A broadband shortwave channel simulation calculation method based on ray tracing algorithm and ITS model

Abstract

The present invention discloses a broadband shortwave channel simulation calculation method based on a ray tracing algorithm and an ITS model, comprising the following steps: step 1, setting the geographical longitude and latitude information of the transmitting point position and the receiving point position; step 2, using the ionosphere background model to calculate the ionosphere electron density and its gradient of change in all directions; step 3, using a three-dimensional ray tracing algorithm to calculate the propagation parameters of the shortwave signal propagating between the transmitting and receiving point positions, including the minimum delay, maximum delay, average delay and Doppler frequency shift; step 4, using the propagation parameters calculated by the three-dimensional ray tracing algorithm or the propagation parameters obtained by experimental data as input, and obtaining the impulse response function of the shortwave channel according to the ITS model. The method disclosed by the present invention realizes broadband shortwave channel simulation calculation, and the obtained shortwave channel model takes into account the shortwave signal delay and Doppler expansion effect caused by the ionosphere, and can simulate and calculate the shortwave link channel in any region of the world.

Description

Technical Field

[0001] The invention belongs to the field of shortwave channel model simulation calculation, and particularly relates to a broadband shortwave channel simulation calculation method based on a ray tracing algorithm and an ITS model in the field. Background Art

[0002] Shortwave and satellite are two important means of communication. Compared with satellite communication, shortwave communication has many advantages, such as low construction and maintenance costs, simple equipment, flexible mobility, and strong anti-destruction ability, so it occupies an important position in the field of military communications. Shortwave communication mainly uses sky waves to propagate through the reflection of the ionosphere, and can achieve long-distance communication without the use of relay stations. At the same time, due to the openness and indestructibility of the ionosphere, compared with other communication means such as cables, optical cables, and satellites, shortwave communication has a great advantage in the process of achieving long-distance communication. The networking method of shortwave communication is very convenient, fast, and highly mobile. It has a strong ability to resist natural disasters and war destruction. In addition, the equipment is small in size, and the frequency change is very convenient. It can effectively avoid human interference and has strong recovery ability.

[0003] In actual applications, the shortwave signal propagation area covers various inhomogeneous structures of the ionosphere in different regions. Existing empirical models based on statistical data cannot solve the problem of high-precision prediction of shortwave signal propagation. In the process of shortwave propagation link calculation, there are often large errors when using these models, and there are various deficiencies in engineering applications. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a broadband shortwave channel simulation calculation method based on a ray tracing algorithm and an ITS model, aiming at the problem of shortwave signal propagation, taking into account the influence of the ionosphere in different latitudes on the propagation path on the shortwave signal.

[0005] The present invention adopts the following technical solution:

[0006] A broadband shortwave channel simulation calculation method based on a ray tracing algorithm and an ITS model, the improvement of which is that it comprises the following steps:

[0007] Step 1, setting the geographical longitude and latitude information of the transmitting point location and the receiving point location;

[0008] Step 2, using the ionospheric background model to calculate the ionospheric electron density and its gradient in all directions: for low and medium latitudes with latitudes less than or equal to 60°, the international reference ionosphere IRI model is used to calculate the three-dimensional electron density distribution; for high latitudes with latitudes greater than 60° and polar regions, the Echarm model is used to calculate the three-dimensional electron density distribution;

[0009] Step 3, using a three-dimensional ray tracing algorithm to calculate the propagation parameters of the shortwave signal between the transmitting and receiving points, including the minimum delay, maximum delay, average delay and Doppler frequency shift;

[0010] Step 4: Using the propagation parameters calculated by the three-dimensional ray tracing algorithm or the propagation parameters obtained by the test data as input, the impulse response function of the shortwave channel is obtained according to the ITS model.

[0011] Furthermore, the step 3 is specifically as follows:

[0012] Step 31, according to the set transmitting point position xA, yA and receiving point position xB, yB, calculate the azimuth angle β from the transmitting point position to the receiving point position:

[0013] Calculate the coordinate difference between the two points Δx = xA-xB, Δy = yA-yB, if Δx>0, Δy>0, then β = arctg(Δy / Δx); if Δx<0, Δy>0, then β = 180°-arctg(Δy / Δx); if Δx<0, Δy<0, then β = 180°+arctg(Δy / Δx); if Δx>0, Δy<0, then β = 360°-arctg(Δy / Δx);

[0014] Step 32, using a three-dimensional ray tracing algorithm to calculate the propagation path of the ray:

[0015]

[0016] In the above formula, ω is the frequency of the incident wave, c is the speed of light, r, θ and is the ray path coordinate in the spherical coordinate system, k r ,k θ and is the component of the wave vector in the spherical coordinate system, P' is the ray group path, Δf is the Doppler frequency shift, t is the time, and H is the Hamiltonian operator:

