High-Speed Multi-User Indoor Optical Wireless Systems

This paper discusses novel aspects to high-speed multi-user indoor optical wireless communication systems. The original aim of the study is to address the impairments of non-direct infrared communications and provide practical solutions, such as by increasing the system data rate and/or enabling high data rate multi-user communications where the increased channel rate is shared among users. This aim is achieved through the combination of diversity reception, spot-diffusing, beam angle, delay and power adaptation, and multicarrier code division multiple access (MC-CDMA). Diversity receivers can reject the background noise components received in directions not associated with the signal. Narrower field of views can be used to restrict the range of incident rays accepted, and hence reduce the signal spread at the cost of poor power efficiency. The power efficiency can be improved if a spot-diffusing technique is introduced and more so if spot power adaptation is allowed. The signal spread can be minimized through delay adaptation. Furthermore, the link design can be improved if angle adaptation is employed. This can result in a compact impulse response and a system that is able to achieve higher data rates (12.5 Gbit/s) or high bit rate multi-user communications through the use of such MC-CDMA schemes.