Sea area cooperative communication path switching method based on energy efficiency

Abstract

The invention provides a sea area cooperative communication path switching method based on energy efficiency, and belongs to the technical field of sea area cooperative communication. The method comprises the following steps: constructing a satellite-ground fusion network graph; calculating a communication rate according to the channel parameters; calculating the energy efficiency of sea area cooperative communication according to the communication rate; taking maximized energy efficiency as a target function, constructing constraint conditions, and forming an optimization problem; a layered optimization framework is adopted, a collaborative solution algorithm is designed for solution, and the global trajectory of the unmanned aerial vehicle is obtained; and evaluating the communication path energy efficiency in real time, and performing dynamic communication path switching according to an evaluation result. Reconfigurable intelligent surfaces are installed on the unmanned aerial vehicle and a high-altitude platform to assist communication of a shoreside base station and a low-orbit satellite, the trajectory of the unmanned aerial vehicle is dynamically optimized, the coverage range of the shoreside base station is expanded, and the maritime communication rate is increased; and meanwhile, energy efficiency evaluation is introduced to carry out system path real-time switching, so that the energy efficiency is effectively improved.

Description

Technical Field

[0001] The present invention relates to sea area cooperative communication technology, and in particular to a sea area cooperative communication path switching method based on energy efficiency. Background Art

[0002] With the surge in ocean economic activities, such as offshore exploration, smart shipping, and ocean monitoring, the demand for maritime communications has increased dramatically. However, due to the particularity of the marine environment, such as wide-area coverage, dynamic channels, and high path loss, traditional land communication technologies are difficult to transplant directly. Existing maritime communication technologies mainly rely on methods such as Coastal Base Station (CBS) and satellite communications. Coastal base stations can provide high-quality communications for ships in nearshore waters, but the coverage range is relatively limited. Low Earth Orbit Satellite (LEO) can provide communications for sea areas that are difficult to cover by shore base stations, but there are problems such as high latency and low speed, which cannot meet the needs of high-bandwidth real-time communications.

[0003] Existing improvement schemes generally have the limitation of single-dimensional optimization. For example, shore base stations transmit through ship relay nodes to enhance communication, but the lack of maneuverability and high mobility costs of ships limit deployment flexibility. Using unmanned aerial vehicles (UAVs) as relays can make up for the lack of maneuverability and mobility costs, but the relays need to build a complete transceiver link system, and high energy loss is generated during signal reception, amplification and forwarding, resulting in too low energy efficiency; low-orbit satellites use fixed high-altitude platforms (HAPs) as relays to improve communication rates, but the overall energy efficiency is at a low level. Although the above-mentioned improvement schemes have targetedly improved the communication rate, they have ignored the overall energy efficiency of the system and made it difficult to balance the communication rate and energy efficiency. Therefore, how to ensure that the communication rate meets actual needs while maximizing the overall energy efficiency of the scheme is an urgent problem to be solved in maritime communications. Summary of the Invention

[0004] Purpose of the invention: In response to the above problems, the purpose of the present invention is to provide a sea area collaborative communication path switching method based on energy efficiency.

[0005] Technical solution: A method for switching sea area cooperative communication paths based on energy efficiency of the present invention comprises the following steps:

[0006] Step 1: Build a satellite-ground fusion network diagram for maritime collaborative communications, including nodes and communication methods between nodes. Nodes include shore base stations, low-orbit satellites, RIS-equipped drones, high-altitude platforms, and target ships.

[0007] Step 2: Calculate the channel parameters between the shore base station and the target ship, and calculate the communication rate based on the channel parameters;

[0008] Step 3: Calculate the channel parameters between the low-orbit satellite and the target ship, and calculate the communication rate based on the channel parameters;

[0009] Step 4: Calculate the energy efficiency of sea area cooperative communication based on the communication rate;

[0010] Step 5: Taking maximizing energy efficiency as the objective function, construct constraints and form an optimization problem;

[0011] Step 6: Using a hierarchical optimization framework, the optimization problem is decomposed into three independent sub-problems: UAV flight trajectory optimization, phase optimization, and path switching. A collaborative solution algorithm is designed to solve them and obtain the UAV global trajectory.

[0012] Step 7: Evaluate the energy efficiency of the communication path in real time and perform dynamic communication path switching based on the evaluation results.

