Beamforming and Multiuser Detection in CDMA Systems with External Interferences

Multiuser detection has been investigated to mitigate the near-far effect in CDMA systems. Antenna arrays have been shown to provide spatial diversity and cancel undesired signals. In this paper we consider the synergy of both multiuser detection and antenna arrays for the base station of a CDMA system. The receiver we proposed consists of the known multiuser decorrelator, which cancels multiple-access interferences followed by a beamformer for each user, which cancels the external interferences. This receiver adds an extra branch to the decorrelator. This additional branch, corresponding to a fictitious user with an unused code and zero power, allows to estimate the external interference signal subspace and compute a suitable beamforming weight-vector that cancels the external interferences. The receiver is also extended to the asynchronous case and all of this without any training signal or any a priori spatial information.Peer ReviewedPostprint (published version

Blind multiuser adaptive combining for asynchronous cdma systems

This paper presents a novel technique to globally estimate and track the direction of arrival (DOA) of different users in an asynchronous CDMA system. The estimates are obtained exploiting the temporal structure of CDMA signals. No training signal nor a priori spatial information is required. The necessary information is extracted directly from the received signals. The proper combining of the overall information present at the receiver after the despreading, jointly with an Eigenvalue Decomposition (EVD), let as estimate the generalized steering vector for each user. Furthermore, a direct iteration method is introduced in our scheme in order to make the array robust to channel variations and to reduce the computational load of the EVD required for each user.Peer ReviewedPostprint (published version

Blind multi-user combining at the base station for asynchronous CDMA systems

This paper studies the potential benefits of antenna arrays in cellular CDMA communications and proposes a powerful scheme to undertake the array processing at the base station in CDMA mobile systems. The proposed technique exploits the temporal structure of CDMA signals. The necessary information is extracted directly from the received signals, thus no training signal orPeer ReviewedPostprint (published version

Approximations of the aggregated interference statistics for outage analysis in massive MTC

This paper presents several analytic closed-form approximations of the aggregated interference statistics within the framework of uplink massive machine-type-communications (mMTC), taking into account the random activity of the sensors. Given its discrete nature and the large number of devices involved, a continuous approximation based on the Gram–Charlier series expansion of a truncated Gaussian kernel is proposed. We use this approximation to derive an analytic closed-form expression for the outage probability, corresponding to the event of the signal-to-interference-and-noise ratio being below a detection threshold. This metric is useful since it can be used for evaluating the performance of mMTC systems. We analyze, as an illustrative application of the previous approximation, a scenario with several multi-antenna collector nodes, each equipped with a set of predefined spatial beams. We consider two setups, namely single- and multiple-resource, in reference to the number of resources that are allocated to each beam. A graph-based approach that minimizes the average outage probability, and that is based on the statistics approximation, is used as allocation strategy. Finally, we describe an access protocol where the resource identifiers are broadcast (distributed) through the beams. Numerical simulations prove the accuracy of the approximations and the benefits of the allocation strategy.Peer ReviewedPostprint (published version

Simulation model for the analysis of the implementation of rfid technology industry of cement

Las operaciones logísticas asociadas al despacho y distribución de productos terminados en la industria del cemento requieren de sistemas de control y tecnologías de trazabilidad que permitan cumplir los requerimientos del cliente. El artículo presenta las bondades de la implementación de tecnología RFID para la industria del cemento. Se desarrolló un modelo de simulación con dinámica de sistemas que muestra el comportamiento del flujo de material en la industria de cementos. Los resultados del modelo muestran el efecto de implementación de tecnología de trazabilidad en los inventarios y una disminución del tiempo de las operaciones logísticas de despacho así como el control y registro de toda la operación.The logistical operations associated with shipping and distribution of finished cement industry products require control systems and traceability technologies that would meet customer requirements. The article presents the benefits of implementing RFID technology for the cement industry. A simulation model was developed with system dynamics showing the flow behavior of material in cement industry. The model results show the effect of implementation of traceability technology in inventories and a decrease in time of dispatch logistics operations as well as the monitoring and recording of the entire operation

Stochastic resource allocation with a backhaul constraint for the uplink

We propose a novel stochastic radio resource alloca- tion strategy for the uplink that achieves long-term fairness in terms of similar bitrates considering backhaul and air-interface capacity limitations. We focus on a single cell scenario based on WCDMA technology. We propose to use a maximin criteria to introduce fairness among the different users’ throughputs. An stochastic approximation is implemented to obtain an online algorithm where the Lagrange multipliers are estimated at each scheduling period. Our results show that the proposed scheme achieves higher fairness among the users and, in some cases, a higher sum-rate compared with the well-known proportional fair scheduler.Postprint (author's final draft

Closed-form capacity bounds for downlink and uplink decoupling

©2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Downlink (DL) and uplink (UL) decoupling (DUDe) is a new architectural paradigm where DL and UL are not constrained to be associated to the same base station (BS). Thus, a user having access to multiple BSs within a dense cellular network can receive the DL traffic from one BS and send its UL traffic through another. Building upon this architectural paradigm, the present paper provides tight analytical bounds in closed form for the UL ergodic capacity that depend solely on the density of the infrastructure. The devised bounds account for the backbone network congestion and the synchronization of the acknowledgments of the decoupled channels. The proposed bounds are compared against extensive numerical simulations demonstrating the tractability and accuracy of the expressions.Peer ReviewedPostprint (author's final draft

