Impacto de mecanismos de seguridad en sensores IEEE 802.15.4

En la actualidad son muchos los mecanismos de seguridad que el estándar IEEE 802.15.4 permite a las redes inalámbricas de sensores [1] Dicho estándar define las especificaciones de la Capa de Acceso al Medio y la Capa Física de los dispositivos inalámbricos de área personal. La última revisión corresponde al 2006. Dichas revisiones y actualizaciones son hechas por el grupo de trabajo 802.15. Sin embargo estos mecanismos consumen recursos como memoria y batería, que son un poco limitados en estos dispositivos. Además de contribuir a los retardos en la comunicación. Por lo cual, en el presente trabajo se presenta de manera práctica el impacto que el uso de mecanismos de seguridad tienen en el desempeño de este tipo de redes. Para ello se hizo una comparación de dicho desempeño de manera teórica basándose en lo presentado en [2], con los valores óptimos apegados a lo especificado en el estándar IEEE 802.15.4, en contraste con pruebas reales. Para estas pruebas se hizo uso del sistema operativo TinyOS [3] y de las operaciones de seguridad MAC (Capa de Acceso al Medio) ofrecidas por el chip CC2420 usado en las motas TelosB. Además se presenta el desgaste de la batería, el cual es otro punto importante que se desea conservar en los sensores.Postprint (published version

Estudio hidrodinámico por CFD del casco de una lancha motora

Esta tesis expone un estudio detallado de la preparación, ejecución y análisis de los resultados obtenidos en una serie de simulaciones por CFD del comportamiento en la interacción casco-fluido de una embarcación de pre planeo, proporcionando una posible validación hidrodinámica fuera de las pruebas experimentales, así como una guía para simulaciones similares futuras de carácter académico, o una herramienta de consulta para otros campos. Esta embarcación es la Lady, construida en los años setenta y recuperada para realizar pruebas de eficiencia energética dentro de los límites del puerto. El objeto principal de trabajo ha sido seis simulaciones con diferentes velocidades y líneas de flotación de modo que se pueda adquirir un estudio lo bastante completo. El autor ha desarrollado el objeto planteado en la generación de un modelo en 3D representando el casco desnudo de la Lady, cubriéndolo de un dominio para que el fluido pueda simularse juntamente con la imposición de unas condiciones en sus bordes y fronteras. Se ha realizado un mallado de suficiente calidad para capturar el efecto del fluido en las proximidades del casco, seguido de un set up en el software de simulación numérica. Debido a las limitaciones de velocidad del puerto los números de Froude empleados han sido bajos comparados con las altas velocidades más características para este tipo de embarcación. Los promedios de nº de Reynolds en toda la superficie mojada para todos los casos planteados han sido mayores del orden de 10+7 por lo que ya se prevé un flujo turbulento en la mayoría de la región ocupada por el casco. La selección de un modelado de turbulencia adecuado ha tenido un gran peso en la preparación del problema. Los resultados obtenidos han tenido que ser analizado y debidamente interpretados para entender sus funciones en las leyes de la física, y de esta manera sacar unas conclusiones apropiadas. El presente trabajo corrobora la enorme capacidad de simular los efectos físicos reales a efectos prácticos que tiene la ciencia de la dinámica de fluidos computacional para aplicaciones de la ingeniería de fluidos

A transmit power control proposal for IEEE 802.11 cellular networks

Actually, the idea of designing an outdoor cellular network based on WLAN IEEE 802.11 results very attractive, due to the several advantages that this technology presents. It offers the equipment at a lower cost, operates in unlicensed spectrum and allows higher data rates.If we realize a comparison of the system performance between a cellular environment and an isolated single cell scenario we observe that the first situation exhibits a considerable decrease, due to co-channel interference, that rises with the growth of the transmission data rate employed. In this paper, we propose a power control mechanism, as a method to reduce the interference influence on network performance, and to homogenize the behavior of the different stations in the system. We present its performance under different load conditions and compare this behavior with the original case, without the employment of any power control mechanism.Peer Reviewe

