u i and perform a random phase shift with an angle of ξ, that is, multiply by e jξ . After the weight vector is optimized, deploy the weight value to the hardware end of the fluid antenna to perform phase modulation and amplitude modulation when the antenna transmits the electromagnetic wireless baseband signal.

[0106] It can be understood that during the optimization process of the weight vector set U, when the increment of the coding gain is lower than the preset perturbation start threshold t f , introduce perturbations to avoid local optima, randomly reconfigure the position of a non-zero element in the weight vector and perform a random phase shift with an angle of ξ.

[0107] Step 3, construct information mapping and modulation, and use the PSK modulation symbol and the shift of the FA weight vector to select the transmitted communication information.

[0108] Divide the signal frame with length W into K reference signal time slots and W - K information signal time slots.

[0109] Divide the B = B1 + B2-bit binary (0 or 1) information bit vector b to be transmitted into two parts, namely b1 (dimension B1 = log2(K)) and b2 (dimension B2 = log2(M)).

[0110] Use b1 to map to the k cs,w cyclic shift FA mode index, and its conversion relationship is In the w-th codeword time slot, according to k w =[k w-1 +k cs,w K select the corresponding FA mode index, and use the vector u4 to control the positions and weights of the FAs.

[0111] Map b2 to the symbols in the M-ary PSK (M-PSK) constellation set where represents the M-PSK symbol index of the corresponding information bit in the w-th codeword time slot; differential modulation of the M-PSK symbol is achieved by multiplying consecutive symbols, i.e., and when w ≤ K, the initial condition is c0 = 1. Model the cyclic shift operation process of the FA mode and the differential operation process of the M-PSK in matrix form for convenient mathematical calculation and analysis. The non-zero positions and values on each row represent the selection of the fluid antenna emission mode and the selection of the communication modulation symbol, respectively.

[0112] Step 4, perform non-coherent modulation on the baseband signal at the transmitter to achieve signal transmission.

[0113] The information vector x in the w-th codeword time slot

[0114] is mapped from B = B1 + B2 bits of information bits, and the specific form is: w where the positions and values of the only non-zero elements in the sparse information vector x

[0115]

[0116] are mapped from b1 and b2 respectively. w The mode selection vector s in the current codeword time slot

[0117] is obtained through the following method: w where C

[0118]

[0119] where C s (·) is the shift extension function, and according to the modulo-K operation of k w =[k w-1 +k cs,w K the cyclic shift of the non-zero element indices in the vector is realized, and its definition is:

[0120] C s (s w-1 )=[s w-1 ,Cs w-1 ,C 2 s w-1 ​​,...,C K-1 s w-1

[0121] The shift matrix E is used to perform circular shifts of vectors, and its specific form is:

[0122]

[0123] The differential modulation iteration process of fluid antenna non - coherent index modulation is expressed as:

[0124]

[0125] where y w represents the baseband signal after sampling the received signal. When w ≤ K, s w does not carry bit information.

[0126] In the mapping process of the information vector x w , when w ≤ K, x w is used as a reference vector and does not carry information bits; when w > K, x w carries information bits and realizes signal transmission through circular shift and differential modulation.

[0127] Step 5: At the receiving end, use the maximum likelihood detection algorithm and the multi - stage decoding algorithm to decode the signal and recover the original binary bit information.

[0128] At the receiving end, use the maximum likelihood (ML) detection algorithm and the low - complexity multi - stage (MS) algorithm for decoding.

[0129] The maximum likelihood decoding process includes:

[0130] According to the probability density function (PDF) of the received signal y w , construct the conditional probability density function, construct

[0131] Obtain the information vector of FA - NIM through the ML detector:

[0132]

[0133] where, when w - 1 ≤ K, when w - 1 > K, V (1-α) and V (α) are the weight matrices of the direct differential demodulation term and the successive decoding demodulation term respectively, and α is the forgetting factor.