[0017]

[0018] In the above formula, n is the ionospheric refractive index:

[0019]

[0020] In the above formula, m is the mass of the electron, e is the charge of the electron, B L is the projection of the geomagnetic field in the direction of electromagnetic wave propagation, B T is the projection of the Earth's magnetic field perpendicular to the direction of electromagnetic wave propagation, N is the electron density, "+" is ordinary wave, "-" is extraordinary wave, ε0 is the vacuum dielectric constant;

[0021] Step 33, setting the azimuth angle according to the calculation result of step 31, and setting the group path calculation step length, elevation angle range, and elevation angle step length;

[0022] Step 34, according to the above steps, calculate the ray paths at different elevation angles at the specified frequency to obtain the maximum delay, minimum delay, average delay and Doppler frequency shift. The calculation method of the delay T is:

[0023] T=P' / c

[0024] In the above formula, c is the speed of light.

[0025] Furthermore, the step 4 is specifically as follows:

[0026] Step 41, the structure of the ITS model is described in the form of a time-varying channel impulse response, which is defined as a function of time t and a delay variable τ, and is expressed as:

[0027]

[0028] In the above formula, n = 1, 2, ... N represents the multipath mode, h n (t,τ) represents the impulse response of the nth shortwave propagation path, which consists of three parts: the random modulation function ψ n (t,τ), determine the phase function D n (t,τ) and the delayed power profile function P n (τ);

[0029] Step 42, random modulation function simulation:

[0030] Use the sine wave superposition method to construct the random modulation function in the broadband channel model;

[0031] Step 43, determine the phase function simulation:

[0032] The phase function is defined as:

[0033]

[0034] According to Euler's formula:

[0035] D(t,τ)=cos2π[f s +b(τ-τ c )]t+jsin2π[f s +b(τ-τ c )]t

[0036] Written in discrete form:

[0037]

[0038] In the above formula, τ is the time delay variable; τc is the delay corresponding to the power peak; τ L is the lower limit of delay when the power is the receiving threshold, b is the rate of change of Doppler frequency shift relative to τ; f s is τ=τ c The Doppler frequency shift at time, f sL Indicates that τ = τ L The Doppler value at time, f Ts Indicates the sampling frequency of the channel;

[0039] Step 44, delay power profile simulation:

[0040] The mathematical statistical model of the delayed power profile function is:

[0041]

[0042] In the above formula, A is the peak power of the receiving channel, α represents the parameter of the delayed power profile curve shape; Γ(·) is the gamma distribution function; τ is the delay variable; τ c is the delay corresponding to the power peak, and Δ controls the width of the delay spread.

[0043] The beneficial effects of the present invention are:

[0044] The method disclosed in the present invention realizes broadband shortwave channel simulation calculation. The obtained shortwave channel model takes into account the shortwave signal delay and Doppler expansion effect caused by the ionosphere, and can simulate and calculate the shortwave link channel in any region of the world. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic flow diagram of the method of the present invention;

[0046] Figure 2 It is the electron concentration profile at the geographical location (40°N, 120°E) at 12:00 (Beijing time) on October 16, 2024;

[0047] Figure 3 This is an example diagram of the ray path of a shortwave signal calculated by the ray tracing algorithm;

[0048] Figure 4 It is a schematic diagram of the channel impulse response function in multipath mode;

[0049] Figure 5 It is a schematic diagram of the scattering function (Gaussian spectrum) in multipath mode. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0051] Embodiment 1, this embodiment discloses a broadband shortwave channel simulation calculation method based on ray tracing algorithm and ITS model, such as Figure 1 As shown, the following steps are included:

[0052] Step 1, setting the geographical longitude and latitude information of the transmitting point location and the receiving point location;

[0053] Step 2: Use the ionospheric background model to calculate the ionospheric electron density and its gradient in all directions: for low and medium latitudes with latitudes less than or equal to 60°, the international reference ionosphere IRI model is used to calculate the three-dimensional electron density distribution; for high latitudes and polar regions with latitudes greater than 60°, the Echarm model is used to calculate the three-dimensional electron density distribution; the calculated electron concentration profile at the geographical location (40°N, 120°E) at 12:00 (Beijing time) on October 16, 2024 is as follows: Figure 2 shown.

