From Aug. 2010 to Feb. 2011, he was a Visiting Scholar at Purdue University, West Lafayette, IN. From Mar. 2012 to Feb. 2013, he was a Postdoctoral Researcher at the Information and Telecommunication Laboratory (ITL), Yonsei University. Since Mar. 2013, he has been with the Korea Railroad Research Institute (KRRI), where he is currently a Senior Researcher. His research interests lie in femtocell networks, multiple antenna systems, interference management techniques, device-to-device communication, cognitive radio networks, energy harvesting wireless communication networks, train position detection, radio frequency identification (RFID), and Long Term Evolution-Railway (LTE-R).