Ultranarrowband Waveform for IoT Direct Random Multiple Access to GEO Satellites

Direct access of small terminals in the Internet of Things (IoT) to geostationary satellites may provide wide coverage and almost 100% availability for remote locations without access to terrestrial networks. However, existing waveforms and IoT solutions do not close the link to the geostationary earth orbit (GEO) for massively deployed small devices. We present a novel modulation and signaling scheme based on chirp-spread spectrum (CSS) that enables reliable transmission at ultra low bit-rate. The proposed structure for the transmit signal applies unipolar codes in a novel manner, which allows random multiple access to a common channel for a large number of devices. Further, the transmit signal is designed to allow robust signal detection with low effort even at high carrier frequency offsets. We propose a system concept for the receiver including synchronization, and provide the results of extensive simulations carried out on system and link levels. As a result, we demonstrate that the proposed scheme, referred to as unipolar-coded CSS (UCSS), enables true random multiple access for a very large number of devices, closing the challenging link between IoT devices and satellites in the GEO even at high carrier frequencies from C-band to Ka-Band.