Marine shore-to-ship wireless channel modeling method based on ray tracing

Abstract

The invention provides an ocean shore-to-ship wireless channel modeling method based on ray tracing, and the method comprises the steps: 1) calculating a TMA shallow water sea wave spectrum, constructing a near-shore sea surface simulation scene based on the TMA shallow water sea wave spectrum, and setting simulation parameters in the near-shore sea surface simulation scene; 2) optimizing the offshore sea surface simulation scene, constructing a land scene, and combining the offshore sea surface simulation scene and the land scene into an ocean shore-to-ship simulation scene; (3) scene refresh time is calculated according to the sea wave self-correlation function, and ray tracing simulation is carried out; and 4) processing the data, and analyzing the ocean shore-to-ship channel characteristics. The method solves the problem that current ocean shore-to-ship channel modeling does not consider seawater depth and dynamic sea surface updating, can support ocean shore-to-ship scene channel simulation under any frequency band, supports sea surface scene refreshing according to coherence time, can also be used for simulating influences of different wind speeds and seawater depths on an ocean shore-to-ship channel, and has a good application prospect. The method has an important reference value for the design of a marine shore-to-ship multi-user wireless communication system.

Description

Technical field:

[0001] The invention belongs to the technical field of wireless communications, and in particular relates to a method for modeling ocean shore-to-ship wireless channels based on ray tracing. Background technology:

[0002] With the rapid development of the blue economy, maritime activities are also increasing, and the importance of maritime communications is also growing rapidly. At the same time, maritime communication systems play an important role in achieving global coverage of the sixth-generation wireless network, so it is worth studying maritime communication systems. Channel models are the basis of communication system design and network planning. Channel modeling methods are mainly divided into deterministic channel modeling and random channel modeling. Under certain circumstances, the ray tracing deterministic channel model is more accurate than the random channel model, but it is also more complex. In view of the sparse scattering characteristics of the marine communication environment and the relatively simple marine communication scene with fewer scatterers, it is suitable to use ray tracing methods for channel modeling and channel characteristic analysis.

[0003] There have been some studies on channel modeling of maritime communication systems. The paper (A novel 3D non-stationary maritime wireless channel model) proposed a geometry-based 3D non-stationary maritime communication random channel model and conducted a detailed analysis of small-scale parameters, but almost no mention of large-scale parameters. The paper (Ray tracing based wireless channel modeling over the sea surface near Diaoyuislands) used a ray tracing-based channel modeling method to model the wireless channel of the maritime drone-to-ship communication scenario. The relevant parameters such as path loss, delay, and angle of arrival were obtained through simulation, but the influence of water depth was not considered. The paper (Ray tracing based maritime channel analysis for millimeter radio waves) gave and analyzed the simulation results of the millimeter wave communication channel in the marine ship-to-ship scenario. The influence of ray spacing, earth curvature and sea surface roughness on the characteristics of the marine channel was studied. It can be found that the above-mentioned marine communication channel modeling methods hardly consider the influence of seawater depth in sea surface modeling. The random fluctuation characteristics of the real sea surface lead to high complexity of the sea surface in the shore-to-ship scenario. At the same time, the large area of ​​the sea surface modeling will further increase the complexity of the ray tracing process. Therefore, the sea surface model needs to be optimized to reduce the complexity of the sea ray tracing. Considering that maritime communication is mainly long-distance communication, the width of the modeled sea surface can be reduced to reduce the number of unnecessary grids in the ray tracing process; at the same time, since the sea surface changes over time, remodeling the sea surface at each moment is too complicated for the ray tracing process. In order to realize ray tracing of dynamic sea surface scenes and reduce the complexity of ray tracing, it is necessary to study the correlation of the sea surface models at different times to achieve a compromise between complexity and accuracy. However, existing research rarely considers these aspects.

[0004] In summary, the present invention provides a method for modeling ocean shore-to-ship wireless channels based on ray tracing, which takes into account the influence of ocean shore on the depth of sea water and the characteristics of dynamic random fluctuations of the sea surface, and can accurately model and analyze the ocean shore-to-ship channel. Summary of the invention:

[0005] The purpose of the present invention is to address the deficiencies in the prior art and to provide a method for modeling ocean shore-to-ship wireless channels based on ray tracing, which solves the problem that the current ocean shore-to-ship channel modeling does not take into account the seawater depth and dynamic sea surface updates. The method can accurately realize dynamic sea surface modeling and ocean shore-to-ship wireless channel simulation according to the channel characteristics of the ocean scene, and can be applied to analyze the characteristics of the ocean shore-to-ship channels in any frequency band.

