Responsible for this page: Lars Wanhammar , larsw@isy.liu.se
Page last update: 2008-05-08
Responsible for this page: Lars Wanhammar , larsw@isy.liu.se
Page last update: 2008-05-08
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(Project Leader: Prof. Håkan Johansson)
The future society foresees globally interconnected digital communication systems offering delivery of information at any time, any place, and in any form. In this context, high-performance analog/digital interfaces and energy-efficient circuits are paramount. Another aspect that is becoming increasingly important is flexibility in the sense that different functions should be reconfigurable in order to suit communication systems that incorporate several different standards. This introduces the need for efficient multimode circuits that feature both flexibility and low energy consumption.
The energy consumption of DSP integrated circuits (ICs) 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 DSP algorithms, a choice that has a large impact upon the energy consumption. The goal is to find new efficient DSP algorithms, in particular algorithms required in communication systems like filtering, signal reconstruction, estimation, etc. There is a distinction between DSP functions and DSP algorithms. A function is the task of the system whereas the algorithm says how we are going to implement this function. For example, a filter is a function, whereas a large number of algorithms exist that implement the same filter function. Algorithms that implement these functions mainly consist of a number of arithmetic operations, most of them being multiplications and additions. It is desired to find efficient algorithms (low-complexity algorithms) that require as few arithmetic operations as possible, as this in the end minimizes the device size and energy consumption, provided that algorithm dedicated ICs (as opposed to general-purpose DSP processors) are used which is the underlying assumption here. The number of operations can be substantially reduced by using a "smart" algorithm instead of a "straightforward" algorithm. The reason is that a straightforward algorithm most often contains redundant (unnecessary) computations. However, it is usually far from trivial to identify and remove this redundancy.
The goal of this project is to attain a fundamental knowledge of the computational properties of different DSP algorithms for important DSP functions. A key is to identify and remove redundant computations which leads to more efficient algorithms and in the end energy-efficient circuits. It should be noted though that there are also other factors, such as data communication and control, that contribute to the power consumption. It is thus important to reduce the number of arithmetic operations and memory accesses in such a way that the cost to implement the additional circuitry (control devices etc.) is not increasing, or at least increases less that the reduction gained by using a more efficient algorithm. In the proposed new algorithms, this is done by using similar structures as conventional ones regarding additional circuitry but that require less arithmetic operations and memory accesses. In this way, one will end up with an implementation with lower energy consumption.
The project is interdisciplinary in the sense that it considers both communication and digital signal processing (DSP) problems. It is common that "communication people" and "DSP people" work in parallel rather than together. Bringing different disciplines together is fruitful in order to come up with new innovative solutions. A long-term goal is to continue along this path and to build up a research group that brings together communications and DSP. It is important to have such research groups since there is a lack of people covering two or several different areas. The research in this area can engage both undergraduate and graduate students. There are also good opportunities for co-operation with other research groups since communication and DSP encompass many different aspects.
Up to now, numerous new low-complexity DSP algorithms for different purposes have been developed. We divide the research into seven main lines of work as described below.
This part is on reconstruction of nonuniformly sampled bandlimited signals. We have proposed a new technique for reconstructing periodically nonuniformly sampled signals that is based on so called fractional delay digital filters. Compared to other techniques to this end, our approach has the following advantages: 1) the distortion can be made arbitrarily small by properly designing the digital fractional delay filters, 2) if properly implemented, the digital filters need not be redesigned in case the sampling pattern is changed. It suffices to adjust a few multiplier coefficient values that are determined by the sampling pattern. A (minor) disadvantage of this approach is that we need to use a certain amount of oversampling. This work has resulted in one journal paper [1], three conference papers [16], [18], [22] and one patent [80], acquired by Ericsson. Further, major parts of this work are included in the doctoral thesis of Dr. Per Löwenborg [62] who graduated in December 2002 and was supervised by the applicant.
