Security gap analysis of some LDPC coded transmission schemes over the flat and fast fading Gaussian wire-tap channels

It is known that the error rate can be used as a measure of reliability and security over the wire-tap channel when practical, finite length codes are used for transmission, and the security gap is an error rate based metric able to jointly treat these two aspects. In this paper, we consider several low-density parity-check (LDPC) coded transmissions, which represent the state of the art for transmissions over the wire-tap channel and we assess and compare their security gap performance. We consider two kinds of wire-tap channels: the flat and the fast fading wire-tap channels with additive white Gaussian noise. As a reference, we use the progressive edge growth (PEG) algorithm for the design of unstructured LDPC codes and compare its performance with that of four approaches for designing structured LDPC codes. We analyze both systematic and non-systematic transmissions and show that some structured code design techniques are able to achieve comparable or even better performance than the PEG algorithm over the considered channels, while taking advantage of their simpler encoding and decoding procedures.