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Papers by Iir Iir

This paper is focused on the learning algorithms for dynamic multilayer perceptron neural network... more This paper is focused on the learning algorithms for dynamic multilayer perceptron neural networks where each neuron synapsis is modelled by an infinite impulse response (IIR) filter (IIR MLP). In particular, the Backpropagation Through Time (BPTT) algorithm and its less demanding approximated on-line versions are considered. In fact it is known that the BPTT algorithm is not causal and therefore can be implemented only in batch mode, while many real problems require on-line adaptation. In this paper we give the complete BPTT formulation for the IIR MLP, derive an already known on-line learning algorithm as a particular approximation of the BPTT, and propose a new approximated algorithm. Several computer simulations of identification of dynamical systems will also be presented to assess the performance of the approximated algorithms and to compare the IIR MLP with more traditional dynamic networks.

IEEE Transactions on Communications, 1982

The paper discusses structures, design methods, and efficiency of digital two-rate filters for sa... more The paper discusses structures, design methods, and efficiency of digital two-rate filters for sampling rate alteration by integer or rational ratios. Four canoic filter structures are demonstrated: the direct form, the parallel form, the ladder/lattice forms, and a structure based on canonic all-pass sections. In addition, a structure exploiting numerator coefficient symmetry is presented. An extended class of filters (hybrid IIR/FIR) where the passband equalization is performed by a combination of poles and off-the-unit-circle zeros is introduced. The author also describes a design method which iteratively utilizes the Remez algorithm. This simple extension of the McClellan et al. (1973) program facilitates the design of virtually any kind of filter including hybrid filters and/or two-rate filters. Several design examples are presented to visualize the different aspects of two-rate filtering.

This paper presents a new technique to control stability of IIR adaptive filters based on the ide... more This paper presents a new technique to control stability of IIR adaptive filters based on the idea of intrinsically stable operations that makes it possible to continually adapt the coefficients with no need of a stability test or pole projection. The coefficients are adapted in a way that intrinsically assures the poles to be in the unit circle. This makes it possible to use a higher step size (also named learning rate here) potentially improving the fastness of adaptation with respect to methods that employ a bound on the learning rate or methods that simply do not control stability. This method can be applied to various realizations: direct forms, cascade or parallel of second order sections, lattice forms. It can be implemented to adapt a simple IIR adaptive filter or a locally recurrent neural network such as the IIR-MLP

This paper extends the recently introduced class of multistage FIR Nyquist filters to cover also ... more This paper extends the recently introduced class of multistage FIR Nyquist filters to cover also the multi-stage IIR and hybrid IIR/FIR Nyquist filters. The filter stages, as well as the overall system, have zero intersymbol interference. The filter stages are simultaneuosly designed to provide a Chebyshev stopband behavior for the overall filter, thereby band-limiting the pulses optimally. Computationally efficient IIR filter stages are obtained by using the polyphase structure with allpass subfilters. Selecting one of the subfilters to be a pure delay results in zero intersymbol interference. Efficient procedures are presented for simultaneously optimizing the filter stages for both IIR and hybrid IIR/FIR cases. Examples demonstrate how the proposed multistage IIR filters provide significant advantages over other existing IIR designs and a slight reduction in the multiplication rate compared to multistage FIR designs.

The performances comparing the results of using plain gradient algorithm (PG) in a second-order a... more The performances comparing the results of using plain gradient algorithm (PG) in a second-order adaptive IIR lattice notch filter (PG_L) and adaptive IIR notch filter with constrained poles and zeros (PG_C) are clearly presented here. It is shown that the PG_L yields the performances over the PG_C. Computer simulations are provided to confirm the performances of PG_L.