Generalizing our system above, one ends up with reconstruction of general irregular (with some mild restrictions though) nonuniformly sampled bandlimited signals using time-varying filters. Such reconstruction algorithms find applications in several areas, e.g., mitigation of certain types of errors in analog-to-digital converters. We have recently shown how to design the time-varying filters in a proper manner. The advantages of this technique, over the one above, are 1) it can handle general irregularly nonuniformly sampled signals, 2) it offers a reduced implementation cost in those cases where the sampling pattern is not changed (or changes rarely), 3) it requires a smaller amount of oversampling. This work has resulted in one journal paper [8] and two conference papers [40], [42]. A problem of this approach is however that it requires on-line filter design whenever the sampling pattern is changed. To solve this problem, we are currently working with different types of polynomial-based time-varying filters. This work has so far resulted in two conference papers [52], [56] and one submitted journal paper [14].
This part concerns filters with adjustable frequency responses. We have developed a new design technique for adjustable fractional-delay FIR filters that leads to a reduced complexity [2], [19]. These filters are suitable for the first reconstruction technique discussed above. Another line of work has been on digital filters with adjustable bandwidth(s). Such filters find applications in e.g. Software-Defined Radio where interpolation and decimation with adjustable factors need to be handled. We have studied the problem of satisfying general specifications including passband and stopband edges for a whole set of specifications [33], [37]. Traditionally, only the passband edges (or stopband edges) have been controlled. Further, we have introduced a linear programming design technique for a class of adjustable-bandwidth linear-phase FIR filters which reduces the overall complexity compared to previously existing design techniques [9], [32], [39]. We have also showed that a bank of fixed overdesigned filters can reduce the complexity compared to techniques that use one filter with adjustable coefficients [6]. We have also proposed new structures for realizing efficient adjustable integer sampling rate converters [7], [38]. In our most recent work, we have proposed a two-rate approach for reducing the complexity of adjustable fractional-delay FIR filters [50], [55], [61]. This approach leads to a complexity that is even lower than the single-rate approaches in [2], [19].
This work is on different types of digital filters and two-channel filter banks suitable for different specifications and applications. We have introduced several new efficient short-delay filters, interpolation and decimation filters, multirate filters, Mth-band filters, and two-channel filter banks. Parts of this work have been done in co-operation with Prof. Tapio Saramäki of Tampere University of Technology in Finland. This work has resulted in three journal papers [3]-[5] (and one submitted paper [11]) and eight conference papers [16], [20], [22], [23], [25], [27], [34], [35]. The paper [4] received the best paper award in J. Circuits, Syst., Comp., Special Issue on Frequency-Response Masking Technique, 2003.
This part is on frequency selective M-channel filter banks which find application in e.g. communication systems where they are used as multiplexers and demultiplexers. The applicant’s work in this area covers supervision of the Ph.D. student Linnéa Rosenbaum (earlier Svensson) who finished her Licentiate degree in September 2003 [63]. The thesis proposes new classes of so called modulated filter banks with lower complexity than previous such types of filter banks. This work has resulted in one journal paper [12] (and one submitted journal paper [15]) and six conference papers [20], [25], [27], [30], [29], [31]. The conference paper [29] received the best paper award of that conference./P>
This part concerns development of new robust and efficient estimation and synchronization algorithms for communication systems. The applicant’s work in this area covers supervision of the Ph.D. student Mattias Olsson. This work has so far resulted in six conference papers [44], [47], [49], [51], [54], [57].
This work is on flexible frequency-band reallocation (redirection-of-information) networks. Together with Per Löwenborg, the applicant has invented a new technique for this purpose based on new classes of flexible complex-modulated filter banks. This new technique has the potentials of substantially outperforming previously existing techniques when all the aspects flexibility, low complexity and inherent parallelism, and perfect frequency-band reallocation are considered simultaneously. This work has so far resulted in one journal paper [11] and two conference papers [45], [58].
This part is on high performance analog/digital interfaces (ADIs). It has become evident during the past years that the ever increasing requirements on ADIs as to the data rates and resolution most likely cannot be met by further progress in analog circuit topologies and technologies alone. To make radical improvements, it appears necessary to find new principles incorporating digital signal processing (DSP) algorithms. A fundamental concept that can be foreseen to be shared between all such principles is parallelization which is the natural way to increase the data rate. Our work in this area follows two different lines.