[0006] The present invention adopts the following technical solutions:

[0007] The present invention provides a method for modeling an ocean shore-to-ship wireless channel based on ray tracing, comprising the following steps:

[0008] S1. Set the parameters required for sea surface modeling, calculate the TMA shallow water wave spectrum, build a nearshore sea surface simulation scene based on the TMA shallow water wave spectrum, and set simulation parameters in the nearshore sea surface simulation scene;

[0009] S2. Optimize the nearshore sea surface simulation scene, construct the land scene, and combine the nearshore sea surface simulation scene and the land scene into an ocean shore-to-ship simulation scene;

[0010] S3, calculating the time autocorrelation function of the waves, calculating the refresh time of the ocean shore-to-ship simulation scene according to the time autocorrelation function of the waves, and performing ray tracing simulation;

[0011] S4. Process ray tracing simulation data and analyze the characteristics of ocean shore-to-ship channels.

[0012] Furthermore, in step S1, the TMA shallow water wave spectrum calculation formula is:

[0013]

[0014] The calculation method of Φ(ω,h) is:

[0015]

[0016] Where ω is the angular frequency of the wave; h is the depth of the sea water; θ is the direction of movement of the wave; g is the acceleration of gravity; Φ(ω,h) is the water depth factor; γ is the peak enhancement factor of the wave spectrum; σ is the peak shape factor of the wave spectrum; D(θ)=2cos 2 (θ) / π, is the wave propagation direction function; α=0.076(gX / u 2 ) -0.22 , represents the intensity of the wave spectrum; ω m is the peak frequency of the wave spectrum, ω m =7π(g / u)(gX / u 2 ) -0.33 ; X is the sea surface acquisition length (the length of the wind blowing over the sea surface); u is the sea surface wind speed.

[0017] Furthermore, in step S1, the sea surface height is modeled by the Longuet-Higgins model according to the TMA shallow water wave spectrum:

[0018]

[0019] Among them, H(x,y,t) represents the sea surface height at the coordinate (x,y) at time t; in sea surface modeling, the sea waves are divided into the superposition of waves with i frequencies and j moving direction angles, a ij is the amplitude of the wave with the i-th frequency and j-th moving direction angle; represents the wave number of the ith wave, ω i and θ j are the values ​​of the i-th frequency and j-th direction angle of the wave respectively; ε ij is a random initial phase uniformly distributed in (0,2π).

[0020] Furthermore, in step S1, the simulation parameters are set in the nearshore sea surface simulation scene specifically as follows: the antenna type, antenna polarization mode, transmission power and antenna gain of the transmitting end and the receiving end in the nearshore sea surface simulation scene are set; the transmitting end is a shore base station, and the receiving end is a receiving device on a ship at sea.

[0021] Furthermore, the step S2 includes: S201, setting the length direction of the sea surface as the positive direction of the x-axis, and the width direction of the sea surface as the positive direction of the y-axis, determining the sea surface range according to the length and width of the sea surface, dividing it into a number of grids, and further dividing the grids where the receiving end, the transmitting end and the mirror reflection point are located into a number of small grids; S202, drawing the shore buildings through scene modeling software to obtain a land scene model; splicing the land scene model with the nearshore sea surface simulation scene model to form an ocean shore-to-ship simulation scene.

[0022] Furthermore, the step S3 includes: S301, calculating the time autocorrelation function of the waves and determining the time interval for scene refresh: according to the set environmental parameters, the time autocorrelation function of the waves is calculated, and the time when the time autocorrelation function first drops to 1 / 2 of the initial value is the time interval for scene refresh; S302, scene update and ray emission: before emitting rays, determine whether the ray emission interval exceeds the time interval for scene refresh. If not, use the last generated scene for ray tracing. If yes, refresh the scene first, and then emit rays uniformly into space from the transmitting end; S303, ray tracing: according to the Delaunay triangulation algorithm, perform Delaunay triangulation on the nearshore sea surface simulation scene, divide the sea surface into several triangular faces, and obtain the vertex coordinates of the triangular faces. ; Monitor whether the ray collides with the triangle face. If a collision occurs, the ray collides with the sea surface or the building on the coast and reflects. If reflection occurs, continue to track the reflected light to determine whether the next reflection will occur; repeat the above monitoring process until the ray energy decays below the threshold or the reflection order reaches the set maximum reflection order, the ray tracing process stops; S304, ray reception: the receiving sphere method is used at the receiving end to perform reception judgment, and whether the ray is received is determined based on the intersection relationship between the ray and the receiving sphere; the radius of the receiving sphere is calculated by the actual path length of the ray between the source point and the receiving end and the angle between two adjacent rays at the source point; finally, the receiving power, delay and angle of each ray are calculated based on the received ray parameters.

