Intelligent reflecting surface assisted high-speed train millimeter wave train-to-train communication method

Abstract

The application provides a kind of intelligent reflecting surface assisted high-speed train millimeter wave train-to-train communication method.The method includes using MR to be deployed outside the roof of high-speed train, data is transmitted by two hops between inside and outside the train, IRS is deployed in the middle of the train to assist communication, data flow transmission is directly carried out between the MR of two trains, or signal transmission is carried out between the MR of two trains through the reflection of IRS, the transmission direction of data flow is changed by changing the amplitude and phase of the reflecting unit of IRS.According to the channel model and interference model, the objective function of the maximum transmission flow number problem is established;The objective function is decomposed into three sub-problems of optimizing IRS phase matrix, link selection and time slot scheduling for solving, to obtain the maximum data flow transmission scheme.The application optimizes the link selection problem between direct link and reflection link, and designs a time slot allocation algorithm to maximize the number of flows scheduled by the system.

Description

Technical Field

[0001] This invention relates to the field of vehicle-to-vehicle communication technology, and in particular to a high-speed train millimeter-wave vehicle-to-vehicle communication method assisted by an intelligent reflective surface. Background Technology

[0002] The future development needs of high-speed railways will be high data volume, low cost, and intelligence. In order to reduce the operating costs and system load of train-to-ground communication, many applications such as real-time monitoring of high-speed rail communication require high-speed transmission, which is difficult to achieve with the current high-speed rail system.

[0003] The vehicle-to-vehicle communication system offers two transmission links: one is direct communication between the two trains' MR (Mobile Relay) links, i.e., MR-MR direct links; the other is established by using MR-IRS (Intelligent Reflecting Surface)-MR reflection links when the MR-MR direct link is blocked, the channel quality is poor, or the communication distance exceeds the reachable range. Under different channel conditions, the choice of different transmission links will affect the final system performance.

[0004] Considering the regularity of high-speed rail operation, the system can implement multi-frame scheduling. Different time slot scheduling schemes can significantly affect system performance. Simultaneously, the streams transmitted within a slot interfere with each other, affecting the signal-to-interference-plus-noise ratio and reducing the transmission rate. Therefore, it is necessary to allocate the concurrently transmitted streams. Based on this, this invention optimizes the time slot allocation scheme, thereby improving system performance.

[0005] Millimeter-wave communication for high-speed rail has attracted widespread attention in academia. One approach proposes a non-uniform beamforming mechanism that minimizes performance differences between beams by dividing the coverage area corresponding to different beams. Another approach proposes an adaptive non-uniform hybrid beamforming algorithm to minimize location-based rate differences.

[0006] Although high-speed rail communication has many characteristics that lead to large performance fluctuations, its movement trajectory is predictable, and this characteristic can be utilized to improve communication quality. By leveraging the regularity of train trajectories, a fast beam alignment mechanism is proposed to achieve rapid beam switching.

[0007] As a promising new technology, IRS (Intelligent Radio Switching) technology can realize reconfigurable intelligent wireless channels and radio propagation environments in B5G and 6G wireless communication systems. From a practical deployment perspective, IRS also has significant advantages. IRS is small and lightweight, making it easy to deploy on walls, ceilings, building facades, etc.; its low cost allows for large-scale deployment. Therefore, IRS can be manufactured to be installed on surfaces of any shape to meet different communication scenarios. Secondly, applying IRS to existing systems does not require changes to the operating standards of the system hardware; only the communication protocol needs to be modified.

[0008] For IRS-assisted millimeter-wave high-speed rail communication systems, an expression for the outage probability of the downlink high-speed rail communication link assisted by IRS has been derived, verifying the effectiveness of the IRS. Based on the SNR distribution, an expression for the outage probability is derived, and a power optimization problem is proposed with the goal of minimizing the outage probability. The impact of IRS deployment location on performance is also studied. In the VI2 scenario with dual IRS assistance, closed-form expressions for outage probability and spectral efficiency are derived for the Nakagami fading environment. In the vehicle communication scenario, an IRS selection mechanism is proposed for multiple IRS deployment strategies, selecting the IRS with the highest SNR. Compared with the mid-transmission relay scheme, the IRS can provide higher traversal capacity, energy efficiency, and lower error probability, and its closed-form expression is derived.

[0009] The shortcomings of the aforementioned existing methods for optimizing the scheduling of IRS-assisted high-speed rail communication systems include: these schemes focus on train-to-ground communication, i.e., data transmission between trains and base stations. However, in the vision of intelligent high-speed rail networks, train-to-train communication is an essential component, where trains directly transmit information via device-to-device (D2D) communication without relying on base stations, thereby reducing the amount of data exchanged between train-to-ground links and reducing system load. Research on train-to-train communication in high-speed rail is still limited. To reduce electromagnetic wave loss when penetrating the train body, high-speed rail communication is typically implemented using MR (Metal-to-Metal) communication deployed on the roof. Therefore, MR-MR communication between trains on different tracks still requires further research.

[0010] These solutions address the scheduling problem in high-speed rail communication systems by focusing on a single frame, where signaling transmission is required before scheduling for each frame. In this scenario, single-frame scheduling fails to utilize the regularity of high-speed rail trajectories, wasting transmission resources and reducing system throughput. In the high-speed rail scenario, train position and speed are predictable; utilizing this information for multi-frame scheduling can reduce signaling overhead. Therefore, multi-frame scheduling in high-speed rail systems requires further research.

