A Class of Improved Low-Density Parity-Check Codes Constructed Based on Gallager´s Form

Focused on the problem that short cycles degrade the iterative decoding performance of finite length LDPC, a class of improved low density parity check (LDPC) codes constructed based on Gallager´s form is designed. On the basis of keeping down the basic form of Gallager´s construction, a quasi-cyclic form is used, then the new codes are free of cycles of length 4 and have good minimum distance. Simulation results demonstrated that the improved codes are better than Gallager´s codes when block length is small