Performance analysis and optimization of unipolar OFDM based relay-assisted visible light communications

In this paper, we consider a relay-assisted visible light communication (VLC) system where an intermediate light source cooperates with the main light source. Following the IEEE 802.15.7r1 VLC reference channel model, we assume the presence of two different light sources in an office space. The first one is the ceiling light that serves as the source terminal while the second one is the desk lamp that serves as the relay terminal. Our system builds upon unipolar optical orthogonal frequency division multiplexing (U-OFDM) where the desk light performs amplify-and-forward relaying to assist the ceiling light and operates in a half-duplex mode. In addition, we consider the use of enhanced U-OFDM (eU-OFDM) which doubles the spectral efficiency of U-OFDM at the expense of additional computational complexity. We analyze the bit error rate performance of the relay-assisted VLC system building on these two OFDM types and quantify performance improvements over point-to-point (i.e., no relaying) VLC systems. In an effort to further improve system performance, we investigate optimal power allocation between source and relay terminals.