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Eghbali, Amir
Publications (10 of 31) Show all publications
Eghbali, A. & Johansson, H. (2015). Design of Modulated Filter Banks and Transmultiplexers With Unified Initial Solutions and Very Few Unknown Parameters. IEEE Transactions on Circuits and Systems - II - Express Briefs, 62(4), 397-401
Open this publication in new window or tab >>Design of Modulated Filter Banks and Transmultiplexers With Unified Initial Solutions and Very Few Unknown Parameters
2015 (English)In: IEEE Transactions on Circuits and Systems - II - Express Briefs, ISSN 1549-7747, E-ISSN 1558-3791, Vol. 62, no 4, p. 397-401Article in journal (Refereed) Published
Abstract [en]

This brief proposes a method for designing modulated filter banks (FBs) with a large number of channels. The impulse response of the long prototype filter is parameterized in terms of a few short impulse responses, thus significantly reducing the number of unknown parameters. The proposed method starts by first obtaining an FB with a few channels. The solution of this FB is then partly reused as an initial (very close to final) solution in the design of FBs with a large number of channels. The number of unknown parameters hence drastically reduces. For example, we can first design a cosine modulated FB (CMFB) with three channels whose prototype filter has a stopband attenuation of about 40 dB. We can then reuse the solution of this CMFB in the design of a CMFB with 16 384 channels whose prototype filter has a similar stopband attenuation. With our proposed method, we need to reoptimize only 14 parameters to design the CMFB with 16 384 channels.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2015
Keywords
Filter banks (FBs); filter design; linear-phase filters; transmultiplexers (TMUXs)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-117648 (URN)10.1109/TCSII.2014.2387678 (DOI)000352306200017 ()
Available from: 2015-05-12 Created: 2015-05-06 Last updated: 2017-12-04Bibliographically approved
Eghbali, A. & Johansson, H. (2014). A class of reconfigurable and low-complexity two-stage Nyquist filters. Signal Processing, 96, 164-172
Open this publication in new window or tab >>A class of reconfigurable and low-complexity two-stage Nyquist filters
2014 (English)In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 96, p. 164-172Article in journal (Refereed) Published
Abstract [en]

This paper introduces a class of reconfigurable two-stage Nyquist filters where the Farrow structure realizes the polyphase components of linear-phase finite-length impulse response (FIR) filters. By adjusting the variable predetermined multipliers of the Farrow structure, various linear-phase FIR Nyquist filters and integer interpolation/decimation structures are obtained, online. However, the filter design problem is solved only once, offline. Design examples, based on the reweighted l(1)-norm minimization, illustrate the proposed method. Savings in the arithmetic complexity are obtained when compared to the reconfigurable single-stage structures.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Pulse shaping; Nyquist filter; Sampling rate conversion
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-104642 (URN)10.1016/j.sigpro.2013.09.024 (DOI)000330203500004 ()
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2017-12-06
Johansson, H. & Eghbali, A. (2014). Add-Equalize Structures for Linear-Phase Nyquist FIR Filter Interpolators and Decimators. IEEE Transactions on Circuits and Systems Part 1: Regular Papers, 61(6), 1766-1777
Open this publication in new window or tab >>Add-Equalize Structures for Linear-Phase Nyquist FIR Filter Interpolators and Decimators
2014 (English)In: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 61, no 6, p. 1766-1777Article in journal (Refereed) Published
Abstract [en]

