Performance of uncoded overlapping PPM under communication constraints

The performance of uncoded overlapping pulse position modulation (OPPM) with at most two pulse positions per pulsewidth is investigated for an optical direct-detection channel under communication constraints. It is shown that under bandwidth and throughput constraints OPPM, with two pulse positions per pulsewidth, outperforms PPM when the overlap is chosen properly and the throughput is greater than 0.2 nats/slot. This makes it possible to increase the throughput and/or decrease the energy of the OPPM system, while maintaining the same performance as PPM. The energy saving when using OPPM instead of PPM to transmit reliably a given amount of information is determined for different values of overlapping indices. The maximum throughput that can be achieved under average power and bandwidth constraints (with error probability not exceeding 10^-5) is also determined