Transmit Power Adaptation for a Mobile Multibeam Spot Diffusing Optical Wireless System in One and Two Planes

The received signal quality in indoor optical wireless (OW) systems is partly influenced by the change in receiver location relative to the optical transmitter. Employment of an angle diversity receiver counters signal degradation caused by background noise sources. While spot diffusing transmitters have been shown to produce better performance over the conventional full diffuse transmitters, transmit power distribution among the multiple beams, in studies to date, takes no account of the change in the transmitter-receiver separation especially when both are fully mobile. We investigate the performance of two new spot diffusing geometries based on clustering of spots on ceiling and walls. The performance is evaluated for both stationary and mobile transmitters in conjunction with diversity detection and is compared with that of the single line strip optical wireless system. Furthermore, single spot power adaptation is carried out on both systems and the discussion of the results highlights the signal-to-noise ratio (SNR) gain in comparison to the single line strip. The results show that while the adaptive transmit power approach achieved as much as 2dB increase in SNR for the single line, the one- plane configuration achieved a 5.7dB SNR gain near corners without power adaptation and 15.8dB with adaptation over the single line strip. The two-plane approach improved the SNR around the room centre (at the locations of the noise sources) by 5.2dB without adaptation and 11.6dB with the adaptive approach compared to the single line for both cases. Moreover, both configurations maintain the same improvement pattern when the transmitter is mobile.