[0011] Because D2D communication distances are short, and considering the high-speed movement of trains, the link is likely to fall outside the communication range, leading to communication interruptions. To address this issue, IRS (Inter-Railway Controller) is typically deployed between the transceiver ends to increase communication coverage. However, research on IRS-assisted inter-railway communication systems remains limited. Summary of the Invention

[0012] Embodiments of the present invention provide a smart reflective surface-assisted high-speed train millimeter-wave vehicle-to-vehicle communication method to achieve efficient transmission of data streams in high-speed train millimeter-wave vehicle-to-vehicle communication.

[0013] To achieve the above objectives, the present invention adopts the following technical solution.

[0014] A smart reflective surface-assisted millimeter-wave vehicle-to-vehicle communication method for high-speed trains includes:

[0015] Mobile relays (MRs) are deployed on the exterior of the roof of high-speed trains, using two-hop communication between the inside and outside of the train to transmit data. Intelligent reflective surfaces (IRSs) are deployed in the middle of the train to assist communication. Data streams can be transmitted directly between the MRs of two trains, or signals can be transmitted between the MRs of two trains through the reflection of the IRS. The direction of data stream transmission can be changed by altering the amplitude and phase of the reflection unit of the IRS.

[0016] Preferably, channel models for the MR-IRS-MR link and MR-MR link between two trains, as well as interference models between multiple data streams, are constructed, and an objective function for maximizing the number of transmission streams is established based on the channel models and interference models.

[0017] The objective function is decomposed into three sub-problems: optimizing the IRS phase matrix, the link selection algorithm, and the scheduling algorithm. These sub-problems are then solved to obtain a data flow transmission scheme that maximizes the data flow.

[0018] Preferably, the channel models for constructing the MR-IRS-MR link and MR-MR link between two trains, as well as the interference model between multiple data streams, include:

[0019] Assuming that MRs operate in half-duplex mode, two streams with the same node cannot transmit simultaneously; these two streams are said to be adjacent. ij =1 indicates that there are some common nodes in the sending and receiving nodes of stream i and stream j;

[0020] The channel model for constructing the MR-IRS-MR link is as follows:

[0021] For the i-th flow, t i For the sending end, r i For the receiving end, Let r be the channel coefficient between the transceiver and the reflection unit in the y-th row and z-th column of the IRS. i The received signal is:

[0022] in p represents the phase of the reflection cell in the y-th row and z-th column of the IRS. i Indicates the sender t of the i-th stream. i The transmission power, σ represents the normalized transmitted symbol. 2 =N0W is the noise power, N0 is the one-sided power spectral density, and W is the system bandwidth;

[0023] Using the Ricean channel model:

[0024]

[0025] Where β is the Rice factor of the MR-IRS-MR link, The LoS channel component of the MR-IRS-MR relay link is constant during the coherence time. This represents the NLoS channel component of the MR-IRS-MR relay link. and The following models are used respectively:

[0026]

[0027] Where β0 = -61.3849 dB represents the channel gain at a reference distance of 1 meter. Indicates t i The distance between the y-th row and z-th column reflective element of the IRS Indicates r i The distance between the reflection unit in the y-th row and z-th column of the IRS, λ is the path fading exponent for the LosS scene, θ' represents a random variable uniformly distributed between [0, 2π], and λ' is the path fading exponent for the NLoS scene. Let represent a random variable that follows a cyclic symmetric complex Gaussian distribution with a mean of 0 and a variance of 1.

[0028] The phase amplitude adjustment of the reflective element in the y-th row and z-th column of the IRS panel is expressed as follows: j represents the imaginary unit. This represents the phase shift coefficient of the IRS. Indicates the amplitude reflection coefficient of the IRS. Corresponding to the phase shift and amplitude of the reflecting element, respectively, the amplitude of the reflecting elements of all IRS remains unchanged, i.e. Divide the interval [0, 2π) evenly using b bits.

[0029]

[0030] The channel model for constructing an MR-MR link is as follows:

[0031]

[0032] Where h0 is a parameter that follows Distributed random variables For sending node t i to r i The distance, λ is the path fading exponent in the Loss of Spectrum (LoS) scenario, p i For transmission power, This indicates a normalized transmission symbol.

[0033] Assume that the MR-IRS-MR channel and the MR-MR channel remain unchanged within each frame but change between different frames. Each frame is divided into a control phase and a transmission phase. There are a total of K frames, and each frame includes T transmission time slots.

[0034] The channel model for constructing the interference model is:

[0035] Assuming that any data stream can only choose either a direct link or a reflected link, two binary variables α are defined. o,d,t and α d,t,k This indicates which link is used for communication. When multiple streams are transmitted in the same time slot, in the k-th frame and t-th time slot, r i The received signal-to-interference-plus-noise ratio is:

[0036]

[0037] This represents the transmission power of the i-th stream. This indicates whether the i-th stream uses an MR-MR direct link to transmit data in the k-th frame and the t-th time slot. Indicates adoption. This indicates that it will not be adopted. Indicates whether the i-th stream uses the MR-IRS-MR reflection link to transmit data in the k-th frame and t-th time slot, α i o,t,k =1 indicates adoption, α i o,t,k =0 indicates that it is not used. It represents the square of the channel coefficient in the k-th frame and the t-th time slot. This represents the transmission power of the j-th stream. This indicates whether the j-th stream uses an MR-MR direct link to transmit data in the t-th time slot of the k-th frame. Indicates adoption. This indicates that it will not be adopted. This indicates whether the j-th stream uses the MR-IRS-MR reflection link to transmit data in the t-th time slot of the k-th frame. Indicates adoption. This indicates that it will not be adopted. (C) k,t σ represents the set of data streams transmitted in the t-th time slot of the k-th frame. 2 Indicates noise power.

