Session C
Tom Van Leeuwen, Ingrid Moerman, Hendrik Rogier, Bart Dhoedt, Daniël De Zutter and Piet Demeester
Broadband Wireless Communication in Vehicles Today our society is struggling more and more with environmental and economical problems related to the ever-increasing traffic on our highways and in our cities. The resulting traffic jams give rise to waste of time and money and are polluting our environment at a rapid pace. As a result, carpooling and public transport will be strongly encouraged by governments and industry. In order to make this more attractive to the frequent commuter, novel technologies for providing virtual offices or virtual homes in vehicles need to be developed. In order to provide high-bit-rate interactive multimedia services to fast-moving mobile users, one has to reuse the limited radio spectrum as efficiently as possible. This is made possible by using a cellular network with very small cells resulting in a high reuse factor of the frequency spectrum. This will result however in frequent handovers (typically every few seconds) because mobile devices may move very fast, crossing many cell boundaries. This paper discusses the major issues related to broadband wireless communication in vehicles, with special emphasis on the handover protocols and smart antennas and their influence on the quality of service (QoS) of the offered services.
Introduction
Authors Tom Van Leeuwen, Ingrid Moerman, Hendrik Rogier, Bart Dhoedt, Daniël De Zutter, Piet Demeester Ghent University, Belgium Contact: Ingrid Moerman Department of Information Technology (INTEC), Ghent University – IMEC, Sint Pietersnieuwstraat 41 B-9000 Ghent, Belgium. Tel: +32 9 267 35 73 Fax: +32 9 267 35 99 Email:
[email protected]
There is no doubt that the Internet is one of the biggest success stories in the history of information and communication technology. Due to its elegant design, it can not only offer us the World Wide Web and email but also various multimedia services like videoconferencing, online gaming and video on demand. On the other hand, mobile and wireless technologies have experienced an unprecedented boom in the last decade. One of the big challenges yet to come, is to merge these two worlds into an all-IP worldwide communication network. Mobile users want to move freely without any disruption in their active multimedia applications: they demand the same quality of service as in the case of wired access. This will enable car-poolers and commuters
to continue their professional activities from their mobile terminal on their way to their job or during a business trip (virtual office), to be connected to their personal home network (virtual home), to participate via videoconferencing at a meeting, to watch a streaming video during a long trip, to play interactive video games, to have continuous access to tourist information, etc1. There are already signs that in hot spots, with low user mobility, this is technically feasible, relying, for example, on the Universal Mobile Telecommunications System (UMTS) and public wireless local area networks (WLANs). But for mobile terminals moving at vehicular speeds, the so-called ‘virtual office’ or ‘virtual home’ is far from a reality. In this paper we discuss the problems we are facing and how they could be tackled.
The Pitfalls Bandwidth shortage The common literature on wireless and cellular systems is clear about one thing: the available bandwidth, in terms of bit rate, for mobile users moving at vehicular speeds is inversely related to their velocity (Figure 1). This implies that the popular Internet applications are not yet available at vehicular speeds, due to the lack of high bandwidth and quality of service. When today’s commuters, for example in a train or in a car, want to access the Internet, they see themselves restricted to simple web surfing or email. Table 1 shows the requirements of some multimedia Internet applications in terms of required data rate, maximum tolerable delay, maximum tolerable packet loss and IP traffic behaviour. Interactive multimedia services, like online gaming and videoconferencing are still unavailable to them, even with promising new technologies like UMTS or WLAN. We further note that some applications, such as video, are not yet adapted for transmission over the Internet. Today’s available video codecs (such as MPEG) are optimised for minimal data storage and lead to very non-uniform data traffic with peak data rates that are much higher than the average data rate. This complicates traffic engineering and quality of service (QoS) support mechanisms a lot. 1
Session C
Figure 1 Mobility versus data rates for various wireless technologies: there is no broadband support for fast-moving users With current cellular technologies, like UMTS, fast-moving users are switched to larger cells to reduce the handover frequency and see themselves restricted to lower data rates. In addition, if the future wireless networks are evolving towards all-IP packetbased access networks, the handover protocols will have to make handovers at the network level as well. Existing IP-based handover protocols make a trade-off between packet loss and handover latency, and Table 1 shows that multimedia applications, like video and voice, are very sensitive to this. The current protocols also suffer from scalability issues when multiple fastmoving subscribers are in play.
4G Cellular 3G Cellular 2G Cellular (for example, GSM) (for example, UMTS) (research only)
Beyond 4G (future research)
Vehicle
Mobility
Walk
Wireless LAN
Bluetooth
LAN
Fixed 0.1
1
10
100
Data Rate (Mbit/s)
Tackling the Problems Table 1 Multimedia requirements Voice
Data
Video
< 100 ms
–
< 100 ms