[0013] Furthermore, step 2 includes:

[0014] The channel coefficient of the direct link from the shore base station to the target ship is calculated using the line-of-sight link. The formula is:

[0015]

[0016] Where n∈{1,2,…,N} represents the time slot, N is the maximum time slot, β0 represents the power gain, and d BU [n] represents the distance from the shore base station to the target ship in the nth time slot;

[0017] The line-of-sight link is used to calculate the channel coefficient of the reflection link from the shore base station to the target ship through the UAV. The formula is:

[0018]

[0019] Where, represents the conjugate transpose of the channel coefficient from the UAV to the target ship in the nth time slot, where θ m [n]∈[0,2π] is the phase shift matrix of RIS, M represents the number of reflection units of RIS, h BR [n] represents the channel coefficient from the shore base station to the UAV in the nth time slot, d RU [n] represents the distance from the drone to the target ship in the nth time slot, d BR [n] represents the distance from the shore base station to the UAV in the nth time slot, d represents the antenna distance, λ represents the carrier wavelength, φ B [n] represents the cosine value of the angle of arrival of the signal from the shore base station to the drone, φ U[n] represents the cosine of the departure angle of the signal from the UAV to the target ship;

[0020] The communication rate of the direct link in time slot n is calculated based on the channel coefficient of the direct link. The formula is:

[0021]

[0022] Where, P b represents the transmission power of the shore base station, σ 2 is the variance of the additive Gaussian white noise at the target ship;

[0023] The communication rate of the reflection link in time slot n is calculated based on the channel coefficient of the reflection link. The formula is:

[0024]

[0025] Furthermore, step 3 includes:

[0026] Free-space optical communication is used between the low-orbit satellite and the target ship. The channel coefficient of the direct link from the low-orbit satellite to the target ship is calculated as follows:

[0027]

[0028] Where h c is the cloud attenuation coefficient, represents the beam spreading loss coefficient from the low-orbit satellite to the target ship;

[0029] Calculate the channel coefficient of the reflection link from the low-orbit satellite to the target ship through the high-altitude platform. The formula is:

[0030]

[0031] Where, represents the conjugate transpose of the channel coefficient from the high-altitude platform to the target ship, Φ s represents the phase shift matrix of the high-altitude platform RIS, h SH represents the channel coefficient from low-orbit satellite to high-altitude platform, represents the beam spreading loss coefficient from low-orbit satellite to high-altitude platform, represents the beam spreading loss coefficient from the high-altitude platform to the target ship, represents the phase shift matrix of RIS, φ H Represents the cosine value of the zenith angle of the high-altitude platform, φ S Indicates the cosine value of the zenith angle at the low-orbit satellite;

[0032] The communication rate of the direct link is calculated based on the channel coefficient of the direct link. The formula is:

[0033]

[0034] Where, P s is the transmission power of the low-orbit satellite;

[0035] The communication rate of the reflection link is calculated based on the channel coefficient of the reflection link. The formula is:

[0036]

[0037] Furthermore, the energy efficiency is calculated as follows:

[0038]

[0039] Where x1 and x2 are path selection coefficients, with values ​​of 0 or 1, x1+x2=1, P r [n] represents the total power of the direct link and reflected link of the shore base station, P h Represents the total power of the direct link and reflected link of the low-orbit satellite.

[0040] Furthermore, the mathematical model of the optimization problem is expressed as:

[0041]

[0042] st‖q r [n]-q r [n-1]‖≤V r d t ,

[0043] R BU +R BRU +R SU +R SHU ≥R th ,

[0044]

[0045] The first constraint represents the UAV's maneuverability constraint, the second constraint represents the target ship's communication rate threshold constraint, and the third constraint represents the RIS phase shift constraint;

[0046] Where q r [n] represents the trajectory of the UAV at time slot n, Φ[n] represents the phase shift matrix, v r Indicates the maximum horizontal speed of the UAV, d t =T / N represents each time slot, R th Indicates the total rate threshold.

[0047] Furthermore, step 6 includes:

[0048] For the reflection link of the shore base station, RIS phase optimization and UAV trajectory optimization are used for alternating optimization iterations:

[0049] In RIS phase optimization, for a given UAV trajectory q r [n], the optimization of the phase shift matrix Φ[n] is to maximize the user rate R BRU , to achieve phase synchronization of the received signal at the user receiving end, set:

[0050]

[0051] Where ω represents any phase shift, ω∈[0,2π],

[0052] Then the optimal phase shift of the mth element in the nth time slot is expressed as:

[0053]

[0054] The maximized channel coefficient is expressed as:

[0055]

[0056] In UAV trajectory optimization, for a given optimal phase shift The target ship's achieved rate is expressed as:

[0057]

[0058] Transmit power P b and circuit power is a fixed cost, and the variable related to the trajectory is the UAV propulsion power P fli [n], so the optimization problem is simplified to:

[0059]

[0060] st‖q r [n]-q r [n-1]‖≤V r d t

[0061] Assuming that the rate of the fixed reflection link is the threshold, the optimization problem is transformed into:

[0062]

[0063] st‖q r [n]-q r [n-1]‖≤V r d t

[0064] The optimization problem is solved by the interior point method to minimize the UAV propulsion power and generate the UAV global trajectory.

