Experimental Comparison of Pulse Position and Hamming-Coded Modulations for High Sensitivity Coherent FSO Communications

We experimentally compared 4PPM-QPSK and Hamming-coded QPSK for coherent FSO applications with low symbol rates. Carrier recovery in 4PPM-QPSK works better because of the higher per-symbol power at pulses, leading to 1.1 dB better sensitivity.