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Layer-independent PCI assignment method for Ultra-Dense multi-layer co-channel mobile Networks

Ultra-Dense Networks (UDNs) are Heterogeneous Networks (HetNets) that deploy a high density of small cells over-laying the traditional macro cells. If several Long Term Evolution (LTE) layers share the available spectrum, assigning the Physical Cell Identities (PCIs) becomes complicated due to the density and the diversity of the network. Since different layers can be managed by different Network Management (NM) and Self-Organizing Network (SON) solutions, it would often be desirable to be able to assign the PCIs in each layer independently. At the same time it must be ensured that the PCI conflicts, also between the layers, are minimized. When the small cell layer is managed independently, high cell density increases the probability that two small cells sharing the same PCI are neighbors to the same macro cell, thereby creating a conflict in inter-layer adjacencies, even when within the layers PCI conflicts are avoided. We propose a method that can minimize these inter-layer conflicts, while still allowing independent assignment between the layers. Starting with an initial intelligent guess for adequate PCI reuse distance, the solution then uses the Automatic Neighbor Relation (ANR) function to learn the full multi-layer network topology and optimize the PCI assignment. Comparing with state of the art strategies, our results show that the proposed approach maintains good performance without requiring the exchange of information across layers.