This paper introduces add-equalize structures for the implementation of linear-phase Nyquist (th-band) finite-length impulse response (FIR) filter interpolators and decimators. The paper also introduces a systematic design technique for these structures based on iteratively reweighted -norm minimization. In the proposed structures, the polyphase components share common parts which leads to a considerably lower implementation complexity as compared to conventional single-stage converter structures. The complexity is comparable to that of multi-stage Nyquist structures. A main advantage of the proposed structures is that they work equally well for all integer conversion factors, thus including prime numbers which cannot be handled by the regular multi-stage Nyquist converters. Moreover, the paper shows how to utilize the frequency-response masking approach to further reduce the complexity for sharp-transition specifications. It also shows how the proposed structures can be used to reduce the complexity for reconfigurable sampling rate converters. Several design examples are included to demonstrate the effectiveness of the proposed structures.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2014
Keywords
FIR filters; fractional-delay filters; interpolation and decimation; l(1)-norm minimization; linear-phase filters; low complexity; Nyquist filters
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-108799 (URN)10.1109/TCSI.2013.2295021 (DOI)000337152900015 ()
Available from: 2014-07-07 Created: 2014-07-06 Last updated: 2017-12-05Bibliographically approved
Eghbali, A., Saramaki, T. & Johansson, H. (2014). Conditions for Lth-band filters of order 2N as cascades of identical linear-phase FIR spectral factors of order N. Signal Processing, 97(April)
Open this publication in new window or tab >>Conditions for Lth-band filters of order 2N as cascades of identical linear-phase FIR spectral factors of order N
2014 (English)In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 97, no AprilArticle in journal (Refereed) Published
Abstract [en]

This paper presents formulas for the number of optimization parameters (degrees of freedom) when designing Type I linear-phase finite-length impulse response (FIR) Lth-band filters of order 2N as cascades of identical linear-phase FIR spectral factors of order N. We deal with two types of degrees of freedom referred to as (i) the total degrees of freedom D-T, and (ii) the remaining degrees of freedom D-R. Due to the symmetries or antisymmetries in the impulse responses of the spectral factors, D-T roughly equals N/2. Some of these parameters are specifically needed to meet the Lth-band conditions because, in an Lth-band filter, every Lth coefficient is zero and the center tap equals 1/L. The remaining D-R parameters can then be used to improve the stopband characteristics of the overall Lth-band filter. We derive general formulas for D-R with given pairs of L and N. It is shown that for a fixed L, the choices of N, in a close neighborhood, may even decrease D-R despite increasing the arithmetic complexity, order, and the delay.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Pulse shaping; Lth-band filters; Spectral factors; FIR filters; Linear-phase
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-105405 (URN)10.1016/j.sigpro.2013.10.013 (DOI)000331506000001 ()
Available from: 2014-03-21 Created: 2014-03-21 Last updated: 2017-12-05
Eghbali, A. & Johansson, H. (2014). On Efficient Design of High-Order Filters With Applications to Filter Banks and Transmultiplexers With Large Number of Channels. IEEE Transactions on Signal Processing, 62(5), 1198-1209
Open this publication in new window or tab >>On Efficient Design of High-Order Filters With Applications to Filter Banks and Transmultiplexers With Large Number of Channels
2014 (English)In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 62, no 5, p. 1198-1209Article in journal (Refereed) Published
Abstract [en]

This paper proposes a method for designing high-order linear-phase finite-length impulse response (FIR) filters which are required as, e.g., the prototype filters in filter banks (FBs) and transmultiplexers (TMUXs) with a large number of channels. The proposed method uses the Farrow structure to express the polyphase components of the desired filter. Thereby, the only unknown parameters, in the filter design, are the coefficients of the Farrow subfilters. The number of these unknown parameters is considerably smaller than that of the direct filter design methods. Besides these unknown parameters, the proposed method needs some predefined multipliers. Although the number of these multipliers is larger than the number of unknown parameters, they are known a priori. The proposed method is generally applicable to any linear-phase FIR filter irrespective of its order being high, low, even, or odd as well as the impulse response being symmetric or antisymmetric. However, it is more efficient for filters with high orders as the conventional design of such filters is more challenging. For example, to design a linear-phase FIR lowpass filter of order 131071 with a stopband attenuation of about 55 dB, which is used as the prototype filter of a cosine modulated filter bank (CMFB) with 8192 channels, our proposed method requires only 16 unknown parameters. The paper gives design examples for individual lowpass filters as well as the prototype filters for fixed and flexible modulated FBs.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2014
Keywords
Filter design; linear-phase FIR filters; filter banks; transmultiplexers; Farrow structure
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-105576 (URN)10.1109/TSP.2014.2299520 (DOI)000332034500013 ()
Available from: 2014-03-31 Created: 2014-03-27 Last updated: 2017-12-05
Eghbali, A., Johansson, H., Gustafsson, O. & Savory, S. J. (2014). Optimal Least-Squares FIR Digital Filters for Compensation of Chromatic Dispersion in Digital Coherent Optical Receivers. Journal of Lightwave Technology, 32(8), 1449-1456
Open this publication in new window or tab >>Optimal Least-Squares FIR Digital Filters for Compensation of Chromatic Dispersion in Digital Coherent Optical Receivers
2014 (English)In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 32, no 8, p. 1449-1456Article in journal (Refereed) Published
Abstract [en]

