Fast and Efficient Sequence Detection for APD Photon-Counting FSO Systems

Designing robust detection algorithms under weak and strong atmospheric turbulence conditions is one of the main challenges in practical implementation of free-space optical (FSO) communication receivers. In this paper, we propose a blind and fast algorithm based on the generalized maximum likelihood sequence detection (GMLSD) for APD photon-counting receivers without requiring the transmission of training sequence. More precisely, our proposed method achieves a higher spectral and energy efficiency compared to the conventional methods. In addition, the proposed algorithm makes the GMLSD receiver more attractive due to a lower computational complexity. We show through different Monte-Carlo simulation results that by increasing the length of the transmitted sequence, the bit error rate (BER) performance of our proposed Fast GMLSD receiver approaches to that achieved under perfect channel state information (CSI). Finally, we address the effect of the average number of noise photoelectrons and the turbulence strength on the BER performance of the considered FSO system.