Routing Protocols in Vehicular Ad hoc Networks: Survey and Research Challenges
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paper_title: Dynamic source routing in ad hoc wireless networks

paper_content:

An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. In such an environment, it may be necessary for one mobile host to enlist the aid of other hosts in forwarding a packet to its destination, due to the limited range of each mobile host’s wireless transmissions. This paper presents a protocol for routing in ad hoc networks that uses dynamic source routing. The protocol adapts quickly to routing changes when host movement is frequent, yet requires little or no overhead during periods in which hosts move less frequently. Based on results from a packet-level simulation of mobile hosts operating in an ad hoc network, the protocol performs well over a variety of environmental conditions such as host density and movement rates. For all but the highest rates of host movement simulated, the overhead of the protocol is quite low, falling to just 1% of total data packets transmitted for moderate movement rates in a network of 24 mobile hosts. In all cases, the difference in length between the routes used and the optimal route lengths is negligible, and in most cases, route lengths are on average within a factor of 1.01 of optimal.
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paper_title: Ad-hoc on-demand distance vector routing

paper_content:

An ad-hoc network is the cooperative engagement of a collection of mobile nodes without the required intervention of any centralized access point or existing infrastructure. We present Ad-hoc On Demand Distance Vector Routing (AODV), a novel algorithm for the operation of such ad-hoc networks. Each mobile host operates as a specialized router, and routes are obtained as needed (i.e., on-demand) with little or no reliance on periodic advertisements. Our new routing algorithm is quite suitable for a dynamic self starting network, as required by users wishing to utilize ad-hoc networks. AODV provides loop-free routes even while repairing broken links. Because the protocol does not require global periodic routing advertisements, the demand on the overall bandwidth available to the mobile nodes is substantially less than in those protocols that do necessitate such advertisements. Nevertheless we can still maintain most of the advantages of basic distance vector routing mechanisms. We show that our algorithm scales to large populations of mobile nodes wishing to form ad-hoc networks. We also include an evaluation methodology and simulation results to verify the operation of our algorithm.
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paper_title: Performance assessment of a geographic routing protocol for vehicular delay-tolerant networks

paper_content:

This paper analyses the performance of a new routing protocol for vehicular delay-tolerant networks, called GeoSpray. This geographic routing protocol performs a store-carry-and-forward, combining replication and forwarding/ routing decisions based on location information, with explicit delivery acknowledgments to improve network resources utilization. The performance of the proposed routing protocol is evaluated through simulation. The results have shown that GeoSpray achieves higher delivery ratios and lower delivery delays with a considerably low communication overhead, compared to six well-known routing protocols for delay-tolerant networks.
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paper_title: Routing protocols for inter-vehicular networks: A comparative study in high-mobility and large obstacles environments

paper_content:

An ad hoc network is composed of mobile nodes without the presence of a fixed infrastructure. Communications among nodes are accomplished by forwarding data packets for each other, on a hop-by-hop basis along the current connection to the destination node. In particular, vehicle-to-vehicle communications have been studied, in recent years, to improve driver safety. As more of such applications of high-mobility ad hoc networks emerge, it is critical that the routing protocol employed is capable of efficiently coping with the high-frequency of broken links (i.e., robust with respect to high-mobility). This paper presents a comprehensive comparative study in a city environment of eight representative routing protocols for wireless mobile ad hoc networks and inter-vehicular networks developed in recent years. In a city environment, communication protocols need adapt fast moving nodes (e.g., vehicles on streets) and large obstacles (e.g., office buildings). In this paper, we elaborate upon extensive simulation results based on various network scenarios, and discuss the strengths and weaknesses of these techniques with regard to their support for highly mobile nodes.
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paper_title: Routing Protocols for Vehicular Ad Hoc Networks That Ensure Quality of Service

paper_content:

Vehicular ad hoc networks (VANETs) allow vehicles to form a self-organized network without the need for permanent infrastructure. Even though VANETs are mobile ad hoc networks (MANETs), because of the intrinsic characteristics of VANETs, routing protocols designed for MANETs cannot be directly applied for VANETs. In this paper, we present a timeline of the development of the existing routing protocols for VANETs that try to support quality of service (QoS). Moreover, we classify and characterize the existing QoS routing protocols for VANETs and also provide a qualitative comparison of them. This classification and characterization helps in understanding the strengths and weaknesses of the existing QoS protocols and also throws light on open issues that remain to be addressed.
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paper_title: Adaptive routing protocols for vehicular ad hoc networks

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Vehicular ad hoc networks based on IEEE 802.11(WLAN) technology are emerging technologies for future Intelligent Transportation Systems (ITS). We investigate the behavior of routing protocols in vehicular networks by using microscopic mobility information based on the real road maps. The simulation results show the remarkable effect of the real mobility models on the performance of routing protocols. We observe a significant reduction in packet delivery ratio in traditional and even position based routing protocols. To address these performance limitations in vehicular networks, we propose several improvements and take into account special characteristics of vehicular networks. The major improvement is the use of link expiration time (LET) as a node mobility and density indicator to provide transmission range adaptation. We proposed two adaptive routing protocols for vehicular ad hoc networks and evaluated through simulation.
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paper_title: Routing Protocols in Vehicular Ad Hoc Networks: A Survey and Future Perspectives

paper_content:

Vehicular Ad hoc Network (VANET), a subclass of mobile ad hoc networks (MANETs), is a promising approach for the intelligent transportation system (ITS). The design of routing protocols in VANETs is important and necessary issue for support the smart ITS. The key difference of VANET and MANET is the special mobility pattern and rapidly changeable topology. It is not effectively applied the existing routing protocols of MANETs into VANETs. In this investigation, we mainly survey new routing results in VANET. We introduce unicast protocol, multicast protocol, geocast protocol, mobicast protocol, and broadcast protocol. It is observed that carry-and-forward is the new and key consideration for designing all routing protocols in VANETs. With the consideration of multi-hop forwarding and carry-and-forward techniques, min-delay and delay-bounded routing protocols for VANETs are discussed in VANETs. Besides, the temporary network fragmentation problem and the broadcast storm problem are further considered for designing routing protocols in VANETs. The temporary network fragmentation problem caused by rapidly changeable topology influence on the performance of data transmissions. The broadcast storm problem seriously affects the successful rate of message delivery in VANETs. The key challenge is to overcome these problems to provide routing protocols with the low communication delay, the low communication overhead, and the low time complexity. The challenges and perspectives of routing protocols for VANETs are finally discussed.
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paper_title: Simulation-Based Study of Common Issues in VANET Routing Protocols

paper_content:

Vehicular communications have been one of the hottest research topics for the last few years. Many routing protocols have been proposed for such kind of networks. Most of them try to exploit the information which may be available at the vehicle by the time that a routing decision must be made. In addition, some solutions are designed taking into account the particular, highly partitioned, network connectivity in vehicular settings. To do so, they embrace the store-carry- forward paradigm of delay-tolerant networks. Despite the great variety of approaches which have been proposed, we found that there is a set of issues which are common to many vehicular ad hoc routing protocols in the literature. In this paper, we perform a simulation-based analysis of five of those protocols, which are representative of the various categories of vehicular routing. We describe in detail every problem and show simulation results which support our reasonings. Moreover, solutions to solve every presented problem are outlined. The paper is concluded with some guidelines which may be helpful to prospective VANET routing protocol designers.
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paper_title: Improvement of vehicular communications by using 3G capabilities to disseminate control information

paper_content:

Cellular networks have gained a lot of popularity in the context of vehicular communication within the last few years. Existing reference architectures such as CALM already consider them to provide enhanced connectivity to vehicles for data communication. Their capabilities, especially 3G and next-generation, translate into great potential in the vehicular environment, far beyond the provision of data connectivity. In this context we present a solution that uses 3G cellular networks not only as a backup for data communication among vehicles, but also and especially as an efficient mechanism for the dissemination of relevant control information for multiple applications, services, and protocols. Our simulation results demonstrate that by using our 3G-based solution to disseminate connectivity information, vehicular ad hoc routing protocols improve their route selections, which results in a higher packet delivery ratio in urban scenarios.
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paper_title: Highly dynamic Destination-Sequenced Distance-Vector routing (DSDV) for mobile computers

paper_content:

