Beam dispersion suppression method for rate splitting assisted near-field broadband communication

Abstract

The invention discloses a beam dispersion suppression method for rate splitting assisted near-field broadband communication, and belongs to the technical field of wireless communication and novel multiple access. The method comprises the following steps: S1, based on spherical wave propagation characteristics, establishing a channel model of a near-field uniform linear array; s2, providing a hybrid beamforming architecture based on a real-time delayer to replace a traditional phase shifter assisted hybrid beamforming architecture; s3, constructing a signal transmission and decoding model based on a coding and decoding principle of a rate splitting multiple access technology; s4, designing a two-stage optimization algorithm, and performing joint optimization on a real-time delayer parameter, a phase shift matrix, a digital beam forming matrix and a common rate allocation variable so as to effectively compensate a space broadband effect; according to the method provided by the invention, beam dispersion can be effectively suppressed; the hardware complexity is remarkably reduced, and meanwhile, the transmission performance close to all-digital beam forming is achieved.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication and novel multiple access technology, and particularly relates to a beam dispersion suppression method for rate splitting-assisted near-field broadband communication. Background Technology

[0002] To improve spectral efficiency and support large-scale access, future communication networks are expected to expand to high-frequency bands such as millimeter waves and terahertz. However, high-frequency signals suffer severe path loss during propagation, leading to unstable communication links. To address this, researchers have proposed deploying very large-scale antenna arrays (VMAs) to compensate for path loss in high-frequency transmission. The deployment of VMAs significantly extends the Rayleigh distance, placing terminal devices in the near-field region. At this point, the propagation characteristics of electromagnetic waves change from a far-field plane wave model to a near-field spherical wave model. Unlike far-field plane waves, near-field spherical waves introduce an additional distance dimension, simultaneously characterizing both the angle and distance information of the signal. This dual-dimensional spatial resolution allows radiated energy to be precisely focused on a specific spatial location, rather than propagating only along a single direction, thus enabling finer spatial multiplexing and high-precision signal enhancement.

[0003] Furthermore, multiple access technologies play a crucial role in spectrum sharing and interference management, serving as a key pillar supporting the demands of ultra-dense connectivity. Current near-field communication systems primarily employ Space Division Multiple Access (SDMA) and Non-Orthogonal Multiple Access (NOMA). SDMA treats inter-user interference as pure noise, while NOMA requires complete decoding of all strong interference signals; both technologies have limitations in terms of interference management flexibility. Therefore, Rate Splitting Multiple Access (RSMA), with its flexible and robust interference management mechanism, is considered a more universal solution. By adaptively adjusting the information splitting ratio, RSMA can unify SDMA and NOMA multiple access strategies within the same framework, thereby significantly improving system performance in complex interference environments. Given its advantages, RSMA has been introduced into the near-field communication field and has demonstrated significant performance gains.

[0004] However, RSMA-assisted near-field communication still faces the following two key technical challenges:

[0005] (1) High hardware overhead: In traditional far-field communication scenarios, due to the relatively small number of base station antennas, each antenna can be configured with an independent RF link, thereby achieving fully digital beamforming. However, in near-field communication systems using very large-scale antenna arrays, fully digital beamforming will result in extremely high power consumption and hardware costs, and may even be difficult to implement in practice. Therefore, near-field communication systems urgently need to reduce their dependence on the number of RF links while ensuring performance.

[0006] (2) Beam dispersion effect: Near-field communication typically operates in a high-frequency broadband environment, where the channel exhibits significant frequency correlation among different subcarriers. However, traditional hybrid analog-to-digital antenna architectures can only achieve frequency-independent analog beamforming, thus inducing beam dispersion. This effect prevents most subcarriers, except for the center frequency, from achieving energy focusing at the target location, leading to severe degradation of system performance. Therefore, it is urgent to construct a beamforming architecture with frequency adaptive capabilities to effectively suppress beam dispersion.

[0007] Current status of research at home and abroad:

[0008] In 2024, Zhaolin Wang et al. published "TTD Configurations for Near-Field Beamforming: Parallel, Serial, or Hybrid?" in IEEE Transactions on Communications. They introduced real-time delay units to effectively suppress beam dispersion effects in near-field broadband communication and systematically analyzed the performance differences of parallel, serial, and hybrid TTD network configurations, providing an important reference for the design of near-field broadband beamforming architectures.

[0009] In 2025, Zhaolin Wang et al. published "Beamfocusing Optimization for Near-Field Wideband Multi-User Communications" in IEEE Transactions on Communications, further employing a hybrid beamforming architecture based on real-time delayers to effectively mitigate near-field broadband effects and achieve multi-user beam focusing. Although this research made significant progress in multi-user near-field beam design, it still treats inter-user interference as noise and directly decodes the target signal, lacking a flexible interference management mechanism, thus limiting the system's performance potential.

