Constructing Reciprocal Channel Coefficients for Secret Key Generation in FDD Systems

Physical layer-based key generation encounters the reciprocity bottleneck when applied in frequency-division duplexing (FDD) systems. This letter constructs the reciprocal channel characteristics of the uplink and downlink transmissions for key generation in FDD systems. The frequency dependence of propagation characteristics in both large-scale fading and small-scale fading is investigated. A general channel model is then established by considering frequency impact. A reciprocal channel construction framework is finally created. Numerical results demonstrate that our algorithm can construct bidirectional channel coefficients with high correlation and thus enable key generation technology to be used in FDD systems.