New algorithm for distributed frequency assignments in IEEE 802.11

The continuous growth of IEEE 802.11 wireless local area networks (WLAN) brings the benefit of a high speed wireless access to packet networks, such as Internet. But it also entails the successive appearance of new unresolved problems. One of these problems consists in the degradation of the performance observed by the users when there is a great number of radio networks coexisting in the same area. In densely populated zones it is not strange to find WLANs of different nature (private, public, etc.) sharing a scarce resource as it is the radio spectrum. This problem can be mitigated with an appropriate channel allocation. In this paper we present an algorithm for the frequency assignment problem (FAP) in IEEE 802.11, based on classical graph colouring but adding the objective of reducing interferences among overlapping cells, and thus improving the global throughput performance. An accurate evaluation of interferences is obtained not only measuring power levels, but also being aware of traffic load. Important performance improvements have been observed on a real scenario

Redes ad-hoc : el próximo reto

El éxito de las comunicaciones inalámbricas y la progresiva reducción en el tamaño de los dispositivos con capacidad para comunicaciones de datos ha situado en un primer plano a las denominadas redes móviles ad-hoc o MANETs (Mobile Ad-hoc NETworks). En este artículo presentamos las características generales de este tipo de redes, haciendo énfasis en las nuevas condiciones que en ellas se asumen y que constituyen la problemática que la comunidad científica trata de resol ver. Presentamos asimismo el estado del arte en temas clave como el encaminamiento y señalamos la familia de aplicaciones de vanguardia que este nuevo paradigma posibilita.Peer Reviewe

Mean waiting time in the M/H2/s queue: application to mobile communications Systems

In this paper a procedure to approximately calculate the mean waiting time in the M/H2/s queue is presented. The approximation is heuristic although based in the intuitive symmetry between the deterministic and balanced hyperexponential-2 distributions. The three parameters which fully describe the H2 distribution are considered, so the approximation can also be used for the M/G/s queue when the first three moments are known. If only the first two moments of the holding time distribution are known, the estimation can also be applied accepting a lesser accuracy. The estimation proposed is a closed formula extremely easy to compute and the results are very accurate. This features makes it helpful in the design of mobile telecommunication systems with more than one channel and queueing allowed (like trunking Private Mobile Radio PMR systems), where holding time distributions with coefficients of variation higher than one may appear. As a second stage, the possibility of calls owning a certain level of priority is studied. Two service classes are considered according to a non-preemtive priority scheme (also known as Head Of the Line or HOL). This priority feature is often required in mobile telecommunications systems to improve the access delay of some special calls by degrading the delay suffered by the rest. If the proportion of calls owning priority is kept low, the degradation is shared by many calls and then kept small. In this paper a procedure to estimate the mean waiting time in queue for each priority class is presented. This procedure is also very easy to compute. The environment for which the results of this paper are intended suggests medium or heavy overall load and light priority load (priority proportion is kept low). This is the situation under which the accuracy of the proposed method is checked. Although simulations are necessary in the final phase of the design, the procedure presented here is helpful as a first quick insight into the system performance.Peer ReviewedPostprint (published version

Redes ad-hoc : el próximo reto

El éxito de las comunicaciones inalámbricas y la progresiva reducción en el tamaño de los dispositivos con capacidad para comunicaciones de datos ha situado en un primer plano a las denominadas redes móviles ad-hoc o MANETs (Mobile Ad-hoc NETworks). En este artículo presentamos las características generales de este tipo de redes, haciendo énfasis en las nuevas condiciones que en ellas se asumen y que constituyen la problemática que la comunidad científica trata de resol ver. Presentamos asimismo el estado del arte en temas clave como el encaminamiento y señalamos la familia de aplicaciones de vanguardia que este nuevo paradigma posibilita.Peer Reviewe

Integration of an adaptive infotainment system in a vehicle and validation in real driving scenarios

