Large-view-field wireless light transmission method and system for unmanned aerial vehicle

Abstract

The invention discloses a large-view-field wireless light transmission method for an unmanned aerial vehicle, and the method comprises the following steps: S100, enabling an MPPC light detector to enable a plurality of detection units to be distributed in a space, carrying out the whole-region LED array layout, increasing the effective area for receiving a light signal, and improving the geometric reception rate; s200, collecting channel data at the same time by using a multi-channel gain algorithm to realize signal acquisition and processing; s300, through an array structure and multi-channel data fusion analysis, target detection and perception performance is improved; the invention further discloses a large-view-field wireless optical transmission system for the unmanned aerial vehicle. According to the technical scheme, horizontal 360-degree full-area coverage of the radiation direction of the LED array can be achieved, and the radiation range of the LED array is remarkably expanded; an array multi-pixel photoelectric detector receiving technology is used for coping with dynamic receiving, so that possibility is provided for realizing communication in motion of the unmanned aerial vehicle; the signal receiving performance is effectively improved, and the method has more excellent performance in the aspects of processing weak light signals and dynamically receiving scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned aerial vehicles, and in particular to a large-field-of-view wireless optical transmission method and system for unmanned aerial vehicles. Background Art

[0002] Wireless optical communication for drones is a broadband wireless transmission and access technology that combines optical communication technology with wireless communication technology. It uses light waves as carrier waves and uses the atmosphere or outer space as a channel for information transmission. Wireless optical communication has high frequency, large information carrying capacity, rich frequency resources, good confidentiality, good directionality, and strong anti-electromagnetic interference ability. In outdoor wireless optical communication, laser communication, also known as free space optical communication, is more commonly used. At present, many research institutions have introduced free space optical communication technology into the field of drones, and have greatly improved the wireless transmission capacity of drones by tapping into rich spectral resources. On the basis of the original links between drones and satellites, links between drones in the air, and links between drones and land terminals, optical wireless modules and subsystems are integrated into various drones and ground terminals to build high-speed, high-confidential, and directional links based on light waves. With the help of complementary wireless optical and traditional radio technologies, the overall performance of drones and air or ground systems in completing complex and critical tasks can be efficiently enhanced. The main frequency bands of drone flight control, communication, and image transmission are currently in the relatively mature traditional GHz radio wave bands of 0.84, 1.43, and 2.4.

[0003] However, LED wireless optical communication for drones is not just a simple transfer of LED visible light communication technology to drones. LED wireless optical communication systems are very different from traditional radio communications and laser communications. Affected by the working mechanism of the transceiver antenna and the detection sensitivity, radio detection is nearly omnidirectional; limited by the generation mechanism of the laser light source beam, the laser beam is generally in the order of millirads mrad, which means that when traditional laser communication is used on drones, the drone end and other transceivers need to remain relatively still, and optical scanning and alignment are required before "static communication" can be carried out. This greatly limits the application field of drone wireless optical systems. Drones are a complex of intelligent devices with limited SWaP. Wireless optical communication "in motion" has great technical difficulty, which brings new challenges to wide-angle reception. Summary of the invention

[0004] The main purpose of the present invention is to propose a large-field-of-view wireless optical transmission method and system for drones, aiming to solve the technical problems that it is difficult to achieve wireless optical "on-the-go" over medium and long distances in existing drones, and when the light source beam is large, the optical power received by the detector will be reduced, thereby affecting the acceptance rate.

[0005] To achieve the above object, the present invention provides a large-field-of-view wireless optical transmission method for unmanned aerial vehicles, comprising the following steps: S100: MPPC optical detector distributes multiple detection units in space and arranges LED arrays in the entire area to increase the effective area for receiving optical signals and improve the geometric reception rate of the detector; S200: Use multi-channel gain algorithm to collect channel data simultaneously to achieve signal acquisition and processing; S300: Improves target detection and perception performance through array structure and multi-channel data fusion analysis.