[0038] Preferably, the objective function for maximizing the number of transport streams based on the channel model and the interference model includes:

[0039] According to Shannon's formula, the transmission rate of the i-th stream in the k-th frame and the t-th time slot is... for:

[0040]

[0041] The total throughput of the i-th stream in K frames is the ratio q of the total transmitted data volume to the total transmission time. i for:

[0042]

[0043] Where K represents the total number of frames in the system, T represents the total number of time slots in each frame, ΔT is the time slot length, and T s It is the scheduling duration within each frame;

[0044] Each flow is accompanied by a Quality of Service (QoS) constraint during its generation. The QoS constraint for the i-th flow is: If the total throughput of the i-th stream reaches the QoS constraint within the specified number of frames, the flag bit of this stream is set to 1, that is:

[0045]

[0046] The objective function for maximizing the number of transport streams is set as follows:

[0047]

[0048] Where F represents the total number of streams generated by the system that need to be transmitted. φ m This represents the phase shift of the m-th reflecting unit in the IRS. The IRS has a total of N... 2 There are n reflection units, and the objective function is to maximize the number of successfully transmitted streams. The optimization variable Θ is an N×N matrix, where each element represents the phase shift of the corresponding reflection unit in the IRS. d It is a matrix of size F×K×T, whose elements are... A oIt is a matrix of size F×K×T, whose elements are... Constraint (1) indicates that a stream can only choose one transmission path in any frame and any time slot, either an MR-MR direct link or an MR-IRS-MR reflection link. Constraint (2) is a half-duplex working constraint, indicating that when the transmitting and receiving nodes of two streams have the same node, the two streams cannot be scheduled at the same time, and at most one stream can be transmitted. Constraint (3) indicates that the amplitude of each reflection unit of the IRS remains unchanged, and only the phase is optimized.

[0049] Preferably, the process of decomposing the objective function into three sub-problems—optimizing the IRS phase matrix, the link selection algorithm, and the scheduling algorithm—to obtain a maximized data flow transmission scheme includes:

[0050] Break it down into 3 subproblems and solve them separately.

[0051] 1) Optimize the IRS phase matrix: When optimizing the IRS phase matrix, first optimize the phase of the first IRS reflection unit, and fix the remaining N. 2 -1 phase of the reflection unit, the first reflection unit traverses all 2 b -1 phase, find the one that makes The maximized phase value is used as the phase optimization result for the first IRS reflector. Then, the same process is used to optimize the phase of the second IRS reflector, and this process is repeated until N. 2 The phase of each reflector unit has been optimized.

[0052] 2) Link selection algorithm:

[0053] Here, S represents the set of F streams generated by the system. For any stream, the factors influencing link selection include channel coefficients and QoS constraints. Since the channel coefficients are assumed to remain constant within each frame in this invention, the link selection result remains constant within each frame, only varying between different frames. The link selection algorithm follows the principle of always selecting the link with the shorter transmission time. Under the premise of fixed QoS constraints, better channel quality means a higher signal-to-noise ratio, resulting in a faster transmission rate and thus a shorter transmission time. Therefore, in the link selection process for a stream, the phase of the IRS reflection unit of its IRS link is first optimized. Then, the channel coefficients of the optimized MR-IRS-MR link and the MR-MR direct link are compared. The link with the larger channel coefficient is the link selection result for this stream. Then, the maximum achievable throughput of this stream is calculated, that is, the throughput that can be obtained by using all time slots for this stream transmission under the condition of no interference from other streams. If the maximum achievable throughput is less than the QoS constraint, it means that this stream cannot be successfully scheduled in this system under any circumstances, and it is removed from S.

[0054] 3) Scheduling Algorithm

[0055] An interference graph-based scheduling algorithm was designed. Each vertex in the interference graph represents a flow, and the edges between vertices represent potential interference between two flows. Interference only occurs when different flows are transmitted in the same time slot; flows transmitted in different time slots do not interfere with each other. The interference received by the receiving node of flow j from the sending node of flow i is as follows:

[0056] or

[0057] The calculation of interference is related to the choice of link. The former corresponds to the case where flow i uses an MR-IRS-MR reflection link, and the latter corresponds to the case where flow i uses an MR-MR direct link. The formula for calculating the potential interference between any flow i and flow j is as follows:

[0058]

[0059] If flow i and flow j are adjacent, their potential interference is set to infinity. If simultaneous transmission of flows causes a significant decrease in the throughput of one of the flows, their potential interference is also set to infinity. δ is used as a threshold value for the potential interference; if the value exceeds this threshold, the potential interference is set to infinity. Let S be the square of the channel coefficient of target stream i, and let S be the set of all transport streams generated by the system, N com To complete the set of scheduled flows, F k L is the set of streams that still need to be scheduled in the k-th frame. k It is the set of streams transmitted simultaneously in the k-th frame. In the k-th frame, the number of time slots required for each stream to complete scheduling without interference is calculated, and the stream i with the fewest required time slots is selected and placed into L. k Inside, then iterate through F. k For each of the other flows in the stream, denoted as vertex j, the sum of that vertex and L is calculated. k Potential interference in each flow, if flow j and L k If the potential disturbance of any flow in F is infinite, then j will be transferred from F. k Delete it. For F k Other streams in the stream, select and L k The flow with the least potential interference within the flow, add L k ;

[0060] Repeat this step until F k If empty, during transmission, for each time slot, L... k Each stream in the process calculates its transmission rate and remaining QoS requirements, once L kIf a flow meets the QoS requirements, the transmission process for this round is terminated, the flow is removed from the interference graph, and the above steps are repeated until all flows are scheduled or the time slot reaches its limit.

