基于粒子谱分布的无线紫外光通信散射传输特性研究

在非直视无线紫外光通信中，利用大气中的粒子对紫外光进行散射作用来传递信息，非直视紫外光通信在近距离隐蔽通信中有广阔的应用前景。雾霾粒子属于气溶胶范畴，由空气中的灰尘、硫化物、有机碳氢化合物等粒子组成。雾霾粒子的尺度、浓度、形状等因素均会对无线紫外光散射通信的传输特性产生较大的影响。首先，基于蒙特卡罗方法建立了非直视紫外光多次散射模型，将霾粒子的半径和浓度这两个物理量引入该模型中，通过模拟大量光子在雾霾条件下经多次散射到达接收端的概率，进而仿真分析了系统路径损耗与粒子半径和浓度之间的关系。结果表明，(1) 在无线紫外光近距离通信条件下，雾霾浓度越大，路径损耗越小，系统通信性能越好；(2) 通信距离大于500 m时，增加雾霾粒子浓度，系统路径损耗总体先减小再增大；(3) 在粒子浓度一定情况下，增大粒子半径，路径损耗先减小后增大，且随着通信距离的增大，路径损耗极小值的位置不断向粒子半径小的一侧移动。其次，在模型中引入粒子尺度谱分布的概念，对粒子尺度谱分布进行分割，分别求出不同粒径及其所对应浓度。假定粒子尺度谱分布中不同粒径的粒子依次对光子产生散射作用，对相应光子到达接收端的概率求和，得到光子到达接收端的总概率，进而求得多种粒径的粒子共同存在情况下系统的路径损耗，使仿真模型更加逼近实际大气信道中多种半径雾霾粒子共同存在的事实。最后，搭建实验平台，分别在良好、严重雾霾、极严重雾霾三种不同天气条件下，实验测量了系统路径损耗和通信距离、收发仰角之间的关系，并与考虑粒子尺度谱分布模型中计算得到的路径损耗进行对比，实验数据与仿真结果趋势一致，雾霾天气下的通信质量优于良好天气，收发仰角越大对应的路径损耗也越大。

Study on Scattering Transmission Characteristics of Wireless UV Communication Based on Particle Size Distribution

In the non-line-of-sight wireless ultraviolet communication, particles in the atmosphere scatter ultraviolet light to help transmit information, which offers a broad prospect for applications in near-range covert communication. Haze particles, belonging to the aerosol category, are composed of dust, sulfide, organic hydrocarbon, and other particles in the air. Physical parameters of haze particles, such as size, concentration, and shape, greatly affect the transmission characteristics of wireless ultraviolet light scattering communications. In this work, we first established an ultraviolet multi-scattering model based on the Monte Carlo method. This model considers the effects of two physical quantities of haze particles-radius and concentration. Using this model, we simulated many photons passing through the multi-scattering transmission channel under various haze conditions. The relations of the path loss to particle radius and concentration level are evaluated and analyzed. The results show that: (1) Under the condition of wireless ultraviolet light short-range communication, higher haze concentration results in lower path loss and better system performance; (2) When the communication distance is longer than 500 meters, as the particle concentration continually increases, the system path loss generally decreases first and then increases; (3) With a fixed particle concentration, enlarging the particle radius causes the system path loss to drop initially, but as concentration continues to increase, the path loss rises again. In addition, the particle radius which produces the minimum path loss reduces monotonically as the transmission distance increases. Secondly, we incorporated the particle size distribution of the atmosphere into the model by segmenting the distribution to obtain different particle sizes and corresponding concentrations. Assuming that particles of different sizes and concentrations sequentially scatter photons, the model evaluates the probability of photons arriving at the receiver by passing them through each channel with a single particle size. Then, the model calculates the total probability of photons received and the path loss of the system when particles of all sizes are present. This way, our model creates a realistic multi-scattering transmission environment similar to the actual atmospheric channel where haze particles of all sizes exist simultaneously. Finally, we built an experimental platform to measure the system path loss to communication distance and transmission and receiving elevation angles under three different weather conditions: fine, severe haze, and extremely severe haze. Comparing the measured results of path loss to those from the simulation model, we found that the experimental and simulation results shared the same trend, the communication quality in haze weather is always better than good weather, and larger transmission and reception elevation angles always cause a higher path loss.