Bit Interleaved and Coded Modulation with Indexed Partitions for Physical Layer Security

In this paper, we propose a new transmission scheme, referred as Bit Interleaved Coded Modulation with Indexed Partitions (BICM-IPM), to secure the transmission on a wiretap channel with a passive eavesdropper. The BICM-IPM is designed to degrade the quality of QAM symbols transmission on a wiretap channel, while preserving the quality at the legitimate receiver. To achieve this, the QAM constellation is divided into several disjoint subsets, each one indexed by a channel-dependent dynamic secret key, known at the sender (Alice) and the legitimate receiver (Bob), but not at the eavesdropper (Eve). The symbols are then decoded at the legitimate receiver considering only the alphabet containing the symbols relative to the partition. However, in the absence of the index-partition knowledge at the eavesdropper, all the constellation symbols will be considered. Thus, the detection zones around Bob’s symbols will be larger than those at Eve. To further degrade the wiretap channel, we propose to inject a uniformly distributed random noise in a domain space totally included in Bob’s detection zone, but exceeding Eve’s one. Our analytical and numerical results show that the BICM-IPM creates a Bit Error Rate (BER) floor of 50% independent of the Signal-to-Noise Ratio (SNR) on the Eavesdropper’s link, while preserving the legitimate link for which the BER decreases with the SNR. This creates a maximal entropy at the eavesdropper side that is close to decoding a random binary sequence.