CIRCUITS AND SYSTEMS DESIGN OF LARGE DELAY BANDWIDTH TRUE-TIME-DELAY-BASED ARRAYS FOR ULTRA-LOW-LATENCY COMMUNICATION AND SENSING

Qiuyan Xu

Beamtraining (BT), also known as beam probing, source localization, direction-finding or sounding, is the process of finding received signals' angle-of-arrival in communication systems. Beamtraning is critical for communications-on-the-move applications in communication and sensing systems, as it helps maximize beamforming gain for beamformer arrays.The sixth-generation wireless standard has attracted great interests requiring higher capacity and lower latency with usage of larger bandwidths. This poses challenges to beamtraining system design to achieve accurate incidence angle estimations with an ultra-low-latency for higher signal bandwidth. True-time-delay-based (TTD) arrays offers an attractive solution for wideband beamformers, which alleviates undesired effects such as loss in the signal-to-noise ratio due to wider bandwidths, aperture, or the number of antennas. This dissertation is proposed to demonstrate the TTD based array signal processing for communication and sensing systems in two aspects: beamtraining system over three-dimensional (3D) spaces, and accurate beamtraining system for wideband communications targeting a multi-Gigabit-per-second data rate. This dissertation will be focusing on the circuit and system designs, with a brief introduction to the relevant BT algorithm used in the works. In real world, scanning both azimuth and elevation is important for accurate localization over a 3D space. The first part in this dissertation presents the system analysis and demonstration of frequency dispersive 3D beam training algorithm using a 2×2 planar array integrated in a single chip suited for low-latency millimeter-wave wireless communications. System-level issues with high search latency in earlier time-division based BT algorithms and the need for multiple integrated circuits for 3D beamtraining are addressed with a large delay range TTD-based spatial signal processor together with the frequency-dependent rainbow beam training algorithm. Trade-offs between angular coverage efficiency over the 3D space and required hardware delay range are analyzed. Measured results on the 2×2 antenna array demonstrate the efficacy of the 3D beamtraining algorithm achieving 50% spherical coverage efficiency realized with the 3.75 nanoseconds IC delay range over 800 MHz bandwidth. In the second part of this dissertation, a proof-of-concept wideband signal processing system with accurate beamtraining is proposed. Hardware solutions with a multi-stage interleaving architecture are proposed to achieve a large delay over a gigahertz signal bandwidth with a multi-channel combination. This work presents a 2-channel 1.5 GHz bandwidth TTD-based signal combiner with maximum 10 nanoseconds delay range demonstrating fast chirp-based BT for the first time. It demonstrates the efficacy of large delay-bandwidth products in obtaining precise AoA estimations reducing errors in measurement from ±7.8° to ±1.1° when delays are increased by 15X. We introduce a algorithmic-hardware co-design approach enabled by an integrated multi-stage switched-capacitor-array architecture including digitally controllable clock generator for large TTD, and a passive-active ring-amplifier-based signal combiner to overcome the bandwidth trade-offs in conventional amplifier-based signal combiners. Further, a reduced gate-load bootstrapped switch and a negative-capacitance stabilized ring-amplifier are proposed to support large bandwidth operation. The proposed design opens up research opportunities for ultra-low-latency beam acquiring in communication systems such as Starlink.

CIRCUITS AND SYSTEMS DESIGN OF LARGE DELAY BANDWIDTH TRUE-TIME-DELAY-BASED ARRAYS FOR ULTRA-LOW-LATENCY COMMUNICATION AND SENSING

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