Differential PPM has a higher throughput than PPM for the band-limited and average-power-limited optical channel

Because of the optimality of the pulse position modulation (PPM) technique for the infinite-bandwidth channel, it has been suggested as a technique for the bandwidth-limited channel. The use of differential pulse position modulation (dPPM) as an alternative coding scheme to PPM is proposed. In dPPM each new word begins at the end of the previous word. To avoid synchronization problems, a simple scheme that decreases the throughput of the dPPM channel but is easy to analyze is chosen. For some parameter values this restricted dPPM scheme has greater throughput (in terms of capacity and cutoff rate) than PPM