On the design of bandwidth efficient signalling for indoor wireless optical channels

It is well known that indoor wireless optical channels are limited not only in transmitted optical power, but also in signalling bandwidth. This bandwidth constraint arises due to multipath dispersion in indoor settings as well as due to response time limitations of optoelectronic components. This paper presents an overview of theoretical and practical issues in the design of signalling for bandwidth constrained intensity modulated, direct detection wireless optical channels. A brief overview of the salient qualities of the wireless optical channel are presented to highlight the amplitude constraints which arise. A survey of modulation design is then presented which includes the review of a general technique to represent optical intensity modulation in a signal space and to construct optical intensity lattice codes. Results on the channel capacity of indoor wireless optical channels are surveyed and particular emphasis is placed on recently derived asymptotically exact bounds. The use of multiple emitters and receivers in wireless optical channels is also presented and particular emphasis is placed on techniques which exploit spatial dimensions to improve spectral performance. The paper concludes with some remarks regarding the status of the research area and suggestions for future work. Copyright (c) 2005 John Wiley & Sons, Ltd.