Entanglement-based Satellite FSO/QKD System using Dual-Threshold/Direct Detection

This paper proposes a new implementation of the BBM92 protocol in satellite continuous-variable quantum key distribution (CV-QKD) systems using dual-threshold/direct detection (DT/DD). The proposed method is less complex and thus possibly cheaper than current discrete-variable (DV) and CV-QKD systems using coherent detection. We model and analyze the performance of the proposed system in the context that a satellite distributes secret keys to two legitimate users. The analytical results are derived by considering the channel loss, atmospheric turbulence-induced fading, and receiver noises. The Gaussian beam model is considered to evaluate the impact of geometrical spreading on the signal received by legitimate users and the possibility of being eavesdropped on. Based on the design criteria for the system and analytical results, we find suitable parameters for the transmitter and the receivers to properly achieve the QKD function for distributing secret keys between two legitimate parties.