Piecewise linear AF in relay-eavesdropper channel with orthogonal components

The four-terminal relay-eavesdropper channel with orthogonal receive components (i.e. the signals transmitted from the source and relay do not interfere each other) is studied in this paper. As the relay node merely repeats the received noisy signal with the conventional amplify-and-forward (AF) relaying strategy, AF is suboptimal. A piecewise linear AF (PLAF) relaying scheme is utilized to the channel model in this paper. Achievable secrecy rate with PLAF is derived and computed numerically. Numerical examples are given to show the performance improvement of PLAF compared with AF. Simulation results show that PLAF outperforms AF and achieves a higher secrecy rate than decode-and-forward (DF) in some certain cases but without complex encoding and decoding.