Collaborative Research: CNS core: Medium: True-Time-Delay based MIMO System and Testbed for Low-Latency Wideband Beam and Interference Management in Millimeter Wave Networks

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Given the shortage of spectrum below 6GHz, millimeter wave (mmW) frequencies have played an important role in the emerging 5G networks and this trend is expected to continue in the next generations. Due to unfavorable propagation conditions and attenuation at high frequencies, mmW networks require the densification of base stations and radios equipped with a large number of antennas to compensate path loss via directional gain using narrow beams. The cost and power consumption of radios with antenna arrays present a significant challenge, and their architecture is of fundamental importance and influence on the entire networking stack. State-of-the-art approaches based on phased antenna array architecture are faced with several fundamental problems when radio bandwidth and the number of antennas increases including prohibitive latency in initial connectivity and link management, distortion in the directionality of the beams, reduced beamforming gain, and ability to suppress the interference in dense deployments. This project aims to develop and demonstrate a novel adaptive true-time-delay (TTD) based array for wideband mmW networks and overcome challenges of phased antenna arrays. The approach involves co-design and optimization of tunable radio frequency (RF) circuits, antenna array system, signal processing, and network protocols for low latency access, wideband beamforming gain, and interference management. The research work will pursue four key thrusts: Thrust 1 will develop TTD array-based fast beam training and spatial interference detection and estimation for mmW networks with large modulated bandwidth. The objective is to reduce the overhead in initial access due to beam training by exploiting frequency-dependent antenna weight vectors in TTD arrays through signal processing and develop a low latency protocol design for simultaneous beam training and interference estimation in dense mmW networks. Thrust 2 will focus on the data communication design using TTD arrays to facilitate multiple-input multiple-output (MIMO) multiplexing and suppress interference from co-channel base stations and users. The main challenge is to achieve high beamforming gain over a wide modulated bandwidth together with effective nulling of wideband interferers. Thrust 3 will develop an experimental testbed for the evaluation of signal processing algorithms and protocols from Thrusts 1 and 2. It will involve the integration of widely reconfigurable delay compensating circuits and custom mmW front-end at 28GHz into a 16-element TTD antenna array. Thrust 4 will experimentally validate TTD array-based beam training, squint-free wideband beamforming and interference nulling, and wideband MIMO communications using the testbed developed in Thrust 3.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.