High-performance iterative Viterbi algorithm for conventional serial concatenated codes

The Viterbi algorithm (1967) and conventional serial concatenated codes (CSCC) have been widely applied in digital communication systems over the last 30 years. We show that the Shannon capacity of additive white Gaussian noise (AWGN) channels can be approached by CSCCs and the iterative VA (IVA). We firstly study the algebraic properties of CSCCs. We then present the IVA to decode these codes. We also analyze the performance of the IVA and conclude that a better performance can be achieved if we replace the powerful block codes by some simple parity codes. One of the key results in this paper shows that by using a proper design for the decoding method, codes with small loops can be very efficiently decoded using a min-sum type algorithm. The numerical results show that the IVA can closely approach the Shannon sphere-packing lower bound and the Shannon limit. For block sizes ranging from 56 information bits to 11970 information bits, the IVA can perform to within about 1 dB of the Shannon sphere-packing lower bound at a block error rate of 10/sup -4/. We show that the IVA has a very low complexity and can be applied to many current standard systems, for example, the Qualcomm code-division multiple-access (CDMA) system and the NASA concatenated system, with very little modification or, for some cases, without any modification.