Test Environment Design for Wireless Vehicle Communications

Transcription

1 Technical report, IDE0710, January 2007 Test Environment Design for Wireless Vehicle Communications Master s Thesis in Computer Systems Engineering Peter Lerchbaumer and Alejandro Ochoa School of Information Science, Computer and Electrical Engineering Halmstad University

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3 Abstract The research in wireless communications and in-vehicle computing systems has opened up new fields of applications for transportation systems. Vehicular ad hoc networks (VANETs) emerge as a contribution to the solution of providing safer and more efficient roads and to increase passenger safety. This thesis treats different issues that influence the performance of wireless vehicle communication systems and it proposes a general design procedure for the construction of a test environment for VANETs. A comprehensive survey of the different parameters that affect the system performance in the field of wireless vehicle communications is provided. These parameters are then analysed and quantified to serve as guidelines when identifying and designing the different components of the test environment. One such component is a simulator that enables VANET performance evaluation and allows identification of bottlenecks in the network functionality. In addition, suggestions for a hardware platform and an operating system for the development of a suitable on-board test-bed for performance measurements are presented. The design procedure of such a test environment is intended to be used by researchers and engineers working in the field of wireless communications and ad hoc networking with special regard to the automotive sector. Keywords: vehicular ad hoc network, test environment, test-bed, simulator, wireless communications.

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5 Acknowledgements The development of this Master s thesis has been a joint undertaking in the Deparment of Transport, Information and Communication at Volvo Technology Corporation in Göteborg, Sweden. Some people have been instrumental in allowing this project to be completed. First and especially we would like to thank our supervisor at Halmstad University and Volvo Technology, Elisabeth Uhlemann, for her encouragement and support throughout the process of this work. Her uncomplicated but professional and efficient way of treating projects was a great help for accomplishing the aims of our thesis. This fact easily let us overlook the declined request for a writing aid in form of another Master s thesis student. We would also like to thank Hossein Zakizadeh at Volvo Technology for his help and support of necessary information regarding the CVIS project for our work especially in the start-up phase of our thesis. We acknowledge the people from the VAS project at Halmstad Universtiy for their comments and suggestions on our work. To our colleagues at Volvo Technology, for making the office a nice place to work. Finally, to our parents, who are enabling us the chance to experience these opportunities at all. Thank you. Peter Lerchbaumer Alejandro Ochoa

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7 List of Abbreviations ADASE ADS AHSRA AODV ASV BER CALM CAN CVIS DSRC FND FTP GPS GPRS GUI ITS IVI LAN LBS MAC MFC NHTSA NTRC OS QoS PATH PER Advanced Driver Assistance Systems in Europe Applied Data Systems Assist Highway System Research Association Ad hoc On-Demand Distance Vector Advanced Safety Vehicles Bit Error Rate Communication Air-interface Long and Medium Controller Area Network Cooperative Vehicle-Infrastructure Systems Dedicated Short Range Communications FleetNeet Demonstrator File Transfer Protocol Global Positioning System General Packet Radio Service Graphical User Interface Intelligent Transportation Systems Intelligent Vehicle Initiative Local Area Networks Location based services Media Access Control Microsoft Foundation Classes National Highway Traffic Safety Administration National Transportation Research Council Operating System Quality of Service Partners for Advanced Transit and Highways Packet Error Rate i

8 RPF SLL SNRA SPL TEV UMTS VANET VAS VoIP V2I V2V VVC VVN WiMAX Rapid Prototyping Platform Simulator Link Layer Swedish National Road Administration Simulator Profile Layer Test Environment for VANETs Universal Mobile Telecommunications System Vehicular Ad Hoc Network Vehicle Alert Systems Voice over Internet Protocol Vehicle to Infrastructure Vehicle to Vehicle Virtual Vehicle Communication Vehicle Virtual Network Worldwide Interoperability for Microwave Access ii

9 Contents 1 Introduction Challenges for Vehicle Communication Systems Problem Statement Chapter Overview Background Intelligent Transportation Systems Swedish Vision Zero Related Work Simulation Platforms FleetNet GrooveSim NHTSA Comparison and Analysis Qualified Parameters for Vehicular ad hoc Networks Parameter Specification Metrics Evaluation View OSI layer View Dependency View iii

10 5 Test Enviroment Design for VANETs Test Environment Architecture Use Cases for the Test Environment Simulator Architecture Simulator Description Operation Modes Architecture Simulator Link Layer Virtual Vehicle Communication Layer Simulator Profile Layer Graphical User Interface Test-Bed for VANETs Test-Bed Hardware Platform Criteria Required Features for a Test-Bed Hardware Evaluation Embedded Systems Comparison The Rapid Prototyping Platform RPF Architecture Operating System and Platform Hardware Software Toolbox Custom Application Dynafleet CVIS Embedded Systems Evaluation Communication Storage iv