[0023] Furthermore, in step S301, the calculation formula of the time autocorrelation function is:

[0024]

[0025] Furthermore, in step S303, when tracing the reflected light, the loss caused by the reflection is affected by the reflection coefficient, and the magnitude of the loss is calculated by multiplying the reflection coefficient by the intensity of the incident wave. According to Snell's law, the Fresnel reflection coefficients of the horizontally polarized wave and the vertically polarized wave are calculated as follows:

[0026]

[0027] Among them, θ g is the grazing incidence angle, is the complex dielectric constant of the reflecting surface, According to the relative dielectric constant of seawater, σ d and the seawater conductivity is Calculated.

[0028] Furthermore, the step S4 includes: S401, setting different ocean shore-to-ship simulation scene parameters, obtaining simulation results under different parameters according to the receiving power, delay and angle of the receiving end ray, and then performing ray tracing simulation on different ocean shore-to-ship scene models to obtain corresponding simulation results, and performing FI fitting on the simulated path loss data; S402, performing FI fitting on the path loss data actually measured under different parameters, and comparing the FI fitting results of the simulated path loss data with the FI fitting results of the actually measured path loss data, and analyzing the accuracy of the model; S403, performing FI fitting on the free space path loss data under different parameters, and comparing the FI fitting results of the simulated path loss data with the FI fitting results of the free space path loss data, and analyzing the loss characteristics of the ocean shore-to-ship wireless channel; S404, comparing the FI fitting results of the simulated path loss data under different data of the same parameter, and analyzing the influence of each parameter on the ocean shore-to-ship wireless channel.

[0029] Furthermore, in step S4: the fitting formula for the simulated path loss data FI under different parameters is:

[0030] PL F IP L (d) = 20nlog 10 (d)+β+X σ

[0031] The FI fitting formula for free space path loss data under different parameters is:

[0032] PL F S P L (d) = 20log 10 (d)+99.05

[0033] Where d is the distance between the receiver and the transmitter, n is the path loss exponent, β is a constant, and X σ is a lognormal random variable with mean 0dB and σ is the standard deviation.

[0034] Beneficial effects of the present invention:

[0035] (1) The present invention proposes a method for modeling ocean shore-to-ship wireless channels based on ray tracing. The method takes into account the impact of sea surface wind speed and water depth on the ocean shore-to-ship channel. The sea surface in the modeling scenario is modeled according to the shallow water wave spectrum, which is more in line with the actual shore-to-ship communication scenario.

[0036] (2) The present invention optimizes the sea surface model by the positions of the receiving end, the transmitting end and the mirror reflection area, thereby reducing the complexity of the sea surface model and accelerating the ray tracing process;

[0037] (3) The present invention calculates the autocorrelation function of the sea waves, determines the refresh time interval of the sea surface, accelerates the ray tracing process, and models the dynamic changes of the sea surface. The ocean shore-to-ship ray tracing channel model established according to the present invention can accurately realize the simulation of dynamic sea surface scenes and the analysis of ocean shore-to-ship channel characteristics. Description of the drawings:

[0038] Figure 1 is a flow chart of the method of the present invention;

[0039] Figure 2 This is a schematic diagram of the sea surface before optimization in a nearshore sea surface simulation scenario according to an embodiment of the present invention;

[0040] Figure 3 2 is a schematic diagram of the optimized sea surface in the nearshore sea surface simulation scene according to an embodiment of the present invention;

[0041] Figure 4 Schematic diagram of a shore-to-ship simulation scenario in an embodiment of the present invention;

[0042] Figure 5 is a path loss fitting diagram of an embodiment of the present invention;

[0043] Figure 6 is the delay power spectrum under different environmental parameters of the embodiment of the present invention, where a is the simulation result of the receiving end at the position (720, 40, 5), b is the simulation result of the receiving end at the position (775, 40, 5), c is the simulation result of the receiving end at the position (845, 40, 5), and d is the simulation result of the receiving end at the position (845, 40, 5);

[0044] Figure 7 is a comparison diagram of path loss under different sea surface wind speeds in an embodiment of the present invention;

[0045] Figure 8 3 is a comparison diagram of path loss at different seawater depths in an embodiment of the present invention. Specific implementation method:

[0046] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] Reference Figure 1 The present invention provides a method for modeling ocean shore-to-ship wireless channels based on ray tracing, comprising:

[0048] Step 1: Calculate the TMA shallow water wave spectrum, construct a nearshore sea surface simulation scene based on the TMA shallow water wave spectrum, and set simulation parameters in the nearshore sea surface simulation scene.

