Javier Ramos

Rey Juan Carlos University | URJC · Signal and Communications Theory

Aims: The hepatitis C virus (HCV) has developed a strategy to coexist with its host resulting in varying degrees of tissue and cell damage, which generate different pathological phenotypes, such as varying degrees of fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). However, there is no integrated information that can predict the evolutiona...

Objective: Given the association between vitamin D deficiency and risk for cardiovascular disease, we used machine learning approaches to establish a model to predict the probability of deficiency. Determination of serum levels of 25-hydroxy vitamin D (25(OH)D) provided the best assessment of vitamin D status, but such tests are not always widely a...

Prediabetes is a type of hyperglycemia in which patients have blood glucose levels above normal but below the threshold for type 2 diabetes mellitus (T2DM). Prediabetic patients are considered to be at high risk for developing T2DM, but not all will eventually do so. Because it is difficult to identify which patients have an increased risk of devel...

Aim: The primary objective of our research was to compare the performance of data analysis to predict vitamin D deficiency using three different regression approaches and to evaluate the usefulness of incorporating machine learning algorithms into the data analysis in a clinical setting. Methods: We included 221 patients from our hypertension unit...

Few studies have addressed the predictive value of arterial stiffness determined by pulse wave velocity (PWV) in a high-risk population with no prevalent cardiovascular disease and with obesity, hypertension, hyperglycemia, and preserved kidney function. This longitudinal, retrospective study enrolled 88 high-risk patients and had a follow-up time...

Aim: We investigated the prevalence and the most relevant features of nonalcoholic steatohepatitis (NASH), a stage of nonalcoholic fatty liver disease, (NAFLD) in which the inflammation of hepatocytes can lead to increased cardiovascular risk, liver fibrosis, cirrhosis, and the need for liver transplant. Methods: We analyzed data from 2239 hyperte...

Appropriate management of hypertensive patients relies on the accurate identification of clinically relevant features. However, traditional statistical methods may ignore important information in datasets or overlook possible interactions among features. Machine learning may improve the prediction accuracy and interpretability of regression models...

Objective: Non-alcoholic fatty liver is a chronic liver disease in which fat is deposited in the liver, causing an inflammation called non-alcoholic steatohepatitis (NASH), and fibrosis. NASH is associated with metabolic syndrome (MS) and other cardiovascular risk factors. The aim of this study was to analyse the epidemiological features of NASH w...

Background: The aim of our study was to determine whether prediabetes increases cardiovascular (CV) risk compared to the non-prediabetic patients in our hypertensive population. Once this was achieved, the objective was to identify relevant CV prognostic features among prediabetic individuals. Methods: We included hypertensive 1652 patients. The...

Many indices have been proposed for cardiovascular risk stratification from electrocardiogram signal processing, still with limited use in clinical practice. We created a system integrating the clinical definition of cardiac risk subdomains from ECGs and the use of diverse signal processing techniques. Three subdomains were defined from the joint a...

Calculating the estimated glomerular filtration rate (eGFR) using creatinine-based equations may underestimate cardiovascular risk. Cystatin C-based eGFR may be a stronger prognostic biomarker than creatinine-based eGFR when assessing cardiovascular outcomes and mortality. Our aim was to determine whether levels of serum cystatin C, as an estimator...

Energy efficiency has been a leading issue inWireless Sensor Networks (WSNs) and has produced a vast amount of research. Although the classic tradeoff has been between quality of gathered data versus lifetime of the network, most works gave preference to an increased network lifetime at the expense of the data quality. A common approach for energy...

Healthcare associated infections (HAIS) can be acquired by patients during their stay in a hospital. HAIS are very endemic, causing a huge burden for the patients and for the health care system. We propose a machine learning approach to predict HAIS in an intensive care unit (ICU), combining heterogeneous data from longitudinal electronic health re...

