A new adaptive equalizer with channel estimator for mobile radiocommunication

摘要

For unknown mobile radio channels with severe intersymbolninterference (ISI), a maximum likelihood sequence estimator, such as andecision feedback equalizer (DFE) having both feedforward and feedbacknfilters, needs to handle both precursors and postcursors. Consequently,nsuch an equalizer is too complex to be practical. This paper presents annew reduced-state, soft decision feedback Viterbi equalizer (RSSDFVE)nwith a channel estimator and predictor. The RSSDFVE uses maximumnlikelihood sequence estimation (MLSE) to handle the precursors andntruncates the overall postcursors with the soft decision of the MLSE tonreduce the implementation complexity. A multiray fading channel modelnwith a Doppler frequency shift is used in the simulation. For fastnconvergence, a channel estimator with fast start-up is proposed. Thenchannel estimator obtains the sampled channel impulse response (CIR)nfrom the training sequence and updates the RSSDFVE during the bursts innorder to track changes of the fading channel. Simulation results shownthe RSSDFVE has nearly the same performance as the MLSE forntime-invariant multipath fading channels and better performance than thenDFE for time-variant multipath fading channels with less implementationncomplexity than the MLSE. The fast start-up (FS) channel estimator givesnfaster convergence than a Kalman channel estimator. The proposed RSSDFVEnretains the MLSE structure to obtain good performance and only uses softndecisions to subtract the postcursor interference. It provides the bestntradeoff between complexity and performance of any Viterbi equalizers