| 11. |
- Johansson, Sven, et al.
(författare)
-
Active Control of Sound using the Actuator-Individual Normalized Filtered-X LMS Algorithm
- 2001
-
Konferensbidrag (refereegranskat)abstract
- The control algorithm is a central part of an active noise control system. The computational power of the DSP hardware is limited, and therefore algorithms with high computational complexity allow fewer control sources and sensors to be used, often with reduced noise attenuation as a result. This paper presents results from practical experiments using an ANC system based on the actuator-individual normalized Filtered-X LMS algorithm. The algorithm combines low computational complexity with high performance. For that reason the algorithm is suitable for use in large multi-channel systems in order to reduce the computional power required by the control system.
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| 12. |
- Johansson, Sven, et al.
(författare)
-
Algoritmer för aktiv bullerundertryckning i propellerflygplan
- 1997
-
Konferensbidrag (refereegranskat)abstract
- I många praktiska tillämpningar generas buller av roterande maskiner, t.ex. av kompressorer, fläktar, motorer och propellrar. Detta buller består huvudsakligen av periodiska komponenter, grundton med tillhörande övertoner. Vid denna typ av tillämpningar där bullret är lågfrekvent och periodiskt är det lämpligt att använda aktiv bullerreglering. Aktiva system baserade på framkopplad reglerteknik har visat sig ge en bra undertryckning av denna typ av buller. Ett framkopplat reglersystem behöver en synkroniseringssignal från den buller alstrande källan. Denna signal används sedan för att generera referenssignaler innehållande de frekvenser man vill undertrycka. Med hjälp av referenssignalerna generar reglersystemet ett ljudfält som är lika starkt som bullret och i motfas med detta. På detta sätt erhålls en reducering av bullret. För att ställa in den adaptiva regulatorn så att bästa möjliga undertryckning erhålls används reglermikrofoner som mäter det erhållna ljudtrycket. För att erhålla god undertryckning är det viktigt att referenssignalerna är väl korrelerade med bullret. I applikationer där endast en eller flera korrelerade källor bidrar till bullret räcker det att använda ett reglersystem baserat på en synkroniseringssignal, dvs ett enreferenssystem. Är det flera okorrelerade bullerkällor är det emellertid nödvändigt att använda en synkroniseringssignal från varje källa för att erhålla effektiv bullerundertryckning, dvs ett flerreferenssystem. I propellerflygplan härrör bullret huvudsakligen från propellrarna och de dominerande frekvenskomponenterna kan relateras till propellrarnas bladpassagefrekvenser (BPF) samt deras övertoner. Idag är de flesta tvåmotoriga flygplan utrustade med en synkroniseringsenhet, som synkroniserar propellrarnas varvtal. När propellrarna är synkroniserade kan de betraktas som fullständigt korrelerade, vilket medför att ett enreferenssystem kan användas för att åstadkomma en effektiv bullerundertryckning. I situationer där propellrarna är osynkroniserade skiljer sig propellrarnas varvtal åt och propellrarna kan nu betraktas som två okorrelerade källor. I dessa fall bör ett flerreferenssystem användas, eftersom denna regulatortyp kan följa varvtalsförändringar hos båda propellrarna. I denna presentation görs en jämförelse mellan prestanda för ett enreferenssystem och ett flerreferenssystem. Utvärderingen görs för två olika flygsituationer, synkroniserade respektive osynkroniserade propellrar.
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| 13. |
- Johansson, Sven, et al.
