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Modulation analysis for wireless infrared communications

The channel model for indoor wireless optical communication links is unusual in that it combines the intensity-modulation constraints of the Poisson photon-counting channel with the multipath dispersion, bandwidth constraints, and additive white Gaussian noise of the conventional radio channel. In this paper we examine the performance of several modulation schemes on the indoor wireless optical channel. Modulation schemes having low duty cycle, such as pulse-position modulation (PPM), offer improved power efficiency at the expense of decreased bandwidth efficiency. We compare the power and bandwidth efficiency of several forms of PPM, including multiple PPM, overlapping PPM, convolutional coded PPM, and trellis coded OPPM. We also examine the differences between the wireless infrared communications channel and the quantum-limited photon-counting channel.