[0061] By optimizing the three sub-problems of IRS phase matrix, link selection algorithm, and scheduling algorithm, the optimization result of optimization problem P1 is obtained. The optimization result includes the phase optimization of the IRS reflection unit of the MR-IRS-MR link of each flow, the transmission link selection result of each flow in each frame, and the set of flows transmitted simultaneously in any time slot. The total achievable throughput of the system is calculated based on the set of flows transmitted in each time slot, which is the sum of the achievable throughput of each flow.

[0062] As can be seen from the technical solutions provided by the embodiments of the present invention described above, the present invention considers a high-speed rail millimeter-wave vehicle-to-vehicle communication system assisted by an intelligent reflective surface, where the train communicates via MR; when the LoS link is blocked or the direct link is out of communication range, an IRS link is used to achieve communication; and system performance is enhanced by adjusting the phase of each reflective unit of the intelligent reflective surface. To address the different quality of service requirements of different data streams, the present invention optimizes the link selection problem between the direct link and the reflective link, and designs a time slot allocation algorithm to maximize the data stream scheduled by the system while improving system throughput.

[0063] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0064] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0065] Figure 1 This is a schematic diagram illustrating how two trains with different tracks communicate with each other using MR on the roof during close-range phases, as provided in an embodiment of the present invention. Detailed Implementation

[0066] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0067] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated 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 say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or couplings. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0068] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0069] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments. These embodiments do not constitute a limitation on the embodiments of the present invention.

[0070] This invention considers millimeter-wave band communication (electromagnetic waves with frequencies from 30 GHz to 300 GHz), which can support high transmission rates of Gbps. Furthermore, to avoid severe penetration loss caused by the metal vehicle body, the MR (Metal Transport Modulation) is deployed on the exterior of the vehicle roof, employing two-hop communication between the inside and outside of the vehicle to transmit data. This invention provides a link selection scheme, selecting the transmission path by comparing the transmission times required for different data streams.

[0071] This invention focuses on the research of vehicle-to-vehicle communication systems assisted by mobile relays. To address the problems of severe attenuation, poor diffraction and scattering capabilities, and susceptibility to blockage leading to transmission link interruptions in millimeter-wave signals, this invention employs an IRS-assisted high-speed rail millimeter-wave communication system. An IRS is deployed between the two vehicles to assist communication. By altering the amplitude and phase of the IRS's reflecting elements, the signal is directed towards the target direction, thereby improving signal quality.

[0072] This invention decomposes the original mixed-integer programming problem into three sub-problems: phase optimization, transmission path selection, and a graph-based scheduling algorithm. First, the phase matrix of the IRS is optimized to improve signal strength. Second, transmission paths are selected for each stream based on transmission time. Finally, a scheduling algorithm based on an interference graph is proposed to solve the problem. Different vertices in the interference graph represent different data streams to be transmitted, and the edges between vertices represent interference between streams. Transmission constraints are transformed into the magnitude of interference values, and a time-slot scheduling algorithm is designed based on this interference graph.

[0073] A schematic diagram of a method for two trains with different track gauges to communicate with each other using MR on the roof of the train during close-range phases is provided in this embodiment of the invention. Figure 1 As shown, the communication bandwidth is 850MHz. Each of the two trains is equipped with 24 evenly distributed MRs, each MR having a height of 3m. The IRS panel is deployed in the middle of the train, and the reflector unit in the lower left corner of the IRS has a height of 3m.

[0074] An IRS panel is a two-dimensional plane composed of numerous reflective elements. By artificially manipulating incident electromagnetic waves, it controls the electromagnetic propagation environment. An IRS reflective element is a metamaterial with subwavelength dimensions, capable of reflecting, scattering, and absorbing incident electromagnetic waves. By adjusting the amplitude and phase of the IRS reflective elements, the propagation direction of an infinite signal can be controlled, achieving the purpose of enhancing the target signal or suppressing interference signals.

[0075] The two trains move at speeds v1 and v2, respectively. The transmit power of the MR is 23dBm. Several streams with different service requirements are randomly generated between the MRs of the trains, and the transmitting and receiving ends of each stream are not on the same train. The scheduling process is limited to K frames. To schedule as many streams as possible, it is necessary to determine the streams transmitted simultaneously in each time slot based on factors such as the location of the MR and channel quality, and to optimize the phase of the IRS reflection unit. It should be noted that all transmissions are carried out on the same frequency band, so the simultaneously transmitted streams interfere with each other, thus affecting the quality of the received signal. The position of the train remains unchanged within a frame, but changes between different frames, and the change in position leads to changes in the channel state. When the direct link between the transmitting and receiving ends of the streams is of poor quality or exceeds the communication range, auxiliary communication can be achieved using the IRS. For example, if the stream between MR1M of train 1 and MR2M of train 2 is blocked by an obstacle and direct link communication is not possible, then communication is achieved using an MR-IRS-MR link, and a Loss of Space (LoS) link is constructed through the IRS. If the streams transmitted at the same time also include the stream between MR11 and MR21, then interference will occur between these two streams. That is, MR2M will receive interference from MR12, and MR21 will receive interference from MR1M.

[0076] In this model, MRs operate in half-duplex mode; two streams with the same node cannot transmit simultaneously and are said to be adjacent. Z ij =1 indicates that there are common nodes in the sending and receiving nodes of stream i and stream j, whether they are sending nodes or receiving nodes.