[0049] 1. Calculate the TMA shallow water wave spectrum. The calculation formula for the TMA shallow water wave spectrum is:

[0050]

[0051] The calculation method of Φ(ω,h) is:

[0052]

[0053] Where ω is the angular frequency of the wave; h is the depth of the sea water; θ is the direction of movement of the wave; g is the acceleration of gravity; Φ(ω,h) is the water depth factor; γ is the peak enhancement factor of the wave spectrum; σ is the peak shape factor of the wave spectrum; D(θ)=2cos 2 (θ) / π, is the wave propagation direction function; α=0.076(gX / u 2 ) -0.22 , represents the intensity of the wave spectrum; ω m is the peak frequency of the wave spectrum, ω m =7π(g / u)(gX / u 2 ) -0.33 ; X is the sea surface acquisition length (the length of the wind blowing over the sea surface); u is the sea surface wind speed.

[0054] 2. Based on the TMA shallow water wave spectrum, the sea surface height is modeled using the Longuet-Higgins model:

[0055]

[0056] Among them, H(x,y,t) represents the sea surface height at the coordinate (x,y) at time t; in sea surface modeling, the sea waves are divided into the superposition of waves with i frequencies and j moving direction angles, a ij is the amplitude of the wave with the i-th frequency and j-th moving direction angle; represents the wave number of the ith wave, ω i and θ j are the values ​​of the i-th frequency and j-th direction angle of the wave respectively; ε ij is a random initial phase uniformly distributed in (0,2π).

[0057] 3. Set simulation parameters in the nearshore sea simulation scene:

[0058] Set the antenna type, antenna polarization mode, transmission power and antenna gain of the transmitter and receiver in the nearshore sea simulation scene; the transmitter is a shore base station and the receiver is a receiving device on a ship at sea.

[0059] Step 2: Optimize the nearshore sea surface simulation scene, construct the land scene, and combine the nearshore sea surface simulation scene and the land scene into an ocean shore-to-ship simulation scene.

[0060] 1. Optimize the nearshore sea simulation scene:

[0061] The length of the sea surface is set as the positive direction of the x-axis, and the width of the sea surface is set as the positive direction of the y-axis. The nearshore sea surface simulation scene is divided into several large grids. Considering that the sea surface scattering is mainly concentrated near the receiving end, the transmitting end and the mirror reflection point (the coordinates of the mirror reflection point are calculated by the values ​​of the transmitting end antenna height, the receiving end antenna height and the sea surface height), a more detailed sea surface can be generated at these locations.

[0062] The optimization operation is: further divide the grids where the receiving end, transmitting end and mirror reflection point are located into several small grids to ensure the accuracy of the ray tracing results. And enlarge the grids at other locations to simplify the sea surface model, that is, increase the length of the grids divided at other locations along the x-axis and y-axis directions, which can speed up the ray tracing process.

[0063] 2. Construct ocean shore-to-ship simulation scene:

[0064] The shore buildings are drawn using scene modeling software to obtain a land scene model; the land scene model is spliced ​​with the nearshore sea surface simulation scene model to form an ocean shore-to-ship simulation scene.

[0065] Step 3: Calculate the time autocorrelation function of the waves, calculate the refresh time interval of the ocean shore-to-ship simulation scene according to the time autocorrelation function of the waves, and perform ray tracing simulation.

[0066] 1. Calculate the time autocorrelation function of the waves and determine the time interval for scene refresh:

[0067] According to the set environmental parameters, the temporal autocorrelation function of the waves is calculated. The time when the temporal autocorrelation function first drops to 1 / 2 of the initial value is the time interval for scene refresh.

[0068] The calculation formula of the time autocorrelation function is:

[0069]

[0070] 2. Scene update and ray emission:

[0071] Before emitting rays, determine whether the ray emission interval exceeds the time interval for scene refresh. If not, use the last generated scene for ray tracing. If yes, refresh the scene first, and then emit rays uniformly into space from the transmitter.

[0072] 3. Ray tracing:

[0073] According to the Delaunay triangulation algorithm, Delaunay triangulation is performed on the nearshore sea surface simulation scene to divide the sea surface into several triangular faces, and the vertex coordinates of these triangular faces are stored; whether the ray collides with the triangular facets is monitored. If a collision occurs, the ray collides with the sea surface or the building on the coast and reflects. If reflection occurs, the reflected light is continued to be traced to determine whether the next reflection will occur; the above monitoring process is repeated until the ray energy decays below the threshold or the order of reflection reaches the set maximum reflection order, and the ray tracing process stops.

