SNR Based DSDV Routing Protocol for MANET

A wireless mobile ad-hoc (MANET) network is a dynamic formation of wireless nodes to perform a temporary network without center administration node. The wireless node which is also known as mobile platform are free to move randomly within its network coverage. The MANET is an autonomous system which operates in isolation (local area network only) or may have gateways to an interface with a fixed network. One of the main parts of MANET is its routing protocol in network layer. The protocol has to decide which path that needs to be taken by packets to ensure the packet transfer from sender to receiver. The algorithms that calculate these paths are referred as routing algorithms (Kurose, 2009) Due to unpredictable behavior of the wireless medium in MANETs environment, the standard routing protocol based on hop count suffers due to the noise that collected at receiving nodes (Douglas, 2003). In this project the Signal-to-Noise (SNR) based routing protocol has been adapted into the standard Destination Sequenced Distance Vector (DSDV) routing algorithm by developing an algorithm to calculate the cumulative average SNR from source to destination and apply the algorithm in the DSDV routing protocol. The expected result is SNR based DSDV routing protocol and the outcome would be comparisons of performance metrics between standard DSDV for the throughput, end-to-end delay and packet delivery ratio versus transmission rate and node numbers

Distributed Flow Control and Medium Access in Multihop Ad Hoc Networks

Recent studies have shown that the performance of wireless multihop ad hoc networks is very poor. In this paper, we first demonstrate that one important reason of the poor performance is the close coupling between medium contention and network congestion. Therefore, we present a framework of distributed flow control and medium access control to address both medium contention and network congestion. The proposed scheme utilizes the MAC layer control frames to efficiently conduct the network layer's flow control function and only allows the upstream nodes to forward enough packets to make it possible for the downstream nodes to fully utilize the shared channel but never introduce severe MAC collisions and network congestion. Extensive simulations illustrate that the proposed scheme well controls congestion and greatly alleviates medium collisions. It achieves up to 12 times of the end-to-end throughput of 802.11, maintains a short delay and a low control overhead, and improves the fairness regardless of the hop count and the traffic load

Diseño de un Esquema Cross-Layer para el Balance entre Eficiencia Energética y Calidad de Servicio en la Transmisión de Tráfico Multimedia en Redes Ad-Hoc

