Downlink cooperation with fractional frequency reuse in DCO-OFDMA optical attocell networks

Abstract

In this paper, downlink cooperation is proposed for indoor visible light communication (VLC) cellular networks, also termed as optical attocell networks, with the aim of improving the spectral efficiency performance. An orthogonal frequency division multiple access (OFDMA) system based on direct current optical orthogonal frequency division multiplexing (DCO-OFDM) with fractional frequency reuse (FFR) planning is considered, and a system level analysis is carried out. A line-of-sight (LOS) light propagation model is used for the indoor VLC channel. The downlink cooperation is realized by means of a relay-assisted transmission with the aid of neighboring base stations (BSs) using a non-orthogonal amplify-and-forward (NAF) protocol. The links between the source BS and the relay BSs are provided by perfectly aligned VLC connections. Four relaying schemes with a different number of relays are considered, and for each scheme analytical signal-to-interference-plus-noise ratio (SINR) and spectral efficiency expressions for a user equipment (UE) with random coordinates in an optical attocell are derived. Also, average spectral efficiency performance of the system is studied using Monte-Carlo simulations.