A PCI planning algorithm for jointly reducing reference signal collisions in LTE uplink and downlink

Abstract

In this paper, a novel automatic planning method is proposed for allocating Physical Cell Identifiers (PCI) to cells in a Long Term Evolution (LTE) system based on handover and cell load measurements. The method aims at avoiding PCI collision and confusion problems, while reducing Reference Signal (RS) collisions between neighbor cells. For this purpose, the problem is formulated to consider RS collisions both in DownLink (DL) and UpLink (UL). Then, a classical graph partitioning algorithm is adapted to solve the graph coloring problem behind PCI planning. The considered algorithm is the multi-level version of the Fiduccia and Mattheyses local refinement algorithm. Performance assessment is carried out on graphs constructed from data collected in live LTE network. Results show that the proposed algorithms can avoid PCI collision and confusion problems, while reducing DL RS collisions and almost eliminating UL RS collisions compared to a random plan.