[0054] Step 3, using a three-dimensional ray tracing algorithm to calculate the propagation parameters of the shortwave signal between the transmitting and receiving points, including parameters such as minimum delay, maximum delay, average delay, and Doppler frequency shift;

[0055] The step 3 is specifically as follows:

[0056] Step 31, according to the set transmitting point position xA, yA and receiving point position xB, yB, calculate the azimuth angle β from the transmitting point position to the receiving point position:

[0057] Calculate the coordinate difference between the two points Δx = xA-xB, Δy = yA-yB, if Δx>0, Δy>0, then β = arctg(Δy / Δx); if Δx<0, Δy>0, then β = 180°-arctg(Δy / Δx); if Δx<0, Δy<0, then β = 180°+arctg(Δy / Δx); if Δx>0, Δy<0, then β = 360°-arctg(Δy / Δx);

[0058] Step 32, using a three-dimensional ray tracing algorithm to calculate the propagation path of the ray:

[0059] The propagation of high-frequency radio waves generally satisfies the geometric optics approximation, and the ray tracing method can be used to study the propagation of radio waves in the ionosphere. The ray tracing equation considering the earth's magnetic field is:

[0060]

[0061] In the above formula, ω is the frequency of the incident wave, c is the speed of light, r, θ and is the ray path coordinate in the spherical coordinate system, k r ,k θ and is the component of the wave vector in the spherical coordinate system, P' is the ray group path, Δf is the Doppler frequency shift, t is the time, and H is the Hamiltonian operator:

[0062]

[0063] In the above formula, n is the ionospheric refractive index:

[0064]

[0065] In the above formula, m is the mass of the electron, e is the charge of the electron, B L is the projection of the geomagnetic field in the direction of electromagnetic wave propagation, B T is the projection of the Earth's magnetic field perpendicular to the direction of electromagnetic wave propagation, N is the electron density, "+" is the ordinary wave, "-" is the extraordinary wave. After entering the ionosphere, the electromagnetic wave splits into ordinary waves and extraordinary waves, and propagates at different speeds. ε0 is the vacuum dielectric constant;

[0066] Step 33, setting the azimuth angle according to the calculation result of step 31, and setting the group path calculation step length, elevation angle range, and elevation angle step length according to the actual calculation accuracy requirements;

[0067] Step 34, according to the above steps, calculate the ray paths at different elevation angles at the specified frequency, calculate the delays of the rays of different propagation modes near the landing point at the receiving point, and obtain the maximum delay, minimum delay, average delay and Doppler frequency shift. The calculation method of the delay T is:

[0068] T=P' / c

[0069] In the above formula, c is the speed of light, c = 3.0 × 10 8 m / s.

[0070] An example of a ray path calculated according to the above steps is as follows Figure 3 shown.

[0071] Step 4: Using the propagation parameters calculated by the three-dimensional ray tracing algorithm or the propagation parameters obtained by the test data as input, the impulse response function of the shortwave channel is obtained according to the ITS model.

[0072] The step 4 is specifically as follows:

[0073] Step 41, the structure of the ITS model is described in the form of a time-varying channel impulse response, which is defined as a function of time t and a delay variable τ, and is expressed as:

[0074]

[0075] In the above formula, n = 1, 2, ... N represents the multipath mode, h n (t,τ) represents the impulse response of the nth shortwave propagation path, which consists of three parts: the random modulation function ψ n (t,τ), determine the phase function D n (t,τ) and the delayed power profile function P n (τ);

[0076] Step 42, random modulation function simulation:

[0077] The essence of the random modulation function is a Rayleigh random process that obeys a Gaussian distribution or a Lorentzian Doppler spread distribution. The Rayleigh fading process can be implemented by a filter method or by using a sine wave superposition method (SoS) simulation. The present invention uses a sine wave superposition method to construct a random modulation function in a broadband channel model;

[0078] Step 43, determine the phase function simulation:

[0079] The Doppler shift of the propagation path is achieved by multiplying the path impulse response by a deterministic phase function D(t,τ), which is defined as:

[0080]

[0081] According to Euler's formula:

[0082] D(t,τ)=cos2π[f s +b(τ-τ c )]t+jsin2π[f s +b(τ-τ c )]t

[0083] Written in discrete form:

[0084]

[0085] In the above formula, τ is the time delay variable; τ c is the delay corresponding to the power peak; τ L is the lower limit of delay when the power is the receiving threshold, b is the rate of change of Doppler frequency shift relative to τ; f s is τ=τ c The Doppler frequency shift at time, f sLIt means that Doppler is at τ = τ L The Doppler value at time, f Ts Indicates the sampling frequency of the channel;

[0086] Step 44, delay power profile simulation:

[0087] The ITS channel model uses the Gamma distribution form for the channel delay power profile function, and its mathematical statistical model is:

[0088]

[0089] In the above formula, A is the peak power of the receiving channel (considered to be a constant under a given propagation mode and can take a random value between 0 and 1), α represents the parameter of the shape of the delay power profile curve, and its value determines the symmetry of the delay power profile function curve; Γ(·) is the gamma distribution function (gamma function); τ is the delay variable; τ c It is the delay corresponding to the power peak, which determines the delay offset; Δ controls the width of the delay spread.

