Title: Quaternion-Valued Antenna Array Signal Processing and Its Applications

Speaker: Prof. Wei Liu

Affiliation: Department of Electrical and Electronic Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong

Abstract: In this tutorial, an introduction to quaternion and quaternion-valued signal processing is first presented, with a particular focus on the quaternion-valued gradient operation in the context of quaternion-valued adaptive signal processing. Its direct application to the equalization problem for quaternion-valued wireless communication systems is then studied, with two schemes provided: one is the reference signal based quaternion-valued least mean square (QLMS) algorithm and the other one is the quaternion-valued constant modulus algorithm (QCMA); the quaternion-valued Wiener solution for possible block-based calculation is also derived. Furthermore, we study a specific adaptive beamforming problem where the direction of the quaternion-valued impinging signal of interest is known and develop an efficient beamforming algorithm to receive the four components of the signal simultaneously while suppressing interfering signals from other directions; such a scenario arises also when the array system is operating in the scanning mode and it corresponds to the traditional Capon beamformer or the more general linearly constrained distortionless response beamformer.

Biography: 

Wei Liu received his BSc and LLB degrees from Peking University, China, MPhil from the Department of Electrical and Electronic Engineering, University of Hong Kong, and PhD from the School of Electronics and Computer Science, University of Southampton, UK. After that he worked as a postdoc first at Southampton and later at Imperial College London. From 2005 to 2023, he was a Lecturer/Senior Lecturer at the Department of Electronic and Electrical Engineering, University of Sheffield, UK and from 2023 to 2024, a Reader at the School of Electronic Engineering and Computer Science, Queen Mary University of London. Since 2024, he has been a Professor at the Department of Electrical and Electronic Engineering, Hong Kong Polytechnic University. He has published 440+ journal and conference papers, six book chapters, and two research monographs titled ``Wideband Beamforming: Concepts and Techniques'' (Wiley, 2010) and ``Low-Cost Smart Antennas'' (Wiley, 2019), respectively. His research interests cover a wide range of topics in signal processing, with a focus on sensor array signal processing and its various applications, such as robotics and autonomous systems, human computer interface, radar, sonar, and wireless communications.

He is a member of the Applied Signal Processing Systems Technical Committee (2023-2025) of the IEEE Signal Processing Society (SPS), the Digital Signal Processing Technical Committee of the IEEE Circuits and Systems Society (Chair for 2022-2024), and the IEEE SPS Education Board (2024-2026, Chair of its Educational Conference Program Committee), and a former member of the Sensor Array and Multichannel Signal Processing Technical Committee of the IEEE SPS (Chair for 2021-2022), the IEEE SPS Technical Directions Board (2021-2022), and the IEEE SPS Conference Board and its Executive Subcommittee (2022-2023). He also acted as an associate editor for IEEE Trans. on Signal Processing, IEEE Access, and Journal of the Franklin Institute, and currently he is an associate editor for IEEE Trans. on Circuits and Systems I, IEEE Antennas and Wireless Propagation Letters, and an Executive Associate Editor-in-Chief of the Frontiers of Information Technology and Electronic Engineering. He is an IEEE Distinguished Lecturer for the Aerospace and Electronic Systems Society (2023-2024).