Channel shortening and Viterbi algorithm based equalization for high data rate baseband communication over a frequency-selective channel
Résumé
Considering a high data rate baseband communication serial link, we introduce three different receivers based on the Viterbi algorithm. The first one, named Falconer-MLSE, combines a channel-shortening linear filter proposed by Falconer and Magee and the Maximum Likelihood Sequence Estimator (MLSE) based on the Viterbi algorithm. The receiver’s complexity is kept low but it remains very sensitive to thermal noise power. The second one, named DFE-MLSE, combines a partial Decision Feedback Equalizer (DFE) and the MLSE. It is supposed to amplify the thermal noise less than the linear filter but it is subject to error propagation. Also, the space occupied by the feedback loop on chip has to be tightly controlled, limiting the number of taps the linear filter in the feedback loop has. The third and last receiver introduced, named MLDFE, combines DFE and MLSE to limit the error propagation phenomenon. It is more complex than the DFE-MLSE but performs better in general. We then compare the performance of these receivers for a typical SerDes channel for optimal parameters before taking into account the requisites set by the IEEE standard working group and discriminating these receivers. We conclude that the best receivers under the standard constraints are the Falconer-MLSE receiver for a 4th order Pulse Amplitude Modulation and the Falconer-DFE-MLSE, combination of a Falconer filter, a DFE and a Viterbi algorithm, for a 8th order Pulse Amplitude Modulation and higher.
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