Speaker: Heng Zhao
Affiliation: UCLA Ph.D. Candidate
Abstract: In the recent decades, there have been dramatic changes in the ways people create and share information, hence a demand for wireless communication systems with over 100 Gb/s data rate has been envisioned. Promising techniques have been devised by researchers to fulfill such expectation, such as interference alignment (IA) and THz communication and many more. In theory, given ideal assumptions, they show extraordinary increase in the promised data rate relative to current wireless communication systems. Nevertheless, because of the hardware impairments, many practical challenges have to be addressed before bringing these advanced techniques from theory to practice. In this presentation, a selection of practical issues of interference alignment and THz communication will be discussed.
First, we consider the synchronization and channel estimation problem associated with enabling IA. Before achieving IA, in view of the uncoordinated interference, a concurrent synchronization and channel estimation mechanism with robustness against co-channel interference is needed. We start by deriving the maximum-likelihood expressions for optimal estimators. Then, it is realized that such estimators are infeasible in practice for requiring a computationally costly 2-D searching. To reduce the complexity, we propose a Zadoff-Chu sequence based pilot structure. By utilizing its unique properties, the 2-D searching problem can be converted into two 1-D searching problems. Experimental results verify the great performance of our proposed method in terms of both the residual frequency offset and the sum rate of an IA network. Second, we focus on the channel reciprocity in time division duplex (TDD) networks. The physical channel is reciprocal, but the channel considered by IA is not, because it also involves the radio frequency (RF) front-ends of the transceiver. The difference between the two individual circuits yields mismatch between the forward and backward channels. We provide the modeling of the non-reciprocity for the TDD MIMO channels, and propose a corresponding calibration method to minimize the mismatch. Experimental validation has been conducted and the results highlight the indispensability of the reciprocity calibration for approaching the network capacity promised by IA. Last, with a view to assessing THz communication system design requirements in practice, we measure the channels for both 350 GHz and 650 GHz carrier frequencies in a typical indoor environment. To obtain the spatial and temporal characteristics of the channel, the power angle profile (PAP) and the power delay profile (PDP) are measured using our proposed measurement systems and methods. Form the measurement results, we have observed important facts regarding the THz wave propagation, which significantly affect the requirements for designing an indoor THz communication system.
Biography: Heng Zhao received his B.S. degree in information engineering from Shanghai Jiao Tong University, Shanghai, China, in 2014 and the M.S. degree in Electrical Engineering from UCLA, Los Angeles, CA, USA, in 2015. He is currently pursuing the Ph.D. degree in Electrical and Computer Engineering as a Graduate Student Researcher at UCLA. His research interests include multiple-input multiple-output wireless network, interference alignment, channel modeling and THz communication.
Date(s) - Jul 12, 2019
10:00 am - 12:00 pm
E-IV Elliott Room #53-135
420 Westwood Plaza - 5th Flr., Los Angeles CA 90095