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Conventional Traffic and Travel Information (=I) systems are based on a centralized structure: Sensors deployed at the roadside nwnitor the traffic and transmit the results to a central unit, which performs a situation analysis. P I is made available to the drivers via bmadcast service (e.g. TMC/RDS) or on demand via cellularphone. In contrast to this centralized approach, a decentralized, Self-organizing Trafic Information System (SOTIS) based on Inter-Vehicle Communication ( W C ) has many advantages: It requires no eqensive. infrastructure, can pmvide detailed information for the local area with low delay and is available everywhere. In such an N C based decentralized system, TTI is sensed by each individual vehicle. The information is analyzed, combined with TTI receivedf" other vehicles and the results are distributed using recurring bmadcast packets.In this paper; an adaptive bmadcast scheme for efficient TTI distribution called Provoked Broadcast is presented. The algorithm favors the propagation of signijicant TTI changes within the self-organizing neiwork Nodes adapt their communication behavior to the local envimnment and avoid redundant transmissions. n e performance of the proposed scheme is evaluated by using simulations of iypical trafJic scenarios. Compared to a strictly periodic broadcast, the new scheme decreases the average ermr of information available at an individual vehicle and still requires signifcantly less bandwidth.

Cellular networks and wireless local area networks (WLAN) are being widely deployed for mobile radio communications Taking into account the advantageous and drawbacks of both network architectures, it becomes obvious that a combination of them is the logical consequence for future mobile radio networks. The scope of this paper is to introduce a future radio network architecture called hierarchical multihop cellular network (HMCN), which includes several multihop cells. The overlaying cellular network coordinates multihop cells in order to reach an optimal load balance in the whole network. The next evolutionary step towards a HMCN structure is to introduce multihop capable nodes (MHNs), which can be fixed or even mobile. The paper shows the challenges and benefits of multihop with fixed nodes, especially the placement of fixed MHNs and reduction of radio protocol overhead io order to provide high performance. When MHNs are normal mobile nodes, multihop routing becomes a key point in the HMCN concept. The paper proposes a cellular based routing scheme and compares it with the ad hoc routing algorithms being developed by IETF.Keywords -Cellular networks, multihop cells, WLAN, future radio networks I. INTRODUCTIONRecently, two types of mobile communication systems have been realized Cellular systems like GSM, GPRS and UMTS and so called wireless local area networks (WLAN), e.g.IEEE802.11 or HIPERLANI2 [3]. The latter systems provide an infrastmcture mode to provide high-speed access to the Internet, and additionally a so-called ad hoc mode without the need of an inhtructure for spontaneous communication between devices. Unlike systems providing an ad hoc mode, cellular systems rely on an i n h t m c t u r e of base stations (BS) and require network-planning and operation in licensed radio spectrums with narrow frequency bands to provide 1 1 1 coverage and the required grade of service (GoS). The traditional application in cellular systems like GSM is speech communication. For mobile data communications with data rates up to 2Mbit/s a new generation of cellular systems, called U M T S , is being developed. This cumulative data rate is still not enough for hot spot areas where the number of mobile nodes (MNs) per area is higher than that of network specifications. To increase the individual data rate of users, WLAN systems are introduced, which can provide transmission rates of 0-7803-7589-0/02/$17.00 02002 IEEE 54