Convolutional codes using nonlinear generators for rate one-fourth and memory order four

Performance of a convolutional code depends on the decoding algorithm and that code´s distance properties. Performance bounds suggest constructing codes with the largest possible free distance. Published tables provide the feed forward encoding equations that are linear generator polynomials over a binary Galois Field. This paper presents results for rate one-forth, memory order four, convolutional codes with at least one feed forward encoding equation that is nonlinear over binary Galois Field. Emphasis is given to nonlinear convolutional codes that achieve Heller-Griesmer upper bound on maximum free distance.