Optical Impulse Modulation for Diffuse Indoor Wireless Optical Channels

In this paper, power efficient signaling over indoor diffuse wireless optical channels is considered. Present-day laser diodes have pulse rates many times higher than the bandwidth of multipath distorted diffuse channels. Despite the fact that the transmitter extra degrees of freedom are not supported by the low-pass channel, they can be used to satisfy the channel non-negativity constraint. In this paper, we define optical impulse modulation (OIM) in which data are confined to the low-pass region while the high-pass region, which is distorted by the channel, is used to satisfy the channel amplitude constraints. A mathematical framework for OIM is presented, and an optimal receiver filter is designed. At a normalized delay spread of 0.2, the gain in average optical power of using decision feedback equalization (DFE) with rectangular pulse-amplitude modulation (PAM) is 4.8 dBo, while that of using the less complex unequalized OIM receiver is shown to be 4.9 dBo.