Inter-cell Interference Mitigation for Mobile Communication System
Xiaodong Xu, Hui Zhang, Qiang Wang · InTech eBooks · 2011
With the commercialization of 3G mobile communication systems, the ability to provide diversiform data services, high mobility vehicle communication experiences and asymmetrical services are enhanced further than 2G systems.But at the same time, users still have higher requirement for high-rate and high-QoS mobile services.Many international standardization organizations have launched the research and standardization of 3G evolution system, such as 3GPP Long Term Evolution (LTE) and LTE Advanced project.The primary three standards of 3G are all based on Code Division Multiple Access (CDMA), but with the in-depth research of Orthogonal Frequency Division Multiplexing (OFDM) techniques, OFDM has been emphasized by the mobile communication industry and used as the basic multiple access technique in the Enhanced 3G (E3G) systems for its merit of high spectrum efficiency.OFDM becomes a key technology in the next cellular mobile communication system.As the sub-carriers in the intra-cell are orthogonal with each other, the intra-cell interference can be avoided efficiently.However, the inter-cell interference problems may become serious since many co-frequency sub-carriers are reused among different cells.Under this background, how to mitigate inter-cell interference and improve the performance for cellular users for vehicular environments become more urgent.In this chapter, the research outcomes about Intel-cell Interference Mitigation technologies and corresponding performance evaluation results will be provided.The Intel-cell Interference Mitigation strategies introduced here will include three categories, which are interference coordination, interference prediction and interference cancellation respectively. Inter-cell interference coordinationFrequency coordination plays important roles in the Inter-cell Interference Coordination scheme.For frequency coordination, one frequency reuse based Interference Coordination scheme will be introduced, called as Soft Fractional Frequency Reuse (SFFR).Its frequency reuse factor will be derived.Simulation results will be provided to show the throughputs in cell-edge are efficiently improved compared with soft frequency reuse (SFR) scheme. www.intechopen.comAdvances in Vehicular Networking Technologies 358 Especially, for Coordinated Multi-point (CoMP) transmission technology, which is the promising technique in LTE-Advanced, a novel frequency reuse scheme -Coordinated Frequency Reuse (CFR) will be introduced, which can support coordination transmission in CoMP system.Simulation results are also provided to show that this scheme enables to improve the throughputs in cell-edge. Soft fractional frequency reuseIn order to improve the performance in cell-edge, the SFFR scheme is introduced, which is based on soft frequency reuse.As shown in Fig. 1, the characteristics of such reuse schemes are given as follows: the whole cell is divided into two parts, cell-centre and cell-edge.In cell-centre, the frequency reuse factor (FRF) is set as 1, while in cell-edge, FRF is dynamic and the frequency allocation is orthogonal with the edge of other cells, which can avoid partial inter-cell interference in cell-edge.Specially, users in each cell are divided into two major groups according to their geometry factors.In cell-edge group, users are interference-limited due to the neighbouring cells, whereas in cell-centre group users are mainly noise-limited.The available frequency resources in cell-edge are divided into non-crossing subsets in SFFR.