NB-IoT NTN Band-Edge Attenuation/EVM Tradeoff with Real-System Verification

In 3GPP 5G narrowband Internet-of-Things (NB-IoT) non-terrestrial networks (NTNs) based on a satellite, a relayed gNodeB (gNB) base station orthogonal frequency-division multiple access (OFDMA) signal is required to meet the highly strict band-edge attenuation constraint and simultaneously maintain acceptable error vector magnitude (EVM) performance. Although these seem to be two conflicting goals, we pursued a favourable tradeoff between gNB band-edge attenuation and EVM by designing a two-stage interpolated finite-impulse response (IFIR) filter. We first follow the 3GPP NB-IoT specification to generate a standard gNB signal, and then we designed and optimized the filter for a relayed gNB signal and simulated its effectiveness. The proposed gNB TX design was not only verified through simulation, but also practically verified by the commercial vector signal analyser (VSA). Hence, this work can be realistically applied to standard NB-IoT signals, making it a critical enabling technology for converting the original NB-IoT TN to NTN and can help NTN operators to flexibly allocate channels, improve overall spectrum efficiency, and avoid waste of spectrum resources.