Forwarding Techniques for IP Fragmented Packets in a Real 6LoWPAN Network

Wireless Sensor Networks (WSNs) are attracting more and more interest since they offer a low-cost solution to the problem of providing a means to deploy large sensor networks in a number of application domains. We believe that a crucial aspect to facilitate WSN diffusion is to make them interoperable with external IP networks. This can be achieved by using the 6LoWPAN protocol stack. 6LoWPAN enables the transmission of IPv6 packets over WSNs based on the IEEE 802.15.4 standard. IPv6 packet size is considerably larger than that of IEEE 802.15.4 data frame. To overcome this problem, 6LoWPAN introduces an adaptation layer between the network and data link layers, allowing IPv6 packets to be adapted to the lower layer constraints. This adaptation layer provides fragmentation and header compression of IP packets. Furthermore, it also can be involved in routing decisions. Depending on which layer is responsible for routing decisions, 6LoWPAN divides routing in two categories: mesh under if the layer concerned is the adaptation layer and route over if it is the network layer. In this paper we analyze different routing solutions (route over, mesh under and enhanced route over) focusing on how they forward fragments. We evaluate their performance in terms of latency and energy consumption when transmitting IP fragmented packets. All the tests have been performed in a real 6LoWPAN implementation. After consideration of the main problems in forwarding of mesh frames in WSN, we propose and analyze a new alternative scheme based on mesh under, which we call controlled mesh under

Wake-up radio systems for cooperative-intelligent transport systems architecture

© 2019 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.Cooperative-Intelligent Transport systems are new applications developed on top of communications between vehicles and between vehicles and fixed infrastructure. Their architecture envisages devices deployed along the routes and streets, transmitting and receiving different kind of messages belonging to different services. Quite often, these devices will be located in isolated places with very low number of vehicles passing nearby. Being in isolated places, these devices will require to be feed with rechargeable batteries and alternative power sources, the usage of which need to be very efficient. The fact of continuously transmitting messages whenever there is no vehicle to receive them demands a solution. In this paper, we propose to use a well-known saving power strategy already used in Internet of Things, the Wake-up Radio systems. As vehicular communications are based on IEEE 802.11 standard, we propose to use a Wake-up Radio system based on this standard as well, being thus no additional hardware needed for the wake-up transmitter. The paper analyses the feasibility of using this solution on several vehicular applications.Peer ReviewedPostprint (author's final draft

Study of asymmetric traffic influence on IEEE 802.11 WLAN family, enhancement proposals

This paper is focused on the study of WLAN performance in IEEE 802.11 networks that are in a situation of asymmetric traffic, where the access point (AP) transmits much more than the user stations (US). This situation is very different from the symmetric one, wherein all the stations have the same traffic load. The paper also presents a discussion of the different mechanisms in order to increase AP priority under the asymmetric traffic situation.Peer Reviewe

Evaluation of IEEE 802.11 coexistence in WLAN deployments

This is a pre-print of an article published in Wireless Networks. The final authenticated version is available online at: https://doi.org/10.1007/s11276-017-1540-z.Wi-Fi has become a successful technology since the publication of its first WLAN standard due to continuous advances and updates while remaining always backwards compatible. Backwards compatibility among subsequent standards is an important feature in order to take advantage of previous equipment when publishing a new amendment. At present, IEEE 802.11b support is still mandatory to obtain the Wi-Fi certification. However, there are several harmful effects of allowing old legacy IEEE 802.11b transmissions in modern WLAN deployments. Lower throughput per device is obtained at slow rates, but also the effect known as performance anomaly, which nearly leads to starvation of fast stations, has to be taken into account. Finally, backwards compatibility mechanisms pose an important penalty in throughput performance for newer specifications. This paper presents a thorough analysis of the current state of IEEE 802.11, comparing coverage range and throughput performance among subsequent amendments, and focusing on the drawbacks and benefits of including protection mechanisms.Peer ReviewedPostprint (author's final draft

IEEE 802.11g performance in presence of beacon control frames

Most studies of the performance of IEEE 802.11 consider scenarios of ad-hoc topology networks and do not contemplate the network broadcast information contained in beacon frames. The paper presents a study of the performance of a WLAN whose infrastructure's topology is such that the access point is in charge of broadcasting the beacon frames. Thus, it is more realistic than previous studies, because beacon frames are usually transmitted in order to announce control information and network identity. Furthermore, in the coverage area, user stations are likely to be working at different data rates, depending on their signal quality. Because beacon frames must be received by all stations, they are transmitted at the lowest data rate operating in the coverage area. The article introduces a mathematical method to calculate the influence of beacon frames on the total throughput, collision probability and delays of the IEEE 802.11g protocol. The model is validated by simulation analysis.Peer Reviewe