Convolutional code constructions resulting in maximal or near maximal free distance

We discuss an upper bound on the free distance for a rate k/n convolutional code with complexity /spl delta/. Using this bound we introduce the notion of a MDS convolutional code. We also give an algebraic way of constructing binary codes of rate 1/2 and large complexity. The obtained distances compare favorably to the distances found by computer searches and probabilistic methods.