1,231 research outputs found

    A power-controlled MAC supporting service differentiation in mobile ad hoc networks

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    The original power controlled multiple access (PCMA) protocol does not support service differentiation. In this paper, we extend PCMA to form a new media access control protocol supporting service differentiation in mobile ad hoc networks. To support QoS, we first introduce the in-station access category concept in 802.1 le to PCMA. For service differentiation between access categories, our major contribution is to propose a sender-initiated busy tone based mechanism that allows a user to gain quick channel access. This quick access mechanism is only performed when the number of access failures exceeds a threshold. An access category with higher priority is assigned a lower threshold for easier channel access, and vice versa. Through analysis and simulation, we demonstrate that our protocol can provide better quality of service than 802.11e in terms of throughput, delay, loss, and fairness. © 2005 IEEE.published_or_final_versio

    An efficient scalable scheduling mac protocol for underwater sensor networks

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    Underwater Sensor Networks (UWSNs) utilise acoustic waves with comparatively lower loss and longer range than those of electromagnetic waves. However, energy remains a challenging issue in addition to long latency, high bit error rate, and limited bandwidth. Thus, collision and retransmission should be efficiently handled at Medium Access Control (MAC) layer in order to reduce the energy cost and also to improve the throughput and fairness across the network. In this paper, we propose a new reservation-based distributed MAC protocol called ED-MAC, which employs a duty cycle mechanism to address the spatial-temporal uncertainty and the hidden node problem to effectively avoid collisions and retransmissions. ED-MAC is a conflict-free protocol, where each sensor schedules itself independently using local information. Hence, ED-MAC can guarantee conflict-free transmissions and receptions of data packets. Compared with other conflict-free MAC protocols, ED-MAC is distributed and more reliable, i.e., it schedules according to the priority of sensor nodes which based on their depth in the network. We then evaluate design choices and protocol performance through extensive simulation to study the load effects and network scalability in each protocol. The results show that ED-MAC outperforms the contention-based MAC protocols and achieves a significant improvement in terms of successful delivery ratio, throughput, energy consumption, and fairness under varying offered traffic and number of nodes

    Performance improvement in mobile ad-hoc networks.

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    The objective of this research is to enhance the network performance under realistic mobile ad-hoc networks environments without modification of the standard. Overview of this research is summarized as follows: First, a packet-fragmentation technique to improve network throughput under the worst channel conditions is proposed. While the conventional packet-fragmentation technique research focuses only on random-bit errors, the proposed technique employs both random bit errors and hidden-node collisions. The analytical models based on Markov-chain model shows that the optimal fragmentation technique can effectively reduce the number of retransmissions caused by both collisions from hidden nodes and corrupted packets by random bit errors, and eventually improving throughput in noisy VANETs channels. As a second contribution, a dynamic service-channel allocation (DSCA) scheme is proposed to maximize the network throughput by dynamically assigning different service channels to the users. The theoretical analysis in this thesis will consider wireless access in the vehicular environment (WAVE) protocol, which is the main characteristic of the vehicular ad-hoc networks standard (the IEEE 802.11p). To summarize, the main contribution of this research is that two schemes will improve the network throughput significantly without modification of the standard. Therefore, there is no implementation issue to deploy the proposed schemes in real devices.PhDCommittee Chair: Copeland, John; Committee Co-Chair: Chang, Yusun; Committee Member: Ammar, Mostafa; Committee Member: Beyah, Raheem; Committee Member: Owen, Henry; Committee Member: Taylor, Davi

    MAC Protocols for Wireless Mesh Networks with Multi-beam Antennas: A Survey

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    Multi-beam antenna technologies have provided lots of promising solutions to many current challenges faced in wireless mesh networks. The antenna can establish several beamformings simultaneously and initiate concurrent transmissions or receptions using multiple beams, thereby increasing the overall throughput of the network transmission. Multi-beam antenna has the ability to increase the spatial reuse, extend the transmission range, improve the transmission reliability, as well as save the power consumption. Traditional Medium Access Control (MAC) protocols for wireless network largely relied on the IEEE 802.11 Distributed Coordination Function(DCF) mechanism, however, IEEE 802.11 DCF cannot take the advantages of these unique capabilities provided by multi-beam antennas. This paper surveys the MAC protocols for wireless mesh networks with multi-beam antennas. The paper first discusses some basic information in designing multi-beam antenna system and MAC protocols, and then presents the main challenges for the MAC protocols in wireless mesh networks compared with the traditional MAC protocols. A qualitative comparison of the existing MAC protocols is provided to highlight their novel features, which provides a reference for designing the new MAC protocols. To provide some insights on future research, several open issues of MAC protocols are discussed for wireless mesh networks using multi-beam antennas.Comment: 22 pages, 6 figures, Future of Information and Communication Conference (FICC) 2019, https://doi.org/10.1007/978-3-030-12388-8_

