ABSTRACT
The performance of optical wireless communication is affected by channel and atmospheric effects such as building sway, scintillation/turbulence, fog, and precipitation. This chapter presents diversity techniques as a means of combating these channel impairments. Spatial diversity, with multiple transmitters and receiver units, are used to provide robustness to the system and exploit the spatial variations in the distribution of the channel impairments. With spatial diversity, each receiver is expected to receive independent and uncorrelated versions of the same information sent by multiple transmitters. Different methods for combining the signals from the multiple receivers are analysed and the error performance for each method is presented. Reduction in the attainable diversity gain due to correlation in the received signals from the different receivers is analysed in this chapter as well. Channel coding for terrestrial optical wireless communication as a form of time diversity is also included here. With channel coding, redundant bits are embedded in the transmission to correct some of the bit errors introduced by the atmospheric channel.
