In this paper, the application of orthogonal frequency division multiplexing (OFDM) over an indoor wireless optical channel is investigated. Previous studies have demonstrated that it can be characterised as almost stationary but with a severe penalty induced by multipath propagation. It is also highly dependent on the spatial distribution of emitters and receivers. OFDM systems have been chosen owing to their capability of supporting high data rates without channel equalisation. They also mitigate the effect of quality fluctuations of the channel induced when the spatial distribution of emitters and receivers varies. We present several results about system performance. Finally, an adaptive OFDM system is proposed to increase data throughput. The obtained results show that a significant throughput is attained over noisy wireless optical channels.

The authors propose an adaptive orthogonal frequency division multiplexing (OFDM) system for communications over the indoor wireless diffuse optical channel. This channel can be characterised as short-term stationary, with severe attenuation and multipath-induced penalty, and high dependence on the space distribution of emitters and receivers. We have chosen OFDM systems because of their capability of supporting high data rates without channel equalisation. They also mitigate the quality of service fluctuations induced when space distribution of emitters and receivers varies. The performance of the new proposed scheme is compared with that of an adaptive system described in a previous work. The obtained results show that a significant increase of the system throughput is attained over noisy wireless optical channels.

An optical code-division multiple access system (OCDMA) is presented for visible light communications (VLC). The OCDMA scheme is based on the recently proposed random optical codes (ROC), which do not present optimal correlation properties but are characterized by their ease of generation when large number of simultaneous users are considered. The synchronism mechanism when using ROCs is an important issue which is adequately addressed and solved by the designed system. An experimental prototype has been developed which allows us to transmit medium-quality audio data from several emitting sources simultaneously through different channels (using different codes), obtaining a practically error-free reception (imperceptible by the human ear) which perfectly agrees with the theoretical analysis.

We present a comparison between the modified Monte Carlo algorithm (MMCA) and a recently proposed ray-tracing algorithm named as photon-tracing algorithm. Both methods are compared exhaustively according to error analysis and computational costs. We show that the new photon-tracing method offers a solution with a slightly greater error but requiring from considerable less computing time. Moreover, from a practical point of view, the solutions obtained with both algorithms are approximately equivalent, demonstrating the goodness of the new photon-tracing method.