A beamforming method based on earth matching

Abstract

The present invention discloses a beamforming method based on earth matching, including S1: determining a satellite beam coverage area target, dividing the satellite beam coverage area, and obtaining a plurality of sub-areas; S2: obtaining a normalized space decay curve according to the geometric relationship between the satellite and the earth; S3: calculating the gain value that needs to be met for each sub-area coverage according to the normalized space decay curve, and using a particle swarm algorithm to perform beamforming coverage design for each sub-area to obtain a beamforming gain pattern; S4: adjusting each sub-area so that the beamforming gain pattern meets the normalized space decay curve coverage requirement; S5: after completing the beamforming coverage design of all sub-areas, counting the coverage rate in the entire satellite beam coverage area. The present invention is based on beam division and color multiplexing in different areas, and the antenna pattern main beam earth matching design, avoiding co-frequency interference and improving the accuracy of beamforming design.

Description

Technical Field

[0001] The present invention relates to the field of satellite communications, and in particular to a beamforming method based on earth matching. Background Art

[0002] For medium and low orbit spacecraft, due to the significant influence of the earth's curvature, the transmission paths of the spacecraft to ground stations at different angles are different. The larger the angle, the longer the transmission path and the greater the path loss. In order to compensate for this loss, on-board shaped beam design is generally used. In LEO satellite mobile communication systems, "equal flux" coverage and optimal beamforming are key technologies to improve the coverage efficiency of onboard antennas and ensure maximum system capacity.

[0003] Beamforming refers to the generation of the required irregular pattern to achieve coverage of a specific area. The coverage pattern of a satellite determines the market it can serve and the flexibility of expanding services. Early shaped beam antennas used a single feed plus a reflector to achieve regional beamforming, which was used to cover a country or hemisphere. Currently, many satellite communication systems use constellations to provide global continuous and seamless coverage. The rise of communication services has led to spectrum congestion, and single-beam coverage often cannot meet user requirements. The use of multiple point beam coverage solutions with frequency reuse can greatly improve system capacity, increase system flexibility, and effectively increase effective isotropic radiated power (EIRP). The frequency resources of the entire system are divided into multiple frequency bands, and adjacent beams avoid mutual interference by using different frequencies or polarization forms. The shape of each beam must also be shaped. The multiple beams required for shaped coverage can be generated by irradiating the reflector with multiple feeds, or by using a phased array antenna through a multi-beam network.

[0004] Common beamforming methods include Chebyshev synthesis and Taylor synthesis, Fourier transform, Woodward-Lawson, and perturbation methods. These synthesis methods have a typical characteristic, that is, they are all for typical aperture distribution. For shaping of array antennas of arbitrary shapes, complex pattern synthesis technology must be used.

[0005] The existing reflection surface beamforming method cannot scan at a large angle, cannot generate more beams, lacks flexibility in beamforming, and cannot be based on earth matching. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the existing reflector beamforming method cannot scan at a large angle, cannot generate more beams, has insufficient flexibility in beamforming, and cannot be based on earth matching. The purpose is to provide a beamforming method based on earth matching to solve the above technical problems.

[0007] The present invention is achieved through the following technical solutions:

[0008] A beamforming method based on earth matching comprises the following steps:

[0009] S1: Determine the satellite beam coverage area target, divide the satellite beam coverage area into multiple sub-areas;

[0010] S2: Obtain the normalized space attenuation curve of antenna scanning angle and path loss based on the geometric relationship between the satellite and the earth;

[0011] S3: According to the normalized empty decay curve, the gain value that needs to be met for the coverage of each sub-area is calculated, and based on the gain value that needs to be met for the coverage of each sub-area, the particle swarm algorithm is used to perform beamforming coverage design for each sub-area to obtain the beamforming gain pattern of each sub-area;

[0012] S4: Adjust each sub-area so that the beamforming gain pattern of each sub-area meets the coverage requirement of the normalized space attenuation curve;

[0013] S5: After completing the beamforming coverage design for all sub-areas, the coverage rate of the entire satellite beam coverage area is counted.

[0014] Further, in step S1, the target of determining the satellite beam coverage area is specifically: determining the spatial area covered by the satellite beam as [Theta n , Phi m ]; n = 1, 2, 3...N; m = 1, 2, 3...M; Phi is the angle in the horizontal plane, ranging from 0 to 360 degrees; Theta is the angle in the pitch plane, ranging from 0 to 60 degrees, N is the maximum number of sampling points in the Theta direction, and M is the maximum number of sampling points in the Phi direction.

