The unprecedented growth in wireless Internet-of-Things and WiFi devices has renewed interest in mechanisms for efficient spectrum reuse. Existing schemes require some level of primary-secondary coordination, cross-channel state estimation and tracking, or activity detection– which complicate implementation. For low-power short-range secondary communication, the main impediment is strong and time-varying (e.g., intermittent) interference from the primary system. This paper proposes a practical underlay scheme that permits reliable secondary communication in this regime. The secondary transmitter merely has to send its signal twice, at very low power - a few dBs above the noise floor, but far below the primary's interference. Exploiting the repetition structure, reliable and computationally efficient recovery of the secondary signal is possible via canonical correlation analysis (CCA). Experiments using a software radio testbed reveal that, for a secondary user with only two receive antennas, reliable detection of the secondary signal is possible for signal to interference plus noise ratio (SINR) in the range of −20 to −40 dB. The approach works with unknown time-varying channels, digital or analog modulation, it is immune to carrier frequency offset, and, as a side-benefit, it provides means for accurate synchronization of the secondary user even at very low SINR.
General Linear Modeling (GLM) is the most commonly used method for signal detection in Functional Magnetic Resonance Imaging (fMRI) experiments, despite its main limitation of not taking into consideration common spatial dependencies between voxels. Multivariate analysis methods, such as Generalized Canonical Correlation Analysis (gCCA), have been increasingly employed in fMRI data analysis, due to their ability to overcome this limitation. This study, evaluates the improvement of sensitivity of the GLM, by applying gCCA to fMRI data after standard preprocessing steps. Data from a block-design fMRI experiment was used, where 25 healthy volunteers completed two action observation tasks at 1.5T. Whole brain analysis results indicated that the application of gCCA resulted in significantly higher intensity of activation in several regions in both tasks and helped reveal activation in the primary somatosensory and ventral premotor area, theoretically known to become engaged during action observation. In subject-level ROI analyses, gCCA improved the signal to noise ratio in the averaged timeseries in each preselected ROI, and resulted in increased extent of activation, although peak intensity was considerably higher in just two of them. In conclusion, gCCA is a promising method for improving the sensitivity of conventional statistical modeling in task related fMRI experiments.
We consider the problem of tensor factorization in the cases where one of the factors is constrained to have orthonormal columns. We adopt the alternating optimization framework and derive an efficient algorithm that is also suitable for parallel implementation. We describe in detail a distributed memory implementation of the algorithm on a three-dimensional processor grid. The speedup attained by a message-passing implementation of the algorithm is significant, indicating that it is a competitive candidate for the solution of very large tensor factorization problems with orthogonality constraints.
Canonical correlation analysis (CCA) is a classic statistical method for discovering latent co-variation that underpins two or more observed random vectors. Several extensions and variations of CCA have been proposed that have strengthened our capabilities in terms of revealing common random factors from multiview datasets. In this work, we first revisit the most recent deterministic extensions of deep CCA and highlight the strengths and limitations of these state-of-the-art methods. Some methods allow trivial solutions, while others can miss weak common factors. Others overload the problem by also seeking to reveal what is not common among the views -- i.e., the private components that are needed to fully reconstruct each view. The latter tends to overload the problem and its computational and sample complexities. Aiming to improve upon these limitations, we design a novel and efficient formulation that alleviates some of the current restrictions. The main idea is to model the private components as conditionally independent given the common ones, which enables the proposed compact formulation. In addition, we also provide a sufficient condition for identifying the common random factors. Judicious experiments with synthetic and real datasets showcase the validity of our claims and the effectiveness of the proposed approach.
Functional magnetic resonance imaging (fMRI) is one of the most popular methods for studying the human brain. Task-related fMRI data processing aims to determine which brain areas are activated when a specific task is performed and is usually based on the Blood Oxygen Level Dependent (BOLD) signal. The background BOLD signal also reflects systematic fluctuations in regional brain activity which are attributed to the existence of resting-state brain networks. We propose a new fMRI data generating model which takes into consideration the existence of common task-related and resting-state components. We first estimate the common task-related temporal component, via two successive stages of generalized canonical correlation analysis and, then, we estimate the common task-related spatial component, leading to a task-related activation map. The experimental tests of our method with synthetic data reveal that we are able to obtain very accurate temporal and spatial estimates even at very low Signal to Noise Ratio (SNR), which is usually the case in fMRI data processing. The tests with real-world fMRI data show significant advantages over standard procedures based on General Linear Models (GLMs).
In this paper, we present a method for decoding uplink messages in Internet of Things (IoT) networks that employ packet repetition. We focus on the Sigfox protocol, but our approach is applicable to other IoT protocols that employ message repetition. Our approach endeavors to enhance the reliability of message capture as well as the error rate performance at the base station. To achieve this goal, we propose a novel technique that capitalizes on the unique features of the IoT network's uplink transmission structure. Through simulations, we demonstrate the effectiveness of our method in various scenarios, including single-user and multi-user setups. We establish the resilience of our approach under higher system loads and interference conditions, showcasing its potential to improve IoT network performance and reliability even when a large number of devices operates over limited spectrum. Our findings reveal the potential of the proposed method as a promising solution for enabling more dependable and energy-efficient communication in IoT Low Power Wide Area Networks.
Graphs are powerful abstractions that naturally capture the wealth of relationships in our interconnected world. This paper proposes a new approach for graph alignment, a core problem in graph mining. Classical (e.g., spectral) methods use fixed embeddings for both graphs to perform the alignment. In contrast, the proposed approach fixes the embedding of the 'target' graph and jointly optimizes the embedding transformation and the alignment of the 'query' graph. An alternating optimization algorithm is proposed for computing high-quality approximate solutions and compared against the prevailing state-of-the-art graph aligning frameworks using benchmark real-world graphs. The results indicate that the proposed formulation can offer significant gains in terms of matching accuracy and robustness to noise relative to existing solutions for this hard but important problem.
We consider the problem of learning smooth multivariate probability density functions. We invoke the canonical decomposition of multivariate functions and we show that if a joint probability density function admits a truncated Fourier series representation, then the classical univariate Fejér-Riesz Representation Theorem can be used for learning bona fide joint probability density functions. We propose a scalable, flexible, and direct framework for learning smooth multivariate probability density functions even from potentially incomplete datasets. We demonstrate the effectiveness of the proposed framework by comparing it to several popular state-of-the-art methods.
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