Optimisation of a Colour-based Spatial Modulation Scheme for VLC Under Illuminance and SINR Constraints

This treatise presents a framework for the optimisation of a colour-based optical spatial modulation framework for visible light communication (VLC). The focus is particularly on the conflicting interests between illuminance and signal transmission. The system under consideration is configured with a non-line-of-sight (NLoS) model, based on the joint use of colour shift keying (CSK) and optical spatial modulation (OSM) with intensity modulation and direct detection (IM/DD). With the adaptation of the aforementioned optical techniques and convex optimisation, the design and development of a colour-based optical wireless system is carried out. Firstly, an optimisation problem with the intention of minimising the total luminous intensities of the light emitting diode (LED) arrays subject to the transmitting LED array's optical power budget, minimum required illuminance level, LED-user channel conditions and latency intolerant users' (LITUs) quality-of-service (QoS) target constraints is defined. Secondly, a coordinated algorithm for the selection of a transmitting LED array, maintenance of a particular illuminance and signal-to-interference-plus noise ratio (SINR) levels during symbol transmission is designed. Lastly, through computer simulations, a numerical analysis is carried out to demonstrate and evaluate the performance of the algorithm. During the transmission of all symbols, the proposed framework is capable of satisfying the SINR target for LITUs while reducing the optical power by approximately 20% to 25% and 20% to 75% for transmitting and non-transmitting LED arrays, respectively. Additionally, provided that the required illuminance level is specified within the standardised levels of 300 lux to 1500 lux, the proposed system can provide adequate illuminance as per the users' requirement at all points where either a LITU or a latency tolerant user (LTU) is located at any given instance. However, fair SINR levels are not guaranteed at the points where the LTUs are positioned. On the other hand, the algorithm disposes low illuminance levels ranging from 100 lux to 250 lux at locations towards the room boundaries where there are no users. The proposed system is able to achieve data rates of 5 Mbps to 25 Mbps using commercially-off-the-shelf LEDs.