[0074] When tracing reflected light, the loss caused by reflection is affected by the reflection coefficient, and the magnitude of the loss is calculated by multiplying the reflection coefficient by the intensity of the incident wave. According to Snell's law, the Fresnel reflection coefficient of horizontally polarized waves and vertically polarized waves is calculated as:

[0075]

[0076] Among them, θ g is the grazing incidence angle, is the complex dielectric constant of the reflecting surface, According to the relative dielectric constant of seawater, σ d and the seawater conductivity is Calculated.

[0077] 4. Ray reception

[0078] The receiving sphere method is used at the receiving end to make a reception judgment, and whether the ray is received is determined based on the intersection relationship between the ray and the receiving sphere; the radius of the receiving sphere is calculated by the actual path length of the ray between the source point and the receiving end and the angle between two adjacent rays at the source point; finally, the receiving power, delay and angle of each ray are calculated based on the received ray parameters.

[0079] Step 4: Process the ray tracing simulation data and analyze the characteristics of the ocean shore-to-ship channel.

[0080] 1. Set different ocean shore-to-ship simulation scenario parameters, obtain simulation results under different parameters according to the receiving power, delay and angle of the receiving end ray, and then perform ray tracing simulation on different ocean shore-to-ship scenario models to obtain corresponding simulation results, and perform FI fitting on the simulated path loss data.

[0081] The FI fitting formula for the simulated path loss data under different parameters is:

[0082] PL F IP L (d) = 20nlog 10 (d)+β+X σ

[0083] Where d is the distance between the receiver and the transmitter, n is the path loss exponent, β is a constant, and X σ is a lognormal random variable with mean 0dB and σ is the standard deviation.

[0084] 2. Perform FI fitting on the path loss data actually measured under different parameters, and compare the FI fitting results of the simulated path loss data with the FI fitting results of the actually measured path loss data to analyze the accuracy of the model.

[0085] 3. Perform FI fitting on the free space path loss data under different parameters, and compare the FI fitting results of the simulated path loss data with the FI fitting results of the free space path loss data to analyze the loss characteristics of the ocean shore-to-ship wireless channel.

[0086] The FI fitting formula for free space path loss data under different parameters is:

[0087] PL F S P L (d) = 20log 10 (d)+99.05

[0088] Where d is the distance between the receiver and the transmitter.

[0089] 4. Compare the FI fitting results of the simulated path loss data under different data of the same parameters, and analyze the impact of different parameters on the ocean shore-to-ship wireless channel.

[0090] Example 1

[0091] The present invention provides a method for modeling an ocean shore-to-ship wireless channel based on ray tracing, and the channel modeling method comprises the following steps:

[0092] (1) Determine the parameters required for sea surface modeling. Determine the sea surface modeling length as 1000m, width as 50m, sea surface wind speed u as 5m / s, sea water depth h as 20m, and sea water relative dielectric constant as σ d The conductivity of seawater is 80. is 4.5S / m, the sea surface acquisition length X is 10000m, the peak enhancement factor γ is 3.3, the peak shape factor σ is 0.07 when the simulated wave frequency value is greater than the peak frequency, and is 0.09 when the simulated wave frequency value is less than the peak frequency. The peak frequency is calculated according to the formula ω m =7π(g / u)(gX / u 2 ) -0.33 Calculate the TMA shallow water wave spectrum according to the set parameters. The calculation formula of TMA shallow water wave spectrum is:

[0093]

[0094] The calculation method of Φ(ω,h) is:

[0095]

[0096] Where ω is the angular frequency of the wave; h is the depth of the sea water; θ is the direction of movement of the wave; g is the acceleration of gravity; Φ(ω,h) is the water depth factor; γ is the peak enhancement factor of the wave spectrum; σ is the peak shape factor of the wave spectrum; D(θ)=2cos 2 (θ) / π, is the wave propagation direction function; α=0.076(gX / u 2 ) -0.22 , represents the intensity of the wave spectrum; ω m is the peak frequency of the wave spectrum, ω m =7π(g / u)(gX / u 2 ) -0.33 ; X is the sea surface acquisition length (the length of the wind blowing over the sea surface); u is the sea surface wind speed.

[0097] (2) According to the TMA shallow water wave spectrum, the sea surface height is modeled using the Longuet-Higgins model. When modeling the sea surface, the number of wave spectrum spectra used in the Longuet-Higgins model is set to 5 and the number of directional angles is set to 30.

[0098]

[0099] Among them, H(x,y,t) represents the sea surface height at the coordinate (x,y) at time t; in sea surface modeling, the sea waves are divided into the superposition of waves with i frequencies and j moving direction angles, a ij is the amplitude of the wave with the i-th frequency and j-th moving direction angle; represents the wave number of the ith wave, ω i and θ j are the values ​​of the i-th frequency and j-th direction angle of the wave respectively; ε ij is a random initial phase uniformly distributed in (0,2π).