This thesis dissertation addresses the problem of energy constraints in ad hoc wireless networks. In this sort of networks nodes are generally powered by means of batteries, which involves significant limitations regarding the time of operation of devices. The nodes whose battery level describes important energy depletion represent potential elements for loss of connectivity, which results in an increase of packet loss rate. Therefore, the management of energy expenditure is one of the main research challenges to face in ad hoc networks, especially when developing applications in real scenarios. However, energy management is not a trivial task due to the inherent features of this kind of networks, such as the distributed operation as well as the access medium mechanism. In that sense, traditional solutions of energy optimization based on the definition of power-saving intervals (sleep mode) are not suitable considering the operational characteristics of an ad hoc network, due to the substantial deterioration of network connectivity. In addition, the exponential growth of applications focused on the transmission of multimedia contents (especially video) available on mobile devices involves specific quality of service levels. Consequently, the design of solutions for the optimization of energy resources should be carried out without degrading the Quality of Experience perceived by the users. The contributions of this thesis are focused, in the first place, on the analysis of those factors which generate an increase of the energy consumption in the wireless medium and are related to the principle of operation of the radio interface. In particular, the intense operation in reception mode on the interference areas, as a result of the overhearing effect, as well as the high number of transmission retries due to channel access contention, are defined as the main aspects that increase energy demand in the network. On the other hand, with the aim of optimizing energy resources in the nodes without causing damage on the Quality of Service, this thesis proposes meaningful improvements to the routing protocol by means of a cross-layer scheme. Specifically, the designed mechanism carries out an evaluation of both the energy capacity available in the nodes and the distribution of devices along the wireless medium. To that end, this proposal introduces a new metric in the routing computation process, called strategic value, which reports the importance of a node in the network in terms of connectivity (i.e. number of neighbor nodes). This scheme aims to reduce the energy expenditure caused by the overhearing effect along the areas with higher node density as well as to extend the lifetime for those nodes with higher number of neighbors which are strategic to preserve network connectivity. Additionally, considering the current pragmatic approach in ad hoc networks focused on the design of specific applications, the evaluation hereby presented has been performed by means of a simulation environment and also through the implementation of a testbed. Specifically, the operation of the proposed scheme has been analyzed on a set of ad hoc nodes which has been implemented through development platforms. Also, a software tool has been developed in order to control and configure the experiments. Results prove that the proposal allows to extend the lifetime of the network as well as to increase packet reception rate as a consequence of the prevention in the route breakages due to energy depletion. Finally, it is worth mentioning that the knowledge acquired by the design, configuration and analysis of experiments by means of hardware devices, has motivated the development of proposals and application studies of ad hoc networks in real environments, which represent an additional contribution of this thesis dissertation.El presente trabajo de tesis doctoral aborda la problemática de las limitaciones de energía en redes inalámbricas ad hoc. En este tipo de redes, los nodos generalmente emplean baterías como fuente de alimentación, lo que limita de forma dramática la autonomía de funcionamiento. Los nodos con mayor agotamiento de energía constituyen potenciales elementos para la pérdida de conectividad parcial o total de la red ocasionando el incremento de la pérdida de paquetes. Por tanto, la gestión eficiente del gasto es uno de los principales desafíos a enfrentar en el ámbito de investigación de redes ad hoc, en especial para el desarrollo de aplicaciones en escenarios reales de operación. Sin embargo, dicha gestión no es una tarea trivial debido a las características inherentes de este tipo de redes, como por ejemplo la operación distribuida, así como el acceso compartido al medio inalámbrico. En tal sentido, los mecanismos usuales de optimización del gasto de energía basados en el establecimiento de períodos de bajo consumo (modo sleep), no se ajustan a las características operativas de una red ad hoc, debido al impacto notable que ocasionan sobre la conectividad en la red. Además, el crecimiento significativo de las aplicaciones y servicios de distribución de contenidos multimedia, especialmente tráfico de vídeo, demandan niveles específicos de calidad de servicio. Por consiguiente, el diseño de soluciones de optimización de los recursos de energía disponible en los nodos no debe implicar la degradación de la calidad de experiencia percibida por los usuarios finales. Las contribuciones del trabajo de tesis se centran, en primer lugar, en el análisis de los factores que incrementan el gasto de energía en el medio inalámbrico y que están relacionados con el principio de operación de la interfaz de radio. En particular, el incremento dramático del funcionamiento en modo recepción ocasionado sobre las zonas de interferencia por el efecto overhearing así como el mayor número de intentos de transmisión debido a la contienda por el acceso al canal, se definen como las principales causas que incrementan la demanda de energía en la red. Por otra parte, con el objetivo de optimizar los recursos de energía disponibles en los nodos sin ocasionar un perjuicio sobre la calidad de servicio, en el presente trabajo de tesis se proponen mejoras al protocolo de encaminamiento mediante un esquema cross-layer. En concreto, el mecanismo diseñado realiza una evaluación de la capacidad de energía disponible en los nodos, así como de la distribución de los dispositivos en el medio inalámbrico. Con tal fin, la propuesta introduce en el cómputo de enrutamiento una métrica nueva denominada valor estratégico, la cual reporta la importancia de un nodo en la red en términos de conectividad (número de dispositivos vecinos). El esquema apunta a reducir el gasto de energía ocasionado por el efecto overhearing en las zonas con mayor densidad de dispositivos, así como extender la autonomía de operación sobre aquellos nodos con mayor número de vecinos, que resultan estratégicos para conservar la conectividad en la red. Además, de forma consecuente con el actual enfoque pragmático en redes ad hoc orientado al diseño de soluciones para escenarios específicos de aplicación, la evaluación de la propuesta se ha realizado tanto en un entorno de simulación, así como mediante la implementación de un testbed. Específicamente, se ha analizado la operación del mecanismo de enrutamiento propuesto sobre un conjunto de nodos ad hoc implementados mediante plataformas de desarrollo. Adicionalmente, se ha desarrollado una herramienta para el control y configuración de los experimentos. Los resultados demuestran que la propuesta permite extender el tiempo de operación de la red, así como incrementar la tasa de paquetes en recepción como consecuencia de la prevención en la ruptura de los enlaces por agotamientoEl present treball de tesi doctoral aborda la problemàtica de les limitacions d'energia en xarxes sense fil ad hoc. En este tipus de xarxes, els nodes generalment empren bateries com a font d'alimentació, la qual cosa limita de forma dramàtica l'autonomia de funcionament. Els nodes amb major esgotament d'energia constituïxen potencials elements per a la pèrdua de connectivitat parcial o total de la xarxa, ocasionant l'increment de la pèrdua de paquets. Per tant, la gestió eficient de la despesa és un dels principals desafiaments a enfrontar en l'àmbit d'investigació de xarxes ad hoc, en especial per al desenvolupament d'aplicacions en escenaris reals d'operació. No obstant això, aquesta gestió no és una tasca trivial a causa de les característiques inherents d'este tipus de xarxes, com per exemple l'operació distribuïda així com l'accés compartit al mitjà sense fil. En este sentit, els mecanismes usuals d'optimització de la despesa d'energia basats en l'establiment de períodes de baix consum (mode sleep), no s'ajusten a les característiques operatives d'una xarxa ad hoc, a causa de l'impacte notable que ocasionen sobre la connectivitat a la xarxa. A més, el creixement significatiu de les aplicacions i serveis de distribució de continguts multimèdia, especialment tràfic de vídeo, demanden nivells específics de qualitat de servei. Per tant, el disseny de solucions d'optimització dels recursos d'energia disponible en els nodes no ha d'implicar la degradació de la qualitat d'experiència percebuda pels usuaris finals. Les contribucions del treball de tesi se centren, en primer lloc, en l'anàlisi dels factors que incrementen la despesa d'energia en el mitjà sense fil i que estan relacionats amb el principi d'operació de la interfície de ràdio. En particular, l'increment dramàtic del funcionament en mode recepció, ocasionat sobre les zones d'interferència per l'efecte overhearing, així com el major nombre d'intents de transmissió a causa de la contesa per l'accés al canal, es definixen com les principals causes que incrementen la demanda d'energia a la xarxa. D'altra banda, amb l'objectiu d'optimitzar els recursos d'energia disponibles en els nodes sense ocasionar un perjudici sobre la qualitat de servici, en el present treball de tesi es proposen millores al protocol d'encaminament mitjançant un esquema cross-layer. En concret, el mecanisme dissenyat realitza una avaluació de la capacitat d'energia disponible en els nodes així com de la distribució dels dispositius en el mitjà sense fil. Amb tal fi, la proposta introduïx en el còmput d'encaminament una nova mètrica denominada valor estratègic, la qual reporta la importància d'un node en la xarxa en termes de connectivitat (nombre de dispositius veïns). L'esquema reduix la despesa ocasionada per l'efecte overhearing a les zones amb major densitat de dispositius i estén l'autonomia d'operació sobre aquells nodes amb major nombre de veïns, que resulten estratègics per conservar la connectivitat a la xarxa. A més, de forma conseqüent amb l'actual enfocament pragmàtic en xarxes ad hoc orientat al disseny de solucions per a escenaris específics d'aplicació, l'avaluació de la proposta s'ha realitzat tant en un entorn de simulació així com per mitjà de la implementació d'un testbed. Específicament, s'ha analitzat l'operació del mecanisme d'encaminament proposat sobre un conjunt de nodes ad hoc implementats mitjançant plataformes de desenvolupament. Addicionalment, s'ha desenvolupat una eina per al control i configuració dels experiments. Els resultats demostren que la proposta permet estendre el temps d'operació de la xarxa així com incrementar la taxa de paquets en recepció com a conseqüència de la prevenció en la ruptura dels enllaços per esgotament d'energia.González Martínez, SR. (2017). Diseño de un Esquema Cross-Layer para el Balance entre Eficiencia Energética y Calidad de Servicio en la Transmisión de Tráfico Multimedia en Redes Ad-Hoc [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/84284TESI

