Queue utilization with hop based enhanced arbitrary inter frame spacing MAC for saturated ad HOC networks

© 2015 IEEE. Path length of a multi hop Ad Hoc networks has an adverse impact on the end-to-end throughput especially during network saturation. The success rate of forwarding packets towards destination is limited due to interference, contention, limited buffer space, and bandwidth. Real time applications streaming data fill the buffer space at a faster rate at the source and its nearby forwarding nodes since the channel is shared. The aim of this paper is to increase the success rate of forwarding the packets to yield a higher end-to-end throughput. In order to reduce loss of packets due to buffer overflow and enhance the performance of the network for a saturated network, a novel MAC protocol named Queue Utilization with Hop Based Enhanced Arbitrary Inter Frame Spacing based (QU-EAIFS) MAC is proposed for alleviating the problems in saturated Ad Hoc networks. The protocol prioritises the nodes based on its queue utilization and hops travelled by the packet and it helps achieving higher end-toend performance by forwarding the packets with higher rate towards the destination during network saturation. The proposed MAC enhances the end-to-end performance by approximately 40% and 34% for a 5hop and 6hop communication respectively in a chain topology as compared to the standard IEEE802.11b. The performance of the new MAC also outperforms the performance of IEEE 802.11e MAC. In order to validate the protocol, it is also tested with short hops and varying packet sizes and more realistic random topologies

A critical analysis of research potential, challenges and future directives in industrial wireless sensor networks

In recent years, Industrial Wireless Sensor Networks (IWSNs) have emerged as an important research theme with applications spanning a wide range of industries including automation, monitoring, process control, feedback systems and automotive. Wide scope of IWSNs applications ranging from small production units, large oil and gas industries to nuclear fission control, enables a fast-paced research in this field. Though IWSNs offer advantages of low cost, flexibility, scalability, self-healing, easy deployment and reformation, yet they pose certain limitations on available potential and introduce challenges on multiple fronts due to their susceptibility to highly complex and uncertain industrial environments. In this paper a detailed discussion on design objectives, challenges and solutions, for IWSNs, are presented. A careful evaluation of industrial systems, deadlines and possible hazards in industrial atmosphere are discussed. The paper also presents a thorough review of the existing standards and industrial protocols and gives a critical evaluation of potential of these standards and protocols along with a detailed discussion on available hardware platforms, specific industrial energy harvesting techniques and their capabilities. The paper lists main service providers for IWSNs solutions and gives insight of future trends and research gaps in the field of IWSNs

Cross-layer signalling and middleware: a survey for inelastic soft real-time applications in MANETs

This paper provides a review of the different cross-layer design and protocol tuning approaches that may be used to meet a growing need to support inelastic soft real-time streams in MANETs. These streams are characterised by critical timing and throughput requirements and low packet loss tolerance levels. Many cross-layer approaches exist either for provision of QoS to soft real-time streams in static wireless networks or to improve the performance of real and non-real-time transmissions in MANETs. The common ground and lessons learned from these approaches, with a view to the potential provision of much needed support to real-time applications in MANETs, is therefore discussed

Multipath routing and QoS provisioning in mobile ad hoc networks

PhDA Mobile Ad Hoc Networks (MANET) is a collection of mobile nodes that can communicate with each other using multihop wireless links without utilizing any fixed based-station infrastructure and centralized management. Each mobile node in the network acts as both a host generating flows or being destination of flows and a router forwarding flows directed to other nodes. Future applications of MANETs are expected to be based on all-IP architecture and be capable of carrying multitude real-time multimedia applications such as voice and video as well as data. It is very necessary for MANETs to have an efficient routing and quality of service (QoS) mechanism to support diverse applications. This thesis proposes an on-demand Node-Disjoint Multipath Routing protocol (NDMR) with low broadcast redundancy. Multipath routing allows the establishment of multiple paths between a single source and single destination node. It is also beneficial to avoid traffic congestion and frequent link breaks in communication because of the mobility of nodes. The important components of the protocol, such as path accumulation, decreasing routing overhead and selecting node-disjoint paths, are explained. Because the new protocol significantly reduces the total number of Route Request packets, this results in an increased delivery ratio, smaller end-to-end delays for data packets, lower control overhead and fewer collisions of packets. Although NDMR provides node-disjoint multipath routing with low route overhead in MANETs, it is only a best-effort routing approach, which is not enough to support QoS. DiffServ is a standard approach for a more scalable way to achieve QoS in any IP network and could potentially be used to provide QoS in MANETs because it minimises the need for signalling. However, one of the biggest drawbacks of DiffServ is that the QoS provisioning is separate from the routing process. This thesis presents a Multipath QoS Routing protocol for iv supporting DiffServ (MQRD), which combines the advantages of NDMR and DiffServ. The protocol can classify network traffic into different priority levels and apply priority scheduling and queuing management mechanisms to obtain QoS guarantees