11 Miscellaneous Recommendation for a Test-Bed Test-Bed Operating System Operating System Importance Operating System Selection Criteria Investigated Operating Systems Windows CE Embedded Linux Operating System Examination Recommendation for a Test-Bed Results Conclusions & Future Work 63 References 64 v

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13 Chapter 1 Introduction Over the past few decades, vehicles have constituted a cornerstone in the industrial development and human mobility. Distances have been reduced and technological improvements did not only increase transportation efficiency, but also resulted in better comfort and convenience for the drivers. However, since the 1980 s, problems such as traffic congestion and roadway accidents have rapidly increased, resulting in a noteworthy number of fatalities, billions of hours of people being stuck in traffic jams and in tons of wasted fuel. The sectors of vehicle and communication technologies have matured and several research initiatives have been launched to overcome such problems by taking advantage of new technologies, equipment and infrastructure. The aim is to achieve reliable and intelligent systems capable to contributing to safer, more efficient roads by e.g. delivering warnings and roadway information on time and thus increasing passenger safety. The topic has gained significant interest and a new scientific field emerges from the varying endeavors under the denotation of Intelligent Transportation Systems (ITS). When vehicles are on the road, one major technical challenge is the timely transfer of data. The high mobility conditions that vehicles are subject to, limit the ability to establish a global, low delay network along the road. Various cellphone operators already provide a global network along the road. However, such networks suffer from long delays or high bit error rates, which qualify them for some, but not all the needs of the vast ITS applications spectrum [1]. For this reason, communication is performed by means of either the use of roadside units or the formation of vehicular networks. Roadside units establish an infrastructure network along the roads. They are intended to communicate important information regarding traffic, road conditions, travel and safety to vehicles. This type of networking is referred to as Vehicle-to- Infrastructure (V2I) Communication. The second type, vehicular networks, states the creation of ad hoc networks capable of organizing themselves to extend the horizon of the drivers and the on-board devices in order to avoid collisions between vehicles and to ensure accurate driving support. This communication is referred to as Vehicle-to-Vehicle (V2V) Communication. 1

14 1.1 Challenges for Vehicle Communication Systems The development of vehicle communication systems involves problems with characteristics that are dramatically different from generic ad hoc networks. The lack of a centralized entity to manage the network and the mobility of the nodes are generally the main problem in the design of such networks. Vehicular Ad Hoc Networks (VANETs) are characterized by rapid topology changes, a small effective network diameter and unfavorable radio channel characteristics [2]. Vehicle communication protocols have to tackle these challenges. A suitable protocol has to be able to handle the unfavorable radio channel characteristics, channel load saturation (congestion), and fluctuations in the received signal in order to provide a solid basis for ITS applications. Further, new routing algorithms have to be developed to meet the requirements for VANETs. At present, designers of ITS applications have not yet agreed on a standardized set of protocols used for the implementation of such systems. Desired improvements aim for example at a better utilization of the channel bandwidth or the use of predefined routes to forward information [3]. 1.2 Problem Statement Currently, most existing test platforms developed in the ITS initiative address only a subset of the challenges involved in wireless vehicle communications. Their main focus is on modeling and simulating specific elements involved in the communication, such as medium access, vehicle mobility, traffic flow, routing, etc. The outlined challenges for VANETs raise the demand for a more comprehensive testing environment. A sophisticated platform will extensively support engineers in their work and will bring valuable benefits to the development process. This is the point to which our thesis makes a contribution. The goal of this thesis work is to determine how to construct an efficient test environment for wireless vehicle communications. To do this, the following problems are addressed: First, it is essential to be thoroughly familiar with the properties characterising wireless vehicle communications. Thus, the initial task is to analyse and quantify the parameters that constitutes the environment of VANETs. The second challenge is to determine the requirements for a platform intended to be used for testing VANET performance. The platform should allow testing, evaluation and verification of as many relevant parameters as possible. Finally, a general architectural proposal for a comprehensive test environment should be given. 1.3 Chapter Overview The remainder of the thesis is structured as follows. Chapter 2 contains a brief overview of the state of art in terms of the various ITS endeavors worldwide. Chapter 3 discusses related simulation platforms, and analyzes the main contributions made when designing the simulation 2

