Tracking Performance of an Adaptive Transmit Beamspace Beamformer in Dynamic Miso Wireless Channels

This paper presents the performance of an Adaptive transmit beamspace beamformer (ATBBF) in a dynamic channel for Multiple input single output (MISO) per user wireless system. ATBBF consists of a of several transmit beamformers on the Transmit antenna array (TAA). The antenna weights of each Transmit beamformer (TB) are held constant while input to a TB is weighted by an adaptive beamspace weight. An algorithm that updates beamspace weights of all transmit beamformers of an ATBBF at the base station is described. It updates on the basis of a single feedback from the mobile. The feedback consists of one bit that indicates which of the two normalized perturbed beamspace weights that were time multiplexed onto the pilot signal from the base station delivered more power to the mobile. This algorithm is named Beamspace gradient sign feedback algorithm (BGSF) as its feedback mechanism is similar to that of Gradient sign feedback (GSF) algorithm that updates antenna weights of a TB. Performance metric of ATBBF is derived and analyzed in a dynamic channel undergoing Rayleigh fading. Performance comparison between an ATBBF with BGSF algorithm and a TB with GSF is made in terms of convergence and tracking of various slow and fast fading channels by simulations. Both full dimension (FD) and Reduced dimension (RD) ATBBF are considered. Comparisons show that FD ATBBF gives equivalent performance to that of TB and outperforms RD ATBBF.