Joint transmission in indoor visible light communication downlink cellular networks

In future visible light communication (VLC) systems, networked multi-cell operation is required to achieve seamless coverage and high data rate in typical indoor environments. We refer to this type of cellular network as optical atto-cell network. In such network, co-channel interference (CCI) between adjacent optical atto-cells limits the performance of the network. In order to maximise system throughput and improve signal quality in the whole coverage area, it is necessary to mitigate CCI. In this paper, the concept of multi-point joint transmission (JT) is adapted to a VLC cellular network. It can generally be described as concurrent data transmission from multiple cooperating base stations (BSs) to a mobile station (MS). In a VLC JT system, strong CCI is avoided by co-ordinated transmission and, in addition, we exploit a particular characteristic of intensity modulation (IM) systems. This is that signals always superimpose constructively which is in stark contrast to radio frequency (RF)-based systems. Therefore, the cell-edge user signal to interference plus noise ratios (SINRs) can be improved. The results show that the JT scheme improves the median SINR by 16.4 dB compared to a full frequency reuse system. Additionally, a JT system exhibits a 67.6% improvement in terms of median system throughput compared to a static resource partitioning system with a reuse factor of 3.