[0077] (2) Channel Model

[0078] ①MR-IRS-MR link: For the i-th flow, t i For the sending end, r i As the receiving end, let... For the channel coefficients corresponding to the y-th row and z-th column of the IRS, therefore r i The received signal is:

[0079]

[0080] in p represents the phase of the reflection cell in the y-th row and z-th column of the IRS. i Indicates the sender t of the i-th stream. i The transmission power, σ represents the normalized transmitted symbol. 2 =N0W is the noise power, N0 is the one-sided power spectral density, and W is the system bandwidth.

[0081] Using the Ricean channel model:

[0082]

[0083] Where β is the Rice factor of the MR-IRS-MR link, The LoS channel component of the MR-IRS-MR relay link is constant during the coherence time. This represents the NLoS channel component of the MR-IRS-MR relay link. and The following models are used respectively:

[0084]

[0085] Where β0 = -61.3849 dB represents the channel gain at a reference distance of 1 meter. Indicates t i The distance between the y-th row and z-th column reflective element of the IRS Indicates r i The distance between the reflection unit in the y-th row and z-th column of the IRS, λ is the path fading exponent for the LosS scene, θ' represents a random variable uniformly distributed between [0, 2π], and λ' is the path fading exponent for the NLoS scene. Let represent a random variable that follows a cyclic symmetric complex Gaussian distribution with a mean of 0 and a variance of 1.

[0086] The phase amplitude adjustment of the reflective element in the y-th row and z-th column of the IRS panel is expressed as follows: j represents the imaginary unit. This represents the phase shift coefficient of the IRS. Indicates the amplitude reflection coefficient of the IRS. These correspond to the phase shift and amplitude of the reflecting element, respectively. This invention uses a constant amplitude value, meaning the amplitude of the reflecting elements of all IRS remains unchanged. Furthermore, from a practical perspective, the phase shift is usually discrete, that is, the interval [0, 2π) is uniformly divided using b bits.

[0087]

[0088] ②MR-MR link:

[0089] Where h0 is a parameter that follows Distributed random variables For sending node t i to r i The distance, λ is the path fading exponent in the Loss of Spectrum (LoS) scenario, p i For transmission power, This indicates a normalized transmission symbol.

[0090] It should be noted that, due to the short frame length, this invention assumes that the MR-IRS-MR channel and the MR-MR channel remain constant within each frame, but vary between different frames. Each frame is divided into a control phase and a transmission phase. There are a total of K frames, and each frame includes T transmission time slots.

[0091] (4) Interference Model

[0092] Since direct links are typically several orders of magnitude faster than reflected links, the benefit of reflected links is minimal when a direct link exists. Therefore, we assume that any data stream can only choose either a direct link or a reflected link, and define two binary variables α. o,d,t and α d,t,k This indicates which link is used for communication. Interference can occur when multiple streams are transmitted in the same time slot. For convenience, let... This represents the square of the channel coefficient in the k-th frame and the t-th time slot. Therefore, in the k-th frame and the t-th time slot, r i The received signal-to-interference-plus-noise ratio is:

[0093]

[0094] in, This represents the transmission power of the i-th stream. This indicates whether the i-th stream uses an MR-MR direct link to transmit data in the k-th frame and the t-th time slot. Indicates adoption. This indicates that it will not be adopted. This indicates whether the i-th stream uses the MR-IRS-MR reflection link to transmit data in the t-th time slot of the k-th frame. Indicates adoption. This indicates that it will not be adopted. It represents the square of the channel coefficient in the k-th frame and the t-th time slot. This represents the transmission power of the j-th stream. This indicates whether the j-th stream uses an MR-MR direct link to transmit data in the t-th time slot of the k-th frame. Indicates adoption. This indicates that it will not be adopted. This indicates whether the j-th stream uses the MR-IRS-MR reflection link to transmit data in the t-th time slot of the k-th frame. Indicates adoption. This indicates that it will not be adopted. (C) k,t σ represents the set of data streams transmitted in the t-th time slot of the k-th frame. 2 Indicates noise power.

[0095] As shown in the above formula, the signal-to-interference-plus-noise ratio (SIR) of any stream is not only related to its own signal quality but also to the interference from other simultaneously transmitted streams. The greater the interference, the lower the SIR of the current stream, and thus the lower the transmission rate. To achieve the target QoS, more time slots are needed for transmission. With the goal of maximizing the number of scheduled streams, the aim is to use time slot scheduling to ensure that each stream completes transmission using as few time slots as possible, thereby reserving more time slots for other streams.

[0096] (4) Establishing the problem of maximizing the number of transmission streams

[0097] According to Shannon's formula, the transmission rate of the i-th stream in the k-th frame and the t-th time slot is... for:

[0098]

[0099] The total throughput of the i-th stream in K frames is the ratio q of the total transmitted data volume to the total transmission time. i for:

[0100]

[0101] Where K represents the total number of frames in the system, T represents the total number of time slots in each frame, ΔT is the time slot length, and T sIt is the scheduling duration within each frame.

[0102] Each flow is generated with Quality of Service (QoS) constraints. If the total throughput within the specified number of frames meets the QoS constraint, the flag for this stream is set to 1, i.e.