[0006] Optionally, in step S100, MPPC is composed of The output can be expressed as , that is, the output of the MPPC is a single SPAD output combination.

[0007] Optionally, in step S100, the SNR received by the MPPC is mainly determined by the optical power and total noise power of the received signal, rather than the thermal noise power, and the SNR of the signal can be derived from the received pixel channel matrix.

[0008] Optionally, the intensity of the optical signal received by each channel is changed by changing the position of the MPPC. The SNR received by the MPPC will change according to its coordinates. The position of the pixel channel of the MPPC has an important influence on the signal quality. The optical power received by the MPPC channels at different positions is different, which leads to different SNR levels.

[0009] Optionally, in step S200, the multi-channel gain algorithm includes an optimized array reception self-identification merging algorithm, namely, the MCSC algorithm, which effectively identifies and excludes channels with larger noise when faced with the influence of low reception power and high pixel channel noise, thereby increasing the weights of the remaining channels to improve signal quality.

[0010] A large-field-of-view wireless optical transmission system for unmanned aerial vehicles comprises an LED secondary optical system, wherein the secondary optical system comprises a light recycling system and a zoom lens, wherein the light recycling system is provided with a free-form surface reflector cup and a plurality of LED light source combinations, wherein the LED light source combinations are provided with LED chips, and the free-form surface reflector cup is provided with an outlet, wherein the zoom lens can move forward and backward to face the outlet, and wherein the LED chip is provided at the inner bottom of the free-form surface reflector cup and faces the outlet.

[0011] Optionally, the LED light source combinations are arranged in sequence and spliced ​​into an LED array, and adjacent LED light source combinations do not overlap.

[0012] Optionally, a light angle is formed between the zoom lens, the LED chip and the outlet along the axial direction of the LED chip, and the angle is no greater than 90°.

[0013] The technical solution of the present invention has the following beneficial effects: (1) A full-area LED array layout design is proposed, which greatly improves the coverage of LED light signals. A secondary optical system is proposed for LED light sources to achieve adjustable light-emitting angles of LED light sources. The LED array layout is optimized according to the adjusted light-emitting angles. Different directions of normal vectors of different LED array elements are designed on drones. By optimizing the normal vector directions of LED array elements, the radiation directions of LED array elements are made independent of each other. The radiation direction of the LED array covers the entire area of ​​360° horizontally, greatly expanding the radiation range of the LED array. (2) Based on the MPPC detector, an array multi-pixel photodetector receiving technology is proposed, which uses its receiving performance advantages to deal with the problem of dynamic reception, thereby making it possible to realize the "mobile communication" of drones. In the application field of VLC technology, the FOV coverage of the receiving equipment is considered to be a key factor restricting its performance. The FOV limitations of traditional photodetectors make signal transmission susceptible to the adverse effects of FOV offset, which in turn limits the stability of the data transmission link. Especially in VLC under mobile conditions, the relative position between the receiver and the transmitter changes, which will cause the distribution of the light spot on the detector to change dynamically. This situation limits the application potential of mobile optical communications; (3) A multi-channel selective merging MCSC algorithm is proposed. This algorithm sets a threshold to filter out signal channels with excessive noise or too low receiving power, and allocates weight gain proportionally according to the different received optical powers of each channel, thereby achieving optimized merging reception of the array MPPC. Simulation verification shows that this method not only effectively improves the performance of the received signal, but also demonstrates superior performance to traditional maximum ratio combining algorithms and selective combining algorithms in processing weak optical signals and dynamic receiving scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0015] Figure 1 A schematic diagram of the process steps of a large-field-of-view wireless optical transmission method for unmanned aerial vehicles according to an embodiment of the present invention; Figure 2A comparative schematic diagram of an MPPC multi-pixel channel signal combination algorithm of a large-field-of-view wireless optical transmission method for unmanned aerial vehicles according to an embodiment of the present invention; Figure 3 This is a schematic diagram of an LED secondary optical system of a large-field-of-view wireless optical transmission system for drones according to another embodiment of the present invention; Figure 4 This is a schematic diagram of an MPPC array receiving signal of a large-field-of-view wireless optical transmission system for unmanned aerial vehicles according to an embodiment of the present invention.