One line of work is on time-interleaved A/D converters where M converters are used in parallel to increase the effective sampling rate by a factor of M. A problem of such converters is however that the parallelization introduces channel mismatch errors that must be estimated and compensated for by DSP algorithms. Together with Per Löwenborg, the applicant has developed new efficient estimation and correction algorithms that outperform previously existing ones. The new techniques incorporate adjustable/adaptive fractional-delay filters for the estimation and the algorithms discussed under 1) above for the correction (reconstruction). Parts of this work are covered in topic 5) above ([54], [57]). This work has also resulted in three patent applications [81]–[82].
A second line of work is on parallel sigma-delta converters which are used to increase the relatively low bandwidth of single sigma-delta converters. A result of this work is a new general formulation of parallel sigma-delta converters in terms of circulant and pseudocirculant matrices derived from multirate filter bank theory [60]. This formulation has not been utilized in this context before, but it turns out to be very powerful as it can be used to analyze the behavior of a practical overall ADC with channel gain, offset, and modulation sequence level mismatches present. This provides new insights that are very useful, not only for analysis of existing schemes, but also for the derivation of new ones. In particular, the new formulation gives us information about a particular scheme’s sensitivity to the different channel mismatch errors. From this, one can deduce that many schemes in fact do not need “full calibration” to eliminate nonlinear distortion (aliasing), which earlier has been the common belief. It suffices to compensate for a subset of the different errors involved, which eases the calibration substantially. Another result is on complexity issues of decimation filters for SD converters [59].
The people involved in this project are:
Prof. Håkan Johansson (Project leader)
Dr. Per Löwenborg
Ph.D. Student Linnea Rosenbaum
Ph.D. Student Mattias Olsson
Ph.D. Student Anton Blad
The applicant co-operates with Per Löwenborg as to research topic six and seven above. Per Löwenborg is funded by CENIIT for the project “Flexible frequency band reallocation”. As to other research groups, the main co-operation partner has up to now been Prof. Tapio Saramäki and his group at Tampere University of Technology in Finland as evidenced by several joint publications. More recently, we have also initiated a co-operation with Ewa Hermanowicz at Gdansk University of Technology in Poland and Christian Vogel at Graz University of Technology in Austria. As to industrial co-operation, this is mainly done through the company Signal Processing Devices (se below).
Parts of the research results in this project (in particular from topic 7.A above) have resulted in the spin-off company Signal Processing Devices Sweden AB, of which the applicant and Per Löwenborg are two of the co-founders. The company is accommodated by the Mjärdevi Business Incubator and has at present four employees.
[1] H. Johansson and P. Löwenborg, "Reconstruction of nonuniformly sampled bandlimited signals by means of digital fractional delay filters," IEEE Trans. Signal Processing, vol. 50, no. 11, pp. 2757-2767, Nov. 2002.
[2] H. Johansson and P. Löwenborg, "On the design of adjustable fractional delay FIR filters," IEEE Trans. Circuits Syst. II, vol. 50, no. 4, pp. 164-169, Apr. 2003.
[3] H. Johansson and T. Saramäki, "Two-channel FIR filter banks utilizing the frequency-response masking approach," Circuits, Syst., Signal Processing, vol. 22, no. 2, pp. 157-192, Feb. 2003.
[4] T. Saramäki, J. Yli-Kaakinen, and H. Johansson "Optimization of frequency-response-masking based FIR filters," J. Circuits, Syst., Comput., vol. 12, no. 5, pp. 563-591, Oct. 2003.
[5] H. Johansson, "Multirate IIR filter structures for arbitrary bandwidths," IEEE Trans. Circuits Syst. I, vol. 50, no. 12, pp. 1515-1529, Dec. 2003.
[6] H. Johansson and P. Löwenborg, "On linear-phase FIR filters with variable bandwidth," IEEE Trans. Circuits Syst. II, vol. 51, no. 4, pp. 181184, Apr. 2004.
[7] 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.
