Tracking with all-analog adaptive antenna arrays

Expanding capacity requirements of wireless networks have led to spectrum scarcity. Most people will, at one point, have experienced a poor Wi-Fi connection because of too many active 2.4 GHz devices in the vicinity. Millimeter waves (especially at 60 GHz) are a promising candidate to solve this problem. In this thesis, a scenario is considered where rooms inside a building are equipped with a mm-wave radio access point connected to a fiber optical backbone. As 60 GHz does not penetrate walls, frequencies can be reused in neighboring rooms. The use of 60 GHz carriers requires antennas that feature high gain and directionality. An adaptive antenna array (i.e., beamformer) suits these needs well. Moreover, when implemented entirely in the analog (optical) domain, such a beamformer can be cost and energy efficient. A challenge for all-analog adaptive beamforming is that the combined beamformer output will be the only source for signal processing. To estimate a signal’s angle of incidence, and track the position of the corresponding (mobile) wireless device, adaptive arrays normally operate on the basis of cross-correlating individually sampled antenna signals. With an all-analog beamformer this is not possible. This thesis presents a tracking algorithm that uses asymmetrically shaped beampatterns to overcome this limitation. The thesis also explains how these unconventionally shaped beampatterns can be synthesized. Tracking and synthesis are first investigated in the context of (equispaced) linear arrays. The necessary beampatterns, one flat-topped and one ramp-shaped, are synthesized using analytical methods that ensure smooth shapes. A tracking mechanism is developed in which the two pattern shapes are alternated. The angle if found by considering the power difference between the two beampatterns. Finally, as linear arrays only provide directionality in one dimension, the entire shaped-pattern tracking approach is extended to planar antenna arrays. Different array geometries are considered, from which hexagonally shaped grid structures appear to be the most suitable. A procedure based on the principle of collapsed distributions is developed to synthesize appropriate beampatterns for this type of array. Tracking in the full azimuth-elevation hemisphere is achieved by utilizing the technique for linear arrays in two orthogonal directions.