Inter-Cell Interference Coordination In LTE System

In LTE systems, the SC-FDMA and OFDMA technique are used for uplink and downlink transmission, respectively. Because of the orthogonal feature, the intra-cell interference is mostly mitigated and can be ignored. But to the inter-cell interference (ICI), when the frequency resource is universally reused in each cell of the system, users, especially at the cell edge, will suffer from high interference from neighboring cells and therefore weak signal quality. More recently the ICI problem has become the key issue in OFDM based cellular networks. To reduce ICI and improve the system performance, inter-cell interference coordination (ICIC) techniques which coordinate the frequency resource and the power resource in multi-cell systems, are proposed and have drawn more and more attention. For example, IEEE802.16m and3GPP LTE systems explicitly require ICIC techniques as the basic system functionality.In this paper, the main research is divided into three parts:frequency coordination, power coordination and ICIC information design. Our main work and contributions are:Firstly, in frequency coordination, the SFR system model and problem formulations are proposed. Then the user distinguished methods and three different resource allocating orders are analyzed. Finally, a novel uplink interference coordination scheme by associating the cell-specific HII design with two simplified HII based methods (CEBS and CCBA) for the uplink ICIC in4G LTE systems. The proposed NHFR scheme has been carried out by means of a reliable semi-static system level simulator. Under some reasonable assumptions, the proposed NHFR scheme provides very promising results, not only increasing the spectral efficiency but also reducing the blocking probability obviously. So to enhance the LTE performance, the proposed scheme will be a very helpful recommendation.Secondly, in power coordination, to overcome the negative effect of inter-cell interference fluctuation, an uplink interference coordination scheme by combining HII with01is proposed for the OFDMA wireless system. While the earlier traditional schemes aim to improve rate of users in the whole network or at the cell edge, the proposed scheme considers the requirement of users’ communication quality and targets the satisfaction of all users in the network. In practice, CCBA based high interference indicator (HII) and FPC using overload indicator (OI) defined in LTE R8Standard are jointed for the first time. The simulation results show that the proposed scheme improves user satisfaction significantly compared with the traditional ICIC schemes.Thirdly, in the ICIC information design, an interference coordination scheme adapting to traffic load is proposed for the LTE system. The proposed scheme calculates HII messages based on the optimal interference thresholds. Using the optimal thresholds of the specific traffic load, the scheme applies the cell center bandwidth avoidance (CCBA). The simulation results show that the proposed scheme improves average SINR and spectral efficiency significantly compared with the traditional schemes. We obtain the optimal interference thresholds at different traffic load by Monte Carlo simulation and theoretical analysis, and interference thresholds obtained by the two approaches are very accordant.Finally, to enhance the performance of the LTE systems, the proposed solution is a good candidate for practical systems, and will be a very helpful technology recommendation.