[0010] In 2025, Shengyu Zhang et al. published "Rate-Splitting Multiple Access for Near-Field Communications with ImperfectCSIT and SIC" in IEEE Transactions on Communications. This paper incorporated the elimination of imperfect channel state information and non-ideal serial interference into system modeling and utilized deep learning techniques to design an efficient precoding algorithm to improve network robustness and performance. However, this research did not consider beam dispersion effects in near-field broadband systems, and the adaptability of its method to broadband channel environments requires further investigation. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a beam dispersion suppression method for rate splitting-assisted near-field broadband communication to address the shortcomings of the prior art. The method proposed in this invention can effectively suppress beam dispersion and achieve transmission performance close to that of fully digital beamforming while significantly reducing hardware complexity.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0013] A beam dispersion suppression method for rate splitting-assisted near-field broadband communication specifically includes the following steps:

[0014] Step S1: Based on the propagation characteristics of spherical waves, establish a channel model for the near-field uniform linear array;

[0015] Step S2: Propose a hybrid beamforming architecture based on real-time delay to replace the traditional phase shifter-assisted hybrid beamforming architecture;

[0016] Step S3: Based on the encoding and decoding principle of rate splitting multiple access technology, construct a signal transmission and decoding model;

[0017] Step S4: Design a two-stage optimization algorithm to jointly optimize the real-time delay parameters, phase shift matrix, digital beamforming matrix, and common rate allocation variables to effectively compensate for the spatial broadband effect.

[0018] As a further preferred embodiment of the beam dispersion suppression method for rate splitting-assisted near-field broadband communication of the present invention, a near-field broadband communication system architecture including rate splitting multiple access and real-time delayer assistance is included; the base station is equipped with a uniform linear array containing N antennas to provide downlink service for K near-field users with single antennas; the antenna spacing of the array is set to d, and the corresponding Rayleigh distance can be expressed as... Where D = (N-1)d and λ represent the array aperture and carrier wavelength, respectively; to mitigate inter-symbol interference in broadband transmission, the system employs orthogonal frequency division multiplexing (OFDM) technology, uniformly dividing the total bandwidth B into M subcarriers. The center frequency of the nth subcarrier is then...

[0019]

[0020] in The center frequency of the system, The speed of light;

[0021] Establish a rectangular coordinate system with the center of the uniform linear array as the origin and the array direction as the y-axis. Then the coordinates of the nth antenna are: in and Let the polar coordinates of the k-th user relative to the origin be (r). k θ k If ), then its rectangular coordinates are r. k =(r k cosθ k r k sinθ k The distance between the nth antenna and the kth user is:

[0022]

[0023] Based on the Fresnel approximation, the channel gain of the k-th user is approximately equal across all antennas in the array. Therefore, the channel modeling of the n-th antenna and the k-th user on the m-th subcarrier is as follows:

[0024]

[0025] in and These represent path loss and complex channel gain, respectively. Represents the imaginary unit. Combining all antennas, the near-field channel vector of the k-th user on the m-th subcarrier. for

[0026]

[0027] The superscript (·) T This represents the transpose of a vector. This is the array response vector in the near field.

[0028] As a further preferred embodiment of the beam dispersion suppression method for rate splitting assisted near-field broadband communication of the present invention, according to the coding criteria of rate splitting multiple access technology, the information W of the k-th user on the m-th subcarrier... k,m Split into common parts and private parts in and The common part of all users on the m-th subcarrier Combined encoding into a common information flow x 0,m ; while private parts Then it is encoded into K independent private information streams {x 1，m , ..., x K，m Information flows through a digital beamforming matrix. Precoding is performed, where A represents the number of radio frequency links configured in the base station; in W m middle, and Let be the digital beamforming vectors representing the common information stream and the k-th private information stream on the m-th subcarrier, respectively; thus, the digital signal on the m-th subcarrier can be represented as:

[0029] As a further preferred embodiment of the beam dispersion suppression method for rate splitting assisted near-field broadband communication of the present invention, in order to suppress broadband beam dispersion effects, the system introduces a partially connected real-time delayer network between the phase shifter and the RF link; in this architecture, each RF link is connected to a network of phase shifters. A subarray composed of antennas, with each real-time delayer driving a subarray composed of... A subarray consisting of antennas, where Q represents the number of real-time delay units connected to each RF link; under this configuration, the real-time delay parameter matrix of the m-th subcarrier. for

[0030]

[0031] Where blkdiag(·) represents a block diagonal matrix. Let be the delay parameters of the real-time delay unit connected to the a-th RF link, where Each real-time delay unit must satisfy the maximum delay constraint t. a,q ∈[0,t max To ensure hardware feasibility, among which Phase shifter matrix Represented as

[0032] F = blkdiag(F1,...,F A (6)

[0033] in and Let f represent the phase shifter parameters connected to the a-th RF link and the q-th real-time delay unit, respectively, and all non-zero elements satisfy the unity modulus constraint |f a,q,i|=1, where f o，q，i This represents the i-th element of the vector.