An ad-hoc network is the cooperative engagement of a collection of Mobile Hosts without the required intervention of any centralized Access Point. In this paper we present an innovative design for the operation of such ad-hoc networks. The basic idea of the design is to operate each Mobile Host as a specialized router, which periodically advertises its view of the interconnection topology with other Mobile Hosts within the network. This amounts to a new sort of routing protocol. We have investigated modifications to the basic Bellman-Ford routing mechanisms, as specified by RIP [5], to make it suitable for a dynamic and self-starting network mechanism as is required by users wishing to utilize ad hoc networks. Our modifications address some of the previous objections to the use of Bellman-Ford, related to the poor looping properties of such algorithms in the face of broken links and the resulting time dependent nature of the interconnection topology describing the links between the Mobile Hosts. Finally, we describe the ways in which the basic network-layer routing can be modified to provide MAC-layer support for ad-hoc networks.
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paper_title: The broadcast storm problem in a mobile ad hoc network

paper_content:

Broadcasting is a common operation in a network to resolve many issues. In a mobile ad hoc network (MANET) in particular, due to host mobility, such operations are expected to be executed more frequently (such as finding a route to a particular host, paging a particular host, and sending an alarm signal). Because radio signals are likely to overlap with others in a geographical area, a straightforward broadcasting by flooding is usually very costly and will result in serious redundancy, contention, and collision, to which we call the broadcast storm problem. In this paper, we identify this problem by showing how serious it is through analyses and simulations. We propose several schemes to reduce redundant rebroadcasts and differentiate timing of rebroadcasts to alleviate this problem. Simulation results are presented, which show different levels of improvement over the basic flooding approach.
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paper_title: A routing strategy for vehicular ad hoc networks in city environments

paper_content:

Routing of data in a vehicular ad hoc network is a challenging task due to the high dynamics of such a network. Recently, it was shown for the case of highway traffic that position-based routing approaches can very well deal with the high mobility of network nodes. However, baseline position-based routing has difficulties to handle two-dimensional scenarios with obstacles (buildings) and voids as it is the case for city scenarios. In this paper we analyze a position-based routing approach that makes use of the navigational systems of vehicles. By means of simulation we compare this approach with non-position-based ad hoc routing strategies (dynamic source routing and ad-hoc on-demand distance vector routing). The simulation makes use of highly realistic vehicle movement patterns derived from Daimler-Chrysler's Videlio traffic simulator. While DSR's performance is limited due to problems with scalability and handling mobility, both AODV and the position-based approach show good performances with the position-based approach outperforming AODV.
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paper_title: Self-organizing wide-area network caches

paper_content:

A substantial fraction of all network traffic today comes from applications in which clients retrieve objects from servers. The caching of objects in locations "close" to clients is an important technique for reducing both network traffic and response time for such applications. In this paper we consider the benefits of associating caches with switching nodes throughout the network, rather than in a few locations. We also consider the use of various self-organizing or active cache management strategies for organizing cache content. We evaluate caching techniques using both simulation and a general analytic model for network caching. Our results indicate that in-network caching can make effective use of cache space, and in many cases self-organizing caching schemes yield better average round-trip latencies than traditional approaches, using much smaller per-node caches.
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paper_title: Routing in a delay tolerant network

paper_content:

We formulate the delay-tolerant networking routing problem, where messages are to be moved end-to-end across a connectivity graph that is time-varying but whose dynamics may be known in advance. The problem has the added constraints of finite buffers at each node and the general property that no contemporaneous end-to-end path may ever exist. This situation limits the applicability of traditional routing approaches that tend to treat outages as failures and seek to find an existing end-to-end path. We propose a framework for evaluating routing algorithms in such environments. We then develop several algorithms and use simulations to compare their performance with respect to the amount of knowledge they require about network topology. We find that, as expected, the algorithms using the least knowledge tend to perform poorly. We also find that with limited additional knowledge, far less than complete global knowledge, efficient algorithms can be constructed for routing in such environments. To the best of our knowledge this is the first such investigation of routing issues in DTNs.
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paper_title: A scalable location service for geographic ad hoc routing

paper_content:

GLS is a new distributed location service which tracks mobile node locations. GLS combined with geographic forwarding allows the construction of ad hoc mobile networks that scale to a larger number of nodes than possible with previous work. GLS is decentralized and runs on the mobile nodes themselves, requiring no fixed infrastructure. Each mobile node periodically updates a small set of other nodes (its location servers) with its current location. A node sends its position updates to its location servers without knowing their actual identities, assisted by a predefined ordering of node identifiers and a predefined geographic hierarchy. Queries for a mobile node's location also use the predefined identifier ordering and spatial hierarchy to find a location server for that node. Experiments using the ns simulator for up to 600 mobile nodes show that the storage and bandwidth requirements of GLS grow slowly with the size of the network. Furthermore, GLS tolerates node failures well: each failure has only a limited effect and query performance degrades gracefully as nodes fail and restart. The query performance of GLS is also relatively insensitive to node speeds. Simple geographic forwarding combined with GLS compares favorably with Dynamic Source Routing (DSR): in larger networks (over 200 nodes) our approach delivers more packets, but consumes fewer network resources.
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paper_title: Vehicular grid communications: the role of the internet infrastructure

paper_content:

Vehicle communications are becoming a reality, driven by navigation safety requirements and by the investments of car manufacturers and Public Transport Authorities. As a consequence many of the essential vehicle grid components (radios, Access Points, spectrum, standards, etc.) will soon be in place (and paid for) paving the way to unlimited opportunities for other car-to-car applications beyond safe navigation, for example, from news to entertainment, mobile network games and civic defense. In this study, we take a visionary look at these future applications, the emerging "Vehicular Grid" that will support them and the interplay between the grid and the communications infrastructure. In essence, the Vehicular Grid is a large scale ad hoc network. However, an important feature of the Vehicular Grid, which sets it apart from most instantly-deployed ad hoc networks, is the ubiquitous presence of the infrastructure (and the opportunity to use it). While the Vehicular Grid must be entirely self-supporting for emergency operations (natural disaster, terrorist attack, etc), it should exploit the infrastructure (when present) during normal operations. In this paper we address the interaction between vehicles and Internet servers through Virtual Grid and Internet Infrastructure. This includes transparent geo-route provisioning across the Internet, mobile resource monitoring, and mobility management (using back up services in case of infrastructure failure). We then focus on routing and show the importance of Infrastructure cooperation and feedback for efficient, congestion free routing.
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paper_title: Drive and share: efficient provisioning of social networks in vehicular scenarios

paper_content:

Social Networks are one of the latest revolutions in networking, allowing users with common interests to stay connected and exchange information. They have enjoyed great success not only for traditional Internet users, but also for mobile users. Recent efforts are also being done to make social networks available within vehicles. However, to exploit social networks at their full potential in a vehicular context a number of technical challenges and design issues need to be faced. In this article, we analyze those challenges and present an innovative solution for providing Social services on the vehicle based on IP Multimedia Subsystem and Machine to Machine capabilities. To demonstrate the viability of the proposed scheme we present a social network service called Drive and Share which offers relevant information to vehicles using our proposed architecture.
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paper_title: IGF: A State-Free Robust Communication Protocol for Wireless Sensor Networks

paper_content:

Wireless Sensor Networks (WSNs) are being designed to solve a gamut of interesting real-world problems. Limitations on available energy and bandwidth, message loss, high rates of node failure, and communication restrictions pose challenging requirements for these systems. Beyond these inherent limitations, both the possibility of node mobility and energy conserving protocols that power down nodes introduce additional complexity to routing protocols that depend on up to date routing or neighborhood tables. Such state-based protocols suffer excessive delay or message loss, as system dynamics require expensive upkeep of these tables. Utilizing characteristics of high node density and location awareness, we introduce IGF, a location-aware routing protocol that is robust and works without knowledge of the existence of neighboring nodes (state-free). We compare our work against established routing protocols to demonstrate the efficacy of our solution when nodes are mobile or periodically sleep to conserve energy. We show that IGF far outperforms these protocols, in some cases delivering close to 100% of the packets transmitted while alternate solutions fail to even find a path between a source and destination. Specifically, we show that our protocol demonstrates a vast improvement over prior work using metrics of delivery ratio, control overhead, and end-to-end delay.
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paper_title: PROMPT: A cross-layer position-based communication protocol for delay-aware vehicular access networks

paper_content:

