Two edge type LDPC codes for the wiretap channel

We consider transmission over a wiretap channel where both the main channel and the wiretapper´s channel are Binary Erasure Channels (BEC). We propose a code construction using two edge type LDPC codes based on the method of Thangaraj, Dihidar, Calderbank, McLaughlin and Merolla. The advantage of our construction is that we can easily calculate the threshold over the main channel. Using standard LDPC codes with a given threshold over the BEC we give a construction for a two edge type LDPC code with the same threshold. Since this construction gives a code for the main channel with threshold zero we also give numerical methods to find two edge type LDPC codes with non-zero threshold for the main channel.