Analysis and design of multirate synchronous sampling schemes for sparse multiband signals

We consider the problem of developing efficient sampling schemes for multiband sparse signals. Previous results on multicoset sampling implementations that lead to universal sampling patterns (which guarantee perfect reconstruction), are based on a set of appropriate interleaved analog to digital converters, all of them operating at the same sampling frequency. In this paper we propose an alternative multirate synchronous implementation of multicoset codes, that is, all the analog to digital converters in the sampling scheme operate at different sampling frequencies, without need of introducing any delay. The interleaving is achieved through the usage of different rates, whose sum is significantly lower than the Nyquist rate of the multiband signal. To obtain universal patterns the sampling matrix is formulated and analyzed. Appropriate choices of the parameters, that is the block length and the sampling rates, are also proposed

Matrices: un modelo para las fotografías digitales

[EN] In this work we emphasize the relationship between two -apparently very different- disciplines: digital photography and mathematics. In fact, digital images -that everybody handles nowadays- are mathematically modeled by matrices. Moreover, all the manipulations over digital pictures can be expressed by means of matricial operations. In particular, here we set a problem of compression of digital images, based in the SVD (singular value decomposition), a concept learnt by the students of Linear Algebra courses. In this way, the students discover, by themselves, some important issues that teachers want to transmit to them: on one hand, that the theoretical concepts of Linear Algebra are directly applied to the technology that surrounds them everyday in our digital world; on the other hand, how mathematical modelization provides a powerful tool for the resolution of real practical problems.[ES] En este trabajo se resalta la relación que existe entre dos disciplinas, aparentemente muy distintas: la fotografía digital y las matemáticas. En efecto, las imágenes digitales -que todos manejamos hoy en día- se modelizan matemáticamente como matrices. Más aún, todas las manipulaciones sobre fotografías digitales se expresan mediante operaciones matriciales. En concreto, aquí se plantea un problema de compresión de imágenes digitales, basado en la DVS (descomposición en valores singulares) que los alumnos aprenden en clase de Álgebra Lineal. De esta forma, los alumnos descubren por sí mismos algunas realidades importantes que los docentes queremos transmitirles: en primer lugar, que los conocimientos teóricos adquiridos en Álgebra Lineal tienen una aplicación directa a la tecnología que les rodea diariamente en este mundo digital; y en segundo lugar, cómo la modelización matemática es una poderosa herramienta para resolver problemas prácticos reales.Domínguez Jiménez, ME. (2011). Matrices: un modelo para las fotografías digitales. Modelling in Science Education and Learning. 4:169-179. doi:10.4995/msel.2011.3070SWORD1691794G. Golub, C. Van Loan, "Matrix Computations," Ed. Johns Hopkins, 1996 (Third Edition).Muller, N., Magaia, L., & Herbst, B. M. (2004). Singular Value Decomposition, Eigenfaces, and 3D Reconstructions. SIAM Review, 46(3), 518-545. doi:10.1137/s003614450138751

Analysis of the Error Signal of the LMS Algorithm.

An analysis of the error signal of the Least-Mean- Square (LMS) algorithm is conducted from the robust control theory viewpoint. The difference equation that relates the input of the LMS algorithm and the error signal is presented. This equation is used to build the matrix that maps the input vector to the error vector. It is shown that has at least one singular value greater than 1. Therefore, the system may amplify noise at high frequencies. Nevertheless, the tap-weight vector may be chosen to prevent that noise amplification and improve the disturbance rejection performance of the LMS algorithm

DCT Type-III for Multicarrier Modulation

In this paper we propose the use of Discrete Cosine Transform Type-III (DCT3) for multicarrier modulation. There are two DCT3 (even and odd) and, for each of them, we derive the expressions for both prefix and suffix to be appended into each data symbol to be transmitted. Moreover, DCT3 are closely related to the corresponding inverse DCT Type-II even and odd. Furthermore, we give explicit expressions for the 1-tap per subcarrier equalizers that must be implemented at the receiver to perform the channel equalization in the frequency-domain. As a result, the proposed DCT3-based multicarrier modulator can be used as an alternative to DFT-based systems to perform Orthogonal Frequency-Division Multiplexing or Discrete Multitone Modulatio

Design of universal multicoset sampling patterns for compressed sensing of multiband sparse signals

Many problems in digital communications involve wideband radio signals. As the most recent example, the impressive advances in Cognitive Radio systems make even more necessary the development of sampling schemes for wideband radio signals with spectral holes. This is equivalent to considering a sparse multiband signal in the framework of Compressive Sampling theory. Starting from previous results on multicoset sampling and recent advances in compressive sampling, we analyze the matrix involved in the corresponding reconstruction equation and define a new method for the design of universal multicoset codes, that is, codes guaranteeing perfect reconstruction of the sparse multiband signal

A Binaural Neuromorphic Auditory Sensor for FPGA: A Spike Signal Processing Approach

