He held various research and teaching positions at TUT 1976-88. In the years 1988 - 1991 he was working as a Design Manager in the area of video signal processing, especially for HDTV, at Nokia Research Centre and Nokia Consumer Electronics. He has been a professor of communications engineering at TUT since 1992. He served as the Department Head during 1992-2010. He has been the Director of the Tampere Doctoral Programme on Information Science and Engineering (TISE) since 2000. During the years he has made research visits to Linköping University, Sweden (1982-84), University of California Santa Barbara, USA (1985 and 1986), TU Dresden, Germany (2010) and Santago State University, USA (2011).

Dr. Renfors is a Fellow of IEEE and recipient of the 1987 IEEE Circuits and Systems Society’s Guillemin-Cauer (best-paper) Award (together with Tapio Saramäki). He has authored over 50 papers in refereed journals and over 300 papers in conferences with review practice, and two patents. He has over 560 citations by other scholars in the ISI Web of Science database. He has supervised 12 doctoral dissertations and about 100 M.Sc. theses. He has served as opponent/examiner in doctoral dissertations in KTH, Sweden; Linköping Univ., Sweden; NTNU, Norway; TU Dresden, Germany; CNAM, Paris, France; Eurecom, France; HUT, Finland; Oulu Univ., Finland. He was an Associate Editor of IEEE Signal Processing Letters 2006-2010. He was the secretary of ISCAS 1988, financial chair in EUSIPCO 2000, vice chairman in ICC 2001, tutorials co-chair in PIMRC 2006, TPC co-chair in SPAWC 2007, and general co-chair in SiPS 2009.

His main research areas include signal processing algorithms for wireless communications, with special focus on multicarrier techniques, DSP enhanced / cognitive / software defined radios and filter bank applications in those areas.