[0065] Furthermore, step 7 includes:

[0066] By solving the optimization problem, we obtain the result with the minimum power of each path, calculate the energy efficiency of the shore-based path and the satellite path at this time, perform real-time energy efficiency evaluation, and select the optimal one. The energy efficiency calculation formula for the shore-based path is:

[0067]

[0068] The energy efficiency of the satellite path at this time is calculated as:

[0069]

[0070] Consider two switching trigger conditions: condition 1 is that the rate threshold is not met, that is, the communication rate of the current working path cannot meet the threshold; condition 2 is the energy efficiency disadvantage, that is, the energy efficiency EE of the current working path is 当前 <EE 备选 ;

[0071] The priority condition is to meet the user communication rate. If condition 1 is triggered, path switching is immediately initiated regardless of energy efficiency. If only condition 2 is triggered, the proportion of continuous time slots to total time slots η must exceed a preset threshold, and the energy efficiency of the original path must not meet the loss threshold compared to the energy efficiency ratio δ of the switched path. If the former meets the former, the path is switched directly. If the former does not meet the latter, the path can be switched only when the latter is met.

[0072] Furthermore, step 7 further includes:

[0073] When path switching is initiated, the transmitter of the current path and the associated reflection link are shut down;

[0074] Activate the alternative path, including activating the shore-based composite path or activating the satellite composite path, and synchronize the optimized parameters of the alternative path to the communication control unit.

[0075] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0076] The present invention integrates various common maritime communication solutions and performs maritime collaborative communication path switching based on energy efficiency. Compared with traditional maritime communication solutions, it has significant advantages in communication rate and energy efficiency.

[0077] First, the present invention effectively improves the communication rate by approximately 3.33 times through airborne reconfigurable intelligent surface-assisted communication, meeting a wider range of maritime communication needs.

[0078] Secondly, with the assistance of drones carrying RIS, the coverage area of ​​the shore base is greatly increased;

[0079] Finally, by dynamically evaluating the energy efficiency of each path and performing real-time path switching, the overall energy efficiency of the solution was effectively improved, increasing the overall energy efficiency by approximately 70%. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 is a flow chart of the present invention;

[0081] Figure 2 This is a schematic diagram of the satellite-ground fusion network architecture;

[0082] Figure 3 This is a comparison chart of the rate and energy efficiency of the traditional solution with only direct links;

[0083] Figure 4 Comparison of drone trajectories at different rate thresholds;

[0084] Figure 5 The figure is a comparison chart of the rates at different thresholds;

[0085] Figure 6 The energy efficiency comparison chart for different thresholds. DETAILED DESCRIPTION

[0086] In order to make the purpose, technical solutions and advantages of this application more clear, this application is further described in detail below with reference to the accompanying drawings and embodiments.

[0087] The present embodiment describes a method for switching sea area cooperative communication paths based on energy efficiency, the flow chart of which is as follows: Figure 1 As shown, the method includes the following steps:

[0088] Step 1: Build a satellite-ground fusion network diagram for maritime collaborative communications, including nodes and communication methods between nodes. Nodes include shore base stations, low-orbit satellites, RIS-installed drones, high-altitude platforms, and target ships.

[0089] like Figure 2 The figure shows a schematic diagram of the satellite-ground fusion network diagram constructed by cooperative communication in the sea area. The figure includes the communication methods between nodes. The nodes include the shore base station B, the low-orbit satellite S, the drone R equipped with RIS (Reconfigurable Intelligent Surface, reconfigurable intelligent surface in the air), the high-altitude platform H and the target ship U. The target ship starts from the starting position and goes to the destination position along a fixed route. Assume that the shore base station, target ship and high-altitude platform use single antennas, and the RIS consists of M reflectors. Consider the flight time T of the drone, which is discretized into N time slots, and each time slot d t =T / N.

[0090] Step 2: Calculate the channel parameters between the shore base station and the target ship, and calculate the communication rate based on the channel parameters.

[0091] Furthermore, step 2 includes:

[0092] The channel coefficient of the direct link from the shore base station to the target ship is calculated using the line-of-sight link. The formula is:

[0093]

[0094] Where n∈{1,2,…,N} represents the time slot, N is the maximum time slot, β0 represents the power gain, and d BU [n] represents the distance from the shore base station to the target ship in the nth time slot.

