Convolutional Codes Using Nonlinear Generators for Rate One-half 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 a new method for testing free distance of generators based on length k bounded synchronization codes. This paper also presents results for rate one-half, memory order four, convolutional codes with at least one feed forward encoding equation that is nonlinear over a binary Galois field.