Investigation of the algorithm to reduce the impact of CSI-RS on LTE legacy UEs

CSI-RS (Channel State Information Reference Signal) is designed for higher-order MIMO in LTE-A. However, it could be problematic for LTE legacy UEs in a LTE-A network deployed higher-order MIMO because LTE UEs cannot distinguish CSI-RS from effectual data. In this paper, the impact of CSI-RS on LTE UEs are firstly evaluated by both link-level and system-level simulations. The evaluation results show that the degradation of LTE UEs´ performance caused by CSI-RS is obvious when the coding rate and modulation scheme are too large. To reduce the performance degradation, two mechanisms, named SLA (Smart Link Adaption) and SS (Smart Scheduling), are investigated and compared. Furthermore, an adaptive ND (Novel Decision) algorithm is proposed to adaptively select a more suitable mechanism according to the proportion of the LTE legacy UEs in the system. Theoretical analysis and simulation results show that the proposed algorithm is effective to maximize the improvement of the system performance.