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  • 1.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Contributions to Flexible Multirate Digital Signal Processing Structures2009Licentiate thesis, monograph (Other academic)
    Abstract [en]

    A current focus among communication engineers is to design flexible radio systems in order to handle services among different telecommunication standards. Efficient support of dynamic interactive communication systems requires flexible and cost-efficient radio systems. Thus, low-cost multimode terminals will be crucial building blocks for future generations of multimode communication systems. Here, different bandwidths, from different telecommunication standards, must be supported and, thus, there is a need for a system which can handle a number of different bandwidths. This can be done using multimode transmultiplexers (TMUXs) which make it possible for different users to share a common channel in a time-varying manner. These TMUXs allow bandwidth-on-demand so that the resulting communication system has a dynamic allocation of bandwidth to users. Each user occupies a specific portion of the channel where the location and width of this portion may vary with time.

    Another focus among communication engineers is to provide various wideband services accessible to everybody everywhere. Here, satellites with high-gain spot beam antennas, on-board signal processing, and switching will be a major complementary part of future digital communication systems. Satellites provide a global coverage and if a satellite is in orbit, customers only need to install a satellite terminal and subscribe to the service. Efficient utilization of the available limited frequency spectrum, by these satellites, calls for on-board signal processing to perform flexible frequency-band reallocation (FFBR).

    Considering these two focuses in one integrated system where the TMUXs operate on-ground and FFBR networks operate on-board, one can conclude that successful design of dynamic communication systems requires high levels of flexibility in digital signal processing structures. In other words, there is a need for flexible digital signal processing structures that can support different telecommunication scenarios and standards. This flexibility (or reconfigurability) must not impose restrictions on the hardware and, ideally, it must come at the expense of simple software modifications. In other words, the system is based on a hardware platform and its parameters can easily be modified without the need for hardware changes.

    This thesis aims to outline flexible TMUX and FFBR structures which can allow dynamic communication scenarios with simple software reconfigurations on the same hardware platform. In both structures, the system parameters are determined in advance. For these parameters, the required filter design problems are solved only once. Dynamic communications, with users having different time-varying bandwidths, are then supported by adjusting some multipliers of the proposed multimode TMUXs and a simple software programming in the channel switch of the FFBR network. These do not require any hardware changes and can be performed online. However, the filter design problem is solved only once and offline.

  • 2.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Contributions to Reconfigurable Filter Banks and Transmultiplexers2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    A current focus among communication engineers is to design flexible radio systems to handle services among different telecommunication standards. Thus, lowcost multimode terminals will be crucial building blocks for future generations of multimode communications. Here,  different bandwidths, from different telecommunication standards, must be supported. This can be done using multimode transmultiplexers (TMUXs) which allow different users to share a common channel in a time-varying manner. These TMUXs allow bandwidth-on-demand. Each user occupies a specific portion of the channel whose location and width may vary with time.

    Another focus among communication engineers is to provide various wideband services accessible to everybody everywhere. Here, satellites with high-gain spot beam antennas, on-board signal processing, and switching will be a major complementary part of future digital communication systems. Satellites provide a global coverage and customers only need to install a satellite terminal and subscribe to the service. Efficient utilization of the available limited frequency spectrum, calls for on-board signal processing to perform flexible frequency-band reallocation (FFBR).

    This thesis outlines the design and realization of reconfigurable TMUX and FFBR structures which allow dynamic communication scenarios with simple software reconfigurations. In both structures, the system parameters are determined in advance. For these parameters, the required filter design problems are solved only once. Dynamic communications, with users having different time-varying bandwidths, are then supported by adjusting some multipliers, commutators, or a channel switch. These adjustments do not require hardware changes and can be performed online. However, the filter design problem is solved offline. The thesis provides various illustrative examples and it also discusses possible applications of the proposed structures in the context of other communication scenarios, e.g., cognitive radios.

