A construction of LDPC convolutional codes with close distance bounds

A trellis code constructed by concatenating a delay processor and a signal mapper to a convolutional code with a short constraint length can be regarded as a convolutional code with a large constraint length. We can obtain a close upper bound and a close lower bound for such a code. In this paper, we use this code structure to construct low-density parity check convolutional codes which are 4-cycles free and hence can be efficiently decoded by the iterative message-passing algorithm.