New short constraint length convolutional code constructions for selected rational rates (Corresp.)

New short constraint length convolutional code constructions are tabulated for rates
R=(n-k)/n, k=1,2, \cdots ,n-1
with
n=2, 3,\cdots ,8
, and for constraint lengths
K=3,4, \cdots,8
. These codes have been determined by iterative search based upon a criterion of optimizing the free distance profile. Specifically, these codes maximize the free distance
d_{f}
while minimizing the number of adversaries in the distance, or weight, spectrum. In several instances we demonstrate the superiority of these codes over previously published code constructions at the same rate and constraint length. These codes are expected to have a number of applications, including combined source-channel coding schemes as well as coding for burst or impulsive noise channels.