A Framework for Performance Evaluation of VANETs Using NS-3 Simulator

During the last decade, the number of vehicles on roads has been rapidly growing. Therefore, the demands for communication on the move are also increasing and the attention from many researchers is focused on the Vehicular Ad hoc NETworks (VANETs) because of their importance for Intelligent Transportation Systems (ITSs). Due to the complexity and cost of practical evaluation of VANETs, the researchers often rely on network simulation in order to evaluate their work. In this paper, we have developed a Network Simulator 3 (NS-3) based framework for VANETs that provides network performance analysis based on the key performance indicators such as throughput, packet loss ratio, overhead, end-to-end delay, jitter, etc. Since VANETs are highly dynamic networks, many researchers have proposed different routing protocols in order to improve the network performance. In this paper we have compared several topology-based routing protocols, and proposed utilization of the commonly used Expected Transmission Count (ETX) metric to improve VANET performance.</p

Mobile Ad Hoc Networks

Guiding readers through the basics of these rapidly emerging networks to more advanced concepts and future expectations, Mobile Ad hoc Networks: Current Status and Future Trends identifies and examines the most pressing research issues in Mobile Ad hoc Networks (MANETs). Containing the contributions of leading researchers, industry professionals, and academics, this forward-looking reference provides an authoritative perspective of the state of the art in MANETs. The book includes surveys of recent publications that investigate key areas of interest such as limited resources and the mobility of mobile nodes. It considers routing, multicast, energy, security, channel assignment, and ensuring quality of service. Also suitable as a text for graduate students, the book is organized into three sections: Fundamentals of MANET Modeling and Simulation—Describes how MANETs operate and perform through simulations and models Communication Protocols of MANETs—Presents cutting-edge research on key issues, including MAC layer issues and routing in high mobility Future Networks Inspired By MANETs—Tackles open research issues and emerging trends Illustrating the role MANETs are likely to play in future networks, this book supplies the foundation and insight you will need to make your own contributions to the field. It includes coverage of routing protocols, modeling and simulations tools, intelligent optimization techniques to multicriteria routing, security issues in FHAMIPv6, connecting moving smart objects to the Internet, underwater sensor networks, wireless mesh network architecture and protocols, adaptive routing provision using Bayesian inference, and adaptive flow control in transport layer using genetic algorithms

Supporting Internet Access and Quality of Service in Distributed Wireless Ad Hoc Networks

In this era of wireless hysteria, with continuous technological advances in wireless communication and new wireless technologies becoming standardized at a fast rate, we can expect an increased interest for wireless networks, such as ad hoc and mesh networks. These networks operate in a distributed manner, independent of any centralized device. In order to realize the practical benefits of ad hoc networks, two challenges (among others) need to be considered: distributed QoS guarantees and multi-hop Internet access. In this thesis we present conceivable solutions to both of these problems. An autonomous, stand-alone ad hoc network is useful in many cases, such as search and rescue operations and meetings where participants wish to quickly share information. However, an ad hoc network connected to the Internet is even more desirable. This is because Internet plays an important role in the daily life of many people by offering a broad range of services. In this thesis we present AODV+, which is our solution to achieve this network interconnection between a wireless ad hoc network and the wired Internet. Providing QoS in distributed wireless networks is another challenging, but yet important, task mainly because there is no central device controlling the medium access. In this thesis we propose EDCA with Resource Reservation (EDCA/RR), which is a fully distributed MAC scheme that provides QoS guarantees by allowing applications with strict QoS requirements to reserve transmission time for contention-free medium access. Our scheme is compatible with existing standards and provides both parameterized and prioritized QoS. In addition, we present the Distributed Deterministic Channel Access (DDCA) scheme, which is a multi-hop extension of EDCA/RR and can be used in wireless mesh networks. Finally, we have complemented our simulation studies with real-world ad hoc and mesh network experiments. With the experience from these experiments, we obtained a clear insight into the limitations of wireless channels. We could conclude that a wise design of the network architecture that limits the number of consecutive wireless hops may result in a wireless mesh network that is able to satisfy users’ needs. Moreover, by using QoS mechanisms like EDCA/RR or DDCA we are able to provide different priorities to traffic flows and reserve resources for the most time-critical applications

Improving TCP behaviour to non-invasively share spectrum with safety messages in VANET

