Adaptive Transmission Techniques for Mobile Satellite Links

Adapting the transmission rate in an LMS channel is a challenging task because of the relatively fast time variations, of the long delays involved, and of the difficulty in mapping the parameters of a time-varying channel into communication performance. In this paper, we propose two strategies for dealing with these impairments, namely, multi-layer coding (MLC) in the forward link, and open-loop adaptation in the return link. Both strategies rely on physical-layer abstraction tools for predicting the link performance. We will show that, in both cases, it is possible to increase the average spectral efficiency while at the same time keeping the outage probability under a given threshold. To do so, the forward link strategy will rely on introducing some latency in the data stream by using retransmissions. The return link, on the other hand, will rely on a statistical characterization of a physical-layer abstraction measure. NOMENCLATURE ACM Adaptive Coding and Modulation ARQ Automatic Repeat Request CDF Cumulative Distribution Function CLT Central Limit Theorem CSI Channel State Information ESM Effective SNR Mapping GEO Geostationary ITS Intermediate Tree Shadowed LMS Land Mobile Satellite LOS Line-of-Sight MIESM Mutual Information ESM MODCOD Modulation and Coding MLC Multi-Layer Coding PDF Probability Density Function SNR Signal-to-Noise Ratio WER Word Error Rate