    Medium Access Control for Opportunistic Concurrent Transmissions under Shadowing Channels

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    We study the problem of how to alleviate the exposed terminal effect in multi-hop wireless networks in the presence of log-normal shadowing channels. Assuming node location information, we propose an extension of the IEEE 802.11 MAC protocol that sched-ules concurrent transmissions in the presence of log-normal shadowing, thus mitigating the exposed terminal problem and improving network throughput and delay performance. We observe considerable improvements in throughput and delay achieved over the IEEE 802.11 MAC under various network topologies and channel conditions in ns-2 simulations, which justify the importance of considering channel randomness in MAC protocol design for multi-hop wireless networks

    Quality of service aware data dissemination in vehicular Ad Hoc networks

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    Des systĂšmes de transport intelligents (STI) seront Ă©ventuellement fournis dans un proche avenir pour la sĂ©curitĂ© et le confort des personnes lors de leurs dĂ©placements sur les routes. Les rĂ©seaux ad-hoc vĂ©hiculaires (VANETs) reprĂ©sentent l'Ă©lĂ©ment clĂ© des STI. Les VANETs sont formĂ©s par des vĂ©hicules qui communiquent entre eux et avec l'infrastructure. En effet, les vĂ©hicules pourront Ă©changer des messages qui comprennent, par exemple, des informations sur la circulation routiĂšre, les situations d'urgence et les divertissements. En particulier, les messages d'urgence sont diffusĂ©s par des vĂ©hicules en cas d'urgence (p.ex. un accident de voiture); afin de permettre aux conducteurs de rĂ©agir Ă  temps (p.ex., ralentir), les messages d'urgence doivent ĂȘtre diffusĂ©s de maniĂšre fiable dans un dĂ©lai trĂšs court. Dans les VANETs, il existe plusieurs facteurs, tels que le canal Ă  pertes, les terminaux cachĂ©s, les interfĂ©rences et la bande passante limitĂ©e, qui compliquent Ă©normĂ©ment la satisfaction des exigences de fiabilitĂ© et de dĂ©lai des messages d'urgence. Dans cette thĂšse, en guise de premiĂšre contribution, nous proposons un schĂ©ma de diffusion efficace Ă  plusieurs sauts, appelĂ© Dynamic Partitioning Scheme (DPS), pour diffuser les messages d'urgence. DPS calcule les tailles de partitions dynamiques et le calendrier de transmission pour chaque partition; Ă  l'intĂ©rieur de la zone arriĂšre de l'expĂ©diteur, les partitions sont calculĂ©es de sorte qu'en moyenne chaque partition contient au moins un seul vĂ©hicule; l'objectif est de s'assurer que seul un vĂ©hicule dans la partition la plus Ă©loignĂ©e (de l'expĂ©diteur) est utilisĂ© pour diffuser le message, jusqu'au saut suivant; ceci donne lieu Ă  un dĂ©lai d'un saut plus court. DPS assure une diffusion rapide des messages d'urgence. En outre, un nouveau mĂ©canisme d'Ă©tablissement de liaison, qui utilise des tonalitĂ©s occupĂ©es, est proposĂ© pour rĂ©soudre le problĂšme du problĂšme de terminal cachĂ©. Dans les VANETs, la Multidiffusion, c'est-Ă -dire la transmission d'un message d'une source Ă  un nombre limitĂ© de vĂ©hicules connus en tant que destinations, est trĂšs importante. Par rapport Ă  la diffusion unique, avec Multidiffusion, la source peut simultanĂ©ment prendre en charge plusieurs destinations, via une arborescence de multidiffusion, ce qui permet d'Ă©conomiser de la bande passante et de rĂ©duire la congestion du rĂ©seau. Cependant, puisque les VANETs ont une topologie dynamique, le maintien de la connectivitĂ© de l'arbre de multidiffusion est un problĂšme majeur. Comme deuxiĂšme contribution, nous proposons deux approches pour modĂ©liser l'utilisation totale de bande passante d'une arborescence de multidiffusion: (i) la premiĂšre approche considĂšre le nombre de segments de route impliquĂ©s dans l'arbre de multidiffusion et (ii) la seconde approche considĂšre le nombre d'intersections relais dans l'arbre de multidiffusion. Une heuristique est proposĂ©e pour chaque approche. Pour assurer la qualitĂ© de service de l'arbre de multidiffusion, des procĂ©dures efficaces sont proposĂ©es pour le suivi des destinations et la surveillance de la qualitĂ© de service des segments de route. Comme troisiĂšme contribution, nous Ă©tudions le problĂšme de la congestion causĂ©e par le routage du trafic de donnĂ©es dans les VANETs. Nous proposons (1) une approche de routage basĂ©e sur l’infonuagique qui, contrairement aux approches existantes, prend en compte les chemins de routage existants qui relaient dĂ©jĂ  les donnĂ©es dans les VANETs. Les nouvelles demandes de routage sont traitĂ©es de sorte qu'aucun segment de route ne soit surchargĂ© par plusieurs chemins de routage croisĂ©s. Au lieu d'acheminer les donnĂ©es en utilisant des chemins de routage sur un nombre limitĂ© de segments de route, notre approche Ă©quilibre la charge des donnĂ©es en utilisant des chemins de routage sur l'ensemble des tronçons routiers urbains, dans le but d'empĂȘcher, dans