Method to improve Gaussian approximation accuracy for calculation of spread-spectrum multiple-access error probabilities

Many papers have described the calculation of error probabilities for a direct-sequence/spread-spectrum multiple-access system. The exact calculation is computationally difficult, so emphasis has been placed on the approximation and the bounds. A simple and attractive approximation is the Gaussian approximation in which the signal/noise ratio is used. Unfortunately, this approximation is not accurate enough in some cases. The authors present a method for improving the Gaussian approximation accuracy. The authors use a number of moments of multiple-access interference (MAI) to make the approximation more accurate.