Research On Interference Management Strategies For Lte-Advanced Systems

As one of the standards of IMT-Advanced, LTE-Advanced system has taken a variety of novel techniques such as enhanced MIMO and heterogeneous networks,, which proposes tiered network cell-aliasing coverage as an effective solution of traditional cellular wireless networks. Deployed with different needs of applications, services and coverage, heterogeneous networks provide users with higher data rates and better service experience.However, since heterogeneous networks are characterized by the coexistence or overlay of macro cells and local low-power cells, local eNodeBs not only provide coverage at the customer premises, but also generate interference toward neighboring houses as well as outdoors, causing dramatic degradation of the existing macro cells and local cells’ performance. Therefore, effective interference management strategies in LTE-Advanced heterogeneous networks need to be provided.Following aspects are covered in this thesis:In order to study the interference management strategies in heterogeneous network scenarios more effectively, an LTE-Advanced downlink system-level simulation platform is established first to evaluate the proposed scheme and algorithms, with results well verified. The platform is mainly designed for Macro-Pico tiered heterogeneous networks, which also has good scalability to support other scenarios by adding necessary modules.For the deployment issues of Macro-Pico heterogeneous networks, factors affecting the system performance are analyzed first. Then important issues on Macro-Pico deployment are studied through system-level simulation. Results show that the system performance of Macro-Pico networks can be greatly improved with good principles in pico eNodeB deployment, i.e. large Macro-to-Pico distances, relatively high transmit power, high deployment density and an optimal value of CRE bias.In order to mitigate both the co-tier and cross-tier interferences, a dynamic spectrum allocation scheme is proposed for Macro-Pico scenario. The available system spectrum is divided into different parts by four steps, i.e. user set partition, service request collection, cross-tier occupation and CRE occupation decision, while the service request of each user is taken into consideration. During the process implementation, the RSRP threshold is derived by mathematical means to judge cell edge macro users when a predefined ratio is given. Simulation results show that the proposed scheme reaches almost the same cell edge performance with the best existing option, meanwhile provides higher overall system throughput and better spectral efficiency. Therefore, much better balance is achieved.Cell range extension is an effective technique to achieve load balance in heterogeneous networks. Thus an adaptive bias configuration strategy is proposed, where the bias value is set adaptively according to the environment variability. Based on this strategy, another dynamic and distributed bias setting scheme is also proposed for LTE-Advanced Macro-Pico heterogeneous networks. The worst user throughput of each cell during an adjusting time interval is mainly employed to change the bias values, where an indicator is introduced to freeze the possibility of increasing biases if needed. Furthermore, to achieve low overheads and computational complexity, the silent state and coarse control process are also defined. Simulation results show that both the two proposed schemes can remarkably improve the cell edge performance compared with the static bias setting strategies, while maintaining the overall cell performance at the same time.