(författare)
-
Comparison of Multiple- and Single-Reference MIMO Active Noise Control Approaches Using Data Measured in a Dornier 328 Aircraft
- 2000
-
Ingår i: International Journal of Acoustics and Vibration. - : Int. Inst. of Acoustics and Vibration (IIAV). - 1027-5851 .- 2415-1408. ; 5:4, s. 77-88
-
Tidskriftsartikel (refereegranskat)abstract
- In many applications of noise control, the greatest annoyance is caused by periodic low frequency noise. Successful reduction of such noise can often be achieved by using an active noise control system with narrowband feedforward control. If several noise sources contribute to the sound field, a multiple-reference control system is usually required. This type of system allows the reference signals from each noise source to be processed individually within the controller, thereby enabling individual control of the sound field from each noise source. The present paper addresses the problem of controlling noise from two sources that are more or less synchronized. A typical application is the control of propeller-generated noise within a twin propeller aircraft. To find out whether a multiple-reference controller is necessary, or if a single-reference controller is sufficient, the performance of a single- versus twin-reference control algorithm is evaluated in a comparative study. The study is performed as a computer simulation (off-line evaluation) using real-life data recorded in a Dornier 328 under different flight conditions. The results demonstrate that the twin-reference controller performs better than the single-reference whenever there is a slight deviation in the rotational speed of the two propellers. The paper also treats the generation of reference signals. The approach presented is based on a fixed sampling rate and uses a sliding FFT filtering technique.
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| 14. |
- Johansson, Sven, et al.
(författare)
-
CONTROL APPROACHES FOR ACTIVE NOISE CONTROL OF PROPELLER-INDUCED CABIN NOISE EVALUATED FROM DATA FROM A DORNIER 328 AIRCRAFT
- 1999
-
Konferensbidrag (refereegranskat)abstract
- In many applications of noise control, the greatest annoyance is caused by periodic low frequency noise. Successful reduction of such noise can often be achieved by using an Active Noise Control (ANC) system with narrowband feedforward control. If several noise sources contribute to the sound field, a multiple-reference control system is usually required. This system allows the reference signals from each noise source to be processed individually within the controller, thereby enabling individual control of the sound field from each noise source. This paper presents a mukiple-reference control algorithm and addresses the problem of controlling noise from two sources that are more or less synchronized. A typical application is the control of propeller-generated noise within a twin propeller aircraft. To find out whether a multiple-reference controller is necessary, or if a single-reference controller can do the job, the performance of a single- versus twin-tacho control algorithm was evaluated in a comparative study. The study is a computer simulation using real life data recorded in a Domier 328 under different flight conditions. The results demonstrate that the twin-tacho controller performs better than the single-tacho whenever there is a slight deviation in the rotational speed of the two propellers.
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| 15. |
- Johansson, Sven, et al.
(författare)
-
Convergence Analysis of a Twin-Reference Complex Least-Mean-Squares Algorithm
- 2002
-
Ingår i: IEEE transactions on speech and audio processing. - : IEE/IEEE. - 1063-6676 .- 1558-2353. ; 10:4, s. 213-221
-
Tidskriftsartikel (refereegranskat)abstract
- In many noise control applications, the noise is dominated by low frequencies and generated by several independent periodic sources. In such situations the tonal noise may be suppressed by using a narrowband multiple-reference feedforward controller. The performance characteristics of the control system, e.g., the convergence behavior and noise reduction are directly related to the controller adaptation rate as well as the frequency separation of the tonal components in the noise, i.e., the beat frequency. This paper treats the convergence performance of a complex least-mean-squares (LMS) algorithm using two reference signals. An analysis of its convergence behavior is presented as well as the results from computer simulations validating the convergence behavior. The convergence of the filter weights and the decrease rate of the squared error (the learning curve) for noise control applications are also discussed.
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| 16. |
- Johansson, Sven, et al.
(författare)
-
Evaluation of a Multiple- versus a Single-Reference MIMO ANC Algorithm on Dornier 328 Test Data Set
- 1998
-
Konferensbidrag (refereegranskat)abstract
- In many applications, such as in propeller aircraft, the dominating noise is periodic. Successful reduction of the periodic noise components can be achieved by using an Active Noise Control (ANC) system based on feedforward techniques. In this paper, a comparison between the performance of single--reference (single-tacho) and multiple--reference (twin-tacho) feedforward control systems is presented. The comparison is made for two different flight conditions, both with and without synchronized propellers. The evaluation results show that a multiple--reference controller provides better performance than a single--reference controller when a slight deviation exists in the propeller synchronization.
