A. Vasilache | Tampere University (original) (raw)
Papers by A. Vasilache
1999 European Control Conference (ECC), 1999
This study presents the idea of a fast algorithm that can be used for the synthesis of the contro... more This study presents the idea of a fast algorithm that can be used for the synthesis of the control law in a neural predictive control strategy. It is compared, as computation time and regulation performance, with a similar procedure that uses Brent's search combined with the golden section search algorithm. The process considered for simulation is a continuous fermentation. The results show that the same regulation performance can be achieved but calculation time and costs are reduced.
2006 IEEE International Conference on Acoustics Speed and Signal Processing Proceedings
The paper introduces a new coding methodology of the spectral modified discrete cosine transform ... more The paper introduces a new coding methodology of the spectral modified discrete cosine transform (MDCT) coefficients of an audio signal. A lattice quantizer is used for each spectral sub-band, having the dimension equal to the size of the respective sub-band. The information that needs to be encoded consists of lattice codevector indexes, side information relative to the number the bits on which the indexes are represented and the integer exponents of the sub-band scaling factors. The nature of the side information, together with the parameterization of the quantization resolution allows the use of the method for a large range of bitrates e.g. for 44.1 kHz sampled mono files, from 128 kbits/s down to 16 kbits/s. Subjective listening tests show similar performance of the proposed method to the advanced audio coding (AAC) codec for high bitrates (128 kbits down to 64 kbits/s) and clearly better performance for lower bitrates
IFAC Proceedings Volumes, 1997
This paper presents a neural networks approach for modelling of a fermentation process kinetics. ... more This paper presents a neural networks approach for modelling of a fermentation process kinetics. Two topics are considered : the estimation of the biomass specific growth rate and the classification and model change detection of the process kinetics. The classification is made in the sense of recognising the appropriate kinetic model for a set of temporal data representing the state variables of the process. This is a new approach that by the use of recurrent neural networks permits both the determination of the kinetic model describing the fermentation data and the change between predefmed existing models. The batch and the continuous modes for a Saccharomyces cerevisiae fermentation are considered. Copy right © 1998 IFAC
International Journal of Systems Science, 2001
While a number of features make fixed wireless access (FWA) technology a candidate for effective ... more While a number of features make fixed wireless access (FWA) technology a candidate for effective high bandwidth network infrastructure solutions, several factors, primarily heavy rainfall, can hamper the availability of a FWA link. To overcome this pitfall, a possible solution is using backup wired routes for most critical/vulnerable segments of the FWA network. In this paper we propose a parameterized configuration model for a switch operating with a primary (FWA) route and secondary (ISDN) backup route. We use data collected during an approx. 3 years experiment to study the impact of the parameter settings and determine optimal configuration in order to maximize the overall system availability.
Image Processing: Algorithms and Systems II, 2003
ABSTRACT This paper presents an image coding method, based on wavelet transform, where the distri... more ABSTRACT This paper presents an image coding method, based on wavelet transform, where the distribution of the subband coefficients is assumed to be generalized Gaussian. The shape factor and the standard deviation are estimated in all subbands. A procedure of bit allocation distributes then the available bitrate to the retained coefficients. The multiple scale leader lattice vector quantization (MSLLVQ) has shown its superiority compared to other structured quantization schemes and now we propose its use for the quantization of the wavelet coefficients. The main contribution of the paper is the procedure for selecting the structure and the leaders for the MSLLVQ. An iterative construction of the MSLLVQ scheme is presented along with the derivation of the operational rate-distortion function. The bit allocation procedure is based on the exponential fitting of the operational rate-distortion curve. The results in terms of peak signal to noise ratio are compared to other image codecs from the literature, the advantage of such a coding structure being particularly important for the fixed rate encoding.
2010 IEEE International Conference on Acoustics, Speech and Signal Processing, 2010
We propose a context conditioning scheme for encoding the prediction residuals when compressing f... more We propose a context conditioning scheme for encoding the prediction residuals when compressing files containing companded signals. Our scheme encompasses decompanding of the signals, performing linear prediction in the decompanded domain, and then companding back the predicted value into a companded prediction (CP) value, which will differ from the true companded value by an amount called companded prediction residual (CPR). The proposed context conditioning scheme for encoding the CPR, uses a probability distribution conditional on a context made up of two quantities:
Lecture Notes in Computer Science, 2004
In this paper we present several algorithms for the construction of min-max optimal partitions of... more In this paper we present several algorithms for the construction of min-max optimal partitions of the parameter space. Two interpretations of the problem lead to two families of practical algorithms that are tested and compared.