[0134] The multi - stage decoding process includes:

[0135] Utilize the information vector x w ​The sparsity of ,a low-complexity MS decoding algorithm is adopted;

[0136] In the first stage, by calculating the vector (in Yes The matrix obtained by normalizing the columns of

[0137] In the second stage, x is detected w The indices of the non-zero elements in and the modulation symbols.

[0138] The multi-stage decoding algorithm in the decoding process utilizes the sparsity of the information vector and reduces the decoding complexity by detecting the index and modulation symbol of non-zero elements in stages.

[0139] like Figure 3 As shown, a block diagram of the FA-NIM communication system based on fluid antenna non-coherent index modulation is shown.

[0140] The non-coherent index modulation method based on fluid antenna of the present invention is described in detail below through specific embodiments.

[0141] Example 1: An example of information mapping in step 3 is: in the wth codeword time slot, FA-NIM selects the kth codeword time slot according to the index value of the previous codeword time slot. w The fluid antenna transmission mode, whose index value relationship is k w =[k w-1 +k cs,w ] K For example, when K=8, the index value k of the previous codeword time slot is w-1 =7, and b1=[1,0,1] T When k cs,w =5, and then calculate the index value k of the current codeword time slot w =[7+5]8=4. At this time, the fourth mode is switched to, and the position and weight of the fluid antenna are controlled by using the vector u4.

[0142] Example 2: Communication scenario parameters follow the FA-IM technique, where large-scale fading is determined by Given, ρ0 = -30dB is the path loss per unit radial distance, d = 25m is the transmit and receive distance, is the path loss index. The carrier frequency is 2.8 GHz, and the wavelength is λ = 0.01 m. The size of the FA port array at the transmitting end is 10λ × 10λ, and the spacing of the FPA array elements at the receiving end is d = 0.5λ.

[0143] Figure 4 and Figure 5It respectively shows the comparison of the bit error rate (BER) performance between the proposed FA-NIM method of the present invention and other existing index modulation methods under quasi-static channel conditions when the communication spectral efficiency is 6 bits per channel use (bpcu) and 8 bpcu. The key comparison factors are whether to rely on channel state information (CSI) and the deployment of fluid antennas FA. Specifically, FA-NIM and RDSM support non-coherent modulation without channel state information, while FA-NIM, FAIM, and FA-PIM adopt FA technology, in contrast to the SM and RDSM methods using fixed-position antennas (FPA).

[0144] In Figure 4 , compared with the RDSM scheme that also adopts non-coherent modulation, the performance gain of FA-NIM reaches 9 dB. Among the antenna selection strategies that do not rely on CSI, when the BER is 10 -4 , FA-NIM only loses 2.1 dB compared with the best coherent modulation multi-antenna FA-IM scheme. This is mainly due to the optimized design of the FA mode vector set and the introduction of the forgetting factor, which reduces the noise interference in differential demodulation and makes the equivalent noise variance lower than and controls the error propagation effect within 3 dB. The 3-dB performance loss is a common performance loss of differential modulation technology compared with coherent modulation technology. Compared with the FA-PIM and single-antenna FA-IM schemes, FA-NIM only loses 1.4 dB and 0.2 dB respectively, and at the same time has a 2-dB performance gain compared with the SM scheme. Compared with the FA position design scheme based on CSI, the BER performance of FA-NIM is slightly inferior but still remains within 3 dB.

[0145] Figure 5 It shows the comparison of the BER performance between FA-NIM and other similar IM schemes when the spectral efficiency is 8 bpcu. The results show that FA-NIM only loses 2.7 dB compared with the multi-antenna FA-IM scheme, while it has a 1.2-dB and 1.6-dB performance gain compared with the FA-PIM and single-antenna FAIM schemes respectively. Compared with the SM scheme optimized based on the CSI port position, FA-NIM even has a 0.9-dB performance gain. For the SM and RDSM schemes based on FPA, the performance advantage of FA-NIM is more significant. The simulation results show that as the number of FAs increases, FA-NIM can make full use of the additional degrees of freedom provided by FAs to achieve high-efficiency spatial diversity and multiplexing gain.

