Fast metric calculation for Viterbi decoder implementation

Abstract

A method and apparatus are used for determining a metric in a decoding algorithm, such as a Viterbi algorithm, using an n-bit processing module, on the basis of plural m-bit soft input words, wherein n≧2×m. The technique comprises: receiving plural m-bit soft input words; assembling at least two of the plural m-bit soft input words into a single n-bit composite soft input word; computing the respective distances between the at least two soft input words in the composite soft input word and expected codeword values to produce a composite distance word; summing the respective distances together to produce the metric; and extracting the metric. The n-bit processing module may comprise a 16-bit processing module employing 16-bit words, and the m-bit soft input words may each comprise a 4-bit word. Processing the plural soft input words en bloc increases the speed and information transfer rate of the decoder, and reduces the memory requirements of the decoder.

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