[0034] Phase shifter and real-time delay matrix FT m After precoding, the signal transmitted by the base station on the m-th subcarrier is represented as follows: Under spherical wave propagation, the signal received by the k-th user on the m-th subcarrier is:

[0035]

[0036] in This represents additive white Gaussian noise, indicated by the superscript (·). H The conjugate transpose of the vector is given by equation (7). The power received by the k-th user on the m-th subcarrier is...

[0037]

[0038] To decode the target signal, the k-th user first treats the private information stream as interference and directly decodes the public information stream; then, it removes the public signal using serial interference cancellation technology before decoding the desired private information stream; the signal-to-interference-plus-noise ratio (SIR) of the k-th user decoding the public and private information streams on the m-th subcarrier are respectively...

[0039]

[0040] According to equation (9), the corresponding public rate and private rate are respectively

[0041]

[0042] Since the common information stream needs to be correctly decoded by all users, the common rate on the m-th subcarrier needs to satisfy... The public rate should be shared by all users, therefore it is possible to obtain in This represents the share of common rate allocated to user k; the total rate for the k-th user is... in It is the transmission rate of the k-th user on the m-th subcarrier;

[0043] By jointly optimizing the real-time delay matrix, phase shifter matrix, digital beamforming matrix, and common rate allocation variables, the minimum transmission rate among all users is maximized; the corresponding optimization problem (11) is modeled as follows:

[0044]

[0045] Where P th(11b) represents the maximum transmit power threshold for each subcarrier; (11c) and (11d) are used to limit the transmit power of each subcarrier; (11e) represents the common rate allocation constraint; (11f) represents the unit modulus constraint of the phase shifter; and (11f) is the hardware constraint condition of the real-time delay.

[0046] As a further preferred embodiment of the beam dispersion suppression method for rate splitting assisted near-field broadband communication of the present invention, in problem (11), a two-stage optimization algorithm is proposed to solve the problem of high coupling between the real-time delay matrix, the phase shifter matrix and the digital beamforming matrix. Specifically, the first stage aims to design an all-digital beamforming matrix to provide a performance upper bound reference for real-time delay-assisted hybrid beamforming. The second stage, based on this, optimizes the real-time delay, the phase shifter and the digital beamforming matrix together to make the system performance approach the upper bound of all-digital beamforming.

[0047] As a further preferred embodiment of the beam dispersion suppression method for rate splitting assisted near-field broadband communication of the present invention, the two-stage optimization algorithm has the following specific steps:

[0048] (1) Phase 1: Design of all-digital beamforming matrix; First, introduce the all-digital beamforming matrix. Where p k,m =FT m w k,m ; The all-digital beamforming matrix P m Substituting into equation (8), the power received by the k-th user is rewritten as follows:

[0049]

[0050] Subsequently, the decoding rates of the public and private information streams for the k-th user are recalculated using equation (12); to eliminate the minimum operator in the objective function, a non-negative auxiliary variable R is introduced. r Refactor problem (11) as

[0051]

[0052] Problem (13) involves the coupling of fractional signal-to-interference-plus-noise ratio and fully digital beamforming variables, making it difficult to solve directly. The MM algorithm framework is adopted, approximating the original complex objective function by optimizing an easily tractable substitution function in each iteration. Based on the idea of ​​first-order accelerated convergence, a low-boundary quadratic concave function is constructed to approximate the logarithmic transmission rate. Specifically, the common rate of the k-th user on the m-th subcarrier... and private rate The substitution functions are respectively

[0053]

[0054] Where Re(·) represents the real part of the complex number, and has

[0055]

[0056] in and

[0057]

[0058] In equation (16), It is the optimal solution obtained in the previous iteration; in the t-th iteration, It is the fully digital beamforming vector output at the (t-1)th iteration; based on the constructed surrogate function, problem (13) is reconstructed as

[0059]

[0060] When the expansion point Given that all constraints of problem (17) define a convex set, it is a convex problem, which can be solved iteratively using the CVX toolbox;

[0061] (2) Phase Two: Jointly optimize the real-time delay matrix, phase shifter matrix, and digital beamforming matrix to approximate the upper bound of the all-digital beamforming performance obtained in Phase One; the optimization problem is modeled as follows:

[0062]

[0063] To obtain an analytical closed-form solution, the optimization variables are divided into three blocks, and the block coordinate descent method is used to alternately update each variable block; the specific optimization steps are as follows;

[0064] 1) Optimization F: Due to the analog beamforming matrix FT composed of the real-time delayer and phase shifter. m With a block diagonal structure, the objective function related to F in problem (18) is rewritten as follows:

[0065]

[0066] in

[0067]

[0068] In equation (20), It is matrix P m The Arrive at the Submatrix formed by rows; W m (:,a) is a matrix W m The vector consisting of the elements in the a-th column; Equation (19) shows that problem (18) is split into AQ independent subproblems; for f a,qThe optimization problem is expressed as

[0069]

[0070] Its optimal closed-form solution is:

[0071]

[0072] 2) Optimize T m Similar to the approach used for F, optimize T. m The problem can also be broken down into AQ independent subproblems; optimizing t a,q Modeling the subproblems as

[0073]

[0074] This problem is a single-variable optimization problem defined within a finite interval, which can be efficiently solved using a one-dimensional search method: Let t a,q The domain is uniformly divided into S sampling points, and a search set is defined.

