Doubly-Generalized LDPC Codes: Stability Bound over the BEC

The iterative decoding threshold of low-density parity-check (LDPC) codes over the binary erasure channel (BEC) fulfills an upper bound depending only on the variable and check nodes with minimum distance 2. This bound is a consequence of the stability condition, and is here referred to as stability bound. In this paper, a stability bound over the BEC is developed for doubly-generalized LDPC codes, where the variable and the check nodes can be generic linear block codes, assuming maximum a posteriori erasure correction at each node. It is proved that in this generalized context as well the bound depends only on the variable and check component codes with minimum distance 2. A condition is also developed, namely the derivative matching condition, under which the bound is achieved with equality.