Routing in heterogeneous wireless ad hoc networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references (p. 135-146).Wireless ad hoc networks are used in several applications ranging from infrastructure monitoring to providing Internet connectivity to remote locations. A common assumption about these networks is that the devices that form the network are homogeneous in their capabilities. However in reality, the networks can be heterogeneous in the capabilities of the devices. The main contribution of this thesis is the identification of issues for efficient communication in heterogeneous networks and the proposed solutions to these issues. The first part of the thesis deals with the issues of unambiguous classification of devices and device identification in ad hoc networks. A taxonomical approach is developed, which allows devices with wide range of capabilities to be classified on the basis of their functionality. Once classified, devices are characterized on the basis of different attributes. An IPv6 identification scheme and two routing services based on this scheme that allow object-object communication are developed. The identification scheme is extended to a multi-addressing scheme for wireless ad hoc networks. These two issues and the developed solutions are applicable to a broad range of heterogeneous networks. The second part of the thesis deals with heterogeneous networks consisting of omnidirectional and directional antennas. A new MAC protocol for directional antennas, request-to-pause-directional-MAC (RTP-DMAC) protocol is developed that solves the deafness issue, which is common in networks with directional antennas. Three new routing metrics, which are extensions to the expected number of transmissions (ETX) metric are developed. The first metric, ETX1, reduces the route length by increasing the transmission power. The routing and MAC layers assume the presence of bidirectional links for their proper operation. However networks with omnidirectional and directional antennas have unidirectional links. The other two metrics, unidirectional-ETX (U-ETX) and unidirectional-ETX1 (U-ETX1), increase the transmission power of the directional nodes so that the unidirectional links appear as bidirectional links at the MAC and the routing layers. The performance of these metrics in different scenarios is evaluated.by Sivaram M.S.L. Cheekiralla.Ph.D

The impact of mobility models on the performance of mobile Ad Hoc network routing protocol

A mobility model represents nodes distribution and movement over the network. Several research works have shown that a selection of mobility model can affect the outcome of routing performance simulation in Mobile Ad Hoc Networks. Thus, a routing protocol may only be effective in a particular mobility model or scenario but performs inferiorly in another. As a result, analyses of routing protocol performance are often based on inadequate information leading to inaccurate argument and conclusion. In this paper, three different mobility models have been selected, where each of them is highly distinctive in terms of nodes movement behavior. In addition, a new measurement technique called probability of route connectivity is introduced. The technique is used to quantify the success rate of route established by a routing protocol. Extensive simulation runs are done and results are compared between each mobility model

A Self-Organization Framework for Wireless Ad Hoc Networks as Small Worlds

Motivated by the benefits of small world networks, we propose a self-organization framework for wireless ad hoc networks. We investigate the use of directional beamforming for creating long-range short cuts between nodes. Using simulation results for randomized beamforming as a guideline, we identify crucial design issues for algorithm design. Our results show that, while significant path length reduction is achievable, this is accompanied by the problem of asymmetric paths between nodes. Subsequently, we propose a distributed algorithm for small world creation that achieves path length reduction while maintaining connectivity. We define a new centrality measure that estimates the structural importance of nodes based on traffic flow in the network, which is used to identify the optimum nodes for beamforming. We show, using simulations, that this leads to significant reduction in path length while maintaining connectivity.Comment: Submitted to IEEE Transactions on Vehicular Technolog

Toward an efficient solution for dynamic ad hoc network interoperability

An ad hoc network is formed by an impromptu grouping of network capable nodes. The nodes forming the network have unconstrained mobility, and so provide a dynamic network topology. Current work in this research area has focused on designing routing protocols capable of efficiently forwarding packets in these dynamic network environments. This has led to several designs for ad hoc routing protocols based on various routing algorithms, each suited to specific usage characteristics. This paper will discuss issues relating to routing in ad hoc networks. We will describe an active networking based solution that provides dynamic routing protocol interoperability and enables migration of nodes between ad hoc groups. Our design is motivated by a squad and base scenario which consists of two groups wishing to communicate. These groups have contrasting deployment characteristics and so use different routing protocols

On the Experimental Evaluation of Vehicular Networks: Issues, Requirements and Methodology Applied to a Real Use Case

One of the most challenging fields in vehicular communications has been the experimental assessment of protocols and novel technologies. Researchers usually tend to simulate vehicular scenarios and/or partially validate new contributions in the area by using constrained testbeds and carrying out minor tests. In this line, the present work reviews the issues that pioneers in the area of vehicular communications and, in general, in telematics, have to deal with if they want to perform a good evaluation campaign by real testing. The key needs for a good experimental evaluation is the use of proper software tools for gathering testing data, post-processing and generating relevant figures of merit and, finally, properly showing the most important results. For this reason, a key contribution of this paper is the presentation of an evaluation environment called AnaVANET, which covers the previous needs. By using this tool and presenting a reference case of study, a generic testing methodology is described and applied. This way, the usage of the IPv6 protocol over a vehicle-to-vehicle routing protocol, and supporting IETF-based network mobility, is tested at the same time the main features of the AnaVANET system are presented. This work contributes in laying the foundations for a proper experimental evaluation of vehicular networks and will be useful for many researchers in the area.Comment: in EAI Endorsed Transactions on Industrial Networks and Intelligent Systems, 201

An enhanced Multipath Strategy in Mobile Ad hoc Routing Protocols

The various routing protocols in Mobile Ad hoc Networks follow different strategies to send the information from one node to another. The nodes in the network are non static and they move randomly and are prone to link failure which makes always to find new routes to the destination. This research mainly focused on the study of the characteristics of multipath routing protocols in MANETS. Two of the multipath routing protocols were investigated and a comparative study along with simulation using NS2 was done between DSR and AODV to propose an enhanced approach to reach the destination maintaining the QoS. A possible optimization to the DSR and AODV routing protocols was proposed to make no node to be overburdened by distributing the load after finding the alternate multipath routes which were discovered in the Route discovery process. The simulation shows that the differences in the protocol highlighted major differences with the protocol performance. These differences have been analyzed with various network size, mobility, and network load. A new search table named Search of Next Node Enquiry Table (SONNET) was proposed to find the best neighbor node. Using SONNET the node selects the neighbor which can be reached in less number of hops and with less time delay and maintaining the QoS

Delay-bounded medium access for unidirectional wireless links

Consider a wireless network where links may be unidirectional, that is, a computer node A can broadcast a message and computer node B will receive this message but if B broadcasts then A will not receive it. Assume that messages have deadlines. We propose a medium access control (MAC) protocol which replicates a message in time with carefully selected pauses between replicas, and in this way it guarantees that for every message at least one replica of that message is transmitted without collision. The protocol ensures this with no knowledge of the network topology and it requires neither synchronized clocks nor carrier sensing capabilities. We believe this result is significant because it is the only MAC protocol that offers an upper bound on the message queuing delay for unidirectional links without relying on synchronized clocks