Gps Solutions, 2008

The clock products of the International Global Navigation Satellite Systems (GNSS) Service (IGS) ... more The clock products of the International Global Navigation Satellite Systems (GNSS) Service (IGS) are used to characterize the timing performance of the GPS satellites. Using 5-min and 30-s observational samples and focusing only on the sub-daily regime, approximate powerlaw stochastic processes are found. The Block IIA Rb and Cs clocks obey predominantly random walk phase (or white frequency) noise processes. The Rb clocks are up to nearly an order of magnitude more stable and show a flicker phase noise component over intervals shorter than about 100 s. Due to the onboard Time Keeping System in the newer Block IIR and IIR-M satellites, their Rb clocks behave in a more complex way: as an apparent random walk phase process up to about 100 s and then changing to flicker phase up to a few thousand seconds. Superposed on this random background, periodic signals have been detected in all clock types at four harmonic frequencies, n 9 (2.0029 ± 0.0005) cycles per day (24 h coordinated universal time or UTC), for n = 1, 2, 3, and 4. The equivalent fundamental period is 11.9826 ± 0.0030 h, which surprisingly differs from the reported mean GPS orbital period of 11.9659 ± 0.0007 h by 60 ± 11 s. We cannot account for this apparent discrepancy but note that a clear relationship between the periodic signals and the orbital dynamics is evidenced for some satellites by modulations of the spectral amplitudes with eclipse season. All four harmonics are much smaller for the IIR and IIR-M satellites than for the older blocks. Awareness of the periodic variations can be used to improve the clock modeling, including for interpolation of tabulated IGS products for higher-rate GPS positioning and for predictions in real-time applications. This is especially true for high-accuracy uses, but could also benefit the standard GPS operational products. The observed stochastic properties of each satellite clock type are used to estimate the growth of interpolation and prediction errors with time interval.

IEEE Transactions on Signal Processing, 1995

Perfect linear-phase two-channel QMF banks require the use of finite impulse response (FIR) analy... more Perfect linear-phase two-channel QMF banks require the use of finite impulse response (FIR) analysis and synthesis filters. Although they are less expensive and yield superior stopband characteristics, perfect linear phase cannot be achieved with stable infinite impulse response (IIR) filters. Thus, IIR designs usually incorporate a postprocessing equalizer that is optimized to reduce the phase distortion of the entire filter bank. However, the analysis and synthesis filters of such an IIR filter bank are not linear phase. In this paper, a computationally simple method to obtain LIR analysis and synthesis filters that possess negligible phase distortion is presented. The method is based on first applying the balanced reduction procedure to obtain nearly allpass IIR polyphase components and then approximating these with perfect allpass IIR polyphase components. The resulting IIR designs already have only negligible phase distortion. However, if required, further improvement may be achieved through optimization of the filter parameters. For this purpose, a suitable objective function is presented. Bounds for the magnitude and phase errors of the designs are also derived. Design examples indicate that the derived IIR filter banks are more efficient in terms of computational complexity than the FIR prototypes and perfect reconstruction FIR filter banks. Although the PR FIR filter banks when implemented with the one-multiplier lattice structure and IIR filter banks are comparable in terms of computational complexity, the former is very sensitive to coefficient quantization effects.

The task of designing an 18 parameter IIR-filter (IIR=infinite impulse response) which has to mee... more The task of designing an 18 parameter IIR-filter (IIR=infinite impulse response) which has to meet tight specifications for both magnitude response and group delay is investigated. This problem is usually tackled by specialized design methods and requires an expert in digital signal processing for its solution. The use of the general purpose minimization method differential evolution (DE), however, allows filter design with a minimum knowledge of digital filters

Applied Acoustics, 2007

There are perceived drawbacks to using adaptive IIR filters, as opposed to adaptive FIR filters, ... more There are perceived drawbacks to using adaptive IIR filters, as opposed to adaptive FIR filters, for active noise control (ANC). These include stability issues, the possible convergence of estimated parameters to biased and/or local minimum solutions and relatively slow rate of convergence. Stability issues can generally be resolved easily using well-established methods. In this Technical Note convergence rates are compared with particular reference to the active control of noise in a duct, for which the dynamics of the cancellation path are important. The characteristics of this application of ANC set it apart from usual signal processing applications of adaptive IIR filters and this has implications for the convergence properties. Various control approaches are considered: IIR least mean squares (IIR-LMS), IIR recursive least squares (IIR-RLS) with FASPIS (Fast Algorithm Secondary Path Integration Scheme) and FIR-LMS. Numerical examples are presented. It is seen that the cancellation path dynamics generally have the effect of changing the performance surface of the estimated IIR filter from bimodal to unimodal, which has consequences for improving the convergence rate of adaptive IIR filters. It is also seen that IIR-RLS has a comparable rate of convergence to FIR-LMS, with the steady-state performance being as good or better.

