Secret sharing in fast fading channels using obfuscated incremental-redundancy hybrid ARQ

In our previous work, we have shown that hybrid ARQ (HARQ) can be used to achieve secret communication over a fast fading channel. This is a physical-layer technique that can be used in conjunction with conventional cryptography to provide further protection from an eavesdropper. The key to our previous work was to use reliability-based HARQ to improve the decoder performance at the desired user much faster than at an eaves-dropper. In this paper, we propose a new HARQ approach that provides better secrecy performance by using the most-reliable received bits at the desired user to obfuscate information transmitted in the HARQ process. In addition, we present several other performance improvements, including transmitting incremental redundancy instead of repeating information and using bit-interleaved coded modulation with higher-order modulation. Performance measures such as information rate and fractional equivocation rate are provided to demonstrate that the obfuscated incremental-redundancy HARQ protocol is a promising candidate for secret sharing.