利用“日盲”紫外波段的光无线通信具有低背景噪声、无需频谱许可的优势以及非视距传输消息的能力，被称为非视距紫外光通信，在军、民领域具有广阔的应用前景。随着紫外光源和探测器的不断发展，非视距紫外光通信技术在近十年受到研究者的广泛关注。然而，非视距紫外光通信技术仍然面临许多问题和挑战。本文围绕非视距紫外光通信的信道建模和调制技术开展了理论研究，设计和开发了紫外光通信样机，并对多场景的测试结果进行展示与分析。具体内容如下：首先，围绕非视距紫外光通信单次散射信道模型展开研究。针对单次散射路径损耗模型具有三重积分、确定积分上下限复杂、无闭合表达式的问题，提出单次散射路径损耗近似模型，其具有闭合表达式且计算耗时显著降低。进一步，首次建立了采用紫外发光二极管作为光源时单次散射路径损耗模型，以及适用于任意光源空间辐照分布的单次散射信道脉冲响应模型，并通过实验结果验证了理论模型的有效性。其次，针对非视距紫外光通信路径损耗高的问题，提出了反射辅助的非视距紫外光通信架构。首次基于蒙特卡洛光子追踪算法建立了反射辅助的非视距紫外光通信路径损耗和信道脉冲响应模型。在单次散射和反射的假设下，首次建立了反射辅助的非视距紫外光通信路径损耗理论模型。同时，通过两个场景下的室外实验对所提模型进行验证。再次，针对非视距紫外光通信系统采用脉冲位置调制频谱效率低的问题，论文首先引入了多脉冲位置调制方式，然后提出了二元脉冲位置调制功率域叠加传输方案，两种调制方法均可明显改善脉冲位置调制的频谱效率。进一步地，推导了两种调制方法的误符号率和可达速率表达式，并通过蒙特卡洛仿真验证了理论结果的正确性。最后，为了进一步验证和应用前述理论，设计并开发了紫外光通信原理样机，在多方向视距通信场景、地面非视距通信场景和无人机非视距通信场景下开展实测工作。在收发距离60米的情况下，利用多脉冲位置调制可达到17千比特/秒的非视距通信速率，误比特率低于3.8×10^{-3}。通过对测试数据的分析和处理，进一步验证了前述理论信道模型的有效性。论文研究成果为设计非视距紫外光通信系统提供了理论支撑和技术参考。
Optical wireless communication exploiting the "solar-blind" ultraviolet spectrum has the advantages of weak background noise, license-free spectral resources, and the ability of non-line-of-sight transmission, which refers to non-line-of-sight ultraviolet communication and has great potential in the military and civilian fields. With the development of ultraviolet light sources and detectors, non-line-of-sight ultraviolet communication has attracted extensive attention from researchers in the past decade. Nevertheless, non-line-of-sight ultraviolet communication still confronts many problems and challenges. This thesis conducts theoretical research on channel modeling and modulation technique for non-line-of-sight ultraviolet communication. In addition, a prototype of ultraviolet communication is designed and developed, and the results of measurements under several scenarios are presented and analyzed. The content of this thesis is given below:First of all, the research is carried out around the single-scatter channel model of non-line-of-sight ultraviolet communication. Aiming at solving the problems that the single-scatter path loss model has triple integrals, the determination of the upper and lower limits of the integral is complicated, and there is no closed-form expression, a simplified single-scatter path loss model is proposed, which has a closed-formed expression and can significantly reduce the calculation time. Furthermore, for the first time, a single-scatter path loss model is established with ultraviolet light-emitting diodes as light sources, and a single-scatter channel impulse response model applicable to the spatial irradiance distribution of any light source is also developed. The validity of theoretical channel models is further verified by experimental results.Secondly, to reduce the path loss of non-line-of-sight ultraviolet communication, a paradigm of reflection-assisted non-line-of-sight ultraviolet communication is proposed. For the first time, the path loss and channel impulse response models of reflection-assisted non-line-of-sight ultraviolet communication are established based on the Monte-Carlo photon-tracing algorithm. Under the assumption that scattering or reflection events occur only once, a theoretical path loss model of reflection-assisted non-line-of-sight ultraviolet communication is developed for the first time. Additionally, the proposed models are verified by outdoor experiments in two scenarios.Thirdly, to improve the spectral efficiency of pulse-position modulation in non-line-of-sight ultraviolet communication systems, multipulse pulse-position modulation is introduced first and then a power-domain multilayer-superposed transmission scheme with binary pulse-position modulation is proposed. Both two methods can significantly improve the spectral efficiency of pulse-position modulation. Furthermore, the expressions of symbol-error rate and achievable data rate for those two methods are derived, and the correctness of the theoretical results is also verified by Monte-Carlo simulations.Finally, to further verify and apply the above theoretical results, a prototype of ultraviolet communication is designed and developed. The field testing is carried out in multi-directional line-of-sight communication scenarios, non-line-of-sight communication scenarios on the ground, and non-line-of-sight communication scenarios over unmanned aerial vehicles. With the distance between a transmitter and a receiver in a non-line-of-sight ultraviolet communication system equaling 60 meters, a data rate of 17 kilobits per second can be achieved, and the corresponding bit-error rate is lower than 3.8×10^{-3} by using multipulse pulse-position modulation. Through the analysis and processing of measurement data, the effectiveness of the aforementioned theoretical channel model is further verified.The results of the thesis provide theoretical foundations and technical references for designing and implementing non-line-of-sight ultraviolet communication systems.