[0015] Furthermore, in step S1, the satellite beam coverage area is divided into multiple sub-areas, specifically: the space area covered by the satellite beam [Theta n , Phi m ] is divided into multiple sub-areas, divided into n_theta conical rings in the Theta direction, and each conical ring is divided into n_Phi k parts, where k = 1, 2, ... n_theta.

[0016] Further, step S2, the normalized space attenuation curve of the antenna scanning angle and the path loss is obtained according to the geometric relationship between the satellite and the earth, specifically: the path loss is calculated according to the geometric relationship between the satellite and the earth, wherein the earth model is spherical, the radius Re, the satellite orbit height is h, the complementary angle of the latitude of a point on the earth's surface is α, and the antenna scanning angle is θ, The distance from a point on the Earth's surface to the antenna The path loss is expressed as: loss is the path loss, f is the frequency, d is the distance from a point on the earth's surface to the antenna, and c is the speed of light.

[0017] Furthermore, step S3 specifically includes: calculating the gain condition that needs to be met for the coverage of each sub-area based on the normalized space attenuation curve, using the gain condition that needs to be met for the coverage of each sub-area as the objective function of the beamforming of each sub-area, and then using the particle swarm algorithm to design a separate beamforming for each sub-area to obtain a beamforming gain pattern.

[0018] Furthermore, step S4 specifically includes: cyclically adjusting sub-area division, antenna sub-array division and algorithm setting, so that the beamforming gain pattern of each sub-area meets the normalized space attenuation curve coverage requirement.

[0019] Further, step S5 specifically includes: after completing all beam coverage designs, counting the entire space [Theta n , Phi m ] area, repeat the beamforming coverage design for each sub-area until the entire space [Theta n , Phi m ]The regional coverage meets the needs.

[0020] Furthermore, for each sub-area, all antenna array elements are used when performing beamforming design.

[0021] For each sub-area, when designing beamforming, all antenna elements can be used or some antenna elements can be used. If some elements are used, the two-dimensional antenna array of T×P scale needs to be divided into K sub-arrays to cover the 〖n_phi〗kth sub-area, where T is an integer greater than or equal to 1, P is an integer greater than or equal to 1, and K is an integer greater than or equal to 1. Each array element channel is used once to cover the 〖n_phi〗kth sub-area, and the number of times it is used is recorded as once. When all 〖n_phi〗_k sub-areas are counted, the number of times each array element channel is used is recorded as U T×P , T×P is the number of array elements. All U T×P Should be equal to ensure that the single channel power is equal when the full beam is used.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] The present invention provides a beamforming method based on earth matching, which takes into account the energy loss caused by the path difference from satellite to earth, and achieves the purpose of equal flux coverage; only phase weighting avoids the power loss caused by amplitude weighting, and according to beam division and color multiplexing in different areas of the same color, the main beam of the antenna pattern is designed to match the earth, and the side lobe forms zero depth to avoid co-frequency interference. The coverage rate statistics method based on the directional angle solves the inaccurate coverage rate statistics caused by different sampling rates at different theta angles of the directional pattern under the polar coordinate expression of the antenna, and improves the accuracy of the beamforming design. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0025] Figure 1 This is a diagram of the geometric relationship between the satellite and the earth;

[0026] Figure 2 It is the normalized attenuation curve of antenna scanning angle and path loss;

[0027] Figure 3 This is a diagram of the 12-color multiplexing allocation method; each number represents a color, with a total of 12 colors;

[0028] Figure 4 This is a schematic diagram of color multiplexing;

[0029] Figure 5 This is the flow chart of particle swarm algorithm;

[0030] Figure 6 Design a flow chart for the method of the present invention;

[0031] Figure 7 is one of the beamforming diagrams in the sub-region within the first conical ring;

[0032] Figure 8 is one of the beamforming diagrams in the sub-region within the second conical ring;

[0033] Fig. 9 is one of the beamforming diagrams in the sub-region within the third conical ring;

[0034] Fig.10 It is the coverage diagram of 18.3dB equal flux at the edge;

[0035] Fig.11Schematic diagram of the beam profile according to the edge 18.3dB equal flux coverage. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0037] Example

[0038] like Figure 6 As shown, this embodiment specifically includes the following steps:

[0039] Step 1: Based on the EIRP coverage requirements, the coverage area is [Theta n , Phi m ]Where n=1, 2, 3...N, m=1, 2, 3...M, N is the maximum number of sampling points in the Theta direction, M is the maximum number of sampling points in the Phi direction, Theta∈(0, 60)deg, Phi∈(0, 360)deg.

