Low-Complexity Viterbi Metrics applied to Bit-Interleaved COFDM

In this paper, we address the problem of deriving bit-wise metrics for the Viterbi decoding of a bitinterleaved coded modulation. We put an emphasis on Gray-mapped high order QAM constellations, and illustrate the performance in the context of the IEEE 802.11a/g wireless OFDM system. Several bit metric formulas are compared, enabling a performance versus complexity trade-off. It is shown that near-optimum performance can be obtained with reasonable complexity, while a further complexity reduction can be achieved by recursively computing bit metrics for a given QAM symbol, at the expense of about 1dB PER performance loss.