15 platform. In Chapter 4, an approach of how to quantify a VANET environment is described. The results of this chapter serve as the basic guideline for the further investigations regarding the construction of an appropriate test environment. Chapter 5 discusses our proposal for how to develop a test environment for wireless vehicle communications. Chapter 6 concerns the first component introduced in Chapter 5: The simulator. The idea behind this component is described and architectural suggestions are made. Chapter 7 is dedicated to the test-bed for vehicle communications. Chapter 8 discusses a process for selecting appropriate hardware and operating system by means of a developed set of criteria. This process is then applied on several hardware platforms and two operating systems. Chapter 9 presents the results achieved in this thesis. Finally, Chapter 10 contains our conclusion and an outlook for future work is given. 3

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17 Chapter 2 Background 2.1 Intelligent Transportation Systems Research and development in the ITS sector is driven by world wide endeavors. Most of the industrialized countries have established official programs to force the development of their ITS sector. Comprehensive research has been done by the European Union and its member states as well as Japan and the USA. A major part of the research within the European Union is hosted by an organization named ERTICO [4]. ERTICO is a multi-sector, public/private partnership pursuing the development and deployment of ITS in Europe. A number of projects addressing the various aspects of ITS have been run since the year 2000 under the coordination of the organization. A recently started project initiated by ERTICO is CVIS [5]. The project aims to design, develop and test the technologies needed to allow cars to communicate and network directly with the roadside infrastructure. CVIS is run in cooperation with a number of European suppliers, manufacturers and universities. Among the participating partners companies like Alcatel, Robert Bosch AG, Ericsson, Siemens and Volvo Technology Corporation can be found. Another driving force in ITS-Europe is the Advanced Driver Assistance Systems initiative (ADASE) [6], and its successor ADASE2. ADASE2 serves as an umbrella project for over 30 sub projects in the fields of autonomous driving, cooperative driving, passive safety, sensor systems, system assessment, collision avoidance and mitigation, vehicle platforms, human machine interface (HMI) issues, maps and multimedia, as well as legal, social and system development issues. A recently completed project making a valuable contribution to the sector is CarTalk2000 [7]. It was focused on a driving assistance system leveraging inter-vehicle communication. Concurrently, non EU financed projects contribute to the development of ITS. FleetNet [8] can be mentioned in this capacity. The main objective of this project is to develop a platform for inter-vehicle communication systems. The project is sponsored by Daimler Chrysler in association with several electronic equipment suppliers and a number of German universities. The Japanese equivalent to the European ADASE is called Advanced Cruise-Assist Highway System Research Association (AHSRA) [9]. Several research and development projects have been carried out under the auspices of Ministry of Land, Infrastructure and Transport. Valuable results were accomplished within the Advanced Safety Vehicles (ASV-3) project [10] which 5

18 was done in cooperation with the car manufacturing company Honda. With the completion of the ASV-3 project in March this year, the first prototypes of ASV-3 equipped cars were tested in Japan. The key feature of ASV-3 is a driver assistance system based on inter-vehicle communication. As an U.S. counterpart in ITS, the U.S. Department of Transportations is leading a number of programs under the denotation ITS Joint Program [11]. An integrated part was completed last year, the Intelligent Vehicle Initiative (IVI) [12] program which mainly focused on crash prevention. An ambitious endeavour within IVI was the PATH [13]. project. It is a cooperating program between universities, private industry, state, local agencies and non-profit institutions and is hosting over 60 projects within the field of ITS. Another, currently ongoing project, within the ITS Joint Program is engaged in inter-vehicle communication. A recently published paper from this project concerns a hybrid simulation platform, which is developed by General Motors in cooperation with Carnegie Mellon University [14]. The given overview about the related work does not claim to be exhaustive. The world wide rapidly growing interests in ITS research leads to numerous newly initiated projects. However, we think that the presented overview covers the most important developments in the sector. 2.2 Swedish Vision Zero Each year around the world people lose their lives and millions are seriously injured due to traffic accidents. Moreover, traffic congestion is reflected in the economy of each nation through millions of euros spent in wasted time and fuel cost. However, for those who have lost a loved one, the cost is immeasurable. According to statistics from the European Commission, approximately lives are lost on EU roads and congestion costs 1% of the EU Gross Domestic Product (GDP) bordering on e100 billion each year [15]. Some countries in the EU and America have expressed a concern by refusing to accept human fatalities or permanent physical injuries on roadways. The work in essence is to contrive policies with the purpose of increasing driver safety. In 1997, Sweden through the Swedish National Road Administration (SNRA) conducted an in-depth investigation into all fatal accidents on Swedish roads. The information that emerged provided an instance of realizing that certain aspects of the road transportation system failed, thereby causing human deaths. As a result, the Swedish Parliament decided to found an ambitious program in order to avoid and alleviate such consequences. The idea was denominated Vision Zero. The head aim was that Nobody should be killed or seriously injured within the road transport system. The road transport system s structure and function should be brought into line with the demands that this goal entails [16]. Indeed, Vision Zero is behind the policy: Zero fatalities and Zero delays. Vision Zero offers a new manner of sharing responsibilities; vehicle manufacturers and dealers as well as drivers have their function during a trip. On the one hand, the former have the task of building and designing safer and better vehicles. On the other hand, the latter are responsible for obeying signals and speed limits. However, one point in which Vision Zero stresses is the fact that drivers are not solely responsible for accidents, but the system designers have the main responsibility [16]. 6

