Teletraffic analysis of a hierarchical cellular network

The authors deal with the blocking probability in a hierarchical network. We consider in our model a continuous coverage achieved with micro-cells that accommodate both fresh calls and handover requests. Over this micro-cell coverage, umbrella-cells are implemented. These umbrella-cells only accept handover requests that cannot be managed by the micro-cells. This hierarchy enables one to reduce the handover failure probability. First the blocking probability in the micro-cells is calculated. By modelling the handover flow from micro-cells to umbrella-cells as a Markov modulated Poisson process (MMPP), the blocking probability may be approximated. The probability that a call is dropped before completion is then calculated. The analysis is compared with a computer simulation. The benefits of a two layer coverage (micro-cells and umbrella-cells) are studied for various mobility factors.