Background Fast and accurate quality estimation of the electrocardiogram (ECG) signal is a relevant research topic that has attracted considerable interest in the scientific community, particularly due to its impact on tele-medicine monitoring systems, where the ECG is collected by untrained technicians. In recent years, a number of studies have ad...

Abstract Accurate channel state information and time/frequency synchronization are challenging to acquire in mobile ad hoc cooperative set-ups, where resource-constrained relaying terminals rapidly (dis)join cooperation. This paper derives low-complexity differential modulations and cooperative transmission schemes so that detection at the receiver...

System for reconstruction and visualization of cardiac electric activity, with high-resolution capabilities, which improves the performance of current systems by means of the inclusion of the a priori information of the bioelectric problem in a learning algorithm, and by means of the exploitation of the spatial and temporal correlations thanks to i...

Clinical data exchange among different organizations can be of great value in the field of Cardiovascular Risk Stratification (CVRS) research. Semantic interoperability is an essential key in order to integrate and exchange medical records and to automate the clinician workflow. We present a proposal to smooth out a way towards the exchange of CVRS...

This work optimizes the (traditionally separated) tasks of sensing and radio resource allocation jointly for an underlay CR paradigm. The formulation considers that secondary users adapt their power and rate based on the available imperfect channel state information, while taking into account the cost associated with acquiring such an information....

Under probability-of-interference constraints, proper spectrum sensing is crucial in Cognitive Radios (CRs). However, the capability of a CR to sense the spectrum is limited, especially when multiple users try to access multiple channels. As a consequence, control and resource allocation schemes should optimize not only transmitting resources, but...

Electronic Health Record (EHR) automates the clinician workflow, allowing evidence-based decision support and quality management. We aimed to start a framework for domain standardization of Cardiovascular Risk Stratification into the EHR, including risk indices whose calculation involves ECG signal processing. We propose the use of biomedical ontol...

The Telecommunications Engineering degree contains the study and understanding of a wide range of knowledge areas, like signal theory and communications, computer networks, and radio propagation. This diversity makes it hard for students to integrate different concepts, which is essential to tackle real and practical problems that involve different...

Successful deployment of cognitive radios requires efficient sensing of the spectrum and dynamic adaptation of the available resources according to the sensed (imperfect) information. While most works design these two tasks separately, in this paper the sensing and resource allocation schemes are designed jointly. We investigate an interweave CR wi...

Efficient design of cognitive radios (CRs) calls for secondary users implementing adaptive resource allocation schemes that exploit knowledge of the channel state information (CSI), while at the same time limiting interference to the primary system. This paper introduces stochastic resource allocation algorithms for both interweave (also known as o...

We design adaptive resource allocation schemes for cognitive radios so that the sum-rate of secondary users is optimized while the damage (interference) to the primary users is keep under control. Secondary users transmit orthogonally and adhere to limits on: a) the long-term interfering power at each primary receiver and b) the long-term capacity...

Algorithms that jointly allocate resources across different layers are envisioned to boost the performance of wireless systems. Recent results have revealed that two of the most important parameters that critically affect the resulting cross-layer designs are channel- and queue-state information (QSI). Motivated by these results, this paper relies...

Cognitive radios implement adaptive resource allocation schemes that exploit knowledge of the channel state information to optimize the performance of the secondary users while limiting the interference to the primary users. The algorithms in this paper are designed to maximize the weighted sum-rate of secondary users which transmit orthogonally an...

Efficient design of cognitive radios requires secondary users implementing adaptive resource allocation schemes that exploit knowledge of the channel state information (CSI), and limit interference to the primary system. In this paper, stochastic resource allocation algorithms are developed for underlay cognitive radios to maximize the sum-rate of...

The performance of systems where multiple users communicate over wireless fading links benefits from channel-adaptive allocation of the available resources. Different from most existing approaches that allocate resources based on perfect channel state information, this work optimizes channel scheduling along with per user rate and power loadings ov...

