Small cells, mainly femtocells, are believed to be a way how to deal with mobile data traffic growth in the upcoming years. To enable easy and massive femtocell deployments, a distributed method of Physical Cell Identifier (PCI) assignment should be implemented in Femtocell Access Points among other self-organizing functionalities. In this paper, we propose such a distributed algorithm enabling correct PCI assignment in a collision-free manner and resolving all confusion events based on neighbouring cells' PCIs. The proposed algorithm is compared with the classical random algorithm by taking into account various femtocell densities, PCI ranges and sizes of neighbourhood area. Based on obtained results, the proposed algorithm leads to fewer confusion events and lower signalling network overhead even in dense femtocell environments such as office buildings or homes in city centres.

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In this chapter, the authors deal with a mechanism of Physical Cell Identifier (PCI) assignment for dense femtocell scenarios within LTE/LTE-Advanced networks. After describing the need for femtocells in future Self-Organizing Networks (SONs), the problem is presented. The chapter discusses background information such as related works in this research field and current assignment methods. Subsequently, challenges are defined, and two mechanisms to assign PCIs are proposed. Both the mechanisms are capable of assigning collision-free PCIs and solving any future confusion events that may occur as the network grows in terms of the number of femtocells. To evaluate the algorithms, a model is described and simulation results for two different scenarios are presented.