Infrared communication channel optimisation for quasi−diffuse multi−spot wireless indoor networking

In this report we develop an indoor infrared (IR) channel model and use it to study optimum configurations for quasi−diffuse multi−spot IR wireless communications. By means of these simulation tools we show how we can reduce multi−path effects and co− channel interference in order to improve detection for high−speed data rates. Introduction Recently there has been growing interest in InfraRed (IR) optical wireless communications [1]. IR wireless forms a practical basis for many applications and provides solutions for environments where wired links or Radio Frequency (RF) wireless may not give the best implementation. For wide applicability, a wireless link should be compact, consume little power, and be easy to align, yet robust against background noise and interference from the other users. As a transmission medium for indoor wireless communications, infrared has several advantages over radio, such as an enormous unregulated bandwidth for high bit rates and absence of interference between links operating in rooms separated by walls. Furthermore infrared components are usually inexpensive, small and consume little power. This paper addresses one of the most promising candidates for high−speed in−house IR wireless communications, called Multi−Spot Diffusing Configuration (MSDC) [2]. MSDC is actually a quasi−diffuse configuration using multi−beam transmitters emitting nearly collimated beams and an array of detectors with each one having a narrow Field− Of−View (FOV). In some cases, the detector array is formed into an imaging receiver [3]. The goal of this paper is to evaluate the impulse response of an indoor free−space optical IR channel with a variety of MSDC configurations for the array of sources and detectors and their angular directivities. We present the results from these simulations and discuss how to optimize the infrared channel for higher data rates. Multi−Spot Quasi−Diffuse IR channel model The geometry of the IR channel considered in this report is shown schematically in Figure 1 in the form of a room. In this figure, we define a pair of transmitters (T) and detectors (D) and assume that their IR beams couple primarily via the ceiling, since this is the best reflecting surface available in most common rooms. In this report, we model the beams and the FOV of the transmitters and detectors using a generalized Lambertian pattern [4]. This pattern is defined by [(n+1) cos(α)]/2π, where α is the angle from the directivity vector of the transmitter/detector and n is an integer for setting the narrowness of the beam/FOV. The patterns of IR light incident on the ceiling and their detected portions are calculated using this expression and assuming a uniform reflectivity function for the ceiling surface. Note that changing these assumptions to more realistic beam/FOV forms and reflectivity functions are not expected to change the main qualitative conclusions of this report for the data−rate optimizations. Infrared communication channel optimization for quasi-di use multi-spot wireless