Announcements
ONLINE SEMINAR: Cracking the Pilot Contamination Nut, Dr. Emil Björnson Wed., Nov. 13, 2020, @15:00, Zoom
November 10, 2020
Within the department's seminar series of 2020-2021 Fall Term, Assoc. Prof. Dr. Emil Björnson from Linköping University, Sweden, will make a talk titled "Cracking the Pilot Contamination Nut".

Seminar Date : Friday, November 13, 2020
Seminar Time : 15:00 (Turkey local time)
Seminar Place : Zoom
Zoom code and password is on the picture below.

For your questions and comments:
Dr. Ýsmail Uyanýk, uyanik@ee.hacettepe.edu.tr
Dr. Barýþ Yüksekkaya, barisy@ee.hacettepe.edu.tr
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ABSTRACT
At the core of the 5G standard for cellular communications is Massive MIMO (multiple-input multiple-output). This refers to the use of antenna arrays with 64 or more radios, which are utilized to spatially multiplex many users at the same time and frequency. In this way, the scarce spectrum resources can be utilized much more efficiently than in previous generations. The Massive MIMO concept was viewed as science fiction just ten years ago, but now over a million base stations have been deployed.

When Thomas Marzetta introduced the Massive MIMO concept in a seminal article in 2010, he concluded that "the phenomenon of pilot contamination impose[s] fundamental limitations on what can be achieved with a noncooperative cellular multiuser MIMO system." More precisely, he showed that the channel capacity converges to a finite limit as the number of base station antennas goes to infinity. This limit was determined by the interference level in the channel estimation phase. Pilot contamination has existed since the beginning of cellular communications, but it is first with the advent of Massive MIMO that it has become a thing. There are hundreds of papers on the IEEEXplore that deals with the pilot contamination issue, trying to push the limit upwards and, particularly, achieve higher performance for a given number of antennas. For example, researchers have developed advanced semi-blind estimation schemes, as well as new resource allocation schemes.

But was pilot contamination a fundamental limitation to start with? In this talk, I will provide a fresh look at the problem and explain why it has been grossly exaggerated. You don't need a sledgehammer to crack the pilot contamination nut, but simple signal processing tools and realistic channel modeling will do. The lesson learned is that we must stop prioritizing analytical tractability when considering the fundamental limits.


Biography
Emil Björnson received the M.S. degree in engineering mathematics from Lund University, Sweden, in 2007, and the Ph.D. degree in telecommunications from the KTH Royal Institute of Technology, Sweden, in 2011. From 2012 to 2014, he held a joint post-doctoral position at the Alcatel-Lucent Chair on Flexible Radio, SUPELEC, France, and the KTH Royal Institute of Technology. He joined Linköping University, Sweden, in 2014, where he is currently an Associate Professor. In September 2020, he became a part-time Visiting Full Professor at the KTH Royal Institute of Technology.

He has authored the textbooks Optimal Resource Allocation in Coordinated Multi-Cell Systems (2013) and Massive MIMO Networks: Spectral, Energy, and Hardware Efficiency (2017). He is dedicated to reproducible research and has made a large amount of simulation code publicly available. He has performed MIMO research for over ten years, his papers have received more than 10000 citations, and he has filed more than twenty patent applications. He has received the 2014 Outstanding Young Researcher Award from IEEE ComSoc EMEA, the 2015 Ingvar Carlsson Award, the 2016 Best Ph.D. Award from EURASIP, the 2018 IEEE Marconi Prize Paper Award in Wireless Communications, the 2019 EURASIP Early Career Award, the 2019 IEEE Communications Society Fred W. Ellersick Prize, and the 2019 IEEE Signal Processing Magazine Best Column Award.