Blind Reconciliation with Protograph LDPC Code Extension for FSO-Based Satellite QKD Systems

A significant breakthrough in space-based quantum key distribution (QKD) inaugurated by the Micius satellite has brought us closer to the era of global QKD networks. An essential step in the post-processing QKD is key reconciliation (KR), which eliminates the mismatch in the raw keys between two legitimate users. However, the fluctuation in the quantum bit-error rate (QBER) caused by the free-space optical (FSO) turbulence channels poses various challenges for the KR design. This paper addresses the design of blind KR schemes for FSO-based low Earth orbit (LEO) satellite QKD systems, which allow operating without a prior QBER estimation. Specifically, we present a novel blind KR scheme with a protograph low-density parity check (LDPC) code extension. The proposed LDPC structure is constructed by gradually extending and exhaustively searching among all possible solutions. The proposed design is evaluated in terms of the final key rate performance over the QKD systems using a dual-threshold/direct detection (DT/DD) scheme. Simulation results confirm the effectiveness of our proposed design compared to the state-of-the-art design in different turbulence channel conditions.