Kevin C. Lee

Enhanced Perimeter Routing for Geographic Forwarding Protocols in Urban Vehicular Scenarios

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 GPSRs 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 GPSRs 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.

GeoDTN+Nav: Geographic DTN Routing with Navigator Prediction for Urban Vehicular Environments

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.

First Experience with CarTorrent in a Real Vehicular Ad Hoc Network Testbed

Content sharing using cooperative peer-to-peer model has become increasingly more popular in a vehicular ad hoc network (VANET). The small transmission window from a vehicle to an access point (AP), high mobility of vehicles, and intermittent and short-lived connectivity to an AP provide incentives for vehicles to cooperate with one another to obtain information from the Internet. These characteristics of VANETs naturally stipulate the use of cooperative peer-to-peer paradigm and motivate related content sharing application such as CarTorrent. Building upon previous research on SPAWN [6, 1], we have implemented CarTorrent and deployed it on a real VANET. We have run extensive field tests to affirm the feasibility of the peer-to-peer file sharing application tailored to VANET. To the best of our knowledge, the deployment of such a content sharing application on a real vehicular ad hoc testbed is the first of its kind.

TO-GO: TOpology-assist geo-opportunistic routing in urban vehicular grids

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.

Geo-opportunistic routing for vehicular networks [Topics in Automotive Networking]

Road topology information has recently been used to assist geographic routing in urban vehicular environments to improve overall routing performance. However, the unreliable nature of wireless channels due to motion and obstructions still makes road topology assisted geographic routing challenging. In this article we begin by reviewing conventional road topology assisted geographic routing protocols, and investigate the robust routing protocols that address and help overcome the unreliable wireless channels. We then present topology-assisted geo-opportunistic routing that incorporates topology assisted geographic routing with opportunistic forwarding. That is, the routing protocol exploits the simultaneous packet receptions induced by the broadcast nature of the wireless medium and performs opportunistic forwarding via a subset of neighbors that have received the packet correctly. Our simulation results confirm TO-GOs superior robustness to channel errors and collisions compared to conventional topology-assisted geographic routing protocols.

GeoCross: A geographic routing protocol in the presence of loops in urban scenarios

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, GeoCrosss packet delivery ratio (PDR) is consistently higher than Greedy Perimeter Stateless Routings (GPSRs) and Greedy Perimeter Coordinator Routings (GPCRs). We have also shown that caching (GeoCross+Cache) provides the same high PDR but uses fewer hops.

Intelligent beaconless geographical forwarding for urban vehicular environments

A Vehicular Ad hoc Network is a type of wireless ad hoc network that facilitates ubiquitous connectivity between vehicles in the absence of fixed infrastructure. Source based geographical routing has been proven to perform well in unstable vehicular networks. However, these routing protocols leverage beacon messages to update the positional information of all direct neighbour nodes. As a result, high channel congestion or problems with outdated neighbour lists may occur. To this end, we propose a street-aware, Intelligent Beaconless (IB) geographical forwarding protocol based on modified 802.11 Request To Send (RTS)/ Clear To Send frames, for urban vehicular networks. That is, at the intersection, each candidate junction node leverage digital road maps as well as distance to destination, power signal strength of the RTS frame and direction routing metrics to determine if it should elect itself as a next relay node. For packet forwarding between Intersections, on the other hand, the candidate node considers the relative direction to the packet carrier node and power signal strength of the RTS frame as routing metrics to elect itself based on intelligently combined metrics. After designing the IB protocol, we implemented it and compared it with standard protocols. The simulation results show that the proposed protocol can improve average delay and successful packet delivery ratio in realistic wireless channel conditions and urban vehicular scenarios.

Opportunistic vehicular routing

In a wireless ad hoc network, an opportunistic routing strategy is a strategy where there is no predefined rule for choosing the next node to destination (as it is the case in conventional schemes such as OLSR, DSR or even Geo-Routing). Rather, an intermediate node en route acts in an impromptu fashion and takes a decision that is based solely on current circumstances. A popular example of opportunistic routing is the “delay tolerant” forwarding to “data mules” when a direct path to destination does not exist. Conventional routing in this case would just “drop” the packet. With opportunistic routing, a node acts upon the available information: it seeks the neighbor best qualified to “carry” the packet to destination. If none is available, it will await the right opportunity. This procedure is also known as “data muling” or Delay Tolerant Network (DTN) routing. The Vehicular Ad Hoc Networks (VANET), because of its intrinsic intermittent connectivity (during off peak hours and at night) is an ideal “playground” for opportunistic routing/multicast. In this paper we will examine two examples of VANET opportunistic routing: Delay Tolerant geo-inspired routing and real time video stream multicast of emergency/accident multimedia reports to vehicles in disconnected platoons using network coding.

A Novel Delay- and Reliability- Aware Inter-Vehicle Routing Protocol

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.

Taking the LOUVRE approach

This article presented landmark overlays for urban vehicular routing environments (LOUVRE), a density-based landmark overlay routing protocol for urban vehicular environments. We described the concept and the protocol as well as a novel distributed traffic density estimation scheme. We implemented the protocol in Qualnet and evaluated the feasibility of LOUVRE by comparing it with the benchmarks GPSR and GPCR protocols using realistic mobility traces. Results showed that due to improved visibility of the overlay network and the routing guarantees of the underlay network, LOUVRE provides a better packet delivery ratio and hop count than the benchmark protocols. Future work includes verifying the necessity of recovery mode and comparison with GyTAR and GSR.