[0016] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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 creative work are within the scope of protection of the present invention.

[0018] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0019] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0020] The present invention provides a large-field-of-view wireless optical transmission method and system for unmanned aerial vehicles.

[0021] like Figure 1 As shown, in one embodiment of the present invention, the large-field-of-view wireless optical transmission method for drones comprises the following steps: S100: MPPC optical detector distributes multiple detection units in space and arranges LED arrays in the entire area to increase the effective area for receiving optical signals and improve the geometric reception rate of the detector; S200: Use multi-channel gain algorithm to collect channel data simultaneously to achieve signal acquisition and processing; S300: Improves target detection and perception performance through array structure and multi-channel data fusion analysis.

[0022] Specifically, in step S100, MPPC is The output can be expressed as , that is, the output of the MPPC is a single SPAD output The SNR received by MPPC is mainly determined by the optical power and total noise power of the received signal, rather than the thermal noise power. The SNR of the signal can be derived from the received pixel channel matrix. By changing the position of the MPPC to change the intensity of the optical signal received by each channel, the SNR received by the MPPC will change according to its coordinates. The position of the MPPC's pixel channel has an important influence on the signal quality. The optical power received by the MPPC channels at different positions is different, which leads to different SNR levels.

[0023] Specifically, in step S200, the multi-channel gain algorithm includes an optimized array receiving self-identification merging algorithm, namely, the MCSC algorithm, which effectively identifies and excludes channels with larger noise when facing the influence of low receiving power and high pixel channel noise, and then increases the weights of the remaining channels to improve signal quality. The specific algorithm is as follows: (1) Optimization of array receiving self-identification merging algorithm Assigning weight gains to different receiving channels can effectively optimize the transmission quality of optical signals in multi-pixel channels. In the proposed multi-pixel channel MCSC algorithm, the accuracy of code synchronization is provided to the receiver. In addition, by receiving the training code sequence, the signal quality can be evaluated in real time at the receiving end based on the correlation between the ambient noise power and the peak value, which can be achieved by deriving the SNR. As the ambient noise power increases, the corresponding peak value decreases, and this characteristic can also be used to estimate the current SNR. The following is the receiving model of the MPPC receiver based on VLC: ; Among them, the vector is the transmission signal of the array channel, is the output signal, represents the channel, is the noise vector. The signal power of the light source is expressed as , the noise power is , the above can be calculated: ,in ; During the communication cycle, assuming that the channel remains constant, the array MPPC is in a mobile state to obtain the instantaneous SNR. Based on the known SNR of each channel, appropriate gains can be assigned to each channel according to these values, and then the signals of each channel are combined to maximize the output SNR. In this process, the weight of each channel can be expressed as .

