Assessment of the access selection gain in multi-radio access networks

In this paper, we investigate the capacity gain of access selection in a multi‐radio access network with heterogeneous radio access technologies (RATs). We classify the kinds of gain that can be achieved by access selection: statistical multiplexing in the multi‐access system leads to a trunking gain, spatial transmission diversity results from the geographic capacity distribution of the cell layout, stochastic transmission diversity exploits the multi‐path fading characteristics. We show how these different properties are affected by the cell layout of the different RATs, the characteristics of each RAT and the traffic load distribution in the network. In a simulation environment the system capacity for the combination of two wide‐area access technologies, as well as, for the combination of a wide‐area and a local‐area access technology is investigated. For this, we compare two different access selection algorithms. One uses the radio link quality as an input parameter, while the other also considers the cell load. We derive quantitative figures for the capacity gain in a large number of scenarios and show that load‐based access selection can significantly increase the capacity. We show that the gain of an overlay of local‐area access cells provides little capacity gain for uniform geographic load distribution, whereas significant gain can be achieved when most users are located at hotspots. Copyright © 2007 John Wiley & Sons, Ltd.