In this study, the authors find the optimum inter-distance between visible light access points (VAPs) in a multi-cell system. This is an important issue to avoid the lack of resources resulting from wiring too few VAPs while minimising the installation cost. This study uses a one-dimensional corridor model suitable for many practical environments such as train aisles and hospital/library corridors. They provide formulas for the average rate achieved per user to determine the optimal inter-VAP distance. These formulas depend on information that is usually available in the design step such as the corridor dimensions, luminaries' parameters, and user density. They consider different power allocation techniques and different frequency reuse factors. The analysis shows that the optimum inter-VAP distance depends mainly on the corridor dimensions and not as much on the communication technique. Higher frequency reuse factors reduce the interference and improve the performance in the case of small cells. Specifically, the results determine the corridor dimensions that are better served by multi-VAP rather than a single centred VAP. Many important design issues are answered throughout this study such as how the ceiling height and the estimated crowdedness in the corridor affect the optimum cell size.

In order to suppress the nonlinearity impact of light-emitting diodes (LEDs) on the performance of visible light communication (VLC), the combined method including companding and predistortion was proposed in this work. The modified companding and predistortion based on the LED characteristic analysis were used corresponding to the output current -input voltage (I-V) and light output-injected current (L-I) nonlinearity, respectively. Using the combined method, the performances of the DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) VLC system were analysed. It is demonstrated that the non-linear distortion of OFDM transmitted signal is alleviated, thus the received signal quality is increased. As a result, the bit error rate (BER) performance of VLC system is improved obviously by using the combined method of companding and predistortion. Furthermore, the applicability of this combined method is also verified by analysing the nonlinearity suppression of the VLC system using different LED. The results reveal that both the impact from LED's I-V and L-I nonlinearity can be alleviated using the proposed method combining from companding and predistortion for DCO-OFDM VLC system.

This study explores how the field-of-view (FOV) of a visible light communications (VLCs) receiver can be manipulated to realise the best signal-to-noise ratio (SNR) while supporting device mobility and optimal access point (AP) selection. The authors propose a dynamic FOV receiver that changes its aperture according to receiver velocity, location, and device orientation. The D-FOV technique is evaluated through modelling, analysis, and experimentation in an indoor environment comprised of 15 VLC APs. The proposed approach is also realised as an algorithm that is studied through analysis and simulation. The results of the study indicate the efficacy of the approach including a 3X increase in predicted SNR over static FOV approaches based on measured received signal strength in the testbed. Additionally, the collected data reveal that D-FOV increases effectiveness in the presence of noise. Finally, the study describes the tradeoffs among the number of VLC sources, FOV, user device velocity, and SNR as a performance metric.

Terrestrial free-space optical (FSO) communication systems with subcarrier intensity modulation have experienced a particular research attention in the recent past. However, their performance strongly degrades in the presence of atmospheric turbulence, pointing errors, and phase noise impairments. In order to overcome these limitations, the authors consider a receiver diversity scheme of a typical subcarrier phase-shift keying (PSK) system and investigate the performance by means of the average symbol error probability (ASEP). They assume a wide range of turbulence conditions, non-zero boresight pointing errors, and phase noise strengths described through the gamma-gamma, Beckmann, and Tikhonov distributions, respectively. Novel approximate ASEP expressions are derived for single-input single-output and single-input multiple-output (SIMO) configurations. Appropriate numerical results are depicted and validated by Monte Carlo simulations.