a method and apparatus for convolutional turbo coding , and an apparatus for a turbo encoder are provided . the method for ctc includes the steps of encoding information bits a and b using a constituent encoder , and outputting parity sequences y 1 and w 1 , interleaving the information bits a and b using a ctc interleaver to obtain information bits c and d , and encoding the interleaved information bits c and d using the constituent encoder to obtain parity sequences y 2 and w 2 , interleaving the information bits a and b , the parity sequences y 1 and w 1 and the parity sequences y 2 and w 2 , respectively , wherein the bits in at least one of a bit group constituted of the information bits a and b , a bit group constituted of the sequences y 1 and w 1 , and a bit group constituted of the sequences y 2 and w 2 are alternately mapped to bits of constellation points with high reliability and low reliability and puncturing the interleaving result to obtain the encoded bit sequences .