Matrix Factorization Techniques for Recommender Systems

The need for low-complexity devices with low-power consumption motivates the application of suboptimal noncoherent ultra-wideband (UWB) receivers. This article provides an overview of the state of the art of recent research activities in this field. It introduces energy detection and autocorrelation receiver front ends with a focus on architectures that perform the initial signal processing tasks in the analog domain, such that the receiver does not need to sample the UWB received signals at Nyquist rate. Common signaling and multiple access schemes are reviewed for both front ends. An elaborate section illustrates various performance tradeoffs to highlight preferred system choices. Practical issues are discussed, including, for low-data-rate schemes, the allowed power allocation per pulse according to the regulator's ruling and the estimated power consumption of a receiver chip. A large part is devoted to signal processing steps needed in a digital receiver. It starts with synchronization and time-of-arrival estimation schemes, introduces studies about the narrowband interference problem, and describes solutions for high-data-rate and multiple access communications. Drastic advantages concerning complexity and robustness justify the application of noncoherent UWB systems, particularly for low-data-rate systems.

Noncoherent ultra-wideband systems

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Advanced Digital Signal Processing And Noise Reduction

A discrete-time equivalent system model is derived for differential and transmitted reference (TR) ultra-wideband (UWB) impulse radio (IR) systems, operating under heavy intersymbol-interference (ISI) caused by multipath propagation. In the systems discussed, data is transmitted using differential modulation on a frame-level, i.e., among UWB pulses. Multiple pulses (frames) are used to convey a single bit. Time hopping and amplitude codes are applied for multi user communications, employing a receiver front-end that consists of a bank of pulse-pair correlators. It is shown that these UWB systems are accurately modeled by second-order discrete-time Volterra systems. This proposed nonlinear equivalent system model is the basis for developing optimal and suboptimal receivers for differential UWB communications systems under ISI. As an example, we describe a maximum likelihood sequence detector with decision feedback, to be applied at the output of the receiver front-end sampled at symbol rate, and an adaptive inverse modeling equalizer. Both methods significantly increase the robustness in presence of multipath interference at tractable complexity.

Equivalent system model and equalization of differential impulse radio UWB systems

In this paper, we present an overview on the topic of noise reduction in the short-time Fourier transform (STFT) domain. First, we briefly review the conventional literature in the single- and multichannel cases separately. In the single-channel scenario, we focus on the spectral subtractive methods, Wiener filter based methods, speech amplitude estimators and estimators of the complex STFT coefficients. In the multi-channel scenario, we investigate in short a selection of key beamforming approaches as well as conventional post-filtering methods. Next, a detailed survey of the most recent advances in the STFT-based noise reduction methods is provided. This includes STSA estimators with super-Gaussian priors, noise power spectral density (PSD ) estimation, estimation methods in the modulation domain, estimation of spectral phase and noise PSD matrix estimation for multi-channel applications. Finally, we summarize the presented material and draw important conclusions on each of the investigated topics.

Recent Developments in Speech Enhancement in the Short-Time Fourier Transform Domain

A communication system based on transmit-reference (TR) ultra-wideband (UWB) is studied and further developed Introduced by Hoctor and Tomlinson, the aim of the TR-UWB transceiver is to provide a straightforward impulse radio system, feasible to implement with current technology, and to achieve either high data rate transmissions at short distances or low data rate transmissions in typical office or industrial environments The main contribution in this paper is the derivation of a signal processing model that takes into account the effects of the radio propagation channel, in particular, for the case where the two pulses in a doublet are closely spaced Several receivers based on the code-division multiple-access-like properties of the proposed model are derived, and the performance of the algorithms is tested in a simulation

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Signal model and receiver algorithms for a transmit-reference ultra-wideband communication system

This paper presents a signal processing model for the delay-hopped transmit-reference ultra wideband communications system introduced by Hoctor and Tomlinson. In that paper, a single-user receiver based on a bank of correlators and a sliding window integrator was proposed. However, the radio propagation channel also introduces correlations, which have a significant effect not taken into account by the Hoctor-Tomlinson receiver. Here we propose an accurate signal processing model for the transmit-reference system, including the effect of the propagation channel, as well as an algorithm to estimate the resulting effective channel coefficients.

Signal processing model for a transmit-reference UWB wireless communication system

In this paper, we introduce a hybrid fingerprint matcher which consists of two stages: local minutiae matching stage and consolidation stage. In the former stage, each minutia in the fingerprint is represented by a local feature vector which is built from the features of the neighboring minutiae within a fixed-radius circle around it. The features of each neighboring minutia are defined according to the spatial relationship with the central minutia and used for matching task. New calculation methods of the adaptive matching conditions for two neighboring minutiae and the local similarity score between two central minutiae are introduced. The latter stage performs multiple alignments based on the pairs of matching minutiae to produce the final matching score between two fingerprints. Extensive experiments over a public database used in Fingerprint Verification Competition 2002 (FVC2002) prove a considerable improvement in accuracy of our proposed algorithm against some well-known techniques and Top 5 participants of FVC2002.

A local feature vector for an adaptive hybrid fingerprint matcher

Thanks to its successful application in recommendation systems, collaborative filtering (CF) technique has become one of the most popular research topic in data mining and information retrieval. The two more dominant approaches to CF are neighborhood-based models and latent factor models. Currently, the state-of-the-art recommendation systems are mainly based on the latter approach owing to its ability to explore hidden factors connecting items to users. In this work, we propose a novel similarity measure which helps improve the accuracy of the neighborhood-based models. Intensive experiments show that our proposed model not only outperforms the best latent factor model with respect to RMSE by 2.2% but also works at least 2 times faster than its counterpart.

An Effective Similarity Measure for Neighborhood-based Collaborative Filtering

These days, automatic information extraction from identity documents is essential for many applications which require users authentication. In previous researches, this task was carried out by using image processing. However, the document identity recognition from images captured by smartphones encounters problems such as various backgrounds, perspective, blurring. Moreover, some cards may have dated backgrounds and diverse fonts printed manually by old typewriters. To solve these problems, this paper proposes an end-to-end system for extracting information from the Vietnamese identity cards captured by camera devices. Firstly, the ID card is aligned with the standard aspect ratio and orientation based on corner detection and national emblem detection. The proposed solution can locate and crop precisely the foreground target area of the oriented ID card in various contexts. In the text localization stage, a deep convolutional neural network model is used to bounding the required texts which are then classified by their positions. Finally, the text recognition is implemented based on the Attention OCR architecture. In experiments, this proposed method reduces processing time in comparison with the state of the art and the average accuracy achieved is higher 91%.

Quang Hieu Dang

Papers

Signal model and receiver algorithms for a transmit-reference ultra-wideband communication system

Signal processing model for a transmit-reference UWB wireless communication system

A local feature vector for an adaptive hybrid fingerprint matcher

An Effective Similarity Measure for Neighborhood-based Collaborative Filtering

A Robust End-To-End Information Extraction System for Vietnamese Identity Cards