Decoding of Z_2S Linear Generalized Kerdock Codes

Many families of binary nonlinear codes (e.g., Kerdock, Goethals, Delsarte-Goethals, Preparata) can be very simply constructed from linear codes over the Z4 ring (ring of integers modulo 4), by applying the Gray map to the quaternary symbols. Generalized Kerdock codes represent an extension of classical Kerdock codes to the Z2S ring. In this paper, we develop two novel soft-input decoders, designed to exploit the unique structure of these codes. We introduce a novel soft-input ML decoding algorithm and a soft-input soft-output MAP decoding algorithm of generalized Kerdock codes, with a complexity of O( NS log2 N), where N is the length of the Z2S code, that is, the number of Z2S symbols in a codeword. Simulations show that our novel decoders outperform the classical lifting decoder in terms of error rate by some 5 dB.