The Study Of Key Technologies And Related Algorithms In LTE Down-link

In order to Compete with new wireless broadband technology such as WiMAX, Wi-Fi,3GPP launched LTE technology standardization in the end of2004.LTE,mainly supported by OFDM and MIMO, not only enhances3G air access technology,has a higher user data rate and system capacity,but also can seamlessly interoperate with existing technology and its good flexibility in spectrum use,as well as network deployment and management of low-cost and other advantages,besides,it consolidates the dominant position of traditional cellular technology,therefore, studying LTE and it’s key technologies are very meaningful. But in practical applications,how to improve the communication quality of the cell edge users, improve the utilization of spectrum resources, how to solve contradiction between the reliability of data transmission and improving the data transfer rate and system throughput, and how to reduce the complexity of signal processing of LTE receiver,etc.These problems need further researching and analyzing.It’s necessary to improve the LTE wireless communication system and overcome its shortcomings for getting ideal performance of LTE.Firstly,we design LTE physical layer simulation Platform based on Matlab software according to technical protocols of3GPP36series,and introduce the design process of main function modules,then further optimize the simulation platform-adding HARQ module, also analyze rationality of the optimized platform and superiority of HARQ technology from the block error rate and throughput.By simulating,we discover that because of adding HARQ technology,block error rate of the system is reduced,system reliability is improved and throughput of the system is increased,thus both improve the performance of cell edge users and solve the problem of data transmission reliability and higher data rates and system throughput. Secondly, coding and modulation technology is researched.By comparing simulation curves,we can see that block error rate performance of QPSK is superior to other,but the throughput is less than16QAM and64QAM,it’s useful for usingAMC and improving the utilization of spectrum resources.Then, in the case of limited feedback,we use codebook based on Grassmanian packing principle to analyze precoding technology, the simulation shows that the more feedback bits, the better the system performance,and with precoding based on SINR criterion can achieve better system performance than no precoding. Finally,in the case of SU/MU MIMO,simulate and analyze MIMO linear precoding algorithm-ZF,MMSE and BD,we find that the performance of BD precoding algorithm is best and more suitable for practical application. And propose an improved BD linear precoding scheme, by comparing simulation results, system performance is better than any single precoding algorithm when using improved BD precoding scheme, especially in lower SNR, it can obtain better BER performance, and also can greatly reduces the complexity of signal processing at receiver.