Self-Pilot Tone Based Adaptive Threshold RZ-OOK Decision for Free-Space Optical Communications

Abstract

This paper studies a novel self-pilot tone based adaptive threshold return-to-zero on-off keying (RZ-OOK) decision for free-space optical (FSO) communications. RZ-OOK has the characteristics of impulse series in the spectrum. Therefore, these impulses can be utilized as the pilot tones of the transmitted signal to convey the channel state information (CSI) of FSO links. Then, the CSI signal is extracted using a local oscillator (LO) with the frequencies of the impulse series and low pass filter. Finally, the adaptive threshold decision (ATD) is realized by assigning optimized weight factors into the extracted CSI signal. The proposed adaptive threshold RZ-OOK decision was studied in simulation under various pulse durations of RZ-OOK signal and frequencies of LO. Simulation results demonstrated that RZ-OOK with the proposed impulse tone-extracted CSI signal under optimized weight factor performs close to the conventional ATD under precise CSI knowledge.