  • 3.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    A class of reconfigurable and low-complexity two-stage Nyquist filters2014In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 96, p. 164-172Article in journal (Refereed)
    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.

  • 4.
    Eghbali, Amir
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronics System.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Complexity reduction in low-delay Farrow-structure-based variable fractional delay FIR filters utilizing linear-phase subfilters2012Conference paper (Refereed)
    Abstract [en]

    This paper proposes a method to design low-delay fractional delay (FD) filters, using the Farrow structure. The proposed method employs both linear-phase and nonlinear-phase finite-length impulse response (FIR) subfilters. This is in contrast to conventional methods that utilize only nonlinear-phase FIR subfilters. Two design cases are considered. The first case uses nonlinear-phase FIR filters in all branches of the Farrow structure. The second case uses linear-phase FIR filters in every second branch. These branches have milder restrictions on the approximation error. Therefore, even with a reduced order, for these linear-phase FIR filters, the approximation error is not affected. However, the arithmetic complexity, in terms of the number of distinct multiplications, is reduced by an average of 30%. Design examples illustrate the method.

  • 5.
    Eghbali, Amir
    et al.
    Thyselius AB, Huawei Technol. Sweden AB, Gothenburg, Sweden.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Design of Modulated Filter Banks and Transmultiplexers With Unified Initial Solutions and Very Few Unknown Parameters2015In: 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)
    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.

  • 6.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    On Efficient Design of High-Order Filters With Applications to Filter Banks and Transmultiplexers With Large Number of Channels2014In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 62, no 5, p. 1198-1209Article in journal (Refereed)
    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.

  • 7.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Reconfigurable two-stage Nyquist filters utilizing the Farrow structure2012Conference paper (Refereed)
    Abstract [en]

    This paper introduces reconfigurable two-stage finite-length impulse response (FIR) Nyquist filters. In both stages, the Farrow structure realizes reconfigurable lowpass linear-phase FIR Nyquist filters. By adjusting the variable multipliers of the Farrow structure, various FIR Nyquist filters and integer interpolation/decimation structures are obtained, online. However, the filter design problem is solved only once, offline. Design examples illustrate the method.

  • 8.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Gustafsson, Oscar
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Savory, Seb J.
    UCL, England .
    Optimal Least-Squares FIR Digital Filters for Compensation of Chromatic Dispersion in Digital Coherent Optical Receivers2014In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 32, no 8, p. 1449-1456Article in journal (Refereed)
    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.

  • 9.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    A Class of Multimode Transmultiplexers Based on the Farrow Structure2012In: Circuits, systems, and signal processing, ISSN 0278-081X, E-ISSN 1531-5878, Vol. 31, no 3, p. 961-985Article in journal (Refereed)
    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.

  • 10.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    A farrow-structure-based multi-mode transmultiplexer2008In: Proceedings of IEEE International Symposium on Circuits and Systems: Seattle, Washington, USA, May. 18-21, 2008, IEEE , 2008, Vol. June, p. 3114-3117Conference paper (Refereed)
    Abstract [en]

    This paper introduces a multi-mode transmultiplexer (TMUX) consisting of Farrow-based variable integer sampling rate conversion (SRC) blocks. The polyphase components of general interpolation/ decimation filters are realized by the Farrow structure making it possible to achieve different linear-phase finite-length impulse response (FIR) lowpass filters at the cost of a fixed set of subfilters and adjustable fractional delay values. Simultaneous design of the subfilters, to achieve overall approximately Nyquist (Mth-band) filters, are treated in this paper. By means of an example, it is shown that the subfilters can be designed so that for any desired range of integer SRC ratios, the TMUX can approximate perfect recovery as close as desired.