[0146] Example 3:

[0147] Communication transmission is carried out under the same communication system configuration parameters as in Example 2. When communication transmission is carried out in a time-varying channel, it can be considered that the transmission angle of the communication path changes slightly within a very small communication time slot, that is:

[0148]

[0149] Among them, represents the angle at the w-th codeword time slot of the l-th transmission path. t The (a) of Figure 6 and Figure 6 (b) of Figure 4 and Figure 5 show the BER performance under time-varying channel conditions, corresponding to Figure 6 and -4 . The CSI of the coherent modulation scheme is updated periodically with a period of W = 400. To be consistent with the CSI update period of the coherent modulation scheme, the frame length of the FA-NIM scheme is set to W. In -4 (a) of -4 , the error floor of FA-NIM is lower than 10 Figure 6 (b) of Figure 6 The simulation results of show that the proposed FA-NIM method of the present invention has significant resistance to fast channel changes. FA-NIM does not rely on CSI for FA position selection and introduces a forgetting factor in demodulation to prevent the accumulation of CSI update errors in the communication decoding register

[0150] Next, a non-coherent index modulation system based on a fluid antenna proposed according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0151] Figure 7 is a block diagram of a non-coherent index modulation system based on a fluid antenna according to an embodiment of the present invention.

[0152] As Figure 7 shown, the non-coherent index modulation system 10 based on a fluid antenna includes:

[0153] The fluid antenna configuration module 100 is used to configure a two-dimensional fluid antenna wide aperture array and a two-dimensional fixed arrangement antenna array, and establish a fluid antenna channel model; the weight vector optimization module 200 is used to preset and optimize the transmission mode of the communication system, and assign corresponding weight vectors to each transmission mode; the information mapping and modulation module 300 is used to split and map information bits to corresponding signal patterns and symbols to realize signal modulation and transmission; the signal transmission and reception module 400 is used to generate a transmission signal according to the mapped information vector and receive the signal at the receiving end; the decoding module 500 is used to perform signal decoding at the receiving end using the maximum likelihood detection algorithm and the multi-stage decoding algorithm to recover the original information bits.

[0154] In an embodiment of the present invention, the weight vector optimization module 200 optimizes the weight vector set through the gradient descent method and the perturbation introduction strategy to improve the coding gain and performance of the system.

[0155] In an embodiment of the present invention, the information mapping and modulation module 300 splits the information bits into two parts, which are respectively used to map the cyclic shift of the FA mode index and the M-PSK symbol index to realize efficient modulation of the signal.

[0156] In an embodiment of the present invention, the decoding module 500 uses the sparsity and differential characteristics of the signal and adopts a multi-stage decoding algorithm for decoding to improve the decoding efficiency and accuracy.

[0157] It should be noted that the foregoing explanation of the embodiment of the non-coherent index modulation method based on the fluid antenna also applies to the non-coherent index modulation system based on the fluid antenna of this embodiment, and will not be repeated here.

[0158] According to the non-coherent index modulation method and system based on the fluid antenna proposed in the embodiment of the present invention, by presetting multiple transmission modes of the fluid antenna for the fluid antenna wireless communication system, using the closed-form expression of the spatial coding gain of the fluid antenna to optimize the beamforming vector corresponding to each transmission mode, the transmitter can implicitly transmit spatial bit information through the cyclic shift value of the fluid antenna transmission mode index value while transmitting phase shift keying modulation symbols, and the entire communication process does not need to rely on channel state information, thus realizing a multi-input multi-output communication method empowered by a fluid antenna without channel estimation. This method can realize high spectral efficiency information transmission of a fluid antenna empowered multi-input multi-output wireless communication system without channel estimation, quickly optimize and configure the antenna weight vector of the fluid antenna in each transmission mode, and implicitly transmit information through the shift amount of the index value of the weight vector in the front and back two communication codeword time slots, and can achieve better bit error rate performance than the existing scheme in a time-varying channel.

