Structured LDPC Codes with Linear Complexity Encoding

Low density parity check (LDPC) codes have stimulated a lot of interest in recent years due to their capacity approaching performance and availability of fast decoding algorithms. The existing encoding scheme for LDPC code usually incurs too high complexity and should be changed to encoding scheme with low complexity. An elementary turbo structured Tanner graph construction and encoding scheme for a family of regular LDPC codes attaining desired high girth is studied in this paper. The construction provides flexibility in choice of parameters like column weight (j > =2), row weight k and arbitrary girth g. Turbo structured low density parity check ( TS-LDPC) codes are regular LDPC codes with their Tanner graph consists of two trees connected by an interleaver. Linear complexity is attained with few alterations and restrictions of in Tanner graph of turbo structured LDPC codes. Simulation results demonstrates that not only the bit error rate (BER) performance of TSLDPC codes at low signal to noise ratio (SNR) is comparable with error performance of corresponding random LDPC codes, with better error performance at high SNR but linear encoding considerably reduces simulation time.