Most of my research interests have to do with high-frequency communication, which is potentially one of the most disruptive communication technologies. The followings represent my personal view on high-frequency communications:
Near-Field MIMO
As frequency goes up, the time-honored far-field assumption ceases to hold and the wavefront curvature becomes visible. The most interesting property of the near-field propagation is that the degrees of freedom (DOF) is not unity for line-of-sight connection. Our research objective is to identify the relevant problems and resolve them.
H. Do, N. Lee, and A. Lozano, “Parabolic wavefront model for line-of-sight MIMO channels”, IEEE Trans. Wireless Commun., 2023.
H. Do, N. Lee, and A. Lozano, “Line-of-sight MIMO via intelligent reflecting surface”, IEEE Trans. Wireless Commun., 2023.
H. Do, S. Cho, J. Park, H.-J. Song, N. Lee, and A. Lozano, “Terahertz line-of-sight MIMO communication: Theory and practical challenges”, IEEE Commun. Mag., vol. 59, no. 3, pp. 104–109, 2021.
H. Do, N. Lee, and A. Lozano, “Reconfigurable ULAs for line-of-sight MIMO transmission”, IEEE Trans. Wireless Commun., vol. 20, no. 5, pp. 2933–2947, 2020.
Wideband Communications
The whole point of going up in frequency is to utilize more bandwidth. At high frequencies, as the isotropic pathloss becomes unprecedently large, a lot of number of antennas are required to countervail it. Traditional analog array can do the job for narrowband systems, but it cannot for wideband systems; as the bandwidth broadens, antenna gains at frequencies away from the central one where the array is optimized is reduced. This phenomenon, termed beam squint, could make the wideband operation obsolete. To resolve this problem, more sophiscated array architectures should be used. Our research objective is to devise such architectures which can mitigate beam squint.
H. Do, N. Lee, R. W. Heath Jr., and A. Lozano, "Hybrid arrays: How many RF chains are required to prevent beam squint?," IEEE Trans. Wireless Commun., 2024.
H. Do, N. Lee, R. W. Heath Jr., and A. Lozano, “Lean beam squint compensation”, in preparation.
Smart Surfaces
Poor propagation characteristic of the high frequencies necessitates network densification. Recently, smart surfaces are emerging as a cost-effective solution. Our research objective is to solve fundamental problems on smart surface assisted communication systems.
H. Do and N. Lee, "Finding optimal configuration of active RIS in linear time", arXiv preprint arXiv:2308.04058, 2023.
H. Do, N. Lee, and A. Lozano, “Line-of-sight MIMO via intelligent reflecting surface”, IEEE Trans. Wireless Commun., 2023.
Revisiting Phased Array Theory
Phased array theory developed in the last century is an oldie but a goodie for analysis of LOS communications. To avoid reinventing the wheel, I think it is a good time to look back.