Design and analysis of a beacon-less routing protocol for large volume content dissemination in vehicular ad hoc networks

Largevolumecontentdisseminationispursuedbythegrowingnumberofhighquality applications for Vehicular Ad hoc NETworks(VANETs), e.g., the live road surveillance service and the video-based overtaking assistant service. For the highly dynamical vehicular network topology, beacon-less routing protocols have been proven to be efficient in achieving a balance between the system performance and the control overhead. However, to the authors’ best knowledge, the routing design for large volume content has not been well considered in the previous work, which will introduce new challenges, e.g., the enhanced connectivity requirement for a radio link. In this paper, a link Lifetime-aware Beacon-less Routing Protocol (LBRP) is designed for large volume content delivery in VANETs. Each vehicle makes the forwarding decision based on the message header information and its current state, including the speed and position information. A semi-Markov process analytical model is proposed to evaluate the expected delay in constructing one routing path for LBRP. Simulations show that the proposed LBRP scheme outperforms the traditional dissemination protocols in providing a low end-to-end delay. The analytical model is shown to exhibit a good match on the delay estimation with Monte Carlo simulations, as well

Enhanced stability of cluster-based location service mechanism for urban vehicular ad hoc networks

Vehicular Ad Hoc Networks (VANETs) are gaining tremendous research interest in developing an Intelligent Transportation System (ITS) for smart cities. The position of vehicles plays a significant role in ITS applications and services such as public emergency, vehicles tracking, resource discovery, traffic monitoring and position-based routing. The location service is used to keep up-to-date records of current positions of vehicles. A review of previous literatures, found various locationbased service mechanisms have been proposed to manage the position of vehicles. The cluster-based location service mechanisms have achieved growing attention due to their advantages such as scalability, reliability and reduced communication overhead. However, the performance of the cluster-based location service mechanism depends on the stability of the cluster, and the stability of the cluster depends on the stability of the Cluster Head (CH), Cluster Member (CM) and cluster maintenance. In the existing cluster-based location service schemes, the issue of CH instability arises due to the non-optimal cluster formation range and unreliable communication link with Road Side Unit (RSU). The non-optimal cluster formation range causes CH instability due to lack of uniqueness of Centroid Vehicle (CV), uncertainty of participating vehicles in the CH election process and unreliability of the Cluster Head Election Value (CHEV). Also, the unreliable link with RSU does not guarantee that CH is stable with respect to its CMs and RSU simultaneously. The issue of CM instability in the existing cluster-based location service schemes occurs due to using instantaneous speed of the CH and fixed CM affiliation threshold values. The instantaneous speed causes the CM to switch the clusters frequently and fixed CM affiliation threshold values increase isolated vehicles. The frequent switching of isolated vehicles augment the CM instability. Moreover, the inefficient cluster maintenance due to non-optimal cluster merging and cluster splitting also contributes to cluster instability. The merging conditions such as fixed merging threshold time and uncertain movement of overlapping CHs within merging threshold time cause the cluster instability. Furthermore, the unnecessary clustering during cluster splitting around the intersection due to CH election parameters also increases cluster instability. Therefore, to address the aforementioned cluster instability issues, Enhanced Stability of Cluster-based Location Service (ESCLS) mechanism was proposed for urban VANETs. The proposed ESCLS mechanism consists of three complementary schemes which are Reliable Cluster Head Election (RCHE), Dynamic Cumulative Cluster Member Affiliation (DCCMA) and Optimized Cluster Maintenance (OCM). Firstly, the aim of the RCHE scheme was to enhance the stability of the CH through optimizing the cluster formation range and by considering communication link reliability with the RSU. Secondly, the DCCMA scheme focussed on improving the stability of the CMs by considering the Cumulative Moving Average Speed (CMAS) of the CH and dynamic CM affiliation threshold values, and finally, the OCM scheme enhanced the cluster stability by improving cluster merging conditions and reducing unnecessary clustering in cluster splitting. The results of the simulation verified the improved performance of the ESCLS in terms of increasing the location query success rate by 34%, and decreasing the query response delay and localization error by 24% and 35% respectively as compared to the existing cluster-based location service schemes such as HCBLS, CBLS and MoGLS. In conclusion, it is proven that ESCLS is a suitable location service mechanism for a wide range of position-based applications of VANETs that require timely and accurate vehicle locations

Node Cluster Stability in Vehicular Ad hoc Networks

In recent years, efforts have been made to deploy communication capabilities in vehicles and the transport infrastructure, leading to a potential of vehicular ad hoc networks (VANETs). In the envisioned VANET, communications among vehicles will enhance the intelligent transportation systems (ITS) and support not only public-safety applications, but also a wide range of infotainment applications. Urban roads and highways are highly susceptible to a large number of vehicles and traffic jams. Therefore, the networking protocols for VANETs should be scalable to support such large sized networks. Node clustering (i.e., organizing the network into smaller groups of nodes) is a potential approach to improve the scalability of networking protocols for VANETs. However, high relative vehicle mobility and frequent network topology changes inflict new challenges on maintaining stable clusters. The communication links between network nodes play an essential role in determining the VANET topology. This thesis presents a stochastic microscopic vehicle mobility model to capture the time variations of the distance between two consecutive vehicles on a highway. The proposed mobility model is used to characterize the length and the duration of a communication link connecting two nodes in the network for different vehicular traffic flow conditions. Vehicle trajectory data from real and simulated highways are used for performance evaluation. In a highly dynamic VANET, vehicles join and leave clusters along their travel route, resulting in changes in cluster structure. This thesis investigates the impact of vehicle mobility on node cluster stability. A lumped stochastic model is proposed to describe the temporal variations of a system of intervehicle distances, where each intervehicle distance is represented by the proposed microscopic mobility model. Two metrics are used to measure cluster stability: the time period of invariant cluster-overlap state between two neighboring clusters as a measure of external cluster stability, and the time period of invariant cluster-membership as a measure of internal cluster stability. Using the proposed lumped stochastic model, the two cluster stability metrics are probabilistically characterized for different vehicular traffic flow conditions. Additionally, the limiting behavior of a system of two neighboring clusters is modeled, and the steady-state number of common/unclustered nodes between two clusters is approximately derived. To the best of our knowledge, this is the first mathematical characterization of node cluster stability which takes account of the effect of microscopic vehicle mobility. In addition to the impact of vehicle mobility on node cluster stability, the notion of cluster stability is also related to the network protocol requirements. This thesis explores the effect of cluster characteristics (cluster size and cluster-overlap) on minimizing the generic routing overhead. Furthermore, using the derived cluster stability metrics, the impact of cluster instability on intra- and inter- cluster routing overhead is investigated. The proposed vehicle mobility model is a useful tool for mathematically analyzing the impact of mobility and node density on the performance of network protocols in VANETs. The node cluster stability analysis and the proposed the external and internal cluster stability metrics provide a useful tool for the development of efficient clustering algorithms for VANETs