[0159] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0160] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0161] Any process or method description depicted in a flowchart or otherwise described herein may be understood to represent a module, segment, or portion of code including one or N executable instructions for implementing a customized logic function or process, and the scope of the preferred embodiments of the present invention includes additional implementations, where the functions may be performed in a substantially simultaneous manner or in a reverse order according to the functions involved, rather than in the order shown or discussed, which should be understood by those skilled in the art to which the embodiments of the present invention pertain.

Claims

1. A non-coherent index modulation method based on a fluid antenna, characterized in that: The following steps are involved: Step 1: deploy a fluid antenna and a traditional fixed antenna at the transmitting end and the receiving end respectively; Step 2, presetting and optimizing K transmission modes of the communication system, and assigning a corresponding weight vector to each transmission mode; Step 3, construct information mapping and modulation, and use the shift of PSK modulation symbols and FA weight vectors to select and transmit communication information; Step 4: Perform non-coherent modulation of the baseband signal at the transmitting end to achieve signal transmission; Step 5: At the receiving end, a maximum likelihood detection algorithm and a multi-stage decoding algorithm are used to decode the signal and restore the original binary bit information.

2. The method according to claim 1, characterized in that: Step 1 specifically includes: Configure the two-dimensional fluid antenna wide-mouth array as P t =P x ×P y The two-dimensional rectangular plane of units, P x , P y are the number of antenna elements per row and per column of the two-dimensional rectangular planar array of fluid antennas, and the unit spacing on the x and y axes is and meters and placed at the base station as a downlink communication transmitter, N t The radio frequency liquid metal can be moved instantly to P t Any N of the ports t Positions are used to quickly reconfigure the flow antenna; Configure a two-dimensional fixed-arrangement antenna array as N r =N x ×N y A two-dimensional rectangular plane with N units, x , N y are the number of antenna elements in each row and column of the two-dimensional rectangular planar array of the receiver fixed antenna, and the unit spacing in the x and y axes is and meters and placed at the user's location as a downlink communication receiver; Establish the fluid antenna channel model as N r ×P t The equivalent channel H of dimension eff .

3. The method according to claim 2, characterized in that Step 2 specifically includes: Configure the corresponding weight vector u for each transmission mode i , 1≤i≤K,u i satisfy The constant power constraint and ||u i ||0≤N t The condition of the maximum sparsity constraint is expressed in the form of a matrix U = [u1,u2,...,u K ] represents a weight vector set, and the optimized weight vector is used to transmit the M-order phase shift keying (M-PSK) symbol c p The coding gain when Let p, q represent the index values ​​of the selected M-PSK symbols, i, j represent the index values ​​of the weight vector, when the combination (p, i) ≠ (q, j), c p u i With c q u j The closed-form expression for the coding gain is c q For the qth symbol in the M-PSK symbol set, traverse all combinations (p,i)≠(q,j) to obtain the minimum value of the U coding gain: Where r represents (c p u i -c q u j )(c p u i -c q u j ) H The rank of the difference matrix after the operation, λ i for (c p u i -c q u j )(c p u i -c q u j ) H Eigenvalues ​​of a matrix; Traverse all combinations and use the gradient descent method to calculate the gradient to maximize f(U), u i The real part of and the imaginary part Gradient of gradient and They are calculated as: Among them, ∈ represents the gradient direction increment; Record the historical optimal coding gain and update the historical optimal value in real time: Among them, β is the learning rate of gradient descent; Perform a gradient descent operation to continuously update all weight vectors: During the optimization process, when the increase in coding gain is lower than t f , t f is the disturbance start threshold, introduces disturbance, and randomly reconfigures u i The position of a non-zero element in and a random phase shift of angle ξ is multiplied by e jξ ,After the weight vector is optimized, the weight is deployed to the hardware end of the ,fluid antenna, so that the antenna performs phase and amplitude modulation when ,sending electromagnetic wireless baseband signals.