2010 4th International Symposium on Communications, Control and Signal Processing (ISCCSP), 2010
Search algorithms in Golay codebooks are necessary both for maximum likelihood decoding and for v... more Search algorithms in Golay codebooks are necessary both for maximum likelihood decoding and for vector quantization applications. This work presents algorithms for fast search on shells (set of codewords having the same Hamming weight) of binary Golay codes. The algorithms are based on the Golay codebook projection into a hexacode codebook. Two cases are considered: when the nearest neighbors within each of the shells are simultaneously determined or when they are independently determined.
IEEE Pacific Rim Conference on Communications, Computers and Signal Processing, 2003
In this paper, we propose a security tool for security enhanced mail gateway (SEMAIL). SEMAIL is ... more In this paper, we propose a security tool for security enhanced mail gateway (SEMAIL). SEMAIL is a mail server package designed to provide PGP (pretty good privacy)-based e-mail security to all the members of an organization. SEMAIL is attempting to solve the problems incurred by implementing PGP in large scale organizations. In this paper we introduce a POP before SMTP
2001 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings (Cat. No.01CH37221), 2001
We present here two methods of entropy coding for the lattice codevectors. We compare our entropy... more We present here two methods of entropy coding for the lattice codevectors. We compare our entropy coding methods with one method previously presented in the literature from the point of view of rate-distortion as well as of the computation complexity and memory requirements. The results are presented for artificial Laplacian and Gaussian data, as well as for LSF parameters of speech signals. In the latter case, the multiple scale lattice VQ (MSLVQ) is used for quantization, which reduces the rate gain of the entropy coding method when compared with the fixed rate case, but allows a dynamic allocation of the bits in the whole speech coding scheme.
2009 Data Compression Conference, 2009
ABSTRACT In this paper we study how to encode W-long vectors, with N in the range of hundreds, at... more ABSTRACT In this paper we study how to encode W-long vectors, with N in the range of hundreds, at low bit rates of 0.5 bit per sample or lower. We adopt a vector quantization structure, where an overall gain is encoded with a scalar quantizer and the remaining scaled vector is encoded using a vector quantizer built out by combining smaller (length L) binary codes known to be efficient in filling the space, the important examples discussed here being the Golay codes. Due to the typical nonstationary distribution of the long vectors, a piecewise stationary plus contamination model is assumed. The generic solution is to encode the outliers using Golomb-Rice codes, and for each L-long subvector to encode the vector of absolute values using the nearest neighbor in a certain shell of a chosen binary {0,1} code, the sign information being transmitted separately. The rate-distortion optimization problem can be very efficiently organized and solved for the unknowns, which include the Hamming weights of the chosen shells for each of the nb = [N/L] subvectors, and the overall gain g. The essential properties which influence the selection of a certain binary code as a building block are its space filling properties, the number of shells of various Hamming weights (allowing more or less flexibility in the rate-distortion optimization), the closeness of N to a multiple of L, and the existence of fast search of nearest neighbor on a shell. We show results when using the Golay codes for vector quantization on audio coding applications.
1999 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings. ICASSP99 (Cat. No.99CH36258), 1999
This paper introduces a new lattice quantization scheme, the multiple-scale lattice vector quanti... more This paper introduces a new lattice quantization scheme, the multiple-scale lattice vector quantization (MSLVQ), based on the truncation of the D + 10 lattice. The codebook is composed of several copies of the truncated lattice scaled with different scaling factors. A fast nearest neighbor search is introduced. We compare the performance of predictive MSLVQ for quantization of LSF coefficients with the quantization technique used in the codec G.729 and show the better performance of our method in terms of spectral distortion. The MSLVQ scheme achieves the transparent quality at 21 bits/frame.
Signal Processing, 2002
In this study we introduce two new quantization structures, namely the multiple scale leader-latt... more In this study we introduce two new quantization structures, namely the multiple scale leader-lattice vector quantization (MSLLVQ) using different lattice truncations and (MSLLVQ) using different unions of leader vectors. The design methods and the corresponding encoding ...
Signal Processing, 2003
ABSTRACT In this paper we develop two families of indexing methods for permutation codes and latt... more ABSTRACT In this paper we develop two families of indexing methods for permutation codes and lattices, the lexicographical and binomial indexing families. The parameters of a method within a family can be optimized with respect to a given criterion in order to obtain a good indexing method on the considered set of vectors to be indexed. The proposed indexing methods can be straightforwardly applied for error resilient coding, but also to other applications as e.g. the magnetic recording which is based on (d,k) constrained codes. We have tested the performance of the proposed method at the optimization of the indexing method of a codebook with respect to the channel distortion for several types of lattices and other structured vector quantizers over binary symmetric channels.