Controlo de acesso ao meio em comunicações veiculares de tempo-real

Despite several preventive measures, the number of roadway accidents is still very high, being considered even a problem of public health by some entities. This thesis has as global purpose of contributing to the reduction of that number of accidents, and consequent fatalities, by using safety-related applications that use communication among vehicles. In particular, the primary goal is guaranteeing that communication between users in vehicular environments is done with appropriate time bounds to transfer safety-critical information. In detail, it is studied how to manage the scheduling of message’s transmissions (medium access control - MAC), in order to define precisely who will communicate and when is the appropriate instant. The preferable situation where a communication infrastructure is present with full coverage (RSUs) is also studied, from which medium access control is defined precisely, and vehicles (OBUs) become aware of medium utilization. Also, sporadic situations (e.g., absence of RSUs) are studied in which the communication network is “ad hoc” and solely formed by the current vehicles. It is used the recently WAVE / IEEE 802.11p standard, specific for vehicular communications, and it is proposed a TDMA based solution, with appropriate coordination between RSUs in order to effectively disseminate a critical safety event. It is taken into account two different ways of choosing the instant for the initial broadcast, and both cases are compared. In case there is no infrastructure available, methods are derived to minimize communication medium access collisions, and to maximize the available bandwidth. The results reflect the total end-to-end delay, and show that adequate times are attained, and meet with the requisites for the type of applications being considered. Also, enhancements are obtained when using the alternate choice for the initial broadcast instant.Apesar de diversas medidas preventivas, o número de acidentes rodoviários continua a ser muito elevado, sendo mesmo considerado uma questão de saúde pública por algumas entidades. Esta tese tem como objetivo geral contribuir para a redução desse número de acidentes, e consequentes fatalidades, através da utilização de aplicações de segurança que envolvem comunicação entre veículos. Em particular, o objetivo principal é garantir que a comunicação entre utentes, em ambientes veiculares, seja efetuada com limites temporais apropriados à transferência de informações críticas. De forma mais detalhada, é estudada a gestão do escalonamento das transmissões (controlo de acesso ao meio – MAC) que irá definir quem vai comunicar e quando o pode fazer. São estudadas situações (desejadas) onde há uma infra-estrutura de comunicações com cobertura integral (RSUs), a partir da qual se faz a coordenação do acesso ao meio pelos veículos (OBUs), e situações (esporádicas, por ausência de RSU) em que a rede de comunicação é “ad hoc” e apenas constituída pelos veículos presentes. Utiliza-se a recente norma WAVE / IEEE 802.11p, específica para comunicações veiculares, e propõe-se uma solução baseada em TDMA, com coordenação apropriada entre RSUs para disseminação efetiva de um evento crítico de segurança. A escolha do instante para o broadcast inicial do evento de segurança também é tida em conta, e são comparados dois casos distintos. No caso da ausência de infraestrutura, derivam-se métodos para minimizar colisões no acesso ao meio de comunicação, e maximizar a largura de banda disponível. Os resultados refletem o atraso total end-to-end, mostrando tempos apropriados para os requisitos das aplicações em causa, e evidenciando melhorias aquando da escolha alternativa para o instante do broadcast inicial.Programa Doutoral em Engenharia Eletrotécnic