Performance evaluation of MAC transmission power control in wireless sensor networks.

In this paper we provide a method to analytically compute the energy saving provided by the use of Transmission Power Control (TPC) at the MAC layer in Wireless Sensor Networks (WSN). We consider a classical TPC mechanism: data packets are transmitted with the minimum required power to achieve a given packet error probability, whereas the additional MAC control packets are transmitted with the nominal (maximum) power. This scheme has been chosen because it does not modify the network topology, since control packet transmission range does not change. This property also allow us to compute analytically the expected energy savings. Besides, this type of TPC can be implemented in the current sensor hardware, and can be applied directly to several MAC protocols already proposed for WSN. The foundation of our analysis is the evaluation of L ratio, defined as the total energy consumed by the network using the original MAC protocol divided by the total energy consumed if the TPC mechanism is employed. In the L computation we emphasize the basic properties of sensor networks. Namely, the savings are calculated for a network that is active a very long time, and where the number of sensors is supposed to be very large. The nodes position is assumed to be random -for the sake of example a normal bivariate distribution is assumed in the paper- and no node mobility is considered. In the analysis we stress the radio propagation and the distribution of the nodes in the network, that will ultimately determine the performance of the TPC. Under these conditions we compute the mean value of L. Finally, we have applied the method to evaluate the benefits of TPC for TDMA and CSMA with two representative protocols, L-MAC and S-MAC using their implementation reference parameters. The conclusion is that, while S-MAC does not achieve a significant improvement, LMAC may reach energy savings up to 10-20%

Simulation scalability issues in wireless sensor networks.

The formidable growth of WSN research has opened challenging issues about their performance evaluation. Despite the steady increase in mathematical analysis and experimental deployments, most of the community has chosen simulation for their study. Although it seems straightforward, this approach becomes a quite delicate matter. Complexity is caused by several issues. First, the large number of nodes heavily impacts simulation performance and scalability. Second, credible results demand an accurate characterization of the sensor radio channel. New aspects, inherent in WSN, must be included in simulators, e.g. a physical environment and an energy model, leading to different degrees of accuracy versus performance. Moreover, many necessary models are in the continuous-time domain (e.g. heat transmission, battery discharge), being complex to integrate into discrete event network simulators. These issues result in an exponential growth of the overall network state information. Through this survey we review these problems both quantitatively and qualitatively while depicting a common suitable simulation model. We also briefly describe the most significant simulation frameworks available.This work has been funded by the Economy, Industry and Innovation Council, with the SOLIDMOVIL project (2I04SU044), by Fundacion Seneca with the ARENA Project (00546/PI/04), both of them from the Region of Murcia, and by the Spanish Research Council with the ARPaq project (TEC2004-05622-C04-02/TCM)

Evaluación de herramientas de simulación de Redes Vehiculares

Las redes vehiculares (VANET) se presentan como una pieza clave en el desarrollo vial para aumentar la seguridad y mejorar la calidad de vida de los usuarios. La simulación juega un papel principal en hacer que estos proyectos sean una realidad. Este tipo de simulación VANET contribuye al estudio del tránsito y las intercomunicaciones propias en su amplia variedad sin tener que realizar experimentos de campo, para llegar a soluciones que no impliquen inversiones a ciegas y sin necesidad de construir nuevas y costosas infraestructuras. Las herramientas de simulación VANET permiten entender los principales retos y dificultades en comparación con otras redes inalámbricas así como llevar a cabo estudios que evalúen nuevos protocolos de comunicación. En este artículo se presenta el resultado de una búsqueda exhaustiva y de un estudio pormenorizado de las herramientas opensource para la simulación vehicular disponibles en la comunidad investigadora.Centro Universitario de la Defensa. Escuela de Turismo de Cartagena. Escuela Técnica Superior de Ingeniería Industrial UPCT. Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT). Escuela de Ingeniería de Caminos y Minas (EICM). Escuela de Arquitectura e Ingeniería de Edificación (ARQ&IDE). Parque Tecnológico de Fuente Álamo. Navantia. Campus Mare Nostru

Despliege de redes inalambricas de entornos industriales

This document discusses the potential of wireless technologies in solving many of the problems found in an industrial environment, where a reliable communication network is needed but a wired system fails to meet all the requirements imposed by such a harsh environment. After a brief review of industrial networks, the requirements of an industrial environment and some emerging wireless technologies of interest, a particular application scenario is shown: applying wireless technologies to a shipyard.Este trabajo ha sido parcialmente financiado por el proyecto nacional FAR-IP (TIC2000-1734-C03-03)

A Stochastic Model for Chain Collisions of Vehicles Equipped With Vehicular Communications

Improvement of traffic safety by cooperative vehicular applications is one of the most promising benefits of vehicular ad hoc networks (VANETs). However, to properly develop such applications, the influence of different driving parameters on the event of vehicle collision must be assessed at an early design stage. In this paper, we derive a stochastic model for the number of accidents in a platoon of vehicles equipped with a warning collision notification system, which is able to inform all the vehicles about an emergency event. In fact, the assumption of communications being used is key to simplify the derivation of a stochastic model. The model enables the computation of the average number of collisions that occur in the platoon, the probabilities of the different ways in which the collisions may take place, as well as other statistics of interest. Although an exponential distribution has been used for the traffic density, it is also valid for different probability distributions for traffic densities, as well as for other significant parameters of the model. Moreover, the actual communication system employed is independent of the model since it is abstracted by a message delay variable, which allows it to be used to evaluate different communication technologies. We validate the proposed model with Monte Carlo simulations. With this model, one can quickly evaluate numerically the influence of different model parameters (vehicle density, velocities, decelerations, and delays) on the collision process and draw conclusions that shed relevant guidelines for the design of vehicular communication systems, as well as chain collision avoidance applications. Illustrative examples of application are provided, although a systematic characterization and evaluation of different scenarios is left as future work.This work was supported in part by the MICINN/FEDER project under Grant TEC2010-21405-C02-02/TCM (CALM) and in part by Fundación Seneca RM under Grants 00002/CS/08 FORMA and 04549/GERM/06. The work of J. Garcia-Haro was supported by Grant PR2009-0337. The work of E. Egea was supported by the Universidad Politécnica de Cartagena under Grant PMPDI-UPCT-2011. The work of J. Tomas- Gabarron was supported by Grant AP2008-02244. The work of C. Garcia-Costa was supported by Grant 12347/FPI/09

