Hierarchical cell structures with adaptive radio resource management

In order to increase the growing capacity demands of cellular mobile communication systems, cell splitting will be applied and/or small pico-cells will be established, since both measures can increase spectral efficiency. Hierarchical cellular networks have been suggested previously to overcome the inherent disadvantage of an increased number of handoffs, which both cell splitting and small pico-cells, bring about. A critical question with respect to hierarchical cellular networks is how to divide the available radio resources (i.e. frequencies, channels) among the micro- and macro-cell layers in an optimal way. Another important aspect is the optimal choice of a threshold velocity above which users are assigned to the macro-cell layer Most research in this area so far has dealt with those issues in a static way, assuming fixed traffic and mobility parameters. However in order to be able to adapt the system parameters to temporal and spatial changes of traffic and mobility properties, in this paper two adaptive algorithms are described, which control the threshold velocity as well as the division of resources among the layers, dynamically. The performance of those algorithms is evaluated by means of computer simulations.