Multicarrier modulation has become the format of choice in modern high-speed wireless and wireline systems, due to its many well-known qualities. Nevertheless, the large IFFT sidelobes result in substantial leakage across subcarriers with the ensuing adjacent channel interference. The usual approach of deactivating a number of guard subcarriers at the edges of the signal spectrum is very inefficient in terms of data rate. In order for OFDM to be adopted by future high-performance systems, e.g., 5G, a number of enhancements will become necessary to overcome this and other drawbacks. The leakage problem is also of concern in wideband OFDM-based cognitive systems, in which deep notches must be sculpted in the spectrum to avoid interfering to narrowband licensed users. Judiciously modulating (a few) cancellation subcarriers in order to reduce leakage is an appealing alternative, which originally incurred in high online implementation complexity. We will review this Active Interference Cancellation approach and present efficient designs recently developed in our group, with extensions to linear symbol precoding.
Roberto Lopez-Valcarce received the Ph.D. degree in electrical engineering from the University of Iowa, Iowa City, in 2000. He was a Postdoctoral Fellow of the Spanish Ministry of Science and Technology from 2001 to 2006, with the Signal Theory and Communications Department, University of Vigo, Spain, where he currently is an Associate Professor. His main research interests lie in the areas of adaptive signal processing, digital communications, and sensor networks, having coauthored over 50 papers in leading international journals. He holds several patents in collaboration with industry. Roberto was the recipient of a 2005 Best Paper Award of the IEEE Signal Processing Society. He served as an Associate Editor of the IEEE TRANSACTIONS ON SIGNAL PROCESSING from 2008 to 2011, and as a member of the IEEE Signal Processing for Communications and Networking Technical Committee from 2011 to 2013.