In the past, people were focused on how to build efficient highways and roads. Over time, focus shifted to mechanical and automotive engineering, in the pursuit of building faster cars to surmount greater distances. Later on, electronics technology impacted the construction of cars, embedding them with sensors, advanced electronics, and communication devices, making cars more intelligent, efficient, and safe to drive on.
The applications and advantages of using Vehicular Networks (VNs) for enhancing road safety and driving efficiency are diverse, which explains why research in this area has recently emerged. In this Thesis, we focus on Vehicular Adhoc Networks (VANETs), which are a particular subclass of Vehicular Networks, that involves a set of equipped vehicles communicating with each other via wireless antennas, without requiring the use of any infrastructure.
In order to enhance the warning message dissemination process, usually necessary in VANET safety applications, we propose an adaptive broadcast dissemination scheme that automatically chooses the optimal broadcast depending on the complexity of the map and the instantaneous vehicle density in the area. Its main goal is to maximize the message delivery effectiveness, while generating a reduced number of messages, and thus, avoiding or mitigating broadcast storms.
Current research on VANETs usually focuses on analyzing scenarios representing common situations with average densities. However, situations with very low or very high vehicle densities are often ignored, whereas they are very common in real vehicular environments. The aim of broadcast dissemination schemes is to maximize message delivery effectiveness, something difficult to achieve in adverse density scenarios. To address this issue, in this Thesis, we propose the Junction Store and Forward (JSF) and the Neighbor Store and Forward (NSF) dissemina- tion schemes, specially designed to be used under low density conditions, as well as the Nearest Junction Located (NJL) scheme, specially developed for high density conditions.
Finally, we present a classification which includes the most relevant broadcast dissemination schemes specially designed for VANETs, highlighting their features, and studying their performance under the same simulation conditions, thus offering researchers a fair comparison. We consider that this evaluation can shed some light into the advantages and drawbacks of each solution.
Table of Contents
1 Motivation, Objectives, and Organization of the Thesis
1.1 Motivation
1.2 Objectives of the Thesis
1.3 Organization of the Thesis
2 Background on Vehicular Networks and Warning Message Dissemination
2.1 Introduction
2.2 Vehicular Networks
2.2.1 Vehicular ad hoc networks (VANETs)
2.2.2 Characteristics and Applications of VANETs
2.3 Warning dissemination process
2.3.1 Existing Broadcast Message Dissemination Schemes
2.3.2 Classification of the Dissemination Schemes
2.4 Simulation Environment, Methodology, and Metrics
2.5 Summary
3 Real-Time Density Estimation
3.1 Introduction
3.2 Related Work
3.3 Real-Time Vehicular Density Estimation
3.3.1 Phase 1: Features of the Cities Studied
3.3.2 Phase 2: Counting the Number of Beacons Received
3.3.3 Phase 3: Density Estimation Function
3.3.3.1 Time Period Analysis
3.3.4 The Concept of Street
3.4 Validation of Our Proposal
3.5 Comparing Our Proposal with a Beacons-Based Density Estimation Approach
3.6 Summary
4 RTAD: Real-Time Adaptive Dissemination System
4.1 Introduction
4.2 Related Work
4.3 Simulation Environment
4.4 RTAD: Analysis of the Optimal Broadcast Scheme
4.4.1 Broadcast Schemes Used
4.4.2 Metric 1: Percentage of Informed Vehicles
4.4.3 Metric 2: Messages Received per Vehicle
4.4.4 Optimal Broadcast Selection Algorithm
4.5 RTAD: Real-time Adaptive Dissemination System for VANETs
4.6 RTAD Performance Evaluation
4.6.1 RTAD vs. Static Dissemination Schemes
4.6.2 RTAD vs. Adaptive Dissemination Schemes
4.7 Summary
5 Topology-based Broadcast Schemes for Urban Scenarios Targeting Adverse Density Conditions
5.1 Introduction
5.2 Related Work
5.2.1 Low Density Conditions
5.2.2 High Density Conditions
5.3 Dissemination Schemes Proposed
5.3.1 Junction Store and Forward (JSF)
5.3.2 Neighbor Store and Forward (NSF)
5.3.3 Nearest Junction Located (NJL)
5.4 Simulation Environment
5.5 Simulation Results
5.5.1 Performance Evaluation in Low Vehicle Density Scenarios
5.5.2 Performance Evaluation in High Vehicle Density Scenarios
5.6 Summary
6 Lessons Learned and Comparison of Existing Broadcast Dissemination Schemes
6.1 Introduction
6.2 Overall Classification of Warning Dissemination Messages Including our Proposed Schemes
6.3 Parameters Used to Assess the Performance of Existing Broadcast Dissemination Schemes
6.4 Simulation Environment
6.5 Simulation Results
6.6 Summary
7 Conclusions, Publications, and Future Work
7.1 Publications Related to the Thesis
7.1.1 Journals
7.1.2 Indexed Conferences
7.1.3 International Conferences
7.1.4 National Conferences
7.2 Future work
Objectives & Topics
The primary research objective is to develop an adaptive broadcast dissemination system for Vehicular Ad-hoc Networks (VANETs) that maximizes message delivery effectiveness across varied traffic density and map topology scenarios while mitigating broadcast storm problems.
