SUPPRESSION OF ADJACENT-CHANNEL, COCHANNEL, AND INTERSYMBOL INTERFERENCE BY EQUALIZERS AND LINEAR COMBINERS

We describe the ability of a linear equalizer/combiner or decision-fee dback equalizer to suppress all received adjacent-channel, intersymbol , and cochannel interference. The emphasis is on values among transmit ter bandwidth, receiver bandwidth, carrier spacing, and antenna divers ity which provide the best opportunities for interference suppression. Through analyses of the number of degrees of freedom and constraints in generalized zero-forcing equalizers, and partial comparisons to cal culations of equalizer minimum-mean-square performance, four results a re obtained. First, with one antenna and a linear equalizer, arbitrari ly large receiver bandwidths allow for marginal improvements in spectr al efficiency through decreased carrier spacing, because the carrier s pacing cannot be reduced to a value below the symbol rate without incu rring unsuppressible interference. Second, large receiver bandwidths a ssist multiple antennas in improving the spectral efficiency in that c arrier spacing values may go below the symbol rate, even in the presen ce of cochannel interference. Third, the use of equalizers and linear combiners, together with large receiver bandwidths, allows large trans mitter bandwidths to be used. Fourth, for cochannel interference and i ntersymbol interference, the number of interferers that may be suppres sible by a generalized zero-forcing linear equalizer/combiner increase s linearly with the product of the number of antennas and the truncate d integer ratio of the total bandwidth to the symbol rate.