Elsevier

Ad Hoc Networks

Volume 8, Issue 5, July 2010, Pages 506-517
Ad Hoc Networks

On the feasibility of UMTS-based Traffic Information Systems

https://doi.org/10.1016/j.adhoc.2009.12.003Get rights and content

Abstract

Intelligent Transportation Systems (ITS) are a hot topic in the communications society. Currently, research is primarily focusing on setting up Vehicular Ad Hoc Networks (VANETs) based on WLAN technology. However, VANETs are heavily dependent on high market penetration or infrastructure support. Third-generation (3G) networks might complement these efforts. They are already widely deployed and can serve as the basis for Car-to-Infrastructure (C2I) applications. We developed a simulation framework for holistic analysis of complex UMTS-based ITS. This framework couples simulation models with corresponding protocols of the UMTS link level, of higher network layers, and of road traffic. Based on our simulation framework and real-world 3G network coverage data, we evaluated a UMTS-based Traffic Information Systems (TIS) in a typical highway scenario in which information about traffic jams needed to be communicated to other cars for optimized route planning. The evaluation clearly outlines the capabilities of the simulation framework and evaluation results are consistent with all expectations. For example, we show that the availability of UMTS multicast distribution services are demanded for an efficient operation of the TIS application.

Introduction

Recently, the communications society intensified its focus on vehicular communication architectures and protocols. This includes scenarios such as safety applications, but at the same time, these mechanisms are also intended for use in general purpose Traffic Information Systems (TISs), e.g. for optimized route planning. Basically, two approaches are competing in this field: Car-to-Car (C2C) and Car-to-Infrastructure (C2I) communication architectures. Presently, mainly WLAN according to the IEEE 802.11p standard [1] is used in this domain. However, for general purpose TISs these C2I applications require massive investments into a new infrastructure, e.g. along highways. C2C communication solutions address this problem by using the moving vehicles as a dynamic infrastructure established by Vehicular Ad Hoc Networks (VANETs) [2], [3]. An example is the approach taken by the Self-Organizing Traffic Information System (SOTIS) [4]. Whereas it has been shown that this system works well even with a low penetration of SOTIS installations, new problem domains are opened, e.g. the increased end-to-end delay and the reduced quality or granularity of the available information. Furthermore, security is an aspect in terms of drivers’ privacy and information security for closed user groups.

3G telecommunication networks, specifically UMTS, are a relatively new player in this field [5], [6] and offer a couple of benefits for TIS applications. Owing to their system design, in conjunction with much larger data rates compared to 2G networks, TIS operation based on 3G networks becomes economically feasible. In addition, unlike C2I solutions using WLAN or WiMAX, UMTS-based solutions can rely on readily-available infrastructure.

Compared to WLAN-based TIS solutions, however, the perceived strengths and weaknesses of UMTS networks are quite different. While, for example, the security of C2C networks cannot easily be guaranteed [7], there already are strong security measures in place to guarantee 3G networks’ integrity, which can be re-used for C2I communication. As a second example, the distance between a message’s sender and its intended receivers is almost a non-issue in 3G networks: its impact on the end-to-end delay is negligible. On the other hand, even for short-distance messages the end-to-end delay is already quite high compared to that of direct radio links.

A key question to be asked about an infrastructure-based C2I communication system is therefore whether end-to-end delays will still be acceptable not only for common TIS applications, but also for the transmission of hazard warnings. Another important question is whether such a system will scale better [8] than more traditional WLAN-based C2C solutions to accommodate high penetration rates, given that in this C2I solution all network traffic has to be routed through the available infrastructure. Together with obvious business reasons, both questions are at the core of the problems which hindered adoption of some of the early 2G-based approaches [9] to C2C and C2I communications via a cellular network proposed in the 1990s. Development of C2I solutions is now picking up again, with new approaches based on 3G networks.

The state of art in cellular communication already allows for interesting and proven applications in the domain of Intelligent Transportation Systems (ITS), one such application being the derivation of estimations on traffic density from passively acquired cellular network data and its distribution to end users within minutes, marketed as, e.g. the TomTom HD Traffic service. New technologies in UMTS networks, however, promise delays of less than one second while at the same time reducing network load.

Recent work in this field has mainly dealt with analytical evaluations of only some of such a communication system’s aspects [6]. By means of an analytical model, the authors quantified the achievable performance in some realistic scenarios. In particular, the advantages of the Multimedia Broadcast Multicast Service (MBMS) were studied, which is needed to support efficient C2I services on top of the UMTS network if the number of users is high [10]. Although MBMS is still lacking widespread commercial adoption, interoperability tests and several trials in operators’ networks have already proven the standard ready for adoption.

Experimental approaches have accomplished post-hoc analysis of implemented testbeds using state of the art technology. In these setups, either detailed studies have been conducted [5] or complex extensible testbed architectures have been developed [11]. However, only the currently deployed UMTS versions could be tested and the size of the experiments was limited. Moreover, an evaluation of the environmental impact of TISs based on real-world experiments is infeasible, and even simulative studies on this topic are rare [12].

