This paper focuses on the return link of a GEO satellite system that collects information from a large number of IoT devices that are sparsely distributed in a large geographical area. Narrow-Band (NB) IoT transmissions, with suitable Modulation and Coding Scheme (MCS), are Detected-and-Forwarded onboard the satellite, mapping each QAM symbol of the radio access link (uplink) into another equivalent PAM symbol that is suitable to modulate the intensity of the optical feeder link (downlink). Given the very large number of IoT devices that is expected to be served by the GEO satellite system, the feeder link (downlink) of the return channel is expected to be bottleneck. To tackle this limitation, apart from using an optical feeder link, time-packing is proposed to reduce the transmission time of the feeder link (downlink) without increasing the signal bandwidth and augment the number of IoT devices that could be simultaneously served in the radio access links (uplink). The Inter-Symbol Interference (ISI) that the time-packed feeder link generates is mitigated in part at the satellite gateway, using for this purpose an adaptive linear equalizer. After optical-to-electrical conversion, the NB-IoT codewords that are received in the gateway are decoded, correcting simultaneously errors introduced in both radio access and optical feeder links. The aim of this paper is to evaluate the error correction capability that the MCS of NB-IoT has when used to protect the hybrid radio/optical end-to-end return link, particularly when using a large overlapping factor to increase the optical feeder link data rate.

Grant numbers : TERESA - Hybrid TERrEstrial/Satellite Air Interface for 5G and Beyond (TEC2017-90093-C3-1-R).