Adaptive antenna array utilizing the conjugate gradient method for multipath mobile communication

Abstract

This paper addresses a multipath fading problem occurring in mobile communications. At each antenna element, there arrives a number of clusters of signals each of which consists of a large number of signal components with their own arrival angles. The clusters are distinguished from each other by distinct group delays. This paper suggests a new efficient method of eliminating the multipath fading that can be used regardless of modulation technique. Since the problem is formulated independently from the arrival angle of each signal component, the array can resolve the multipath effects with a reasonable number of antenna elements even when there exist a large number of signal components. The angles of arrival may be distributed very closely to each other. In fact, the array designed in this paper can reduce the multipath effects once the number of antenna elements is equal to the number of distinct clusters. The new method utilizes a modified conjugate gradient method (CGM) for iteratively computing the optimal weights of the antenna elements. To generate the excitation vector which is required by the CGM, it is assumed that a set of known symbols are sent at each frame. This paper includes many practical examples of various PSKs and 16QAM, and the array performances are shown in many different signal environments in terms of bit-error-rate (BER) performance. From the extensive analysis and various computer simulations, we conclude that the CGM shown in this paper is suitable to adapt for an antenna array in an efficient way for mobile communication.