Orthogonal Spatial Coding in Indoor Wireless Optical Link Reducing Power and Bandwidth Requirements

Although uniform distribution of optical power is one of the main requirements for multi-access support in a wireless optical link, Multi Spot Diffusing Configuration (MSDC) provides uniformity along with spatial independence that allows spatial diversity techniques over the link. Independent spatial channels are generated by a multibeam transmitter producing spatially confined diffusing spots, and a multibranch receiver with narrow field-of-view branches. In this paper, we propose an orthogonal spatial coding technique that utilizes the independence of channels to reduce power and bandwidth requirements. The technique is based on treating the m channels between a transmitter and a receiver as an m-dimensional space. Thus, enabling data transmission through varying signal level and its location in space. Our study shows that using 8 channels, the proposed technique enables transmission at rates 10 and 12 times higher than combining when power per channel and user are constrained, respectively.