Investigation of Multi-Hop Cellular Networks

The preferred air interface for future mobile communication systems is WCDMA. WCDMA is inherently an interference-limited system. If a mobile is near the coverage boundary of a given cell, it has to use a high transmission power to be able to reach the base station, which generates high interference to the neighbouring cells. As a result of this, the capacity of the overall system is reduced. Hence, as we try to increase the coverage of a cell, we are effectively reducing the capacity of the system, and vice versa. A possible solution to this coverage-capacity trade off is to extend the currently centralised cellular networks, where every communication has to pass through the base station, towards multi-hop cellular networks where there is a possibility of relaying. By breaking down connections that require high transmission power into a set of smaller quasi line of sight "hops", the total transmission power can be reduced. This is expected to result in a simultaneous increase of coverage and capacity of a cellular system. The preliminary investigation and identification of main challenges of such systems have been carried out. The main challenges include the choice of radio access technique (whether to use FDD or TDD), how to do the packet routing, how to handle longer connection establishment and longer round trip time (due to the routing involved), incentives for relaying (why would a user relay a packet for the sake of others?), and billing (how to handle billing if peer-to-peer connections are allowed). This project was part of the ongoing project, "Future Adaptive Communication Environment" (FACE) within the Department of Communications Technology. The project was ended by March 2003. (Oumer Teyeb, Laurent Schumacher, Preben E. Mogensen)