Vehicular communication systems facilitate communication devices for exchange of information among vehicles and between vehicles and roadside equipment. These systems are used to provide a myriad of services ranging from traffic safety application to convenience applications for drivers and passengers. In this paper, we focus on the design of communication protocols for vehicular access networks where vehicles access a wired backbone network by means of a multi-hop data delivery service. Key challenges in designing protocols for vehicular access networks include quick adaptability to frequent changes in the network topology due to vehicular mobility and delay awareness in data delivery. To address these challenges, we propose a cross-layer position-based delay-aware communication protocol called PROMPT. It adopts a source routing mechanism that relies on positions independent of vehicle movement rather than on specific vehicle addresses. Vehicles monitor information exchange in their reception range to obtain data flow statistics, which are then used in estimating the delay and selecting best available paths. Through a detailed simulation study using ns-2, we empirically show that PROMPT outperforms existing routing protocols proposed for vehicular networks in terms of end-to-end packet delay, packet loss rate, and fairness of service.
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paper_title: A vehicle-to-vehicle communication protocol for cooperative collision warning

paper_content:

This paper proposes a vehicle-to-vehicle communication protocol for cooperative collision warning. Emerging wireless technologies for vehicle-to-vehicle (V2V) and vehicle-to-roadside (V2R) communications such as DSRC are promising to dramatically reduce the number of fatal roadway accidents by providing early warnings. One major technical challenge addressed in this paper is to achieve low-latency in delivering emergency warnings in various road situations. Based on a careful analysis of application requirements, we design an effective protocol, comprising congestion control policies, service differentiation mechanisms and methods for emergency warning dissemination. Simulation results demonstrate that the proposed protocol achieves low latency in delivering emergency warnings and efficient bandwidth usage in stressful road scenarios.
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paper_title: GeOpps: Geographical Opportunistic Routing for Vehicular Networks

paper_content:

Vehicular networks can be seen as an example of hybrid delay tolerant network where a mixture of infostations and vehicles can be used to geographically route the information messages to the right location. In this paper we present a forwarding protocol which exploits both the opportunistic nature and the inherent characteristics of the vehicular network in terms of mobility patterns and encounters, and the geographical information present in navigator systems of vehicles. We also report about our evaluation of the protocol over a simulator using realistic vehicular traces and in comparison with other geographical routing protocols.
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paper_title: Vehicle-to-vehicle safety messaging in DSRC

paper_content:

This paper studies the design of layer-2 protocols for a vehicle to send safety messages to other vehicles. The target is to send vehicle safety messages with high reliability and low delay. The communication is one-to-many, local, and geo-significant. The vehicular communication network is ad-hoc, highly mobile, and with large numbers of contending nodes. The messages are very short, have a brief useful lifetime, but must be received with high probability. For this environment, this paper explores the efficacy of rapid repetition of broadcast messages. This paper proposes several random access protocols for medium access control. The protocols are compatible with the Dedicated Short Range Communications (DSRC) multi-channel architecture. Analytical bounds on performance of the proposed protocols are derived. Simulations are conducted to assess the reception reliability and channel usage of the protocols. The sensitivity of the protocol performance is evaluated under various offered traffic and vehicular traffic flows. The results show our approach is feasible for vehicle safety messages in DSRC.
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paper_title: Simulation-Based Study of Common Issues in VANET Routing Protocols

paper_content:

Vehicular communications have been one of the hottest research topics for the last few years. Many routing protocols have been proposed for such kind of networks. Most of them try to exploit the information which may be available at the vehicle by the time that a routing decision must be made. In addition, some solutions are designed taking into account the particular, highly partitioned, network connectivity in vehicular settings. To do so, they embrace the store-carry- forward paradigm of delay-tolerant networks. Despite the great variety of approaches which have been proposed, we found that there is a set of issues which are common to many vehicular ad hoc routing protocols in the literature. In this paper, we perform a simulation-based analysis of five of those protocols, which are representative of the various categories of vehicular routing. We describe in detail every problem and show simulation results which support our reasonings. Moreover, solutions to solve every presented problem are outlined. The paper is concluded with some guidelines which may be helpful to prospective VANET routing protocol designers.
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paper_title: GeOpps: Geographical Opportunistic Routing for Vehicular Networks

paper_content:

Vehicular networks can be seen as an example of hybrid delay tolerant network where a mixture of infostations and vehicles can be used to geographically route the information messages to the right location. In this paper we present a forwarding protocol which exploits both the opportunistic nature and the inherent characteristics of the vehicular network in terms of mobility patterns and encounters, and the geographical information present in navigator systems of vehicles. We also report about our evaluation of the protocol over a simulator using realistic vehicular traces and in comparison with other geographical routing protocols.
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paper_title: Beacon-less geographic routing made practical: challenges, design guidelines, and protocols

paper_content:

Geographic routing has emerged as one of the most efficient and scalable routing solutions for wireless sensor networks. In traditional geographic routing protocols, each node exchanges periodic one-hop beacons to determine the position of its neighbors. Recent studies proved that these beacons can create severe problems in real deployments due to the highly dynamic and error-prone nature of wireless links. To avoid these problems, new variants of geographic routing protocols that do not require beacons are being proposed. In this article we review some of the latest proposals in the field of beacon-less geographic routing and introduce the main design challenges and alternatives. In addition, we perform an empirical study to assess the performance of beacon-based and beacon-less routing protocols using a real WSN deployment.
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paper_title: Contention-Based Forwarding for Street Scenarios

paper_content:

In this paper, we propose to apply Contention-Based Forwarding (CBF) to Vehicular Ad Hoc Networks (VANETs). CBF is a greedy position-based forwarding algorithm that does not require proactive transmission of beacon messages. CBF performance is analyzed using realistic movement patterns of vehicles on a highway. We show by means of simulation that CBF as well as traditional position-based routing (PBR) achieve a delivery rate of almost 100 given that connectivity exists. However, CBF has a much lower forwarding overhead than PBR since PBR can achieve high delivery ratios only by implicitly using a trial-and-error next-hop selection strategy. With CBF, a better total throughput can be achieved. We further discuss several optimizations of CBF for its use in VANETs, in particular a new position-encoding scheme that naturally allows for communication paradigms such as `street geocast` and `street flooding`. The discussions show that CBF can be viewed as a concept for convergence of intelligent flooding, geocast, and multi-hop forwarding in the area of inter-vehicle communication.
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paper_title: Priority-based receiver-side relay election in wireless ad hoc sensor networks

paper_content:

Receiver-side relay election has been recently proposed as an alternative to transmitter-side relay selection in wireless ad hoc networks. In this paper we study different prioritization schemes among potential relay nodes to achieve a better delay and contention resolution performance. We consider a priority criteria based on least remaining distance to the destination and propose a generalized mapping function to introduce relative priority among the eligible relay nodes. We show that, a suitable mapping can be found to achieve an optimum relay election performance, which also outperforms the random forwarding approach. Our intuition is guided by an analytic framework and verified by network simulation.
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paper_title: Beacon-Less Geographic Routing in Real Wireless Sensor Networks

paper_content:

Geographic Routing (GR) algorithms require nodes to periodically transmit HELLO messages to allow neighbors to know their positions (beaconing mechanism). Beacon-less routing algorithms have recently been proposed to reduce the control overheads due to these messages. However, existing beacon-less algorithms have not considered realistic physical layers. Therefore, those algorithms cannot work properly in realistic scenarios. In this paper we present a new beaconless routing protocol called BOSS. Its design is based on the conclusions of our open-field experiments using Tmote-sky sensors. BOSS is adapted to error-prone networks and incorporates a new mechanism to reduce collisions and duplicate messages produced during the selection of the next forwarder node. We compare BOSS with Beacon-Less Routing (BLR) and Contention-Based Forwarding (CBF) algorithms through extensive simulations. The results show that our scheme is able to achieve almost perfect packet delivery ratio (like BLR) while having a low bandwidth consumption (even lower than CBF). Additionally, we carried out an empirical evaluation in a real testbed that shows the correctness of our simulation results.
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paper_title: Beaconless Position-based Routing with Guaranteed Delivery for Wireless Ad hoc and Sensor Networks

paper_content:

Existing position-based routing algorithms, where packets are forwarded in the geographic direction of the destination, normally require that the forwarding node should know the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages that each node sends out periodically. Several beaconless greedy routing schemes have been proposed recently. However, none of the existing beaconless schemes guarantee the delivery of packets. Moreover, they incur communication overhead by sending excessive control messages or by broadcasting data packets. In this paper, we describe how existing localized position based routing schemes that guarantee delivery can be made beaconless, while preserving the same routes. In our guaranteed delivery beaconless routing scheme, the next hop is selected through the use of control RTS/CTS messages and biased timeouts. In greedy mode, the neighbor closest to destination responds first. In recovery mode, nodes closer to the source will select shorter timeouts, so that other neighbors, overhearing CTS packets, can eliminate their own CTS packets if they realize that their link to the source is not part of Gabriel graph. Nodes also cancel their packets after receiving data message sent by source to the selected neighbor. We analyze the behavior of our scheme on our simulation environment assuming ideal MAC, following GOAFR+ and GFG routing schemes. Our results demonstrate low communication overhead in addition to guaranteed delivery.
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paper_title: Trajectory based forwarding and its applications

paper_content:

Trajectory based forwarding (TBF) is a novel methodto forward packets in a dense ad hoc network that makes it possible to route a packet along a predefined curve. It is a hybrid between source based routing and Cartesian forwarding in that the trajectory is set by the source, but the forwarding decision is based on the relationship to the trajectory rather than names of intermediate nodes. The fundamental aspects of TBF are: it decouples path naming from the actual path; it provides cheap path diversity; it trades off communication for computation. These aspects address the double scalability issue with respect to mobility rate and network size. In addition, TBF provides a common framework for many services such as: broadcasting, discovery, unicast, multicast and multipath routing in ad hoc networks. TBF requires that nodes know their position relative to a coordinate system. While a global coordinate system afforded by a system such as GPS would be ideal, approximate positioning methods provided by other algorithms are also usable.
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paper_title: Knowledge-based opportunistic forwarding in vehicular wireless ad hoc networks

paper_content:

When highly mobile nodes are interconnected via wireless links, the resulting network can be used as a transit network to connect other disjoint ad-hoc networks. In this paper, we compare five different opportunistic forwarding schemes, which vary in their overhead, their success rate, and the amount of knowledge about neighboring nodes that they require. In particular, we present the MoVe algorithm, which uses velocity information to make intelligent opportunistic forwarding decisions. Using auxiliary information to make forwarding decisions provides a reasonable trade-off between resource overhead and performance.
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paper_title: GPSR: greedy perimeter stateless routing for wireless networks

paper_content:

We present Greedy Perimeter Stateless Routing (GPSR), a novel routing protocol for wireless datagram networks that uses the positions of routers and a packet's destination to make packet forwarding decisions. GPSR makes greedy forwarding decisions using only information about a router's immediate neighbors in the network topology. When a packet reaches a region where greedy forwarding is impossible, the algorithm recovers by routing around the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's scalability on densely deployed wireless networks.
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paper_title: A routing strategy for vehicular ad hoc networks in city environments

paper_content:

Routing of data in a vehicular ad hoc network is a challenging task due to the high dynamics of such a network. Recently, it was shown for the case of highway traffic that position-based routing approaches can very well deal with the high mobility of network nodes. However, baseline position-based routing has difficulties to handle two-dimensional scenarios with obstacles (buildings) and voids as it is the case for city scenarios. In this paper we analyze a position-based routing approach that makes use of the navigational systems of vehicles. By means of simulation we compare this approach with non-position-based ad hoc routing strategies (dynamic source routing and ad-hoc on-demand distance vector routing). The simulation makes use of highly realistic vehicle movement patterns derived from Daimler-Chrysler's Videlio traffic simulator. While DSR's performance is limited due to problems with scalability and handling mobility, both AODV and the position-based approach show good performances with the position-based approach outperforming AODV.
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paper_title: Connectivity-Aware Routing (CAR) in Vehicular Ad-hoc Networks

paper_content:

Vehicular ad hoc networks using WLAN technology have recently received considerable attention. We present a position-based routing scheme called Connectivity-Aware Routing (CAR) designed specifically for inter-vehicle communication in a city and/or highway environment. A distinguishing property of CAR is the ability to not only locate positions of destinations but also to find connected paths between source and destination pairs. These paths are auto-adjusted on the fly, without a new discovery process. "Guards" help to track the current position of a destination, even if it traveled a substantial distance from its initially known location. For the evaluation of the CAR protocol we use realistic mobility traces obtained from a microscopic vehicular traffic simulator that is based on a model of driver behavior and the real road maps of Switzerland.
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paper_title: Enhanced Perimeter Routing for Geographic Forwarding Protocols in Urban Vehicular Scenarios

paper_content:

Geographic stateless routing schemes such as GPSR have been widely adopted to routing in vehicular ad hoc networks (VANET). However, due to the particular urban topology and the non-uniform distribution of cars, the greedy routing mode often fails and needs a recovery strategy such as GPSR's perimeter mode to deliver data successfully to the destination. It has been shown that the cost of planarization, the non-uniform distribution of cars, and radio obstacles make GPSR's perimeter mode inefficient in urban configurations. Some enhancements have been proposed such as GPCR, which uses the concept of junction nodes to control the next road segments that packets should follow. However, the concept of junction nodes itself is problematic and hard to maintain in a dynamic urban environment. In this paper, we describe GpsrJ+, a solution that further improves the packet delivery ratio of GPCR with minimal modification by predicting on which road segment its neighboring junction node will forward packets to. GpsrJ+ differs from GPCR as decisions about which road segment to turn does not need to be made by junction nodes. Moreover, GpsrJ+ does not need an expensive planarization strategy since it uses the natural planar feature of urban maps. Consequently, GpsrJ+ reduces the hop count used in the perimeter mode by as much as 200% compared to GPSR. It therefore allows geographic routing schemes to return to the greedy mode faster.
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paper_title: A static-node assisted adaptive routing protocol in vehicular networks

paper_content:

Vehicular networks have attracted great interest in the research community recently, and multi-hop routing becomes an important issue. To improve data delivery performance, we propose SADV, which utilizes some static nodes at road intersections in a completely mobile vehicular network to help relay data. With the assistance of static nodes at intersections, a packet can be stored in the node for a while and wait until there are vehicles within communication range along the best delivery path to further forward the packet, which reduces the overall data delivery delay. In addition, we let adjacent nodes measure the delay of forwarding data between each other in real time, so that the routing decision can adapt to changing vehicle densities. Our simulation results show that SADV outperforms other multi-hop data dissemination protocols, especially under median or low vehicle density where the network is frequently partitioned.
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paper_title: A-STAR: A Mobile Ad Hoc Routing Strategy for Metropolis Vehicular Communications

paper_content:

One of the major issues that affect the performance of Mobile Ad hoc NETworks (MANET) is routing. Recently, position-based routing for MANET is found to be a very promising routing strategy for inter-vehicular communication systems (IVCS). However, position-based routing for IVCS in a built-up city environment faces greater challenges because of potentially more uneven distribution of vehicular nodes, constrained mobility, and difficult signal reception due to radio obstacles such as high-rise buildings. This paper proposes a new position-based routing scheme called Anchor-based Street and Traffic Aware Routing (A-STAR), designed specifically for IVCS in a city environment. Unique to A-STAR is the usage of information on city bus routes to identify an anchor path with high connectivity for packet delivery. Along with a new recovery strategy for packets routed to a local maximum, the proposed protocol shows significant performance improvement in a comparative simulation study with other similar routing approaches.
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paper_title: LOUVRE: Landmark Overlays for Urban Vehicular Routing Environments

paper_content:

In this paper, we introduce a routing solution called "landmark overlays for urban vehicular routing environments" (LOUVRE), an approach that efficiently builds a landmark overlay network on top of an urban topology. We define urban junctions as overlay nodes and create an overlay link if and only if the traffic density of the underlying network guarantees the multi-hop vehicular routing between the two overlay nodes. LOUVRE contains a distributed traffic density estimation scheme which is used to evaluate the existence of an overlay link. Then, efficient routing is performed on the overlay network, guaranteeing a correct delivery of each packet. We evaluate LOUVRE against the benchmark routing protocols of GPSR and GPCR and show that LOUVRE performs higher in packet delivery and achieves lower hop count.
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paper_title: Beaconless Position-based Routing with Guaranteed Delivery for Wireless Ad hoc and Sensor Networks

paper_content:

Existing position-based routing algorithms, where packets are forwarded in the geographic direction of the destination, normally require that the forwarding node should know the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages that each node sends out periodically. Several beaconless greedy routing schemes have been proposed recently. However, none of the existing beaconless schemes guarantee the delivery of packets. Moreover, they incur communication overhead by sending excessive control messages or by broadcasting data packets. In this paper, we describe how existing localized position based routing schemes that guarantee delivery can be made beaconless, while preserving the same routes. In our guaranteed delivery beaconless routing scheme, the next hop is selected through the use of control RTS/CTS messages and biased timeouts. In greedy mode, the neighbor closest to destination responds first. In recovery mode, nodes closer to the source will select shorter timeouts, so that other neighbors, overhearing CTS packets, can eliminate their own CTS packets if they realize that their link to the source is not part of Gabriel graph. Nodes also cancel their packets after receiving data message sent by source to the selected neighbor. We analyze the behavior of our scheme on our simulation environment assuming ideal MAC, following GOAFR+ and GFG routing schemes. Our results demonstrate low communication overhead in addition to guaranteed delivery.
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paper_title: Location-aided routing (LAR) in mobile ad hoc networks

paper_content:

A mobile ad hoc network consists of wireless hosts that may move often. Movement of hosts results in a change in routes, requiring some mechanism for determining new routes. Several routing protocols have already been proposed for ad hoc networks. This report suggests an approach to utilize location information (for instance, obtained using the global positioning system) to improve performance of routing protocols for ad hoc networks.
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paper_title: Contention-Based Forwarding for Street Scenarios

paper_content:

In this paper, we propose to apply Contention-Based Forwarding (CBF) to Vehicular Ad Hoc Networks (VANETs). CBF is a greedy position-based forwarding algorithm that does not require proactive transmission of beacon messages. CBF performance is analyzed using realistic movement patterns of vehicles on a highway. We show by means of simulation that CBF as well as traditional position-based routing (PBR) achieve a delivery rate of almost 100 given that connectivity exists. However, CBF has a much lower forwarding overhead than PBR since PBR can achieve high delivery ratios only by implicitly using a trial-and-error next-hop selection strategy. With CBF, a better total throughput can be achieved. We further discuss several optimizations of CBF for its use in VANETs, in particular a new position-encoding scheme that naturally allows for communication paradigms such as `street geocast` and `street flooding`. The discussions show that CBF can be viewed as a concept for convergence of intelligent flooding, geocast, and multi-hop forwarding in the area of inter-vehicle communication.
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paper_title: Contention-Based Forwarding for Mobile Ad Hoc Networks

paper_content:

Existing position-based unicast routing algorithms which forward packets in the geographic direction of the destination require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. Due to mobility, the information that a node receives about its neighbors becomes outdated, leading either to a significant decrease in the packet delivery rate or to a steep increase in load on the wireless channel as node mobility increases. In this paper, we propose a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding scheme (CBF) the next hop is selected through a distributed contention process based on the actual positions of all current neighbors. For the contention process, CBF makes use of biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy position-based routing approach by means of simulation with ns-2. Our results show that CBF significantly reduces the load on the wireless channel required to achieve a specific delivery rate compared to the load a beacon-based greedy forwarding strategy generates.
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paper_title: VANET Routing on City Roads Using Real-Time Vehicular Traffic Information

paper_content:

This paper presents a class of routing protocols called road-based using vehicular traffic (RBVT) routing, which outperforms existing routing protocols in city-based vehicular ad hoc networks (VANETs). RBVT protocols leverage real-time vehicular traffic information to create road-based paths consisting of successions of road intersections that have, with high probability, network connectivity among them. Geographical forwarding is used to transfer packets between intersections on the path, reducing the path's sensitivity to individual node movements. For dense networks with high contention, we optimize the forwarding using a distributed receiver-based election of next hops based on a multicriterion prioritization function that takes nonuniform radio propagation into account. We designed and implemented a reactive protocol RBVT-R and a proactive protocol RBVT-P and compared them with protocols representative of mobile ad hoc networks and VANETs. Simulation results in urban settings show that RBVT-R performs best in terms of average delivery rate, with up to a 40% increase compared with some existing protocols. In terms of average delay, RBVT-P performs best, with as much as an 85% decrease compared with the other protocols.
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paper_title: TO-GO: TOpology-assist geo-opportunistic routing in urban vehicular grids

paper_content:

Road topology information has recently been used to assist geo-routing, thereby improving the overall performance. However, the unreliable wireless channel nature in urban vehicular grids (due to motion, obstructions, etc) still creates problems with the basic greedy forwarding. In this paper, we propose TO-GO (TOpology-assisted Geo-Opportunistic Routing), a geo-routing protocol that exploits topology knowledge acquired via 2-hop beaconing to select the best target forwarder and incorporates opportunistic forwarding with the best chance to reach it. The forwarder selection takes into account of wireless channel quality, thus significantly improving performance in error and interference situations. Extensive simulations confirm TO-GO superior robustness to errors/losses as compared to conventional topology-assisted geographic routing.
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paper_title: VanetMobiSim: generating realistic mobility patterns for VANETs

paper_content:

In this paper, we present and describe VanetMobiSim, a generator of realistic vehicular movement traces for telecommunication networks simulators. VanetMobiSim mobility description is validated by illustrating how the interaction between featured macro- and micro-mobility is able to reproduce typical phenomena of vehicular traffic.
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paper_title: Towards Efficient Geographic Routing in Urban Vehicular Networks

paper_content:

Vehicular ad hoc networks (VANETs) have received considerable attention in recent times. Multihop data delivery between vehicles is an important aspect for the support of VANET-based applications. Although data dissemination and routing have extensively been addressed, many unique characteristics of VANETs, together with the diversity in promising applications, offer newer research challenges. This paper introduces the improved greedy traffic-aware routing protocol (GyTAR), which is an intersection-based geographical routing protocol that is capable of finding robust and optimal routes within urban environments. The main principle behind GyTAR is the dynamic and in-sequence selection of intersections through which data packets are forwarded to the destinations. The intersections are chosen considering parameters such as the remaining distance to the destination and the variation in vehicular traffic. Data forwarding between intersections in GyTAR adopts an improved greedy carry-and-forward mechanism. Evaluation of the proposed routing protocol shows significant performance improvement in comparison with other existing routing approaches. With the aid of extensive simulations, we also validate the optimality and sensitivity of significant GyTAR parameters.
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paper_title: DIR: diagonal-intersection-based routing protocol for vehicular ad hoc networks

paper_content:

In this paper, we present a diagonal-intersection-based routing (DIR) protocol for vehicular ad hoc networks. The DIR protocol constructs a series of diagonal intersections between the source and destination vehicles. The DIR protocol is a geographic routing protocol. Based on the geographic routing protocol, source vehicle geographically forwards data packet toward the first diagonal intersection, second diagonal intersection, and so on, until the last diagonal intersection, and finally geographically reach to the destination vehicle. For given a pair of neighboring diagonal intersections, two or more disjoint sub-paths exist between them. The novel property of DIR protocol is the auto-adjustability, while the auto-adjustability is achieved that one sub-path with low data packet delay, between two neighboring diagonal intersections, is dynamically selected to forward data packets. To reduce the data packet delay, the route is automatically re-routed by the selected sub-path with lowest delay. The proposed DIR protocol allows the mobile source and destination vehicles in the urban VANETs. Experimental results show that the DIR protocol outperforms existing solutions in terms of packet delivery ratio, data packet delay, and throughput.
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paper_title: Dynamic source routing in ad hoc wireless networks

paper_content:

An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. In such an environment, it may be necessary for one mobile host to enlist the aid of other hosts in forwarding a packet to its destination, due to the limited range of each mobile host’s wireless transmissions. This paper presents a protocol for routing in ad hoc networks that uses dynamic source routing. The protocol adapts quickly to routing changes when host movement is frequent, yet requires little or no overhead during periods in which hosts move less frequently. Based on results from a packet-level simulation of mobile hosts operating in an ad hoc network, the protocol performs well over a variety of environmental conditions such as host density and movement rates. For all but the highest rates of host movement simulated, the overhead of the protocol is quite low, falling to just 1% of total data packets transmitted for moderate movement rates in a network of 24 mobile hosts. In all cases, the difference in length between the routes used and the optimal route lengths is negligible, and in most cases, route lengths are on average within a factor of 1.01 of optimal.
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paper_title: Ad-hoc on-demand distance vector routing

paper_content:

An ad-hoc network is the cooperative engagement of a collection of mobile nodes without the required intervention of any centralized access point or existing infrastructure. We present Ad-hoc On Demand Distance Vector Routing (AODV), a novel algorithm for the operation of such ad-hoc networks. Each mobile host operates as a specialized router, and routes are obtained as needed (i.e., on-demand) with little or no reliance on periodic advertisements. Our new routing algorithm is quite suitable for a dynamic self starting network, as required by users wishing to utilize ad-hoc networks. AODV provides loop-free routes even while repairing broken links. Because the protocol does not require global periodic routing advertisements, the demand on the overall bandwidth available to the mobile nodes is substantially less than in those protocols that do necessitate such advertisements. Nevertheless we can still maintain most of the advantages of basic distance vector routing mechanisms. We show that our algorithm scales to large populations of mobile nodes wishing to form ad-hoc networks. We also include an evaluation methodology and simulation results to verify the operation of our algorithm.
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paper_title: A Novel Delay- and Reliability- Aware Inter-Vehicle Routing Protocol

paper_content:

Intelligent transportation systems could improve transportation safety, driving assistance and traffic management system. Vehicular Ad hoc Network (VANET) is an emerging field of technology, embedding wireless communication networks into vehicles to achieve intelligent transportation systems. The development of such systems pose many unique challenges like designing routing protocols that not only forward packets with good end to end delay but also take into consideration the reliability and progress in data packets forwarding. In this article, we begin by presenting a review of recent unicast, geocast and broadcast routing protocols for message transmission. We then outline a novel Delay and Reliability aware Routing (DR 2 ) protocol that addresses these challenges (forwarding packets with low latency, high reliability and fast progress toward destination). Furthermore, our DR 2 protocol uses cross layer communication between MAC (Medium Access Control) and network layer. That is, the MAC layer observes the Signal to Noise (SNR), delay and velocity vector difference metrics for all paths of neighboring nodes, network layer then could select the best preferable path based on fuzzy inference system. We also used H∞ technique to optimize the membership functions and then tune it with rapid changing topology of VANET. To achieve a fair comparison with other routing protocols, we have implemented the proposed DR 2 protocol in Network Simulator 2 (NS 2). The preliminary results show that the proposed DR 2 protocol is able to improve end- to-end delay in sparse traffic conditions and packet delivery ratio in error prone urban vehicular scenarios.
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paper_title: Fuzzy-assisted social-based routing for urban vehicular environments

paper_content:

In the autonomous environment of Vehicular Ad hoc NETwork (VANET), vehicles randomly move with high speed and rely on each other for successful data transmission process. The routing can be difficult or impossible to predict in such intermittent vehicles connectivity and highly dynamic topology. The existing routing solutions do not consider the knowledge that behaviour patterns exist in real-time urban vehicular networks. In this article, we propose a fuzzy-assisted social-based routing (FAST) protocol that takes the advantage of social behaviour of humans on the road to make optimal and secure routing decisions. FAST uses prior global knowledge of real-time vehicular traffic for packet routing from the source to the destination. In FAST, fuzzy inference system leverages friendship mechanism to make critical decisions at intersections which is based on prior global knowledge of real-time vehicular traffic information. The simulation results in urban vehicular environment for with and without obstacles scenario show that the FAST performs best in terms of packet delivery ratio with upto 32% increase, average delay 80% decrease, and hops count 50% decrease compared to the state of the art VANET routing solutions.
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paper_title: A Load Balancing and Congestion-Avoidance Routing Mechanism for Teal-Time Traffic over Vehicular Networks

paper_content:

With the growth up of internet in mobile commerce, researchers have reproduced various mobile applications that vary from entertainment and commercial services to diagnostic and safety tools. Resource management for real-time traffic has widely been recognized as one of the most challenging problems for seamless access to vehicular networks. In this paper, a novel load balancing and congestion-avoidance routing mechanism over short communication range is proposed to satisfy the stringent QoS requirement of real-time traffic in vehicular ad hoc networks. Fuzzy logic systems are used to select the intermediate nodes on the routing path via inter-vehicle communications, and H-infinity technique is used to adjust the membership functions employed in the fuzzy logic systems to adapt to the volatile characteristics of the vehicular networks. Notably, a prediction of the remaining connection time among each vehicle and its neighbors is derived to assisting in the determination of the intermediate nodes on the routing path. The experimental results verify the effectiveness and feasibility of the proposed schemes, in terms of several performance metrics such as packet delivery ratio, end-to-end delay, control overhead, throughputs, call blocking probability and call dropping probability.
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paper_title: Multi-metric Routing Decisions in VANET

paper_content:

Due to the rapidly changing topology of Vehicular Ad Hoc network (VANET), it requires the routing protocol can be able to find out comparatively more stable routes. But the routing protocols in existence are not taking the distinguishing features of vehicles and roadway into consideration, and this brought about challenges to these routing protocols’ applicability in VANET. In this paper, we take the characteristics of VANET into account, and using the method of fuzzy logic and fuzzy control to make routing decision under multiple selection criteria, then we developed a new routing protocol based on the classical AODV which name is Fcar(Fuzzy control based AODV routing). Simulations have been carried out comparing AODV and Fcar, the results indicate that Fcar is superior to AODV in several aspects, so Fcar shows its adaptability in VANET.
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paper_title: Fuzzy logic-assisted geographical routing over vehicular ad hoc networks

paper_content:

Vehiculiu: Ad Hoc Network" (VANET,,) i" a type of ad hoc network that allows vehicles to communicate with each other in the absence of ji'J:ed infrastruct'ure. Inter-vehicle geographic ro'uting has been proven to perform well in high speed vehic'ular environments. In connected and reliable cehicular scenarios, greedy based geographical toutuu; protocol" could forward data packet" efficiently and q'uiekly toward" the de"tination. However, e'J:tremely dynamic cehicular euoironmcnts and 'uneven distrib'ution of vehicles could create 'unreliable wireless charmels between vehicles and disconnected cehicular partitions. On the one hand, in connected uehiculur networks, an intelligent multi-metric ro'uting protocol must be e'J:ploited in consideration of the 'unreliable nature of wireless channcls between vehicles and vehic'ular mobility characteristics. On the other hand, a mechanism must be 'utilized to create a tnrtuu! bridge between vehicles in disconnected cehicular scenurios. To thi" end, we fir"tly propose a novel Stability and Reliability aware Routinq (SRR) protocol that forward" packet" with a high degree of reliability and "tability toward" the destination. That is, the SRR protocol incorporate" fuzzy loou: with geographical ro'uting when making packet forwarding decisions. Ro'uting metric», sucl: as direction and distance, are considered as inp'uts of the fuzzy decision making system so that the best preferable neighbo'ur annuul a "mart vehiele i" "elected. We then 'utilize a mechanism to cache data packets once the network is disconnected and then switch back to SRR in a connected vehic'ular scenario. Traffic density is considered as an inp'ut when estimating network dis-connectivity. After devcloping an analytical modcl of our protocol, we implemented it and compared it with standard protocols. In a realistic highway uchicular scetuirio, the results "how that the propo"ed protocol perform" better than Greedy Perimeter Coordinator RO'uting (GPCR) with increases of 'up to 21.12 %, 2.9.,14 % and //..98 %in packet dcliver;1J ratio in high lossy clumnel, sparse, and dense traffic conditions respectivcly. In terms of average packet dclay, SRR performs better with performance increases of 'up to 2,1..92 % in deus« traffic condition". But, GPCR perform" better in sparse traffic condition" by 'up to ,16.,10 %. Finally, SRR ha" Ie"" control overhead than the "tate of the art protocol".
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paper_title: GeoDTN+Nav: Geographic DTN Routing with Navigator Prediction for Urban Vehicular Environments

paper_content:

Position-based routing has proven to be well suited for highly dynamic environment such as Vehicular Ad Hoc Networks (VANET) due to its simplicity. Greedy Perimeter Stateless Routing (GPSR) and Greedy Perimeter Coordinator Routing (GPCR) both use greedy algorithms to forward packets by selecting relays with the best progress towards the destination or use a recovery mode in case such solutions fail. These protocols could forward packets efficiently given that the underlying network is fully connected. However, the dynamic nature of vehicular network, such as vehicle density, traffic pattern, and radio obstacles could create unconnected networks partitions. To this end, we propose GeoDTN+Nav, a hybrid geographic routing solution enhancing the standard greedy and recovery modes exploiting the vehicular mobility and on-board vehicular navigation systems to efficiently deliver packets even in partitioned networks. GeoDTN+Nav outperforms standard geographic routing protocols such as GPSR and GPCR because it is able to estimate network partitions and then improves partitions reachability by using a store-carry-forward procedure when necessary. We propose a virtual navigation interface (VNI) to provide generalized route information to optimize such forwarding procedure. We finally evaluate the benefit of our approach first analytically and then with simulations. By using delay tolerant forwarding in sparse networks, GeoDTN+Nav greatly increases the packet delivery ratio of geographic routing protocols and provides comparable routing delay to benchmark DTN algorithms.
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paper_title: An evaluation of inter-vehicle ad hoc networks based on realistic vehicular traces

paper_content:

Vehicular ad hoc networks (VANETs) using WLAN tech-nology have recently received considerable attention. The evaluation of VANET routing protocols often involves simulators since management and operation of a large number of real vehicular nodes is expensive. We study the behavior of routing protocols in VANETs by using mobility information obtained from a microscopic vehicular traffic simulator that is based on the on the real road maps of Switzerland. The performance of AODV and GPSR is significantly in uenced by the choice of mobility model, and we observe a significantly reduced packet delivery ratio when employing the realistic traffic simulator to control mobility of nodes. To address the performance limitations of communication pro-tocols in VANETs, we investigate two improvements that increase the packet delivery ratio and reduce the delay until the first packet arrives. The traces used in this study are available for public download.
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paper_title: A survey of mobility models for ad hoc network research

paper_content:

In the performance evaluation of a protocol for an ad hoc network, the protocol should be tested under realistic conditions including, but not limited to, a sensible transmission range, limited buffer space for the storage of messages, representative data traffic models, and realistic movements of the mobile users (i.e., a mobility model). This paper is a survey of mobility models that are used in the simulations of ad hoc networks. We describe several mobility models that represent mobile nodes whose movements are independent of each other (i.e., entity mobility models) and several mobility models that represent mobile nodes whose movements are dependent on each other (i.e., group mobility models). The goal of this paper is to present a number of mobility models in order to offer researchers more informed choices when they are deciding upon a mobility model to use in their performance evaluations. Lastly, we present simulation results that illustrate the importance of choosing a mobility model in the simulation of an ad hoc network protocol. Specifically, we illustrate how the performance results of an ad hoc network protocol drastically change as a result of changing the mobility model simulated.
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paper_title: Mobility modeling in wireless networks: categorization, smooth movement, and border effects

paper_content:

The movement pattern of mobile users plays an important role in performance analysis of wireless computer and communication networks. In this paper, we first give an overview and classification of mobility models used for simulation-based studies. Then, we present an enhanced random mobility model, which makes the movement trace of mobile stations more realistic than common approaches for random mobility. Our movement concept is based on random processes for speed and direction control in which the new values are correlated to previous ones. Upon a speed change event, a new target speed is chosen, and an acceleration is set to achieve this target speed. The principles for direction changes are similar. Finally, we discuss strategies for the stations' border behavior (i.e., what happens when nodes move out of the simulation area) and show the effects of certain border behaviors and mobility models on the spatial user distribution.
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paper_title: The networking shape of vehicular mobility

paper_content:

Mobility is the distinguishing feature of vehicular networks, affecting the evolution of network connectivity over space and time in a unique way. Connectivity dynamics, in turn, determine the performance of networking protocols, when they are employed in vehicle-based, large-scale communication systems. Thus, a key question in vehicular networking is: which effects does nodes mobility generate on the topology of a network built over vehicles? Surprisingly, such a question has been quite overlooked by the networking research community. In this paper, we present an in-depth analysis of the topological properties of a vehicular network, unveiling the physical reasons behind the peculiar connectivity dynamics generated by a number of mobility models. Results make one think about the validity of studies conducted under unrealistic car mobility and stimulate interesting considerations on how network protocols could take advantage of vehicular mobility to improve their performance.
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paper_title: Ad-hoc on-demand distance vector routing

paper_content:

An ad-hoc network is the cooperative engagement of a collection of mobile nodes without the required intervention of any centralized access point or existing infrastructure. We present Ad-hoc On Demand Distance Vector Routing (AODV), a novel algorithm for the operation of such ad-hoc networks. Each mobile host operates as a specialized router, and routes are obtained as needed (i.e., on-demand) with little or no reliance on periodic advertisements. Our new routing algorithm is quite suitable for a dynamic self starting network, as required by users wishing to utilize ad-hoc networks. AODV provides loop-free routes even while repairing broken links. Because the protocol does not require global periodic routing advertisements, the demand on the overall bandwidth available to the mobile nodes is substantially less than in those protocols that do necessitate such advertisements. Nevertheless we can still maintain most of the advantages of basic distance vector routing mechanisms. We show that our algorithm scales to large populations of mobile nodes wishing to form ad-hoc networks. We also include an evaluation methodology and simulation results to verify the operation of our algorithm.
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paper_title: An integrated mobility and traffic model for vehicular wireless networks

paper_content:

Ad-hoc wireless communication among highly dynamic, mobile nodes in a urban network is a critical capability for a wide range of important applications including automated vehicles, real-time traffic monitoring and vehicular safety applications. When evaluating application performance in simulation, a realistic mobility model for vehicular ad-hoc networks (VANETs) is critical for accurate results. This paper analyzes ad-hoc wireless network performance in a vehicular network in which nodes move according to a simplified vehicular traffic model on roads defined by real map data. We show that when nodes move according to our street mobility model, STRAW, network performance is significantly different from that of the commonly used random waypoint model. We also demonstrate that protocol performance varies with the type of urban environment. Finally, we use these results to argue for the development of integrated vehicular and network traffic simulators to evaluate vehicular ad-hoc network applications, particularly when the information passed through the network affects node mobility.
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paper_title: Contention-Based Forwarding for Street Scenarios

paper_content:

In this paper, we propose to apply Contention-Based Forwarding (CBF) to Vehicular Ad Hoc Networks (VANETs). CBF is a greedy position-based forwarding algorithm that does not require proactive transmission of beacon messages. CBF performance is analyzed using realistic movement patterns of vehicles on a highway. We show by means of simulation that CBF as well as traditional position-based routing (PBR) achieve a delivery rate of almost 100 given that connectivity exists. However, CBF has a much lower forwarding overhead than PBR since PBR can achieve high delivery ratios only by implicitly using a trial-and-error next-hop selection strategy. With CBF, a better total throughput can be achieved. We further discuss several optimizations of CBF for its use in VANETs, in particular a new position-encoding scheme that naturally allows for communication paradigms such as `street geocast` and `street flooding`. The discussions show that CBF can be viewed as a concept for convergence of intelligent flooding, geocast, and multi-hop forwarding in the area of inter-vehicle communication.
---
paper_title: Fuzzy logic-assisted geographical routing over vehicular ad hoc networks

paper_content:

