Performance improvement of ad hoc networks using directional antennas and power control

Au cours de la dernière décennie, un intérêt remarquable a été éprouvé en matière des réseaux ad hoc sans fil capables de s'organiser sans soutien des infrastructures. L'utilisation potentielle d'un tel réseau existe dans de nombreux scénarios, qui vont du génie civil et secours en cas de catastrophes aux réseaux de capteurs et applications militaires. La Fonction de coordination distribuée (DCF) du standard IEEE 802.11 est le protocole dominant des réseaux ad hoc sans fil. Cependant, la méthode DCF n'aide pas à profiter efficacement du canal partagé et éprouve de divers problèmes tels que le problème de terminal exposé et de terminal caché. Par conséquent, au cours des dernières années, de différentes méthodes ont été développées en vue de régler ces problèmes, ce qui a entraîné la croissance de débits d'ensemble des réseaux. Ces méthodes englobent essentiellement la mise au point de seuil de détecteur de porteuse, le remplacement des antennes omnidirectionnelles par des antennes directionnelles et le contrôle de puissance pour émettre des paquets adéquatement. Comparées avec les antennes omnidirectionnelles, les antennes directionnelles ont de nombreux avantages et peuvent améliorer la performance des réseaux ad hoc. Ces antennes ne fixent leurs énergies qu'envers la direction cible et ont une portée d'émission et de réception plus large avec la même somme de puissance. Cette particularité peut être exploitée pour ajuster la puissance d'un transmetteur en cas d'utilisation d'une antenne directionnelle. Certains protocoles de contrôle de puissance directionnel MAC ont été proposés dans les documentations. La majorité de ces suggestions prennent seulement la transmission directionnelle en considération et, dans leurs résultats de simulation, ces études ont l'habitude de supposer que la portée de transmission des antennes omnidirectionnelles et directionnelles est la même. Apparemment, cette supposition n'est pas toujours vraie dans les situations réelles. De surcroît, les recherches prenant l'hétérogénéité en compte dans les réseaux ad hoc ne sont pas suffisantes. Le présent mémoire est dédié à proposer un protocole de contrôle de puissance MAC pour les réseaux ad hoc avec des antennes directionnelles en prenant tous ces problèmes en considération. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Réseaux ad hoc, Antennes directives, Contrôle de puissance

Interference-Aware Scheduling for Connectivity in MIMO Ad Hoc Multicast Networks

We consider a multicast scenario involving an ad hoc network of co-channel MIMO nodes in which a source node attempts to share a streaming message with all nodes in the network via some pre-defined multi-hop routing tree. The message is assumed to be broken down into packets, and the transmission is conducted over multiple frames. Each frame is divided into time slots, and each link in the routing tree is assigned one time slot in which to transmit its current packet. We present an algorithm for determining the number of time slots and the scheduling of the links in these time slots in order to optimize the connectivity of the network, which we define to be the probability that all links can achieve the required throughput. In addition to time multiplexing, the MIMO nodes also employ beamforming to manage interference when links are simultaneously active, and the beamformers are designed with the maximum connectivity metric in mind. The effects of outdated channel state information (CSI) are taken into account in both the scheduling and the beamforming designs. We also derive bounds on the network connectivity and sum transmit power in order to illustrate the impact of interference on network performance. Our simulation results demonstrate that the choice of the number of time slots is critical in optimizing network performance, and illustrate the significant advantage provided by multiple antennas in improving network connectivity.Comment: 34 pages, 12 figures, accepted by IEEE Transactions on Vehicular Technology, Dec. 201

Virtual sensing directional hub MAC (VSDH-MAC) protocol with power control

Medium access control (MAC) protocols play a vital role in making effective use of a multiple access channel as it governs the achievable performance such as channel utilization and corresponding quality of service of wireless sensor networks (WSNs). In this paper, a virtual carrier sensing directional hub (VSDH) MAC protocol incorporating realistic directional antenna patterns is proposed for directional single hub centralized WSNs. While in most instances, MAC protocols assume idealized directional antenna patterns, the proposed VSDH-MAC protocol incorporates realistic directional antenna patterns to deliver enhanced link performance. We demonstrate that the use of directional antennas with a suitable MAC protocol can provide enhanced communication range and increased throughput with reduced energy consumption at each node, compared to the case when only omnidirectional antennas are used. For the scenarios considered in this study, results show that the average transmit power of the sensor nodes can be reduced by a factor of two, and at the same time offer significantly extended lifetime

On Capacity and Delay of Multi-channel Wireless Networks with Infrastructure Support

In this paper, we propose a novel multi-channel network with infrastructure support, called an MC-IS network, which has not been studied in the literature. To the best of our knowledge, we are the first to study such an MC-IS network. Our proposed MC-IS network has a number of advantages over three existing conventional networks, namely a single-channel wireless ad hoc network (called an SC-AH network), a multi-channel wireless ad hoc network (called an MC-AH network) and a single-channel network with infrastructure support (called an SC-IS network). In particular, the network capacity of our proposed MC-IS network is $\sqrt{n \log n}$ times higher than that of an SC-AH network and an MC-AH network and the same as that of an SC-IS network, where $n$ is the number of nodes in the network. The average delay of our MC-IS network is $\sqrt{\log n/n}$ times lower than that of an SC-AH network and an MC-AH network, and $\min\{C_I,m\}$ times lower than the average delay of an SC-IS network, where $C_I$ and $m$ denote the number of channels dedicated for infrastructure communications and the number of interfaces mounted at each infrastructure node, respectively. Our analysis on an MC-IS network equipped with omni-directional antennas only has been extended to an MC-IS network equipped with directional antennas only, which are named as an MC-IS-DA network. We show that an MC-IS-DA network has an even lower delay of $\frac{c}{\lfloor \frac{2\pi}{\theta}\rfloor \cdot C_I}$ compared with an SC-IS network and our MC-IS network. For example, when $C_I=12$ and $\theta=\frac{\pi}{12}$, an MC-IS-DA network can further reduce the delay by 24 times lower that of an MC-IS network and reduce the delay by 288 times lower than that of an SC-IS network.Comment: accepted, IEEE Transactions on Vehicular Technology, 201