Improving fractional frequency reuse (FFR) for interference mitigation in Multi-tier 4G wireless networks

Master Thesis


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University of Cape Town

The need to provide quality indoor coverage for mobile network users in an indoor environment has become paramount to communication service providers (CSPs). Femto-cells due to their low capital expenditure (CAPEX) and operating expenditure (OPEX) have seen widespread adoption as a possible solution to the indoor coverage challenge. The major drawback of its adoption is the possibility of erratic but significant interference to both the Femto-cell and the Macro-cell tiers owing to their Ad-hoc mode of deployment. The Fractional Frequency Reuse (FFR) is an interference mitigation scheme, due to its effectiveness and low complexity; it has been proposed to be an efficient technique of solving the problem of interference in the cross-boundary region. In this study, a critical analysis of the existing schemes revealed that Femto-cell users at the border between the cell centre region (CCR) and the cell edge region (CER) suffer cross-boundary interference. An algorithm that integrates a buffer zone between the existing CCR and CER has been developed to solve the cross-boundary interference challenge experienced by the Femto-cell users. A system level simulation implemented in MATLAB was used to evaluate the developed algorithm. The network performance (in terms of user-achieved signal-to-interference-plus-noise ratio (SINR) and its daughter metrics such as channel capacity and throughput) was estimated. In terms of the SINR, the performance improvement recorded for Femto-cell users at the border region after the implementation of the buffer zone was more than eighty per cent (80%). There were significant improvements in terms of the channel capacity and throughput for the Femto-users present at the buffer region with the implementation of the developed algorithm.

Includes bibliography.