19 In this sense, ITS rises as the main endeavour in the design and implementation of future roads. The sector adopted Vision Zero as its motto addressing people can be transported without delays, injuries, or fatalities by integrated systems mounted not only in vehicles but also along the road. Providing enabling technology, real-time travel information and traffic management, driver safety and comfort is and further will be improved. According to statistics, in the year 2000, 600 people were killed on Swedish roads [17]. Six years after, Sweden has reached second place behind Malta in lowest number of road fatalities per million population. The number of casualties has reduced since 2000, from 67 deaths per million to 59 [16, 18]. In 2006, countries all around the world have included this guiding principle into their transportation systems and programs. It has permitted the start of new programs such as the EU 1/2 death concept, with the same basics as Vision Zero. The need of vehicles, technologically equipped, capable of dealing with hazardous events along roadways open the doors for the creation of vehicular networks. A worldwide ITS network will significantly improve drivers safety and transport efficiency. 7

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21 Chapter 3 Related Work For an understanding of the requirements and problem areas for the development of a test environment for vehicle communications, it is important to be thoroughly familiar with the overall concept of the test-bed based VANET evaluation. Numerous developments and studies on the characteristics of VANET exist. However only few projects have been able to evaluate real performance of their designs by means of a test-bed. This chapter presents a comprehensive analysis of existing test-bed based VANET evaluations. Therein, each test-bed is investigated according to its strengths and weaknesses. The analysis relies on crucial components and requirements which are studied with special regard to their influence on the development of a reliable platform. 3.1 Simulation Platforms FleetNet The FleetNet project designed a platform based on the results from network simulations and a software prototype implementation of a position-based router called FleetNeet Demonstrator (FND) [19, 20]. This work on VANETs in the development of software for realistic evaluation has shared the same general goals, but it has been directed more towards the problems of performance and reliability of inter-vehicle communication. The demonstrator was mainly focused on providing a proof-of-concept in real world how mobility is tackled leveraging a position-based routing protocol. The experimental setup consisted of a convoy of six Smart T M vehicles, each equipped with two laptops; one serving as a Linux-based router and the other one serving as a Windows-based communication interface respectively. The former controls the communication between the vehicle and any other vehicle or infrastructure through a IEEE b wireless interface. The latter controls the graphical interface for the driver as well as the communication with the GPS receiver. The two notebooks are connected via cable. The FND tried to draw some conclusions by investigating the behaviour of the vehicle 9

22 network under highway and city scenarios with a varying set of distance among vehicles, data transmission, velocity and cost fashion GrooveSim Groovesim [14] was created to provide a tool in the evaluation of vehicular networks performance in the ITS initiative. The idea of having such a platform was inspired mainly from the modeling and forecasting of vehicle traffic flows, where realistic traffic density and trip models are important. Groovesim is the first application in the VANET evaluation concept since it provides the possibility of testing real events such as time-critical safety messages or road hazard notifications. The toolkit was built under a Linux operating system core. C++ and Matlab were employed for the graphical interface development and as the interface in the elaboration of graphs and diagrams respectively. A database for creating maps and visualizing geographic characteristics was used. The test-bed consists of a DSRC 5.9GHz transceiver, a laptop, a differential GPS receiver, a cellular modem, and audio/video equipment. The software is able to operate in five modes: on-road, simulation, hybrid (on-road and simulation), research (log-based), and predetermined. These modes compare the real performance of the test-beds with simulation and provide further analysis for research purposes. Simulation settings can be varied regarding different speed, mobility and communication models. The simulation was tested with the help of five equipped vehicles traveling in city and highway environments. Parameters such as message penetration, packet delivery delay, vehicle group size, packet drops and message lifetime are addressed and calculated in the simulator. Real-time applications, scalability and performance were also considered NHTSA An alternative approach to test-bed based VANET evaluation is provided by National Highway Traffic Safety Administration (NHTSA) [21]. Mainly designed to introduce requirements in the standardization of DSRC as medium access protocol, the simulator is focused on giving a global perspective about VANET performance. Different from Groovesim, the NHTSA platform offers a computer-based tool capable of taking external input (text file or TCP/IP socket connection) for the vehicle traffic during the simulation. The platform provides a good approach on supporting large-scale and realistic simulation tests of generic time-critical applications in arbitrary complex roadway configurations [22]. The NHTSA simulator was built on top of the discrete simulator platform NS-2 targeted at networking research. It is a flexible, C++ based open-source network communication simulator supporting different environments such as Win32 and Linux. To simplify compatibility and configuration issues, C++ was used in order to implement the graphical user interface. The hardware used in the test-bed comprises a GPS receiver, an on-board unit, which was 10

