This book takes a modern multidisciplinary view on radio system - sign: the advantages of digital signal processing are exploited to satisfy the ever increasing demands on better performing ?exible radio f- quency (RF) circuits. By accepting that analog circuits are inherently imperfect but by searching for methods to mitigate and compensate for this signi?cant steps can be made to improve the overall system so- tion. This is in contrast to the more traditional approach of designing RF circuits themselves to satisfy the demanding speci?cations set by current standards. Wireless communication has progressed dramatically in past years. Yet the main research challenges changed focus to sustain this growth over many decades. In the early days the main challenge of radio c- munications was to cover large distances. When in late 1980s digital mobile communication emerged as a precursor to today s mass-market cell phones the priority shifted to achieving reliable communication over a di?cult i. e. time-varying and frequency-selective mobile ch- nel. About a decade or research in many institutes around the world has been devoted to this challenge exploiting the opportunities given by increasing computational power in digital circuits. Today we face a di?erent paradigm: the technology for analog front-ends progress sign- icantly slower than that of digital processors. So the imperfections of the RF have increasingly become the major bottleneck in our drive - wards faster yet more power-e?cient radio circuits.