Differential amplitude pulse-position modulation for indoor wireless optical channels

We propose a novel differential amplitude pulse-position modulation (DAPPM) for indoor optical wireless communications. We present the symbol structure and the properties of DAPPM. The power spectral density of DAPPM is also derived and compared to other modulation schemes. DAPPM yields advantages over PPM and DPPM in terms of bandwidth efficiency, capacity and peak-to-average power ratio (PAPR). The power efficiency is also examined. Over a non-dispersive channel, DAPPM gives better bandwidth and/or power efficiency depending on the number of amplitude levels (A) and the maximum length (L) of a symbol. We also show that, over a dispersive channel, DAPPM has better bandwidth efficiency but requires more power than PPM and DPPM for the same value of L.