EE SEMINAR:Research activities in the areas of satellite com....
Speaker: Dr.Cüneyd Öztürk
Title: Research activities in the areas of satellite communications, the coexistence of passive and active systems, and the utilization of reconfigurable intelligent surfaces (RIS) for localization purposes.
Date/Time: January 31, 2024 17.00
Abstract: This talk will provide an overview of some of my recent research activities in the areas of satellite communications, the coexistence of passive and active systems, and the utilization of reconfigurable intelligent surfaces (RIS) for localization purposes.
First, I will discuss the downlink spectral efficiency per unit area of low earth orbit (LEO) constellations. We demonstrate that the spectral efficiency per unit area is fundamentally limited for satellite networks, in contrast to cellular networks. By utilizing the nearest neighbor association between the satellites and the ground stations, we suggest establishing a regular configuration to effectively approximate the highest spectral efficiency. Additionally, we note that by rearranging associations, it is possible to achieve additional enhancements by ensuring that nearby links do not direct to the same area.
Second, we propose implementing a beacon-assisted scheme to facilitate coexistence between passive sensing systems and the satellite network. We focus on the interference from the LEO satellites to a radio-telescope. We compare the beacon approach with two versions of radio-quiet zones: fixed quiet zones on the ground and in sky, and dynamic quiet zones that vary across satellites. The beacon-assisted approach utilizes channel reciprocity to account for short-term channel variations between the satellite and radio telescope. Numerical simulations demonstrate that the beacon approach enables more active satellite links relative to quiet zones for a given outage probability, i.e., the probability of excessive radio frequency interference at the radio telescope.
In the final part, I will present RIS-aided localization problems under hardware impairments: (i) When the UE is unaware of amplitude variations of the RIS elements and (ii) when there are failures in the RIS elements. To quantify the degradation in the localization performance, we use misspecified Cramer-Rao bound analysis. We illustrate that both the failing elements and the unawareness of the amplitude variations can lead to severe performance penalties. When the UE is unaware of the amplitude variations, to mitigate the performance loss, we propose to jointly estimate the UE location and the RIS amplitude model parameters. For the failure scenario, we develop two different diagnosis strategies to determine which elements are failing. In both scenarios, we greatly reduce the performance loss due to the hardware impairments.
Bio: Cuneyd Ozturk received the B.S and Ph.D. degrees from the Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, and the M.S. degree from the Department of Electrical and Computer Engineering, UCLA, Los Angeles, USA, in, 2016, 2022, and 2017, respectively. He is currently a post-doc with the Department of Electrical and Computer Engineering at Northwestern University, Evanston, IL, USA. His current research interests include satellite communication systems, coexistence between passive and active systems and RIS-aided localization.