Tutorials / Short Courses

2015 IEEE International Symposium on Circuits and Systems (Nuit de la litterature 2015)

Sunday, 21 May 2015


M6: Advanced Signal Processing Techniques for Compensation of Analog RF Impairments in Software Defined Radios

, Dr. Tech., and Prof.

08:30 - 12:30



In the field of mobile communications, there are strong needs for architecture, algorithm, and circuit level solutions for highly integrated, energy efficient, and flexible receivers for various communications systems. In this context, there are great expectations for the so-called software-defined radio (SDR) approach for implementing multiband/multistandard receivers. Increased use of DSP in receiver signal processing can be seen as a major trend in these developments, but it has also been generally recognized that sampling and A/D-conversion technologies are the main bottle-neck for increased use of DSP in implementing RF functionalities.

A relatively novel approach in receiver signal processing context is to develop advanced baseband DSP techniques for restoring the quality of the signals that are captured at the A/D interface. Such techniques would greatly relieve the requirements of the analog front-end circuitry, thus facilitating the implementation of the analog functionalities on low-cost RF-ASICS with low power consumption. During the recent years, this approach has been demonstrated to be practical for relieving the effects of amplitude and phase imbalances that greatly limit the performance and applicability of analog I/Q signal processing, especially in wideband multichannel type receivers. Similar ideas are emerging, e.g., for compensating the intermodulation effects due to the nonlinearities of the receiver analog front-end components.

This tutorial aims to provide a comprehensive overview of the crucial elements of such compensation methods, also known as “Dirty RF” techniques. In addition to various algorithm level developments, it also includes multiple case studies where the overall receiver performance is analyzed based on actual signals measured and captured from real-world receiver analog front-ends.


1. Adaptive DSP Techniques for I/Q Imbalance Compensation

  • Signal models for direct-conversion and low-IF type receiver architectures under I/Q imbalance

  • I/Q imbalance compensation schemes based on blind signal estimation techniques

  • Extensions to frequency-dependent I/Q imbalance compensation

  • Role of modulation – single-carrier, OFDM and CDMA cases

  • Performance examples with practical analog receiver front-ends

  • Signal model and algorithm extensions to multi-antenna/MIMO systems

  • Advanced bandpass sampling and I/Q imbalance – enhancing the image rejection in the second-order sampling context using DSP

2. Advanced DSP for Compensation of the Effects of Analog Front-End Non-Linearities

  • Introduction to RF intermodulation effects in receivers

  • Signal models for nonlinear analog front-ends

  • Compensation scheme based on interference cancellation principle

  • Simulation and measurement based results and performance examples

  • System level discussions

3. I/Q Signal Processing in Frequency Synthesizers

  • Digitally synthesized complex tone and analog I/Q mixing principle

  • I/Q imbalance problem revisited – predistortion principle for improved signal quality


Short Biographies

Mikko Valkama (Member, IEEE) was born in Pirkkala, Finland, on November 27, 1975. He received the M.Sc. and Ph.D. degrees (both with honors) in Electrical Engineering (EE) from Tampere University of Technology (TUT), Finland, in 2004 and 2005, respectively. In 2015 he received the Best Ph.D. Thesis -award by the Finnish Academy of Science and Letters for his thesis entitled "Advanced I/Q Signal Processing for Wideband Receivers: Models and Algorithms". In 2007, he was working as a visiting researcher with the Communications Systems and Signal Processing Institute at SDSU, San Diego, CA. Currently, he is working as a senior researcher and docent with the Institute of Communications Engineering at TUT, Finland. His general research interests include communications signal processing, estimation and detection techniques, signal processing algorithms for software defined flexible radios, and digital transmission techniques such as different variants of multicarrier modulation methods and OFDM.

Markku Renfors (Senior Member, IEEE) was born in Suoniemi, Finland, on January 21, 1953. He received the Diploma Engineer, Licentiate of Technology, and Doctor of Technology Degrees from Tampere University of Technology (TUT), Finland, in 1978, 1981, and 1982, respectively. He held various research and teaching positions at TUT during 1976 to 1988. 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. Since 1992 he has been a Professor of Telecommunications at TUT. His main research areas are multicarrier systems and signal processing algorithms for flexible radio receivers and transmitters.



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