The discrete complex Kalman filter is considered as an equalizer for quadrature phase shift keyed (QPSK) systems in the presence of additive noise and intersymbol interference (ISI). For a known linear time-invariant channel with finite duration impulse response, the finite n-dimension complex Kalman filter equalizer is able to reduce the degradation caused by ISI. When the channel is unknown, an adaptive Kalman equalizer is used in which the channel complex tap gains are estimated by decision feedback. A two component multipath channel QPSK system is used as an example. Using the Chernoff upper bound to calculate the error probabilities, the computer simulation shows that both the Kalman filter equalizer and adaptive equalizer have a better performance than the integrate-and-dump correlator with no equalizer --Abstract, page ii