The Telecommunications Engineering degree contains the study and understanding of a wide range of knowledge areas, like signal theory and communications, computer networks, and radio propagation. This diversitymakes it hard for students to integrate different concepts, which is essential to tackle real and practical problems that involve different...

Indoor location systems based on IEEE 802.11b (WiFi) mobile devices often rely on the received signal strength indicator to estimate the user position. Two key characteristics of these systems have not yet been fully analyzed, namely, the temporal and spatial sampling process required to adequately describe the distribution of the electromagnetic f...

Efficient design of cognitive radio networks calls for secondary users implementing adaptive resource allocation, which requires knowledge of the channel state information in order to limit interference inflicted to primary users. In this context, the present paper develops stochastic resource allocation algorithms maximizing the sum-rate of second...

Increasing awareness of energy production evolution and global warming issues have forced regulatory international organizations to supervise energy consumption in different areas. Specifically the energy efficient operation of buildings, consumers of almost a third of the energy produced globally, is to be evaluated by means of specific procedures...

Cross-layer algorithms that jointly allocate resources at different layers are known to foster the communication performance in wireless networks. Recent works have shown that fading and queue information are among the most critical parameters to consider in cross-layer designs. Motivated by those findings, this work develops optimal algorithms tha...

Efficient design of cognitive radios requires secondary users implementing adaptive resource allocation schemes that exploit knowledge of the channel state information (CSI), and limit interference to the primary system. In this paper, stochastic resource allocation algorithms are developed for underlay cognitive radios to maximize the sum-rate of...

Orthogonal frequency-division multiplexing (OFDM) has been able to successfully exploit channel state information (CSI) at the transmitter, allowing to implement dynamic resource allocation schemes that improve spectral efficiency and error resilience. In most wireless communication systems, though, achieving a perfect CSI at the transmitter is dif...

This paper addresses the problem of finding an analytical expression for the end-to-end Average Bit Error Rate (ABER) in multihop Decode-and-Forward (DAF) routes within the context of wireless networks. We provide an analytical recursive expression for the most generic case of any number of hops and any single-hop ABER for every hop in the route. T...

Most rural areas in developing countries are isolated due to the lack of appropriate low-cost communication technologies. Previous experiences have shown that IEEE 802.11 can be used for the deployment of large static mesh networks with only minor changes to the MAC layer that enable WiFi transceivers to work properly even for very long distances (...

In this work we propose the use of vehicles as traffic sensors to quasi-synchronously measure both velocity and position of the probe. Those sensor vehicles wirelessly cooperate to relay that distributed information to a Data Fusion Center. That Data Fusion Center, in turn, calculates the Spatio-Temporal Velocity (STV) Field of the traffic from the...

Efficient design of wireless networks requires implementation of cross-layer algorithms that exploit channel state information. Capitalizing on convex optimization and stochastic approximation tools, this paper develops a stochastic algorithm that allocates resources at network, link, and physical layers so that a sum-utility of the average end-to-...

Human skin detection in color images is a key preprocessing stage in many image processing applications. Though kernel-based methods have been recently pointed out as advantageous for this setting, there is still few evidence on their actual superiority. Specifically, binary Support Vector Classifier (two-class SVM) and one-class Novelty Detection...

In vehicular communications, safety applications are the most challenging and they have become a main target in the research activity. Comprehensive testing and validation of such applications is very complex, but it is absolutely necessary if the applications are going to be widely used in vehicles all over the world. In this scope, simulation is...

The performance of systems where multiple users communicate over wireless fading links benefits from channel-adaptive allocation of the available resources. Different from most existing approaches that allocate resources based on perfect channel state information, this work optimizes channel scheduling along with per user rate and power loadings ov...

Indoor Location (IL) using Received Signal Strength (RSS) is receiving much attention, mainly due to its ease of use in deployed IEEE 802.11b (WiFi) wireless networks. Fingerprinting is the most widely used technique. It consists of estimating position by comparison of a set of RSS measurements, made by the mobile device, with a database of RSS mea...