[0103]

[0104] Therefore, the proposed problem of maximizing the number of transport streams can be modeled as follows:

[0105]

[0106] Where F represents the total number of streams generated by the system that need to be transmitted. φ m This represents the phase shift of the m-th reflecting unit in the IRS. The IRS has a total of N... 2 There are n reflection units, and the objective function is to maximize the number of successfully transmitted streams. The optimization variable Θ is an N×N matrix, where each element represents the phase shift of the corresponding reflection unit in the IRS. d It is a matrix of size F×K×T, whose elements are... A o It is a matrix of size F×K×T, whose elements are... Constraint (1) indicates that a stream can only choose one transmission path in any frame and any time slot, either an MR-MR direct link or an MR-IRS-MR reflection link. Constraint (2) is a half-duplex working constraint, indicating that when the transmitting and receiving nodes of two streams have the same node, the two streams cannot be scheduled at the same time, and at most one stream can be transmitted. Constraint (3) indicates that the amplitude of each reflection unit of the IRS remains unchanged, and only the phase is optimized.

[0107] To solve problem P1, we break it down into three subproblems and solve them separately.

[0108] 1) Optimize the IRS phase matrix:

[0109]

[0110]

[0111] When optimizing the IRS phase matrix, first optimize the phase of the first IRS reflection unit, and fix the remaining N. 2 -1 phase of the reflection unit, the first reflection unit traverses all 2 b -1 phase, find the one that makes The maximized phase value is used as the phase optimization result for the first IRS reflector. Then, the same process is used to optimize the phase of the second IRS reflector, and this process is repeated until N. 2 The phase of each reflector unit has been optimized.

[0112] 2) Link selection algorithm:

[0113] For any given stream, the first step is to determine whether to use a direct link or a reflected link for transmission, taking into account QoS requirements and channel quality. Since the channel remains constant within each frame, the link selection also remains constant. For each stream, the maximum transmission rate achievable using either link is calculated, and the link with the higher transmission rate is selected. Furthermore, if neither link can meet the QoS requirements, the stream is deleted. The complete algorithm is shown below.

[0114]

[0115]

[0116] Here, S represents the set of F streams generated by the system. For any stream, the factors influencing link selection include channel coefficients and QoS constraints. Since the channel coefficients are assumed to remain constant within each frame in this invention, the link selection result remains constant within each frame, only varying between different frames. The link selection algorithm follows the principle of always selecting the link with the shorter transmission time. Under the premise of fixed QoS constraints, better channel quality means a higher signal-to-noise ratio, resulting in a faster transmission rate and thus a shorter transmission time. Therefore, in the link selection process for a stream, the phase of the IRS reflection unit of its IRS link is first optimized. Then, the channel coefficients of the optimized MR-IRS-MR link and the MR-MR direct link are compared. The link with the larger channel coefficient is the link selection result for this stream. Then, the maximum achievable throughput of this stream is calculated, that is, the throughput that can be obtained by using all time slots for this stream transmission under the condition of no interference from other streams. If the maximum achievable throughput is less than the QoS constraint, it means that this stream cannot be successfully scheduled in this system under any circumstances, and it is removed from S.

[0117] 3) Scheduling Algorithm

[0118] A scheduling algorithm based on an interference graph was designed. Each vertex in the interference graph represents a flow, and the edges between vertices represent potential interference between two flows. Interference only occurs when different flows are transmitted within the same time slot; flows transmitted in different time slots do not interfere with each other. The interference received by the receiving node of flow j from the sending node of flow i is:

[0119]

[0120] The calculation of interference is related to the choice of link. The former corresponds to the case where flow i uses an MR-IRS-MR reflection link, while the latter corresponds to the case where flow i uses an MR-MR direct link. The formula for calculating the potential interference between any flow i and flow j is as follows:

[0121]

[0122] If flow i and flow j are adjacent, their potential interference is set to infinity to ensure that they are not scheduled simultaneously, thus meeting the requirements for half-duplex operation. Additionally, if simultaneous transmission of flows causes a significant drop in throughput for one of the flows, their potential interference is also set to infinity to avoid simultaneous scheduling. δ is used as a threshold for the potential interference value; if it exceeds this threshold, the potential interference is set to infinity. Let S be the square of the channel coefficients of target stream i. Let S be the set of all transport streams generated by the system, and N be the set of all transport streams generated by the system. com To complete the set of scheduled flows, F k L is the set of streams that still need to be scheduled in the k-th frame. k It is the set of streams transmitted simultaneously in the k-th frame. In the k-th frame, first calculate the number of time slots required for each stream to complete scheduling without interference, and select the stream i with the fewest required time slots to put it into L. k Inside, then iterate through F. k For each of the other flows in the stream, denoted as j (for each vertex), the sum of that vertex and L is calculated. k Potential interference in each flow, if flow j and L k If the potential disturbance of any flow in F is infinite, then j will be transferred from F. k Delete it. For F k Other streams in the stream, select and L k The flow with the least potential interference within the flow, add L k Repeat this step until F. k Empty. During transmission, for each time slot, L... k Each stream in the process calculates its transmission rate and remaining QoS requirements, once L k If a flow meets the QoS requirements, the transmission process terminates and the flow is removed from the interference graph. This process is repeated until all flows are scheduled or the time slot limit is reached. The following algorithm summarizes the specific execution steps:

[0123]

[0124]

[0125]

[0126] By optimizing the three sub-problems of IRS phase matrix, link selection algorithm, and scheduling algorithm, the optimization result of optimization problem P1 is obtained. The optimization result includes the phase optimization of the IRS reflection unit of the MR-IRS-MR link of each flow, the transmission link selection result of each flow in each frame, and the set of flows transmitted simultaneously in any time slot. The total achievable throughput of the system is calculated based on the set of flows transmitted in each time slot, which is the sum of the achievable throughput of each flow.