[0040] Step 2: According to the required number of beams Num, the above spatial area [Theta n , Phi m ] is divided into Num sub-regions, and in the Theta direction it is divided into n_theta conical rings. For each conical ring, it is divided into n_Phi k where k = 1, 2, ... n theta. Figure 4 As shown, in this embodiment, the Theta direction is divided into 3 conical rings, the first conical ring is divided into 4 sub-regions, the second conical ring is divided into 16 sub-regions, and the third conical ring is divided into 32 sub-regions.

[0041] Step 3: Based on the empty attenuation curve, calculate the gain condition that needs to be met for each sub-area coverage, and use this as the objective function of the beamforming for each sub-area.

[0042] Step 4: Use the particle swarm algorithm to perform beamforming design for each sub-area. For each sub-area, all antenna elements can be used or some antenna elements can be used. If some elements are used, the two-dimensional antenna array of T×P scale needs to be divided into K sub-arrays to cover the n_Phi k Each array channel is used as the n_Phi k The coverage of sub-areas is counted as one time. When all n_Phi kWhen the sub-areas are counted, the number of times each array channel is used is recorded as U T×P , T×P is the number of array elements. All U T×P Should be equal to ensure that the single channel power is equal when the full beam is used.

[0043] Step 5: Use the ion group algorithm to shape the sub-array sub-area beam, and cyclically adjust the sub-area division, sub-array division and algorithm settings to make the shaping gain pattern meet the coverage requirements of the empty attenuation curve.

[0044] Step 6: After completing the design of all Num beam coverage, count the entire space [Theta n , Phi m ] area, repeat the design of each sub-area coverage until the entire space [Theta n , Phi m ]The regional coverage meets the needs.

[0045] The present invention will be further described in detail below in conjunction with the embodiments and drawings:

[0046] 1. Isoflux Calculation

[0047] For low earth orbit satellites, due to the large beam scanning angle, the path transmission loss in each scanning direction under the satellite varies greatly. The geometric relationship between the satellite and the earth is as follows: Figure 1 As shown, the antenna is installed on the satellite, the normal of the antenna surface points to the center of the earth, the earth model is spherical, the radius is Re, the satellite orbit height is h, the complementary angle of the latitude of a point on the earth's surface is α, and the antenna scanning angle is θ. The distance from a point on the Earth's surface to the antenna

[0048] The satellite-to-ground communication loop channel environment is mainly a Rice channel, and the path loss is mainly a free space path loss, and the path loss increases with the increase of the scanning angle θ: Where loss is the path loss, f is the frequency, d is the distance from a point on the earth's surface to the antenna, and c is the speed of light, c = 3 × 10 11 m / s.

[0049] By analyzing the geometric relationship between the satellite and the earth, we can get the following according to the satellite altitude: Figure 2 The normalized attenuation curve of antenna scanning angle (elevation angle) and path loss is shown in Figure 1. Figure 2 As shown in the figure, the maximum scanning angle of this earth-matching-based digital multi-beam research is 55°. It can be seen that the path transmission loss difference between the beam edge point and the sub-satellite point is about 7.5dB.

[0050] 2. Beam division 12-color multiplexing According to the EIRP coverage requirements, the covered space area is [Theta n , Phi m ] Where n=1, 2, 3...N, m=1, 2, 3...M, Theta∈(0,60)deg, Phi∈(0,360)deg.

[0051] According to the required number of beams Num, the above space area [Theta n , Phi m ] is divided into Num sub-regions, and in the Theta direction it is divided into n_theta conical rings. For each conical ring, it is divided into n_Phi k parts, where k = 1, 2, ..., n_theta.

[0052] like Figure 4 As shown, in this embodiment, it is divided into 3 conical rings in the Theta direction, the first conical ring is divided into 4 sub-regions, the second conical ring is divided into 16 sub-regions, and the third conical ring is divided into 32 sub-regions, for a total of 52 sub-regions.

[0053] like Figure 3 As shown in the figure, 52 sub-areas correspond to 52 beams, beams 1 to 4 use one color each, and the middle and outer beams use one color every 6 beams, and the 6 beams correspond to the same frequency. In order to avoid co-frequency interference between adjacent beams, different frequencies are used for adjacent areas, and the purpose of reducing interference and increasing capacity is achieved through reasonable frequency allocation.

[0054] According to the normalized attenuation curve of antenna scanning angle and path loss, the gain condition that needs to be met for coverage of each sub-area is calculated, which is used as the objective function of beamforming for each sub-area.

