Performance of indoor visible light systems using OOK and PPM modulations under multipath channels

In this paper, the performances of On-Off Keying (OOK) and Pulse Position Modulation (PPM) modulation schemes in multipath indoor optical wireless links are investigated. It is shown that PPM is more resilient to Inter-Symbol Interference (ISI) induced by multipath channels when one array of Light Emitting Diode (LED) transmitters is employed compared with OOK schemes. However, the OOK arrangement is capable of outperforming the PPM counterpart in a highly diffused channel. More explicitly, the effect of ISI on BER performance fundamentally determined by the interplay of the delay spread of the indoor wireless channel and the duration of one transmission symbol, which is captured by `normalized delay spread´. Finally, numerous simulation results were provided in order to demonstrate the system performance under various normalized delay spreads.