[0075]

[0076] An approximate optimal solution can be obtained by performing an exhaustive search within this set. The result is

[0077]

[0078] 3) Optimize W m : With F and T fixed m Then, the digital beamforming matrix W m The optimization problem can be simplified into an unconstrained quadratic optimization problem:

[0079]

[0080] Because the objective function has respect to W m Given a quadratic concave function, its optimal solution can be obtained directly through the first-order optimality condition; its closed-form solution is...

[0081]

[0082] The two-stage optimization algorithm includes:

[0083]

[0084]

[0085] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0086] This invention proposes a rate-split-assisted beam dispersion suppression method for near-field broadband communication. This method combines rate-split multiple access (RFA) technology to flexibly manage inter-user interference and introduces a real-time delayer to achieve frequency-dependent analog beamforming. Simultaneously, by designing a two-stage optimization algorithm, the real-time delayer parameters, phase shift matrix, digital beamforming matrix, and common rate allocation variables are jointly optimized, thereby effectively suppressing beam dispersion effects and significantly improving the overall system performance. Attached Figure Description

[0087] Figure 1 This is a schematic diagram of near-field broadband communication assisted by rate splitting multiple access and real-time delay device according to the present invention.

[0088] Figure 2 It is a performance comparison diagram showing the maximum and minimum rates as the number of users changes;

[0089] Figure 3 It depicts the trend of maximum-minimum rate as a function of the transmit power threshold for each subcarrier;

[0090] Figure 4 The impact of the number of antennas on system performance was analyzed.

[0091] Figure 5 It provides a schematic diagram showing the results of the maximum and minimum rates varying with the number of RF links. Detailed Implementation

[0092] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0093] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become clearer. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0094] This invention discloses a beam dispersion suppression method for rate splitting-assisted near-field broadband communication, belonging to the field of wireless communication and novel multiple access technology; the method includes the following steps:

[0095] S1. Based on the propagation characteristics of spherical waves, establish a channel model for a near-field uniform linear array;

[0096] S2. A hybrid beamforming architecture based on real-time delay is proposed to replace the traditional phase shifter-assisted hybrid beamforming architecture.

[0097] S3. Based on the encoding and decoding principle of rate splitting multiple access technology, a signal transmission and decoding model is constructed.

[0098] S4. Design a two-stage optimization algorithm to jointly optimize the real-time delay parameters, phase shift matrix, digital beamforming matrix and common rate allocation variables to effectively compensate for the spatial broadband effect.

[0099] The method proposed in this invention can effectively suppress beam dispersion; while significantly reducing hardware complexity, it achieves transmission performance close to that of fully digital beamforming.

[0100] Figure 1 This paper presents the proposed near-field broadband communication system architecture based on rate-split multiple access and real-time delayer assistance. The base station is equipped with a uniform linear array of N antennas to provide downlink service to K near-field users with single antennas. The antenna spacing of the array is denoted as d, and the corresponding Rayleigh distance can be expressed as... Where D = (N-1)d and λ represent the array aperture and carrier wavelength, respectively. To mitigate inter-symbol interference in broadband transmission, the system employs orthogonal frequency division multiplexing (OFDM) technology, uniformly dividing the total bandwidth B into M subcarriers. The center frequency of the m-th subcarrier is then...

[0101]

[0102] in The center frequency of the system, It is the speed of light.

[0103] Establish a rectangular coordinate system with the center of the uniform linear array as the origin and the array direction as the y-axis. Then the coordinates of the nth antenna are: in and Let the polar coordinates of the k-th user relative to the origin be (r). k ,θ k If ), then its rectangular coordinates are r. k =(r k cosθ k ,r k sinθ k Therefore, the distance between the nth antenna and the kth user is:

[0104]

[0105] Based on the Fresnel approximation, the channel gain of the k-th user is approximately equal across all antennas in the array. Therefore, the channel between the n-th antenna and the k-th user on the m-th subcarrier can be modeled as follows:

[0106]

[0107] in and These represent path loss and complex channel gain, respectively. Represents the imaginary unit. Combining all antennas, the near-field channel vector of the k-th user on the m-th subcarrier. for

[0108]

[0109] The superscript (·) T This represents the transpose of a vector. This is the array response vector in the near field.

