Downlink data transmission of multi-user indoor optical wireless communications and its corresponding fairness analysis is studied by the authors. It is assumed that access points (APs) may use infrared beam (IR-beam) laser or light emitting diodes (LEDs) for data transmissions. For the case of APs with IR-beams, since the bandwidth of the transmitted optical signal can be very large than that of the LED’s, a typical time-division multiple access (TDMA) scheme is utilised to serve multiple users and the respective achievable rates are derived. Then, for a general fairness-scheduling utility function with the capability of adjusting the degree of fairness known as α-proportional fairness, optimal time-sharing coefficients are analytically derived in closed-forms. To compare the performance of the IR-based communications for the LED-based APs, two non-cooperative and cooperative data transmission schemes are also studied and the corresponding achievable rates are presented based on the classical superposition coding. Finally, to compare the performance of the two types of APs, per user data rate of the proposed systems are compared through numerical results for different scenarios to highlight advantages and drawbacks of the two types of APs. Also, by considering the Jain's index as a fairness metric, the impact of the system parameters on the fairness is discussed through numerical results.

中文翻译：

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通过可控红外光束进行室内多用户通信的公平性分析

作者研究了多用户室内光无线通信的下行链路数据传输及其相应的公平性分析。假设接入点 (AP) 可以使用红外光束 (IR 光束) 激光器或发光二极管 (LED) 进行数据传输。对于带有红外光束的 AP，由于传输光信号的带宽可能比 LED 的带宽大很多，因此利用典型的时分多址 (TDMA) 方案为多个用户和各自可实现的速率提供服务是派生的。那么，对于一个具有调整公平程度能力的一般公平调度效用函数，称为α- 比例公平，最佳分时系数以封闭形式解析导出。为了比较基于 LED 的 AP 的基于 IR 的通信性能，还研究了两种非合作和合作数据传输方案，并基于经典叠加编码提出了相应的可实现速率。最后，为了比较两种类型 AP 的性能，通过针对不同场景的数值结果比较所提出系统的每用户数据速率，以突出两种类型 AP 的优缺点。此外，通过将 Jain 指数作为公平性度量，通过数值结果讨论了系统参数对公平性的影响。