This paper presents a new architecture, design flow, and field-programmable gate array (FPGA) implementation analysis of a neuromorphic binaural auditory sensor, designed completely in the spike domain. Unlike digital cochleae that decompose audio signals using classical digital signal processing techniques, the model presented in this paper processes information directly encoded as spikes using pulse frequency modulation and provides a set of frequency-decomposed audio information using an address-event representation interface. In this case, a systematic approach to design led to a generic process for building, tuning, and implementing audio frequency decomposers with different features, facilitating synthesis with custom features. This allows researchers to implement their own parameterized neuromorphic auditory systems in a low-cost FPGA in order to study the audio processing and learning activity that takes place in the brain. In this paper, we present a 64-channel binaural neuromorphic auditory system implemented in a Virtex-5 FPGA using a commercial development board. The system was excited with a diverse set of audio signals in order to analyze its response and characterize its features. The neuromorphic auditory system response times and frequencies are reported. The experimental results of the proposed system implementation with 64-channel stereo are: a frequency range between 9.6 Hz and 14.6 kHz (adjustable), a maximum output event rate of 2.19 Mevents/s, a power consumption of 29.7 mW, the slices requirements of 11 141, and a system clock frequency of 27 MHz.Ministerio de Economía y Competitividad TEC2012-37868-C04-02Junta de Andalucía P12-TIC-130

Estimation of Symmetric Channels for Discrete Cosine Transform Type-I Multicarrier Systems: A Compressed Sensing Approach

The problem of channel estimation for multicarrier communications is addressed. We focus on systems employing the Discrete Cosine Transform Type-I (DCT1) even at both the transmitter and the receiver, presenting an algorithm which achieves an accurate estimation of symmetric channel filters using only a small number of training symbols. The solution is obtained by using either matrix inversion or compressed sensing algorithms. We provide the theoretical results which guarantee the validity of the proposed technique for the DCT1. Numerical simulations illustrate the good behaviour of the proposed algorithm

On the use of discrete cosine transforms for multicarrier communications

In this correspondence, the conditions to use any kind of discrete cosine transform (DCT) for multicarrier data transmission are derived. The symmetric convolution-multiplication property of each DCT implies that when symmetric convolution is performed in the time domain, an element-by-element multiplication is performed in the corresponding discrete trigonometric domain. Therefore, appending symmetric redun-dancy (as prefix and suffix) into each data symbol to be transmitted, and also enforcing symmetry for the equivalent channel impulse response, the linear convolution performed in the transmission channel becomes a symmetric convolution in those samples of interest. Furthermore, the channel equalization can be carried out by means of a bank of scalars in the corresponding discrete cosine transform domain. The expressions for obtaining the value of each scalar corresponding to these one-tap per subcarrier equalizers are presented. This study is completed with several computer simulations in mobile broadband wireless communication scenarios, considering the presence of carrier frequency offset (CFO). The obtained results indicate that the proposed systems outperform the standardized ones based on the DFT

Worldwide prevalence of inadequate work ability among hospital nursing personnel: A systematic review and meta-analysis

Purpose To estimate the worldwide pooled prevalence of inadequate work ability among hospital nursing personnel using the Work Ability Index (WAI). Design Systematic review and meta-analysis. Methods A systematic search was conducted on Medline/PubMed, Scopus, Web of Science, Scielo, PsychInfo, CINAHL, Nursing and Allied Health, LILACS, and Google Scholar from inception to July 2021 to identify observational studies on work ability among hospital nursing personnel using the WAI. Two researchers independently completed the study selection, quality assessments, and data extraction on the prevalence of inadequate work ability that was pooled using the random effects model. Finally, subgroup analyses were performed to explore sources of heterogeneity. Findings A total of 42 studies were included, consisting of 24,728 subjects worldwide from 14 countries. Of these, 35 studies were included in the meta-analytical analyses. The worldwide pooled prevalence of inadequate work ability among hospital nursing personnel was 24.7% (95% CI = 20.2%-29.4%). High levels of heterogeneity were detected in all studies. Prevalence was higher in studies where samples were composed of nurses and nursing assistive personnel (26.8%; 95% CI = 22.4%-31.5%) than in those of nurses alone (22.2%; 95% CI = 13.1%-32.9%) and in studies where the sample was over 40 (28.1%; 95% CI = 19.5%-37.5%) than in those with a sample under that age (22.4%; 95% CI = 15.8%-29.7%). Conclusions Almost one in four members of hospital nursing staff in the world has inadequate work ability and therefore are at risk of several negative outcomes during their working life. These prevalence data correspond to the pre-pandemic period, so new studies should also be especially useful in quantifying the impact of the COVID-19 pandemic on work ability in the hospital nursing workforce. Clinical relevance The above findings justify the launch of initiatives that include annual assessment for the early identification of inadequate work ability, offering the possibility of anticipated corrective measures. Nursing workforce older than 40 years and those belonging to the professional category of nursing assistive personnel should be priority target groups for screening and intervention to improve work ability

Relaxation time for the alignment between quark spin and angular velocity in a rotating QCD medium

We compute the relaxation times for massive quarks and anti-quarks to align their spins with the angular velocity in a rigidly rotating medium at finite temperature and baryon density. The rotation effects are implemented using a fermion propagator immersed in a cylindrical rotating environment. The relaxation time is computed as the inverse of the interaction rate to produce an asymmetry between the quark (anti-quark) spin components along and opposite to the angular velocity. For conditions resembling heavy-ion collisions, the relaxation times for quarks are smaller than for anti-quarks. For semi-central collisions the relaxation time is within the possible life-time of the QGP for all collision energies. However, for anti-quarks this happens only for collision energies $\sqrt{s_{NN}}\gtrsim 50$ GeV. The results are quantified in terms of the intrinsic quark and anti-quark polarizations, namely, the probability to build the spin asymmetry as a function of time. Our results show that these intrinsic polarizations tend to 1 with time at different rates given by the relaxation times with quarks reaching a sizable asymmetry at a faster pace. These are key results to further elucidate the mechanisms of hyperon polarization in relativistic heavy-ion collisions.Comment: 9 pages, 10 figure