Abstract:Narrowband IoT technology is widely used in data communication for massive low-speed and low-power consumption devices, but it is limited by ground The coverage of the network cannot provide services to remote areas. Low-orbit satellite constellations have the characteristics of supporting global coverage and can supplement and expand terrestrial NB-IoT infrastructure, which provides an effective solution for space-based IoT. Facing the application requirements of space-based IoT, on the basis of reviewing the NB-IoT system architecture, the low-orbit satellite IoT integrating NB-IoT technology faces challenges such as high dynamic delay and frequency offset in the channel environment. For the uplink random access process, an effective user detection and timing synchronization method is designed. This method has the advantages of high performance and low complexity, and can effectively solve the efficient random access problem in the low-orbit satellite IoT integrated with NB-IoT.
Keywords:NB-IoT; low orbit satellite; random access; timing synchronization
1 Introduction
Currently, various terrestrial wide-area IoT solutions and standards including Sigfox, Long Range Radio (LoRa) and Narrow Band Internet of Things (NB-IoT) are being actively promoted and applied. Sigfox has a coverage range of 10 to 40 km and a transmission capacity of 140 messages per day. LoRa is an open, low-power, long-range IoT technology. Each LoRa gateway can manage up to millions of nodes. NB-IoT is built on cellular networks, which enables wide-area communications with lower node costs and lower power consumption. However, terrestrial IoT is difficult to deploy to remote areas or areas with complex terrain, such as deserts, oceans, forests, etc. At this time, non-ground nodes can be utilized for auxiliary communications to support global IoT operations.
Compared with geostationary orbit (GEO) satellites, low earth orbit (LEO) satellites