| 1. |
- Eghbali, Amir, et al.
(författare)
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A Class of Multimode Transmultiplexers Based on the Farrow Structure
- 2012
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Ingår i: Circuits, systems, and signal processing. - : Springer Verlag (Germany). - 0278-081X .- 1531-5878. ; 31:3, s. 961-985
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Eghbali, Amir, et al.
(författare)
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A class of reconfigurable and low-complexity two-stage Nyquist filters
- 2014
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Ingår i: Signal Processing. - : Elsevier. - 0165-1684 .- 1872-7557. ; 96, s. 164-172
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Eghbali, Amir, et al.
(författare)
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A farrow-structure-based multi-mode transmultiplexer
- 2008
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Ingår i: Proceedings of IEEE International Symposium on Circuits and Systems. - : IEEE. - 9781424416844 - 9781424416837 ; , s. 3114-3117
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 4. |
- Eghbali, Amir, et al.
(författare)
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A method for the design of Farrow-structure based variable fractional-delay FIR filters
- 2013
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Ingår i: Signal Processing. - : Elsevier. - 0165-1684 .- 1872-7557. ; 93:5, s. 1341-1348
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Eghbali, Amir, et al.
(författare)
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A Multimode Transmultiplexer Structure
- 2008
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Ingår i: IEEE transactions on circuits and systems. 2, Analog and digital signal processing (Print). - : Institutionen för systemteknik. - 1057-7130 .- 1558-125X. ; 55:3, s. 279-283
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Eghbali, Amir, 1980-, et al.
(författare)
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A new structure for reconfigurable two-stage Nyquist pulse shaping filters
- 2011
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Ingår i: Circuits and Systems (MWSCAS), 2011. - Piscataway, NJ, United States : IEEE. - 9781612848563 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 7. |
- Eghbali, Amir, et al.
(författare)
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An arbitrary bandwidth transmultiplexer and its application to flexible frequency-band reallocation networks
- 2007
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Ingår i: Proc. European Conf. Circuit Theory Design, Seville, Spain, Aug. 26-30, 2007. - : IEEE. - 9781424413416 - 9781424413423 ; , s. 248-251
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Eghbali, Amir, 1980-, et al.
(författare)
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Complexity reduction in low-delay Farrow-structure-based variable fractional delay FIR filters utilizing linear-phase subfilters
- 2012
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 9. |
- Eghbali, Amir, et al.
(författare)
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Conditions for Lth-band filters of order 2N as cascades of identical linear-phase FIR spectral factors of order N
- 2014
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Ingår i: Signal Processing. - : Elsevier. - 0165-1684 .- 1872-7557. ; 97:April
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Eghbali, Amir, 1980-
(författare)
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Contributions to Flexible Multirate Digital Signal Processing Structures
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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