la mesure du possible, les congestions locales dans les VANETs; et (2) une approche basĂ©e sur le rĂ©seau dĂ©fini par logiciel (SDN) pour surveiller la connectivitĂ© VANET en temps rĂ©el et les dĂ©lais de transmission sur chaque segment de route. Les donnĂ©es de surveillance sont utilisĂ©es en entrĂ©e de l'approche de routage.Intelligent Transportation Systems (ITS) will be eventually provided in the near future for both safety and comfort of people during their travel on the roads. Vehicular ad-hoc Networks (VANETs), represent the key component of ITS. VANETs consist of vehicles that communicate with each other and with the infrastructure. Indeed, vehicles will be able to exchange messages that include, for example, information about road traffic, emergency situations, and entertainment. Particularly, emergency messages are broadcasted by vehicles in case of an emergency (e.g., car accident); in order to allow drivers to react in time (e.g., slow down), emergency messages must be reliably disseminated with very short delay. In VANETs, there are several factors, such as lossy channel, hidden terminals, interferences and scarce bandwidth, which make satisfying reliability and delay requirements of emergency messages very challenging. In this thesis, as the first contribution, we propose a reliable time-efficient and multi-hop broadcasting scheme, called Dynamic Partitioning Scheme (DPS), to disseminate emergency messages. DPS computes dynamic partition sizes and the transmission schedule for each partition; inside the back area of the sender, the partitions are computed such that in average each partition contains at least a single vehicle; the objective is to ensure that only a vehicle in the farthest partition (from the sender) is used to disseminate the message, to next hop, resulting in shorter one hop delay. DPS ensures fast dissemination of emergency messages. Moreover, a new handshaking mechanism, that uses busy tones, is proposed to solve the problem of hidden terminal problem. In VANETs, Multicasting, i.e. delivering a message from a source to a limited known number of vehicles as destinations, is very important. Compared to Unicasting, with Multicasting, the source can simultaneously support multiple destinations, via a multicast tree, saving bandwidth and reducing overall communication congestion. However, since VANETs have a dynamic topology, maintaining the connectivity of the multicast tree is a major issue. As the second contribution, we propose two approaches to model total bandwidth usage of a multicast tree: (i) the first approach considers the number of road segments involved in the multicast tree and (ii) the second approach considers the number of relaying intersections involved in the multicast tree. A heuristic is proposed for each approach. To ensure QoS of the multicasting tree, efficient procedures are proposed for tracking destinations and monitoring QoS of road segments. As the third contribution, we study the problem of network congestion in routing data traffic in VANETs. We propose (1) a Cloud-based routing approach that, in opposition to existing approaches, takes into account existing routing paths which are already relaying data in VANETs. New routing requests are processed such that no road segment gets overloaded by multiple crossing routing paths. Instead of routing over a limited set of road segments, our approach balances the load of communication paths over the whole urban road segments, with the objective to prevent, whenever possible, local congestions in VANETs; and (2) a Software Defined Networking (SDN) based approach to monitor real-time VANETs connectivity and transmission delays on each road segment. The monitoring data is used as input to the routing approach

    A Comprehensive Analysis of Literature Reported Mac and Phy Enhancements of Zigbee and its Alliances

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    Wireless communication is one of the most required technologies by the common man. The strength of this technology is rigorously progressing towards several novel directions in establishing personal wireless networks mounted over on low power consuming systems. The cutting-edge communication technologies like bluetooth, WIFI and ZigBee significantly play a prime role to cater the basic needs of any individual. ZigBee is one such evolutionary technology steadily getting its popularity in establishing personal wireless networks which is built on small and low-power digital radios. Zigbee defines the physical and MAC layers built on IEEE standard. This paper presents a comprehensive survey of literature reported MAC and PHY enhancements of ZigBee and its contemporary technologies with respect to performance, power consumption, scheduling, resource management and timing and address binding. The work also discusses on the areas of ZigBee MAC and PHY towards their design for specific applications
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