Channel Quality Approximation Using Large Scale Model in GEO Mobile Satellite System

CQI(Channel Quality Indicator) is an essential indicator for AMC(Adaptive Modulation and Coding) technique in LTE. Due to the long delay of GEO satellite channel, CQI prediction is necessary to ensure effective AMC when adaptive to satellite system. However most prediction algorithms' ability are limited by input sequences' correlation time, and the correlation time of CQI sequence containing small scale fading is much shorter than needed prediction range, so it is difficult to do prediction. Large scale fading can be obtained by smoothing out the small scale fading from the real data, and its correlation time increases significantly. This paper proposes the approximation from real CQI data containing small scale fading to that containing only large scale fading to do prediction. The concrete correlation features and the difference between the approximation and the original data are all analyzed. Simulation is done for confirmation. It shows that the approximate large scale CQI data is feasible and rational for prediction and ensuring AMC efficiency.