Channel Feature Extraction and Physical Layer Key Generation in FDD Massive MIMO Systems

Abstract

While Physical Layer Key Generation (PKG) offers lightweight security for 6G IoT, channel non-reciprocity in FDD massive MIMO degrades key consistency. This paper presents a comprehensive review of Physical Layer Key Generation (PKG) techniques within Frequency Division Duplex (FDD) massive MIMO systems. While PKG leverages the inherent randomness of wireless channels to establish lightweight security for communication nodes, FDD systems pose a significant challenge. The separated uplink and downlink bands produce non-reciprocal fast-fading channel responses, which inherently degrade the consistency of keys generated from instantaneous channel state information (CSI). To address this, this study categorizes existing methodologies into three primary routes: stable propagation feature extraction, intelligent feature mapping, and system engineering optimization. It examines their mechanisms across the angle, beam, and statistical covariance domains, comparing representative schemes in terms of Key Disagreement Rate (KDR), overhead, and computational complexity. Ultimately, future research must integrate physical priors with data-driven models to ensure robust security in practical 6G networks.