[0110] According to the coding principles of rate split multiple access (RSA), the information W of the k-th user on the m-th subcarrier... k,m Split into common parts and private parts in and The common part of all users on the m-th subcarrier Combined encoding into a common information flow x 0,m ; while private parts Then it is encoded into K independent private information streams {x 1,m ,...,x K,m This information flows through the digital beamforming matrix. Precoding is performed, where A represents the number of radio frequency links configured for the base station. In W... m middle, and Let be the digital beamforming vectors representing the common information stream and the k-th private information stream on the m-th subcarrier, respectively. Therefore, the digital signal on the m-th subcarrier is:

[0111] To suppress broadband beam dispersion, a partially connected real-time delayer network is introduced between the phase shifter and the RF link. In this architecture, each RF link connects to a network of phase shifters. A subarray composed of antennas, with each real-time delayer driving a subarray composed of... A subarray consisting of antennas, where Q represents the number of real-time delay units connected to each RF link. Under this configuration, the real-time delay parameter matrix of the m-th subcarrier... for

[0112]

[0113] Where blkdiag(·) represents a block diagonal matrix. Let be the delay parameters of the real-time delay unit connected to the a-th RF link, where In addition, each real-time delay unit must satisfy the maximum delay constraint t. a，q ∈[0, t max To ensure hardware feasibility, among which Phase shifter matrix for

[0114] F = blkdiag(F1, ..., F) A (6)

[0115] in and Let f represent the phase shifter parameters connected to the a-th RF link and the q-th real-time delay unit, respectively, and all non-zero elements satisfy the unity modulus constraint |f a,q,i |=1, where f a，q，i This represents the i-th element of the vector.

[0116] Phase shifter and real-time delay matrix FT m After precoding, the signal transmitted by the base station on the m-th subcarrier is Under spherical wave propagation, the signal received by the k-th user on the m-th subcarrier is:

[0117]

[0118] in This represents additive white Gaussian noise, indicated by the superscript (·). H This represents the conjugate transpose of a vector. According to equation (7), the power received by the k-th user on the m-th subcarrier is...

[0119]

[0120] To decode the target signal, the k-th user first treats the private information stream as interference and directly decodes the public information stream. Then, it removes the public signal using serial interference cancellation technology before decoding the desired private information stream. Therefore, the signal-to-interference-plus-noise ratio (SNR) of the k-th user decoding the public and private information streams on the m-th subcarrier are respectively...

[0121]

[0122] According to equation (9), the corresponding public rate and private rate are respectively

[0123]

[0124] However, since the common information stream needs to be correctly decoded by all users, the common rate on the m-th subcarrier needs to satisfy... Furthermore, the public rate should be shared by all users, therefore it is possible to obtain in Let represent the share of the common rate allocated to user k. Therefore, the total rate for user k is . in It is the transmission rate of the k-th user on the m-th subcarrier.

[0125] The goal of this system is to maximize the minimum transmission rate among all users by jointly optimizing the real-time delay matrix, phase shifter matrix, digital beamforming matrix, and common rate allocation variables. The corresponding optimization problem can be modeled as follows:

[0126]

[0127] Where P th (11b) represents the maximum transmit power threshold for each subcarrier; (11c) and (11d) correspond to the common rate allocation constraints; (11e) represents the unit modulus constraint of the phase shifter; (11f) is the hardware constraint condition of the real-time delay.

[0128] Two-stage optimization algorithm design:

[0129] In problem (11), there is a high degree of coupling between the real-time delay matrix, the phase shifter matrix, and the digital beamforming matrix, making the problem difficult to solve directly. Therefore, this system proposes a two-stage optimization algorithm. Specifically, the first stage aims to design the all-digital beamforming matrix to provide a performance upper bound reference for real-time delay-assisted hybrid beamforming; the second stage, based on this, optimizes the real-time delay, phase shifter, and digital beamforming matrix together to bring the system performance close to the upper bound of all-digital beamforming. The specific steps are as follows:

[0130] (1) Phase 1: Design of the all-digital beamforming matrix. First, the all-digital beamforming matrix is ​​introduced. Where p k，m =FT m w k，m The all-digital beamforming matrix P m Substituting into equation (8), the power received by the k-th user is rewritten as follows:

[0131]

[0132] Subsequently, the decoding rates of the public and private information streams for the k-th user are recalculated using equation (12). To eliminate the minimum operator in the objective function, a non-negative auxiliary variable R is introduced. T Refactor problem (11) as

[0133]

[0134] Problem (13) involves the coupling of fractional signal-to-interference-plus-noise ratio and fully digital beamforming variables, making it difficult to solve directly. Therefore, this system adopts the MM (Majorization-Minimization) algorithm framework, approximating the original complex objective function by optimizing an easily tractable substitution function in each iteration. The effectiveness of this framework depends on the tightness of the lower bound of the constructed substitution function and the feasibility of optimization. Based on the idea of ​​first-order accelerated convergence, this system constructs a low-boundary quadratic concave function to approximate the logarithmic transmission rate. Specifically, the common rate of the k-th user on the m-th subcarrier... and private rate The substitution functions are respectively

[0135]

[0136] Where Re(·) represents the real part of the complex number, and has

[0137]

[0138] in and

[0139]

[0140] In equation (16), This is the optimal solution obtained in the previous iteration. For example, in the t-th iteration, It is the fully digital beamforming vector output at the (t-1)th iteration. Based on the constructed surrogate function, problem (13) can be reconstructed as

[0141]

[0142] When the expansion point Given that all constraints of problem (17) can define a convex set, the problem is a convex problem that can be solved iteratively using the CVX toolbox.