[0100] Set the length of the sea surface as the positive direction of the x-axis and the width of the sea surface as the positive direction of the y-axis. Divide the nearshore sea surface simulation scene into several large grids. The length of the large grid along the x-axis and y-axis is 10m. The initial modeled sea surface is as follows: Figure 2 shown.

[0101] (3) The antenna type of the transmitter (shore base station) and the receiver (receiving device on the ship at sea) is set to omnidirectional antenna, the polarization mode is vertical polarization, the antenna power of the transmitter is set to 23dBm, the antenna power of the receiver is set to 25dBm, the antenna gain of the transmitter and the receiver is set to 0dBi, and the center frequency of the transmitted signal is 2.4GHz.

[0102] (4) Optimize the nearshore sea surface simulation scene: Set the transmitter coordinates (0, 0, 30) and the receiver coordinates (700, 40, 5). Calculate the coordinates of the possible mirror reflection points based on the mirror reflection principle. The reflection plane is the xy plane, and the mirror reflection point is (600, 34.2, 0). The grids where these three points are located are set to have a length of 10 m in the x-axis direction and 5 m in the y-axis direction. The length of the grids in other parts is 50 m in the x-axis direction and 10 m in the y-axis direction. The optimized sea surface is as follows: Figure 3 shown.

[0103] (5) Constructing an ocean shore-to-ship simulation scene: Draw the shore buildings using scene modeling software (SketchUp software) to obtain a land scene model, and then splice the land scene model with the nearshore sea surface simulation scene model to form an ocean shore-to-ship simulation scene.

[0104] The length of the coast is set to 100m, and the width is the same as the sea surface width, which is 50m. There are two buildings on the coast with a height of 20m. The length and width of the buildings are both 10m. The center point of the bottom of one building is 15m away from the coastline and 10m away from the x-axis. The center point of the bottom of the other building is 30m away from the coastline and 30m away from the x-axis. The land on the coast is made of sand, and the buildings are made of concrete. Figure 4 shown.

[0105] (6) Calculate the temporal autocorrelation function of the waves and determine the time interval for scene refresh: Calculate the temporal autocorrelation function of the waves according to the set environmental parameters (sea surface wind speed u and sea water depth h). The time when the temporal autocorrelation function first drops to 1 / 2 of the initial value is the time interval T for scene refresh. r .

[0106] The calculation formula of the time autocorrelation function is:

[0107]

[0108] (7) Before emitting rays, determine whether the ray emission interval exceeds the scene refresh time interval T r If not, the last generated scene is used for ray tracing. If yes, the scene is refreshed first, and then the emitting end emits rays uniformly into the space.

[0109] (8) Considering the reflection mechanism, the emitted rays will be reflected by the sea surface, buildings and land surface. The reflection coefficient is calculated according to Snell's law, and the reflected rays are determined according to the law of reflection.

[0110] According to the Delaunay triangulation algorithm, the nearshore sea surface simulation scene is Delaunay triangulated to divide the sea surface into several triangular faces, and the vertex coordinates of the triangular faces are obtained; monitor whether the ray collides with the triangular face. If a collision occurs, the ray collides with the sea surface or the building on the coast and reflects. If reflection occurs, continue to trace the reflected light to determine whether the next reflection will occur; repeat the above monitoring process until the ray energy decays below the threshold or the reflection order reaches the set maximum reflection order (3rd order), and the ray tracing process stops.

[0111] When tracing reflected rays, the Fresnel reflection coefficients for horizontally and vertically polarized waves are calculated as:

[0112]

[0113] Among them, θ g is the grazing incidence angle, is the complex dielectric constant of the reflecting surface, According to the relative dielectric constant of seawater, σ d and the seawater conductivity is Calculated.

[0114] (9) The receiving sphere method is used at the receiving end to make a reception judgment. Whether the ray is received is determined based on the intersection relationship between the ray and the receiving sphere. The emitted ray undergoes a single reflection or multiple reflections, and some of the rays reach the receiving end and are effectively received. Finally, the receiving power, delay, and angle of each ray are calculated based on the received ray parameters.

[0115] (10) Process ray tracing simulation data and analyze the characteristics of ocean shore-to-ship channels:

[0116] 1) Set different sea surface wind speeds and sea water depths, and obtain simulation results under different parameters (sea surface wind speed, sea water depth) according to the receiving power, delay and angle of the receiving end ray. Then, perform ray tracing simulation on different ocean shore-to-ship scenario models, obtain corresponding simulation results, and perform FI fitting on the simulated path loss data.