23 a Windows-based notebook and a IEEE a wireless radio device adapted to the DSRC standard. Flexibility and scalability in respect to the implementation of new models and protocols are addressed in the platform. Researchers can set different configurations according to different patterns. For example, one could set the type of antenna based on the propagation model. Additionally different MAC layers, link models and applications such as time-critical warnings and Internet browsing can be configured. 3.2 Comparison and Analysis The platforms described above are regarded as test-beds for the evaluation of VANETs in real world. While the platforms basically provide a sensing of the vehicle s environments, the aim is to establish criteria that can help to select a prototype for the VANET environment. Within the research project we would like to conduct a feasibility study to bring a vehicle communication system from an idea into the real world. Starting from the point of analyzing the strengths and shortcomings in the design of previous research implementations, we will be able to define parameters and complementary methods which will be used in a software prototype having the objective of investigating crucial characteristics in the VANET creation and management. Table 3.1 summaries the software, hardware and technologies used in the implementations. All the platforms employed Linux as the operating system on their test-beds. FND, additionally deployed Windows based notebooks for the user interaction. Linux presents a robust and flexible architecture besides providing a wide range of possibilities and resources in the open source field. Groovesim and the NHTSA simulator opted to employ C++ as the programming language in the software toolkit. Notebooks were employed as prototypes which gives the opportunity of implementing and modifying easily characteristics in lower layers such as routing and MAC layers. The use of notebooks facilitates the development of a first testing software. However, it can be considered as a limitation in the VANET evaluation since the full power of notebooks will not be provided to the computing unit in a vehicle later. Notebooks do not have to deal with problems such as processing capacity or memory constraints and storage constraints in contrast to embedded GrooveSim NHTSA FleetNet Operating System Linux Linux Linux/Windows Programming laguage C++ C++ MFC Wireless technology DSRC DSRC b On-board device Notebook Notebook Notebook Run-time configuration convoy predetermined convoy/distributed Research physical, routing physical, MAC, routing routing, application Table 3.1: Layer-based analysis 11

24 systems. Two more shortcomings can be mentioned further. The test-bed implementations focused on a narrow angle in the vehicle communication performance (routing and application layers) which does not give an overall perspective about the processes such as delays, packet drops, interference, handover, etc. The topology used in all of them was a mixture of road types including highway and city road. While the study basically addressed the analysis of a convoy of five or six vehicles (Groovesim and FND), only Groovesim performed random configurations in which the simulation studies usually selected a random starting and ending location for each vehicle. In order to provide a guideline for the modeling and implementation of a test environment for vehicle communications the following ideas can be taken into account. Outline and analyze the parameters affecting the performance of VANETs. Establish hardware requirements for a test-bed. A good selection can be expected to be serially embedded in vehicles and considered as a first reliable prototype. Consider a well defined software environment in which the desired platform is supposed to work. A scalable architecture alleviates refinements and extensions. This gives the opportunity of implementing new features according to future models and protocols in the evaluation of VANETs. 12

25 Chapter 4 Qualified Parameters for Vehicular ad hoc Networks This section analyses the environment of a VANET. The analyses have been carried out by describing a collection of qualified parameters, where each parameter covers an integral part of the vehicular network characteristics. The entire collection of parameters tries to provide a complete as possible view over the field of VANETs with its unique conditions and demands. It also outlines the key requirements for applications in this area. In order to provide a more comprehensive overview, metrics representing different views on the parameter collection are defined later in this chapter. The parameter specification further serves as a guideline for a test environment design which will be discussed in the succeeding chapter. The sensing of the parameters was mainly driven by the characterizing cornerstones of VANETs on the one hand and the desired applications on the other hand. The influencing factors can be reduced to the following four: wireless communication ad hoc networking mobile nodes application profiles Further ideas evolved within the research environment of the VAS project at Halmstad University and the CVIS project at Volvo. 4.1 Parameter Specification The following section presents the outlined collection of parameters and gives a definition for each parameter. A parameter is represented by the parameter s name and an eventually assigned unit in brackets. The parameter are sorted after a first somewhat obvious coherence. 13