4. The method according to claim 1, characterized in that: Step 3 specifically includes: Divide a signal frame of length W into K reference signal time slots and WK information signal time slots; The binary information bit vector b of B = B1 + B2 bits to be transmitted is divided into two parts, namely b1 and b2, where the dimension of b1 is B1 = log2(K) and the dimension of b2 is B2 = log2(M); Use b1 to map to k cs,w The conversion relationship of the cyclic shift FA mode index is In the wth codeword time slot, according to k w =[k w-1 +k cs,w ] K Select the corresponding FA mode index and use vector u4 to control the position and weight of FAs; Map b2 to the M-ary PSK (M-PSK) constellation set The symbol c in mw ,in represents the M-PSK symbol index of the corresponding information bit in the wth codeword time slot; differential modulation of the M-PSK symbol is achieved by multiplying consecutive symbols, that is, And when w≤K, the initial condition is c0=1; The cyclic shift operation process of the FA mode and the differential operation process of M-PSK are modeled in the form of vectors and matrices, and the non-zero position and value on each row represent the selection of the fluid antenna transmission mode and the selection of the communication modulation symbol, respectively.

5. The method according to claim 4, characterized in that Step 4 specifically includes: The information vector x of the wth codeword time slot w It is obtained by mapping B=B1+B2 information bits, and the specific form is: Among them, the sparse information vector x w The position and value of the only non-zero element in are mapped by b1 and b2 respectively; The mode selection vector s of the current codeword time slot w Obtained through: Among them, C s (·) is the shift expansion function, according to k w =[k w-1 +k cs,w ] K The modulo K operation realizes the circular shift of the non-zero element index in the vector, which is defined as: C s (s w-1 )=[s w-1 ,Cs w-1 ,C 2 s w-1 ,...,C K-1 s w-1 ] The shift matrix E is used to perform circular shift of the vector, and its specific form is: The differential modulation iterative process of the fluid antenna incoherent index modulation is expressed as: Among them, y w Represents the baseband signal of the received signal after sampling.

6. The method according to claim 1, characterized in that Step 5 specifically includes: At the receiving end, the maximum likelihood detection algorithm and the low-complexity multi-stage algorithm are used for decoding; The maximum likelihood decoding process includes: According to the received signal y w The probability density function of , construct the conditional probability density function, construct Obtain the information vector of FA-NIM through maximum likelihood detection: Among them, when w-1≤K, When w-1>K, V (1-α) and V (α) are the weight matrices of direct differential demodulation terms and continuous decoding demodulation terms, respectively, and α is the forgetting factor; The multi-stage decoding process includes: The sparse matrix x designed using the FA-NIM system w Sparsity, using a low-complexity multi-stage decoding algorithm; In the first stage, by calculating the vector To compress the search space X; In the second stage, the sparse matrix x is detected w The indices of the non-zero elements in and the modulation symbols.

7. A non-coherent index modulation system based on a fluid antenna, used in the non-coherent index modulation method based on a fluid antenna according to any one of claims 1 to 6, characterized in that: include: The fluid antenna configuration module is used to configure a two-dimensional fluid antenna wide-mouth array and a two-dimensional fixed-arrangement antenna array, and to establish a fluid antenna channel model; A weight vector optimization module, used to preset and optimize the transmission mode of the communication system and assign a corresponding weight vector to each transmission mode; The information mapping and modulation module is used to divide the information bits and map them to corresponding signal modes and symbols to achieve signal modulation and transmission; A signal transmission and reception module, used to generate a transmission signal according to the mapped information vector and receive the signal at the receiving end; The decoding module is used to decode the signal at the receiving end using the maximum likelihood detection algorithm and the multi-stage decoding algorithm to restore the original information bits.

8. The system according to claim 7, characterized in that The weight vector optimization module optimizes the weight vector set through gradient descent method and perturbation introduction strategy.

9. The system according to claim 7, characterized in that The information mapping and modulation module divides the information bits into two parts, which are used to map the cyclic shifted FA mode index and the M-PSK symbol index respectively.

10. The system according to claim 7, characterized in that The decoding module utilizes the sparsity and differential characteristics of the signal and adopts a multi-stage decoding algorithm to perform decoding.

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