High-capacity 32 Gbps DWDM free-space optical communication with LDPC-coded BPSK under turbulence-induced fading

Free-space optical (FSO) systems offer high-capacity and license free wireless links but suffer severely from atmospheric turbulence, which causes random amplitude and phase fluctuations. This paper investigates a 32-channel dense wavelength division multiplexed (DWDM) FSO link operating at an aggregate rate of 32 Gbps using binary phase shift keying (BPSK) modulation with and without low-density parity-check (LDPC) coding for a terrestrial network. The Gamma–Gamma distribution is employed to model weak, moderate, and strong turbulence regimes. Each channel carries 1 Gbps at 50 GHz spacing across the C-band, and the LDPC code employs a (64,800, R = 1/2) quasi-cyclic structure decoded using the sum-product algorithm with 50 iterations. Simulation results show that LDPC coding reduces the bit error rate (BER) by 4–6 orders of magnitude compared to the uncoded system. At a target BER of 10 −6 , the LDPC-coded system provides a coding gain of 5.2 dB under weak turbulence and increases the link range from 0.9 km to 1.5 km under moderate turbulence. The system achieves reduced outage probability under turbulence induced fading. These results confirm that LDPC coding significantly improves the reliability of DWDM-FSO links.