TCM coding of PPM based modulations for infrared WLAN´s impaired by ISI

In this communication we consider the use of PPM based modulation methods, such as the hybrid modulation method called amplitude and pulse-position modulation (APPM) and overlapping pulse-position modulation (OPPM) to improve the performance of infrared WLAN´s, by the use of trellis-coded modulation (TCM) codes. We describe the best code search and results, which demonstrate that, even with trellis codes of moderate complexity, non-negligible coding gains can be obtained without bandwidth expansion. Monte Carlo simulations have been done to compare uncoded PPM against APPM and OPPM TCM coded systems performances, on ceiling-bounce channel models for various values of delay spread. Although our codes were derived for the AWGN channel without inter-symbol interference (ISI) awareness, their behavior in multipath dispersion channels is quite effective.