A study on hierarchical cellular structures with inter-layer reuse in an enhanced GSM radio network

In today´s cellular networks it becomes harder to provide the resources for the increasing and fluctuating traffic demand exactly in the place and at the time where and when they are needed. Moreover, frequency planning for a hierarchical cellular network, especially to cover indoor areas and hot-spots is a complicated and expensive task. Therefore, we study the ability of hierarchical cellular structures with inter-layer reuse to increase the capacity of a GSM (Global System for Mobile Communications) radio network by applying total frequency hopping (T-FH) and adaptive frequency allocation (AFA) as a strategy to reuse the macro- and microcell resources without frequency planning in indoor picocells. The presented interference analysis indicates a considerable interference reduction gain by T-FH in conjunction with AFA, which can be used for carrying an additional indoor traffic of more than 300 Erlang/km², i.e. increasing the spectral efficiency by over 50%, namely 33 Erlang/km²/MHz. From these results we draw a number of general conclusions for the design of hierarchical cellular structures in future mobile radio networks. For example, we may conclude that they require reuse strategies that not only adapt to the current local interference situation, but additionally distribute the remaining interference to as many resources as possible. For a hierarchical GSM network this requirement is fulfilled by the T-FH/AFA technique very well