  • 11.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    A Multimode Transmultiplexer Structure2008In: IEEE transactions on circuits and systems. 2, Analog and digital signal processing (Print), ISSN 1057-7130, E-ISSN 1558-125X, Vol. 55, no 3, p. 279-283Article in journal (Refereed)
    Abstract [en]

    This paper introduces a multimode transmultiplexer (TMUX) structure capable of generating a large set of user-bandwidths and center frequencies. The structure utilizes fixed integer sampling rate conversion (SRC) blocks, Farrow-based variable interpolation and decimation structures, and variable frequency shifters. A main advantage of this TMUX is that it needs only one filter design beforehand. Specifically, the filters in the fixed integer SRC blocks as well as the subfilters of the Farrow structure are designed only once. Then, all possible combinations of bandwidths and center frequencies are obtained by properly adjusting the variable delay parameter of the Farrow-based filters and the variable parameters of the frequency shifters. The paper includes examples for demonstration. It also shows that, using the rational SRC equivalent of the Farrow-based filters, the TMUX can be described in terms of conventional multirate building blocks which may be useful in further analysis of the overall system.

  • 12.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    An arbitrary bandwidth transmultiplexer and its application to flexible frequency-band reallocation networks2007In: Proc. European Conf. Circuit Theory Design, Seville, Spain, Aug. 26-30, 2007, IEEE , 2007, p. 248-251Conference paper (Refereed)
    Abstract [en]

    In this paper, we introduce a non-uniform transmultiplexer capable of generating arbitrary-bandwidth user signals. The transmultiplexer consists of linear-phase finite-length impulse response (FIR) filters and Farrow structures for arbitrary-rate interpolation/decimation. By applying the FIR rational sampling rate conversion (SRC) equivalent of the Farrow structure, we model the behavior of the multiplexer and derive the conditions under which the system can approximate perfect reconstruction. Futhermore, we illustrate the functionality of the proposed transmultiplexer and we analyze the performance and functionality of a flexible frequency-band reallocation (FFBR) network using this transmultiplexer.

  • 13.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Flexible Frequency-Band Reallocation: Complex Versus Real2009In: Circuits, systems, and signal processing, ISSN 0278-081X, E-ISSN 1531-5878, Vol. 28, no 3, p. 409-431Article in journal (Refereed)
    Abstract [en]

    This paper discusses a new approach for implementing flexible frequency-band reallocation (FFBR) networks for bentpipe satellite payloads which are based on variable oversampled complex-modulated filter banks (FBs). We consider two alternatives to process real signals using real input/output and complex input/output FFBR networks (or simply real and complex FFBR networks, respectively). It is shown that the real case has a lower overall number of processing units, i.e., adders and multipliers, compared to its complex counterpart. In addition, the real system eliminates the need for two Hilbert transformers, further reducing the arithmetic complexity. An analysis of the computational workload shows that the real case has a smaller rate of increase in the arithmetic complexity with respect to the prototype filter order and number of FB channels. This makes the real case suitable for systems with a large number of users. Furthermore, in the complex case, a high efficiency in FBR comes at the expense of high-order Hilbert transformers; thus, trade-offs are necessary. Finally, the performance of the two alternatives based on the error vector magnitude (EVM) for a 16-quadrature amplitude modulation (QAM) signal is presented.

  • 14.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Flexible frequency-band reallocation MIMO networks for real signals2007In: Proc. Int. Symp. Image, Signal Processing, Analysis, Istanbul, Turkey, Sept. 27-29, 2007, IEEE , 2007, p. 75-80Conference paper (Refereed)
    Abstract [en]

    In this paper, alow-complexity approach to implement a class of flexible frequency-band reallocation (FFBR) multi-input multi-output (MIMO) networks, which use variable oversampled complex-modulated filter banks, is introduced. Two alternatives in processing real signals using real input/output and complex input/output FFBR networks (or simply, real and complex FFBR networks, respectively) are considered. It is shown that to process each sample, the real case requires less number of real operations compared to its complex counterpart. Furthermore, the real case has a smaller growth rate in the number of real operations with respect to the prototype filter order. In addition, the real FFBR network eliminates the need for two Hilbert transformers whereas in the complex FFBR case, to achieve high efficiency in FBR, there is a need for high-order Hilbert transformers.

