A new modulation technique called combinatorial pulse position modulation (CPPM) is presented as a power-efficient alternating to quaternary pulse position modulation (QPPM) for direct-detection, free-space laser communications. The special case of ₁₆C₄PPM is compared to QPPM in terms of data throughput and bit error rate (BER) performance for similar laser power and pulse duty cycle requirements. The increased throughput from CPPM enables the use of forward error corrective (FEC) encoding for a net decrease in the amount of laser power required for a given data throughput compared to uncoded QPPM. A specific, practical case of coded CPPM is shown to reduce the amount of power required to transmit and receive a given data sequence by at least 4.7 dB. Novel hardware techniques for maximum likelihood detection and symbol timing recovery are presented.

Date Published: 6 August 1993
PDF: 12 pages
Proc. SPIE 1866, Free-Space Laser Communication Technologies V, (6 August 1993);

Published in SPIE Proceedings Vol. 1866:
Free-Space Laser Communication Technologies V
G. Stephen Mecherle, Editor(s)