[8] H. Johansson and Per Löwenborg, "Reconstruction of nonuniformly sampled bandlimited signals by means of time-varying discrete-time FIR filters, J. Applied Signal Processing: Special Issue on Frames and Overcomplete Representations in Signal Processing, Communications, and Information Theory, vol. 2006, Article ID 64185, 18 pages, 2006.
[9] 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.
[10] H. Johansson, “Two classes of frequency-response masking linear-phase FIR filters for interpolation and decimation,” Circuits, Syst., Signal Processing – Special issue on Computationally Efficient Digital Filters: Design and Applications, vol. 25, no. 2, pp. 175–200, Apr. 2006.
[11] H. Johansson and P. Löwenborg, “Flexible frequency-band reallocation MIMO network based on variable oversampled complex-modulated filter banks,” accepted for publication in J. Applied Signal Processing – Special Issue on Multirate Systems and Applications.
[12] L. Rosenbaum, P. Löwenborg, and H. Johansson, “An approach for synthesizing cosine modulated filter banks based on the frequency-response masking technique,” accepted for publication in J. Applied Signal Processing – Special Issue on Multirate Systems and Applications.
[13] L. Rosenbaum and H. Johansson, “On low-delay frequency masking FIR filters,” accepted for publication in Circuits, Syst., Signal Processing.
[14] 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.
[15] L. Rosenbaum, P. Löwenborg, and H. Johansson, “Cosine modulated causal IIR/IIR and IIR/FIR filter banks,” Signal Processing.
[16] H. Johansson, and P. Löwenborg, "Reconstruction of nonuniformly sampled bandlimited signals using digital fractional delay filters," in Proc. IEEE Int. Symp. Circuits Syst., Sydney, Australia, May 6-9, 2001, vol. 2, pp. 593-596.
[17] T. Saramäki and H. Johansson, "Optimization of FIR filters using the frequency-response masking approach," in Proc. IEEE Int. Symp. Circuits Syst., Sydney, Australia, May 6-9, 2001, vol. 2, pp. 177-180.
[18] H. Johansson, and P. Löwenborg, "Reconstruction of nonuniformly sampled bandlimited signals using digital fractional delay filters: Error and quantization noise analysis," in Proc. European Conf. Circuit Theory Design, Espoo, Finland, Aug. 28-31, 2001, vol. 2, pp. 293-296.
[19] H. Johansson and P. Löwenborg, "On adjustable fractional delay FIR filters and their design," in Proc. European Conf. Circuit Theory Design, Espoo, Finland, Aug. 28-31, 2001, vol. 2, pp. 297-300.
[20] L. Svensson, P. Löwenborg, and H. Johansson, "Cosine modulated causal IIR NPMR and NPR filter banks," in Proc. Swedish System-on-Chip Conf., Falkenberg, Sweden, Mar. 18-19, 2002.
[21] H. Johansson, "Multirate approximately linear-phase IIR filter structures for arbitrary bandwidths," in Proc. IEEE Int. Symp. Circuits Syst., Phoenix, USA, May 26-29, 2002.
[22] H. Johansson and P. Löwenborg, "Reconstruction of a class of nonuniformly sampled and decimated bandlimited signals," in Proc. IEEE Int. Symp. Circuits Syst., Phoenix, USA, May 26-29, 2002.
[23] L. Svensson and H. Johansson, "Frequency-response masking FIR filters with short delay," in Proc. IEEE Int. Symp. Circuits Syst., Phoenix, USA, May 26-29, 2002.
[24] L. Svensson and H. Johansson, "Narrow-band and wide-band frequency masking FIR filters with short delay," in Proc. National Conf. Radio Science (RVK), Stockholm, Sweden, June 10-13, 2002, pp. 496-500.
[25] L. Svensson, P. Löwenborg, and H. Johansson, "A class of cosine modulated causal IIR filter banks," in Proc. IEEE Int. Conf. Electronics Circuits Syst., Dubrovnik, Croatia, Sept. 15-18, 2002.
[26] H. Johansson, "Efficient FIR filter structures based on the frequency-response masking approach for interpolation and decimation by a factor of two," in Proc. Second Int. Workshop Spectral Methods Multirate Signal Processing, Toulouse, France, Sept. 7-8, 2002, pp. 73-76.
