An evolved cellular system architecture incorporating relay stations

Shrinking cell sizes, primarily a result of keeping up with the increasing demand for higher data rates, are stretching thin the notion of our traditional cellular system architecture. More and more base stations are serving smaller and smaller areas (cells) which in effect is driving up deployment costs. The option of deploying relay stations is increasingly beginning to look like a solution to the problem of providing a cost-effective way to extend the coverage and capacity in a cellular network. A relay station can be used to extend the point-to-multipoint link between the base station and mobile stations. Relay stations connect to the base stations without wires and are expected to be deployed to cover smaller geographic areas. Primarily the deployment costs but also the equipment costs are expected to be substantially lower than those of base stations. In this article we first introduce the relay station and discuss the place it is likely to carve out for itself in the traditional cellular architecture. We highlight the important economic and performance benefits relay stations could potentially offer, and outline a few scenarios where relays are likely to be deployed in the beginning. The multihop relay standard developed by the IEEE 802.16 working group is then used as a basis to provide an overview of the relay-enhanced cellular architecture and the key choices that can be made in developing relay support within a cellular system-a precursor to what can be expected in later releases of the Mobile WiMAX system. Finally, we discuss some future directions in the development of relay systems.