This paper proposes optimal finite-length impulse response (FIR) digital filters, in the least-squares (LS) sense, for compensation of chromatic dispersion (CD) in digital coherent optical receivers. The proposed filters are based on the convex minimization of the energy of the complex error between the frequency responses of the actual CD compensation filter and the ideal CD compensation filter. The paper utilizes the fact that pulse shaping filters limit the effective bandwidth of the signal. Then, the filter design for CD compensation needs to be performed over a smaller frequency range, as compared to the whole frequency band in the existing CD compensation methods. By means of design examples, we show that our proposed optimal LS FIR CD compensation filters outperform the existing filters in terms of performance, implementation complexity, and delay.

Place, publisher, year, edition, pages
Optical Society of America, 2014
Keywords
Chromatic dispersion (CD); digital filter; fiber optics; optimal least-squares (LS) FIR filter
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106013 (URN)10.1109/JLT.2014.2307916 (DOI)000332966300004 ()
Available from: 2014-04-17 Created: 2014-04-17 Last updated: 2017-12-05
Johansson, H. & Eghbali, A. (2014). Two Polynomial FIR Filter Structures With Variable Fractional Delay and Phase Shift. IEEE Transactions on Circuits and Systems Part 1: Regular Papers, 61(5), 1355-1365
Open this publication in new window or tab >>Two Polynomial FIR Filter Structures With Variable Fractional Delay and Phase Shift
2014 (English)In: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 61, no 5, p. 1355-1365Article in journal (Refereed) Published
Abstract [en]

This paper introduces two polynomial finite-length impulse response (FIR) digital filter structures with simultaneously variable fractional delay (VFD) and phase shift (VPS). The structures are reconfigurable (adaptable) online without redesign and do not exhibit transients when the VFD and VPS parameters are altered. The structures can be viewed as generalizations of VFD structures in the sense that they offer a VPS in addition to the regular VFD. The overall filters are composed of a number of fixed subfilters and a few variable multipliers whose values are determined by the desired FD and PS values. A systematic design algorithm, based on iteratively reweighted l(1)- norm minimization, is proposed. It generates fixed subfilters with many zero-valued coefficients, typically located in the impulse response tails. The paper considers two different structures, referred to as the basic structure and common-subfilters structure, and compares these proposals as well as the existing cascaded VFD and VPS structures, in terms of arithmetic complexity, delay, memory cost, and transients. In general, the common-subfilters structure is superior when all of these aspects are taken into account. Further, the paper shows and exemplifies that the VFDPS filters under consideration can be used for simultaneous resampling and frequency shift of signals.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2014
Keywords
l(1)-norm minimization; finite-length impulse response (FIR) filters; frequency shift; low complexity; polynomial impulse responses; resampling; variable fractional delay; variable phase shift
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-107116 (URN)10.1109/TCSI.2014.2309863 (DOI)000335566500007 ()
Available from: 2014-06-05 Created: 2014-06-05 Last updated: 2017-12-05
Eghbali, A., Johansson, H. & Saramaki, T. (2013). A method for the design of Farrow-structure based variable fractional-delay FIR filters. Signal Processing, 93(5), 1341-1348
Open this publication in new window or tab >>A method for the design of Farrow-structure based variable fractional-delay FIR filters
2013 (English)In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 93, no 5, p. 1341-1348Article in journal (Refereed) Published
Abstract [en]

