Initial access in existing multiple-input multiple-output communication systems is a procedure which aims to achieve synchronization between the base station and the user and to estimate the dominant propagation directions. Traditionally, the directions are found through beam training, an exhaustive channel probing technique which results in a significant control overhead when large antenna arrays and narrow beams are used. In this project, we leverage recent advancements in circuit implementation of true-time-delay (TTD) arrays to accelerate the beam training procedure. A TTD array has controllable delay elements in all of its antenna branches, enabling frequency-dependent beam steering. With delays set up properly, the TTD array can probe all angular directions of the channel simultaneously using different frequencies and thus reduce the overhead. Our goal is to address the following challenges in this project:

1. We design TTD-based initial access procedures to minimize the beam training overhead. Additionally, we study the dependence of these TTD-based designs on wideband system parameters and practical TTD hardware constraints. The procedures are designed for network scenarios with a single base station, multiple coordinated base stations, and multiple non-coordinated base stations.
2. We develop and analyze digital signal processing algorithms for high accuracy estimation of useful signals and interferers, when as few as one wideband symbol is used for beam training. We study the impact of practical hardware impairments on the beam training performance of TTD arrays.

Staff

• Principal Investigator: Danijela Cabric
• Students: Han Yan, Veljko Boljanovic, Aditya Wadaskar

Selected Publications