Channel Estimation and Receiver Design in Single- and Multiuser Multiantenna Systems : Dissertation Submitted for the Degree of Doctor of the Hungarian Academy of Sciences

Abstract: As an engineer and researcher, I have been dealing with the research, standardization and industrial-ization of wireless communication systems since the late 90’s. Specifically, I have been witnessing andcontributing to the evolution of the 3rd, 4th and currently to the 5th generation of cellular networks.The impact of this evolution on the society, public administration, businesses and individuals has beenprofound and played a key role in defining the information age and shaping the fully connected societies.Indeed, the technology footprint of cellular networks has lead to unprecedented economies of scale,which, in turn resulted in a rapid growth of technology solutions that enable them to operate with highspectral and energy efficiency in a great number of spectrum bands.My contributions to the advances of cellular technologies lie in the fields of radio resource managementand signal processing for multi-antenna systems, and specifically in the areas of channel estimation andreceiver design. In particular, my contributions as a researcher are threefold: (i) conducting research forthe purpose of proposing channel estimation and receiver designs that are superior to their state-of-the-artcounterparts, (ii) identifying the necessary changes in communication standards that ensure the inter-operability of such novel designs and (iii) developing suitable methodology for the performance analysisof the proposed channel estimation and receiver techniques. The results of these efforts include researchpapers in internationally recognized journals and book chapters, communication standards specificallydeveloped for the inter-operability of cellular systems and more than 40 internationally granted patentsthat are deployed in cellular systems around the world.In this thesis, I develop methodology and techniques to develop receiver algorithms that are optimalin terms of minimizing the mean squared error of the received data symbols in the presence of theestimation errors of the prevailing wireless channels through which communication takes place. Theproposed methodology and techniques enable me to prove that the state-of-the-art receiver structures aresuboptimal in the presence of wireless channel estimation errors, while the proposed receivers are optimalin terms of minimizing the symbol errors at multi-antenna receivers. I also developed methodology thatenables the exact analysis of the symbol errors as functions of the resources used for obtaining channelestimates at the wireless receiver and transmitting data through the wireless channel.These methods have lead to channel estimation techniques and receiver algorithms that significantlyimprove the spectral and energy efficiency of multi-antenna cellular systems, and simplify the designof receiver algorithms when the number of deployed antennas at cellular infrastructure nodes increasesover time.