[0117] In this embodiment, the wind speed is first set to 5m / s, the sea depth is 5m, and the wave model sampling time is set to 0s, 1s, 2s, and 3s respectively, and different sea surface models are established, and then different ocean shore-to-ship scene models are generated for ray tracing simulation to obtain corresponding simulation results. The wind speed is set to 5m / s, 10m / s, 15m / s, and 20m / s respectively, and the sea depth is set to 10m. Different scene models are established for simulation to obtain simulation results under different wind speed conditions. Then the sea depth is set to 2m, 5m, 10m, and 25m respectively, and the sea surface wind speed is set to 10m / s. The scene model is established for simulation to obtain simulation results under different sea depths.

[0118] 2) Perform FI fitting on the path loss data actually measured under different parameters, and compare the FI fitting results of the simulated path loss data with the FI fitting results of the actually measured path loss data to analyze the accuracy of the model.

[0119] In this embodiment, the simulation results of different wave model sampling times under the parameters of wind speed 5m / s and sea water depth 10m are taken to perform FI fitting on the simulated path loss results. According to the FI model formula, the path loss index n is 2.08, the fitting intercept constant β is 37.2dB, and the shadow fading standard deviation σ is 0.57dB; in the measured fitting results, the path loss index n is 2.09, the fitting intercept constant β is 36.4dB, and the shadow fading standard deviation σ is 3.24dB; the fitting results of the path loss simulation data are very close to the fitting results of the measured data, such as Figure 5 As shown, the calculated root mean square error value is 0.044dB, which proves the accuracy of the model proposed in the present invention.

[0120] 3) Perform FI fitting on the free space path loss data under different parameters, and compare the FI fitting results of the simulated path loss data with the FI fitting results of the free space path loss data to analyze the loss characteristics of the ocean shore-to-ship wireless channel. Figure 5 As shown, the simulated path loss data FI fitting results are compared with the free space path loss data FI fitting results. The path loss is reduced, which proves that the simulation model has a sea surface reflection component reaching the receiving end, increasing the signal energy at the receiving end.

[0121] 4) Compare the path loss data FI fitting results of simulation results with different wind speeds and different sea depths, and analyze the impact of wind speed and sea depth on the ocean shore-to-ship wireless channel. The simulation results are as follows: Figures 6 to 8 As shown. Figure 6 It can be seen that there is at least one reflection path on the sea surface. At the same time, as the wind speed increases, the waves become more violent and will block part of the reflection path. Figures 7-8It can be seen that when the wind speed increases, the sea surface fluctuates more violently, the sea surface reflection path component decreases, and the path loss increases. When the sea water depth increases, the sea surface fluctuates more violently, which reduces the sea surface reflection path component and increases the path loss.

[0122] The above are only preferred implementations of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for modeling ocean shore-to-ship wireless channels based on ray tracing, characterized in that: The following steps are involved: S1. Set the parameters required for sea surface modeling, calculate the TMA shallow water wave spectrum, build a nearshore sea surface simulation scene based on the TMA shallow water wave spectrum, and set simulation parameters in the nearshore sea surface simulation scene; S2. Optimize the nearshore sea surface simulation scene, construct the land scene, and combine the nearshore sea surface simulation scene and the land scene into an ocean shore-to-ship simulation scene; S3, calculating the time autocorrelation function of the waves, calculating the refresh time of the ocean shore-to-ship simulation scene according to the time autocorrelation function of the waves, and performing ray tracing simulation; S4. Process ray tracing simulation data and analyze the characteristics of ocean shore-to-ship channels.

2. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 1 is characterized in that: In step S1, the TMA shallow water wave spectrum calculation formula is: The calculation method of Φ(ω,h) is: Where ω is the angular frequency of the wave; h is the depth of the sea water; θ is the direction of movement of the wave; g is the acceleration of gravity; Φ(ω,h) is the water depth factor; γ is the peak enhancement factor of the wave spectrum; σ is the peak shape factor of the wave spectrum; D(θ)=2cos 2 (θ) / π, is the wave propagation direction function; α=0.076(gX / u 2 ) -0.22 , represents the intensity of the wave spectrum; ω m is the peak frequency of the wave spectrum, ω m =7π(g / u)(gX / u 2 ) -0.33 ; X is the sea surface acquisition length (the length of the wind blowing over the sea surface); u is the sea surface wind speed.

3. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 2 is characterized in that: In step S1, the sea surface height is modeled by the Longuet-Higgins model according to the TMA shallow water wave spectrum: Among them, H(x,y,t) represents the sea surface height at the coordinate (x,y) at time t; in sea surface modeling, the sea waves are divided into the superposition of waves with i frequencies and j moving direction angles, a ij is the amplitude of the wave with the i-th frequency and j-th moving direction angle; represents the wave number of the ith wave, ω i and θ j are the values ​​of the i-th frequency and j-th direction angle of the wave respectively; ε ij is a random initial phase uniformly distributed in (0,2π).

4. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 1 is characterized in that: In step S1, the simulation parameters are set in the nearshore sea surface simulation scene as follows: Set the antenna type, antenna polarization mode, transmission power and antenna gain of the transmitter and receiver in the nearshore sea simulation scene; the transmitter is a shore base station and the receiver is a receiving device on a ship at sea.

5. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 1 is characterized in that: The step S2 comprises: S201, setting the length direction of the sea surface as the positive direction of the x-axis, and the width direction of the sea surface as the positive direction of the y-axis, determining the sea surface range according to the length and width of the sea surface, dividing it into a number of grids, and further dividing the grids where the receiving end, the transmitting end and the mirror reflection point are located into a number of small grids; S202, using scene modeling software to draw shore buildings to obtain a land scene model; splicing the land scene model with the nearshore sea surface simulation scene model to form an ocean shore-to-ship simulation scene.

6. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 1 is characterized in that: The step S3 comprises: S301, calculating the time autocorrelation function of the ocean waves, and determining the time interval for scene refresh: According to the set environmental parameters, the time autocorrelation function of the waves is calculated. The time when the time autocorrelation function first drops to 1 / 2 of the initial value is the time interval for scene refresh. S302, scene update and ray emission: Before emitting rays, determine whether the interval between ray emission exceeds the time interval of scene refresh. If not, use the last generated scene for ray tracing. If yes, refresh the scene first, and then emit rays uniformly into space from the emission end. S303, Ray Tracing: According to the Delaunay triangulation algorithm, the nearshore sea surface simulation scene is Delaunay triangulated to divide the sea surface into several triangular faces, and the vertex coordinates of the triangular faces are obtained; monitor whether the ray collides with the triangular face, if a collision occurs, the ray collides with the sea surface or the building on the coast and reflects, if a reflection occurs, continue to track the reflected light to determine whether the next reflection will occur; repeat the above monitoring process until the ray energy decays below the threshold or the reflection order reaches the set maximum reflection order, the ray tracing process stops; S304, ray reception The receiving sphere method is used at the receiving end to make a reception judgment, and whether the ray is received is determined based on the intersection relationship between the ray and the receiving sphere; the radius of the receiving sphere is calculated by the actual path length of the ray between the source point and the receiving end and the angle between two adjacent rays at the source point; finally, the receiving power, delay and angle of each ray are calculated based on the received ray parameters.

7. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 6 is characterized in that: In step S301, the calculation formula of the time autocorrelation function is:

8. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 6 is characterized in that: In step S303, when tracing the reflected light, the loss caused by the reflection is affected by the reflection coefficient, and the magnitude of the loss is calculated by multiplying the reflection coefficient by the intensity of the incident wave; According to Snell's law, the Fresnel reflection coefficients of horizontally polarized waves and vertically polarized waves are calculated as: Among them, θ g is the grazing incidence angle, is the complex dielectric constant of the reflecting surface, According to the relative dielectric constant of seawater, σ d and the conductivity of seawater is ò s Calculated.

9. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 1 is characterized in that: The step S4 comprises: S401, setting different ocean shore-to-ship simulation scenario parameters, obtaining simulation results under different parameters according to the receiving power, delay and angle of the receiving end ray, and then performing ray tracing simulation on different ocean shore-to-ship scenario models to obtain corresponding simulation results, and performing FI fitting on the simulated path loss data; S402, performing FI fitting on the path loss data actually measured under different parameters, and comparing the FI fitting result of the simulated path loss data with the FI fitting result of the actually measured path loss data to analyze the accuracy of the model; S403, performing FI fitting on the free space path loss data under different parameters, and comparing the FI fitting result of the simulated path loss data with the FI fitting result of the free space path loss data, to analyze the loss characteristics of the ocean shore-to-ship wireless channel; S404, comparing the simulated path loss data FI fitting results under different data of the same parameter, and analyzing the influence of each parameter on the ocean shore-to-ship wireless channel.

10. The ocean shore-to-ship wireless channel modeling method based on ray tracing according to claim 9 is characterized in that: In step S4: The FI fitting formula for the simulated path loss data under different parameters is: PL FIPL (d)=20nlog 10 (d)+β+X σ The FI fitting formula for free space path loss data under different parameters is: PL FSPL (d)=20log 10 (d)+99.05 Where d is the distance between the receiver and the transmitter, n is the path loss exponent, β is a constant, and X σ is a lognormal random variable with mean 0dB and σ is the standard deviation.

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