  • 15.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    On the complexity of multiplierless direct and polyphase FIR filter structures2007In: Proc. Int. Symp. Image, Signal Processing, Analysis, Istanbul, Turkey, Sept. 27-29, 2007, 2007, p. 200-205Conference paper (Refereed)
    Abstract [en]

    This paper discusses the complexity trend in different finite length impulse response (FIR) filter structures when using multiplierless (shift-and-add) realization. We derive the total number of adders required by the transposed direct form, polyphase, and reduced-complexity polyphase FIR filter structures. A comparison of the arithmetic complexities of these structures for different filter characteristics is performed. The simulation results show that considering both the high level structure and the algorithm used to realize the subfilters gives a more accurate measure of complexity comparison between different FIR filter structures.

  • 16.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    On the filter design for a class of multimode transmultiplexers2009In: Proceedings - IEEE International Symposium on Circuits and Systems, 2009, p. 89-92Conference paper (Refereed)
    Abstract [en]

    This paper discusses some issues related to the filter design in a class of multimode transmultiplexers (TMUXs). These TMUXs cover a large set of frequency division multiplexed (FDM) scenarios with simple reconfigurations. The reconfiguration is performed by changing the values of some multipliers. The paper outlines a direct filter design to decrease the level of inter-symbol and inter-carrier interference by the use of time-varying periodic filters. These time-varying periodic filters are derived from the known FDM scenarios and they are included as additional constraints in the filter design. Both minimax and constrained least-squares approaches are treated and it is shown that by including the additional constraints, the level of the TMUX noise can be reduced. This results in a better approximation of perfect reconstruction and makes the filter design direct.

  • 17.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Reconfigurable nonuniform transmultiplexers based on uniform filter banks2010Conference paper (Refereed)
    Abstract [en]

    This paper introduces reconfigurable nonuniform transmultiplexers (TMUXs) based on uniform modulated filter banks (FBs). Polyphase components, of any user, are processed by a number of synthesis FB and analysis FB branches of a uniform TMUX. One branch, of the TMUX, represents one granularity band and any user occupies integer multiples of a granularity band. By adjusting the number of branches, assigned to each user, a nonuniform TMUX is obtained. This only requires adjustable commutators which add no extra arithmetic complexity. The application of both cosine modulated and modified discrete Fourier transform FBs are considered and the formulations related to the appropriate choice of parameters are outlined. Examples are provided for illustration.

  • 18.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Reconfigurable Nonuniform Transmultiplexers Using Uniform Modulated Filter Banks2011In: IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I-REGULAR PAPERS, ISSN 1549-8328, Vol. 58, no 3, p. 539-547Article in journal (Refereed)
    Abstract [en]

    This paper introduces reconfigurable nonuniform transmultiplexers (TMUXs) based on fixed uniform modulated filter banks (FBs). The TMUXs use parallel processing where polyphase components, of any user, are processed by a number of synthesis FB and analysis FB branches. One branch represents one granularity band, and any user can occupy integer multiples of a granularity band. The proposed TMUX also requires adjustable commutators so that any user occupies any portion of the frequency spectrum. The location and width of this portion can be modified without additional arithmetic complexity or filter redesign. This paper considers both cosine modulated and modified discrete Fourier transform FBs. It discusses the filter design, TMUX realization, and the parameter selection. It is shown that one can indeed decrease the arithmetic complexity by proper choice of system parameters. For the critically sampled case and if the number of channels is higher than necessary, we can reduce the arithmetic complexity. In case of an oversampled system, the arithmetic complexity can be reduced by proper choice of the number of channels and the roll-off factor of the prototype filter. The proposed TMUX is compared to existing reconfigurable TMUXs, and examples are provided for illustration.