[0095] The line-of-sight link is used to calculate the channel coefficient of the reflection link from the shore base station to the target ship through the UAV. The formula is:

[0096]

[0097] Where, represents the conjugate transpose of the channel coefficient from the UAV to the target ship in the nth time slot, where θ m [n]∈[0,2π] is the phase shift matrix of RIS, M represents the number of reflection units of RIS, h BR [n] represents the channel coefficient from the shore base station to the UAV in the nth time slot, d RU [n] represents the distance from the drone to the target ship in the nth time slot, d BR [n] represents the distance from the shore base station to the UAV in the nth time slot, d represents the antenna distance, λ represents the carrier wavelength, φ B [n] represents the cosine value of the angle of arrival of the signal from the shore base station to the drone, φ U [n] represents the cosine value of the departure angle of the signal from the UAV to the target ship; x r [n] represents the x coordinate of the drone at the nth time slot, x b represents the x coordinate of the shore base station, x u [n] represents the x-coordinate of the target ship at the nth time slot;

[0098] in represents the distance from node i to node j, i, j∈{B, R, U}, q i [n]=(x i [n],y i [n]) represents the horizontal coordinate, (x i ,y i ,hi ) represents the position coordinates;

[0099] The communication rate of the direct link in time slot n is calculated based on the channel coefficient of the direct link. The formula is:

[0100]

[0101] Where, P b represents the transmission power of the shore base station, σ 2 is the variance of the additive Gaussian white noise at the target ship;

[0102] The communication rate of the reflection link in time slot n is calculated based on the channel coefficient of the reflection link. The formula is:

[0103]

[0104] Step 3: Calculate the channel parameters between the low-orbit satellite and the target ship, and calculate the communication rate based on the channel parameters.

[0105] Furthermore, step 3 includes:

[0106] Free-space optical communication is used between the low-orbit satellite and the target ship. Taking into account beam spreading loss and cloud attenuation, the channel coefficient of the direct link from the low-orbit satellite to the target ship is calculated as follows:

[0107]

[0108] Where h c is the cloud attenuation coefficient, represents the beam spreading loss coefficient from the low-orbit satellite to the target ship;

[0109] Calculate the channel coefficient of the reflection link from the low-orbit satellite to the target ship through the high-altitude platform. The formula is:

[0110]

[0111] Where, represents the conjugate transpose of the channel coefficient from the high-altitude platform to the target ship, Φ s represents the diagonal matrix of phase shift coefficients of the high-altitude platform RIS, h SH represents the channel coefficient from low-orbit satellite to high-altitude platform, represents the beam spreading loss coefficient from low-orbit satellite to high-altitude platform, represents the beam spreading loss coefficient from the high-altitude platform to the target ship, represents the phase shift matrix of RIS, φ H Represents the cosine value of the zenith angle of the high-altitude platform, φ S Indicates the cosine value of the zenith angle at the low-orbit satellite;

[0112] The communication rate of the direct link is calculated based on the channel coefficient of the direct link. The formula is:

[0113]

[0114] Where, P s is the transmission power of the low-orbit satellite;

[0115] The communication rate of the reflection link is calculated based on the channel coefficient of the reflection link. The formula is:

[0116]

[0117] Step 4: Calculate the energy efficiency of sea area cooperative communication based on the communication rate.

[0118] Furthermore, the energy efficiency is calculated as follows:

[0119]

[0120] Where x1 and x2 are path selection coefficients, with values ​​of 0 or 1, and x1+x2=1, P r [n] represents the total power of the direct link and reflected link of the shore base station, represents the propulsion power of the UAV, V[n] is the speed of the UAV at time slot n, a[n] is the acceleration of the UAV, k1, k2 and g are constants, Indicates the base station circuit power required for network operation, namely the power amplifier and baseband unit, Represents the total power of the satellite's direct path and reflected path, P hap Indicates the flight power of the high-altitude platform, Indicates the satellite circuit power required for network operation, P h Represents the total power of the direct link and reflected link of the low-orbit satellite.

[0121] When x1=1 and x2=0, it means that the communication path at this time is switched to the shore base station path. When x1=0 and x2=1, it means that the communication path at this time is switched to the low-orbit satellite path.

[0122] Step 5: Taking maximizing energy efficiency as the objective function, construct constraints and form an optimization problem.

[0123] Furthermore, the mathematical model of the optimization problem is expressed as:

[0124]

[0125] st‖q r [n]-q r [n-1]‖≤V r dt ,

[0126] R BU +R BRU +R SU +R SHU ≥R th ,

[0127]

[0128] The first constraint represents the UAV's maneuverability constraint, the second constraint represents the target ship's communication rate threshold constraint, and the third constraint represents the RIS phase shift constraint;

[0129] Where q r [n] represents the trajectory of the UAV at time slot n, Φ[n] represents the phase shift matrix, V r Indicates the maximum horizontal speed of the UAV, d t =T / N represents each time slot, R th Indicates the total rate threshold.

[0130] In step 6, a hierarchical optimization framework is used to decompose the optimization problem into three independent sub-problems: UAV flight trajectory optimization, phase optimization, and path switching. A collaborative solution algorithm is designed to solve the problem and obtain the global trajectory of the UAV.