Simulation experiments of UMTS networks are usually performed using proprietary models without focus on application in vehicular environments, e.g. in [13], and without incorporating realistic mobility models. Furthermore, such simulations are not using a holistic approach, i.e. they are not including all system aspects from the wireless links to the core 3G network as well as influence of the road traffic. Even for WLAN-based C2C approaches, it has been shown that coupled simulation of network communication and road traffic is necessary [14], [15].

Comprehensive evaluations of such vehicular communication systems, using features which are still in the early planning stages, can, however, be performed if all components of such a system are modeled in sufficient detail and assembled into a simulative testbed. Therefore, we developed a new simulation framework that allows such a holistic analysis of complex 3G-based TISs. Our simulation framework, Veins (Vehicles in Network Simulation), is based on a bidirectionally coupled environment for network simulation and road traffic microsimulation.1 Veins has also been used for recent studies of VANET protocols [16].

Our simulation framework Veins is being used for the simulative evaluation of a planned real-world communication system, which is currently being designed in the Cooperative Cars (CoCar) project [17]. Aside from examining the technological feasibility of such a system, CoCar also addresses establishing a solid business case [18]. The project is part of the German government funded research initiative Aktiv,2 which encompasses research in the fields of traffic management, active vehicle safety, and cooperative systems.

The simulation framework also includes a set of CoCar application layer protocols, to be used in both the up- and downlink direction. These protocols benefit from new features of cellular communication systems, e.g. the current High Speed Packet Access (HSPA) system which improves up- and downlink data rates and transmission latencies. For easy integration into existing, standardized communication systems, these protocols are implemented above the cellular communication protocol stacks.

In this paper, we show first simulation results for a typical highway scenario, based on real-world 3G network coverage data. The results clearly outline the capabilities of the simulation framework and evaluation results are consistent with all expectations. Fig. 1 depicts an overview of the CoCar communication system, along with the various models that have been integrated to form the testbed we will use for evaluations. Based on the example of the CoCar system, we describe in this paper each of the models the framework is composed of and detail how the models interact with each other.

The paper is structured as follows. First, Section 2 introduces the application models. Section 3 gives an overview on the Internet, Core Network, and radio access network models used. Section 4 details the UMTS channel model that was integrated with the simulator and Section 5 introduces the road traffic model. Finally, first results that we obtained in a proof-of-concept study are outlined in Section 6, focusing on the single use case of traffic jam warning exchange. This also includes a discussion of the impact they will have on a real-world implementation. Section 7 concludes the paper.

Section snippets

Application models

In the simulative testbed, components at the network edge are represented using detailed application-layer models of the respective services. These components are the Traffic Information Center (TIC) and the CoCar-enabled vehicles. Both send and act upon bit-precise representations of CoCar messages.

Three application-layer protocols have been specified in order to handle communication among vehicles in the CoCar system. One protocol, called Traffic Probe Data Protocol (TPDP), is a lightweight

Network models

The number of parallel unicast connections in UMTS is limited by the cell size: The distance between a mobile terminal and its associated NodeB determines the path loss for the radio connections. A vehicle that is far from the cell’s center will require a higher transmit power to communicate with the NodeB. This, in turn, increases the overall interference level of the cell. Since UMTS is an interference limited system, this reduces the number of possible simultaneous connections in the cell,

Channel model

Actually performing all signal processing tasks that take place on the UMTS physical layer for every single network connection is infeasible in terms of computational effort and memory consumption. Instead, performance measures should ideally be modeled on a higher level.

Therefore, realistic simulation of UMTS channels was accomplished by creating a dedicated link level simulator and performing extensive simulations of packet transmissions. In the following, we detail how a set of statistical

Road traffic model

One of the goals of the simulator was measuring the impact of the CoCar communication system on the road traffic, in terms of metrics such as users’ travel times, smoothness of traffic flow, and the associated environmental impact of the TIS. The choice of the mobility model has been shown to influence the outcome of simulations to a large degree [15], [25]. Simulations were hence based on the Veins framework, which allows a realistic node mobility model to be employed [14].

Traffic simulation

Performance evaluation

The first and foremost benefit of any TIS is, of course, the increase in overall road safety which it can effect not only by assisting users, e.g. with route planning, but also by providing early and accurate jam and hazard warnings. Secondly, TISs can facilitate dynamic re-distribution of traffic, decrease local traffic densities and thus lead to smoother traffic. However, operational parameters of a 3G-based TIS (in particular when optimizing for timeliness of messages) have to be balanced

Conclusion

Based on a proof-of-concept study, we presented in this paper a comprehensive simulation framework to help in the design and evaluation of upcoming, UMTS-based C2I communication systems. Such 3G approaches might complement recent efforts to establish VANET-based Intelligent Transportation Systems such as TIS applications – basically because they are already widely deployed and provide capabilities such as inherent security measures and low latency communication independent of the current

Acknowledgment

This work was partially supported by the German Aktiv CoCar project, funded by the Federal Ministry of Education and Research under grants 01BU0690 to -94.