  • 19.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Göckler, Heinz G
    Ruhr-Universität Bochum, Germany.
    Dynamic Frequency-Band Reallocation and Allocation: from Satellite-Based Communication Systems to Cognitive Radios2011In: Journal of VLSI Signal Processing Systems for Signal, Image and Video Technology, ISSN 0922-5773, E-ISSN 1573-109X, Vol. 62, no 2, p. 187-203Article in journal (Refereed)
    Abstract [en]

    This paper discusses two approaches for the baseband processing part of cognitive radios. These approaches can be used depending on the availability of (i) a composite signal comprising several user signals or, (ii) the individual user signals. The aim is to introduce solutions which can support different bandwidths and center frequencies for a large set of users and at the cost of simple modifications on the same hardware platform. Such structures have previously been used for satellite-based communication systems and the paper aims to outline their possible applications in the context of cognitive radios. For this purpose, dynamic frequencyband allocation (DFBA) and reallocation (DFBR) structures based on multirate building blocks are introduced and their reconfigurability issues with respect to the required reconfigurability measures in cognitive radios are discussed.

  • 20.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Saramaki, Tapio
    Tampere University of Technology, Finland .
    A method for the design of Farrow-structure based variable fractional-delay FIR filters2013In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 93, no 5, p. 1341-1348Article in journal (Refereed)
    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.

  • 21.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Saramäki, Tapio
    Tampere University of Technology, Finland.
    A new structure for reconfigurable two-stage Nyquist pulse shaping filters2011In: Circuits and Systems (MWSCAS), 2011, Piscataway, NJ, United States: IEEE , 2011, p. 1-4Conference paper (Refereed)
    Abstract [en]

    This paper introduces a new structure for reconfigurable two-stage finite-length impulse response (FIR) Nyquist filters using the Farrow structure. The Nyquist filter is split into two equal and linear-phase FIR spectral factors. In the first stage, the Farrow structure realizes reconfigurable lowpass linear-phase FIR interpolation/decimation filters whereas the second stage is composed of a fixed lowpass linear-phase FIR filter. By adjusting the variable multipliers of the Farrow structure, the overall filter can be modified. Hence, various FIR Nyquist filters and integer interpolation/decimation structures are obtained. However, the filter design problem is solved only once and offline. Design examples illustrate the method.

  • 22.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Saramäki, Tapio
    Tampere University of Technology.
    Löwenborg, Per
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    On the design of adjustable fractional delay FIR filters using digital differentiators2010In: Proc. IEEE Int. Conf. Green Circuits Syst., IEEE , 2010, p. 289-292Conference paper (Refereed)
    Abstract [en]

    This paper proposes a systematic method to design adjustable fractional delay (FD) filters using the Farrow structure. The Farrow structure has even-order subfilters and the maximum magnitude approximation error determines the number of these subfilters. In the Farrow structure, different powers of the FD value are multiplied by the subfilters. As both the FD value and its powers are smaller than unity, they are considered as weighting functions. The approximation error for each subfilter can then increase in proportion to the power of the FD value. With the proposed design method, the first Farrow subfilter is a pure delay whereas the remaining subfilters are digital differentiators. Examples illustrate the proposed design method and comparison to some earlier designs shows an average reduction of 20% in arithmetic complexity.

  • 23.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Saramaki, T.
    Tampere University of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    On two-stage Nyquist pulse shaping filters2012In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, no 1, p. 483-488Article in journal (Refereed)
    Abstract [en]

    This correspondence outlines a method for designing two-stage Nyquist filters. The Nyquist filter is split into two equal and linear-phase finite-length impulse response spectral factors. The per-time-unit multiplicative complexity, of the overall structure, is included as the objective function. Examples are then provided where Nyquist filters are designed so as to minimize the multiplicative complexity subject to the constraints on the overall Nyquist filter. In comparison to the single-stage case, the two-stage realization reduces the multiplicative complexity by an average of 48%. For two-stage sampling rate conversion (SRC), the correspondence shows that it is better to have a larger SRC ratio in the first stage. © 2006 IEEE.

