An Adaptive Combining Hybrid FSO/RF Terrestrial-Satellite Links Communication System Based on DCSK

In response to the problem that free-space optical (FSO) communication in terrestrial-satellite links is susceptible to factors such as atmospheric turbulence, pointing errors, and angle of arrival (AOA) fluctuations, this paper proposes a High-Altitude Platform (HAP)-assisted adaptive combining hybrid FSO/Radio Frequency (RF) terrestrial-satellite links communication system. The system employs FSO as the primary link for the terrestrial-HAP links, with RF serving as an on-demand, activated backup link. At the HAP receiving end, Maximum Ratio Combining (MRC) technology integrates the dual signals to enhance reception quality. At the same time, the HAP-satellite links utilize FSO transmission to leverage their high-speed advantages. At the physical layer, Differential Chaotic Shift Keying (DCSK) modulation is integrated with Bose-Chaudhuri-Hocquenghem (BCH) coding to efficiently suppress channel interference and reduce the Bit Error Rate (BER). The system employs theM-distribution model to simulate light intensity scintillation, atmospheric attenuation, beam wander, pointing error, and AOA fluctuations, and derives the closed-form expression for the BER of the proposed adaptive combining terrestrial-HAP-satellite system. Under typical atmospheric conditions, the influence of different link switching strategies and modulation methods on system performance was analyzed through simulation.