[0090] In order to verify the effectiveness of the method of the present invention for the shortwave channel model, this embodiment provides the impulse response function and scattering function of the shortwave channel under two propagation modes, as shown in FIG. Figure 4 and Figure 5 shown.

Claims

1. A broadband shortwave channel simulation calculation method based on ray tracing algorithm and ITS model, characterized in that: The steps include: Step 1, setting the geographical longitude and latitude information of the transmitting point location and the receiving point location; Step 2, using the ionospheric background model to calculate the ionospheric electron density and its gradient in all directions: for low and medium latitudes with latitudes less than or equal to 60°, the international reference ionosphere IRI model is used to calculate the three-dimensional electron density distribution; for high latitudes with latitudes greater than 60° and polar regions, the Echarm model is used to calculate the three-dimensional electron density distribution; Step 3, using a three-dimensional ray tracing algorithm to calculate the propagation parameters of the shortwave signal between the transmitting and receiving points, including the minimum delay, maximum delay, average delay and Doppler frequency shift; Step 4: Using the propagation parameters calculated by the three-dimensional ray tracing algorithm or the propagation parameters obtained by the test data as input, the impulse response function of the shortwave channel is obtained according to the ITS model.

2. The broadband shortwave channel simulation calculation method based on ray tracing algorithm and ITS model according to claim 1 is characterized in that: The step 3 is specifically as follows: Step 31, according to the set transmitting point position xA, yA and receiving point position xB, yB, calculate the azimuth angle β from the transmitting point position to the receiving point position: Calculate the coordinate difference between the two points Δx = xA-xB, Δy = yA-yB, if Δx>0, Δy>0, then β = arctg(Δy / Δx); if Δx<0, Δy>0, then β = 180°-arctg(Δy / Δx); if Δx<0, Δy<0, then β = 180°+arctg(Δy / Δx); if Δx>0, Δy<0, then β = 360°-arctg(Δy / Δx); Step 32, using a three-dimensional ray tracing algorithm to calculate the propagation path of the ray: In the above formula, ω is the frequency of the incident wave, c is the speed of light, r, θ and is the ray path coordinate in the spherical coordinate system, k r ,k θ and is the component of the wave vector in the spherical coordinate system, P' is the ray group path, Δf is the Doppler frequency shift, t is the time, and H is the Hamiltonian operator: In the above formula, n is the ionospheric refractive index: In the above formula, m is the mass of the electron, e is the charge of the electron, B L is the projection of the geomagnetic field in the direction of electromagnetic wave propagation, B T is the projection of the Earth's magnetic field perpendicular to the direction of electromagnetic wave propagation, N is the electron density, "+" is ordinary wave, "-" is extraordinary wave, ε0 is the vacuum dielectric constant; Step 33, setting the azimuth angle according to the calculation result of step 31, and setting the group path calculation step length, elevation angle range, and elevation angle step length; Step 34, according to the above steps, calculate the ray paths at different elevation angles at the specified frequency to obtain the maximum delay, minimum delay, average delay and Doppler frequency shift. The calculation method of the delay T is: T=P' / c In the above formula, c is the speed of light.

3. The broadband shortwave channel simulation calculation method based on ray tracing algorithm and ITS model according to claim 1 is characterized in that: The step 4 is specifically as follows: Step 41, the structure of the ITS model is described in the form of a time-varying channel impulse response, which is defined as a function of time t and a delay variable τ, and is expressed as: In the above formula, n = 1, 2, ... N represents the multipath mode, h n (t,τ) represents the impulse response of the nth shortwave propagation path, which consists of three parts: the random modulation function ψ n (t,τ), determine the phase function D n (t,τ) and the delayed power profile function P n (τ); Step 42, random modulation function simulation: Use the sine wave superposition method to construct the random modulation function in the broadband channel model; Step 43, determine the phase function simulation: The phase function is defined as: According to Euler's formula: D(t,τ)=cos2π[f s +b(τ-τ c )]t+jsin2π[f s +b(τ-τ c )]t Written in discrete form: In the above formula, τ is the time delay variable; τ c is the delay corresponding to the power peak; τ L is the lower limit of delay when the power is the receiving threshold, b is the rate of change of Doppler frequency shift relative to τ; f s is τ=τ c The Doppler frequency shift at time, f sL Indicates that τ = τ L The Doppler value at time, f Ts Indicates the sampling frequency of the channel; Step 44, delay power profile simulation: The mathematical statistical model of the delayed power profile function is: In the above formula, A is the peak power of the receiving channel, α represents the parameter of the delayed power profile curve shape; Γ(·) is the gamma distribution function; τ is the delay variable; τ c is the delay corresponding to the power peak, and Δ controls the width of the delay spread.

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