There is a broad range of technologies available for wireless communications for moving vehicles, such as Worldwide Interoperability for Microwave Access (WiMax), 3G, Dedicated Short Range Communication (DSRC)/ Wireless Access for Vehicular Environment (WAVE) and Mobile Broadband Wireless Access (MBWA). These technologies are needed to support delay-sensitive safety related applications such as collision avoidance and emergency breaking. Among them, the IEEE802.11p standard (aka DSRC/WAVE), a Wi-Fi based medium RF range technology, is considered to be one of the best suited draft architectures for time-sensitive safety applications. In addition to safety applications, however, services of non-safety nature like electronic toll tax collection, infotainment and traffic control are also becoming important these days. To support delay-insensitive infotainment applications, the DSRC protocol suite also provides facilities to use Internet Protocols. The DSRC architecture actually consists of WAVE Short Messaging Protocol (WSMP) specifically formulated for realtime safety applications as well as the conventional transport layer protocols TCP/UDP for non-safety purposes. But the layer four protocol TCP was originally designed for reliable data delivery only over wired networks, and so the performance quality was not guaranteed for the wireless medium, especially in the highly unstable network topology engendered by fast moving vehicles. The vehicular wireless medium is inherently unreliable because of intermittent disconnections caused by moving vehicles, and in addition, it suffers from multi-path and fading phenomena (and a host of others) that greatly degrade the network performance. One of the TCP problems in the context of vehicular wireless network is that it interprets transmission errors as symptomatic of an incipient congestion situation and as a result, reduces the throughput deliberately by frequently invoking slow-start congestion control algorithms. Despite the availability of many congestion control mechanisms to address this problem, the conventional TCP continues to suffer from poor performance when deployed in the Vehicular Ad-hoc Network (VANET) environment. Moreover, the way non-safety applications, when pressed into service, will treat the existing delay-sensitive safety messaging applications and the way these two types of applications interact between them are not (well) understood, and therefore, in order for them to coexist, the implication and repercussion need to be examined closely. This is especially important as IEEE 802.11p standards are not designed keeping in view the issues TCP raises in relation to safety messages. This dissertation addresses the issues arising out of this situation and in particular confronts the congestion challenges thrown up in the context of heterogenous communication in VANET environment by proposing an innovative solution with two optimized congestion control algorithms. Extensive simulation studies conducted by the author shows that both these algorithms have improved TCP performance in terms of metrics like Packet Delivery Fraction (PDF), Packet Loss and End-to-End Delay (E2ED), and at the same time they encourage the non-safety TCP application to behave unobtrusively and cooperatively to a large extent with DSRC’s safety applications. The first algorithm, called vScalable-TCP – a modification of the existing TCPScalable variant – introduces a reliable transport protocol suitable for DSRC. In the proposed approach, whenever packets are discarded excessively due to congestion, the slow-start mechanism is purposely suppressed temporarily to avoid further congestion and packet loss. The crucial idea here is how to adjust and regulate the behaviour of vScalable-TCP in a way that the existing safety message flows are least disturbed. The simulation results confirm that the new vScalable-TCP provides better performance for real-time safety applications than TCP-Reno and other TCP variants considered in this thesis in terms of standard performance metrics. The second algorithm, named vLP-TCP – a modification of the existing TCP-LP variant – is designed to test and demonstrate that the strategy developed for vScalable-TCP is also compatible with another congestion control mechanism and achieves the same purpose. This expectation is borne out well by the simulation results. The same slow-start congestion management strategy has been employed but with only a few amendments. This modified algorithm also improves substantially the performance of basic safety management applications. The present work thus clearly confirms that both vScalable-TCP and vLP-TCP algorithms – the prefix ‘v’ to the names standing for ‘vehicular’ – outperform the existing unadorned TCP-Scalable and TCP-LP algorithms, in terms of standard performance metrics, while at the same time behaving in a friendly manner, by way of sharing bandwidth non-intrusively with DSRC safety applications. This paves the way for the smooth and harmonious coexistence of these two broad, clearly incompatible or complementary categories of applications – viz. time-sensitive safety applications and delay-tolerant infotainment applications – by narrowing down their apparent impedance or behavioural mismatch, when they are coerced to go hand in hand in a DSRC environment

Quality of service on ad-hoc wireless networks

Over the last years, Mobile Ad-hoc Networks (MANETs) have captured the attention of the research community. The flexibility and cost savings they provide, due to the fact that no infrastructure is needed to deploy a MANET, is one of the most attractive possibilities of this technology. However, along with the flexibility, lots of problems arise due to the bad quality of transmission media, the scarcity of resources, etc. Since real-time communications will be common in MANETs, there has been an increasing motivation on the introduction of Quality of Service (QoS) in such networks. However, many characteristics of MANETs make QoS provisioning a difficult problem.In order to avoid congestion, a reservation mechanism that works together with a Connection Admission Control (CAC) seems to be a reasonable solution. However, most of the QoS approaches found in literature for MANETs do not use reservations. One reason for that, is the difficulty on determining the available bandwidth at a node. This is needed to decide whether there are enough resources to accommodate a new connection.This thesis proposes a simple, yet effective, method for nodes in a CSMA-based MANET to compute their available bandwidth in a distributed way. Based on this value, a QoS reservation mechanism called BRAWN (Bandwidth Reservation over Ad-hoc Networks) is introduced for multirate MANETs, allowing bandwidth allocation on a per flow basis. By multirate we refer to those networks where wireless nodes are able to dynamically switch among several link rates. This allows nodes to select the highest possible transmission rate for exchanging data, independently for each neighbor.The BRAWN mechanism not only guarantees certain QoS levels, but also naturally distributes the traffic more evenly among network nodes (i.e. load balancing). It works completely on the network layer, so that no modifications on lower layers are required, although some information about the network congestion state could also be taken into account if provided by the MAC (Medium Access Control) layer. The thesis analyzes the applicability of the proposed reservation mechanism over both proactive and reactive routing protocols, and extensions to such protocols are proposed whenever needed in order to improve their performance on multirate networks. On mobile scenarios, BRAWN also achieves high QoS provisioning levels by letting the nodes to periodically refresh QoS reservations. This extension of the protocol for mobile nodes is referred as BRAWN-R (BRAWN with Refreshments).Summarizing, the outstanding features of the reservation mechanism proposed by this thesis are: (i) Multirate, i.e. it allows wireless nodes to choose among different transmission rates, in order to accommodate to different channel conditions. (ii) Targeted to CSMA-based wireless MAC protocols, e.g. 802.11. (iii) Reservation based, allowing the network nodes to pro-actively protect ongoing QoS flows, and applying an effective CAC. (iv) Adaptive to topology changes introduced by the mobility of the nodes, re-routing QoS flows to more efficient paths. (v) Feasible and simple to implement over existing MANET routing protocols (as it is shown by the prototype presented at the end of the study).Postprint (published version

Mobile Ad-Hoc Networks

Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks