LTE Downlink Inter-Cell Interference Assessment in an Existing GSM Metropolitan Deployment

In a loaded 1-reuse cellular network as e.g. 3GPP Long Term Evolution (LTE) the inter-cell interference limits the user bitrate for link adaptive packet data access. The cell isolation together with the link performance defines the spectrum efficiency and the achievable gain of higher order modulation or other link improving features. In this paper the cell isolation is measured as geometry factor in a dense city network. The measurements are performed on commercial GSM live traffic capturing the real spatial distribution including indoor usage. The cell plan of the studied metropolitan network is found to be very good and well optimised with the potential to support high user bitrates and high capacity for future LTE high speed radio accesses. The measured geometry factor distribution is superior to those that have been used for capacity evaluations in 3GPP indicating good performance of a possible LTE in existing deployments. A very good match between the live traffic measurements and simulations is found when introducing a tilted 3D antenna model into the cellular radio network simulation environment. Further, the tilted 3D antenna model results in a more realistic amount of interfering cells experienced at simulation estimations of spectrum efficiency.