True-Time-Delay Arrays for Fast Beam Training in Wideband Millimeter-Wave Systems

Abstract

The best beam steering directions are estimated through beam training, which is one of the most important and challenging tasks in millimeter-wave and sub-terahertz communications. Novel array architectures and signal processing techniques are required to avoid prohibitive beam training overhead associated with large antenna arrays and narrow beams. In this work, we leverage recent developments in true-time-delay (TTD) arrays with large delay-bandwidth products to accelerate beam training using frequency-dependent probing beams. We propose and study two TTD architecture candidates, including analog and hybrid analog-digital arrays, that can facilitate beam training with only one wideband pilot. We also propose a suitable algorithm that requires a single pilot to achieve high-accuracy estimation of angle of arrival. The proposed array architectures are compared in terms of beam training requirements and performance, robustness to practical hardware impairments, and power consumption. The findings suggest that the analog and hybrid TTD arrays achieve a sub-degree beam alignment precision with 66% and 25% lower power consumption than a fully digital array, respectively. Our results yield important design trade-offs among the basic system parameters, power consumption, and accuracy of angle of arrival estimation in fast TTD beam training. Index Terms-True-time-delay array, array architecture, beam training, millimeter-wave communication, wideband systems I. INTRODUCTIONA BUNDANT spectrum at millimeter-wave (mmW) frequencies is seen as the key resource for providing high data rates in the fifth generation of cellular systems [1]. However, the use of mmW communication bands comes at the cost of less favorable propagation conditions [2]. Both the base station (BS) and user equipment (UE) are required to use large antenna arrays to achieve high beamforming (BF) gain and compensate for severe propagation loss. Beam pointing directions are estimated through beam training, a procedure that identifies the angle of arrival (AoA) and angle

mmFlexible: Flexible Directional Frequency Multiplexing for Multi-user mmWave Networks

“…Past work on TTD array [1]- [3], [6] have shown that this architecture creates a prism-type response by radiating all the frequencies in all the directions in a linear fashion (Fig. 3(c)) by using a fixed set of delays at each antenna given by τ n = n B , for bandwidth B.…”