Signal Mapping for Bit-Interleaved Coded Modulation Schemes to Achieve Secure Communications

In this letter, we investigate different signal mappings for bit-interleaved coded modulation (BICM) and their effect on the secrecy information rate of a wire-tap channel exhibiting Rayleigh fading. By focusing on BICM schemes using 64 QAM, 16 QAM and (1, 5, 10) signal constellations, we show that the optimal mapping depends on the range of signal-to-noise ratios (SNRs) we are interested in. We propose a new mapping algorithm, called maximum error event (MEE), to optimize the secrecy rate over a wide range of SNRs. At low SNR, MEE mapping achieves a lower secrecy rate than other well known mappings, but at medium-to-high SNRs MEE mapping achieves a significantly higher secrecy rate over a wide range of SNRs. Simulation results on 16 QAM, 64 QAM and (1, 5, 10) constellations are presented to show the achievable secrecy rates of various mappings for BICM from low to high SNRs.

I. Introduction

THE area of physical layer security has received a great deal of attention over the past few years due to its simplicity over existing cryptographic methods. It is a promising technique to establish a secured transmission link between two legitimate communication terminals, while guaranteeing that any eavesdropper has no access to that information. In general, the communication scheme is modeled using the well-known wiretap channel model introduced by Wyner in 1975 [1]. In this model, the communication system consists of three terminals: the transmitter (Alice), the legitimate receiver (Bob) and the eavesdropper (Eve ). In his seminal work, Wyner showed that Alice and Bob are actually able to establish secure communication provided that the channel between Alice and Eve, known as the wiretap channel, is a degraded version of that between Alice and Bob, known as the main channel.