Rate 1/2 binary convolutional codes are analyzed and a lower bound on free distance in terms of the minimum distances of two associated cyclic codes ìs derived. Next, the complexity of computing the free distance is discussed and a counterexample to a conjecture on the relationship of row distance to free distance for systematic codes Ìs presented. Finally, an improved Gilbert bound for definite decoding is derived.
Rudolph, Luther D. and Miczo, Alexander, "SOME RESULTS ON THE DISTANCE PROPERTIES OF CONVOLUTIONAL CODES" (1970). Electrical Engineering and Computer Science Technical Reports. Paper 12.