Low-cost hybrid analog-digital beamformer evaluation in spectrum sharing systems

Abstract

This paper evaluates different analog-digital beam-forming solutions for future spectrum sharing mm-wave scenarios. In contrast to sub-6 GHz multiantenna schemes where all-digital solutions provide an excellent performance-cost tradeoff, in the mm-wave bands where a very large number of antennas is required, all-digital designs cannot be deployed due to their cost and complexity. In order to solve this problem, sub-array solutions are conceived such that a reduced number of radiofrequency chains are simultaneously connected to different antennas through an analog beamforming network formed by phase shifters (i.e. with no amplitude control). Different connectivity solutions are evaluated; namely, full-connected, localized and interleaved considering that either the phase shifters have full resolution or only one control bit. As reported in the paper, while for the full resolution case the same performance is obtained for all connectivity schemes, in case the phase shifters have one control bit, differences show up. The numerical evaluation is done with an alternating feasible point pursuit successive convex approximation (FPP-SCA) optimization which yields to efficient solutions even for this non-convex optimization problem.