[0143] (2) Phase Two: Jointly optimize the real-time delay matrix, phase shifter matrix, and digital beamforming matrix to approximate the upper bound of the all-digital beamforming performance obtained in Phase One. Therefore, the optimization problem can be modeled as follows:

[0144]

[0145] To obtain an analytical closed-form solution, the optimization variables are divided into three blocks, and the block coordinate descent method is used to alternately update each variable block. The specific optimization steps are as follows.

[0146] 1) Optimization F: Due to the analog beamforming matrix FT composed of the real-time delayer and phase shifter. mGiven the block diagonal structure, the objective function related to F in problem (18) can be rewritten as follows:

[0147]

[0148] in

[0149]

[0150] In equation (20), It is matrix P m The Arrive at the Submatrix formed by rows; W m (:,a) is a matrix W m The vector consisting of the elements in the a-th column. Equation (19) shows that problem (18) consists of AQ independent subproblems. For f a,q The optimization problem can be expressed as

[0151]

[0152] Its optimal closed-form solution is:

[0153]

[0154] 2) Optimize T m Similar to the approach used for F, optimize T. m The problem can also be broken down into AQ independent subproblems. Optimize t a,q The subproblem can be modeled as

[0155]

[0156] This problem is a univariate optimization problem defined within a finite interval, which can be solved efficiently using a one-dimensional search method. Specifically, let t a，q The domain is uniformly divided into S sampling points, and a search set is defined.

[0157]

[0158] An approximate optimal solution can be obtained by performing an exhaustive search within this set. The result is

[0159]

[0160] 3) Optimize W m : With F and T fixed m Then, the digital beamforming matrix W m The optimization problem can be simplified into an unconstrained quadratic optimization problem:

[0161]

[0162] Because the objective function has respect to W m Given a quadratic concave function, its optimal solution can be obtained directly through the first-order optimality condition; its closed-form solution is...

[0163]

[0164] The two-stage optimization algorithm includes:

[0165]

[0166] Simulation results:

[0167] In the simulation test, the base station uses a uniform linear array with an antenna spacing of half a wavelength and the number of antennas set to N = 128; the number of RF links is A = 8, and each RF link connects Q = 4 real-time delayers, with the maximum delay t of each real-time delayer being... max =N / (2f) = 2.13 nanoseconds, the number of steps for the one-dimensional search is set to S = 10 3 K = 4 users are randomly generated within a range of 10 to 20 meters from the base station; the system's center frequency f = 30 GHz, total bandwidth B = 10 GHz, and number of subcarriers M = 10. The base station's maximum transmit power P th =20dBm, background noise power spectral density σ 2 = -174dBm / Hz.

[0168] Figure 2 The performance comparison of maximum and minimum rates as the number of users is presented. It can be observed that the performance of all schemes decreases with the increase in the number of users, but the proposed scheme consistently outperforms traditional spatial division multiple access (SDMA) technologies, demonstrating its significant advantage in interference management. Furthermore, compared to hybrid beamforming architectures that only employ phase shifters, the proposed scheme effectively suppresses broadband beam dispersion effects and achieves near-fully digital beamforming performance using only eight RF links, thus striking a good balance between hardware complexity and performance.

[0169] Figure 3 The maximum-minimum rate is depicted as a function of the transmit power threshold for each subcarrier. With increasing transmit power, the communication rate of all schemes significantly improves, but the proposed scheme shows a greater increase. Furthermore, the proposed scheme consistently outperforms hybrid beamforming and far-field hybrid beamforming schemes using only phase shifters, and the performance gap widens further with increasing power. The proposed hybrid beamforming architecture achieves near-perfect performance using only 1 / 16th the number of RF links in a fully digital architecture.

[0170] Figure 4The impact of antenna number on system performance was analyzed. With increasing array size, the maximum-minimum rate improved for all schemes, due to the higher spatial diversity and multiple access gain resulting from larger antenna arrays. However, the proposed scheme achieved performance improvements of approximately 0.65 bps / Hz and 0.2 bps / Hz compared to spatial division multiple access (SDMA) and phase shifter-based hybrid beamforming schemes, respectively. Notably, when the number of antennas exceeds a certain threshold (e.g., N≥128), the performance of the far-field beamforming scheme significantly degrades, even falling below that of SDMA schemes. This indicates that in large-scale array scenarios, near-field beamforming has irreplaceable advantages in interference suppression and signal enhancement.

