Performance of a reversible hierarchical cellular system

In order to provide mobile worldwidecommunication services, cellular systems can be based ona multilayered, multisized cells architecturecharacterized by the use of different technologies.Satellites can cover lightly populated areas, as well asthose areas where other means cannot be used (like thesea); fixed base stations, with different transmissionpowers and thus different cell sizes, can cover relatively highly populated areas. As a result,a given area could simultaneously be served by more thanone Base Station, and the structure of such a systemmust be carefully designed. A Hierarchical Architecture(HA) scheme is a possible solution. HA is based on amultilevel cell configuration: microcells (or evenindoor picocells) cover more densely populated areas andare given the majority of the traffic load as they are able to operate with very highcapacity, while overlaying macrocells (or satellitarcells) provide a group of overflow channels.Occasionally, when microcells are not able to satisfychannel requests, the overflow channels are consumed.HA schemes are divided in two categories: ReversibleHierarchical (RH) and Non Reversible (NRH). Thedifference is given by the handover directions between cells allowed. In a RH handover, attemptsbetween macrocells and microcells occur in bothdirections. This paper compares RH and NRH schemes bymeans of an analytical model based on birth-deathprocesses. The main performance indexes and the controloverhead are shown.