Reliable and secure regions for the Gaussian wiretap channel using LDPC codes with granular HARQ

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. Increasing the HARQ granularity aims at sending coded data at the minimum rate required for legitimate successful decoding. This minimizes the information leakage that may benefit to eavesdropping. It will be shown that the granularity increases the frame error rate of the eavesdropper. Since the secrecy level can be assessed through the bit error rate (BER) at the unintended receiver, intraframe and interframe error contamination is employed to convert the loss of only few packets into much higher BERs. After obtaining the BERs at the legitimate and illegitimate receivers the reliable and secret regions can be determined. It is observed that with granular HARQ and interframe error contamination, regions that are reliable and secure at the same time are expanded.