[0024] , in ; Set the gain of each channel To ensure that the SNR of the output signal is the maximum value of the sum of the SNRs of each channel. For multi-channel output signals, it is the best choice to select the path gain as the gain of each channel: ; The threshold is determined dynamically based on the signal changes in the multi-pixel channel and communication channel environment. This has a significant impact and further determines the reception strategy. Therefore, the channel must be analyzed The characteristics of the output signal This is the key to optimizing the array receiving communication performance. The noise power also depends on And get the gain, where The noise power is: ; In one embodiment of the present invention, an algorithm is proposed to effectively identify and exclude channels with large noise when facing the influence of low received power and high pixel channel noise, thereby increasing the weights of the remaining channels to improve signal quality. The algorithm adjusts the weight distribution, optimizes the ratio analysis of signal and noise power, and ensures the final signal output quality. In particular, the algorithm uses the maximum correlation peak to not only determine the synchronization point but also measure the SNR of the signal, which is crucial for evaluating signal quality. As the noise increases, the overall SNR decreases, and the maximum correlation peak also decreases. When the noise power reaches or exceeds the signal power, the calculated SNR will turn negative; conversely, when the signal power exceeds the noise, the SNR remains positive. Noise filtering and signal gain weight distribution constitute the core steps of the algorithm, so that the system can also improve the SNR of the signal output in a noisy environment, thereby improving the overall quality of the signal. In summary, the algorithm summarizes the main steps of the MCSC algorithm, i.e., the multi-channel self-identification merging algorithm, which are summarized as follows: S1: Initialization: Y = Hx+n,W Rm×n,C Zm×n S2: begin: S3: Add the formula to middle, ; S4: ; S5: Introducing the Lagrange multiplier operator S6: is an arbitrary non-zero constant, taking ; S7: , ; S8: , , ; S9: ; S10:end (2) Error analysis of array reception The MCSC algorithm distributes power to the gain of each channel in proportion to the channel weight to improve the output SNR. The algorithm comprehensively considers the signal reception of all channels and determines their respective gains to maximize the overall output SNR. To achieve this goal, the receiving power status of each channel must be accurately calculated. The final output SNR can be calculated as follows: , in ; It can be deduced from the above equation that after considering the multi-channel effect, the output It can be regarded as a linear multiple of SNR. When there are multiple selective channels in the array receiving system, the total output SNR received by each channel is improved due to the recognition and adjustment of the MCSC algorithm. The algorithm sets the gain by self-identifying the SNR of each channel. The best strategy is to adjust the gain to maximize the output SNR. Under OOK modulation, BER can be derived from SNR using a standard method. This calculation formula not only takes into account the relationship between signal and noise, but also the impact of modulation mode on data transmission, thus providing a comprehensive and accurate performance evaluation indicator: ; For the BER output by the system, it is not feasible to directly add the BER of each channel. The Chi-Squar function can be used to calculate the BER of each channel. By derivation of , we can deduce that the BER of the proposed scheme is: ; (3) BER of different algorithms at the receiving end The optical communication system is simulated to compare the communication transmission of MCSC, MRC and SC algorithms in the presence of noise, and the BER of the MPPC received signal at different locations.

[0025] like Figure 2 As shown in the figure, by comparing the BER performance of different signal receiving algorithms at different SNR levels, the analyzed data includes the SNR of MCSC algorithm reception, MRC algorithm reception, and SC algorithm reception. As the SNR increases, the MCSC algorithm reduces the BER and optimizes the receiving performance by effectively filtering out noise and weighted gain. The MRC algorithm also improves performance as the SNR increases, and performs well in utilizing the enhanced output from multiple received signals, but is not as good as the MCSC algorithm in noise processing. At the same time, the SC algorithm shows a steady performance improvement under different SNR conditions, and its performance improvement is far less significant than that of the MCSC and MRC algorithms.

[0026] like Figure 3 and Figure 4 As shown, on the other hand, the present invention also proposes a large-field-of-view wireless optical transmission system for unmanned aerial vehicles, which is used to implement the above method, including an LED secondary optical system, the secondary optical system including a light recycling system and a zoom lens, the light recycling system is provided with a free-form surface reflector cup and a plurality of LED light source combinations, the LED light source combination is provided with an LED chip, the free-form surface reflector cup is provided with an outlet, the zoom lens can be moved forward and backward to face the outlet, the LED chip is arranged at the inner bottom of the free-form surface reflector cup and faces the outlet, and after optimization, the reflector cup reflects as much light energy as possible back to the surface of the LED chip to achieve light recycling, thereby increasing the brightness of the LED chip by about 1 times.

