Eigensequences for Multiuser Communication over the Real Adder Channel

Shape-invariant signals under the Discrete Fourier Transform are investigated, leading to a class of eigenfunctions for the unitary discrete Fourier operator. Such invariant sequences (eigensequences) are suggested as user signatures over the real adder channel (t-RAC) and a multiuser communication system over the t-RAC is presented.Comment: 6 pages, 1 figure, 1 table. VI International Telecommunications Symposium (ITS2006

Orthogonal Multilevel Spreading Sequence Design

Finite field transforms are offered as a new tool of spreading sequence design. This approach exploits orthogonality properties of synchronous non-binary sequences defined over a complex finite field. It is promising for channels supporting a high signal-to-noise ratio. New digital multiplex schemes based on such sequences have also been introduced, which are multilevel Code Division Multiplex. These schemes termed Galois-field Division Multiplex (GDM) are based on transforms for which there exists fast algorithms. They are also convenient from the hardware viewpoint since they can be implemented by a Digital Signal Processor. A new Efficient-bandwidth code-division-multiple-access (CDMA) is introduced, which is based on multilevel spread spectrum sequences over a Galois field. The primary advantage of such schemes regarding classical multiple access digital schemes is their better spectral efficiency. Galois-Fourier transforms contain some redundancy and only cyclotomic coefficients are needed to be transmitted yielding compact spectrum requirements.Comment: 9 pages, 5 figures. In: Coding, Communication and Broadcasting.1 ed.Hertfordshire: Reseach Studies Press (RSP), 2000. ISBN 0-86380-259-

Introducing an Analysis in Finite Fields

Looking forward to introducing an analysis in Galois Fields, discrete functions are considered (such as transcendental ones) and MacLaurin series are derived by Lagrange's Interpolation. A new derivative over finite fields is defined which is based on the Hasse Derivative and is referred to as negacyclic Hasse derivative. Finite field Taylor series and alpha-adic expansions over GF(p), p prime, are then considered. Applications to exponential and trigonometric functions are presented. Theses tools can be useful in areas such as coding theory and digital signal processing.Comment: 6 pages, 1 figure. Conference: XVII Simposio Brasileiro de Telecomunicacoes, 1999, Vila Velha, ES, Brazil. (pp.472-477

A Factorization Scheme for Some Discrete Hartley Transform Matrices

Discrete transforms such as the discrete Fourier transform (DFT) and the discrete Hartley transform (DHT) are important tools in numerical analysis. The successful application of transform techniques relies on the existence of efficient fast transforms. In this paper some fast algorithms are derived. The theoretical lower bound on the multiplicative complexity for the DFT/DHT are achieved. The approach is based on the factorization of DHT matrices. Algorithms for short blocklengths such as $N \in \{3, 5, 6, 12, 24 \}$ are presented.Comment: 10 pages, 4 figures, 2 tables, International Conference on System Engineering, Communications and Information Technologies, 2001, Punta Arenas. ICSECIT 2001 Proceedings. Punta Arenas: Universidad de Magallanes, 200

Multilayer Hadamard Decomposition of Discrete Hartley Transforms

Discrete transforms such as the discrete Fourier transform (DFT) or the discrete Hartley transform (DHT) furnish an indispensable tool in signal processing. The successful application of transform techniques relies on the existence of the so-called fast transforms. In this paper some fast algorithms are derived which meet the lower bound on the multiplicative complexity of the DFT/DHT. The approach is based on a decomposition of the DHT into layers of Walsh-Hadamard transforms. In particular, fast algorithms for short block lengths such as $N \in \{4, 8, 12, 24\}$ are presented.Comment: Fixed several typos. 7 pages, 5 figures, XVIII Simp\'osio Brasileiro de Telecomunica\c{c}\~oes, 2000, Gramado, RS, Brazi

A Low-throughput Wavelet-based Steganography Audio Scheme

This paper presents the preliminary of a novel scheme of steganography, and introduces the idea of combining two secret keys in the operation. The first secret key encrypts the text using a standard cryptographic scheme (e.g. IDEA, SAFER+, etc.) prior to the wavelet audio decomposition. The way in which the cipher text is embedded in the file requires another key, namely a stego-key, which is associated with features of the audio wavelet analysis.Comment: 2 pages, 1 figure, conference: 8th Brazilian Symposium on Information and Computer System Security, 2008, Gramado, RS, Brazi

Efficient Multiplex for Band-Limited Channels: Galois-Field Division Multiple Access

A new Efficient-bandwidth code-division-multiple-access (CDMA) for band-limited channels is introduced which is based on finite field transforms. A multilevel code division multiplex exploits orthogonality properties of nonbinary sequences defined over a complex finite field. Galois-Fourier transforms contain some redundancy and just cyclotomic coefficients are needed to be transmitted yielding compact spectrum requirements. The primary advantage of such schemes regarding classical multiplex is their better spectral efficiency. This paper estimates the \textit{bandwidth compactness factor} relatively to Time Division Multiple Access TDMA showing that it strongly depends on the alphabet extension. These multiplex schemes termed Galois Division Multiplex (GDM) are based on transforms for which there exists fast algorithms. They are also convenient from the implementation viewpoint since they can be implemented by a Digital Signal Processor.Comment: 6 pages, 5 figures, in: Workshop on Coding and Cryptography, INRIA, 1999, Paris. pp.235-241. arXiv admin note: text overlap with arXiv:1502.0588

The Discrete Cosine Transform over Prime Finite Fields

This paper examines finite field trigonometry as a tool to construct trigonometric digital transforms. In particular, by using properties of the k-cosine function over GF(p), the Finite Field Discrete Cosine Transform (FFDCT) is introduced. The FFDCT pair in GF(p) is defined, having blocklengths that are divisors of (p+1)/2. A special case is the Mersenne FFDCT, defined when p is a Mersenne prime. In this instance blocklengths that are powers of two are possible and radix-2 fast algorithms can be used to compute the transform.Comment: 5 pages, 1 table, Lecture Notes in Computer Science, LNCS 3124, Heidelberg: Springer Verlag, 2004, vol.1, pp.482-487, 200

Infinite Sequences, Series Convergence and the Discrete Time Fourier Transform over Finite Fields

Digital Transforms have important applications on subjects such as channel coding, cryptography and digital signal processing. In this paper, two Fourier Transforms are considered, the discrete time Fourier transform (DTFT) and the finite field Fourier transform (FFFT). A finite field version of the DTFT is introduced and the FFFT is redefined with a complex kernel, which makes it a more appropriate finite field version of the Discrete Fourier Transform. These transforms can handle FIR and IIR filters defined over finite algebraic structures.Comment: 8 pages. arXiv admin note: text overlap with arXiv:1502.0337

A Full Frequency Masking Vocoder for Legal Eavesdropping Conversation Recording

This paper presents a new approach for a vocoder design based on full frequency masking by octaves in addition to a technique for spectral filling via beta probability distribution. Some psycho-acoustic characteristics of human hearing - inaudibility masking in frequency and phase - are used as a basis for the proposed algorithm. The results confirm that this technique may be useful to save bandwidth in applications requiring intelligibility. It is recommended for the legal eavesdropping of long voice conversations.Comment: 7 pages, 3 figures, 3 tables, XXXV Cong. Nac. de Matematica Aplicada e Computacional, Natal, RN, Brazil 201