A Modified Viterbi Equalization Algorithm for Mitigating Timing Errors in Optical Turbulence Channels

In high-speed optical wireless communication (OWC) systems, timing errors can blur the edges of the received symbols, defined by the deviation of a signal's timing event from its intended occurrence. The timing errors introduce the inter-symbol interference (ISI) to the neighboring symbols. In order to mitigate the degradation, a maximum likelihood (ML) based Timing Error Viterbi Equalization (TEVE) algorithm is proposed, in which the probability density functions (PDF) of the channel conditions and the timing errors are priori information. The mathematical form of each branch metric (BM) is deduced by those statistics in different situations of neighboring signs of timing errors. The summations of BMs form the cumulative metrics (CM). By adopting the add-compare-select iterations, we are able to detect symbols with the largest CMs. The theoretical closed-form average bit error rates (BER) are also deduced and compared in the cases whether the TEVE algorithm is utilized. Experimental results indicate that our proposed method can reduce timing errors' impairment significantly with an acceptable complexity.