[0027] Specifically, the LED light source combinations are arranged and spliced ​​into LED arrays in sequence, and adjacent LED light source combinations do not overlap. The layout design of the LED light source array, that is, the differentiated design of the normal vector directions of different LED array elements, realizes autonomous control of communication signals, and the radiation direction is selectable and controllable. That is, the LED array is spliced ​​by combining multiple LED light sources. During the splicing process, it is necessary to ensure that the LED light source can send light signals to the greatest extent, and the half-power lighting areas corresponding to each LED light source are as independent as possible, without overlapping areas, thereby expanding the radiation range of the entire system and covering the entire area of ​​360° horizontally.

[0028] Specifically, a light angle is formed between the zoom lens, the LED chip and the outlet along the axial direction of the LED chip, and the angle is no greater than 90°. The size of the outlet determines the light output angle θ of the free-form reflector cup, and this angle must also match the maximum incident light angle of the zoom lens. Finally, the system zoom (i.e., the system light output angle is modulated) is achieved by moving the zoom lens forward and backward.

[0029] The specific principles of the present invention are as follows: 1. UAV wireless optical communication is a broadband wireless transmission and access technology that combines optical communication technology with wireless communication technology. It uses light waves as carriers and the atmosphere or outer space as channels for information transmission. Wireless optical communication has high frequency, large information carrying capacity, rich frequency resources, good confidentiality, good directionality, and strong anti-electromagnetic interference ability. In outdoor wireless optical communication, laser communication, also known as free space optical communication, is more commonly used. At present, many research institutions have introduced free space optical communication technology into the field of UAVs, and have greatly improved the wireless transmission capacity of UAVs by tapping into rich spectral resources. On the basis of the original links between UAVs and satellites, links between UAVs in the air, and links between UAVs and land terminals, optical wireless modules and subsystems are integrated into various types of UAVs and ground terminals to build high-speed, high-confidentiality, and directional links based on light waves. With the help of wireless optical and traditional radio technologies with complementary characteristics, the overall performance of UAVs and air or ground systems in completing complex and critical tasks can be efficiently enhanced.

[0030] In terms of optical channel modeling: for weak turbulence conditions, a simpler and easier to use log-normal turbulence environment channel model is studied, and then a closed expression for the link interruption probability under weak turbulence conditions is given. At the same time, for medium or strong turbulence conditions, a new closed statistical channel model for gamma-gamma turbulent channels is derived. This model takes into account the influence of link configuration factors such as the receiver's field of view, spatial position, and drone pointing deviation, and compares the model results with traditional Monte Carlo simulation results to verify the accuracy of the novel model. However, in this model, both the transmitting and receiving drones are hovering in the air; at the same time, it is assumed that due to the influence of many random parameters, the drone's instantaneous position and azimuth will deviate randomly from the expected position.

[0031] In terms of experimental system research: Several domestic units such as China Electronics Technology Group have also carried out preliminary experimental work. A small rotor UAV platform successfully transmitted high-definition images to the ground receiving end through a wireless optical link at a fixed position 6.7 km away. The transmission rate of the above work can reach up to 1.25Gbps. However, it must be pointed out that although one end of the transceiver in the above experiment is a UAV platform, in the specific wireless optical communication process, both the transceiver and the receiver are always limited to a fixed position, and it is still a "static communication" mode.

[0032] In summary, UAV LED wireless optical communication is not just a simple transfer of LED visible light communication technology to UAVs. UAVs are a complex of intelligent devices with limited SWaP. Wireless optical communication in motion is extremely technically difficult and brings new challenges to wide viewing angle reception.

[0033] At present, the main frequency bands for drone flight control, communication, and image transmission are in the relatively mature traditional GHz radio wave frequency bands such as 0.84, 1.43, and 2.4. However, factors such as the complex electromagnetic space environment and strong electromagnetic interference in cities can easily limit the application of drone flight control, communication, navigation and positioning based on traditional radio GHz bands. The GHz band signals of traditional drone communications are easily maliciously attacked, interfered, deceived, and stolen by other radio equipment, resulting in frequent drone safety accidents and public privacy security leaks. The drone communication security defense and privacy protection capabilities have become an urgent need for economic and social development.

