1,722,796 research outputs found
On the Design of Oversampled Filter Banks for Channel Coding
Full text linkOversampled filter banks have been considered for channel coding, because they introduce redundancy into the subband representation of signals and permit more freedom in their design than critically sampled structures. In this paper, based on the knowledge of the channel noise's covariance matrix, we propose a constrained design for the synthesis filter bank in order to minimise the noise power in the decoded signal, subject to admitting perfect reconstruction. For the special case of paraunitary filter banks, a suboptimal iterative design is presented, which highlights the potential benefits of this approach, as demonstrated by a design example
Design of Overcomplete Expansions for Channel Coding
No full textThe redundancy afforded by overcomplete expansions have been recently been considered for channel coding. In this paper, we utilise this approach in order to propose a channel coder design to for a correlated additive Gaussian noise channel, of which the noise covariance matrix is assumed to be known. We demonstrate that this approach can lead to a significant reduction of the noise interference by exploiting both the correlation of the channel and the redundancy of the filter banks. Simulation results providing some insight into these mechanisms are provided
Heinrich Weiss s/m Fr. Vögeli zur freundl. Erg
No full textDedikationssilhouette nach rechts von Heinrich Weiss, gewidmet Fr. VögeliAnonyme DruckgrafikHandschriftliche Widmung unterhalb des Porträts "Heinrich Weiss s[eine]m Fr. Vögeli zur freundl[ichen] Er[innerun]g.
Convergence Behaviour of LMS-Type Algorithms for Adaptive Noise Control in Noisy Doppler Environments (862kB)
No full textThis paper discusses the convergence and tracking behaviour of LMS-type algorithms in a certain type of environment, which is characterised by a Doppler shift in frequency between the two signals available to the algorithm and rapid variations in signal power. We show the linear time-varying characteristics of the underlying system and derive optimum trajectories to which we can compare the adaptation and tracking ability of first order LMS and NLMS adaptive filters. We also present simulations using higher filter orders and real world noise, for which particular emphasis is put on the presence of observation noise. An excursion into the theory of non-stationary convergence and tracking of adaptive algorithms provides justification for the observed behaviour of the algorithms
F. Weiss s. H. Landolt zur frdl. Erinnerung
No full textDedikationssilhouette nach rechts von F. Weiss, gewidmet Johann Heinrich Landolt (1831-1885)Anonyme/r Künstler/inAngaben zum Widmungsempfänger gemäss interner NotizHandschriftliche Widmung unterhalb des Bildes "F. Weiss s[einem] H. Landolt zur fr[eun]dl[ichen] Erinnerung
On Adaptive Filtering in Oversampled Subbands
No full textFor a number of applications like acoustic echo cancellation, adaptive filters are required to identify very long impulse responses. To reduce the computational cost in implementations, adaptive filtering in subband is known to be beneficial. Based on a review of popular fullband adaptive filtering algorithms and various subband approaches, this thesis investigates the implementation, design, and limitations of oversampled subband adaptive filter systems based on modulated complex and real valued filter banks. The main aim is to achieve a computationally efficient implementation for adaptive filter systems, for which fast methods of performing both the subband decomposition and the subband processing are researched. Therefore, a highly efficient polyphase implementation of a complex valued modulated generalized DFT (GDFT) filter bank with a judicious selection of properties for non-integer oversampling ratios is introduced. By modification, a real valued single sideband modulated filter bank is derived. Non-integer oversampling ratios are particularly important when addressing the efficiency of the subband processing. Analysis is presented to decide in which cases it is more advantageous to perform real or complex valued subband processing. Additionally, methods to adaptively adjust the filter lengths in subband adaptive filter (SAF) systems are discussed. Convergence limits for SAFs and the accuracy of the achievable equivalent fullband model based on aliasing and other distortions introduced by the employed filter banks are explicitly derived. Both an approximation of the minimum mean square error and the model accuracy can be directly linked to criteria in the design of the prototype filter for the filter bank. Together with an iterative least-squares design algorithm, it is therefore possible to construct filter banks for SAF applications with pre-defined performance limits. Simulation results are presented which demonstrate the validity and properties of the discussed SAF methods and their advantage over fullband and critically sampled SAF systems
Multiple transitions in rotating turbulent Rayleigh-Bénard convection
No full textSharp transitions between potentially different turbulent states are unexpected because one might think that they should be washed out by the prevailing intense fluctuations and short coherence lengths and times. Contrary to this expectation, we found a sequence of such transitions in turbulent rotating Rayleigh-Bénard convection as the rotation rate was increased. This phenomenon became most prominent at very large Rayleigh numbers up to 2 × 10^12 where the fluctuations are extremely vigorous. It was found in the heat transport as well as in the temperature gradient near the sample center. We conjecture that the transitions are between different large-scale structures which involve changes of symmetry and thus can not be gradual
On the Analysis and Fast Implementation of Oversampled Modulated Filter Banks
No full textOversampled modulated filter banks (OSFBs) play an important role in reducing the computational cost of numerically intensive problems. The concern of this paper is an efficient implementation of the OSFB itself. The proposed method is based on a polyphase description to remove redundancies in the filter operations. Using OSFBs that are modulated from a prototyep filter, a factorisation can be obtained which depends on the filter coefficients the prototype filter and the modulating transform only. Based on a state-space representation of this polyphase factorisation, signal flow graphs can be obtained by minor modifications, which allow us a very simple and efficient implementation of OSFBs. A comparison to existing methods is drawn
Categorisation of Panic Disorder by Time-Frequency Methods
No full textAnxiety patients that are presented with neutral and panic disorder triggering stimuli show different event-related brain potentials (ERP) within the electroencephalogram (EEG). In this paper, we investigate this difference by time-frequency (TF) revealing transforms leading to an identification of a small number of significant parameterising coefficients to be able to differentiate between the presented stimulus categories
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