Cross-layer design and optimization of medium access control protocols for wlans

This thesis provides a contribution to the field of Medium Access Control (MAC) layer protocol design for wireless networks by proposing and evaluating mechanisms that enhance different aspects of the network performance. These enhancements are achieved through the exchange of information between different layers of the traditional protocol stack, a concept known as Cross-Layer (CL) design. The main thesis contributions are divided into two parts. The first part of the thesis introduces a novel MAC layer protocol named Distributed Queuing Collision Avoidance (DQCA). DQCA behaves as a reservation scheme that ensures collision-free data transmissions at the majority of the time and switches automatically to an Aloha-like random access mechanism when the traffic load is low. DQCA can be enriched by more advanced scheduling algorithms based on a CL dialogue between the MAC and other protocol layers, to provide higher throughput and Quality of Service (QoS) guarantees. The second part of the thesis explores a different challenge in MAC layer design, related to the ability of multiple antenna systems to offer point-to-multipoint communications. Some modifications to the recently approved IEEE 802.11n standard are proposed in order to handle simultaneous multiuser downlink transmissions. A number of multiuser MAC schemes that handle channel access and scheduling issues and provide mechanisms for feedback acquisition have been presented and evaluated. The obtained performance enhancements have been demonstrated with the help of both theoretical analysis and simulation obtained results

Análisis de técnicas de acceso al medio avanzadas basadas en colas distribuidas y mecanismos Cross-Layer para sistemas de comunicaciones inalámbricas

En este proyecto se partirá de los resultados previos realizados sobre el rendimientos de protocolos de la familia DQ* como DQCA o DQMAN para sistemas de comunicaciones inalámbricas. Estos protocolos se basan en colas distribuidas y permiten incluir de forma sencilla mecanismos Cross-Layer que mejoran sustancialmente las comunicaciones en términos de throughput, retardo y jitter de los paquetes. Se pretende analizar a partir de simulaciones el rendimiento de algunas mejoras propuestas recientemente sobre los protocolos, así como su comportamiento en entornos multicelulares (con múltiples AP o nodos móviles).El uso de las redes inalámbricas 802.11 está en continua expansión en la actualidad. Este hecho provoca que cada vez se requiera un mayor control para garantizar una cierta calidad de servicio (QoS) en diferentes aplicaciones, especialmente las que trabajan en tiempo real. Un primer objetivo de este trabajo ha sido estudiar el comportamiento de un sistema WLAN haciendo uso de la variación MS de un protocolo MAC de alta eficiencia llamado DQCA (Distributed Queueing Collision Avoidance), dando soporte a cuatro clases de servicio, diferenciando y priorizando cada servicio. Este escenario ha requerido realizar la adaptación del funcionamiento del protocolo para dar soporte a la situación multi-servicio. Otro objetivo era poder estudiar el sistema haciendo uso de la capa física del estándar 802.11g partiendo de la base de los estudios ya realizados a partir de la capa física de 802.11b. Una vez realizado el primer paso y obtenido un sistema DQCA multiservicio (MS systems) con cuatro clases de servicios de diferente prioridad, se han propuesto y estudiado dos técnicas basadas en el diseño Cross-Layer, con el fin de mejorar la eficiencia y el aprovechamiento de los recursos disponibles en redes WLAN. La idea fundamental del diseño Croos- Layer consiste en permitir un intercambio de información entre las capas del modelo OSI que forman el sistema de comunicaciones. En el presente trabajo se han propuesto técnicas Cross-Layer que utilizan la información proveniente de la capa física en la capa MAC, adaptando las transmisiones según el estado del canal radio. El estudio del rendimiento de las diferentes técnicas se han llevado a cabo con simulaciones por ordenador, que han permitido evaluar y cuantificar las mejoras que las técnicas propuestas ofrecen en distintos escenarios significativos. El análisis de los resultados obtenidos ha permitido concluir que las técnicas propuestas ofrecen mejoras significativas en los distintos escenarios de trabajo considerados, especialmente en términos de throughput y retardo medio. Sus principales virtudes son la sencillez de implementación y los buenos resultados que ofrecen en cuanto al aprovechamiento de los recursos del sistema. Tras el estudio realizado concluimos que las técnicas propuestas permiten mejorar la eficiencia de sistemas WLAN de forma significativa y por tanto se trata de propuestas interesantes a tener en cuenta en el diseño de futuras redes inalámbricas

Radio Communications

In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks

Emerging Communications for Wireless Sensor Networks

Wireless sensor networks are deployed in a rapidly increasing number of arenas, with uses ranging from healthcare monitoring to industrial and environmental safety, as well as new ubiquitous computing devices that are becoming ever more pervasive in our interconnected society. This book presents a range of exciting developments in software communication technologies including some novel applications, such as in high altitude systems, ground heat exchangers and body sensor networks. Authors from leading institutions on four continents present their latest findings in the spirit of exchanging information and stimulating discussion in the WSN community worldwide

Opportunistic scheduling using an enhanced channel state information update scheme for WLAN systems with DQCA

This paper studies the feasibility of using low-power wireless technologies such as Bluetooth, IEEE 802.15.4 and ZigBee in high-speed railway scenarios that involve bidirectional ground-to-train communication. The presented results have been obtained through experimental tests conducted at the Madrid-Barcelona high-speed rail line. A multiplatform communication system has been installed in a high-speed train, circulating at velocities up to 300 km/h, whereas autonomous devices have been disseminated along of the railway path to communicate with the onboard devices. The conclusions drawn from this work will be used as guidelines for the future implementation of autonomous communication platforms for high-speed rail connectivity.Peer Reviewe

Opportunistic scheduling using an enhanced channel state information update scheme for WLAN systems with DQCA

This paper studies the feasibility of using low-power wireless technologies such as Bluetooth, IEEE 802.15.4 and ZigBee in high-speed railway scenarios that involve bidirectional ground-to-train communication. The presented results have been obtained through experimental tests conducted at the Madrid-Barcelona high-speed rail line. A multiplatform communication system has been installed in a high-speed train, circulating at velocities up to 300 km/h, whereas autonomous devices have been disseminated along of the railway path to communicate with the onboard devices. The conclusions drawn from this work will be used as guidelines for the future implementation of autonomous communication platforms for high-speed rail connectivity.Peer Reviewe