  • 24.
    Eghbali, Amir
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Saramaki, Tapio
    Tampere University of Technology, Finland .
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Conditions for Lth-band filters of order 2N as cascades of identical linear-phase FIR spectral factors of order N2014In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 97, no AprilArticle in journal (Refereed)
    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.

  • 25.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    A realization of FIR filters with simultaneously variable bandwidth and fractional delay2012In: Signal Processing Conference (EUSIPCO), 2012, IEEE , 2012, p. 2178-2182Conference paper (Refereed)
    Abstract [en]

    This paper introduces a realization of finite-length impulse response (FIR) filters with simultaneously variable bandwidth and fractional delay (FD). The realization makes use of impulse responses which are two-dimensional polynomials in the bandwidth and FD parameters. Unlike previous polynomial-based realizations, it utilizes the fact that a variable FD filter is typically much less complex than a variable-bandwidth filter. By separating the corresponding subfilters in the overall realization, significant savings are thereby achieved. A design example, included in the paper, shows about 65 percent multiplication and addition savings compared to the previous polynomial-based realizations. Moreover, compared to a recently introduced alternative fast filter bank approach, the proposed method offers significantly smaller group delays and group delay errors.

  • 26.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, The Institute of Technology.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Add-Equalize Structures for Linear-Phase Nyquist FIR Filter Interpolators and Decimators2014In: 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)
    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.

  • 27.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    FIR Filter With Variable Fractional Delay and Phase Shift: Efficient Realization and Design Using Reweighted l(1)-Norm Minimization2013Conference 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.

  • 28.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Two Polynomial FIR Filter Structures With Variable Fractional Delay and Phase Shift2014In: 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)
    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.

  • 29.
    Johansson, Håkan
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Lahti, Jimmie
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Tree-Structured Linear-Phase Nyquist FIR Filter Interpolators and Decimators2012In: 2012 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS 2012), IEEE , 2012, p. 2329-2332Conference paper (Refereed)
    Abstract [en]

    This paper introduces a new class of linear-phase Nyquist (Mth-band) FIR interpolators and decimators based on tree structures. Through design examples, it is shown that the proposed converter structures have a substantially lower computational complexity than the conventional single-stage converter structures. The complexity is comparable to that of multi-stage Nyquist converters, although the proposed ones tend to have a somewhat higher complexity. A main advantage of the proposed structures is however that they can be used for arbitrary integer conversion factors, thus including prime numbers which cannot be handled by the regular multi-stage Nyquist converters.

  • 30.
    Mehdi, Ghulam
    et al.
    CESAT, Islamabad, Pakistan.
    Ahsan, Naveed
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Altaf, Amjad
    CESAT, Islamabad, Pakistan.
    Eghbali, Amir
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering.
    A 403-MHz fully differential class-E amplifier in 0.35 um CMOS for ISM band applications2008In: IEEE East-West Design Test Symposium 2008,2008, 2008, p. 239-242Conference paper (Refereed)
  • 31.
    Sheikh, Zaka Ullah
    et al.
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Eghbali, Amir
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Johansson, Håkan
    Linköping University, Department of Electrical Engineering, Electronics System. Linköping University, The Institute of Technology.
    Linear-Phase FIR Digital Differentiator Order Estimation2011In: Proceedings of The 20th European Conference on Circuit Theory and Design, ECCTD2011, 2011, p. 310-313Conference paper (Refereed)
    Abstract [en]

    Commonly used design procedures for design of digital differentiators are based on various optimization techniques and are also iterative in nature. The order estimation, for differentiators is important from design point of view as it can help in reducing the design time by providing a good initial guess of the order to the iterative design procedures. Moreover, order estimation helps in giving a fairly good estimation of the computational complexity in the overall design. This paper presents the linear-phase, finite-length impulse response (FIR) filter order estimation for integral degree differentiators of up to fourth degree. The minimax optimization based technique for the filter design and the curve fitting is used.

1 - 31 of 31
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