5.1 Introduction

When there is a single bandwidth to be shared between the microcell and the macrocell layers in a mobile cellular telecommunications system with a HCS, spectrum partitioning becomes an important issue. The optimal amount of bandwidth has to be given to every layer so that the overall blocking in the HCS is at a minimum.

Spectrum partitioning is a function of several parameters but depends primarily on the speed of users in the microcells and macrocells and on the number of microcells overlaid by a single macrocell.

This chapter contains a teletraffic analysis to model a hierarchical cellular structure formed of two layers and a dynamic method to divide the spectrum. Both the teletraffic analysis and the spectrum partitioning technique are based on more general methods that have previously been presented individually in the literature. They are combined, after some modifications, to perform the partitioning.

Although in the rest of this book a grade of service (i.e., blocking probability) of 1% is always ensured in the evaluation of system performances, in this chapter the spectrum partitioning is calculated using the criterion that the blocking probability in each layer (macrocellular and microcellular), when allowing overflow traffic from microcells to macrocells, ensures a grade ofservice of 2%. This is done for a reason. At the end of this chapter a comparison is made between the results obtained with the methodology given here and those previously obtained by an older method of spectrum partitioning that used a criterion of 2% in...