Mobile adaptive multi-beam spot-diffusing indoor optical wireless system

Multi-beam spot-diffusing optical wireless systems have been shown to offer performance improvement over conventional diffuse systems. In this work, the authors introduce a new adaptive technique to adjust the transmit power for each beam produced by a multi-beam optical transmitter aimed at the room ceiling so as to optimise the received signal-to-noise ratio (SNR) at a given receiver location. The transmitter receives computed tap weights for transmit powers from the receiver through a feedback link between the transceivers. In addition to a single spot power adaptation, adaptation of the power of clusters of five, ten and twenty spots (which reduces the complexity of the adaptation process) was used and the performance was evaluated. The effect of transmitter mobility was investigated with the system employing an angle diversity receiver. Performance comparison with the results of a non-adaptive transmitter system is presented in terms of SNR and delay spread. The adaptive method achieved a considerable gain in SNR, especially at the weakest links for both the mobile and non-mobile transmitters. Over 6 dB increase in SNR is achieved when the distance between the transceivers is largest for the non-mobile transmitter and over 3 dB for the same situation in the case of a mobile transmitter. The influence of the field of view of a multidetector receiver was examined with the adaptive transmitter. The adaptive technique can be used with a two-dimensional multi-beam clustering having clusters of spots on the walls as well as on the ceiling. This is currently under investigation.