  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 (NB-IoT) systems has been approved within the 3rd Generation Partnership
Project (3GPP) standardization body. However, as NB-IoT 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 NB-IoT 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 NBIoT RA
waveform. Performance evaluations demonstrate the proposal's capability of
addressing different NTN configurations recently defined by 3GPP for the 5G new
radio system.

Signal Processing