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| 17. |
- Johansson, Sven, et al.
(författare)
-
Evaluation of Multiple Reference Active Noise Control Algorithms on Dornier 328 Aircraft Data
- 1999
-
Ingår i: IEEE transactions on speech and audio processing. - New York : IEEE Signal Processing Society. - 1063-6676. ; 7:4, s. 473-477
-
Tidskriftsartikel (refereegranskat)abstract
- This correspondence presents an evaluation of multiple-reference adaptive algorithms. Two LMS-types and a Newton-type algorithm are considered. The special structure of the adaptive filtering problem implies that the Newton-type algorithm can be implemented with the same numerical complexity as LMS-type algorithms. The concept of a fast filtered-x Newton algorithm is thus introduced.
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| 18. |
- Nordberg, Jörgen, et al.
(författare)
-
Acoustic Echo Cancellation Employing Delayless Subband Adaptive Filters
- 1996
-
Konferensbidrag (refereegranskat)abstract
- The use of hands-free communication in cars, computer applications and video conferencing has created a demand for high-quality acoustic echo cancellation. In these applications these acoustic channel has typically a long impulse response in the order of 100ms. Typical lengths of adaptive FIR-filters can be 500-1500 taps. In order to reduce the complexity and also to improve the convergence rate, subband processing schemes have been suggested. This paper presents an implementation of a delayless subband adaptive filter. The study shows a possible suppression of about 30 dB and also a more rapid convergence compared to a fullband LMS-filter.
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| 19. |
- Nordberg, Jörgen, et al.
(författare)
-
Digital Beamforming as a Means for Interference Cancellation
- 1997
-
Konferensbidrag (refereegranskat)abstract
- The increasing demand for user capacity is one of the major challenges to network operators today. In order to increase the capacity in a mobile radio network, it is desirable to exploit the spatial domain in an efficient way. An array adds spatial domain selectivity in order to improve the Carrier-to-Interference ration (C/I). An adaptive antenna ray can further improve the Carrier-to-Interference ratio (C/I) by suppressing interfering signals. The proposed circular array consists of M elements and combines fixed beamformers with interference cancellors. The fixed beamformers use a weight matrix to form multiple beams. The radius of the circular array is assumed to be half the wavelenght of the signal. The interference cancellor suppresses undesired signals, so called jammers, leaking into the desired beam. The desired signal is filtered out by the fixed beamforming structure. Due to the sidelobes, interfering signals will also, however, be present in this beam. Two alternative strategies may be chosen to cancel these interferers; use the other fixed beam outputs as inputs to an adaptive interference canceller, or demodulate the outputs from the other fixed beams and regenerate clean signals which are used as inputs to adaptive interference cancellers. Results are presented using beamformer weights obtained from an LS minimization as well as minimax.
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| 20. |
- Nordberg, Jörgen, et al.
(författare)
-
Digital Beamforming as a Means for Interference Cancellation
- 1998
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The increasing demand for user capacity is a major challenge to network operators today. In order to increase the capacity of a mobile radio network, it is desirable to exploit the spatial domain in an efficient way. An array adds spatial domain selectivity in order to improve the Carrier-to-Interference ratio(C/I). An adaptive antenna array can further improve the Carrier-to-Interference ratio(C/I) by suppressing interfering signals. The proposed circular array consists of K elements and combines fixed beamformers with interference cancellers. The fixed beamformers use a weight matrix to form multiple beams. The interference canceller suppresses undesired signals, called jammers, leaking into the desired beam. The desired signal is filtered out by the fixed beamforming structure. Due to the side-lobes, interfering signals will also be present in this beam. Two alternative strategies may be chosen to cancel these interferers; use the other fixed beam outputs as inputs to an adaptive interference canceller, or regenerate the outputs from the other fixed beams and generate clean signals which are used as inputs to adaptive interference cancellers. Results are presented using beamformer weights obtained from a Least Square (LS) minimisation as well as minimax.
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