A communication control method and system for a high-speed rail millimeter wave communication system

Abstract

The present invention provides a communication control method and system for a high-speed rail millimeter wave communication system, comprising: obtaining channel state information and a pre-constructed system capacity maximization problem function; the pre-constructed system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization; based on the channel state information, and using an alternating optimization algorithm, iteratively solving the beamforming sub-problem optimization and phase shift design sub-problem optimization in the pre-constructed system capacity maximization problem function to obtain optimal beamforming and optimal phase shift; and performing vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning based on the optimal beamforming and optimal phase shift. The present invention can overcome the high transmission loss problem of millimeter waves, achieve system sum rate maximization under the constraints of a minimum perceived signal-to-noise ratio threshold and the maximum transmit power of a base station, and ensure a good trade-off between communication performance and perceived performance.

Description

Technical Field

[0001] The present invention relates to the field of signal transmission technology, and in particular to a communication control method and system for a high-speed rail millimeter wave communication system. Background Art

[0002] As high-speed rail gradually evolves from information technology to intelligent technology, diverse data-intensive services, such as high-definition video surveillance, onboard broadband internet services, and railway Internet of Things services, are increasingly demanding high-capacity railway communications. This poses a significant challenge to existing railway wireless communication systems. To address this issue, ISAC is being leveraged to significantly improve spectrum and energy efficiency while reducing hardware and signaling costs by integrating communication and sensing functions into a single system.

[0003] However, while some existing ISAC research integrates sensing and communication functions into the same base station system, radar and communication antennas are still deployed separately within the base station. The communication system only transmits signals when the radar is not occupying space and spectrum resources. This radar and communication coexistence approach, while easier to implement in hardware, does not allow radar and communication to operate simultaneously, thus failing to effectively improve resource utilization and spectrum efficiency. A more effective approach would be for communication and radar functions to share all hardware and software resources. However, in this case, there is the problem of mutual interference and restriction between radar and communication signals.

[0004] Meanwhile, existing ISAC research has not considered the millimeter wave frequency band. Faced with the impending spectrum crunch, millimeter wave communication technology extends cellular communications to higher millimeter wave frequency bands. The large bandwidth of millimeter waves can provide extremely high communication transmission rates, while their narrow beams and significant directional gain can effectively improve sensing efficiency. However, millimeter wave transmission can experience severe penetration attenuation, especially for sensing signals, which face double path loss.

[0005] Furthermore, to address the ISAC signal's dependence on the wireless propagation environment and the high penetration loss of millimeter waves, existing research has begun considering the use of intelligent reflective surfaces to improve the propagation environment and design RIS-assisted ISAC systems. However, existing RIS-assisted ISAC system research primarily focuses on using RIS to enhance communication signal transmission and interference suppression, and does not consider using RIS to assist in target perception. However, in high-speed rail systems, communication targets and perception targets are often concentrated or located in the same direction as the base station, resulting in significant wireless signal propagation loss. These issues lead to a serious imbalance in communication and perception performance in RIS-assisted ISAC systems. Summary of the Invention

[0006] Embodiments of the present invention provide a communication control method and system for a high-speed railway millimeter wave communication system to overcome the shortcomings of the prior art.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions.

[0008] In a first aspect, the present invention provides a communication control method for a high-speed rail millimeter wave communication system, comprising:

[0009] Acquiring channel state information and a pre-constructed system capacity maximization problem function; the pre-constructed system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization;

[0010] According to the channel state information, an alternating optimization algorithm is used to iteratively solve the beamforming subproblem optimization and the phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function to obtain optimal beamforming and optimal phase shift;

[0011] Vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning are performed based on the optimal beamforming and optimal phase shift.

[0012] Optionally, the iteratively solving the beamforming sub-problem optimization and the phase shift design sub-problem optimization in the pre-constructed system capacity maximization problem function by using an alternating optimization algorithm includes:

[0013] Step 1: Under a fixed phase shift, the initial beamforming is optimized using a preset beamforming optimization algorithm based on continuous convex approximation to obtain an initial optimized beamforming;

[0014] Step 2: Based on the initial optimized beamforming, the initial phase shift is optimized using a preset local search-based phase shift optimization algorithm to obtain an initial optimized phase shift;

[0015] Step 3: Using the initial optimized phase shift as a new fixed phase shift, repeat steps 1 to 3 until the system transmission rate difference between consecutive iterations is less than a preset rate threshold, thereby obtaining the optimal beamforming and the optimal phase shift.

[0016] Optionally, the channel state information includes the RIS-MR channel h of user k ir,k , BS-RIS channel coefficient H bi ;

[0017] Accordingly, the pre-built system capacity maximization problem function is:

[0018]

[0019]

[0020]

[0021]

[0022] Where, is the set of all MRs, σ 2 is the power of the noise, γ th is the threshold of the perceived signal-to-noise ratio, P max is the maximum transmission power of the base station, a(θ a ,θ e ) is RIS at (θ a ,θ e ) direction, Φ is the effective phase shift introduced by all elements of RIS, is the phase shift corresponding to the lth row, m l is the quantization number, e is the set number of quantization bits, and the constraint condition The minimum beam pattern of the radar detection received signal is greater than the threshold γ th ; Constraints is the BS transmit power constraint, w is the beamforming vector corresponding to the beamforming; the constraint condition is the discrete phase shift of the RIS element.

