On the weight distribution of terminated convolutional codes

In this correspondence, the low-weight terms of the weight distribution of the block code obtained by terminating a convolutional code after x informa tion blocks are expressed as a function of x. It is shown that this functio n is linear in x for codes with noncatastrophic encoders, but quadratic in x for codes with catastrophic encoders, These results are useful to explain the poor performance of convolutional codes with a catastrophic encoder at low-to-medium signal-to-noise ratios.