Maximizing throughput over an average-power-limited and band-limited optical pulse position modulation channel

Given an optical pulse position modulation (PPM) channel, with an average power constraint and a bandwidth constraint, the word length needed to maximize the information throughput achievable by the channel is determined. It is shown that, to achieve the maximal capacity, the channel must be operated with a high erasure probability. This implies that coding schemes capable of compensating for a high percentage of erasures are needed for the PPM channel.