Some optimal partial-unit-memory codes (Corresp.)

A new class of time-invariant binary convolutional codes is defined, called partial-unit-memory codes. These codes are optimal in the sense of having maximum free distance for given values of
R, k
(the number of encoder inputs), and
\mu
(the number of encoder memory cells). New optimal codes are given for rates
R=l/4, 1/3, 1/2, \and 2/3
with
\mu \leq 4 \and k \leq \mu + \3
, whenever such a code is better than previously known An infinite class of optimal partial-unit-memory codes is also constructed based on equidistant block codes.