Multi-Hop Wireless Optical Backhauling for LiFi Attocell Networks: Bandwidth Scheduling and Power Control

The backhaul of hundreds of light fidelity (LiFi) base stations (BSs) constitutes a major challenge. Building on an indoor wireless optical backhauling approach, this paper presents the top-down design of a multi-hop wireless backhaul configuration for multi-tier optical attocell networks by proposing super cells. Such cells incorporate multiple clusters of attocells that are connected to the core network via a single gateway. Consequently, new challenges arise for managing the bandwidth and power of the bottleneck backhaul. By putting forward user-based bandwidth scheduling (UBS) and cell-based bandwidth scheduling (CBS) policies, the system-level modeling and analysis of the end-to-end multi-user sum rate is elaborated. In addition, optimal bandwidth scheduling under both UBS and CBS policies are formulated as constrained convex optimization problems, and solved by using the projected subgradient method. Furthermore, the transmission power of the backhaul system is opportunistically reduced using a fixed power control (FPC) strategy. The notion of backhaul bottleneck occurrence (BBO) is introduced. An accurate approximate expression of the probability of BBO is derived, and verified using Monte Carlo simulations. Several insights are provided by studying different aspects of the performance of super cells including the average sum rate, the BBO probability and the backhaul power efficiency (PE).