1999 European Control Conference (ECC), 1999
This study presents the idea of a fast algorithm that can be used for the synthesis of the contro... more This study presents the idea of a fast algorithm that can be used for the synthesis of the control law in a neural predictive control strategy. It is compared, as computation time and regulation performance, with a similar procedure that uses Brent's search combined with the golden section search algorithm. The process considered for simulation is a continuous fermentation. The results show that the same regulation performance can be achieved but calculation time and costs are reduced.
2006 IEEE International Conference on Acoustics Speed and Signal Processing Proceedings
The paper introduces a new coding methodology of the spectral modified discrete cosine transform ... more The paper introduces a new coding methodology of the spectral modified discrete cosine transform (MDCT) coefficients of an audio signal. A lattice quantizer is used for each spectral sub-band, having the dimension equal to the size of the respective sub-band. The information that needs to be encoded consists of lattice codevector indexes, side information relative to the number the bits on which the indexes are represented and the integer exponents of the sub-band scaling factors. The nature of the side information, together with the parameterization of the quantization resolution allows the use of the method for a large range of bitrates e.g. for 44.1 kHz sampled mono files, from 128 kbits/s down to 16 kbits/s. Subjective listening tests show similar performance of the proposed method to the advanced audio coding (AAC) codec for high bitrates (128 kbits down to 64 kbits/s) and clearly better performance for lower bitrates
IFAC Proceedings Volumes, 1997
This paper presents a neural networks approach for modelling of a fermentation process kinetics. ... more This paper presents a neural networks approach for modelling of a fermentation process kinetics. Two topics are considered : the estimation of the biomass specific growth rate and the classification and model change detection of the process kinetics. The classification is made in the sense of recognising the appropriate kinetic model for a set of temporal data representing the state variables of the process. This is a new approach that by the use of recurrent neural networks permits both the determination of the kinetic model describing the fermentation data and the change between predefmed existing models. The batch and the continuous modes for a Saccharomyces cerevisiae fermentation are considered. Copy right © 1998 IFAC
International Journal of Systems Science, 2001
While a number of features make fixed wireless access (FWA) technology a candidate for effective ... more While a number of features make fixed wireless access (FWA) technology a candidate for effective high bandwidth network infrastructure solutions, several factors, primarily heavy rainfall, can hamper the availability of a FWA link. To overcome this pitfall, a possible solution is using backup wired routes for most critical/vulnerable segments of the FWA network. In this paper we propose a parameterized configuration model for a switch operating with a primary (FWA) route and secondary (ISDN) backup route. We use data collected during an approx. 3 years experiment to study the impact of the parameter settings and determine optimal configuration in order to maximize the overall system availability.
Image Processing: Algorithms and Systems II, 2003
ABSTRACT This paper presents an image coding method, based on wavelet transform, where the distri... more ABSTRACT This paper presents an image coding method, based on wavelet transform, where the distribution of the subband coefficients is assumed to be generalized Gaussian. The shape factor and the standard deviation are estimated in all subbands. A procedure of bit allocation distributes then the available bitrate to the retained coefficients. The multiple scale leader lattice vector quantization (MSLLVQ) has shown its superiority compared to other structured quantization schemes and now we propose its use for the quantization of the wavelet coefficients. The main contribution of the paper is the procedure for selecting the structure and the leaders for the MSLLVQ. An iterative construction of the MSLLVQ scheme is presented along with the derivation of the operational rate-distortion function. The bit allocation procedure is based on the exponential fitting of the operational rate-distortion curve. The results in terms of peak signal to noise ratio are compared to other image codecs from the literature, the advantage of such a coding structure being particularly important for the fixed rate encoding.
2010 IEEE International Conference on Acoustics, Speech and Signal Processing, 2010
We propose a context conditioning scheme for encoding the prediction residuals when compressing f... more We propose a context conditioning scheme for encoding the prediction residuals when compressing files containing companded signals. Our scheme encompasses decompanding of the signals, performing linear prediction in the decompanded domain, and then companding back the predicted value into a companded prediction (CP) value, which will differ from the true companded value by an amount called companded prediction residual (CPR). The proposed context conditioning scheme for encoding the CPR, uses a probability distribution conditional on a context made up of two quantities:
Lecture Notes in Computer Science, 2004
In this paper we present several algorithms for the construction of min-max optimal partitions of... more In this paper we present several algorithms for the construction of min-max optimal partitions of the parameter space. Two interpretations of the problem lead to two families of practical algorithms that are tested and compared.
