Efficient and Flexible Digital Signal Processing Algorithms

(Project Leader: Prof. Håkan Johansson)

Project Motivation and Objectives

Communication systems are expected to continue to be heterogeneous, as it is foreseen that different operators will continue to deploy different standards in different regions of the world in order to exploit the forces of market to their own profit. On the other hand, few users will accept to carry around dedicated terminals for different networks and standards in different areas in the world. These facts have led to the concept of multimode terminals that supports different communication modes in a way that is transparent to the user. The traditional approach to cope with multimode problems is to use a custom device for each communication mode, but with the growing number of standards and communication modes, as well as the growing demand for more and more functionality, this approach is becoming increasingly infeasible and economically unacceptable both in terms of manufacturing cost and energy consumption of the terminal. Therefore, unless radical improvements as to the efficiency of multimode terminals take place, the full potentials of the multimode concept will remain unutilized. Major improvements are required not only for the digital baseband processing but also for the analog radio frequency (RF) front-end which should handle a large range of carrier frequencies, possess a flexible bandwidth, and cope with a wide variety of operational conditions. The multimode concept has thus given rise to new and very tough challenges in terms of minimizing the terminal cost, size, and power consumption while, at the same time, the flexibility and quality must be maximized.

The energy consumption of multimode circuits is affected by decisions taken at all steps in the design and implementation process, from system level down to circuit and transistor level. This project studies the parts concerning the choice of digital signal processing (DSP) algorithms, a choice that has a large impact upon the energy consumption. The objective is to develop efficient DSP algorithms that are reconfigurable, i.e., DSP algorithms that combine efficiency (low complexity) and flexibility. Such algorithms are key components for efficient realization of terminals with multiple different modes. Our approach is to combine fixed parts with adjustable parts having a simple updating routine. This has earlier been used only for a few DSP functions, mainly linear filters with an adjustable frequency response. In this project we aim to extend this approach to other key functions and investigate possibilities and limitations. In focus are algorithms needed in analog-digital, digital-analog, and digital-digital interfaces (ADIs, DAIs, and DDIs), as these are critical components in all communication environments and as they incorporate fundamental DSP functions, in particular filtering, interpolation and decimation, signal reconstruction, and frequency multiplexing and demultiplexing.

Publications

Journal papers

[1] H. Johansson and O. Gustafsson, "Linear-phase FIR interpolation, decimation, and Mth-band filters utilizing the Farrow structure," IEEE Trans. Circuits Syst. I, vol. 52, no. 10, pp. 2197-2207, Oct. 2005.

[2] P. Löwenborg and H. Johansson, “Minimax design of adjustable-bandwidth linear-phase FIR filters,” IEEE Trans. Circuits Syst. I, vol. 53, no. 2, pp. 431–439, Feb. 2006.

[3] H. Johansson and P. Löwenborg, “Flexible frequency-band reallocation MIMO network based on variable oversampled complex-modulated filter banks,” EURASIP J. Advances Signal Processing – Special Issue on Multirate Systems and Applications, vol. 2007, Article ID 63714, 15 pages, 2007.

[4] H. Johansson, P. Löwenborg, and K. Vengattaramane, “Least-squares and minimax design of polynomial impulse response FIR filters for reconstruction of two-periodic nonuniformly sampled signals,” IEEE Trans. Circuits Syst. I, vol. 54, no. 4, pp. 877–888, Apr. 2007.

[5] E. Hermanowicz and H. Johansson, “A complex variable fractional delay FIR filter structure,” IEEE Trans. Circuits, Syst. II, vol. 54, no. 9, pp. 785–789, Sept. 2007.

[6] A. Eghbali, H. Johansson, and P. Löwenborg, “A multi-mode transmultiplexer structure,” IEEE Trans. Circuits Syst. II: Special Issue on Multifunctional circuits and systems for future generations of wireless communications-I, vol. 55, no. 3, pp. 279–283, Mar. 2008.

[7] E. Hermanowicz, H. Johansson, and M. A. Rojewski, “A fractionally delaying complex Hilbert transform filter,“ IEEE Trans. Circuits Syst. II, vol. 55, no. 5, pp. 452–456, May 2008.

[8] A. Eghbali, H. Johansson, and P. Löwenborg, “Flexible frequency-band reallocation: Complex versus real,” Circuits, Syst., Signal Processing, accepted.

