Fully digitalized transversal equalizer for digital radio systems

Abstract

In digital radio communication employing multilevel modulation, the waveform equalizer is needed to eliminate the waveform distortion generated in the transmission channel or in other components. This paper aims at a highly accurate automatic equalizer which is applicable to the ultramultilevel modulation, such as 256 QAM, and discusses the fully digital realization of the equalizer which has been constructed by analog circuits. First, the transversal equalizer to be used in 256 QAM is considered, and the relation between the number of taps and the equalizer performance is described theoretically. Then the construction of the fully digital waveform equalizer is proposed based on the digital signal processing techniques. The decision range expanded (DRE) method is proposed, aiming at the maximum utilization of the equalization performance of the waveform equalizer. Finally, the transversal automatic equalizer is implemented on LSI. As a result of experiment with the clock rate of 12.5 Mbaud and 256 QAM signal, a satisfactory result agreeing with the theoretical investigation is obtained. Especially, it is demonstrated that the DRE method is very useful in constructing the digital waveform equalizer. Thus, a highperformance transversal automatic equalizer is realized, which is applicable to the ultramultilevel modulation system.