This paper proposes a method to design variable fractional-delay (FD) filters using the Farrow structure. In the transfer function of the Farrow structure, different subfilters are weighted by different powers of the FD value. As both the FD value and its powers are smaller than 0.5, our proposed method uses them as diminishing weighting functions. The approximation error, for each subfilter, is then increased in proportion to the power of the FD value. This gives a new distribution for the orders of the Farrow subfilters which has not been utilized before. This paper also includes these diminishing weighting functions in the filter design so as to obtain their optimal values, iteratively. We consider subfilters of both even and odd orders. Examples illustrate our proposed method and comparisons, to various earlier designs, show a reduction of the arithmetic complexity.

Place, publisher, year, edition, pages
Elsevier, 2013
Keywords
Farrow structure; Fractional-delay
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96151 (URN)10.1016/j.sigpro.2012.11.010 (DOI)000316586300029 ()
Available from: 2013-08-14 Created: 2013-08-14 Last updated: 2017-12-06
Johansson, H. & Eghbali, A. (2013). FIR Filter With Variable Fractional Delay and Phase Shift: Efficient Realization and Design Using Reweighted l(1)-Norm Minimization. In: : . Paper presented at 2013 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS) (pp. 81-84). IEEE
Open this publication in new window or tab >>FIR Filter With Variable Fractional Delay and Phase Shift: Efficient Realization and Design Using Reweighted l(1)-Norm Minimization
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This paper introduces a finite-length impulse response (FIR) digital filter having both a variable fractional delay (VFD) and a variable phase shift (VPS). The realization is reconfigurable online without redesign and without transients. It can be viewed as a generalization of the VFD Farrow structure that offers a VPS in addition to the regular VFD. The overall filter is composed of a number of fixed subfilters and a few variable multipliers whose values are determined by the desired FD and PS values. It is designed offline in an iterative manner, utilizing reweighted l(1)-norm minimization. This design procedure generates fixed subfilters with many zero-valued coefficients, typically located in the impulse response tails.

Place, publisher, year, edition, pages
IEEE, 2013
Series
INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS), ISSN 0271-4302 ; 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106530 (URN)10.1109/ISCAS.2013.6571787 (DOI)000332006800021 ()978-1-4673-5760-9 (ISBN)
Conference
2013 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS)
Available from: 2014-05-12 Created: 2014-05-09 Last updated: 2014-12-03
Eghbali, A., Johansson, H. & Löwenborg, P. (2012). A Class of Multimode Transmultiplexers Based on the Farrow Structure. Circuits, systems, and signal processing, 31(3), 961-985
Open this publication in new window or tab >>A Class of Multimode Transmultiplexers Based on the Farrow Structure
2012 (English)In: Circuits, systems, and signal processing, ISSN 0278-081X, E-ISSN 1531-5878, Vol. 31, no 3, p. 961-985Article in journal (Refereed) Published
Abstract [en]

This paper introduces multimode transmultiplexers (TMUXs) in which the Farrow structure realizes the polyphase components of general lowpass interpolation/decimation filters. As various lowpass filters are obtained by one set of common Farrow subfilters, only one offline filter design enables us to cover different integer sampling rate conversion (SRC) ratios. A model of general rational SRC is also constructed where the same fixed subfilters perform rational SRC. These two SRC schemes are then used to construct multimode TMUXs. Efficient implementation structures are introduced and different filter design techniques such as minimax and least-squares (LS) are discussed. By means of simulation results, it is shown that the performance of the transmultiplexer (TMUX) depends on the ripples of the filters. With the error vector magnitude (EVM) as the performance metric, the LS method has a superiority over the minimax approach.

Place, publisher, year, edition, pages
Springer Verlag (Germany), 2012
Keywords
Multistandard communications, Transmultiplexers, Sampling rate conversion, Farrow structure
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-77317 (URN)10.1007/s00034-011-9351-4 (DOI)000302740700009 ()
Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2017-12-07
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