Vehiculiu: Ad Hoc Network" (VANET,,) i" a type of ad hoc network that allows vehicles to communicate with each other in the absence of ji'J:ed infrastruct'ure. Inter-vehicle geographic ro'uting has been proven to perform well in high speed vehic'ular environments. In connected and reliable cehicular scenarios, greedy based geographical toutuu; protocol" could forward data packet" efficiently and q'uiekly toward" the de"tination. However, e'J:tremely dynamic cehicular euoironmcnts and 'uneven distrib'ution of vehicles could create 'unreliable wireless charmels between vehicles and disconnected cehicular partitions. On the one hand, in connected uehiculur networks, an intelligent multi-metric ro'uting protocol must be e'J:ploited in consideration of the 'unreliable nature of wireless channcls between vehicles and vehic'ular mobility characteristics. On the other hand, a mechanism must be 'utilized to create a tnrtuu! bridge between vehicles in disconnected cehicular scenurios. To thi" end, we fir"tly propose a novel Stability and Reliability aware Routinq (SRR) protocol that forward" packet" with a high degree of reliability and "tability toward" the destination. That is, the SRR protocol incorporate" fuzzy loou: with geographical ro'uting when making packet forwarding decisions. Ro'uting metric», sucl: as direction and distance, are considered as inp'uts of the fuzzy decision making system so that the best preferable neighbo'ur annuul a "mart vehiele i" "elected. We then 'utilize a mechanism to cache data packets once the network is disconnected and then switch back to SRR in a connected vehic'ular scenario. Traffic density is considered as an inp'ut when estimating network dis-connectivity. After devcloping an analytical modcl of our protocol, we implemented it and compared it with standard protocols. In a realistic highway uchicular scetuirio, the results "how that the propo"ed protocol perform" better than Greedy Perimeter Coordinator RO'uting (GPCR) with increases of 'up to 21.12 %, 2.9.,14 % and //..98 %in packet dcliver;1J ratio in high lossy clumnel, sparse, and dense traffic conditions respectivcly. In terms of average packet dclay, SRR performs better with performance increases of 'up to 2,1..92 % in deus« traffic condition". But, GPCR perform" better in sparse traffic condition" by 'up to ,16.,10 %. Finally, SRR ha" Ie"" control overhead than the "tate of the art protocol".
---
paper_title: AN EFFICIENT, UNIFYING APPROACH TO SIMULATION USING VIRTUAL MACHINES

paper_content:

Due to their popularity and widespread utility; discrete event simulators have been the subject of much research. Systems researchers have built many types of simulation kernels and libraries, while the languages community has designed numerous languages specifically for simulation. In this dissertation, I propose a new approach for constructing simulators that leverages virtual machines and thus combines the advantages of both the traditional systems-based and language-based approaches to simulator construction. ::: I present JiST, a Java-based simulation engine that exemplifies virtual machine-based simulation. JiST executes discrete event simulations by embedding simulation time semantics directly into the Java execution model. The system provides all the standard benefits that the modern Java runtime affords. In addition, JiST is efficient, out-performing existing highly optimized simulation runtimes, and inherently flexible, capable of transparently performing cross-cutting program transformations and optimizations at the bytecode level. I illustrate the practicality of the JiST approach through the construction of SWANS, a scalable wireless ad hoc network simulator that can simulate million node wireless networks, which is more than an order of magnitude in scale over what existing simulators can achieve on equivalent hardware and at the same level of detail.
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paper_title: GeoCross : A geographic routing protocol in the presence of loops in urban scenarios

paper_content:

In this paper,we propose GeoCross, a simple, yet novel, event-driven geographic routing protocol that removes cross-links dynamically to avoid routing loops in urban Vehicular Ad Hoc Networks (VANETs). GeoCross exploits the natural planar feature of urban maps without resorting to cumbersome planarization. Its feature of dynamic loop detection makes GeoCross suitable for highly mobile VANET. We have shown that in pathologic cases, GeoCross's packet delivery ratio (PDR) is consistently higher than Greedy Perimeter Stateless Routing's (GPSR's) and Greedy Perimeter Coordinator Routing's (GPCR's). We have also shown that caching (GeoCross+Cache) provides the same high PDR but uses fewer hops.
---
paper_title: Multi-metric Routing Decisions in VANET

paper_content:

Due to the rapidly changing topology of Vehicular Ad Hoc network (VANET), it requires the routing protocol can be able to find out comparatively more stable routes. But the routing protocols in existence are not taking the distinguishing features of vehicles and roadway into consideration, and this brought about challenges to these routing protocols’ applicability in VANET. In this paper, we take the characteristics of VANET into account, and using the method of fuzzy logic and fuzzy control to make routing decision under multiple selection criteria, then we developed a new routing protocol based on the classical AODV which name is Fcar(Fuzzy control based AODV routing). Simulations have been carried out comparing AODV and Fcar, the results indicate that Fcar is superior to AODV in several aspects, so Fcar shows its adaptability in VANET.
---
paper_title: VANET Routing on City Roads Using Real-Time Vehicular Traffic Information

paper_content:

This paper presents a class of routing protocols called road-based using vehicular traffic (RBVT) routing, which outperforms existing routing protocols in city-based vehicular ad hoc networks (VANETs). RBVT protocols leverage real-time vehicular traffic information to create road-based paths consisting of successions of road intersections that have, with high probability, network connectivity among them. Geographical forwarding is used to transfer packets between intersections on the path, reducing the path's sensitivity to individual node movements. For dense networks with high contention, we optimize the forwarding using a distributed receiver-based election of next hops based on a multicriterion prioritization function that takes nonuniform radio propagation into account. We designed and implemented a reactive protocol RBVT-R and a proactive protocol RBVT-P and compared them with protocols representative of mobile ad hoc networks and VANETs. Simulation results in urban settings show that RBVT-R performs best in terms of average delivery rate, with up to a 40% increase compared with some existing protocols. In terms of average delay, RBVT-P performs best, with as much as an 85% decrease compared with the other protocols.
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Title: Routing Protocols in Vehicular Ad hoc Networks: Survey and Research Challenges

Section 1: Introduction
Description 1: Write about the need for improvements in transportation systems due to the growth in the number of vehicles, and introduce the concept of VANET and its significance.

Section 2: Previous Surveys of VANET Routing
Description 2: Provide an overview of previous surveys conducted on VANET routing, highlighting the limitations and gaps in those studies.

Section 3: VANET Routing Protocols
Description 3: Discuss the potential and requirements for VANET routing protocols and the challenges specific to vehicular environments.

Section 4: Geographical and Topology-based Routing Protocols
Description 4: Describe the purpose of routing protocols in VANET and provide a general classification into geographical and topology-based routing protocols.

Section 5: Topology-based Routing Protocols
Description 5: Explain the general concept of topology-based routing, focusing on reactive and proactive routing protocols.

Section 6: Proactive Routing Protocols
Description 6: Detail the working mechanism of proactive routing protocols and discuss representative examples like Destination Sequenced Distance-Vector (DSDV).

Section 7: Reactive Routing Protocols
Description 7: Describe the operating principles of reactive routing protocols with specific examples like AODV and DSR.

Section 8: Geographical Routing Protocols
Description 8: Elaborate on the principles of geographical routing protocols, including neighbor discovery, and real-time identification of destination positions.

Section 9: Packet Buffering based Geographical Routing Protocols
Description 9: Discuss delay-tolerant routing protocols that use packet buffering mechanisms like Geographical Opportunistic Routing and Vehicle-Assisted Data Delivery.

Section 10: Connectionless Geographical Routing Protocols
Description 10: Describe connectionless routing protocols that do not maintain neighbor information, such as Contention Based Forwarding and GDBF.

Section 11: Connection-Oriented Geographical Routing Protocols
Description 11: Explain connection-oriented routing protocols that maintain local information and the distinction into trajectories-based and source and map-based routing, with examples.

Section 12: Hybrid (Packet and Non-Packet Buffering) Geographical Routing Protocols
Description 12: Cover hybrid routing protocols that combine packet buffering and non-buffering techniques, exemplified by protocols like GeoDTN+Nav and SRR.

Section 13: Influence of Mobility Model
Description 13: Analyze the impact of different mobility models on the performance of VANET routing protocols.

Section 14: Performance Evaluation
Description 14: Present the results of performance evaluations of geographical and topology-based routing protocols under various conditions in urban environments.

Section 15: Research Directions and Open Issues
Description 15: Discuss the open research issues in VANET routing and propose potential future research directions.

Section 16: Conclusions
Description 16: Summarize the main findings of the survey and suggest the importance of continuing research in developing efficient and optimal VANET routing solutions.