Wireless Optical Communication Systems

The use of optical free-space emissions to provide indoor wireless com- nications has been studied extensively since the pioneering work of Gfeller and Bapst in 1979 [1]. These studies have been invariably interdisciplinary - volving such far flung areas such as optics design‚ indoor propagation studies‚ electronics design‚ communications systems design amongothers. The focus of this text is on the design of communications systems for indoor wireless optical channels. Signalling techniques developed for wired fibre optic n- works are seldom efficient since they do not consider the bandwidth restricted nature of the wireless optical channel. Additionally‚ the elegant design meth- ologies developed for electrical channels are not directly applicable due to the amplitude constraints of the optical intensity channel. This text is devoted to presenting optical intensity signalling techniques which are spectrally efficient‚ i. e. ‚ techniques which exploit careful pulse design or spatial degrees of freedom to improve data rates on wireless optical channels. The material presented here is complementary to both the comprehensive work of Barry [2] and to the later book by Otte et al. [3] which focused prim- ily on the design of the optical and electronic sub-systems for indoor wireless optical links. The signalling studies performed in these works focused p- marily on the analysis of popular signalling techniques for optical intensity channels and on the use of conventional electrical modulation techniques with some minor modifications (e. g. ‚ the addition of a bias).

Wireless Optical Communication Systems addresses the problem of designing efficient signaling and provides a link between the areas of communication theory and modem design for amplitude constrained linear optical intensity channel. Topics include historical perspective, channel impairments, amplitude constraints and the characteristics of popular optoelectronic components. A variety of wireless optical channel topologies are presented along with a survey and analysis of present day signalling techniques employed for these channels. The author provides a unifying framework for signalling design which allows the channel constraints to be represented geometrically and permits the use of modem design principles from electrical channels. Modulation schemes are designed using the formalism of lattice codes and a design process for signalling sets is specified.

The use of multiple-input/multiple-output (MIMO) wireless optical channels to improve the spectral efficiency of links is explored. The basic spatio-temporal modem design problem is specified and a spatial multiplexing gain is quantified. New spatial discrete multitone modulation is proposed and the unique features are discussed. Based on measurements on an experimental prototype, a channel model is formulated and a realizable spatio-temporal coding scheme is simulated to quantify performance gains.

This volume is organized for professional and academic readers engaged in modem design for wireless optical intensity channels. Significant background material is presented on both the properties as well as on fundamental communications principles. Wireless Optical Communication Systems can be used by physicists and experimentalists as an introduction to signalling design as well as communication systems designers.