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
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Interoperation of different fixed and mobile networks is one key feature of systems beyond 3G, specifically between wireless local area networks, covering hot-spots with high data rates, and mobile cellular systems with full coverage. This comprises the vertical handover, i.e. the handover between systems with different air-interfaces, which are investigated in the paper. In contrast to several approaches that investigate solutions for the IP layer, the focus of the paper is on mechanisms on the link layer to improve the handover, respectively scanning other airinterfaces, measurements and appropriate triggers from the link layer that are considered in the handover decision process. Finally, the benefits for the handover performance are indicated and the potential of the proposed new concepts is highlighted.
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