[0171] Figure 5 The results of the maximum and minimum data rates as a function of the number of RF links are presented. As the number of RF links increases, the performance gap between the proposed scheme and all-digital beamforming gradually narrows, reaching only 0.5 bps / Hz at A=14. This is mainly due to the higher-dimensional digital beamforming capability brought about by more RF links, which further enhances the interference suppression effect. Under the same RF link configuration, the proposed scheme consistently outperforms the other three benchmark schemes, highlighting its practical application potential and hardware efficiency advantages in near-field communication systems.

[0172] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention. All technical features in this embodiment can be freely combined according to actual needs.

[0173] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A beam dispersion suppression method for rate splitting-assisted near-field broadband communication, characterized in that: Specifically, the following steps are included: Step S1: Based on the propagation characteristics of spherical waves, establish a channel model for the near-field uniform linear array; Step S2: Propose a hybrid beamforming architecture based on real-time delay to replace the traditional phase shifter-assisted hybrid beamforming architecture; Step S3: Based on the encoding and decoding principle of rate splitting multiple access technology, construct a signal transmission and decoding model; Step S4: Design a two-stage optimization algorithm to jointly optimize the real-time delay parameters, phase shift matrix, digital beamforming matrix, and common rate allocation variables to effectively compensate for the spatial broadband effect.

2. The beam dispersion suppression method for rate splitting-assisted near-field broadband communication according to claim 1, characterized in that: A near-field broadband communication system architecture incorporating rate splitting multiple access and real-time delay assistance; the base station is equipped with... A uniform linear array of antennas, used for A single antenna provides downlink service to near-field users; the antenna spacing of the array is set to... The corresponding Rayleigh distance can be expressed as ,in and These represent the array aperture and carrier wavelength, respectively. To mitigate inter-symbol interference in broadband transmission, the system employs orthogonal frequency division multiplexing (OFDM) technology to distribute the total bandwidth... Evenly divided into The nth subcarrier, then the nth The center frequency of each subcarrier is ;in The center frequency of the system, The speed of light; With the center of the uniform linear array as the origin and the array direction as... Establish a rectangular coordinate system around the axes, then the first... The coordinates of the root antenna are ,in and ; will the first The polar coordinates of each user relative to the origin are: Then its rectangular coordinates are ;No. root antenna and the first The distance between users is: ; Based on the Fresnel approximation, the... The channel gain for each user is approximately equal across all antennas in the array, therefore the first user's channel gain is approximately equal across all antennas in the array. root antenna and the first The user in the first Channel modeling on each subcarrier is as follows ;in and These represent path loss and complex channel gain, respectively. Represents the imaginary unit. ; Combining all antennas, the first The user in the first Near-field channel vectors on each subcarrier for ; where superscript This represents the transpose of a vector. ; represents the array response vector in the near field.

3. The beam dispersion suppression method for rate splitting-assisted near-field broadband communication according to claim 2, characterized in that: According to the coding principles of rate splitting multiple access (RSMA), the first... The user in the first Information on each subcarrier Split into common parts and private parts ,in and All users in the first Common part on each subcarrier Combined into a common information flow ; while private parts Then it is encoded as An independent private information flow ; Information flows through digital beamforming matrix Perform precoding, where Represents the number of radio frequency links configured in the base station; middle, and Representing the first The common information flow on each subcarrier and the first The digital beamforming vector of the private information stream; from this, we can obtain the first... The digital signal on each subcarrier is .

4. The beam dispersion suppression method for rate splitting-assisted near-field broadband communication according to claim 3, characterized in that: To suppress broadband beam dispersion, the system introduces a partially connected real-time delayer network between the phase shifter and the RF link; in this architecture, each RF link connects to a network of... A subarray composed of antennas, with each real-time delayer driving a subarray composed of... A sub-array composed of root antennas, in which This represents the number of real-time delay units connected to each RF link; under this configuration, the... Real-time delay parameter matrix of subcarriers for ;in Represents a block diagonal matrix. To connect to the first The delay parameters of the real-time delay unit of each RF link, where Each real-time delay unit must meet the maximum delay constraint. To ensure hardware feasibility, among which , Phase shifter matrix for ;in and They respectively represent the connection to the first The first radio frequency link and the first The phase shifter parameters of each real-time delay unit, and all non-zero elements satisfy the unity modulus constraint. ,in The first vector represents the first vector. element ; Phase shifter and real-time delay matrix After precoding, the base station in the 1st The signal transmitted on each subcarrier is represented as follows: ; Under spherical wave propagation, the first The user in the first The signal received on each subcarrier is ;in Represents additive white Gaussian noise, superscript The conjugate transpose of the vector; according to equation (7), the first... The user in the first The power received on each subcarrier is In order to decode the target signal, the first The user first treats the private information flow as interference and directly decodes the public information flow; Subsequently, common signals are removed using serial interference cancellation technology, and then the required private information stream is decoded; The user in the first The signal-to-interference-plus-noise ratios (SIRs) for decoding the public and private information streams on each subcarrier are respectively... According to equation (9), the corresponding public rate and private rate are respectively ; Because public information streams need to be correctly decoded by all users, the first The common rate on each subcarrier must meet the following requirements. The public rate should be shared by all users, therefore it is possible to obtain... ,in Indicates allocation to user The common rate share; the first The total rate for each user is ,in It is the first The user in the first Transmission rate on each subcarrier; By jointly optimizing the real-time delay matrix, phase shifter matrix, digital beamforming matrix, and common rate allocation variables, the minimum transmission rate among all users is maximized; the corresponding optimization problem (11) is modeled as follows: ;in (11b) represents the maximum transmit power threshold for each subcarrier; (11c) and (11d) are used to limit the transmit power of each subcarrier; (11e) represents the common rate allocation constraint; (11f) represents the unit modulus constraint of the phase shifter; and (11f) is the hardware constraint condition of the real-time delay.