An efficient method is proposed to design infinite impulse response (IIR) all-pass filters for sy... more An efficient method is proposed to design infinite impulse response (IIR) all-pass filters for synthesizing general multiband filters of low sensitivity. The method is based on minimizing a quadratic measure of the error derived from the phase design of a certain filter. The problem of stability is of no concern, and the performance of the obtained filter is comparable to that of existing methods. The solution is obtained directly with no need for iteration. The complex coefficient filters can also be designed with minor modification of the proposed method

IEEE Transactions on Instrumentation and Measurement, 2001

A novel hybrid adaptive FIR/IIR filter configuration is presented. The aim is to reduce the main ... more A novel hybrid adaptive FIR/IIR filter configuration is presented. The aim is to reduce the main obstacles limiting the use of adaptive IIR filters: namely convergence and stability. The hybrid scheme attempts to exploit the good qualities of both adaptive FIR filters (good convergence and stability) and those for adaptive IIR filters (sharp transition bands, lower order, and complexity). In this paper, the hybrid scheme is presented for a system identification problem, and the task is achieved in three main steps: a) A training signal is applied to an adaptive FIR filter to achieve a near optimum approximation; b) the FIR coefficients are mapped through the balanced model reduction technique to a smaller set of coefficients initializing an adaptive IIR filter; c) there is a process of fine tuning (small adaptive stepsize) the adaptive IIR coefficients for further approximation precision. The IIR filter in the hybrid scheme makes use of the Steiglitz McBride algorithm that assures the stability of the filter. Furthermore, the convergence to the minimum error performance is enforced by the fact that the adaptive IIR filter is operating close to the optimum, requiring very small pole perturbation.

The L2 Civil Signal (L2CS) will be transmitted by modernized IIR(IIR-M), IIF and all subsequent G... more The L2 Civil Signal (L2CS) will be transmitted by modernized IIR(IIR-M), IIF and all subsequent GPS satellites. It contains two codes of different length; CM code contains 10,230chips, repeats every 20milliseconds and is modulated with message data, and CL code contains 767,250chps, repeats every 1.5second Z-count and has no data modulation. And the message data is encoded for Forward Error Correction (FEC). Although it has a good cross-correlation performance by the long code length, but the acquisition time should be long. Because the acquisition time is directly proportional to the code length and/or code period. Therefore it takes about 100 hours for L2C signal acquisition in case of 20ms integration. So, there should be a fast signal acquisition scheme. There are many methods to reduce the acquisition time, but most of them require the modification of the correlator. The L1 aiding method does not require any modifications and it can acquire the L2C signal as fast as the L1 signal. Finally, the L1 aiding method would be confirmed by experimental results in this paper and the acquisition and tracking of L1 and L2C signal also would be shown.

Aeu-international Journal of Electronics and Communications, 2005

Adaptive digital filters have proven their worth in a wide range of applications such as channel ... more Adaptive digital filters have proven their worth in a wide range of applications such as channel equalisation, noise reduction, echo cancelling, and system identification. These filters can be broadly classified into two groups: finite impulseresponse (FIR) and infinite ...

... Narrowband inter-ference suppression using filterbank analysis/synthesis techniques. Proceedi... more ... Narrowband inter-ference suppression using filterbank analysis/synthesis techniques. Proceedings MILCOM, pages 898-902, 1992. [4] Michael Medley, Gary Saulnier, and P. Das. Applica-tions of the wavelet transform in spread spectrum com-munications systems. ...

Signal Processing, 1994

IEEE Transactions on Signal Processing, 2010

A learning algorithm for the training of quaternion valued adaptive infinite impulse (IIR) filter... more A learning algorithm for the training of quaternion valued adaptive infinite impulse (IIR) filters is introduced. This is achieved by taking into account specific properties of stochastic gradient approximation in the quaternion domain and the recursive nature of the sensitivities within the IIR filter updates, to give the quaternion-valued stochastic gradient algorithm for adaptive IIR filtering (QSG-IIR). Further, to reduce computational complexity, a variant of the QSG-IIR is introduced, which for small stepsizes makes better use of the available information. Stability analysis and simulations on both synthetic and real world 4D data support the approach.

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2009

In this study, we address the increased computational demands of a frequency-diverse ultrasonic t... more In this study, we address the increased computational demands of a frequency-diverse ultrasonic target detection system by developing a zero-phase IIR (ZP-IIR) filter. Several ZP-IIR filter types including Chebyshev-I, Chebyshev- II, and Butterworth were analyzed for their detection performance. The 4th-order filters with 8-bit quantized coefficients are shown to improve the flaw-to-clutter ratio by approximately 10 dB. Furthermore, the reduced adder graph algorithm is used for a hardware realization of ZP-IIR filters that does not require any dedicated multipliers. A small number of coefficients inherent to IIR filters and their multiplierless implementation provide efficient architecture suitable for compact, real-time ultrasonic imaging devices.