[0023] Optionally, step 1, in the case of a fixed phase shift, optimizing the initial beamforming using a preset beamforming optimization algorithm based on continuous convex approximation to obtain an initial optimized beamforming, includes:

[0024] In the case of a fixed phase shift, the pre-constructed system capacity maximization problem function is the beamforming sub-problem optimization function:

[0025]

[0026]

[0027]

[0028] By introducing G k =diag(h ir,k )H bi , W=ww H , The beamforming subproblem optimization function is simplified to obtain a simplified beamforming subproblem optimization function:

[0029]

[0030]

[0031] Tr(W)≤P max ,

[0032]

[0033] Rank(W)≤1;

[0034] in,

[0035] The simplified beamforming subproblem optimization function F1(W) is expanded using a first-order Taylor expansion to convert the simplified beamforming subproblem optimization function into a convex function, thereby obtaining the final beamforming subproblem optimization function:

[0036]

[0037]

[0038]

[0039]

[0040] Tr(W)≤P max ,

[0041]

[0042] Rank(W)≤1;

[0043] Among them, W i is the value of W in the i-th iteration;

[0044] The final beamforming subproblem optimization function is solved using a preset convex optimization algorithm to obtain an initial optimized beamforming.

[0045] Optionally, the preset convex optimization algorithm is a CVX solver.

[0046] Optionally, step 2, based on the initial optimized beamforming, optimizing the initial phase shift using a preset local search-based phase shift optimization algorithm to obtain the initial optimized phase shift, includes:

[0047] Based on the initial optimized beamforming, the pre-built system capacity maximization problem function is the phase shift design sub-problem optimization function:

[0048]

[0049]

[0050] l=1,…,L,m l ∈{0,2,…,2e -1};

[0051] The process of solving the optimization function of the phase shift design subproblem includes:

[0052] Step 21: Take one of the L unit phase shifts as the current phase shift φ l , the remaining L-1 unit phase shifts of the L unit phase shifts are fixed;

[0053] Step 22, the current phase shift φ l Traverse all the values and take the value with the largest sum rate among the traversed values as the optimized phase shift of the current phase shift;

[0054] Step 22, repeating steps 21 to 22 until the L unit phase shifts all have corresponding optimized phase shifts.

[0055] In a second aspect, the present invention further provides a communication control system for a high-speed rail millimeter wave communication system, comprising:

[0056] An information and function acquisition module, configured to acquire channel state information and a pre-built system capacity maximization problem function; the pre-built system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization;

[0057] a function solving module, configured to iteratively solve the beamforming subproblem optimization and the phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function according to the channel state information and using an alternating optimization algorithm to obtain an optimal beamforming and an optimal phase shift;

[0058] The communication link selection module is used to perform vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning based on the optimal beamforming and optimal phase shift.

[0059] Optionally, the function solving module includes:

[0060] A beamforming unit is configured to optimize the initial beamforming using a preset beamforming optimization algorithm based on continuous convex approximation under a fixed phase shift to obtain an initial optimized beamforming;

[0061] A phase shift optimization unit is used to optimize the initial phase shift based on the initial optimized beamforming by using a preset local search-based phase shift optimization algorithm to obtain an initial optimized phase shift;

[0062] The iterative optimization unit is configured to use the initially optimized phase shift as a new fixed phase shift and repeat the steps from the beamforming unit to the phase shift optimization unit until a difference in system transmission rate between consecutive iterations is less than a preset rate threshold, thereby obtaining an optimal beamforming and an optimal phase shift.

[0063] In a third aspect, the present invention also provides an electronic device comprising a memory and a processor, wherein the processor and the memory communicate with each other, the memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the above-mentioned communication control method of the high-speed rail millimeter wave communication system.

[0064] In a fourth aspect, the present invention further provides a computer-readable storage medium storing a computer program, which implements the above-mentioned communication control method of the high-speed rail millimeter wave communication system when the computer program is executed by a processor.

[0065] Beneficial effects of the present invention: The communication control method and system of the high-speed rail millimeter wave communication system provided by the present invention provide an active reflection link for communication and perception through an intelligent reflection surface, jointly design the transmitting end beamforming scheme and the RIS phase adjustment parameter matrix, and determine that the corresponding optimization goal is to achieve the maximum system sum rate under the premise of meeting the perception performance threshold. However, since the optimization variables in the optimization process are coupled, it is difficult to obtain a closed-form solution. Therefore, the present invention decomposes the system capacity maximization problem into the optimization of the beamforming sub-problem and the optimization of the phase shift design sub-problem, and adopts an alternating optimization algorithm to iteratively solve it, so as to obtain the optimal beamforming and the optimal phase shift under the premise of meeting the perception performance threshold, so that the sum rate of the high-speed rail millimeter wave communication system is maximized. In addition, in order to further improve the robustness of the system, the present invention takes into account extreme cases, that is, assuming that the direct links between the transmitter and the receiver / detection target are blocked, and RIS is required to provide a reflection link for them, that is, the directional pattern gain of RIS toward the Target is used to measure the perception performance, and the RIS device is obtained in (θ a ,θ e ) direction, thereby ensuring a certain degree of communication and perception functions even in extremely poor propagation environments.

[0066] Additional aspects and advantages of the present invention will be set forth in part in the following description, will become apparent from the following description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0068] Figure 1 A schematic diagram of the structure of a high-speed rail millimeter wave communication system provided by an embodiment of the present invention;

[0069] Figure 2 A flow chart of a communication control method for a high-speed railway millimeter wave communication system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0070] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and are not to be construed as limiting the present invention.