[0055] Phase-only beamforming

[0056] Beamforming can use amplitude and phase weighting. Amplitude weighting will reduce the input power of the antenna port, which will lead to a reduction in EIRP. Since EIRP is equal to gain plus input power, this will lead to an increase in power or a larger array size. Therefore, the beamforming method based on earth matching in this embodiment adopts only phase weighting.

[0057] Assume that the i-th particle is represented by X = [xi1, xi2, ..., xiD], the speed and best position experienced by the particle are X = [xi1, xi2, ..., xiD], Pbest = [pi1, pi2, ..., piD], and the best position experienced by all particles in the group is Gbest. The speed and position update formulas of each generation of individuals in the j-dimensional (1≤j≤D) are as follows:

[0058] (1)Vij=W*Vij+C1*rand1*(Pbest-Xij)+C2*rand2*(Gbest-Xij)

[0059] (2) Xij = Xij + Vij

[0060] In the formula, rand1 and rand2 are two random numbers between 0 and 1; c1 and c2 are learning factors, usually c1=c2=2; w is a weighting coefficient, ranging from 0.1 to 0.9. In addition, if the particle's speed vij should be less than a maximum speed vmax, when the particle's speed is accelerated to exceed vmax, the speed of this dimension should be limited to vmax. Analyzing formula (1), it can be found that the updated speed of the particle consists of three parts: the first part is the speed of the particle itself; the second part is the result of the particle's cognitive update through its own search; the third part is the result of the particle's further update through communication and learning with the group.

[0061] This embodiment uses a particle swarm algorithm to implement antenna beamforming, such as Figure 5 As shown, Figure 5 The flowchart of particle swarm algorithm is as follows:

[0062] Step 3.1: Initialize the position and velocity of the particle swarm;

[0063] Step 3.2: Calculate the fitness value of each particle in the particle swarm;

[0064] Step 3.3: For each particle, compare its current fitness value with the fitness value corresponding to its individual historical best position (pbest). If the current fitness value is higher, use the current position to update the individual particle's historical best position pbest.

[0065] Step 3.4: For each particle, compare its current fitness value with the fitness value corresponding to the global best position (gbest). If the current fitness value is higher, use the current position to update the historical best position gbest of the particle group.

[0066] Step 3.5: Record the optimal value of the particle and the optimal value of the group, and update the speed and position of the particle;

[0067] Step 3.6: If the termination condition is not met, go to step 3.2.

[0068] According to Figure 2 The normalized attenuation curve of antenna scanning angle and path loss is shown in the figure. The gain condition that needs to be met for each sub-area coverage is calculated, which is used as the objective function of beamforming for each sub-area. The particle swarm algorithm is used to design the beamforming for each sub-area separately.

[0069] like Figure 7-9 As shown, from Figure 7 It can be seen from the figure that through beamforming, a circle of beams covers the target area; Figure 8 It can be seen from the figure that through beamforming, two circles of beams cover the target area; Fig. 9 It can be seen that through beamforming, three circles of beams cover the target area.

[0070] For each sub-area, when performing beamforming design, all antenna array elements can be used, or some antenna array elements can be used. If some antenna elements are used, the two-dimensional antenna array of T×P scale needs to be divided into K sub-arrays to cover the 〖n_phi〗_kth sub-area.

[0071] Each array element channel is used to cover the 〖n_phi〗_kth sub-area once, and the number of times used is recorded as once. When all 〖n_phi〗_k sub-areas are counted, the number of times each array element channel is used is recorded as U. T×P , T×P is the number of array elements. All U T×P Should be equal to ensure that the single channel power is equal when the full beam is used.

[0072] The ion group algorithm is used to shape the sub-array sub-area beam, and the sub-area division, sub-array division and algorithm settings are cyclically adjusted to make the shaping gain radiation pattern meet the coverage requirements of the empty attenuation curve.

[0073] 3. Beam Coverage Statistics

[0074] After completing the design of all Num beam coverage, the entire space [Theta n , Phi m ] area, repeat the design of each sub-area coverage until the entire space [Theta n , Phi m ]The regional coverage meets the needs.

[0075] This embodiment adopts a coverage statistics method based on azimuth. For polar coordinates under antenna coordinates, the directional pattern is expressed by a (theta, phi) matrix, and the coverage rate is calculated using the stereo azimuth corresponding to each coordinate as a weight, which better expresses the spatial coverage. For the polar coordinate matrix P, integration can obtain the direction angle weight matrix Ω, and the coverage rate is: (P>Eq)*Ω / Ωtotal, where Ωtotal represents the total direction angle within the coverage range.