More services, functionalities, and interfaces are increasingly being incorporated into current vehicles and may overload the driver capacity to perform primary driving tasks adequately. For this reason, a strategy for easing driver interaction with the infotainment system must be defined, and a good balance between road safety and driver experience must also be achieved. An adaptive Human Machine Interface (HMI) that manages the presentation of information and restricts drivers’ interaction in accordance with the driving complexity was designed and evaluated. For this purpose, the driving complexity value employed as a reference was computed by a predictive model, and the adaptive interface was designed following a set of proposed HMI principles. The system was validated performing acceptance and usability tests in real driving scenarios. Results showed the system performs well in real driving scenarios. Also, positive feedbacks were received from participants endorsing the benefits of integrating this kind of system as regards driving experience and road safety.Postprint (published version

CoAP congestion control for the Internet of Things

“© © 2017 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.” August Betzler, Javier Isern, Carles Gomez, Ilker Demirkol, Josep Paradells, "Experimental evaluation of congestion control for CoAP communications without end-to-end reliability", Ad Hoc Networks, pp. , 2016, ISSN 15708705. DOI: 10.1109/MCOM.2016.7509394CoAP is a lightweight RESTful application layer protocol devised for the IoT. Operating on top of UDP, CoAP must handle congestion control by itself. The core CoAP specification defines a basic congestion control mechanism, but it is not capable of adapting to network conditions. However, IoT scenarios exhibit significant resource constraints, which pose new challenges on the design of congestion control mechanisms. In this article we present CoCoA, an advanced congestion control mechanism for CoAP being standardized by the Internet Engineering Task Force CoRE working group. CoCoA introduces a novel round-trip time estimation technique, together with a variable backoff factor and aging mechanisms in order to provide dynamic and controlled retransmission timeout adaptation suitable for the peculiarities of IoT communications. We conduct a comparative performance analysis of CoCoA and a variety of alternative algorithms including state-of-the-art mechanisms developed for TCP. The study is based on experiments carried out in real testbeds. Results show that, in contrast to the alternative methods considered, CoCoA consistently outperforms the default CoAP congestion control mechanism in all evaluated scenarios.Peer ReviewedPostprint (author's final draft

Development and implantation of two teleradiology and teleconsulting applications in Catalunya: RAIM and CARE

Two teleradiology applications with the added-value of teleconsulting are described: CARE, a high level diagnostic oriented application with videoconference and image and cursor synchronization based on SUN stations, and RAIM, a lower level PC-based application oriented to the transmission of patients' results, reports and associated images. Their technical characteristics and solutions adopted are presented together with the context in which they have been developed and thought to fit in.Peer ReviewedPostprint (published version

Integration of wireless communications in a GIS platform

This paper presents a new developed platform for the Commercialisation of Advanced Services of Geographical Information, focussed in portables devices, and that makes use of the telecommunication networks available today: Internet as the backbone and cellular networks (GSM + GPRS) as access networks. The platform implements a system for commercialising cartographic information in form of vectorial maps for different amount of time, guarantying property rights of the provided information. The problem with vectorial maps is that they have additional information, as points of interest or street names, that is very important to have them updated. So it is more interesting, for both the provider and the customer, to rent the maps for a small period of time, and also for a low fee, than selling them for ever and for a big amount of money. The client accesses to the service using a vectorial map player, that runs over PC or PDA (Personal Digital Assistant) platforms, and using a GPS receiver, it has navigation facilities. Before accessing to the information the player will request authorization to the server. Mobile devices will access Internet, where the server is connected, using WLAN, circuit switched cellular network (GSM) or packet switched cellular network (GPRS). The server side will control user access and download required maps. The platform includes also a system to improve GPS localization (Differential GPS). The communication between the client and the server uses SMS messages of GSM system, one for the request and another for the answer. This operation is very sensitive to response delay and it has been optimised in order to work properly.Peer Reviewe

From 6LoWPAN to 6Lo: expanding the universe of IPv6-supported technologies for the Internet of Things

© 2017 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 worksLeveraging 6LoWPAN, the IETF 6Lo Working Group has targeted adaptation of IPv6 over a new generation of communication technologies for the IoT. These comprise Bluetooth LE, ITU-T G.9959, DECT ULE, MS/TP, NFC, IEEE 1901.2, and IEEE 802.11ah. This article comprehensively analyzes the 6Lo technologies and adaptation layers, giving the motivation for critical design decisions, highlighting crucial aspects for performance, and presenting main challenges.Postprint (author's final draft