[0071] Those skilled in the art will appreciate that, unless expressly stated otherwise, the singular forms "a", "an", "" and "the" used herein may also include the plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, "connected" or "coupled" as used herein may include wireless connections or couplings. The term "and / or" as used herein includes any unit and all combinations of one or more of the associated listed items.

[0072] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention pertains. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such herein, will not be interpreted in an idealized or overly formal sense.

[0073] Explanation of terms:

[0074] Smart reflective surface: Smart reflective surface is a groundbreaking new technology that integrates a large number of low-cost passive metamaterial units on a two-dimensional plane and uses artificial programmable software to reconfigure the radio wave propagation environment.

[0075] High-speed rail millimeter wave communication system: The high-speed rail communication system operating in the millimeter wave frequency band can meet the needs of train-to-ground communication with large data volumes and high transmission rates.

[0076] Integrated perception and communication: This refers to new information processing technologies that enable the synergy of perception and communication functions through the sharing of software and hardware resources or information. By integrating communication and perception functions into a single system, it is expected to significantly improve spectrum and energy efficiency while reducing hardware and signal costs.

[0077] High-Speed Rail Millimeter Wave Communication Systems: The rapid development of railway transportation systems has greatly enriched railway wireless services and increased demand for wireless transmission. To achieve 10G data rates, the application of ultra-wideband millimeter wave bands is an inevitable trend. To promote the application of millimeter waves (mmWave) in HSR, the propagation characteristics of 40GHz millimeter waves in railway environments were tested, focusing on propagation losses and snow attenuation in elevated lines. In addition, some literature has thoroughly analyzed the wireless channel characteristics of HSR millimeter wave communications based on large-scale antennas, and some literature has analyzed the characteristics of 22.6GHz wireless channels in typical high-speed rail environments. Other literature has established a complete propagation channel model for mmWave and THz waves in high-speed rail, taking into account weather factors such as rain, fog, sand, and dust.

[0078] RIS technology: In recent years, RIS has attracted widespread attention as a revolutionary and innovative technology. RIS is a planar surface containing a large number of passive reflective elements, each of which independently induces controllable amplitude and / or phase variations in the incident signal. By densely deploying RIS in a wireless network and cleverly adjusting the phase shifts generated by all reflective elements, it is possible to increase the expected power gain of received signals and destructively reduce interference, thereby improving communication performance. As a two-dimensional implementation of metamaterials, RIS inherently offers low cost, low complexity, and ease of deployment, making it well suited to address the challenges posed by intelligent high-speed rail communication scenarios. Prior art research has explored the optimization of minimum base station transmit power in MISO and MIMO systems, respectively, but both employ continuous RIS phase shifting. In actual RIS hardware, RIS phase shifting is achieved by adjusting the switching state of PIN diodes, with one PIN diode capable of achieving two-bit phase shifts. Therefore, due to component size limitations, continuous phase shifting is impractical. Other research addresses the system sum rate maximization problem for multiple D2D links by jointly optimizing the transmission power of all links and the discrete phase shifts of the surface. In addition, some literature has studied minimizing the transmit power by optimizing the transmit beamforming vector and the phase shift of the RIS element under imperfect channel state information (CSI).

[0079] ISAC Technology: By integrating communication and perception functions into a single system, ISAC promises to significantly improve spectrum and energy efficiency while reducing hardware and signal costs. This article comprehensively reviews the state-of-the-art in ISAC systems from a signal processing perspective, including communication-centric, radar-centric, and joint design and optimization. Prior art research explores enabling technologies for ISAC, including transmission waveform design, environmental modeling, sensor sources, signal processing, and data processing. Other research investigates the fundamental limitations of ISAC to understand the gap between the current state-of-the-art and performance limits. Prior art design utilizes hybrid analog-digital (HAD) beamforming technology to design a transceiver architecture and frame structure for DFRC base stations in the mmWave band. Furthermore, considering that communication channel strength cannot be directly derived from radar perception, a novel ISAC transmission framework based on spatially extended orthogonal time-frequency-space (SS-OTFS) modulation is proposed. Other research examines how to achieve performance improvements through optimization without changing the existing architecture. In another paper, the omnidirectional and directional beam pattern design problems for DFRC downlink communication are considered, and based on the obtained waveform closed-form solution, weighted optimization for flexible trade-off between radar and communication performance is further considered.

[0080] IRS-Assisted ISAC Systems: To overcome the ISAC system's dependence on the wireless propagation environment, some research has incorporated RIS into ISAC systems, leveraging RIS to enhance communication and perception performance. A centralized ISAC system based on distributed intelligent reflecting surfaces (RIS) has been established, and a detailed workflow has been designed, including transmission protocols, location detection, and beamforming optimization. Communication and perception performance is maximized by jointly optimizing the transmit signal waveform, sensing signal waveform, and RIS phase shift. Key metrics include transmission rate, Cramer-Rao bounds for angle estimation, and sensor mutual information (MI). Furthermore, studies have been conducted on the reflection and amplification effects of dual-RIS, multiple-RIS-assisted ISAC systems, active RIS, and hybrid RIS on communication and perception signals, as well as the physical layer security of multi-user multiple-input single-output (MU-MISO) ISAC systems when eavesdropped by malicious unmanned aerial vehicles (UAVs). It has been found that by jointly optimizing the radar receive beamformer, RIS reflection coefficient, and transmit beamforming, the system's achievable confidentiality can be maximized. Prior art also considers uplink ISAC systems, in which single-antenna users transmit to multi-antenna base stations using a distributed semi-passive IRS. Within a given framework, the transmission cycle is divided into two time periods. During each time period, the distributed semi-passive IRS simultaneously performs position sensing and data transmission. Simple and effective position sensing and beamforming design schemes have been proposed.

