Time Domain Analysis of NB-IoT Signals

The NB-IoT (NarrowBand-Internet of Things) radio technology is now widely implemented by mobile phone network operators to support the communication of IoT devices such as smart meters, insurance black boxes for cars, network connected waste bins, smart bicycles. In the present work, some LTE800 cells of different mobile phone network operators implementing the NB-IoT technology in the guard band mode have been investigated. The signals, consisting of a PRB (Physical Resource Block) 180 kHz wide, have been analyzed and characterized in the time domain by means of a narrow band instrumental chain equipped with a Rohde & Schwarz FSH8 spectrum analyzer. Time domain analysis allows us to identify, within the transmission frame, the position of the NB-IoT signaling channels such as the Narrowband Reference Signal (NRS), the primary (NPSS) and secondary (NSSS) synchronization signals and the broadcast channel (NPBCH), but, above all, to measure the power received during the transmission of the NRS. This value has been compared with that measured by the NB-IoT decoding module supplied on the same analyzer, in order to verify the equivalence of these measurement methods. This would allow use of a more diffuse and cheaper instrumentation rather than more expensive vector analyzers, currently required to assess electric fields due to the NB-IoT signals through the extrapolation techniques set by Italian CEI 211-7/E technical standard.