[0131] Furthermore, step 6 includes:

[0132] For the reflection link of the shore base station, RIS phase optimization and UAV trajectory optimization are used for alternating optimization iterations:

[0133] In RIS phase optimization, for a given UAV trajectory q r [n], the optimization of the phase shift matrix Φ[n] is to maximize the user rate R BRU , to achieve phase synchronization of the received signal at the user receiving end, set:

[0134]

[0135]

[0136] Where ω represents any phase shift, ω∈[0,2π], φ U [n] represents the cosine of the departure angle of the signal from the UAV to the target ship, φ B [n] represents the cosine of the angle of arrival of the signal from the shore base station to the drone;

[0137] Then the optimal phase shift of the mth element in the nth time slot is expressed as:

[0138]

[0139] The maximized channel coefficient is expressed as:

[0140]

[0141] In UAV trajectory optimization, the reflection link rate threshold is fixed, and for a given optimal phase shift The target ship's achieved rate is expressed as:

[0142]

[0143] The satellite communication link will not affect the shore base station link. The direct link of the shore base station has nothing to do with the UAV. The transmission power P b and circuit power The only variable related to the trajectory is the UAV propulsion power P fli [n], so the optimization problem is simplified to:

[0144]

[0145] st‖q r [n]-q r [n-1]‖≤V r d t

[0146] Assuming that the rate of the fixed reflection link is the threshold, the optimization problem is transformed into:

[0147]

[0148] st‖q r [n]-q r [n-1]‖≤V r d t

[0149] The optimization problem is solved by the interior point method to minimize the UAV propulsion power and generate the UAV global trajectory.

[0150] For the UAV trajectory optimization problem, a step-by-step recursive algorithm based on dynamic programming is proposed with a fixed reflection path rate threshold. This method constructs a set of feasible trajectory points that satisfy communication constraints, implements local power optimization decisions within each time slot, and ultimately generates a flight trajectory with the best global energy efficiency.

[0151] Step 7: Evaluate the energy efficiency of the communication path in real time and perform dynamic communication path switching based on the evaluation results.

[0152] Furthermore, step 7 includes:

[0153] By solving the optimization problem, the result with the minimum power of each path is obtained. The energy efficiency of the shore-based path and the satellite path at this time is calculated respectively. Real-time energy efficiency evaluation is performed and the optimal one is selected to determine the working path and alternative paths. The energy efficiency calculation formula of the shore-based path is:

[0154]

[0155] The energy efficiency of the satellite path at this time is calculated as:

[0156]

[0157] Consider two switching trigger conditions: condition 1 is that the rate threshold is not met, that is, the communication rate of the current working path cannot meet the threshold; condition 2 is the energy efficiency disadvantage, that is, the energy efficiency EE of the current working path is 当前 <EE 备选 , where the alternative path is another unactivated path;

[0158] The priority condition is to meet the user communication rate. If condition 1 is triggered, path switching is immediately initiated regardless of energy efficiency. If only condition 2 is triggered, the proportion of continuous time slots to total time slots η must exceed a preset threshold (e.g., η ≥ 5%), and the energy efficiency ratio δ of the inferior original path compared to the energy efficiency ratio of the switched path does not meet the loss threshold (e.g., δ ≤ 95%). If the former is met, direct switching is performed. If the former is not met, the latter must be met before path switching can be performed. This balances switching frequency and system stability to avoid frequent jitter.

[0159] Furthermore, step 7 further includes:

[0160] When path switching is initiated, the transmitting end of the current path, such as a shore base station or a low-orbit satellite, and the associated reflection link are shut down;

[0161] Activate alternative paths, including activating shore-based composite paths and activating satellite composite paths, and synchronize the optimized parameters of the alternative paths (such as UAV trajectory and RIS phase) to the communication control unit.

[0162] Shore-based composite path activation: The shore base station is activated, and the drone optimizes the trajectory and configures the RIS phase in real time.

[0163] Satellite composite path activation: Low-orbit satellites are activated, the high-altitude platform maintains a stable hover and configures the RIS phase.

[0164] During the path switching process, dual-path parallel transmission is briefly enabled for, for example, 10ms to avoid communication interruption.

[0165] To further illustrate the effectiveness and superiority of the path switching method of the present invention, the following examples are provided for illustration.

[0166] In a 600m×600m sea area, the target ship is set to travel from (100,0) to (500,600), and the drone's flight altitude is fixed at h r =20m, maximum speed V r =15m / s, and the operation parameters are set to k1=9.26×10 -4 , k2=500,g=9.8,initial position(x r ,y r ,h r )=(100,0,20), time slot N=40, RIS reflection unit M=128, shore base station transmission power P b =0.01W, coordinate (x b ,y b ,h b )=(0,50,10), the channel gain related parameters are set as β0=-20dB, λ=1550nm, d=λ / 2, σ 2 =-80dBm. The satellite channel beam loss related parameters are set as: satellite zenith angle ξ S =10°. Satellite transmission power P s =0.68W, base station circuit power High altitude platform flight power P hap =60W.