2010 4th International Symposium on Communications, Control and Signal Processing (ISCCSP), 2010
Search algorithms in Golay codebooks are necessary both for maximum likelihood decoding and for v... more Search algorithms in Golay codebooks are necessary both for maximum likelihood decoding and for vector quantization applications. This work presents algorithms for fast search on shells (set of codewords having the same Hamming weight) of binary Golay codes. The algorithms are based on the Golay codebook projection into a hexacode codebook. Two cases are considered: when the nearest neighbors within each of the shells are simultaneously determined or when they are independently determined.
IEEE Pacific Rim Conference on Communications, Computers and Signal Processing, 2003
In this paper, we propose a security tool for security enhanced mail gateway (SEMAIL). SEMAIL is ... more In this paper, we propose a security tool for security enhanced mail gateway (SEMAIL). SEMAIL is a mail server package designed to provide PGP (pretty good privacy)-based e-mail security to all the members of an organization. SEMAIL is attempting to solve the problems incurred by implementing PGP in large scale organizations. In this paper we introduce a POP before SMTP
2001 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings (Cat. No.01CH37221), 2001
We present here two methods of entropy coding for the lattice codevectors. We compare our entropy... more We present here two methods of entropy coding for the lattice codevectors. We compare our entropy coding methods with one method previously presented in the literature from the point of view of rate-distortion as well as of the computation complexity and memory requirements. The results are presented for artificial Laplacian and Gaussian data, as well as for LSF parameters of speech signals. In the latter case, the multiple scale lattice VQ (MSLVQ) is used for quantization, which reduces the rate gain of the entropy coding method when compared with the fixed rate case, but allows a dynamic allocation of the bits in the whole speech coding scheme.
2009 Data Compression Conference, 2009
ABSTRACT In this paper we study how to encode W-long vectors, with N in the range of hundreds, at... more ABSTRACT In this paper we study how to encode W-long vectors, with N in the range of hundreds, at low bit rates of 0.5 bit per sample or lower. We adopt a vector quantization structure, where an overall gain is encoded with a scalar quantizer and the remaining scaled vector is encoded using a vector quantizer built out by combining smaller (length L) binary codes known to be efficient in filling the space, the important examples discussed here being the Golay codes. Due to the typical nonstationary distribution of the long vectors, a piecewise stationary plus contamination model is assumed. The generic solution is to encode the outliers using Golomb-Rice codes, and for each L-long subvector to encode the vector of absolute values using the nearest neighbor in a certain shell of a chosen binary {0,1} code, the sign information being transmitted separately. The rate-distortion optimization problem can be very efficiently organized and solved for the unknowns, which include the Hamming weights of the chosen shells for each of the nb = [N/L] subvectors, and the overall gain g. The essential properties which influence the selection of a certain binary code as a building block are its space filling properties, the number of shells of various Hamming weights (allowing more or less flexibility in the rate-distortion optimization), the closeness of N to a multiple of L, and the existence of fast search of nearest neighbor on a shell. We show results when using the Golay codes for vector quantization on audio coding applications.
1999 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings. ICASSP99 (Cat. No.99CH36258), 1999
This paper introduces a new lattice quantization scheme, the multiple-scale lattice vector quanti... more This paper introduces a new lattice quantization scheme, the multiple-scale lattice vector quantization (MSLVQ), based on the truncation of the D + 10 lattice. The codebook is composed of several copies of the truncated lattice scaled with different scaling factors. A fast nearest neighbor search is introduced. We compare the performance of predictive MSLVQ for quantization of LSF coefficients with the quantization technique used in the codec G.729 and show the better performance of our method in terms of spectral distortion. The MSLVQ scheme achieves the transparent quality at 21 bits/frame.
Signal Processing, 2002
In this study we introduce two new quantization structures, namely the multiple scale leader-latt... more In this study we introduce two new quantization structures, namely the multiple scale leader-lattice vector quantization (MSLLVQ) using different lattice truncations and (MSLLVQ) using different unions of leader vectors. The design methods and the corresponding encoding ...
Signal Processing, 2003
ABSTRACT In this paper we develop two families of indexing methods for permutation codes and latt... more ABSTRACT In this paper we develop two families of indexing methods for permutation codes and lattices, the lexicographical and binomial indexing families. The parameters of a method within a family can be optimized with respect to a given criterion in order to obtain a good indexing method on the considered set of vectors to be indexed. The proposed indexing methods can be straightforwardly applied for error resilient coding, but also to other applications as e.g. the magnetic recording which is based on (d,k) constrained codes. We have tested the performance of the proposed method at the optimization of the indexing method of a codebook with respect to the channel distortion for several types of lattices and other structured vector quantizers over binary symmetric channels.