Pulsewidth-constrained signaling and trellis coded modulation on the direct-detection optical channel

Pulsewidth-constrained signals are developed for use on the degraded direct-detection optical channel. A two-dimensional representation for these signals is obtained and used to design a trellis-coded-modulation (TCM) system for use on the optical channel. The theoretical advantage of optical TCM is shown, through use of the cutoff rate, to range from 7.5 to 9 dB, depending on the throughput rate of the system. The practical potential is shown, through the actual design of a TCM system, to be as high as 6.7 dB