Conference papers

[1] H. Johansson and Per Löwenborg, "Flexible frequency-band reallocation network based on variable oversampled complex-modulated filter banks, in Proc. IEEE Int. Conf. Acoust. Speech, Signal Processing, Philadelphia, USA, Mar. 2005.

[2] E. Hermanowicz and H. Johansson, "On designing minimax adjustable wideband fractional delay FIR filters using two-rate approach," in Proc. European Conf. Circuit Theory Design, Cork, Ireland, Aug. 29-Sept. 1, 2005.

[3] H. Johansson, P. Löwenborg, and K. Vengattaramane, “Reconstruction of two-periodic nonuniformly sampled signals using polynomial impulse response time-varying FIR filters,” in Proc. IEEE Int. Symp. Circuits Syst., Kos, Greece, May 21–24, 2006.

[4] M. Olsson, P. Löwenborg, and H. Johansson, “Delay estimation using adjustable fractional delay all-pass filters,” in Proc. IEEE Nordic Signal Processing Symp., Iceland, June. 7–9, 2006.

[5] H. Johansson and E. Hermanowicz, “Adjustable fractional-delay filters utilizing the Farrow structure and multirate techniques,” in Proc. Sixth Int. Workshop Spectral Methods Multirate Signal Processing, Florence, Italy, Sept. 1–2, 2006.

[6] H. Johansson, P. Löwenborg, and K. Vengattaramane, “Reconstruction of M-periodic nonuniformly sampled signals using multivariate polynomial impulse response time-varying FIR filters,” in Proc. XII European Signal Processing Conf., Florence, Italy, Sept. 4–8, 2006.

[7] M. Olsson, H. Johansson, and P. Löwenborg, “Time-delay estimation using Farrow-based fractional-delay FIR filters: Approximation vs. estimation errors,” in Proc. XII European Signal Processing Conf., Florence, Italy, Sept. 4–8, 2006.

[8] L. Rosenbaum, H. Johansson, and P. Löwenborg, “Oversampled complex-modulated causal IIR filter banks for flexible frequency-band reallocation networks,” in Proc. XII European Signal Processing Conf., Florence, Italy, Sept. 4–8, 2006.

[9] H. Johansson, O. Gustafsson, K. Johansson, and L. Wanhammar “Adjustable fractional-delay FIR filters using the Farrow structure and multirate techniques,” in Proc. IEEE Asia Pacific Conf. Circuits Syst., Singapore, Dec. 4–7, 2006.

[10] A. Eghbali, H. Johansson, and P. Löwenborg, "An arbitrary bandwidth transmultiplexer and its application to flexible frequency-band reallocation networks," in Proc. European Conf. Circuit Theory Design, Seville, Spain, Aug. 26-30, 2007.

[11] A. Eghbali, H. Johansson, and P. Löwenborg, "Flexible frequency-band reallocation MIMO networks for real signals," in Proc. Int. Symp. Image, Signal Processing, Analysis, Istanbul, Turkey, Sept. 27-29, 2007.

[12] M. Olsson, H. Johansson, and P. Löwenborg, “Simultaneous estimation of gain, delay, and offset utilizing the Farrow structure,” in Proc. European Conf. Circuit Theory Design, Seville, Spain, Aug. 26-30, 2007.

[13] A. Eghbali, H. Johansson, and P. Löwenborg, “A multi-standard transmultiplexer based on the Farrow structure” in Proc. IEEE Int. Symp. Circuits Syst., Seattle, Washington, USA, May 18–21, 2008.

Theses

[1] M. Olsson, Contributions to Frequency Offset and Time-Delay Estimation, Linköping Studies in Science and Technology, thesis. no. 1252, Linköping University, May 2006.

[2] L. Rosenbaum, On Low-Complexity Frequency Selective Digital Filters and Filter Banks, Linköping Studies in Science and Technology, Dissertation No. 1097, Linköping University, Sweden, June 2007.

[3] M. Olsson, Contributions to Delay, Gain, and Offset Estimation, Linköping Studies in Science and Technology, Dissertation, Linköping University, June 2008.

Patents

[1] H. Johansson, P. Löwenborg, Ulrik Lindblad, and Patrik Thalin, "Estimation of timing errors in a time-interleaved analog-to-digital converter system," patent pending.

[2] H. Johansson and P. Löwenborg, “Time-Interleaved Analog-to-Digital Converter System”, patent pending.

[3] H. Johansson, “Compensation of mismatch errors in a time-interleaved analog-to-digital converter”, patent pending.

Funding

The project is funded by Vetenskapsrådet.