NB-IoT Random Access for Non-Terrestrial Networks: Preamble Detection and Uplink Synchronization

The satellite component is recognized as a promising
solution to complement and extend the coverage of future Internet of things (IoT) terrestrial networks (TNs). In this context,
a study item to integrate satellites into narrowband-IoT (NBIoT) systems has been approved within the 3rd Generation Partnership Project (3GPP) standardization body. However, as NBIoT systems were initially conceived for TNs, their basic design
principles and operation might require some key modifications
when incorporating the satellite component. These changes in
NB-IoT systems, therefore, need to be carefully implemented
in order to guarantee a seamless integration of both TN and
non-terrestrial network (NTN) for a global coverage. This paper
addresses this adaptation for the random access (RA) step in NBIoT systems, which is in fact the most challenging aspect in the
NTN context, for it deals with multi-user time-frequency synchronization and timing advance for data scheduling. In particular,
we propose an RA technique which is robust to typical satellite
channel impairments, including long delays, significant Doppler
effects, and wide beams, without requiring any modification
to the current NB-IoT RA waveform. Performance evaluations
demonstrate the proposal’s capability of addressing different
NTN configurations recently defined by 3GPP for the 5G new
radio system.