Christoph Sommer received his M.Sc. in computer science from the University of Erlangen, Germany in 2006. Focusing on questions regarding efficiency and security aspects of Car-to-X communication in heterogeneous environments, he is a research assistant in the Computer Networks and Communication Systems group at the Department of Computer Science, University of Erlangen. He is currently researching SSU/RSU-supported information dissemination techniques for improved traffic performance and

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    Christoph Sommer received his M.Sc. in computer science from the University of Erlangen, Germany in 2006. Focusing on questions regarding efficiency and security aspects of Car-to-X communication in heterogeneous environments, he is a research assistant in the Computer Networks and Communication Systems group at the Department of Computer Science, University of Erlangen. He is currently researching SSU/RSU-supported information dissemination techniques for improved traffic performance and safety at the Electrical and Computer Engineering Department of Carnegie Mellon University.

    Armin Schmidt received his master degree in computational engineering (M.Sc.) from the University of Erlangen, Germany in 2006. He is a research assistant at the Chair of Mobile Communications at the Department of Electrical, Electronic and Communication Engineering. Between 2007 and 2009 he worked in the AKTIV CoCar project funded by the German Federal Ministry of Education and Research (BMBF), where he investigated physical layer related issues and conducted feasibility studies regarding the suitabiliy of the UTMS air interface for future telematic services. He is currently researching physical layer supported techniques for increasing the throughput in wireless multi-hop networks.

    Yi Chen received her bachelor degree (B.Sc.) from the Department of Computer Science at Hunan University, China in 2001. From 2001 until 2004 she worked as a network system engineer in Guangxi Mobile Communications Co., Ltd before pursuing graduate study in communication networks. She completed her master degree (M.Sc.) in Communication and Information Technology from University of Bremen, Germany in 2007.

    Following the completion of her master study she joined the Communication Networks Group at the University of Bremen as a Research Assistant and a Ph.D. candidate. During her master study, she was involved in a Nokia Siemens Networks (NSN) UMTS project, focused on UTRAN network simulation setup and performance analysis. From 2007 until 2009 she worked in the AKTIV CoCar project founded by the German Federal Ministry of Education and Research (BMBF). The main responsibility was to investigate the feasibility of using cellular mobile communication technologies (3G+) for the transmission of telematic information for future cooperative applications in the automotive domain. Since September of 2009, she started doing research on LTE (Long Term Evolution) systems and working on the related network dimensioning issues. Her research interests include modeling and simulation of LTE radio access networks.

    Reinhard German received a diploma in computer science in 1991, his Ph.D. in 1994 and his Habilitation degree in 2000 from the Computer Science Department, Technical University of Berlin. Then he joined the Department of Computer Science at the University Erlangen-Nuremberg first as an associate professor (system simulation) and since 2004 as a full professor (computer networks and communication systems) where he is currently the head of department. His research interests include model-based and measurement-based performance analysis, modeling and simulation paradigms and tools, numerical analysis of Markovian and non-Markovian models, vehicular communications and autonomous sensor/actuator networks.

    Wolfgang Koch received his Dipl.-Ing. (TU) 1977 and his Dr.-Ing. 1982 from the university of Hannover in the field of communication technology. From 1983 to 1995 he was with Philips Kommunikations Industrie AG in Nuremberg in various positions, latest as head of the advanced development department. During this time he supported actively the GSM standardization process. From 1995 to 2001 he was head of the research department of Ericsson Eurolab Germany GmbH at Nuremberg. Since November 2001 he is full time professor and head of the research group of Mobile Communications at the university of Erlangen-Nuremberg. His research interest are cellular mobile communication systems (UMTS/HSDPA/LTE, W-LANs), coding and equalization, radio network aspects, multiple antenna systems (MIMO) and channel models.

    Falko Dressler is an assistant professor at the Department of Computer Science, University of Erlangen. He teaches on self-organizing sensor and actor networks, network security, and communication systems. Dr. Dressler received his M.Sc. and Ph.D. degree from the Dept. of Computer Sciences, University of Erlangen in 1998 and 2003, respectively. In 2003, he joined the Computer Networks and Internet group at the University of Tuebingen. Since 2004, he is with the Computer Networks and Communication Systems group at the University of Erlangen. Dr. Dressler is an Editor for journals such as Elsevier Ad Hoc Networks and ACM/Springer Wireless Networks (WINET). He was guest editor of special issues on self-organization, autonomic networking, and bio-inspired computing and communication for IEEE Journal on Selected Areas in Communications (JSAC), Elsevier Ad Hoc Networks, and Springer Transactions on Computational Systems Biology (TCSB). Besides chairing a number of workshops associated to high-level conferences, he regularly acts in the TPC of leading networking conferences such as IEEE INFOCOM, IEEE ICC, IEEE Globecom, IEEE MASS, and others. Dr. Dressler published two books including Self-Organization in Sensor and Actor Networks, published by Wiley in 2007.

    Dr. Dressler is a Senior Member of the IEEE (Communications Society, Computer Society, Vehicular Technology Society) as well as a Senior Member of ACM (SIGMOBILE), and member of GI (KuVS, Real-time). His research activities are focused on self-organizing networks addressing issues in wireless ad hoc and sensor networks, inter-vehicular communication systems, bio-inspired networking, and adaptive network security techniques.

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