Enhancing secrecy of the Gaussian wiretap channel using rate compatible LDPC codes with error amplification

This paper proposes a physical layer coding scheme to secure communications over the Gaussian wiretap channel. This scheme is based on non-systematic Rate-Compatible Low-Density-Parity-Check (RC-LDPC) codes. The rate compatibility involves the presence of a feedback channel that allows transmission at the minimum rate required for legitimate successful decoding. Whenever the decoding is unsuccessful, a feedback request is sent back by the intended receiver, favoring the legitimate recipient over an unauthorized receiver (eavesdropper). The proposed coding scheme uses a finer granularity rate compatible code to increase the eavesdropper decoding failure rate. However, finer granularity also implies longer decoding delays. For this reason, a rate estimator based on the wiretap channel capacity is used. For this purpose, a set of packets is sent at once and then successive small packets are added subsequently as needed until successful decoding by the legitimate receiver is achieved. Since the secrecy level can be assessed through the bit error rate (BER) at the unintended receiver, an error amplifier is proposed to convert the loss of only few packets in the wiretap channel into much higher BERs for the eavesdroppers. Simulation results show the secrecy improvements obtained in terms of error amplification with the proposed coding scheme. Negative security gaps can also be achieved at the physical layer.