[0081] As high-speed rail gradually develops from informatization to intelligence, the demand for large-capacity railway communications for diversified data-intensive services is increasing, such as high-definition video surveillance, on-board broadband Internet services, railway Internet of Things services, etc. This is a huge challenge for existing railway wireless communication systems. In order to solve this problem, the present invention considers using the millimeter wave frequency band to provide services for high-speed rail wireless communication systems. The millimeter wave frequency band has a huge bandwidth of 30-300GHz and can provide multi-gigabit communication services. Millimeter waves also have the advantages of short wavelength, narrow beam, and small antenna size, and are easy to integrate into massive multiple-input-multiple-output (Massive MIMO) systems. Integrated Sensing and Communication (ISAC) refers to a new information processing technology that realizes the coordination of perception and communication functions based on software and hardware resource sharing or information sharing. By integrating communication and perception functions into one system, ISAC is expected to significantly improve spectrum and energy efficiency while reducing hardware and signal costs. This invention applies ISAC to high-speed railway communications. This technology leverages radar sensing capabilities to detect foreign objects on rails and trains, as well as train position sensing. This technology also eliminates the need for additional radar antennas, minimizing hardware costs. Therefore, this invention primarily focuses on high-speed railway millimeter-wave integrated sensing and communication systems.

[0082] Although millimeter waves have abundant bandwidth resources, their high frequency bands also bring serious penetration loss and path attenuation problems. They are easily blocked by obstacles, resulting in link interruption, which has a serious impact on communication capacity and system performance. Especially in the railway operation environment, in harsh terrain conditions such as mountainous areas and tunnels, the propagation of millimeter wave signals faces great challenges. Therefore, the present invention proposes a high-speed railway millimeter wave integrated perception and communication system assisted by an intelligent reflective surface (Reconfigurable Intelligent Surface, RIS), which utilizes the programmable properties of RIS to provide additional reflected signals by adjusting the amplitude and / or phase of the incident signal, thereby improving perception accuracy and transmission rate. In order to further improve the communication and perception performance of the high-speed railway ISAC system, the present invention considers extreme conditions, that is, the case where there is no direct link between the transceiver and the transmitter, focuses on the high-speed railway millimeter wave integrated perception and communication system assisted by RIS, and proposes an ISAC base station transmit beamforming and RIS reflection unit phase shift matrix optimization algorithm to maximize communication and rate while ensuring perception performance.

[0083] After the introduction of RIS, the communication transmission rate is maximized while maintaining the perceived performance and transmission power budget by optimizing the transmit beamforming vectors of the ISAC base station and the discrete phase shift matrix of the RIS. However, these two optimization variables are coupled within the established optimization objective, making this problem difficult to solve. Therefore, the present invention devises an alternating optimization algorithm. This decouples the global optimization problem into two subproblems, and separately designs the beamforming and RIS phase shift optimization algorithms to achieve the goal of maximizing system performance.

[0084] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each embodiment does not constitute a limitation on the embodiments of the present invention.

[0085] Before introducing a communication control method of a high-speed rail millimeter wave communication system of the present invention, the RIS-assisted Integrated Sensing and Communication (ISAC) system (i.e., a high-speed rail millimeter wave communication system) is described. In the ISAC system, there is an ISAC base station equipped with an N-antenna uniform linear array (ULA), which has both communication and sensing functions. By utilizing the sensing echo signal of the ISAC BS, it is possible to detect illegal intrusion targets on the train body, on the track, and on the platform, and it is also possible to achieve high-precision positioning of illegal intrusion targets or carriages. Whether it is detection, estimation, or recognition, the accuracy is determined by the quality of the sensing echo signal. The ISAC BS provides services for K single-antenna users, and detects or tracks targets by receiving echo signals. Due to the obstruction of obstacles such as buildings or vegetation and the weak penetration of millimeter waves, the distance from the ISAC BS to the user (i.e. Figure 1 User) and target (i.e. Figure 1 The direct link to the target in the network is blocked. Therefore, the present invention considers deploying a RIS within the system, leveraging its reflection to help signals reach the receiver. Furthermore, the RIS can enhance the reflected signal by adjusting its amplitude and phase via a centralized controller to support communication and radar detection tasks. Deploying a RIS controller with L reflection units on the side walls of a building can maintain good channel conditions between the user and the target. For convenience, a quasi-static flat-fading channel model is assumed, in which the channel varies independently within a coherent block and remains unchanged within a transmission block. Furthermore, it is assumed that channel information for all links is fully available at the ISAC BS.

[0086] Example 1

[0087] Figure 2 A flow chart of a communication control method for a high-speed rail millimeter wave communication system provided by an embodiment of the present invention; Figure 2As shown, a communication control method for a high-speed railway millimeter wave communication system includes the following steps:

[0088] S101, obtaining channel state information and a pre-constructed system capacity maximization problem function; the pre-constructed system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization.

[0089] In this step, the channel state information includes the RIS-MR channel h of user k ir,k , BS-RIS channel coefficient H bi .