5. The beam dispersion suppression method for rate splitting-assisted near-field broadband communication according to claim 4, characterized in that: In problem (11), a two-stage optimization algorithm is proposed to solve the problem of high coupling between the real-time delay matrix, the phase shifter matrix and the digital beamforming matrix. Specifically, the first stage aims to design an all-digital beamforming matrix to provide a performance upper bound reference for real-time delay-assisted hybrid beamforming. The second stage, based on this, optimizes the real-time delay, phase shifter and digital beamforming matrix together to make the system performance approach the upper bound of all-digital beamforming.

6. The beam dispersion suppression method for rate splitting-assisted near-field broadband communication according to claim 5, characterized in that: The two-stage optimization algorithm has the following specific steps: (1) Phase 1: Design of all-digital beamforming matrix; First, introduce the all-digital beamforming matrix. ,in ; All-digital beamforming matrix Substituting into equation (8), then the first... The power received by each user is Subsequently, the first equation is recalculated using equation (12). The rate at which each user decodes public and private information streams; to eliminate the minimum operator in the objective function, a non-negative auxiliary variable is introduced. Refactor problem (11) as ； Problem (13) involves the coupling of fractional signal-to-interference-plus-noise ratio and fully digital beamforming variables, making it difficult to solve directly. The MM algorithm framework is adopted, approximating the original complex objective function by optimizing an easily tractable substitution function in each iteration. Based on the idea of ​​first-order accelerated convergence, a low-boundary quadratic concave function is constructed to approximate the logarithmic transmission rate. Specifically, the first... The user in the first Common rate on each subcarrier and private rate The substitution functions are respectively ;in Represents the real part of the complex number, and has ;in and ； In equation (16), It is the optimal solution obtained in the previous iteration; in the... In the next iteration It is in the The all-digital beamforming vector output at the next iteration; based on the constructed surrogate function, problem (13) is reconstructed as When the expansion point Given that all constraints of problem (17) are a convex set, it is a convex problem, which can be solved iteratively using the CVX toolbox; (2) Phase Two: Jointly optimize the real-time delay matrix, phase shifter matrix, and digital beamforming matrix to approximate the upper bound of the all-digital beamforming performance obtained in the first phase; the optimization problem is modeled as follows: To obtain an analytical closed-form solution, the optimization variables are divided into three blocks, and the block coordinate descent method is used to alternately update each variable block; the specific optimization steps are as follows. 1) Optimization Due to the analog beamforming matrix composed of real-time delayers and phase shifters Having a block diagonal structure, in problem (18) and The relevant objective function is rewritten as follows ； in In equation (20), It is a matrix The Arrive at the A submatrix formed by rows; It is a matrix The A vector composed of column elements; Equation (19) shows that problem (18) is broken down into Each independent subproblem; for The optimization problem is represented as Its optimal closed-form solution is ; 2) Optimization Similar to Optimize the processing method Time can also be broken down into Each independent subproblem; optimization Modeling the subproblems as ； The problem is a single-variable optimization problem defined within a finite interval, which can be efficiently solved using a one-dimensional search method: The domain is uniformly divided into S sampling points, and a search set is defined. ; An approximate optimal solution can be obtained by performing an exhaustive search within this set. The result is ； 3) Optimization : in fixed and Then, digital beamforming matrix The optimization problem can be simplified into an unconstrained quadratic optimization problem: ； Because the objective function is about Given a quadratic concave function, its optimal solution can be obtained directly through the first-order optimality condition; its closed-form solution is... ； The two-stage optimization algorithm includes: Phase 1: Optimization of the all-digital beamforming matrix; initialization ,in and ; The process continues while the increment of the objective function in problem (17) is less than the tolerance threshold. renew ; Solving the problem using CVX (17); end Output the optimal ; Phase Two: Real-time delayer-assisted hybrid beamforming matrix optimization; initialization and ,in ; The process is executed while the objective function of problem (18) is reduced to a tolerance threshold; Update the phase shifter matrix based on equation (22) ; Update the real-time delay matrix based on equation (25) ; Update the digital precoding matrix based on equation (27) ; end Output the final hybrid beamforming result and calculate the maximum-minimum transmission rate.

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