Scalable HetNet interference management and the impact of limited channel state information

Abstract

Interference management is important in wireless cellular networks such as long-term evolution (LTE) and LTE-A, where orthogonal frequency division multiple access (OFDMA), dense frequency reuse and heterogeneous cell sizes and capabilities provide great performance at the cost of increased network complexity. The layered structures of emerging cellular networks and their dynamic environments limit greatly the efficacy of traditional static interference management methods. Furthermore, conventional interference coordination techniques assume that perfect channel knowledge is available and that the signalling overhead can be neglected. In this paper, we analyse a heterogeneous LTE OFDMA downlink network composed by macro-, pico- and femtocells. We propose a low-complexity, distributed and cooperative interference mitigation method which is aware of network load and propagation conditions. The proposed method is fully scalable and addresses the interference received by the macro and pico layer and the interference received by femtocells separately. The new solution makes use of the iterative Hungarian algorithm, which effectively reduces interference and enhances the quality of service of starved users when compared to other state-of-the-art solutions. The proposed method outperforms static solutions by providing comparable results for the cell edge users (the proposed solution delivers 86% of the gain of a static frequency reuse 3) while presenting no loss at the cell centre, compared to an 18% loss of the frequency reuse 3 in a homogeneous scenario. In a heterogeneous network (HetNet) deployment, it generates a gain of 45% for the combined macro and pico edge users at a very small cost for the cell centre lower than 4% when compared with standard resource allocation. It optimizes greatly picocell performance, with improvements of more than 50% at a small cost for femtocell users (15%). In order to apply the proposed method to a practical network, the impact of the necessary quantization of channel state information on the interference management solution is studied and results show that signalling overhead can be contained while performance is improved by increasing resolution on the portions of the bandwidth more likely to be assigned to the users.