Securing Wireless Channels: Reliable Shared Secret Extraction through OTFS

Abstract

Physical layer key generation (PLKG) has emerged as a promising strategy for securing wireless communication using shared channel knowledge between two legitimate users. Traditional PLKG systems rely on time-frequency domain channels using metrics such as Received Signal Strength Indicator (RSSI) or Channel State Information (CSI) to generate secure keys. As a result of the rapid variation in the time-frequency domain channels, these systems are prone to error and suffer from a high reconciliation overhead requirement. Conversely, the same channels have a sparse and static representation in the delay-Doppler domain, which is utilized by the recently introduced Orthogonal Time Frequency Space (OTFS) modulation scheme. Furthermore, the channel representation in the delay-Doppler domain is uniquely determined by the scattering environment between the transmitter-receiver pair. In this paper, we leverage the sparsity of the delay-Doppler domain channel as well as the uniqueness of the channel representation to introduce two OTFS based PLKG schemes. We show through extensive simulations that the introduced OTFS schemes can get < 10% bit disagreement ratio (BDR) in scenarios where time-frequency domain based RSSI methods break down.