Abstract
OFDMA is accepted as the most appropriate air-interface for 4G OFDMA based systems by both researchers in industry and academia. A major problem that arises in OFDMA based systems is intercell interference that stems from aggressive frequency reuse and is particularly worse in cell-edge areas. Therefore, Inter-Cell Interference Coordination (ICIC) has been proposed as a promising method to mitigate inter-cell interference (ICI) mainly in the overlapping (cell-edge) areas of a multi-cell cellular network. The main objectives of this thesis are to investigate inter-cell interference in a heterogeneous system comprising of both macro and femto cells, propose and evaluate less complex novel inter-cell interference coordination/avoidance techniques that increase both cell-edge throughput and overall cell throughput. Initially, our scenario focuses on the investigation of co-channel interference in macrocell deployments. In this direction, we propose a static ICIC technique for OFDMA macrocell networks based on cyclic difference sets a branch of combinatorial mathematics to minimize the inter-cell interference. Then, we formulate the dynamic ICIC problem in a linear way in order to minimize the complexity issues with the scalability of the problem. We show that with minimal loss of optimality, this linear problem can be simplified into two smaller problems i. e. the multi-user scheduling (base station) problem and the multi-cell scheduling (network) problem. Simulation results confirm the increased effectiveness of proposed ICIC schemes in both metrics (i. e. cell-edge and total cell throughput) over a number of state-of-the-art (static and dynamic) interference avoidance schemes. After, the ICIC technique is optimized to minimize the total transmit power by employing inter-cell and intra-cell power control without compromising the cell-edge throughput. Here, we formulate the multi-objective problem as a multi-dimensional knapsack problem. Our simulation results of the proposed scheme show its increased energy efficiency and user fairness compared with the state-of-the-art energy efficient schemes. Finally, the complexity of the ICIC problem and the need of a centralised controller are further reduced in order to benefit small-cell deployments. Here, it is shown that the complexity of the ICIC version can be further reduced by employing a dual decomposition method from optimization theory. Extensive simulation results show a significant improvement of the proposed scheme compared with some distributed reference schemes in terms of cell-edge and total cell throughput and thus it is a promising candidate for next generation mobile systems.