Channelization for Multi-Standard Software-Defined Radio Base Stations By Álvaro Palomo Navarro A thesis presented to the National University of Ireland in partial fulfilment of the requirements for the degree of Doctor of Philosophy Department of Electronic Engineering National University of Ireland Maynooth October 2011 Research supervisors: Dr. Rudi Villing and Dr. Ronan Farrell Head of department: Dr. Seán McLoone Abstract As the number of radio standards increase and spectrum resources come under more pressure, it becomes ever less efficient to reserve bands of spectrum for exclusive use by a single radio standard. Therefore, this work focuses on channelization structures compatible with spectrum sharing among multiple wireless standards and dynamic spectrum allocation in particular. A channelizer extracts independent communication channels from a wideband signal, and is one of the most computationally expensive components in a communications receiver. This work specifically focuses on non-uniform channelizers suitable for multi-standard Software-Defined Radio (SDR) base stations in general and public mobile radio base stations in particular. A comprehensive evaluation of non-uniform channelizers (existing and developed during the course of this work) shows that parallel and recombined variants of the Generalised Discrete Fourier Transform Modulated Filter Bank (GDFT-FB) represent the best trade-off between computational load and flexibility for dynamic spectrum allocation. Nevertheless, for base station applications (with many channels) very high filter orders may be required, making the channelizers difficult to physically implement. To mitigate this problem, multi-stage filtering techniques are applied to the GDFT-FB. It is shown that these multi-stage designs can significantly reduce the filter orders and number of operations required by the GDFT-FB. An alternative approach, applying frequency response masking techniques to the GDFT-FB prototype filter design, leads to even bigger reductions in the number of coefficients, but computational load is only reduced for oversampled configurations and then not as much as for the multi-stage designs. Both techniques render the implementation of GDFT-FB based non-uniform channelizers more practical. Finally, channelization solutions for some real-world spectrum sharing use cases are developed before some final physical implementation issues are considered. ii Declaration I hereby declare that this thesis is my own work and has not been submitted in any form for another award at any other university or institute of tertiary education. Information derived from the published or unpublished work of others has been acknowledged in the text and a list of references is given. ___________________________ ___________________________ Signature Date iii “Don’t worry, you will get there in the end. This is just one of those days that you knew would come. Don’t ever forget that someone believes in you. One step at a time!” iv Acknowledgements Some people say that doing a PhD is similar to running a marathon. The most important thing is to concentrate on putting one foot in front of the other, without looking ahead, just keep doing it and finally you will get to the finish line. Well, if a PhD is a marathon, then the people around you during those years are the water points that refresh you and give you energy to keep going. First, I would like to thank my family, especially my parents and brother. Their support did not start with this PhD, but many years ago. It is thanks to them that this thesis has become a reality. Also to Aisling, for so many things, but especially for going on this journey, full of challenges with me and fuelling it with continuous faith and encouragement. I would especially like to dedicate this to my grandmother Teresa, as I think she would be very proud of this moment. I would like to thank my supervisor Rudi Villing for his continuous support, encouragement, dedication and patience. Also, I thank my co-supervisor Ronan Farrell, for giving me the opportunity of doing this PhD. Both of them have been very inspirational professionals and sources of learning. I would like to express my gratitude to everyone in the Callan Institute (IMWS when this PhD started) for not only being good colleagues but also good friends. Among them, I would like to thank John Dooley, Magdalena Sánchez, Tomasz Podsiadlik and Justine McCormack for so many great moments inside and outside the lab. There are many good friends, here in Ireland and Spain, who I would like to thank for their help along these years. I cannot mention them all, as I am sure I would be forgetting someone, but Carol, David, Dani, Pablo, Mario, Kiko, Toni, Rosa, Gustavo, Carla, Ciara, Michael, thanks to all of you. Finally, I would like to thank the sponsors IRCSET and EADS for the PhD program, in special Jean-Christophe Schiel and François Montaigne for their assistance and support. v Table of contents Abstract ................................................................................................................... ii Declaration ............................................................................................................. iii Acknowledgements ................................................................................................. v Table of contents .................................................................................................... vi List of figures ......................................................................................................... xi List of tables ......................................................................................................... xvi List of notations .................................................................................................. xix List of abbreviations ........................................................................................... xxi List of publications ............................................................................................. xxiv Chapter 1 Introduction ............................................................................................ 1 1.1 Research motivation ................................................................................. 4 1.2 Thesis layout and contributions ................................................................ 5 Chapter 2 Dynamic Spectrum Allocation and Software-Defined Radio ................ 9 2.1 Introduction .............................................................................................. 9 2.2 Fixed spectrum allocation and dynamic spectrum allocation................. 10 2.3 Multi-Standard PMR Base Stations ....................................................... 15 2.3.1 TETRA V&D and TEDS modulation schemes .............................. 17 2.3.2 TETRA V&D and TEDS radio transmission and reception ........... 20 2.3.3 TETRA V&D and TEDS joint implementation .............................. 21 2.4 SDR as a DSA enabling technology ....................................................... 22 2.4.1 What is SDR? .................................................................................. 24 2.4.2 SDR and ideal SDR ......................................................................... 25 2.4.3 SDR physical implementation limitations ...................................... 27 2.4.3.1 Analogue and digital front-ends .............................................. 28 vi 2.4.3.2 Digital back-end: SDR architectures ....................................... 29 2.4.4 An SDR multi-standard base station implementation: the channelization challenge ............................................................................... 31 2.5 Conclusions ............................................................................................ 33 Chapter 3 Uniform Wideband Channelization ...................................................... 34 3.1 Introduction ............................................................................................ 34 3.2 Wideband complex baseband signal channelization .............................. 34 3.3 Per-channel channelization ..................................................................... 38 3.3.1 The CORDIC algorithm .................................................................. 42 3.4 Multirate efficient filter implementation ................................................ 43 3.4.1 Cascade integrator comb (CIC) filters ............................................ 43 3.4.2 Noble identities and polyphase filter decomposition ...................... 44 3.4.3 Half-band filters .............................................................................. 51 3.4.4 Frequency response masking (FRM) .............................................. 53 3.5 Filter bank based channelizers ............................................................... 57 3.5.1 Filter bank and transmultiplexer basis ............................................ 58 3.5.2 Design issues: perfect reconstruction and oversampling ................ 60 3.5.3 Complex uniform modulated filter banks ....................................... 63 3.5.3.1 DFT modulated filter banks (DFT-FB) ................................... 64 3.5.3.2 Exponential modulated filter banks (EMFB)........................... 69 3.6 Computational load analysis for per-channel and complex modulated filter bank channelizers ..................................................................................... 75 3.7 Conclusions ...........................................................................................