[0127] In summary, this invention aims to improve the data stream transmission quality of inter-railway vehicle-to-vehicle communication systems. It proposes an IRS-assisted high-speed rail millimeter-wave vehicle-to-vehicle communication system model. Under the constraints of service quality and the amplitude modulus of the reflection unit constant, a successful scheduling stream optimization problem is established, and the phase matrix of the IRS reflection unit and the binary scheduling matrix are jointly optimized.

[0128] This invention proposes a link selection transmission scheme, choosing the better-performing link from MR-MR direct links and MR-IRS-MR reflective links. Furthermore, when the direct link is blocked or the channel quality is poor, a reflective link is used to construct a Loss of Space (LoS) channel for data transmission. The IRS is utilized to expand the communication range between MRs and enhance system performance. Considering the half-duplex operation of MRs, the scheduling process must consider not only interference between flows but also half-duplex constraints. Therefore, this invention proposes a time-slot scheduling algorithm based on an interference graph. First, the half-duplex communication constraints are transformed into potential interference values. Then, the set of simultaneous transmissions is determined by calculating the potential interference values ​​between vertices in the interference graph, thereby performing scheduling. Finally, to maximize the number of scheduled flows, the current scheduling process is terminated whenever a flow completes transmission, thus ensuring that the flow with the fewest required time slots is always given the highest priority.

[0129] This invention improves system performance by optimizing time slot allocation and phase shift. Considering the predictable nature of high-speed rail tracks, this invention utilizes the ability to predict train locations for multi-frame optimization, thereby maximizing the number of successfully transmitted streams.

[0130] This invention considers vehicle-to-vehicle communication, enabling inter-rail trains to send information directly without relying on base stations, thereby reducing the amount of data exchanged between vehicle and ground links and thus reducing system load. This invention also optimizes the time slot allocation scheme, improving system performance.

[0131] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of one embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing the present invention.

[0132] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that the present invention can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of the present invention.

[0133] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for apparatus or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The apparatus and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0134] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-speed train millimeter-wave vehicle-to-vehicle communication method assisted by a smart reflective surface, characterized in that, include: Mobile relays (MRs) are deployed on the exterior of the roof of high-speed trains, using two-hop communication between the inside and outside of the train to transmit data. Intelligent reflective surfaces (IRSs) are deployed in the middle of the train to assist communication. Data streams can be transmitted directly between the MRs of two trains, or signals can be transmitted between the MRs of two trains through the reflection of the IRS. The direction of data stream transmission can be changed by changing the amplitude and phase of the reflection unit of the IRS. Construct channel models for the MR-IRS-MR link and MR-MR link between two trains, as well as interference models between multiple data streams. Based on the channel models and interference models, establish an objective function for maximizing the number of transmission streams. The objective function is decomposed into three sub-problems: optimizing the IRS phase matrix, the link selection algorithm, and the scheduling algorithm. These sub-problems are then solved to obtain a data flow transmission scheme that maximizes the data flow.

2. The method according to claim 1, characterized in that, The aforementioned channel models for constructing the MR-IRS-MR link and MR-MR link between two trains, as well as the interference model between multiple data streams, include: If MRs operate in half-duplex mode, two streams with the same node cannot transmit simultaneously; these two streams are said to be adjacent. Represents a stream Sending and receiving nodes and streams There are identical nodes in the sending and receiving nodes; The channel model for constructing the MR-IRS-MR link is as follows: For the Stream, For the sending end, For the receiving end, For the transceiver and IRS OK Channel coefficients between column reflection units, The received signal is: ; in Indicates the IRS number OK The phase of the column reflector unit, Indicates the first The sender of the stream The transmission power, Indicates the normalized transmission symbol. For noise power, For one-sided power spectral density, For system bandwidth; Using the Ricean channel model: in, Rice factor for the MR-IRS-MR link The LoS channel component of the MR-IRS-MR relay link is constant during the coherence time. This represents the NLoS channel component of the MR-IRS-MR relay link. and The following models are used respectively: in, dB represents the channel gain at a reference distance of 1 meter. express and IRS OK The distance between the column reflective units, express and IRS OK The distance between the column reflective units, It is the path decay index in the Loss of Path (LoS) scenario. Indicating obedience A random variable that is uniformly distributed between two points. It is the path fading index in NLoS scenarios. Let represent a random variable that follows a cyclic symmetric complex Gaussian distribution with a mean of 0 and a variance of 1. IRS panel OK The phase of the reflective unit of the column is expressed as j represents the imaginary unit. This represents the phase shift coefficient of the IRS. Indicates the amplitude reflection coefficient of the IRS. , Corresponding to the phase shift and amplitude of the reflecting element, respectively, the amplitude of the reflecting elements of all IRS remains unchanged, i.e. ,use Each bit will be in the interval Evenly divided, ; The channel model for constructing an MR-MR link is as follows: ； in, To obey the parameter is Random variables with a Nakagami distribution For sending node arrive distance, It is the path decay index in the Loss of Path (LoS) scenario. For transmission power, Indicates the normalized transmission symbol. Indicates noise power; Assuming the MR-IRS-MR channel and the MR-MR channel remain constant within each frame but vary between different frames, and each frame is divided into a control phase and a transmission phase, there are a total of Frames, each frame includes One transmission time slot; The channel model for constructing the interference model is: Assuming any data stream can only choose either a direct link or a reflected link, two binary variables are defined. and This indicates which link is used for communication. When multiple streams are transmitted in the same time slot, the link used is the one in the first time slot. Frame number Time slot, The received signal-to-interference-plus-noise ratio is: Indicates the first The transmit power of the stream, Indicates the first The stream in the first Frame number Whether the time slot uses an MR-MR direct link to transmit data Indicates adoption. This indicates that the option is not adopted. Indicates the first The stream in the first Frame number Whether the time slot uses the MR-IRS-MR reflection link to transmit data, Indicates adoption. This indicates that the option is not adopted. , Indicates the first Frame number The square of the channel coefficient of the time slot, Indicates the first The transmit power of the stream, Indicates the first The stream in the first Frame number Whether the time slot uses an MR-MR direct link to transmit data Indicates adoption. This indicates that the option is not adopted. Indicates the first The flow in the first Frame number Whether the time slot uses the MR-IRS-MR reflection link to transmit data, Indicates adoption. This indicates that the option is not adopted. Indicates the first Frame number A collection of data streams transmitted in time slots. Indicates noise power.