26 Position Position addresses the exact geographical location of a vehicle. Precise position data is an essential factor in this field since a number of decisions are based upon this information and its timely change. Also geographical routing protocols are currently being researched at present, where the routing algorithm creates the routing tables based upon positioning data (see parameter routing protocols). Location based services provide the user with information depending on and tailored to his position. Position awareness is also crucial for navigation aids. Position information can be gained from a GPS device (in the future also from the European pendant, GALILEO [23]). Acceleration [m/s 2 ] A vehicle s acceleration is a calculated parameter. It is determined through the changing position coordinates. A test-bed platform is to investigate how acceleration influences the behavior of the network regarding latency, jitter, transmission rate etc. Velocity [m/s] Velocity is calculated with the help of position information. The pace at which the participating nodes are moving is one of the big challenges for VANETs. The higher the velocity, the more dynamic and unpredictable the communication network becomes. Also determinate through positioning data. Wireless Technology The used wireless technology is a key factor for VANETs. The majority of the specified parameters are affected by wireless transmission properties. The test-bed should allow to test different technologies and if necessary combine them to meet the different requirements for varying application profiles. Communication Costs [SEK] This parameter aims to roughly estimate the costs incurred in a VANET by using an existing communication environment. Costs for communication have to be considered when using 2G/3G links. The parameter should outline the costs for one vehicle during the time of a test run. Interference This parameter is dedicated to the occurring disturbances between the wireless technology systems used in VANET communication and other wireless communication standards as well as to the interference caused by natural obstacles. The standards addressed here are for instance wireless LAN (IEEE ), cellular phone networks, toll collection systems, etc. A possible implementation for this parameter could be to investigate the decrease in the transmission quality in the defined traffic areas compared to a non-disturbance environment. Signal Propagation [m] One possibility for characterizing the propagation of signals through the air is measuring the maximum distance the antennas are able to radiate and propagate the signal properly. 14

27 Antennas are designed depending on application requirements. Omni-directional antennas are used in order to propagate the information in all directions. If an application only focuses on a specific area, directional antennas with an adequate gain are designed for these purposes. However, the deployment of a test-bed should offer valuable clues about the most efficient configuration for the vehicles antennas in different applications. Transmission Scheme This parameter addresses the variation in the transmitting power for wireless technologies. Different transmission schemes could be established to adapt to a given environment. For example in an urban environment a vehicle might not need to cover such a large area as on a countryside road. Adaptive transmission schemes will allow an increase in the networks efficiency and help to decrease interference at the same time. It should be possible to apply different transmission schemes in a test-bed. The combined assessment of this parameter with other parameters such as type of coverage area, power consumption, interference, etc. should result in suggestions for optimal transmission schemes for the different network areas. Power Consumption [W ] Power consumption implies the amount of energy that a test-bed uses in different processes. Under specific circumstances devices consume more power resulting in a higher demand of energy in the vehicle. Factors influencing the power consumption are for example the used wireless technologies and different transmission schemes. Another aspect here to consider is the possible power consumption while a vehicle is parked. This parameter is not essential for the initial development phase in VANETs but will gain importance when it comes to the development of more advanced prototypes. Latency [ms] This parameter specifies the delay in the packet transmission. It is an important criterion for determining the feasibility for different applications such as incident warning, VoIP, etc. Latency is determined by the wireless technology in use on the one hand and by occurring interference on the other hand. Observing the latency for different wireless carriers in a vehicular network environment will offer valuable clues for the feasibility of desired applications. Latency has to be considered in both V2V and V2I communications in a VANET. Jitter [ms] Jitter characterizes the variation of the latency. It is also an important criterion for applications. For jitter the same distinctions are made as for latency. Transmission Rate [kb/s] This parameter measures the data rate at which information is exchanged in the network. Higher transmission capacities are mainly demanded by multimedia applications such as video streaming. The transmission rate must not fall below a certain level for guaranteeing the reliable use of specific services. A test-bed should enable the measurements of the average transmission rates which are achieved in different communication environments. 15