[0090] More specifically, the base station BS, relay equipment MR and RIS have perfect channel state information, and there are both LoS components and NLoS components in the high-speed rail millimeter wave communication system, and all links follow Rician fading. The channel coefficient H of BS-RIS is bi It can be expressed in terms of Rician fading as:

[0091]

[0092] Among them, K R =4 is the Rice factor, is the LoS component from BS to RIS, L and N are the number of rows and columns of RIS units, respectively. It is related to the link distance and remains stable in each time slot. represents the NLoS Rayleigh fading component from BS to RIS, The element in row l and column n of and Respectively expressed as:

[0093]

[0094]

[0095] Where β0 = -61.3849 dB represents the path loss at the reference distance of 1 m, d bi is the distance from the base station to the RIS panel, α1=2.5, α2=3.6 are the path loss indices in the LoS and NLoS scenarios respectively, ψ l,n is a phase randomly distributed in [0,2π], Each term of is a cyclically symmetric complex Gaussian random variable with zero mean and unit variance, which is used to characterize small-scale fading.

[0096] Similarly, the channel of RIS-MR k can be Expressed as:

[0097]

[0098] Where, is the LoS component from RIS to MR, is the NLoS Rayleigh fading component from RIS to MR.

[0099] Accordingly, the pre-built system capacity maximization problem function is:

[0100]

[0101]

[0102]

[0103]

[0104] Where, is the set of all MRs, σ 2 is the power of the noise, γ th is the perceived signal-to-noise ratio threshold, P max is the maximum transmission power of the base station, a(θ a ,θ e ) is RIS at (θ a ,θ e ) direction, Φ is the effective phase shift introduced by all elements of RIS, Indicates the phase shift corresponding to the lth row, l=1,…,L,m l It is expressed as a quantization number, and e is the set number of quantization bits. Constraint (12a) indicates that the minimum beam pattern of the radar detection received signal must be greater than the threshold γ th ; Constraint (12b) is the BS transmit power constraint, w is the beamforming vector (i.e., beamforming); Constraint (12c) is the discrete phase shift of the RIS element.

[0105] Considering the bad situation that the LoS link between ISAC BS and Target is blocked, the present invention uses RIS to create a virtual LoS link. The perception performance is measured by the directional pattern gain of RIS toward Target. x Line, L y Column (L x ×L y =L) for RIS, its a ,θ e ) direction of the response a(θ a ,θ e )for:

[0106]

[0107] in,

[0108]

[0109]

[0110] Among them, θ a is the azimuth angle, θ e is the pitch angle. At this time, the wave pattern gain from RIS toward Target for:

[0111]

[0112] S102: Iteratively solving the beamforming sub-problem optimization and the phase shift design sub-problem optimization in the pre-constructed system capacity maximization problem function according to the channel state information and using an alternating optimization algorithm to obtain optimal beamforming and optimal phase shift.

[0113] In this step, the pre-constructed system capacity maximization problem function (i.e., Equation (12)) is a non-convex optimization problem and contains two optimization variables: beamforming w and phase shift Φ. During the sum rate optimization process, these two optimization variables, w and Φ, are coupled and difficult to optimize simultaneously. Therefore, the present invention employs an alternating optimization algorithm: first, Φ is fixed, w is optimized, then w is fixed again, Φ is optimized, and ultimately, the optimal w and Φ that satisfy the constraints are found to maximize the sum rate.

[0114] Specifically, when Φ is fixed and w is optimized, the system capacity maximization problem function (i.e., formula (12)) becomes to reasonably optimize the transmit waveform on the basis of satisfying the radar echo signal SINR constraint and the transmit power constraint to maximize the system sum rate:

[0115]

[0116]

[0117]

[0118] In the case of optimizing Φ with fixed w, the system capacity maximization problem function (i.e., formula (12)) is transformed into e The best phase shift is selected from the phase shifts to maximize the system sum rate. At this point, the optimization sub-problem can be written as:

[0119]

[0120]

[0121] l=1,…,L,m l ∈{0,2,…,2e -1}.#(14b)

[0122] Through the above-mentioned alternating optimization algorithm, the high-speed rail millimeter wave communication system can achieve the goal of maximizing the system and rate while satisfying the constraints.

[0123] It should be noted that the specific calculation process of the sum rate includes: Assume that the signal y received by user k is k for:

[0124] y k =h ir,k ΦH bi ws k +n,#(1)

[0125] in, Denote the channel coefficient matrices from the base station to RIS and from RIS to K users, respectively. represents the BS's transmit beamforming vector, s k Represents the information sent to user k, n~CN(0,σ 2 ) represents the additive white Gaussian noise received by user k. is a diagonal matrix that takes into account the effective phase shift introduced by all elements of RIS, Represents phase shift, where l=1,…,L,m l ∈{0,1,…,2 e -1}, e is the set number of quantization bits.

[0126] Assuming that all channels are block-fading and remain constant within each frame, and assuming that all channels are perfectly estimated at the BS using pilot symbols, the SINR received by the kth user is:

[0127]

[0128] At this time, all communication users normalize and rate R k for:

[0129]

[0130] Among them, B and C k They represent the available bandwidth of the spectrum and the system capacity corresponding to user K respectively.

[0131] S103: Perform vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning based on the optimal beamforming and optimal phase shift.

