LTE-based mobile satellite communication system is a combination of terrestrial LTE system and satellite communication techniques, which aims at improving the current LTE system's technical specifications for better service quality. AMC (Adaptive Modulation and Coding) technique is applied in current LTE system to improve system capacity and data transmission efficiency. CQI (Channel Quality Indicator), which is measured by UE, is an essential indicator for AMC process. However in satellite system, the said data received by eNodeB are all outdated due to the long delay caused by satellite link. So there exists need for predicting CQI data in advance. ARIMA (Autoregressive Integrated Moving Average Model) is a good choice for predicting CQI in terrestrial system, but its prediction ability is limited when prediction length is too long in satellite communication system. To solve this problem, a prediction scheme is proposed in this paper. This method predicts CQI states, instead of predicting the specific CQI values, and provides the reference CQI for AMC. A modified ARIMA model is applied for reducing the prediction complexity and delay. Simulation shows that the proposed method can realize CQI prediction with acceptable RMSE performance.
Abstract-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 in LTE-compatible GEO mobile satellite communications system. The complete procedure and problem encountered when doing AMC in satellite system are introduced and the difficulties of prediction are analyzed. In order to obtain meaningful and feasible CQI prediction results, a complete prediction scheme is proposed. By using approximate CQI data which is smoothed and with only shadow fading influence, various prediction models are compared. Taking both computation complexity and prediction performance into account, two models, ARIMA (Autoregressive Integrated Moving Average) and Kalman filter are chosen to be applied in this scheme. Simulation results show that the prediction performance is very well with the proposed method, which can surely guarantee AMC performance.
Reference signal (RS) is a crucial signal which is used for channel estimation and data demodulation in 3GPP long term evolution (LTE) system. However, due to the differences of channel environment, interference situation and system physical resource between multiple-beam satellite system and terrestrial system, the original downlink reference signal (DL-RS) design in LTE specifications cannot meet the satellite system demands, leading to performance degradation and waste of resource. In this paper, based on the feature of satellite channel, interference model and physical resource, we calculate the time and frequency domain interval; design the pattern of DL-RS in multiple beam satellite communication system. Furthermore, two DL-RS improvement technology: power boosting, re-transmit and combined receive scheme are mentioned. Simulation results and performance analysis prove the effectiveness of the proposed DL-RS design.
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