Research On Link Adaptation And Adaptive MIMO Mode Selection Technologies In TDD LTE Downlink

MIMO-OFDM are the key technologies in LTE (Long Term Evolution) system, LTE provide high speed broadband data services that can satisfy people’s requirement for high quality multi-media services. Various MIMO transmission modes defined in LTE protocol is the key to guarantee high throughput in LTE system. However the environment of mobile communication is complex and levity. In order to play the biggest advantage of all the kinds of MIMO modes, the base station should adaptive dynamic select the appropriate transmission mode among the MIMO modes to special UE base on its real time channel environment.In this thesis, the fundamental of all kinds of MIMO transmission modes are firstly studied in detail, including space-frequency block code, spatial multiplex and beam-forming, and we mastery theirs implementation. Secondly we analyze the link adaptation schemes in LTE system, namely AMC (Adaptive Modulation Coding) and HARQ (Hybrid Automatic Retransmission reQuest). And we provide an improved AMC scheme which can increase the system performance.Then we further deepen the study of link adaptation techniques focus on the feedback algorithms of channel state parameters in downlink. Based on these two classical algorithms, a new algorithm is provided that can achieve a good compromise between complexity and performance loss. Simulations results show that the computation of the algorithm presented in the thesis is26%-33%those of above these traditional algorithms while performance loss is very small. And the Rank Indicator/Precoding Matrix Indicator/Channel Quality Indicator joint feedback algorithm simulation are also verificated, the result show that the link adaptation techniques are of great help to the increase of system capacity.Base on the research results above, AMC and HARQ module are plused in the TDD LTE downlink platform, we simulate all kinds of MIMO mode transmission mode and invest their adaptive environment. Lastly we design a MIMO modes adaptive scheduling algorithm, correspond to fixed MIMO mode, it can greatly improve system performance.