3. The method according to claim 2, characterized in that, The objective function for maximizing the number of transport streams based on the channel model and interference model includes: According to Shannon's formula, the first The flow in the first Frame number Time slot transmission rate for: For system bandwidth; No. A stream in The total throughput of a frame is the ratio of the total amount of data transmitted to the total transmission time. for: in This indicates that the system contains a total of frame, This indicates that there are a total of [number] frames per frame. Each time slot It is the time slot length. It is the scheduling duration within each frame; Each flow is generated with Quality of Service (QoS) constraints. The QoS constraints for each stream are If the first If the total throughput of a stream within a specified number of frames meets the QoS constraint, the flag bit of this stream is set to 1, that is: The objective function for maximizing the number of transport streams is set as follows: in, This indicates that the system generated a total of The stream needs to be transmitted. , , Indicates the IRS number The phase shift of each of the reflecting units, the IRS has a total of There are one reflection unit, and the objective function is to maximize the number of successfully transmitted streams. The optimization variables are... It is a size of A matrix, where each element represents the phase shift of the corresponding reflector element in the IRS. It is a size of The matrix whose elements are... , It is a size of The matrix whose elements are... Constraint (1) indicates that a stream can only choose one transmission path in any frame and any time slot, either MR-MR direct link or MR-IRS-MR reflection link. Constraint (2) is a half-duplex working constraint, indicating that when the transmitting and receiving nodes of two streams have the same node, the two streams cannot be scheduled at the same time, and at most one stream can be transmitted. Constraint (3) indicates that the amplitude of each reflection unit of the IRS remains unchanged, and only the phase is optimized.

4. The method according to claim 3, characterized in that, The aforementioned method decomposes the objective function into three sub-problems: optimizing the IRS phase matrix, the link selection algorithm, and the scheduling algorithm, and solves these sub-problems to obtain a maximized data flow transmission scheme, including: Break it down into 3 sub-problems and solve them separately; 1) Optimize the IRS phase matrix: When optimizing the IRS phase matrix, first optimize the phase of the first IRS reflection unit, and fix the remaining phases. The phase of each reflecting unit, the first reflecting unit traversing all Phase, find the The maximized phase value is used as the phase optimization result for the first IRS reflector. Then, the same process is used to optimize the phase of the second IRS reflector, and this process is repeated until... The phase of each reflector unit has been optimized. 2) Link selection algorithm: in, For system generation For a given set of flows, the factors influencing link selection for any given flow include channel coefficients and QoS constraints. Channel coefficients remain constant within each frame, while link selection results also remain constant within each frame, though they vary between frames. The link selection algorithm follows the principle of always selecting the link with the shorter time requirement. During the link selection process for a given flow, the IRS reflection unit phase of its IRS link is first optimized. Then, the channel coefficients of the optimized MR-IRS-MR link and the MR-MR direct link are compared. The link with the larger channel coefficient is the link selection result for this flow. Next, the maximum achievable throughput of this flow is calculated, which is the throughput obtainable if all time slots were used for transmission of this flow without interference from other flows. If the maximum achievable throughput is less than the QoS constraint, it means that this flow cannot be successfully scheduled in this system under any circumstances and is removed from the system. Delete; 3) Scheduling Algorithm A scheduling algorithm based on an interference graph was designed. Each vertex in the interference graph represents a flow, and the edges between vertices represent potential interference between two flows. Interference only occurs when different flows are transmitted within the same time slot; flows transmitted in different time slots do not interfere with each other. The receiving node receives from the stream The interference from the transmitting node is: or For sending node arrive Distance; The calculation of interference is related to the selection of the link; the former corresponds to the flow. In the case of using an MR-IRS-MR reflection link, the latter corresponds to the flow. In the case of using an MR-MR direct link, any flow Heliu The formula for calculating potential interference between them is as follows: If the flow Heliu If they are adjacent, then the potential interference between them is set to infinity. If simultaneous transmission of streams causes a significant drop in the throughput of one of the streams, the potential interference between them is also set to infinity. This serves as a threshold for potential interference; if the value exceeds this threshold, the potential interference is set to infinity. For target flow The square of the channel coefficient; By optimizing the three sub-problems of IRS phase matrix, link selection algorithm, and scheduling algorithm, the optimization result of optimization problem P1 is obtained. The optimization result includes the phase optimization of the IRS reflection unit of the MR-IRS-MR link of each flow, the transmission link selection result of each flow in each frame, and the set of flows transmitted simultaneously in any time slot. The total achievable throughput of the system is calculated based on the set of flows transmitted in each time slot, which is the sum of the achievable throughput of each flow.

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