Reliable and secure communications over Gaussian wiretap channel using HARQ LDPC codes and error contamination

This paper investigates reliable and secure transmissions over the Gaussian wiretap channel. A physical layer coding scheme based on Low-Density-Parity-Check (LDPC) codes with granular Hybrid Automatic Repeat reQuest(HARQ) protocol is presented. HARQ granularity aims at sending coded data at the minimum rate required for legitimate successful decoding while minimizing the information leakage that may benefit to eavesdropping. It will be shown that the granularity increases the frame error rate at the eavesdropping receiver. Since the secrecy level can be assessed through the bit error rate (BER) at the unintended receiver, intraframe and interframe error contaminations are employed to convert the loss of only few packets in the wiretap channel into much higher BERs at the eavesdropper. From the BERs at the legitimate and illegitimate receivers, the reliability and security regions can be determined. It is observed that with granular HARQ and interframe error contamination, signal to noise (SNR) regions that are simultaneously reliable and secure are expanded significantly.