[0167] The path switching results of the traditional sea area communication scheme with only direct links are displayed, as well as the comparative results of the UAV flight trajectory, communication rate, and energy efficiency after setting different communication rate thresholds in the scheme of the present invention.

[0168] The satellite-ground fusion network constructed by the present invention is as follows Figure 2 As shown in the figure, it consists of the following nodes: shore base station, low-orbit satellite, UAV equipped with RIS, high-altitude platform and target user ship. The communication link includes two types of paths: direct link refers to the link established directly between the low-orbit satellite and the shore base and the target ship U; reflection link refers to the link that reflects the signal through RIS. The target ship starts from the starting position and goes to the end position along a fixed route. This solution addresses the existing rate requirements and energy efficiency challenges. Under the constraints of meeting the communication rate threshold and UAV mobility, it maximizes the overall energy efficiency by jointly designing the UAV's two-dimensional trajectory and path switching. The energy efficiency-based path switching method includes the following steps:

[0169] Please refer to the simulation results Figures 3 to 6 .

[0170] Figure 3 The optimization results after path switching in the traditional maritime communication scheme are shown. In this scheme, only the shore base station and the satellite provide direct links respectively, and the communication rate threshold R is set. th=1.2bps / Hz. Figure 3 Figure (a) shows the rates of the two direct links and the coordinated path respectively. As the target ship gradually moves away from the shore, the shore link rate gradually decays, while the satellite link rate remains unchanged. In the first four time slots, only the shore direct link is used, and the satellite path is in a dormant state. In the fifth time slot, it switches to using only the satellite direct link. At this time, the target ship moves to (154,24), which can be regarded as the effective coverage range of the shore base station in this scheme. Figure 3 Figure (b) shows the energy efficiency maximization achieved in the aforementioned scenario. The fading rate of the shore-based path causes a simultaneous decline in its energy efficiency, with the efficiency starting to lag behind that of the satellite path at the fifth time slot. While the shore-based satellite dual-link parallel transmission scheme can achieve higher communication rates, the additional power consumption results in lower overall energy efficiency. Therefore, compared to both fixed single-link transmission and dual-link parallel transmission, alternating and coordinated use of the two paths maximizes energy efficiency.

[0171] Figure 4 The comparison of UAV trajectories with different communication rate thresholds in the method of the present invention is shown. The initial position of the UAV and the trajectory of the target ship remain unchanged. The blue and green trajectories are the communication rate thresholds R th =5.2bps / Hz and R th = UAV trajectory when bps=6.2bps / Hz. Considering that the satellite path may not meet the threshold when working alone, the satellite transmission power P is also increased when the threshold is increased to 6.2bps / Hz. s = 1.05W. In the initial phase, due to the close distance between the drone and the target ship, the drone's reflected link provided sufficient communication rate, significantly exceeding the threshold requirement. To avoid resource redundancy, the drone in both scenarios adopted a cruise strategy along the nearshore area, but the cruise duration varied. As the target ship gradually moved away from the shore-based coverage area, the direct link performance dropped sharply. At this point, the drone dynamically adjusted its flight trajectory toward the shore-based base to enhance the channel rate of the reflected link, thereby compensating for the rate loss in the direct link.

[0172] Figure 5 The comparison results of the communication rates under different threshold constraints of the present invention are shown respectively. Figure 5 The middle figure (a) shows the communication rate comparison of each path when the total rate threshold is 5.2bps / Hz. Figure 5The middle figure (b) is a comparison of the communication rates of each path when the total rate threshold is 6.2bps / Hz, revealing the dynamic coupling characteristics of the UAV reflection link rate and the direct link rate. Compared with the traditional solution with only two direct links, the method of the present invention can achieve a higher rate, which is increased by about 3.33 to 4.17 times, meeting more practical application scenarios. Under different threshold conditions, the change trend of the optimized UAV reflection link rate is similar, and both show a non-monotonic change trend of first attenuation and then enhancement. In the initial stage, thanks to the close deployment of the UAV and the target ship, the reflection link can provide a communication rate that significantly exceeds the threshold. As the target ship gradually moves away from the shore-based coverage, the direct rate decays. The present invention enhances the reflection link channel gain by dynamically adjusting the UAV trajectory, so that the overall shore-based rate is maintained above the threshold. It is worth noting that the threshold R th =6.2bps / Hz, the reflected link rate attenuates in the later stage as the target ship becomes increasingly farther away from the shore base station, and eventually fails to meet the threshold. At this time, considering energy efficiency, it is possible to consider switching the satellite path.

