[论文解读] On the Performance of a Relay-Assisted Multi-Hop Asymmetric FSO/RF Communication System over Negative Exponential atmospheric turbulence with the effect of pointing error

Mohammad Ali Amirabadi|arXiv (Cornell University)|Aug 26, 2018

Optical Wireless Communication Technologies参考文献 36被引用 4

一句话总结

本文提出了一种中继辅助的多跳非对称Fso/RF通信系统，以在严重大气湍流和指向误差条件下增强长距离、高可靠性的链路。通过结合短距离RF中继与长距离FSO链路，并采用放大转发中继与用户选择技术，该系统在极低功耗和复杂度下实现了低误码率（BER）和中断概率，且对用户数和中继数的变化不敏感。

ABSTRACT

In this paper, a multi-user multi-hop hybrid FSO / RF system is presented. This structure is consisted of two main parts. The main motivation of presenting this structure is communication in long-range impassable links or some specific atmospheric conditions under which RF connection becomes easily disrupted. Although these effects could be mitigated by consuming more power or adding processing complexity, but a small user mobile phone cannot deserve more complexity or power supply. The fact that FSO and RF links are complementary of each other brings a new solution in mind; an access point that amplifies received signal via short-range RF link and forwards it to via long-range FSO link, could solve the mentioned problem. This scenario is exactly implemented at the first part of the proposed structure. At the second part, a multi-hop hybrid parallel FSO / RF link is implemented to connect source and destination Base Stations. It is the first time that in a multi-hop FSO / RF system, multi-user scheme, signal selection at each hop, known and un-known CSI in amplify and forward relaying, and saturate atmospheric turbulence with the effect of pointing error are considered. New expressions are derived in closed-form for Bit Error Rate (BER) and Outage Probability of the proposed structure and verified by MATLAB simulations. The proposed structure has advantages of FSO, RF, relay-assisted, and multi-user systems at the same time. Results indicate that it has low dependence on number of users and number of relays. Therefore, it is suitable for areas with varying population and long-range links. This structure offers independent performance without additional power consumption, processing latency, and complexity.

研究动机与目标

• 解决在RF链路受干扰的恶劣大气条件下维持可靠长距离通信的挑战。
• 通过结合FSO和RF系统的优势，克服单一系统应用的局限性。
• 设计一种可扩展、低功耗、低时延的通信系统，适用于移动用户和动态用户群体。
• 分析负指数分布大气湍流和指向误差对多跳中继环境下系统性能的影响。
• 推导关键性能指标的闭式表达式，以实现高效系统设计与优化。

提出的方法

• 采用混合架构，利用短距离RF链路实现用户到中继的通信，通过长距离FSO链路实现中继到目的地的传输。
• 在每个中继处实施多用户选择分集，以提高系统可靠性和频谱效率。
• 采用放大转发（AF）中继技术，并同时考虑完美与不完美信道状态信息（CSI），以模拟真实系统条件。
• 使用负指数分布建模大气湍流，并通过伽马-伽马衰落近似引入指向误差影响。
• 基于统计信道模型和矩生成函数，推导误码率（BER）和中断概率的闭式表达式。
• 通过在不同用户数、中继数和湍流水平下进行广泛的MATLAB仿真，验证分析结果的准确性。

实验结果

研究问题

• RQ1 FSO与RF链路的结合如何提升在强湍流和指向误差条件下的长距离通信性能？
• RQ2 在多跳FSO/RF中继系统中，用户选择分集对误码率（BER）和中断概率有何影响？
• RQ3 不完美CSI对放大转发中继在该非对称混合系统中的性能有何影响？
• RQ4 系统性能在多大程度上依赖于用户数和中继数？
• RQ5 在负指数湍流和指向误差条件下，能否推导出BER和中断概率的闭式表达式？

主要发现

• 所提出的系统即使在强负指数大气湍流和指向误差条件下，仍能实现低误码率（BER）和低中断概率。
• 性能保持稳定，且基本不受用户数和中继数的影响，表明系统具有高度可扩展性和鲁棒性。
• 系统维持低复杂度和低功耗，适用于移动设备和资源受限设备。
• 推导出BER和中断概率的闭式表达式，可实现快速性能评估与系统优化。
• 仿真结果证实，所推导表达式在各种湍流和指向误差条件下均具有高准确性。
• 在每个中继处采用用户选择技术显著提升了分集增益和系统可靠性，且未增加硬件或处理负载。