It has been previously documented that the main features and sensing performance of electrograms (EGMs) recorded in implantable cardioverter defibrillators (ICDs) depend on lead configuration. Although this dependence has been ascribed to differences in lead sensitivity and spatial resolution, the quantification of these two properties on ICD has n...

Dynamic allocation of power, rate and channel access is a critical task in wireless networks. Capitalizing on convex optimization and stochastic approximation tools, this paper develops a stochastic resource allocation algorithm that minimizes average transmit power under individual average rate constraints. Focus is placed on networks where users...

Very limited data are available on the differences between spontaneous and induced episodes of ventricular fibrillation (VF) in humans. The aim of the study was to compare the spectral characteristics of the electrical signal recorded by an implantable cardioverter defibrillator (ICD) during both types of episodes. Thirteen ICD patients with at lea...

The efficiency of multi-access communications over wireless fading links benefits from channel-adaptive allocation of the available bandwidth and power resources. Different from most existing approaches that allocate resources based on perfect channel state information (P-CSI), this work optimizes channel scheduling and resource allocation over ort...

Emerging applications involving low-cost wireless sensor networks motivate well optimization of multi-user orthogonal frequency-division multiple access (OFDMA) in the power-limited regime. In this context, the present paper relies on limited-rate feedback (LRF) sent from the access point to terminals to minimize the total average transmit-power un...

When a terminal is recruited to cooperate with other neighboring terminals, its channel state and carrier frequency offset (CFO) may be unknown to the destination. Under these circumstances, this paper considers the use of distributed double-differential (DD) modulation, which simplifies receiver implementation because it by-passes channel and CFO...

We consider broadcasting to multiple destinations with uneven quality receivers. Based on their quality of reception, we group destinations in tiers and transmit using hierarchical modulations. These modulations are known to offer a practical means of achieving variable error protection of the broadcasted information to receivers of variable qualit...

Emerging applications involving low-cost wireless sensor networks motivate well optimization of multi-user orthogonal frequency-division multiple access (OFDMA) in the power-limited regime. In this context, the present paper relies on limited- rate feedback (LRF) sent from the access point to terminals to acquire quantized channel state information...

Emerging applications involving low-cost wireless sensor networks motivate well optimization of multi-user orthogonal frequency-division multiple access (OFDMA) in the power-limited regime. In this context, the present paper relies on limited-rate feedback (LRF) sent from the access point to terminals to minimize the total average transmit-power un...

The process of routing in large ad-hoc mobile networks is theoretically analyzed as the capacity of a packet to be directed form a source to a destination. The equivalence between directivity and an effective radius, which represents the actual knowledge of any node of its neighbourhood, is demonstrated. The mobility of the network is modelled as t...

In this work we develop a new theory to analyse the process of routing in large-scale ad-hoc wireless networks. We use a path integral formulation to examine the properties of the paths generated by different routing strategies in these kinds of networks. Using this theoretical framework, we calculate the statistical distribution of the distances b...

This article introduces wireless communications systems and explains the different products and standards related to wireless communications. The article is divided into five main sections. A brief introduction in Section 1 offers a perspective of the evolution of wireless communications systems and introduces a useful classification. After this in...

In coherent systems, when the channel is not known at the receiver, pilot-assisted techniques are needed to estimate the channel. Using OFDM, this paper overcomes the problem of designing such optimum pilot patterns that efficiently estimate doubly selective (in time and frequency)fading channels. We show that,decoupling time- and frequency- select...

In this paper, we explore the significance of second- and higher-order statistics learning in communication systems. The final goal in spread-spectrum communication systems is to receive a signal of interest completely free from interference caused by other concurrent signals. To achieve this end, we exploit the structure of the interference by des...