[27] L. Svensson, P. Löwenborg, and H. Johansson, "Asymmetric cosine modulated causal IIR/FIR NPR filter banks," in Proc. Second Int. Workshop Spectral Methods Multirate Signal Processing, Toulouse, France, Sept. 7-8, 2002.
[28] H. Johansson, "A class of Mth-band linear-phase FIR filters synthesized using the frequency-response masking approach," in Proc. IEEE Nordic Signal Processing Symp., Hurtigruten, Norway, Oct. 4-7, 2002.
[29] L. Svensson, P. Löwenborg, and H. Johansson, "Modulated M-channel FIR filter banks utilizing the frequency response masking approach," in Proc. IEEE Nordic Signal Processing Symp., Hurtigruten, Norway, Oct. 4-7, 2002.
[30] L. Rosenbaum and H. Johansson, "Design of modulated FIR filter banks using the frequency-response masking approach," in Proc. Swedish System-on-Chip Conf., Apr. 2003.
[31] L. Rosenbaum, P. Löwenborg, and H. Johansson, "Cosine and Sine modulated M-channel FIR filter banks utiling the frequency response masking approach," in Proc. IEEE Int. Symp. Circuits Syst., Bangkok, Thailand, May 25-28, 2003.
[32] P. Löwenborg and H. Johansson, "Linear programming design of linear-phase FIR filters with variable bandwidth," in Proc. IEEE Int. Symp. Circuits Syst., Bangkok, Thailand, May 25-28, 2003.
[33] H. Johansson, "On lowpass and highpass IIR filters with an adjustable bandwidth," in Proc. European Conf. Circuit Theory Design, Krakow, Poland, Sept. 1-4, 2003.
[34] L. Rosenbaum and H. Johansson, "Two-channel linear-phase FIR filter banks utilizing the frequency-response masking approach," in Proc. European Conf. Circuit Theory Design, Krakow, Poland, Sept. 1-4, 2003.
[35] H. Johansson, "Efficient frequency-response-masking based FIR filter structures for interpolation and decimation," Third Int. Workshop Spectral Methods Multirate Signal Processing, Barcelona, Spain, Sept. 13-14, 2003.
[36] B. Soltanian, T. Saramäki, and H. Johansson, "Design of optimum recursive filters with double zeros on the unit circle leading to symmetric ladder wave digital filter structures," in Proc. Int. Symp. Image, Signal Processing, Analysis, Rome, Italy, Sept. 18-20, 2003.
[37] H. Johansson, "On the design of IIR bandpass filters with an adjustable bandwidth and centre frequency," in Proc. IEEE Int. Symp. Circuits Syst., Vancouver, Canada, May 2004.
[38] H. Johansson and Oscar Gustafsson, "Mth-band linear-phase FIR filter interpolators and decimators utilizing the Farrow structure," in Proc. IEEE Int. Symp. Circuits Syst., Vancouver, Canada, May 2004.
[39] B. Soltanian, T. Saramäki, and H. Johansson, "Design of optimum recursive filters with double zeros on the P. Löwenborg and H. Johansson, "Minimax design of linear-phase FIR filters with adjustable bandwidths," in Proc. EEE Int. Symp. Circuits Syst., Vancouver, Canada, May 2004.
[40] H. Johansson and Per Löwenborg, "Reconstruction of nonuniformly sampled bandlimited signals using time-varying discrete-time FIR filters," in Proc. XII European Signal Processing Conf., Vienna, Austria, Sept. 610, 2004.
[41] M. Olsson, P. Löwenborg, and H. Johansson, "Scaling of multistage interpolators," in Proc. XII European Signal Processing Conf., Vienna, Austria, Sept. 610, 2004.
[42] H. Johansson and Per Löwenborg, "Reconstruction of periodically nonuniformly sampled bandlimited signals using time-varying FIR filters," in Proc. Fourth Int. Workshop Spectral Methods Multirate Signal Processing, Vienna, Austria, Sept. 1112, 2004.
