Modulation analysis for outdoors applications of optical wireless communications

For optical wireless communication systems, the most frequently used system is intensity modulated direct detection (IM/DD). We analyze the modulation schemes that could be used in an outdoor environment. We keep our concern on the direct detection method. We discuss uncoded on-off keying (OOK) (proposed for its simplicity), pulse position modulation (PPM) (proposed for its power efficiency) and digital pulse interval modulation (DPIM). We compare OOK with the PPM and DPIM schemes for power and bandwidth efficiency. DPIM offers higher transmission capacity compared to OOK/PPM, and that can be employed to improve either the bandwidth efficiency or power efficiency of the system. It is very suitable for outdoors applications.