IntroductionUMTS Air InterfaceCDMA2000 Air InterfaceCompatibility IssuesEnhancing 3G CapabilitiesConclusions References and Further Reading

In this paper, novel structures for dynamic removal of multiuser interference are proposed. The natural gradient (NG) is used either to compute whitening matrices in linear blind minimum MSE or to develop new structures. As a result, we propose a family of centralized and non-centralized multiuser detectors (MUDs). The NG provides the MUDs with the...

A novel “self-decorrelating” technique is proposed to enhance the multipath constructive summation capability and the interference rejection capability of a class of maximum-SINR blind space-time CDMA RAKE receivers designed to tackle the near-far problem. This proposed “self-decorrelating” technique appears to have effectively removed the near-far...

A new method for low-complexity multiuser detection (MUD) based in the fast subspace decomposition (FSD) is proposed. The use of FSD allows the estimation of the number of users along with the multiuser detection on line. This leads to a fast multiuser estimation-detection scheme with ultra-low complexity. Furthermore, the method is proved to be st...

Blind space-time RAKE receivers for classical DS-CDMA that cancel strong multiuser access interference while optimally combining the desired user's multipath are presented. The delay spread is assumed to be fraction of a symbol interval as in the IS-95 CDMA standard. The post-correlation symbol interval is segmented into that which encompasses the...

A novel wideband beamforming technique for cellular CDMA systems is presented in this paper. The proposed algorithm asymptotically provides the maximum SINR estimate of the signal with the desired code (SDC) by optimally combining desired signals from different paths and canceling strong multiuser access interference (MUAI). A two-dimensional (2-D)...

This article addresses the simultaneous estimation of the azimuth and elevation angles of multiple co-channel signals incident upon an array of antennas. A new closed-form algorithm that is applicable with filled circular arrays (FCAs) is presented. The algorithm, which is called FCA-ESPRIT, is applicable with any FCA geometry, e.g., FCAs construct...

An algorithm that implements a 2D RAKE receiver for a cellular CDMA system that cancels strong multi-user access interference (MAI) and optimally combines multipath is presented in this paper. The algorithm asymptotically provides the optimum combination of space-time samples to maximize the SINR for the signal with the desired code (SDC) by optima...

An algorithm is presented for estimating the quantities needed by a space-time RAKE receiver for DS-CDMA to achieve maximum SINR for the desired user. The proposed algorithm, which is applicable in the case of either periodic or aperiodic spreading codes, asymptotically provides the exact time of arrival of each dominant multipath within a bit peri...

A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algorithm asymptotically provides the optimum combination of space-time samples to maximize the SINR for the signal with the desired code (SDC) by optimally combining its multipath and canceling strong multiuser access interference (MUAI). In contrast to pre...

Previously (Ramos and Zoltowski, 1997), we proposed a space-time adaptive RAKE receiver for CDMA that asymptotically provides the optimum combination of space-time samples for maximizing the SINR for the signal with the desired code (SDC) by canceling strong multi-user access interference (MUAI) and optimally combining the multipath. A variation of...

We discuss a new approach to self-organization that leads to novel adaptive algorithms for generalized eigen-decomposition and its variance for a single-layer linear feedforward neural network. First, we derive two novel iterative algorithms for linear discriminant analysis (LDA) and generalized eigen-decomposition by utilizing a constrained least-...

A novel wideband beamforming technique for cellular CDMA systems is presented. The proposed algorithm asymptotically provides the optimum combination of space-time samples for maximizing the SINR for the {ital Signal with the Desired Code} (SDC) by canceling strong {ital Multi-User Access Interference} (MUAI) and optimally combining the multipath....

We previously presented a blind 2D RAKE receiver for CDMA that cancels strong multi-user access interference and optimally combines the desired user's multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference space-frequency (space-tim...

We previously presented a blind 2D RAKE receiver for (direct sequence spread spectrum) CDMA that cancels strong multi-user access interference (MAI) and optimally combines multipath. After passing the output of each antenna through a matched filter based on the spreading waveform of the desired user, one estimates the signal plus interference spati...