In this paper, we investigate relay-assisted visible light communications (VLC) where a mobile user acts as a relay and forwards data from a transmitter to the end mobile user. We analyse the utilization of the amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes. The focus of the paper is on analysis of the behavior of the mobile user acting as a relay while considering a realistic locations of the receivers and transmitters on a standard mobile phone, more specifically with two photodetectors on both sides of a mobile phone and a transmitting LED array located upright. We also investigate dependency of the bit error rate (BER) performance on the azimuth and elevation angles of the mobile relay device within a typical office environment. We provide a new analytical description of BER for AF and DF-based relays in VLC. In addition we compare AF and DF-based systems and show that DF offers a marginal improvement in the coverage area with a BER < 10^–3 and a data rate of 100 Mb/s. Numerical results also illustrate that relay-based systems offer a significant improvement in terms of the coverage compared to direct non-line of sight VLC links.

This letter investigates a vehicle-to-vehicle relay-assisted visible light communications link with amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes and analyze the effect of the relay vehicle's orientation with respect to the source vehicle. Results show up to 150 % increase in the link span under emulated sunlight for the DF relay link compared with AF at the end of the second hop using the same system parameters at the forward error correction bit error rate limit of 3.8×10 ^-3 . A method to mitigate the effect of system performance degradation due to misalignment between communicating vehicles is also proposed.

In multi-band carrier-less amplitude and phase modulation (m-CAP), the transmitter and receiver pulse shaping filters have a significant impact on the signal performance. Since m-CAP is an emerging and promising modulation format for visible light communications (VLC), it is necessary to balance the system performance and the filter length, due to limited integration density in field programmable gate arrays (FPGAs). In this paper we investigate the m-CAP VLC system performance for different number of sub-bands m = {2, 5, 10} under varying finite impulse response (FIR) filter parameters, such as the filter length Lf and the roll-off factor β. We show that increasing both β and Lf improves the bit error rate (BER) performance of the system substantially. We demonstrate that a BER target of 10-4 is achieved using Lf ≤ 12 symbols for m = 5 and 10 for low order subcarriers. Moreover, the BER limit is attained for β = 0.2 by all subcarriers, except the last two for m = 5 and 10, which is a significant improvement, even considering the slightly increased excess bandwidth in comparison to the literature.