Research Of The LTE Downlink MIMO Model Adaptive Switching Technology

Multiple input multiple output (MIMO) system configure multiple antennas onthe transmitting device and receiving device in order to achieve space diversity, andthis is conducive to increasing the transmission rate and spectrum efficiency ofwireless communication system. The3rd Generation Partnership (3rd GenerationPartnership Project,3GPP) adapts to the development of mobile communicationsindustry through the long-term Evolution of the third Generation mobilecommunication system (Long Term Evolution, LTE) projects. MIMO is a keytechnology of the LTE project, which has received wide attention and research.LTE defines the eight kinds of MIMO transfer modes. When the UE move slowerand channel environment is good, the closed-loop MIMO transmission scheme bringsbetter throughput gain good; When the UE moves faster and transmission channelsignal noise ratio (SNR) is high, LTE can use open-loop MIMO scheme. When thechannel is high, the quality of the eNodeB (LTE base station) can use the spatialmultiplexing scheme in order to improve the system throughput; When channelquality is low especially channel correlation is strong, In order to improve thereliability of transmission, transmit diversity scheme should be adopted. However, notransfer mode can adapt to any kind of scene all radio channel environments. so Inorder to satisfy the transmission quality and throughput requirements, LTE shouldswitch the transmission mode dynamically according to the actual channelcharacteristic. Due to user demand in mobile and heterogeneity, also has atime-varying channel status, base stations and terminals on the premise of meet thetransmission reliability, based on the transmission environment changes quicklyswitch to meet the requirements for the channel transmission model, improve thespectrum efficiency, increase the system capacity. But the algorithms and methods to switch the MIMO transmission mode are not provided in LTE protocol.The purpose of this paper is to study the switching algorithm between MIMOmodels in the LTE system downlink link. The paper proposes the switching thresholdmethod between TM2(transfer mode2) and TM3(transfer mode3), and betweenTM2(transfer mode2) and TM4(transfer mode4), and write C code to achieve thealgorithm. At the same time, the paper respectively gives switching process ofjudgment mode in the L3(RRC layer, Radio Resource Control: Radio ResourceControl), and the process switching from TM3to TM2.Finally we set up theexperimental test platform to verify the rationality of the algorithm. The experimentalresults show that the switching threshold between TM2and TM3, and between TM2and TM4is consistent with the theory in the LTE system downlink link, and theswitching threshold method is verified by measurement.