09-07-2012, 11:34 AM
mobile ad-hoc networks (MANETs)
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ABSTRACT
A fundamental issue arising in mobile ad-hoc networks (MANETs) is the selection of the optimal path between any two nodes. Mobile ad hoc networks enable users to maintain connectivity to the fixed network or exchange information when no infrastructure, such as a base station or an access point, is available. This is achieved through multi hop communications, which allow a node to reach far away destinations by using intermediate nodes as relays. A method that has been advocated to improve routing efficiency is to select the most stable path so as to reduce the latency and the overhead due to route reconstruction. In this work, we study both the availability and the duration probability of a routing path that is subject to link failures caused by node mobility. In particular, we focus on the case where the network nodes move according to the Random Direction model, and we derive both exact and approximate expressions of these probabilities. Through our results, we study the problem of selecting an optimal route in terms of path availability. Finally, we propose an approach to improve the efficiency of the reactive routing protocols.
INTRODUCTION
Mobile wireless networks are receiving an increasing interest due to possibility of ubiquitous communications they offer. In particular, mobile ad hoc networks (MANETs) enable users to maintain connectivity to the fixed network or exchange information when no infrastructure, such as a base station or an access point, is available. This is achieved through multi hop communications, which allow a node to reach far away destinations by using intermediate nodes as relays.
The selection and maintenance of a multi hop path, however, is a fundamental problem in MANETs. Node mobility, signal interference and power outages make the network topology frequently change as a consequence, the links along a path may fail and an alternate path must be found. To avoid the degradation of the system performance, several solutions have been proposed in the literature, taking into account various metrics of interest. A method that has been advocated to improve routing efficiency is to select the most stable path so as to avoid packet losses and limit the latency and overhead due to path reconstruction.
In this work, we focus on the stability of a routing path, which is subject to link failures caused by node mobility. We define the path duration as the time interval from when the route is established until one of the links along the route becomes unavailable, while we say that a path is available at a given time instant t when all links along the path are active at time t. Then, our objective is to derive the probability of path duration till time t and the probability of path availability at time t.
Clearly, the probabilities of path duration and path availability strongly depend on the mobility pattern of the network nodes. Indeed, the path duration is determined by the duration of its links, which on its turn depends on the movement of a node with respect to the other. To characterize the nodes position with respect to each other, we need the spatial distribution of a single node over time. Here we focus on bi-dimensional random mobility and we consider nodes moving according to the Random Direction (RD) mobility model.
The main contributions of our work are as follows,
We derive for the first time an expression for the transform of the distribution of a node moving according to the RD model. This expression can be numerically inverted to obtain the temporal evolution of the probability density function of the node position, given an assigned initial condition. Closed-form expressions for the temporal evolution of the distribution moments can also be derived directly from the transform.
We propose a simple, approximate expression for the probability of link availability under the RD model, which leverages the derivation of the second moment of the node spatial distribution. Our findings suggest that, as time proceeds, the probability of link availability under a generic mobility model can be obtained through a similar approximation. The same approach can be applied to the computation of the probability of path duration.
Based on our results on the probabilities of link availability and link duration, we study the same metrics for multi hop paths, again in the case of RD mobility. We discuss the validity of the link independence assumption, which is widely used, and compare it against refined assumption that accounts for link correlation. We observe that the link independence assumption provides sufficiently accurate results.
We show how our analysis can be exploited to improve the efficiency of traffic routing in MANETs. In particular, we show how to select the optimal route in terms of path availability and how to determine the optimal number of hops between source and destination, taking into account the initial distance between the nodes. We then propose an approach to find and select routes, which accounts for the expected data transfer time over the path and allows to reduce the overhead of reactive routing protocols.
MOTIVATION:
In this section, we highlight the reasons why a theoretical analysis of route stability in MANETs is useful, and how our contribution differs from previous work.
Why is route stability analysis needed?
To meet the quality of service requirements of mobile users, several metrics can be considered for selecting a source destination routing path. Here, we focus on route stability, which is an aspect of fundamental importance as one can judge from the following considerations.
Stable routes: To maximize throughput and reduce traffic latency, it is essential to ensure reliable source-destination connections over time. A route should therefore be selected based on some knowledge of the nodes motion and on a probability model of the path future availability.
Efficient route repair: If an estimate of the path duration is available, service disruption due to route failure can be avoided by creating an alternative path before the current one breaks. Note that having some information on the path duration avoids waste of radio resources due to pre-allocation of backup paths.
Network connectivity: Connectivity and topology characteristics of a MANET are determined by the link dynamics. These are fundamental issues to network design, since they determine the system capability to support user communications and their reliability level.
Performance evaluation: The performances achieved by high-layer protocols, such as transport and application protocols, heavily depend on the quality of service metrics obtained at the network layer.
PROPOSED MODEL AND SYSTEM ARCHITECTURE SOFTWARE PROJECT MANAGEMENT PLAN (SPMP): PROJECT OVERVIEW:
A fundamental issue arising in mobile ad-hoc networks (MANETs) is the selection of the optimal path between any two nodes. Mobile ad hoc networks enable users to maintain connectivity to the fixed network or exchange information when no infrastructure, such as a base station or an access point, is available.
This is achieved through multi hop communications, which allow a node to reach far away destinations by using intermediate nodes as relays. A method that has been advocated to improve routing efficiency is to select the most stable path so as to reduce the latency and the overhead due to route reconstruction.
In this work, we study both the availability and the duration probability of a routing path that is subject to link failures caused by node mobility. In particular, we focus on the case where the network nodes move according to the Random Direction model, and we derive both exact and approximate expressions of these probabilities.
Through our results, we study the problem of selecting an optimal route in terms of path availability. Finally, we propose an approach to improve the efficiency of reactive routing protocols.