Convolutional Codes

The difference between block codes and convolutional codes is the encoding principle. In the block codes, the information bits are followed by the parity bits. In convolutional codes the information bits are spread along the sequence. That means that the convolutional codes map information to code bits not block wise, but sequentially convolve the sequence of information bits according to some rule. The code is defined by the circuit, which consists of different number of shift registers allowing building different codes in terms of complexity. Consider the following circuit (all registers are initially zero):