A Reversible Hierarchical Scheme for Microcellular Systems with Overlaying Macrocells

Future cellular systems are expected to use multilayered, multisized cells to cover non-homogeneous populated areas. An example in literature is given by a 2 level hierarchical architecture in which an overlaying macrocell provides a group of overfow channels utilized when a microcell, which covers a densely populated area, is not able to accommodate a new call, or a handoverpom another microcell. The macrocell has the higher hierarchical position, meaning that it can receive handover requests @om microcells, lower in the hierarchy, as well aspom other macrocells. On the contrary, a call served by the macrocell cannot handover to a microcell. This paper proposes a Reversible Hierarchical Scheme characterized by the presence of handover attempts @om macrocells to microcells. The scheme is conceived so that the microcells are given the majority of the traflc load as they are able to operate with very high capacity, while the macrocells, having lower channel utilization, can better carry out their support task. An analytical study is carried out showing that the system performance can be improved, at the expense of relatively little increase of network control overhead, when compared with the classical, i.e. Non Reversible, Hierarchical Scheme.