28 Transmission Error Rate [%] This parameter addresses the probability of data errors during a transmission. Particularly in wireless communications a number of factors affecting the signal transmission over a noisy channel are manifested. However, low bit error rates (BER) or packet error rates (PER) have to be achieved in order to avoid re-transmissions and potential data losses. Message Spreading Time [ms] This parameter represents the time a message needs to spread out from the origin location to the vehicles of interest in the zone of evaluation. In the case of important messages such as alerts and warnings, the network must be able to prioritize their transmission in order to minimize the message spreading time. In VANET research the varying message spreading time under changing environments is of interest. Connection Setup Time [ms] The time needed to establish a communication link between two network nodes is termed Connection Setup Time. Especially in rapidly changing ad hoc networks the connection setup time must be low to ensure a dynamic and flexible communication environment. The connection setup time is basically determined by the implemented wireless protocol. Connection Handover [ms] An ad hoc network involves the rapid change of network topologies. The handover time determines the time required to continue an already established connection while the connection experiences a change in its logical structure, e.g., roaming. Such a change can result from several circumstances. For example, a vehicle leaves the supported area of an infrastructure node, or the routing protocol suggests exchanging the primary link to another node in order to increase link quality, while a concurrent data transfer must not be interrupted. A connection handover will also be performed when an intermediate vehicle, such as a routing node, has to be quickly established because the distance between two vehicles having a connection is close to exceeding the physical limits of the connection range. The connection handover time is an important parameter to guarantee dynamic and flexible ad hoc networking. Routing Protocols The deployed routing protocol is also an important key factor. ITS communication claims a number of unique requirements for routing [24 26]. The demand for a test-bed here is to facilitate the usage of several routing protocols and to observe their performance under different load conditions. Further the idea of combining several routing protocols for different applications in the same physical network evolves in the context of VANETs. Network Connectivity [number of connected nodes] Network connectivity establishes if a node is connected to a VANET. Depending on several factors such as connection setup time, handover and reliability, it is determined whether a node is able to participate in the network or not. The number of connected nodes could also be taken into account as a parameter for routing decisions. Using the test-bed platform it should be investigated how the network connectivity is affected by varying conditions e.g. the type of 16

29 coverage area, wireless technology, velocity, etc. Connection Reliability [s] The parameter addresses the average connection duration of a link between nodes in the ad hoc network. A VANET node will maintain a high number of fast changing links for different networks. In order to extract more instructive information the type of link can be categorized in groups such as the used wireless technology, the type of coverage area or the type of network (V2V or V2I). Connection reliability could further be used as a criterion for routing decisions. Subject to test is to determine characteristics of this parameter under varying set of environmental conditions, traffic area and wireless carries. Message Prioritization for Critical Applications With message prioritization the approach to provide quality of service features within VANETs is addressed. Quality of service in ITS communication ensures the on-time serving of critical applications, such as incident warning. A desired simulation result could be the proof that a released incident alert is spread out without being delayed by other lower priority applications. Network Attachment There will be several different instances of network types co-existing in VANETs, each serving a particular purpose. Such networks will comprise the network among vehicles on the street, toll collection systems, networks among emergency vehicles, police cars, etc. Different vehicles will be connected to these various networks, if demanded at the same time. This involves increasing complexity for the protocols as well as raises the demands on the communication technology. Using a test-bed will help to investigate the behavior of such a multi-network environment and define procedures for network attachment. Network Prioritization In order to guarantee the proper functioning of services within a VANET a prioritization among the different networks will be required. Higher prioritized networks can claim communication resources before the others or even obtain resources from already established networks. This parameter extends the definition of the Network attachment parameter from above. Traffic Area [rural, urban, highway] This parameter addresses the environment in which the vehicles communicate. A major distinction here can roughly be made between the areas of cities, freeways and the countryside. These areas differ in terms of number of vehicles, driving behavior, velocity, radio coverage and experienced interference. Type of Coverage Area With the type of coverage area the logical communication district is addressed. Types can be distinguished for example between circular area, the area limited to a specific intersection, or the area along a defined section on a freeway, etc. Through testing the most efficient logical area type for the different applications should be outlined. 17

30 Test-bed Compatibility This parameter addresses the fact that vehicles will be equipped with differences in their hard- and software composition of the deployed test-bed equipment. Different equipment formats could be the result of several different circumstances. Examples could be limited space (a car provides more space for additional electronics than a motorcycle), varying firmware, different positioning systems, different application profile implementation, etc. A test-bed should allow the observation of the impacts on the network functionality caused by unequal equipped VANET nodes interesting for later prototypes such as power consumption. Location Based Services Location based services (LBS) is a recently developed set of applications for cellular phone networks. Migrating this service into ITS systems would provide further convenience for the drivers. A test-bed should prove the functionality of LBS under the premises of VANETs. LBS are considered as a special case of the parameter VANET applications, since they have to communicate with an existing network environment. Minimum Throughput [kb/s] The minimum throughput can be seen as a threshold for the transmission rate upon which a reasonable communication for a specific application can be expected. The parameter is used for establishing a certain quality level for applications. Elaborating on this parameter should result in a table consisting of the different applications in VANETs and their required minimum throughput. Maximum Latency [ms] The maximum latency is the supplementing value to the minimum throughput. It aims to outline an upper latency tolerance level for applications. The parameter assessment should also result in a table with VANET applications and their related maximum allowed latency values. Traffic Pattern This parameter treats the shape of the traffic whereas inbound as well as outbound traffic is addressed. Herein, the view from a particular vehicle is represented. The traffic pattern is mainly influenced by the belonging application. The challenge within VANETs is to meet the requirements resulting from the applications different traffic patterns. This involves the consideration of different carriers for different type of traffic patterns. The parameter can be represented by a diagram indicating the amount of transmitted and received data by time. Message Corruption and Intrusion Detection This parameter investigates the network behavior when it is manipulated through corrupted messages. For the testing purpose messages can be deliberately modified in order to mock an attack. Possible attack scenarios among others could be the faking of alarm signals of emergency cars in order to clear the way or the interception of video chat sessions, etc. A test-bed should provide the possibility to test different security mechanisms averting the infiltration of the network. New prototypes. 18