OBIWAN: wireless sensor networks with OMNET++

Simulation is essential in WSN study. However, the nature of WSN makes it an unexpectedly complex task. The extremely large number of nodes, the need for an environment model, and the cross-layer dependencies of the models are some of the reasons for this complexity. Many of the existing simulation tools do not properly handle these issues. In this paper, OBIWAN, a new simulator for WSN is presented. In its design, critical issues like reusability, scalability and cross-layer dependencies have been addressed. The results on its capabilities and performance are provided through a case study involving several thousand nodes and an environment modelThis, work has been funded by the Economy,Industry and Innovation Council,with the SOLIDMOVIL project(2I04SU044),by Fundación Séneca both from the Region of Murcia with the ARENA Project(00546/PI/04)and by the Spanish Research Council with the ARPaq project(TEC2004-05622-C04-02/TCM)and CSI-RHET project(TEC2005-08068–C04-01/TCM)

Performance evaluation of non-persistent CSMA as anti-collision protocol for active RFID tags.

In this paper we propose the use of non-persistent CSMA as an anti-collision procedure for RFID active tags. Current proposals for both passive and active tags are based on the framed slotted ALOHA protocol, which does not scale well requiring additional procedures for frame length adaptation. However, active RFID devices already include carrier sense capabilities with no additional cost and, thus, CSMA may be employed seamlessly. Nevertheless, selecting the contention micro-slots of CSMA in the classical way (i.e., with a uniform distribution and an exponential back-off algorithm) does not result in an efficient identification process, as we will demonstrate. Fortunately, better choices can be found. Recently, an optimal distribution for the selection of micro-slots for event-driven sensor networks has been computed, as well as a practical implementation: the Sift distribution. In this work we propose the application of the quasi-optimal Sift distribution along with CSMA for active tag identification. By means of an analytical study, we evaluate the average time needed for identification with this mechanism and compare it with the current ISO 18000-7 and EPC “Gen 2” standard. The results reveal that the Sift-based non-persistent CSMA outperforms both of them. Moreover, it also scales much better, without the need for further adaptation mechanismsThis work has been funded by the Spanish Ministerio de Educación y Ciencia with the projects DEP2006-56158-C03-03/EQUI and m:ciudad (FIT-330503- 2006-2, partially funded by ERDF) and by the Spanish Research Council with the ARPaq project (TEC2004-05622-C04-02/TCM)

Sistemas de localización e identificación para el sector logístico y de servicios

La presentación nos muestra la inclusión de las nuevas tecnologías en todos los modos de transporte, su diseño e implantación de tecnologías ITS, ( Sistemas Inteligentes de Transportes).Fundación Séneca. Ministerio de Educación y Ciencia. Fondo Social Europeo

Una introducción a las redes de sensores inalámbricos

La creación de entornos inteligentes, creados a partir de la incorporación de dispositivos simples a los objetos que nos rodean, es el objetivo de la Computación Ubicua. Dentro de este campo se encuentran las Redes de Sensores Inalámbricos o WSN (Wireless Sensor Networks). Estas redes están formadas por cientos o miles de pequeños nodos inteligentes pero simples y de muy bajo coste, conformando una red que es autónoma donde ellos mismos se auto-organizan y la gestionan y, a su vez, colaboran y cooperan para medir un parámetro físico del entorno. En este artículo se presentan las características de estas redes, sus usos potenciales y acusadas restricciones en el diseño, que hacen que los retos que plantean tengan un gran interés investigadorEscuela Técnica Superior de Ingeniería de Telecomunicació

A wireless sensor networks MAC protocol for real-time applications.

Wireless Sensor Networks (WSN) are designed for data gathering and processing, with particular requirements: low hardware complexity, low energy consumption, special traffic pattern support, scalability, and in some cases, real-time operation. In this paper we present the Virtual TDMA for Sensors (VTS) MAC protocol, which intends to support the previous features, focusing particularly on real-time operation. VTS adaptively creates a TDMA arrangement with a number of timeslots equal to the actual number of nodes in range. Thus, VTS achieves an optimal throughput performance compared to TDMA protocols with fixed size of frame. The frame is set up and maintained by a distributed procedure, which allows sensors to asynchronously join and leave the frame. In addition, duty cycle is increased or decreased in order to keep latency constant below a given deadline. Therefore, a major advantage of VTS is that it guarantees a bounded latency, which allows soft real-time applications.This work has been cofunded by the Economy, Industry and Innovation Council, with the SOLIDMOVIL project (2I04SU044), supported by Fundacion Seneca, from the Region of Murcia with the ARENA Project (00546/PI/04), with the ARPaq project (TEC2004-05622-C04-02/TCM) by the Spanish Research Council and the CSI-RHET project (TEC2005-08068-C04-01/TCM)