Physical Cell ID Allocation in Cellular Networks

Abstract: In LTE networks, there are several properties that need to be carefully planned for thenetwork to be well performing. As the networks’ traffic increases and the networks aregetting denser, this planning gets even more important. The Physical Cell Id (PCI) is theidentifier of a network cell in the physical layer. This property is limited to 504 values, andtherefore needs to be reused in the network. If the PCI assignment is poorly planned, therisk for network conflicts is high. In this work, the aim is to develop a distributed approach where the planning is performedby the cells involved in the specific conflict. Initially, the PCI allocation problem isformulated mathematically and is proven to be NP-complete by a reduction to the vertexcolouring problem. Two optimisation models are developed which are minimising thenumber of PCI changes and the number of PCIs used within the network respectively. An approach is developed which enlargers the traditional decision basis for a distributedapproach by letting the confused cell request neighbour information from its confusioncausingneighbours. The approach is complemented with several decision rules for theconfused cell to be able to make an as good decision as possible and by that mimic the behaviourof the optimisation models. Three different algorithms are implemented using theapproach as a basis. For evaluation purpose, two additional algorithms are implemented,one which is applicable to today’s standard and one inspired by the work by Amirijoo et al. The algorithms were tested against three different test scenarios where the PCI rangewas narrowed, the number of cells was increased and the network was extended. Thealgorithms were also tested on a small world network. The testing showed promisingresults for the approach, especially for larger and denser networks.