BER Degradations Caused by Switching in Digital Mobile Radio Systems Using Base Station Diversity

Abstract

This paper presents a study of the Bit Error Rate (BER) degradation resulting from base station switching in digital mobile radio systems using base station diversity to combat shadow fading. The degradation is caused by the discontinuities of the signal received by the mobile unit when transmission is switched from one base station to another. To evaluate this effect, a simple statistical model has been devised for the spatial variations of shadow fading. It consists of a one-parameter spatial autocorrelation function for the (Gaussian) decibel value of the fading loss, which can be easily simulated. The single parameter is a correlation length, which can be varied to emulate different fading conditions in the urban environment. The shape of the autocorrelation function can similarly be varied. This model was used to evaluate the BER degradation of mobile radio systems using Phase-Shift-Keying (PSK) modulation. The results show that, in worst-case conditions, the BER is insignificantly affected by switching for BER values above 9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> for two-PSK and 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> for four-PSK. Adding a threshold into the switching test can reduce or increase the switching degradation, depending on the threshold value.