A novel variable-rate pulse-position modulation system with near quantum limited performance

Pulse-position modulation (PPM), a form of orthogonal signaling, can use modulator and receiver hardware similar to that of the simple on-off-keying (OOK) modulation, but with the advantage of providing its own bit-by-bit decision threshold. This feature is of special interest when channel conditions are varying or when other non-ideal conditions, such as imperfect modulator extinction, are present. We have developed a novel PPM signaling format that takes advantage of the average power limited characteristics of erbium-doped-fiber amplifiers (EDFAs). This format permits the data rate to be varied over a wide range with near-quantum-limited performance at all rates, yet with only a single filter at the receiver. We have built a free-space optical communication system using our novel PPM signaling format demonstrating simplicity, high sensitivity, wide dynamic range, and multiple data rates