[43] M. Olsson, P. Löwenborg, and H. Johansson, "Scaling and round-off noise in multistage interpolators and decimators," in Proc. Fourth Int. Workshop Spectral Methods Multirate Signal Processing, Vienna, Austria, Sept. 1112, 2004.
[44] M. Olsson and H. Johansson, "Blind OFDM carrier frequency offset estimation by locating null subcarriers," in Proc. 9th Int. OFDM-Workshop, Dresden, Germany, Sept. 1516, 2004.
[45] 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.
[46] P. Löwenborg, L.Rosenbaum, and H. Johansson, "On flexible analog/digital interfaces for multi-mode communication," in Proc. Swedish System-on-Chip Conf., Tamsvik Konferens & Herrgård, Sweden, Apr. 18-19, 2005.
[47] M. Olsson and H. Johansson, "Estimating the OFDM carrier frequency offset by locating null subcarriers," in Proc. Swedish System-on-Chip Conf., Tamsvik Konferens & Herrgård, Sweden, Apr. 18-19, 2005.
[48] L. Rosenbaum and H. Johansson, "Narrow-band and wide-band short-delay frequency-masking FIR filters," in Proc. National Conf. Radio Science (RVK), Linköping, Sweden, June 14-16, 2005.
[49] M. Olsson and H. Johansson, "An overview of OFDM synchronization techniques," in Proc. National Conf. Radio Science (RVK), Linköping, Sweden, June 14-16, 2005.
[50] 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.
[51] M. Olsson and H. Johansson, "OFDM carrier frequency offset estimation using null subcarriers", in Proc. 10th Int. OFDM Workshop, Hamburg, Germany, Aug. 31-Sept. 1, 2005.
[52] 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.
[53] C. Vogel and H. Johansson, “Time-interleaved analog-to-digital converters: Status and future directions,” in Proc. IEEE Int. Symp. Circuits Syst., Kos, Greece, May 21–24, 2006.
[54] M. Olsson and H. Johansson, “Delay estimation using adjustable fractional delay all-pass filters,” in Proc. IEEE Nordic Signal Processing Symp., Iceland, June. 7–9, 2006.
[55] 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.
[56] 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.
[57] M. Olsson, H. Johansson, and Per 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.
[58] 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.
[59] A. Blad, H. Johansson, and P. Löwenborg, “Design trade-offs for linear-phase FIR filters and SD-modulators,” in Proc. XII European Signal Processing Conf., Florence, Italy, Sept. 4–8, 2006.
[60] A. Blad, H. Johansson, and P. Löwenborg, “A general formulation of analog-to-digital converters using parallel sigma-delta modulators and modulation sequences,” in Proc. IEEE Asia Pacific Conf. Circuits Syst., Singapore, Dec. 4–7, 2006.
[61] 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.
[62] P. Löwenborg, Asymmetric Filter Banks for Mitigation of Mismatch Errors in High-speed Analog-to-digital Converters, Linköping Studies in Science and Technology, dissertation no. 787, Linköping University, Dec. 2002.
[63] Linnéa Rosenbaum, Contributions to Low-Complexity Maximally Decimated Filter Banks, Linköping Studies in Science and Technology, thesis. no. 1035, Linköping University, Sept. 2003.
[64] M. Olsson, Contributions to Frequency Offset and Time-Delay Estimation, Linköping Studies in Science and Technology, thesis. no. 1252, Linköping University, May 2006.
[65] O. Gustafsson, H. Johansson and L. Wanhammar, "Single-filter frequency masking high-speed recursive digital filters," Circuits, Syst., Signal Processing, vol. 22, no. 2, pp. 219-238, Feb. 2003.
[66] O. Gustafsson, H. Johansson and L. Wanhammar, "Single filter frequency-response masking FIR filters," J. Circuits, Syst., Comput., vol. 12, no. 5, pp. 601-630, Oct. 2003.
[67] P. Löwenborg, H. Johansson, and L. Wanhammar, "First-order sensitivity of complementary diplexers," IEEE Trans. Circuits Syst. II, vol. 51, no. 8, pp. 421-425, 2004.