- Real-time estimation of vehicular density using map topology and beacon data.
- Development of the Real-Time Adaptive Dissemination System (RTAD).
- Design of topology-based broadcast schemes for adverse density conditions (JSF, NSF, NJL).
- Comparative performance evaluation of broadcast dissemination schemes under uniform simulation conditions.
Extract from the book
2.3 Warning dissemination process
Regarding safety in Vehicular Networks, efficient warning message dissemination schemes are required since the main goal is to reduce the latency of such critical information while ensuring the correct reception of the alert information by nearby vehicles. When a vehicle detects an abnormal situation on the road (e.g., accident, slippery road, etc.), it immediately starts notifying the anomaly to nearby vehicles to rapidly spread the information in a short period of time. Hence, broadcasting warning messages is of utmost importance to alert nearby vehicles.
However, this dissemination is strongly affected by: (i) the signal attenuation due to the distance between sender and receiver (especially in low vehicular density areas), (ii) the effect of obstacles in signal transmission (very usual in urban areas, e.g., due to buildings), and (iii) the instantaneous vehicle density.
Regarding (i) and (ii), the topology of the roadmap is an important factor that affects the average distance between the sender and the receiver, as well as the different obstacles in the scenario. As for (iii), the warning message propagation scheme should be aware of vehicle density. In fact, lower densities can provoke message losses due to reduced communication capabilities, whereas higher densities can provoke a reduced message delivery effectiveness due to serious redundancy, contention, and massive packet collisions caused by simultaneous forwarding, usually known as broadcast storm [TNCS02].
Summary of Chapters
1 Motivation, Objectives, and Organization of the Thesis: Introduces the research context in vehicular communications, defines the thesis objectives, and outlines the structure of the work.
2 Background on Vehicular Networks and Warning Message Dissemination: Provides an overview of VANETs, traffic safety applications, and existing broadcast dissemination schemes, including an assessment of the simulation environment.
3 Real-Time Density Estimation: Presents an infrastructureless mechanism to estimate vehicle density using received beacon data and topological roadmap characteristics.
4 RTAD: Real-Time Adaptive Dissemination System: Proposes the RTAD system, which dynamically adapts the broadcast scheme based on vehicle density and roadmap topology to optimize delivery effectiveness.
5 Topology-based Broadcast Schemes for Urban Scenarios Targeting Adverse Density Conditions: Introduces JSF, NSF, and NJL schemes specifically designed to handle extremely low or high vehicle density conditions in urban environments.
6 Lessons Learned and Comparison of Existing Broadcast Dissemination Schemes: Evaluates 19 different dissemination schemes under the same simulation conditions to provide a fair assessment of their performance in various scenarios.
7 Conclusions, Publications, and Future Work: Summarizes the contributions of the thesis, lists publications produced during the research, and identifies potential directions for future study.
Keywords
VANETs, Vehicular Ad-hoc Networks, Warning Message Dissemination, Broadcast Storm, Traffic Safety, Real-Time Density Estimation, Adaptive Systems, Roadmap Topology, RTAD, Infrastructureless Mechanism, Urban Environments, Simulation Environment, JSF, NSF, NJL.
Frequently Asked Questions
What is the core focus of this thesis?
The thesis focuses on improving the efficiency of warning message dissemination in Vehicular Ad-hoc Networks (VANETs), particularly in urban environments with variable and often adverse traffic density conditions.
What are the central thematic areas?
The research centers on vehicular network communication, real-time vehicle density estimation, adaptive broadcast selection, and performance optimization for road safety applications.
What is the primary objective of the proposed RTAD system?
The primary goal of RTAD is to allow each vehicle to automatically adopt the optimal dissemination scheme for its current environment, thereby maximizing message delivery while minimizing channel contention and avoiding broadcast storms.
Which methodology is utilized for the performance assessment?
The research employs a simulation-based approach, utilizing the ns-2 simulator modified for IEEE 802.11p, to compare various dissemination schemes under controlled and realistic urban road map scenarios.
What does the main part of the thesis cover?
The main body addresses density estimation techniques, the RTAD adaptive system, specialized dissemination schemes for adverse density conditions (JSF, NSF, NJL), and a comparative analysis of existing literature.
Which keywords best characterize this work?
Key terms include VANETs, warning message dissemination, real-time density estimation, RTAD, broadcast storm, and topology-based dissemination.
How does the proposed density estimation differ from previous approaches?
Unlike previous methods that relied solely on beacon counts, this research incorporates topological characteristics of the roadmap, such as street/junction ratios, to achieve significantly higher estimation accuracy.
What role does the 'SJ Ratio' play in the study?
The SJ Ratio (streets per junction) is a proposed metric used to categorize roadmap complexity, which is then used as a parameter to accurately estimate vehicular density in different cities.
What makes the NJL scheme particularly useful for high-density environments?
The Nearest Junction Located (NJL) scheme is designed to be highly restrictive in high-density areas by only allowing vehicles nearest to junctions to forward messages, which effectively prevents redundant packet collisions and broadcast storms.
- Quote paper
- Julio A. Sangüesa Escorihuela (Author), 2014, Adaptive Mechanisms to Improve Message Dissemination in Vehicular Networks, Munich, GRIN Verlag, https://www.grin.com/document/284223