[0132] According to the communication control method of the high-speed rail millimeter wave communication system provided by the embodiment of the present invention, an active reflection link is provided for communication and perception through an intelligent reflection surface, and the transmitting end beamforming scheme and the RIS phase adjustment parameter matrix are jointly designed, and the corresponding optimization goal is determined to achieve the maximum system sum rate under the premise of meeting the perception performance threshold. However, since the optimization variables in the optimization process are coupled, it is difficult to obtain a closed-form solution. Therefore, the present invention decomposes the system capacity maximization problem into the optimization of the beamforming sub-problem and the optimization of the phase shift design sub-problem, and adopts an alternating optimization algorithm to iteratively solve it, so as to obtain the optimal beamforming and the optimal phase shift under the premise of meeting the perception performance threshold, so that the sum rate of the high-speed rail millimeter wave communication system is maximized. In addition, in order to further improve the robustness of the system, the present invention considers extreme cases, that is, assuming that the direct links between the transmitter and the receiver / detection target are blocked, and RIS is required to provide a reflection link for them, that is, the RIS pattern gain toward the Target is used to measure the perception performance, and the RIS device is obtained in (θ a ,θ e ) direction, thereby ensuring a certain degree of communication and perception functions even in extremely poor propagation environments.

[0133] Furthermore, based on the above embodiment, the iterative solution of the beamforming subproblem optimization and the phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function using the alternating optimization algorithm includes:

[0134] Step 1: Under a fixed phase shift, the initial beamforming is optimized using a preset beamforming optimization algorithm based on continuous convex approximation to obtain an initial optimized beamforming.

[0135] Step 2: Based on the initial optimized beamforming, the initial phase shift is optimized using a preset local search-based phase shift optimization algorithm to obtain the initial optimized phase shift.

[0136] Step 3: Using the initial optimized phase shift as a new fixed phase shift, repeat steps 1 to 3 until the system transmission rate difference between consecutive iterations is less than a preset rate threshold, thereby obtaining the optimal beamforming and the optimal phase shift.

[0137] Specifically, random initialization is performed first, and the specific initialization objects include the number of quantization bits e, the threshold γ th , convergence threshold Initial iteration factor i, Φ, W, and let Φ * is the initial Φ, W * is the initial W.

[0138] The transmission waveform and phase shift are then updated in an alternating manner until the system capacity maximization problem function converges, that is, the difference in system transmission rate between two consecutive iterations is less than a certain threshold:

[0139] More specifically, the system and rate maximization algorithm include:

[0140]

[0141]

[0142] Among them, Φ (i+1) ,W (i+1) ,R (i+1) are the intermediate values of phase shift Φ, beamforming W, and system transmission rate R in the (i+1)th iteration, Φ * ,W * ,R * They are the optimal values of phase shift Φ, beamforming W, and system transmission rate R. is the convergence threshold.

[0143] Furthermore, based on the above embodiment, step 1, in the case of a fixed phase shift, optimizes the initial beamforming using a preset beamforming optimization algorithm based on continuous convex approximation to obtain an initial optimized beamforming, including:

[0144] In the case of a fixed phase shift, the pre-constructed system capacity maximization problem function is the beamforming sub-problem optimization function:

[0145]

[0146]

[0147]

[0148] By introducing G k =diag(h ir,k )H bi , W=ww H , Transform the optimization function of the beamforming subproblem:

[0149]

[0150] in, Now, the beamforming subproblem optimization function is simplified to obtain a simplified beamforming subproblem optimization function:

[0151]

[0152]

[0153] Tr(W)≤P max , #(16b)

[0154]

[0155] Rank(W)≤1.#(16d)

[0156] F1(W) is expanded using a first-order Taylor expansion to convert the simplified beamforming subproblem optimization function into a convex function to obtain the final beamforming subproblem optimization function:

[0157]

[0158]

[0159]

[0160] st(16a)-(16d).

[0161] The final beamforming subproblem optimization function is solved using a preset convex optimization algorithm, which is a CVX solver, to obtain an initial optimized beamforming.

[0162] More specifically, the beamforming optimization algorithm based on continuous convex approximation includes:

[0163]

[0164]

[0165] Furthermore, based on the above embodiment, step 2, based on the initial optimized beamforming, optimizes the initial phase shift using a preset local search-based phase shift optimization algorithm to obtain the initial optimized phase shift, including:

[0166] Based on the initial optimized beamforming, the pre-built system capacity maximization problem function is the phase shift design sub-problem optimization function:

[0167]

[0168]

[0169] l=1,…,L,m l ∈{0,2,…,2 e -1}.#(14b)

[0170] The process of solving the optimization function of the phase shift design subproblem includes:

[0171] Step 21: Take one of the L unit phase shifts as the current phase shift φ l , the remaining L-1 unit phase shifts of the L unit phase shifts are fixed unchanged.

[0172] Step 22, the current phase shift φ l All values are traversed, and the value with the largest sum rate among the traversed values is used as the optimized phase shift of the current phase shift.

[0173] Step 22, repeating steps 21 to 22 until the L unit phase shifts all have corresponding optimized phase shifts.

[0174] Specifically, the phase shift optimization algorithm based on local search includes:

[0175]

[0176]

[0177] According to the communication control method of the high-speed railway millimeter wave communication system provided by the embodiment of the present invention, the phase shift is optimized by a phase shift optimization algorithm based on local search, which greatly reduces the time complexity compared with the existing exhaustive algorithm and makes the optimization process faster.

