It is well-known that the dispersive characteristics of multipath fading experienced by digital radio causes severe degradation in performance,especially over long paths.The mitigation of this degradation by using transversal and other equalizers has been attempted and it has been shown that performance can be improved by orders of magnitude.Since the error rate of digital radio is one of the primary measures of performance and since the computation of the error rate as a function of muitipath parameters,tap weight coefficients,filter characteristics,etc.is extremely complex,we use a simulation method to determine this performance.The average error rate is determined by using a Monte Carlo simulation for a set of channel parameters selected from a random distribution appropriate to the muitipath channel and equalization coefficients determined for this channel Since the estimation of the performance using simulation can be computationally ntensive,especially for low error rates and high order communication systems (such as 64-QAM),we use a quasi-analytic approach for both determination of equalizer taps and error rate.Equalizer taps are expressed directly in terms of the parameters of the channel and modulation characteristics of the signal.Error rate is estimated by using the moment method.Simulation techniques are used to evaluate the residual intersymbol interference after using the equalizers,and moments of this intersymboi interference are calculated using a very fast and accurate recursive method of computation.We thenuse the standard techniques of Gaussian quadrature to obtain the error rate of the system.Using the quasianalytical techniques resnlts in simulation that is fast,accurate and well-suited for the determination of performance of digital radio for line-of-sight transmission.
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