[0173] Figure 6 The path energy efficiency comparison results of the method described in the present invention under different threshold constraints are respectively shown. Figure 6 The middle figure (a) shows the path energy efficiency comparison when the total rate threshold is 5.2 bps / Hz. Figure 6 The middle figure (b) shows the path energy efficiency comparison when the total rate threshold is 6.2bps / Hz. th =5.2bps / Hz, the energy efficiency advantage of the shore-based path can last until the 36th time slot, after which the energy efficiency of the satellite path surpasses and triggers path switching; th =6.2bps / Hz, the energy efficiency advantage of the satellite path is apparent as early as the 23rd time slot. Compared to not performing path switching, the overall energy efficiency of the present invention is improved by approximately 70%. Compared to the traditional solution, switching paths at time slots 36 and 23 significantly increases the shore-based coverage range. At this time, the target ship positions are (497, 521) and (420, 278), respectively, and the coverage radius increases by 3.38 times and 2.05 times, respectively. The experimental results verify the adaptive ability of the dynamic path switching mechanism under different requirements and the effectiveness of optimization.

[0174] The energy-efficiency-based sea area collaborative communication path switching method described in the present invention utilizes relay nodes to assist communication and utilizes aerial reconfigurable intelligent surfaces (RIS) to enhance communication rates, thereby avoiding the high energy consumption defect of traditional relays. Specifically, reconfigurable intelligent surfaces are installed on drones and high-altitude platforms to assist shore base stations and low-orbit satellite communications, respectively, dynamically optimize drone trajectories, expand shore base station coverage, and achieve enhanced maritime communication rates. At the same time, energy efficiency evaluation is introduced. Based on the evaluation results of the energy efficiency of each path and the dynamic communication path switching mechanism, system paths are switched in real time while meeting user rate requirements, thereby effectively improving energy efficiency, maximizing the overall energy efficiency of the solution, and ultimately achieving sea area collaborative communication that takes into account both communication rate and energy efficiency.

Claims

1. A method for switching sea area cooperative communication paths based on energy efficiency, characterized in that: The steps include: Step 1: Build a satellite-ground fusion network diagram for maritime collaborative communications, including nodes and communication methods between nodes. Nodes include shore base stations, low-orbit satellites, RIS-equipped drones, high-altitude platforms, and target ships. Step 2: Calculate the channel parameters between the shore base station and the target ship, and calculate the communication rate based on the channel parameters; Step 3: Calculate the channel parameters between the low-orbit satellite and the target ship, and calculate the communication rate based on the channel parameters; Step 4: Calculate the energy efficiency of sea area cooperative communication based on the communication rate; Step 5: Taking maximizing energy efficiency as the objective function, construct constraints and form an optimization problem; Step 6: Using a hierarchical optimization framework, the optimization problem is decomposed into three independent sub-problems: UAV flight trajectory optimization, phase optimization, and path switching. A collaborative solution algorithm is designed to solve them and obtain the UAV global trajectory. Step 7: Evaluate the energy efficiency of the communication path in real time and perform dynamic communication path switching based on the evaluation results.

2. The method for switching sea area cooperative communication paths based on energy efficiency according to claim 1, characterized in that: Step 2 includes: The channel coefficient of the direct link from the shore base station to the target ship is calculated using the line-of-sight link. The formula is: Where n∈{1,2,…,N} represents the time slot, N is the maximum time slot, β0 represents the power gain, and d BU [n] represents the distance from the shore base station to the target ship in the nth time slot; The line-of-sight link is used to calculate the channel coefficient of the reflection link from the shore base station to the target ship through the UAV. The formula is: Where, represents the conjugate transpose of the channel coefficient from the UAV to the target ship in the nth time slot, where θ m [n]∈[0,2π] is the phase shift matrix of RIS, M represents the number of reflection units of RIS, h BR [n] represents the channel coefficient from the shore base station to the UAV in the nth time slot, d RU [n] represents the distance from the drone to the target ship in the nth time slot, d BR [n] represents the distance from the shore base station to the UAV in the nth time slot, d represents the antenna distance, λ represents the carrier wavelength, φ B [n] represents the cosine value of the angle of arrival of the signal from the shore base station to the drone, φ U [n] represents the cosine of the departure angle of the signal from the UAV to the target ship; The communication rate of the direct link in time slot n is calculated based on the channel coefficient of the direct link. The formula is: Where, P b represents the transmission power of the shore base station, σ 2 is the variance of the additive Gaussian white noise at the target ship; The communication rate of the reflection link in time slot n is calculated based on the channel coefficient of the reflection link. The formula is:

