Decision-feedback equalization of pulse-position modulation on measured non-directed indoor infrared channels

We examine the performance of two decision-feedback equalizers (DFEs) for pulse-position modulation (PPM) on measured non-directed indoor infrared channels with intersymbol interference (ISI). PPM offers high average-power efficiency, but on ISI channels, unequalized PPM suffers severe performance penalties. We have previously examined the performance of the maximum-likelihood sequence detector (MLSD), and found that it yields significant improvements. However the MLSD often requires such large complexity and delay that it may be impractical. We investigate suboptimal, reduced-complexity equalization techniques for PPM, providing a performance analysis of zero-forcing chip-rate and symbol-rate DFEs. Detailed performance results for 2-, 4-, 8-, and 16-PPM links at bit rates of 10 Mb/s and 30 Mb/s over 46 actual measured indoor infrared channels are presented for these two DFEs. Our results show that a symbol-rate DFE provides performance that closely approaches that of the optimal MLSD.