Effects of multipath fading on the performance of the CMA adaptive antenna

Abstract

Adaptive antennas can suppress the interference signals under multipath fading environments. Among various algorithms of adaptive antennas, the CMA (Constant Modulus Algorithm) is one of the effective methods to cope with multipath fading. When the CMA adaptive antenna is used for land mobile communication systems, it is necessary to understand the effects of propagation phenomena on the suppression performance of the CMA adaptive antenna because the propagation environment changes every moment in land mobile communication systems. This paper discusses the effects of Doppler shift, time delay and arrival angle on the suppression performance by means of computer simulation assuming one desired and one interference signals as input signals to the antenna. and presents the relation between the suppression performance of the CMA adaptive antenna and a step size which corresponds to the feedback gain. As conclusions, the Doppler shift does not give any effect on the suppression performance and the suppression performance deteriorates when time delay difference between the desired and interference signals is small in comparison with symbol duration or when the difference of arrival angle between the desired and interference signals is small, and the step size is desired to be as small as practical when time delay of the interference signal is small.