Characterization of small trapping sets in LDPC codes from Steiner triple systems

The error-floor performance of low-density parity-check (LDPC) codes under iterative decoding is governed by combinatorial configurations in the Tanner graph of the code termed trapping sets. Finding the smallest trapping set in a Tanner graph is an NP-hard problem. However, for codes constructed from designs one can partially characterize trapping sets and enumerate them efficiently. We focus on LDPC codes based on Steiner triple systems (STS), and quantify small trapping sets for bit-flipping decoding over the BSC and small trapping sets for the AWGN channel. Furthermore, we provide simulation results that show that the enumeration scheme at hand provides good estimates for the error-floor behavior of STS LDPC codes.