Robust Adaptive Margin for ACM in Satellite Links at EHF Bands

The use of adaptive coding and modulation (ACM) to counter the effect of rain fades has become a standard approach in broadband satellite links operated in Ka-band. Now proposals are being made to operate such systems in Q/V band (33 - 75 GHz) which experience a wider range of rain fade levels. Due to the higher rate of change in fade levels, a major aspect of the ACM design is how to set margins accurately in order to avoid frame losses at the next operation point when the link state is not yet perfectly known. Existing techniques have focused on using predetermined margins but this approach results in poor performance when the actual rain fade profile is different from the pattern assumed. In order to improve performance, we propose the use of adaptive margins derived dynamically during the actual rain event. Simulation results show a robust performance in spectral efficiency at a low frame error rate (FER) in comparison with the existing techniques.