Tightening union bound by applying Verdu theorem for LDPC

A tight bound on the bit error probability for low density parity check codes is derived by eliminating the useless codewords out of the union bound. The elimination of these codewords is done by applying Verdu´s theorem and calculating tin Hamming weight of the codewords that belong to the irreducible set. This approach is simpler than other bound techniques in the sense of the complexity of computation and it also extends the reliable region of E_b/N₀ in which the bound yields meaningful results.