Improved Intersymbol Interference Error Bounds in Digital Systems

In many cases the transmission efficiency of a digital system is largely limited by intersymbol interference rather than by additive noise. Intersymbol interference may result from imperfect design of the filters, distortion in the transmission channel, nonideal sampling instant, or nonideal demodulating carrier phase. In analyzing such a digital data system, it is important to determine the system error rate due to intersymbol interference and additive noise. 2585 2586 T H E BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1971 Various methods 1-7 to evaluate the error rate have been proposed. They provide either a loose upper bound of the error rate or the error rate of a channel with truncated impulse response. In this paper we present a simple method to evaluate both an upper and a lower bound of the error rate without invoking the finite pulsetrain approximation. Furthermore, it is shown that for a system with a normalized peak distortion less than unity, the upper and lower bounds can be made arbitrarily close thus obtaining an accurate estimate of the error rate of the system. This method can be applied to 2M-ary AM and coherent phase-shift-keyed systems. T h e d a t a s y s t e m m o d e l will b e described briefly i n Section I I . V a r i o u s