3. The method for switching sea area cooperative communication paths based on energy efficiency according to claim 2, characterized in that: Step 3 includes: Free-space optical communication is used between the low-orbit satellite and the target ship. The channel coefficient of the direct link from the low-orbit satellite to the target ship is calculated as follows: Where h c is the cloud attenuation coefficient, represents the beam spreading loss coefficient from the low-orbit satellite to the target ship; Calculate the channel coefficient of the reflection link from the low-orbit satellite to the target ship through the high-altitude platform. The formula is: Where, represents the conjugate transpose of the channel coefficient from the high-altitude platform to the target ship, Φ s represents the phase shift matrix of the high-altitude platform RIS, h SH represents the channel coefficient from low-orbit satellite to high-altitude platform, represents the beam spreading loss coefficient from low-orbit satellite to high-altitude platform, represents the beam spreading loss coefficient from the high-altitude platform to the target ship, represents the phase shift matrix of RIS, φ H Represents the cosine value of the zenith angle of the high-altitude platform, φ S Indicates the cosine value of the zenith angle at the low-orbit satellite; The communication rate of the direct link is calculated based on the channel coefficient of the direct link. The formula is: Where, P s is the transmission power of the low-orbit satellite; The communication rate of the reflection link is calculated based on the channel coefficient of the reflection link. The formula is:

4. The method for switching sea area cooperative communication paths based on energy efficiency according to claim 3, characterized in that: The formula for calculating energy efficiency is: Where x1 and x2 are path selection coefficients, with values ​​of 0 or 1, x1+x2=1, P r [n] represents the total power of the direct link and reflected link of the shore base station, P h Represents the total power of the direct link and reflected link of the low-orbit satellite.

5. The method for switching sea area cooperative communication paths based on energy efficiency according to claim 4, characterized in that: The mathematical model of the optimization problem is expressed as: s.t.‖q r [n]-q r [n-1]‖≤V r d t , R BU +R BRU +R SU +R SHU ≥R th , The first constraint represents the UAV's maneuverability constraint, the second constraint represents the target ship's communication rate threshold constraint, and the third constraint represents the RIS phase shift constraint; Where q r [n] represents the trajectory of the UAV at time slot n, Φ[n] represents the phase shift matrix, V r Indicates the maximum horizontal speed of the UAV, d t =T / N represents each time slot, R th Indicates the total rate threshold.

6. The method for switching sea area cooperative communication paths based on energy efficiency according to claim 5, characterized in that: Step 6 includes: For the reflection link of the shore base station, RIS phase optimization and UAV trajectory optimization are used for alternating optimization iterations: In RIS phase optimization, for a given UAV trajectory q r [n], the optimization of the phase shift matrix Φ[n] is to maximize the user rate R BRU , to achieve phase synchronization of the received signal at the user receiving end, set: Where ω represents any phase shift, ω∈[0,2π], Then the optimal phase shift of the mth element in the nth time slot is expressed as: The maximized channel coefficient is expressed as: In UAV trajectory optimization, for a given optimal phase shift The target ship's achieved rate is expressed as: Transmit power P b and circuit power is a fixed cost, and the variable related to the trajectory is the UAV propulsion power P fli [n], so the optimization problem is simplified to: s.t.‖q r [n]-q r [n-1]‖≤V r d t Assuming that the rate of the fixed reflection link is the threshold, the optimization problem is transformed into: s.t.‖q r [n]-q r [n-1]‖≤V r d t The optimization problem is solved by the interior point method to minimize the UAV propulsion power and generate the UAV global trajectory.

7. The method for switching sea area cooperative communication paths based on energy efficiency according to claim 6, characterized in that: Step 7 includes: By solving the optimization problem, we obtain the result with the minimum power of each path, calculate the energy efficiency of the shore-based path and the satellite path at this time, perform real-time energy efficiency evaluation, and select the optimal one. The energy efficiency calculation formula for the shore-based path is: The energy efficiency of the satellite path at this time is calculated as: Consider two switching trigger conditions: condition 1 is that the rate threshold is not met, that is, the communication rate of the current working path cannot meet the threshold; condition 2 is the energy efficiency disadvantage, that is, the energy efficiency EE of the current working path is 当前 <EE 备选 ; The priority condition is to meet the user communication rate. If condition 1 is triggered, path switching is immediately initiated regardless of energy efficiency. If only condition 2 is triggered, the proportion of continuous time slots to total time slots η must exceed a preset threshold, and the energy efficiency of the inferior original path must not meet the loss threshold compared to the energy efficiency ratio δ of the switched path. If the former is met, the path is switched directly. If the former is not met, the latter must be met before the path can be switched.

8. The method for switching sea area cooperative communication paths based on energy efficiency according to claim 7, characterized in that: Step 7 also includes: When path switching is initiated, the transmitter of the current path and the associated reflection link are shut down; Activate the alternative path, including activating the shore-based composite path or activating the satellite composite path, and synchronize the optimized parameters of the alternative path to the communication control unit.

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