[0034] The problem of long-distance wireless optical "communication in motion" in drones. LED wireless optical communication systems are very different from traditional radio communications and laser communications. Affected by the working mechanism of the transceiver antenna and the detection sensitivity, radio detection is nearly omnidirectional; limited by the generation mechanism of the laser light source beam, the laser beam is generally in the order of millirads mrad, which means that when traditional laser communication is used on drones, the drone end and other transceivers need to remain relatively still, and optical scanning and alignment are required before "communication in stillness" can be carried out. This greatly limits the application field of drone wireless optical systems.

[0035] Glossary: LED: Light Emitting Diode, light-emitting diode; SWaP: SizeWeight and Power, size, weight and power consumption; MPPC: Multi-Pixel Photon Counter, array silicon photomultiplier tube; SPAD: Single Photon Avalanche Diode, single photon avalanche diode; SNR: Signal to Noise Ratio, signal to noise ratio; MCSC: Multi-Channel Selective Combining, multi-channel selective merging; OOK: On-Off Keying, on-off keying modulation; BER: Bit Error Rate, bit error rate; MRC: Maximum Ratio Combining, maximum ratio merging; SC:Selection Combining,selection merging; FOV:Field of View, field of view.

[0036] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A large-field-of-view wireless optical transmission method for unmanned aerial vehicles, characterized in that: The following steps are involved: S100: MPPC optical detector distributes multiple detection units in space and arranges LED arrays in the entire area to increase the effective area for receiving optical signals and improve the geometric reception rate; S200: Use multi-channel gain algorithm to collect channel data simultaneously to achieve signal acquisition and processing; S300: Improves target detection and perception performance through array structure and multi-channel data fusion analysis.

2. The large-field-of-view wireless optical transmission method for drones according to claim 1 is characterized in that: In step S100, MPPC is composed of The output can be expressed as , that is, the output of the MPPC is a single SPAD output combination.

3. The large-field-of-view wireless optical transmission method for drones according to claim 1 is characterized in that: In step S100, the SNR received by the MPPC is mainly determined by the optical power and total noise power of the received signal, rather than the thermal noise power. The SNR of the signal can be derived from the received pixel channel matrix.

4. The large-field-of-view wireless optical transmission method for drones according to claim 3 is characterized in that: By changing the position of the MPPC to change the intensity of the light signal received by each channel, the SNR received by the MPPC will change according to its coordinates. The position of the pixel channel of the MPPC has an important impact on the signal quality. The optical power received by the MPPC channels at different positions is different, which leads to different SNR levels.

5. The large-field-of-view wireless optical transmission method for drones according to claim 1, characterized in that: In step S200, the multi-channel gain algorithm includes an optimized array receiving self-identification merging algorithm, namely, the MCSC algorithm, which effectively identifies and excludes channels with larger noise when facing the influence of low receiving power and high pixel channel noise, and then increases the weights of the remaining channels to improve signal quality.

6. A large-field-of-view wireless optical transmission system for unmanned aerial vehicles, which implements the large-field-of-view wireless optical transmission method for unmanned aerial vehicles as described in any one of claims 1 to 5, characterized in that: It comprises an LED secondary optical system, which comprises a light recycling system and a zoom lens. The light recycling system is provided with a free-form surface reflector cup and a plurality of LED light source combinations. The LED light source combination is provided with an LED chip. The free-form surface reflector cup is provided with an outlet. The zoom lens can move forward and backward to face the outlet. The LED chip is arranged at the inner bottom of the free-form surface reflector cup and faces the outlet.

7. The large-field-of-view wireless optical transmission system for unmanned aerial vehicles according to claim 6, characterized in that: The LED light source combinations are sequentially arranged and spliced ​​into an LED array, and adjacent LED light source combinations do not overlap.

8. The large-field-of-view wireless optical transmission system for drones according to claim 6, characterized in that: A light angle is formed between the zoom lens, the LED chip and the outlet along the axial direction of the LED chip, and the angle is no greater than 90°.

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