[0178] In addition, it should be noted that in this embodiment, the beamforming sub-problem optimization adopts a beamforming optimization algorithm based on continuous convex approximation, and the phase shift design sub-problem optimization adopts a phase shift optimization algorithm based on local search. In other embodiments of the present invention, other optimization algorithms in the prior art or deep learning algorithms may also be used, and the present invention does not limit this.

[0179] Example 2

[0180] On the basis of Example 1, this Example 2 provides a communication control system for a high-speed rail millimeter wave communication system. The communication control system of the high-speed rail millimeter wave communication system corresponds to the communication control of the above-mentioned high-speed rail millimeter wave communication system, specifically including:

[0181] The information and function acquisition module is used to obtain channel state information and a pre-built system capacity maximization problem function; the pre-built system capacity maximization problem function includes the optimization of the beamforming sub-problem and the optimization of the phase shift design sub-problem.

[0182] The function solving module is used to iteratively solve the beamforming subproblem optimization and phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function according to the channel state information and using an alternating optimization algorithm to obtain optimal beamforming and optimal phase shift.

[0183] The communication link selection module is used to perform vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning based on the optimal beamforming and optimal phase shift.

[0184] For specific details, please refer to the description of the communication control method of the high-speed rail millimeter wave communication system, which will not be repeated here.

[0185] Example 3

[0186] Embodiment 3 of the present invention provides an electronic device, including a memory and a processor, wherein the processor and the memory communicate with each other, the memory stores program instructions executable by the processor, and the processor calls the program instructions to execute a communication control method for a high-speed rail millimeter wave communication system. The method includes the following process steps:

[0187] Acquiring channel state information and a pre-constructed system capacity maximization problem function; the pre-constructed system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization;

[0188] According to the channel state information, an alternating optimization algorithm is used to iteratively solve the beamforming subproblem optimization and the phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function to obtain optimal beamforming and optimal phase shift;

[0189] Vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning are performed based on the optimal beamforming and optimal phase shift.

[0190] Example 4

[0191] Embodiment 4 of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, a communication control method for a high-speed rail millimeter wave communication system is implemented. The method includes the following steps:

[0192] Acquiring channel state information and a pre-constructed system capacity maximization problem function; the pre-constructed system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization;

[0193] According to the channel state information, an alternating optimization algorithm is used to iteratively solve the beamforming subproblem optimization and the phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function to obtain optimal beamforming and optimal phase shift;

[0194] Vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning are performed based on the optimal beamforming and optimal phase shift.

[0195] In summary, the embodiment of the present invention provides an active reflection link for communication and perception through an intelligent reflection surface, jointly designs the transmitting end beamforming scheme and the RIS phase adjustment parameter matrix, and determines that the corresponding optimization goal is to achieve the maximum system sum rate under the premise of meeting the perception performance threshold. However, since the optimization variables in the optimization process are coupled, it is difficult to obtain a closed-form solution. Therefore, the present invention decomposes the system capacity maximization problem into the optimization of the beamforming sub-problem and the optimization of the phase shift design sub-problem, and adopts an alternating optimization algorithm to iteratively solve it, so as to obtain the optimal beamforming and the optimal phase shift under the premise of meeting the perception performance threshold, so that the sum rate of the high-speed rail millimeter wave communication system is maximized. In addition, in order to further improve the robustness of the system, the present invention considers extreme cases, that is, assuming that the direct links between the transmitter and the receiver / detection target are blocked, and RIS is required to provide a reflection link for them, that is, the directional pattern gain of RIS toward the Target is used to measure the perception performance, and the RIS device is obtained in (θ a ,θ e ) direction, thereby ensuring a certain degree of communication and perception functions even in extremely poor propagation environments.

[0196] Those skilled in the art will appreciate that the accompanying drawings are merely schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0197] Each embodiment in this specification is described in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. In particular, for method or system embodiments, since they are basically similar to method embodiments, the description is relatively simple. For relevant parts, refer to the partial description of the method embodiment. The method and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Ordinary technicians in this field can understand and implement it without expending creative work.

[0198] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A communication control method for a high-speed railway millimeter wave communication system, characterized in that: include: Acquiring channel state information and a pre-constructed system capacity maximization problem function; the pre-constructed system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization; According to the channel state information, an alternating optimization algorithm is used to iteratively solve the beamforming subproblem optimization and the phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function to obtain optimal beamforming and optimal phase shift; Performing vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning based on the optimal beamforming and optimal phase shift; The channel state information includes the RIS-MR channel h of user k ir,k , BS-RIS channel coefficient H bi ; Accordingly, the pre-built system capacity maximization problem function is: Where, is the set of all relay devices MR, σ 2 is the power of the noise, γ th is the threshold of the perceived signal-to-noise ratio, P max is the maximum transmission power of the base station, a(θ a ,θ e ) is RIS at (θ a ,θ e ) direction, θ a is the azimuth angle, θ e is the elevation angle, Φ is the effective phase shift introduced by all elements of RIS, is the phase shift corresponding to the lth row, m l is the quantization number, e is the set number of quantization bits, and the constraint condition Indicates that the minimum beam pattern of the radar detection received signal is greater than the threshold γ th ; Constraints is the BS transmit power constraint, w is the beamforming vector corresponding to the beamforming; the constraint condition is the discrete phase shift of the RIS element, L is the total number of unit phase shifts, and l is the lth unit phase shift.

