High performance Viterbi decoder for OFDM systems

It is well-known that, for systems that deploy conventional convolutional codes, a Viterbi decoder is the best solution in maximum likelihood sense to decode an information sequence. Typically, a Viterbi decoder uses Euclidean or Hamming distance as a metric. The use of a conventional metric leads to a high performance for systems that are employed for frequency nonselective channels (e.g., additive white Gaussian noise (AWGN), or Rayleigh fading). However, if the system is based on orthogonal frequency division multiplexing (OFDM) and the channel has frequency selective multipath fading, then the performance can be further improved. In this paper we propose a simple modification to the conventional Viterbi metric (Euclidean distance) that improves the performance substantially if the channel is frequency selective. Simulation results on wireless local area network (WLAN) standard IEEE 802.11a show that the performance is improved about 10 dB when the proposed metric is used. Furthermore, the proposed metric gives the same high performance as the conventional Viterbi metric if the channel is AWGN or flat fading.