31 Scalability This parameter aims to investigate a networks behavior with an increasing number of participating nodes. The possible number of participating vehicles is a significant criterion for determining the network capacity and to recognize bottlenecks premature. An idea for a test is to estimate the average amount of vehicle data traffic for the defined traffic areas and to test for how many participants it is possible to provide a reasonable communication link under a certain set of quality parameters. Another interesting aspect will be to observe a routing protocols performance with an increasing number of network nodes. The expertise gained by evaluating this parameter should support the planning for the required capacities in different VANET environments. VANET Applications [Application] This parameter is to test actual applications under the conditions of a VANET. An instance of a parameter therefore is a specific application. Applications are demanding for certain qualities of the communication environment in order to work properly. This parameter represents the direct interface for the end users and hence is the final proof for a successful network implementation. 4.2 Metrics In order to provide a more comprehensive view, we categorized the parameters according to different perspectives. The different perspectives are denoted as metrics. A metric in this context is defined as a system of parameters. Three different metrics were outlined: Evaluation view, OSI layer view and Dependency view Evaluation View For the first perspective we considered the nature of the parameters. In more detail, we determined whether a parameter can be evaluated or tested. An evaluated parameter can be mathematically described and it can have a certain unit assigned. Evaluated parameters are obtained either by means of measurement or by calculation of one or more other parameters. As tested parameters we considered types of parameters which neither can be measured nor calculated but a determine VANET s characteristics. This category comprises parameters like the used wireless technology, the type of traffic area and also routing protocols. Tested parameters can be understood as degrees of freedom in the configuration for VANETs and also as the test for the desired applications. Parameters in the Evaluated category can be seen as performance measurements of a given VANET composition. Table 4.1 shows the Evaluation view of the conceived parameters. It can be seen that the number of parameters is evenly distributed over the two categories. This implies that a VANET underlies a variety of configurations given by parameters listed under the category Tested. 19

32 Transmission error rate Minimum throughput Message spreading time Maximum latency Position Traffic area Latency Scalability Jitter Test-Bed compatibility Connection handover Location based services Connection setup time VANET applications Evaluated Connection reliability Tested Routing protocols Network connectivity Message prioritization Interference Network attachment Transmission rate Network prioritization Power consumption Wireless technologies Signal propagation Type of coverage area Communication costs Message corruption Traffic pattern Transmission schemes Table 4.1: Metric: Evaluation view For investigation it should be possible to test varying compositions of these parameters. Thus, it should be possible to simulate the efficiency of a routing protocol under varying types of coverage areas, or to simulate the impacts on the scalability for different wireless technologies, etc OSI layer View As the second perspective the parameters are classified according to their layer of affiliation in the OSI [27] network model. Additional to the seven layer model, we introduced an artificial layer for parameters which obviously could not be assigned to any specific layer. This artificial layer was named layer 0. The distinction of the parameters among the OSI layers provides a dedicated view over the research responsabilities in the VANET development. Table 4.2 lists the OSI layers with their belonging parameters. On the first sight, the table reveals that our parameters are distinguished among the artificial introduced layer 0 and then the layers one, two, three and seven. The layers four, five and six are missing in our listing. This can be explained by the fact that for the layers five and six there were no essential issues outlined to be solved for the VANET development yet (at the same time, we do not claim that there are no layer five and six related issues to be solved for VANETs). For the layer four this reason is not valid as there are parameters in layer three which could be also considered to be a matter of layer four. Connection reliability can be mentioned as an example here. However, we did not introduce a layer four here because the focus did not lay on the exact weighed grouping of the parameters but we rather tried to give an insight about the problem areas instead. The layer of a parameter will be finally decided in the real implementation of a test-bed. 20