Key Techniques Of Lte Downlink Link Amc Feedback Mapping

In order to match the characteristics of the channel and maximize the effectivecommunication rate, adaptive modulation and coding (AMC) and hybrid automaticrepeat-request (HARQ) are uesed in Long Term Evolution (LTE) system and itsevolution version LTE-Advanced system. AMC mapping process, according to the stateof the user channel, selects the appropriate grade of the channel quality information(CQI) for the transmitter, and match the quality of the channel by adjusting themodulation mode and channel error correction coding rate, in order to improve theeffective communication rate of the physical layer. Meantime, jointing with the HARQretransmission mechanism, it can improve the transmission efficiency of the system,and make system throughput approach the theoretical limit.Traditional AMC mapping methods includes exponential effective SINR mapping(EESM) and mutual information based effective SINR (MIESM), whoes shortcomingsreflected in: the achievement of the algorithm highly depends on the accuracy of SINRestimated; CQI mapping entirely depends on the signal-to-interference plus noise ratio(SINR), lacking of direct involvement of the channel correlation parameters; thecomplexity of the operation is high.First, according to the limitations of commonly used AMC mapping algorithm, weproposed an AMC mapping method based on the correlation of channel beforeequalization. Channel correlation and channel rank are introduced in the mappingprocess, then jointed receiver side’s SINR estimates before equalization, and found thetemplate curve to complete the CQI mapping and layers of feedback. Complexityanalysis show that the new AMC mapping method’s operating complexity is lower thanEESM one order of magnitude.Secondly, in order to improve the system throughput, using the advantage of HARQtechnology, combined HARQ and AMC mapping method is proposed based on thecorrelation of channel before equalization in LTE downlink system.Through systemsimulation, counted throughput and block error rate (BLER). The simulation resultsshow that the system rank adaptive throughput can match the fixed rank throughputenvelop, at the same time, BLER fluctuation did not exceed10%.Finally, we build a LTE downlink full link simulation platform using Matlab, withthe link configuration frequency division duplex (FDD), single user multiple inputmultiple output (MIMO) channel and open-loop spatial multiplexing (OLSM) mode.The link functions include channel coding, layer mapping and precoding, ideal channelestimation, minimum mean square error (MMSE) signal detection, HARQretransmissions, CQI feedback and layer feedback.Overall, according to the limitations of commonly AMC mapping algorithm using inLTE downlink system, we proposed a AMC mapping method based on the correlationof channel before equalization; builded a simulation platform for LTE downlink link; compared and verified the system throughput and block error rate performance.Thesimulation results show that throughput can match the fixed rank throughput envelopand block error rate can meet fluctuation constraint condition.The research results couldbe directly used for the AMC mapping process of LTE downlink system, to reduce thecomplicated to operate and improve system throughput.