Trellis-coded modulation for the optical direct-detection channel

Summary form only given, as follows. Overlapping pulse-position modulation (OPPM) is a modulation format derived from pulse-position modulation (PPM) by allowing overlap between adjacent pulse-positions. Recently, Bar-David et al have shown that the capacity of a direct-detection optical channel increases significantly with OPPM compared to that for PPM. It is shown here that simple Ungerboeck trellis-codes over expanded sets of OPPM signals can achieve practically some of the capacity gains predicted theoretically. Specifically, it is shown that with four-state trellis-codes, throughput can be doubled at no bandwidth expansion and still have a nominal performance gain of about 1 dB. With eight-state codes, an extra 1 dB in performance gain can be achieved. Other results reported include the derivation of the performance of optimal receivers utilizing OPPM, the derivation of a distance metric suitable for OPPM signals and the direct-detection channel, and bounds on the coded error-probability of direct-detection systems with trellis-coding. The background noise as well as the quantum-limited case are considered.

Trellis-coded modulation for the optical direct-detection channel Conference Paper