Research Oon Adaptive Modulation And Coding Technology In LTE System

To improve the competitive of 3GPP, contending with the rapid rise of WiMAX, 3GPP hadstarted 3GPP Long Term Evolution(LTE) in November of 2004. By using OFDM and MIMO as itskey technologies, LTE system can provide a maximum data transfer rate up to 100Mbps on 20MHzbandwidth in the downlink, and it can also provide a maximum data transfer rate up to 50Mbps inthe uplink. It has not only improved the system's spectrum efficiency, but also greatly satisfieduser's needs for high-speed data transfer rate.As there is strong time-varying fading in the wireless channel, to reduce the system FrameError Rate(FER) and get the maximum system throughput, OFDM system will use AdaptiveModulation and Coding(AMC) technology at transmitting side. There are 3 adaptive modulationalgorithms based on sub-band division. In this thesis, we use the fixed threshold algorithm, bywhich there are 3 determined sub-band SNR algorithms: the worst subcarrier alternative algorithm,the best subcarrier alternative algorithm, average value algorithm, corrected average valuealgorithm. In adaptive modulation and coding scheme(MCS), adaptive modulation and coding ratewill be binded together, and it will choose different modulation and coding mode based on ChannelQuality Indicator(CQI) from channel estimation.In this thesis, LTE downlink physical layer system is used as model, we first analyze an AMCscheme which is searching for optimal threshold based on sub-band, then make a comparison ofsystem performance with other schemes under different conditions. Analysis and simulation resultsshow that, under the condition of satisfying target FER, system's throughput of using this schemehas significantly improved than fixed MCS scheme and other 4 commonly used AMC schemes.When the number of subcarrier groups increases, system's FER will decrease first and increase after,but they all satisfy the target FER. The system's throughput will increase all the time, but theincreasing amplitude will be more and more smaller. When the terminal speed increases, advantagesof system's throughput by using AMC scheme than using fixed MCS scheme will no longer beobvious, even under the condition of high SNR, the AMC scheme will be lower.