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

Abstract

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 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.

A Survey on Nongeostationary Satellite Systems: The Communication Perspective

“…The objective here is to identify a set of features and adaptations enabling the operation of NB-IoT within NTN structure with a priority on satellite access. In this context, some works have already started to adapt and evaluate these protocols under the NGSO system constraints specifically the relative satellite motion [296]- [299]. Nevertheless, the progress is still in an early stage and more research efforts are required for a seamless integration, particularly in connecting NGSO satellites to mobile or stationary IoT devices and supporting ultra reliable low latency communications.…”

A NB-IoT Random Access Scheme Based on Change Point Detection in NTNs

“…1. The flowchart aims to provide readers with a rough framework of To be specific, in step 2, a system level solution based on the information of initial downlink synchronization is used to reduce the large CFO to a relatively small scale [22]. In most cases, the residual frequency offset is about 600Hz [23] which is still much larger than estimation range of existed studies [11]- [18].…”

Grant-Free NOMA-OTFS Paradigm: Enabling Efficient Ubiquitous Access for LEO Satellite Internet-of-Things

“…While the different groups are allocated to the orthogonal RBs to alleviate the potential interference caused by channel correlation impairment and to maximize the average signal-to-interference-plus-noise ratio. Without requiring any modification to the current NB-IoT waveform, [6] addressed the issues of multiple access caused by the typical satellite channel impairments, including long round-trip delays, significant Doppler effects, and wide beams. Furthermore, [7], [8] integrated the OTFS modulation with the GB-RA protocols and formulated new resource allocation schemes to accommodate the heterogenous mobility demands of differnt IoT applications.…”

“…• The access latency (e.g., 14.5 ms [4]) caused by standard handshakes and grant requests may far exceed the roundtrip latency of TSL (e.g., 3 ms [6]) and constitutes as the main latency source. • The scheduling signaling overheads are prone to exceed the length of the short-packet payload data generated by IoT applications, leading to excessive waste of resources.…”

“…Meanwhile, Doppler precompensation is only precise for terminals located at the beam centre. Inevitably, there will be Doppler residual for others [6]. • For the active schemes, the pilots and data are usually multiplexed in the TF domain, such as orthogonal frequency division multiplexing (OFDM) systems.…”