Research And Implementation On TD-LTE System Downlink Link Adaptation

To cope with the challenge from the new wireless access technology like WIMAX, and to meet the badly demand of wireless network access,3GPP came up with the 3G long term evolution (LTE) project. The LTE project is to provide higher transmission rate with more series of service, while the customers’ pay bill can be declined. Nowadays, the LTE system has come to commercialization by Amercia operator Verizon. The stardardization of LTE Advanced is approaching to the end.This paper emphasizes the link adaptation of LTE system downlink. Compared with 3G system which is based on the Code Division Multiple Access (CDMA), for the sake of no intra-cell interference, the fast power control is no longer the core function of lte link adaptation, and the Adapative Modulation Coding (AMC) becomes the most important. A dynamic system level simulation platfonn is set up to research the lte system, which is supported by the major national science and technology fund. The implementation of lte link adaptation has been studied, and some functions have been realized in this simulation platform. To be precise, the Channel Quality Indication (CQI), Rank Indication (RI) and Precoding Matrix Indication (PMI) are the core function of downlink link adaptation; while the Hybrid ARQ (HARQ), Out Loop Link adatation (OLLA) and MIMO transmit mode adaptation are the compensations of the core function. A comprehensive link adaptation module of the lte downlink has been finished as above.With the help of link adaptation algorithm in the simulation platfonn, the radio resource management (RRM) of lte physical downlink control signal is studied. Different with 3G system, all the service transportation in the LTE system are carried on the downlink share channel, which means the downlink control channel design is more difficult. To make the simulation platform throughput tests more accurate, we have taken the effects of downlink control channel into consideration and a downlink control channel radio resource management module has been finished. Considering that the performance and response speed can’t conside, an appropriate CCE mapping algorithm is used, so is the link adaptation algorithm. Finally, a simulation is presented to verify the module.The Mobility Load Balancing (MLB) which is one of the use cases in the Self Optimization Network (SON) is also studied in this paper. Referring to the specifications and proposals of 3GPP and considering the platform current situation, we have implemented an applied MLB algorithm in the system simulation platform, which has exploited the existing results of link adaptation in order to evaluate the shift load. At last, we present a simulation case to test it.