Beam Pattern Evolution of an Adaptive Transmit Beamspace Beamformer

Abstract

This paper presents evolution of beam pattern of an Adaptive transmit beamspace beamformer(ATBBF) at the base station of a 3rd generation code division multiple access (3G-CDMA) system for Multiple input single output (MISO) per user wireless channel, bridging the respective interest of antenna and signal processing groups. ATBBF establishes a set of orthogonal beams in space, each of which is weighted by an adaptive beamspace weight. The overall beam pattern is determined by the superposition of beamspace weighted orthogonal beams. The ATBBF algorithm perturbs beamspace weights at the base station to generate even and odd beamspace weights which are time multiplexed with the pilot signal. The mobile feedbacks a single bit to indicate which of the two beamspace weights delivered more power. This weight becomes the new beamspace weight. The beamspace weights and the beam pattern continue to be updated, finally converging to the optimum. Simulations in single, double and triple multipath wireless channels demonstrate the unique evolution of ATBBF's beam pattern in relation to the convergence of its beamspace weights. The dependence of magnitude and convergence time of a beamspace weight upon the multipath wireless channel is clarified to understand this evolution.