Optimising the performance of digital pulse interval modulation with guard slots for diffuse indoor optical wireless links

The intersymbol interference (ISI) in a diffuse indoor optical wireless communication channel limits the maximum data rate for error-free transmission. In this study, simpler decoding approaches are suggested for digital pulse interval modulation (DPIM) with guard slot(s) (GSs) to reduce the effect of ISI. The unique patterns in DPIM symbols with GSs are exploited to carry out optimum decoding without utilising an equaliser at the receiver. The simplest decoding approaches would be to find an optimum threshold level that offers the least power penalty. However, performance can be enhanced by employing a hybrid decoding scheme in which the amplitudes of adjacent slots are compared in order to carry out the slot decision. The decoding algorithm that maximises the likelihood of 'one' can offer the optimum performance. These decoding approaches are simpler to implement and offer a relatively high gain (>6 dB) at a moderately dispersive channel.