| 1. |
- Andgart, Niklas, et al.
(författare)
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PSD-constrained PAR reduction for DMT/OFDM
- 2004
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Ingår i: Eurasip Journal on Applied Signal Processing. - 1110-8657. ; 2004:10
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Tidskriftsartikel (refereegranskat)abstract
- Common to all DMT/OFDM systems is a large peak-to-average ratio (PAR), which can lead to low power efficiency and nonlinear distortion. Tone reservation uses unused or reserved tones to design a peak-canceling signal to lower the PAR of a transmit block. In DMT ADSL systems, the power allocated to these tones may be limited due to crosstalk issues with many users in one twisted pair bundle. This PSD limitation not only limits PAR reduction ability, but also makes the optimization problem more challenging to solve. Extending the recently proposed active set tone reservation method, we develop an efficient algorithm with performance close to the optimal solution.
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| 2. |
- Isaksson, Ola, et al.
(författare)
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Trends in product modelling : an ENDREA perspective
- 2000
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Ingår i: Proceedings / Produktmodeller 2000. - Linköping : Linköping universitet.
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Konferensbidrag (refereegranskat)abstract
- The success of engineering companies is highly dependent on how well product information is managed, engineered and communicated. From marketing through development to after sales activities, data needs to be accessible and used in the best way. Today, geographical distance, the need for close co-operation and data complexity are all natural parts of the working environment. Product modelling techniques are continuously evolving with new requirements and opportunities emerging daily. This paper will outline and discuss some of these trends, and at the same time present some of the areas where research is being carried out within projects in the Product Model Cluster in the national graduate school - The Swedish Engineering Design Research and Education Agenda (ENDREA).
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| 3. |
- Olsson, Jan-Ola, et al.
(författare)
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Closed-loop System Identification of an HCCI Engine
- 2004
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Ingår i: Advances in Automotive Control. - 0080442501 ; 37:22, s. 239-244
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Konferensbidrag (refereegranskat)abstract
- Homogeneous Charge Compression Ignition (HCCI) is a promising but challenging combustion engine concept. The potential for good fuel economy and low emissions is high but the transient performance required for automotive applications presents a few problems still to be solved. The focus of this work is identification of the process dynamics. An ARX type model is fitted to input-output data. A method applicable under closed-loop control is suggested and demonstrated. The resulting models are evaluated in terms of the repeatability of model characteristics, prediction accuracy, residual characteristics and comparison to spectral models is made.
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| 4. |
- Petersson, Niklas, et al.
(författare)
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A performance bound on PSD-constrained PAR reduction
- 2003
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Ingår i: 2003 IEEE International Conference on Communications (Cat. No.03CH37441). - 0780378024 ; , s. 3498-3502
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Konferensbidrag (refereegranskat)abstract
- Communication systems using multicarrier modulation suffer from a high peak-to-peak ratio, PAR. In this work we use the tone reservation approach to PAR reduction, where a subset of the tones are used for PAR reduction. We derive a bound on the achievable performance under a PSD constraint on the transmit signal. Using this bound, we show that as long as a moderate reduction performance is needed, this could be achieved with an almost arbitrary selection of the PAR reduction tones. This bounding technique also demonstrates that, applied to an ADSL-like system, the tone reservation approach could be used for PAR reduction down to about 12 dB, considering critically sampled signals
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| 5. |
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| 6. |
- Pfeiffer, Roland, et al.
(författare)
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System Identification and LQG Control of Variable-Compression HCCI Engine Dynamics
- 2004
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Ingår i: Proceedings of the 2004 IEEE International Conference on Control Applications.. - 1085-1992. - 0780386337 ; 2, s. 1442-1447
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Konferensbidrag (refereegranskat)abstract
- The Homogenous Charge Compression Ignition (HCCI) combustion engine has potential to replace the spark ignition and compression ignition engines of today. One of the main problems in making the engine commercially attractive is the lack of direct means of controlling the ignition phasing. In this paper, we investigate the potential of inlet air temperature as a means to ignition actuation. This article describes a method for system identification of the HCCI process, and development of an effective LQG regulator for the combustion process, Matlab and Simulink being used in computations and simulations.
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| 7. |
- Tunestål, Per, et al.
(författare)
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Closed-Loop Combustion Control of HCCI Engines
- 2003
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Ingår i: Nonlinear and Hybrid Systems in Automotive Control. ; , s. 321-334
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The HCCI engine, with its excellent potential for high efficiency and low NOx emissions, is investigated from a control perspective. Combustion timing, i.e., where in the thermodynamic cycle combustion takes place, is identified as the most challenging problem with HCCI engine control. A number of different means for controlling combustion timing are suggested, and results using a dual-fuel solution are presented. This solution uses two fuels with different ignition characteristics to control the time of autoignition. Cylinder pressure measurement is suggested for feedback of combustion timing. A simple net-heat release algorithm is applied to the measurements, and the crank angle of 50% burnt is extracted. Open-loop instability is detected in some high-load regions of the operating range. This phenomenon is explained by positive feedback between the cylinder wall heating and ignition timing processes. Closed-loop performance is hampered by time delays and model uncertainties. This problem is particularly pronounced at operating points that are open-loop unstable.
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| 8. |
- Ödling, Per, et al.
(författare)
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How much PAR to bring to the party?
- 2002
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Ingår i: Proceedings of the 5th Nordic Signal Processing Symposium.
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Konferensbidrag (refereegranskat)abstract
- Reducing Peak-to-Average power Ratios (PAR) is an established research topic that has now begun to find its way into products. This gives rise to new questions of dimensioning. Here we address how much PAR reduction that should be applied in a practical system. We demonstrate that the amount of PAR reduction can be found with the appropriate system models. This is applied to the tonereservation PAR reduction method in an ADSL system. In some frequency regions, the SNR is in practice often limited by the dynamic of the transmitter’s analog frontend. Other frequency regions are strongly attenuated by the channel and contribute very little to the system’s capacity. Using multicarrier modulation, we address how much of the spectrum that could be used to improve the SNR in the other regions by reducing the amplitude swing of the transmit signal.
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| 9. |
- Ödling, Per, et al.
(författare)
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The Cyclic Prefix of OFDM/DMT - An Analysis
- 2002
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Ingår i: Proceedings of the 2002 International Zurich Seminar on Broadband Communications (IZS 2002).
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Konferensbidrag (refereegranskat)abstract
- We address the impact of a too short cyclic prefix on multicarrier systems such as orthogonal frequency division multiplexing (OFDM) and discrete multitone (DMT). The main result is that the intersymbol interference (ISI) and intercarrier interference (ICI) may be spectrally concentrated and analytical expressions showing this are given. A practical implication is, e.g., that the cyclic prefix in some xDSL systems can be surprisingly short, as shown in one example of ADSL transmission
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| 10. |
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