Coding of PPM based modulation techniques to improve the performance of infrared WLANs

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 WLANs. The bandwidth efficiency expressions of these modulation schemes are presented and compared against the one of pulse-position modulation (PPM), which allows to conclude that both APPM and OPPM can be used to improve the performance of PPM without significant bandwidth expansion, using trellis-coded modulation (TCM) codes. We also derive the best codes for some APPM and OPPM schemes, and the results show that non-negligible coding gains without bandwidth expansion can be obtained with trellis codes of moderate complexity