Adaptive algorithms for spatial adaptive interference rejection

In the mobile communications field, smart technologies are not only being applied at the antenna level, but also at the receiver (for direction of arrival estimation, detection. diversity combining and equalization). The ultimate benefit of these techniques is to increase cellular capacity and range. Furthermore, with the use of CDMA, where multiaccess interference power is a fundamental capacity limiting factor, adaptive beamforming is revealed to be another complementary means for signal-to-interference-plus-noise ratio (SINR) optimization. The problem in this case deals with the formation of a lobe structure that results from the variation of an element-space processing weight vector. The beamforming in such adaptive arrays is controlled by an adaptive algorithm minimizing a particular cost function, ideally directing beams toward the signal of interest and nulls in the direction of interference. In this paper we examine the characteristics of two such algorithms, least mean square (LMS) and sampled matrix inversion (SMI) and discuss a modification in the SMI algorithm to handle some situations.