Impact of Imperfect Channel State Information on Physical Layer Security by Precoding and Diversity

Physical layer security (PLS) is an emerging paradigm that makes use of wireless channel characteristics to provide security. Many PLS schemes require knowledge of the channel state information (CSI). However, CSI is usually imperfect due to factors such as noisy feedback channels, channel estimation errors and outdated CSI. In this paper, we investigate the impact of imperfect CSI on the secrecy and error rate performances of a PLS scheme that combines adaptive matched-filter (MF) precoding and diversity in orthogonal frequency division multiplexing (OFDM). Particularly, we derive the secrecy capacity and error rate expressions for the legitimate and eavesdropper's channels under imperfect CSI assumption. The impact of the imperfect CSI is studied via theoretical as well as numerical techniques in frequency-selective Rayleigh fading wiretap channel. The analysis is done in both frequency division duplex (FDD) and time division duplex (TDD) modes.