2. The communication control method of the high-speed railway millimeter wave communication system according to claim 1, characterized in that: The iterative solution of the beamforming sub-problem optimization and the phase shift design sub-problem optimization in the pre-constructed system capacity maximization problem function by using the alternating optimization algorithm includes: Step 1: Under a fixed phase shift, the initial beamforming is optimized using a preset beamforming optimization algorithm based on continuous convex approximation to obtain an initial optimized beamforming; Step 2: Based on the initial optimized beamforming, the initial phase shift is optimized using a preset local search-based phase shift optimization algorithm to obtain an initial optimized phase shift; Step 3: Using the initial optimized phase shift as a new fixed phase shift, repeat steps 1 to 3 until the system transmission rate difference between consecutive iterations is less than a preset rate threshold, thereby obtaining the optimal beamforming and the optimal phase shift.

3. The communication control method of the high-speed railway millimeter wave communication system according to claim 2, characterized in that: The step 1, in the case of a fixed phase shift, optimizes the initial beamforming using a preset beamforming optimization algorithm based on continuous convex approximation to obtain an initial optimized beamforming, including: In the case of a fixed phase shift, the pre-constructed system capacity maximization problem function is the beamforming sub-problem optimization function: By introducing G k =diag(h ir,k )H bi , W=ww H , The beamforming subproblem optimization function is simplified to obtain a simplified beamforming subproblem optimization function: Tr(W)≤P max Rank(W)≤1, in, The simplified beamforming subproblem optimization function F1(W) is expanded using a first-order Taylor expansion to convert the simplified beamforming subproblem optimization function into a convex function, thereby obtaining the final beamforming subproblem optimization function: Tr(W)≤P max , Rank(W)≤1; Among them, W i is the value of W in the i-th iteration; The final beamforming subproblem optimization function is solved using a preset convex optimization algorithm to obtain an initial optimized beamforming.

4. The communication control method of the high-speed railway millimeter wave communication system according to claim 3, characterized in that: The preset convex optimization algorithm is the CVX solver.

5. The communication control method of the high-speed railway millimeter wave communication system according to claim 3, characterized in that: The step 2, based on the initial optimized beamforming, optimizes the initial phase shift using a preset local search-based phase shift optimization algorithm to obtain the initial optimized phase shift, including: Based on the initial optimized beamforming, the pre-built system capacity maximization problem function is the phase shift design sub-problem optimization function: l=1,…,L,m l ∈{0,2,…,2 e -1}; The process of solving the optimization function of the phase shift design subproblem includes: Step 21: Take one of the L unit phase shifts as the current phase shift φ l , the remaining L-1 unit phase shifts of the L unit phase shifts are fixed; Step 22, the current phase shift φ l Traverse all the values and take the value with the largest sum rate among the traversed values as the optimized phase shift of the current phase shift; Step 22, repeating steps 21 to 22 until the L unit phase shifts all have corresponding optimized phase shifts.

6. A communication control system for a high-speed rail millimeter wave communication system, characterized in that: include: An information and function acquisition module, configured to acquire channel state information and a pre-built system capacity maximization problem function; the pre-built system capacity maximization problem function includes a beamforming sub-problem optimization and a phase shift design sub-problem optimization; a function solving module, configured to iteratively solve the beamforming subproblem optimization and the phase shift design subproblem optimization in the pre-constructed system capacity maximization problem function according to the channel state information and using an alternating optimization algorithm to obtain an optimal beamforming and an optimal phase shift; A communication link selection module, configured to perform vehicle-to-ground communication data transmission and / or obstacle detection and / or train positioning based on the optimal beamforming and optimal phase shift; Among them, among them, The channel state information includes the RIS-MR channel h of user k ir,k , BS-RIS channel coefficient H bi ; Accordingly, the pre-built system capacity maximization problem function is: Where, is the set of all relay devices MR, σ 2 is the power of the noise, γ th is the threshold of the perceived signal-to-noise ratio, P max is the maximum transmission power of the base station, a(θ a ,θ e ) is RIS at (θ a ,θ e ) direction, θ a is the azimuth angle, θ e is the elevation angle, Φ is the effective phase shift introduced by all elements of RIS, is the phase shift corresponding to the lth row, m l is the quantization number, e is the set number of quantization bits, and the constraint condition Indicates that the minimum beam pattern of the radar detection received signal is greater than the threshold γ th ; Constraints is the BS transmit power constraint, w is the beamforming vector corresponding to the beamforming; the constraint condition is the discrete phase shift of the RIS element, L is the total number of reflection units, and l is the lth reflection unit.

7. The communication control system of the high-speed railway millimeter wave communication system according to claim 6, characterized in that: The function solving module includes: A beamforming unit is configured to optimize the initial beamforming using a preset beamforming optimization algorithm based on continuous convex approximation under a fixed phase shift to obtain an initial optimized beamforming; A phase shift optimization unit is used to optimize the initial phase shift based on the initial optimized beamforming by using a preset local search-based phase shift optimization algorithm to obtain an initial optimized phase shift; The iterative optimization unit is configured to use the initially optimized phase shift as a new fixed phase shift and repeat the steps from the beamforming unit to the phase shift optimization unit until a difference in system transmission rate between consecutive iterations is less than a preset rate threshold, thereby obtaining an optimal beamforming and an optimal phase shift.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the communication control method of the high-speed rail millimeter wave communication system as described in any one of claims 1-5 is implemented.

9. A computer-readable storage medium, characterized in that It stores a computer program, which, when executed by a processor, implements the communication control method of the high-speed rail millimeter wave communication system as described in any one of claims 1 to 5.

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