Stochastic Geometry Analysis and Design of Wireless Powered MTC Networks

Machine-type-communications (MTC) are being crucial in the development of next generation mobile networks. Given that MTC devices are usually battery constrained, wireless power transfer (WPT) and energy harvesting (EH) have emerged as feasible options to enlarge the lifetime of the devices, leading to wireless powered networks. In that sense, we consider a setup where groups of sensors are served by a base station (BS), which is responsible for the WPT. Additionally, EH is used to collect energy from the wireless signals transmitted by other sensors. To characterize the energy obtained from both procedures, we model the sporadic activity of sensors as Bernoulli random variables and their positions with repulsive Mat\'ern cluster processes. This way, the random activity and spatial distribution of sensors are introduced in the analysis of the energy statistics. This analysis can be useful for system design aspects such as energy allocation schemes or optimization of idle-active periods, among others. As an example of use of the developed analysis, we include the design of a WPT scheme under a proportional fair policy.Comment: This work has been accepted at the 2020 21st IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2020). Copyright held by IEE

A stochastic approach for resource allocation with backhaul and energy harvesting constraints

We propose a novel stochastic radio-resource-allocation strategy that achieves long-term fairness considering backhaul and air-interface capacity limitations. The base station (BS) is powered only with a finite battery that is recharged by an energy harvester. The energy harvesting is also taken into account in the proposed resource-allocation strategy. The constrained scenario is often found in remote rural areas where the backhaul connection is limited, and the BSs are fed with solar panels of reduced size. Our results show that the proposed scheme achieves higher fairness among the users and provides greater worst user rate and sum rate if an average backhaul constraint is considered.Peer ReviewedPostprint (published version

Estudio de la función de SFRP1 en la ontogenia de los linfocitos T y en la patogenia de la leucemia T linfoblástica aguda

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 21-07-2017Esta tesis tiene embargado el acceso al texto completo hasta el 21-01-2019La señalización a través de Notch1 juega un papel fundamental en la determinación de linaje T y la diferenciación intratímica, pero su desregulación provoca la transformación oncogénica de los timocitos en desarrollo dando lugar a la leucemia T linfoblástica aguda (T-ALL). Estudios recientes han demostrado que la señalización a través de Nocth1 es modulada negativamente durante el proceso de neurogénesis de retina de ratón por Sfrp1, un regulador de la vía de Wnt capaz de unirse a la metaloproteasa ADAM10 e inhibir su actividad. Teniendo en cuenta que la activación de Notch1 depende de ADAM10 en los timocitos en desarrollo, el objetivo general de este estudio fue establecer si Sfrp1 era capaz de regular tanto la diferenciación de las células T como la patogénesis de la T-ALL dependientes de Notch1. Aproximaciones experimentales de pérdida de función utilizando ratones mutantes Sfrp1-/- revelaron que Sfrp1 regula los números de timocitos y la dinámica de diferenciación durante dos estadios madurativos consecutivos, antes e inmediatamente después de la selección-β. En etapas tempranas de la ontogenia (E15,5), los timos Sfrp1-/- presentan un incremento en los números de timocitos, que sobre-expresan el IL-7R, una conocida diana de Notch1, pero además presentan un incremento en la apoptosis y una diferenciación acelerada. Un día después, la pérdida de Sfrp1 impide el resacate de la apoptosis y la expansion de los timocitos que han superado la selección-β, provocando un bloqueo en la transición de los progenitors DN al estadio DP. Sin embargo, el defecto en el desarrollo de los embriones Sfrp1-/- es superado en los ratones adultos, que aún así presentan una pérdida significativa de los progenitors intratímicos más inmaduros, reflejando su diferenciación acelerada. Aproximaciones de ganancia de función fueron empleadas para estudiar el papel de SFRP1 en la patogénesis de la T-ALL mediada por NOTCH1. Nuestros resultados mostraron que la sobre-expresión de SFRP1 en líneas celulares humanas T-ALL dependientes de NOTCH1 y en T-ALLs primarias resulta en una disminución en la activación de NOTCH1 y en la proliferación celular in vitro, además de impedir la progresión tumoral in vivo. Apoyando el papel de SFRP1 durante la patogénesis de la TALL, "next generation sequencing" de los exones codificantes de SFRP1, nos permitió identificar una mutación en SFRP1, y análisis epigenéticos revelaron quince regiones hipermetiladas en SFRP1, sugiriendo que existe una regulación epigenética de la expresión de SFRP1 en la T-ALL humana. En resumen, nuestro estudio aporta evidencias de que la estrecha regulación de la señalización de Notch por Sfrp1 juega un papel esencial durante el desarrollo de los linfocitos T y en la patogénesis de la T-ALL, posicionando a Sfrp1 como una prometedora diana terapéutica para el tratamiento de la T-ALL dependiente de Notch