Suppression of adjacent channel interference using feedback equalizers

Abstract

Abstract Abstract An analytical technique for evaluating the performance of nonlinearly equalized M-ary quadrature amplitude modulation (QAM) systems in the presence of interfering channels is developed. The equalizer is allowed to have either synchronously- or fractionally-spaced taps for its feedforward filter (FFF). Both a decision feedback equalizer (DFE) and a decision-aided intersymbol-inierference canceller (DIC are considered. The tap gains are evaluated in the minimum mean-square-error sense. Asymptotic analysis is also provided for the case of a synchronously-spaced FFF. Numerical results indicate that by employing a DIC equalizer (1/2-fractionally-spaced FFF), with sufficient feedforward and feedback taps, the transmission efficiency of a 256-ary QAM can be increased to 10 bits−1 Hz−1 in the presence of an interfering channel with a normalized channel spacing of 0-8 at the expense of 1-85 dB additional increase in Eb/No given a bit error-rale of I0+4