Fairness analysis of indoor multi-user communications through steerable IR-beam

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.