[0076] Fig.10 This is a beam coverage statistics chart. According to the edge 18.3dB equal flux coverage, the 18.3dB antenna coordinate coverage rate reaches 99.89%. Fig.11 Schematic diagram of beam coverage outline at edge 18.3dB.

[0077] The following table lists the carrier-to-interference ratio C / I for reception conditions.

[0078] Table 1 C / I of 12 colors

[0079]

[0080]

[0081] In this embodiment, beamforming is used to achieve a carrier-to-interference ratio C / I greater than 16 dB.

[0082] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A beamforming method based on earth matching, characterized in that: The following steps are involved: S1: Determine the satellite beam coverage area target, divide the satellite beam coverage area into multiple sub-areas; S2: Obtain the normalized space attenuation curve of antenna scanning angle and path loss based on the geometric relationship between the satellite and the earth; S3: According to the normalized space attenuation curve, the gain condition that needs to be met for the coverage of each sub-area is calculated, and the gain condition that needs to be met for the coverage of each sub-area is used as the objective function of the beamforming of each sub-area. Based on the objective function, a particle swarm algorithm is used to perform beamforming on each sub-area to obtain a beamforming gain pattern of each sub-area. S4: Adjust each sub-area so that the beamforming gain pattern of each sub-area meets the coverage requirement of the normalized space attenuation curve; S5: After completing the beam coverage design of all sub-areas, count the coverage rate of the entire satellite beam coverage area, and repeat the coverage design of each sub-area until the coverage rate of the entire satellite beam coverage area meets the requirements.

2. The beamforming method based on earth matching according to claim 1, characterized in that: In step S1, the target of determining the satellite beam coverage area is specifically: determining the spatial area covered by the satellite beam as [Theta n , Phi m ]; n = 1, 2, 3...N; m = 1, 2, 3...M; Phi is the angle in the horizontal plane, ranging from 0 to 360 degrees; Theta is the angle in the pitch plane, ranging from 0 to 60 degrees, N is the maximum number of sampling points in the Theta direction, and M is the maximum number of sampling points in the Phi direction.

3. The beamforming method based on earth matching according to claim 2, characterized in that: In step S1, the satellite beam coverage area is divided into multiple sub-areas, specifically: the space area covered by the satellite beam [Theta n , Phi m ] is divided into multiple sub-areas, divided into n_theta conical rings in the Theta direction, and each conical ring is divided into n_Phi k parts, where k = 1, 2, ... n_theta.

4. The beamforming method based on earth matching according to claim 3, characterized in that: Step S2, obtaining a normalized space attenuation curve of antenna scanning angle and path loss according to the geometric relationship between the satellite and the earth, specifically includes: calculating the path loss according to the geometric relationship between the satellite and the earth, wherein the earth is spherical, the earth radius is Re, the satellite orbit height is h, the complementary angle of the latitude of a point on the earth surface is α, and the antenna scanning angle is θ, The distance from a point on the Earth's surface to the antenna The path loss is expressed as: loss is the path loss, f is the frequency, d is the distance from a point on the earth's surface to the antenna, and c is the speed of light.

5. The beamforming method based on earth matching according to claim 1, characterized in that: Step S4 specifically includes: cyclically adjusting sub-area division, antenna sub-array division and algorithm setting, so that the beamforming gain pattern of each sub-area meets the normalized space attenuation curve coverage requirement.

6. The beamforming method based on earth matching according to claim 1, characterized in that: Step S5 specifically includes: after completing all beam coverage designs, counting the entire space [Theta n , Phi m ] area, repeat the beamforming coverage design for each sub-area until the entire space [Theta n , Phi m ]The regional coverage meets the needs.

7. The beamforming method based on earth matching according to claim 1, characterized in that: For each sub-area, all antenna array elements are used when designing beamforming.

8. The beamforming method based on earth matching according to claim 1, characterized in that: For each sub-area, when designing beamforming, partial antenna elements are used to divide the T×P-scale two-dimensional antenna array into K sub-arrays to cover the n_Phi k sub-areas, wherein T is an integer greater than or equal to 1, P is an integer greater than or equal to 1, and K is an integer greater than or equal to 1.

9. The beamforming method based on earth matching according to claim 7 or 8, characterized in that: Each array element channel is used as a n_Phi k The coverage of sub-areas is counted as one time. When all n_Phi k When the sub-areas are counted, the number of times each array channel is used is recorded as U T×P , T×P is the number of array elements, all U T×P Should be equal to ensure that the single channel power is equal when the full beam is used.

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