[68] O. Gustafsson, H. Johansson, and L. Wanhammar, "Narrow-band and wide-band single filter frequency masking FIR filters," in Proc. IEEE Int. Symp. Circuits Syst., Sydney, Australia, May 6-9, 2001, vol. 2, pp. 181-184.
[69] O. Gustafsson, H. Johansson, and Lars Wanhammar, "An MILP approach for the design of linear-phase FIR filters with minimum number of signed-power-of-two terms," in Proc. European Conf. Circuit Theory Design, Espoo, Finland, Aug. 28-31, 2001.
[70] H. Ohlsson, O. Gustafsson, H. Johansson, and L. Wanhammar, "Implementation of bit-parallel lattice wave digital filters with increased maximal sample rate," in Proc. IEEE Int. Conf. Electronics Circuits Syst., Malta, Sept. 2-5, 2001, vol. 1, pp. 71-74.
[71] O. Gustafsson, H. Johansson, and L. Wanhammar, "Narrow-band and wide-band high-speed recursive digital filters using single filter frequency masking techniques," in Proc. IEEE Int. Symp. Signal Processing, Applications, Kuala-Lumpur, Malaysia, Aug. 13-16, 2001, vol. 1, pp. 36-39.
[72] P. Löwenborg, H. Johansson, and L. Wanhammar, "First-order sensitivity of constant-resistance analog filters with applications to filter banks," in Proc. IEEE Nordic Signal Processing Symp., Hurtigruten, Norway, Oct. 4-7, 2002.
[73] P. Löwenborg and H. Johansson, "Analysis of continuous-time-input SD A/D modulators and their generalizations," in Proc. European Conf. Circuit Theory Design, Krakow, Poland, Sept. 1-4, 2003.
[74] O. Gustafsson, H. Johansson, and L. Wanhammar, "MILP design of frequency-response masking FIR filters with few SPT terms," in Proc. 1st Int. Symp. Control, Commun., Signal Processing, Hammamet, Tunisia, Mar. 2124, 2004.
[75] H. Ohlsson, B. Mesgarzadeh, K. Johansson, O. Gustafsson, P. Löwenborg, H. Johansson, and A. Alvandpour, "A 16 GSPS 0.18mm CMOS decimator for single-bit sigma-delta-modulation," in Proc. 22nd NORCHIP Conf., Oslo, Norway, Nov. 89, 2004.
[76] O. Gustafsson, K. Johansson, H. Johansson, and L. Wanhammar, “Implementation of polyphase decomposed FIR filters for interpolation and decimation using multiple constant multiplication techniques,” in Proc. IEEE Asia Pacific Conf. Circuits Syst., Singapore, Dec. 4–7, 2006.
[77] O. Gustafsson and H. Johansson, “Complexity comparison of linear-phase half-band and general FIR filters,” in Proc. IEEE Asia Pacific Conf. Circuits Syst., Singapore, Dec. 4–7, 2006.
[78] O. Gustafsson and H. Johansson, “Efficient implementation of FIR filter based rational sampling rate converters using constant matrix multiplication,” in Proc. IEEE Asilomar Conf. Signals, Syst., Comp., Pacific Grove, California, USA, Oct. 29 – Nov. 1, 2006.
[79] A. Blad, C. Svensson, H. Johansson, S. Andersson, “An RF Sampling Radio Frontend Based on Sigma-Delta Conversion,” in Proc. IEEE Nordic Event in ASIC Design Conf., Linköping, Sweden, Nov. 20-21, 2006.
[80]H. Johansson and P. Löwenborg, "Reconstruction of nonuniformly sampled bandlimited signals using digital filter banks," Swedish patent 0003549-3, United States Patent 6,476,754. .
[81]H. Johansson, P. Löwenborg, Ulrik Lindblad, and Patrik Thalin, "Estimation of timing errors in a time-interleaved analog-to-digital converter system," patent pending.patent pending.
[82]H. Johansson and P. Löwenborg, “Time-Interleaved Analog-to-Digital Converter System”, patent pending.
The project is funded by Centrum för
industriell informationsteknologi (CENIIT).
