Error probability of a multilevel digital system with intersymbol interference and Gaussian noise

In a previous paper a series expansion method for calculating the error probability of a binary digital AM system in the presence of intersymbol interference and additive gaussian noise was derived.1 In this paper those results are extended to the multilevel case. In the examples calculated for a four-level system, this method is 104 times faster than the exhaustive method and is 102 times more accurate than the Chernoff bound. The actual computation time with an 11-sample approximation to the real system impulse response is only 1.3 seconds with the GE Mark II time-sharing system.