Centralized Rate Allocation and Control in 802.11-based Wireless Mesh Networks

Wireless Mesh Networks (WMNs) built with commodity 802.11 radios are a cost-effective means of providing last mile broadband Internet access. Their multihop architecture allows for rapid deployment and organic growth of these networks. 802.11 radios are an important building block in WMNs. These low cost radios are readily available, and can be used globally in license-exempt frequency bands. However, the 802.11 Distributed Coordination Function (DCF) medium access mechanism does not scale well in large multihop networks. This produces suboptimal behavior in many transport protocols, including TCP, the dominant transport protocol in the Internet. In particular, cross-layer interaction between DCF and TCP results in flow level unfairness, including starvation, with backlogged traffic sources. Solutions found in the literature propose distributed source rate control algorithms to alleviate this problem. However, this requires MAC-layer or transport-layer changes on all mesh routers. This is often infeasible in practical deployments. In wireline networks, router-assisted rate control techniques have been proposed for use alongside end-to-end mechanisms. We evaluate the feasibility of establishing similar centralized control via gateway mesh routers in WMNs. We find that commonly used router-assisted flow control schemes designed for wired networks fail in WMNs. This is because they assume that: (1) links can be scheduled independently, and (2) router queue buildups are sufficient for detecting congestion. These abstractions do not hold in a wireless network, rendering wired scheduling algorithms such as Fair Queueing (and its variants) and Active Queue Management (AQM) techniques ineffective as a gateway-enforceable solution in a WMN. We show that only non-work-conserving rate-based scheduling can effectively enforce rate allocation via a single centralized traffic-aggregation point. In this context we propose, design, and evaluate a framework of centralized, measurement-based, feedback-driven mechanisms that can enforce a rate allocation policy objective for adaptive traffic streams in a WMN. In this dissertation we focus on fair rate allocation requirements. Our approach does not require any changes to individual mesh routers. Further, it uses existing data traffic as capacity probes, thus incurring a zero control traffic overhead. We propose two mechanisms based on this approach: aggregate rate control (ARC) and per-flow rate control (PFRC). ARC limits the aggregate capacity of a network to the sum of fair rates for a given set of flows. We show that the resulting rate allocation achieved by DCF is approximately max-min fair. PFRC allows us to exercise finer-grained control over the rate allocation process. We show how it can be used to achieve weighted flow rate fairness. We evaluate the performance of these mechanisms using simulations as well as implementation on a multihop wireless testbed. Our comparative analysis show that our mechanisms improve fairness indices by a factor of 2 to 3 when compared with networks without any rate limiting, and are approximately equivalent to results achieved with distributed source rate limiting mechanisms that require software modifications on all mesh routers