Prediction of mobile radio delay spread from frequency correlations

A simple method is studied for estimating the delay spread needed for understanding the transmission quality of land mobile communication by means of a narrow frequency band. There exists a certain relationship between the delay spread and the receiving level correlations of multiple waves. There is a method for estimating the delay spread by measuring the receiving level correlation of multiple waves in a relatively narrow frequency band based on the forementioned relationship. However, since the previous method is based on the relationship between the delay spread and the receiving level in the case where the delay profile is of an exponential function, there is an error in the delay spread estimated if a profile is other than the one with an exponential function. In this paper, this error is obtained first quantitatively. Next, a new estimation method which can reduce the error is proposed. Specifically, a profile selecting-type estimation method is proposed in which a delay profile function considered optimum is selected from the measured receiving level correlation function and the delay spread function is found based on such a delay profile function. In addition to carrying out a computer simulation of the error evaluation of the proposed method, the estimation accuracy is confirmed from the measured data of the delay spread and the receiving level in an actual propagation path. As a result, the estimation error of the average delay spread in a 50-m section is reduced to 40 percent in the proposed method which is an improvement of about 10 percent over the previous method.