Link adaptation and SINR errors in practical multicast multibeam satellite systems with linear precoding

The application of linear precoding at the gateway side enables broadband multibeam satellite systems to use more aggressive frequency reuse patterns increasing the overall capacity of future high-throughput satellites (HTS). In any practical precoded system, receivers can estimate only a few coefficients of the channel state information (CSI), while the others, in what is known as nullification, are set to zero. In this paper, the impact of the CSI nullification to the SINR estimation is analyzed statistically and geographically for a multicast multibeam satellite system. The errors in the SINR calculated by the gateway affect to the modulation and coding schemes (MCSs) selection, increasing the rate of erroneous frames or leading to an underutilization of the available resources. Therefore, as countermeasure, a link adaptation algorithm based on an adaptive margin per user is proposed, helping to achieve the error rate constraints of DVB-S2X systems without compromising the throughput, even under severe CSI degradation due to nullification and Rician fading.