Uplink Performance Analysis for Grant-Free Narrowband IoT with Widely Linear Receiver

Narrowband Internet of Things (NB-IoT) is one of the most prominent low power wide area (LPWA) technologies to support massive connections among low-cost devices with enhanced coverage. Addressing the further increase in the number of supported connections in IoT applications, we investigate the use of real-valued modulated signals together with widely linear detection (WLD) to NB-IoT. In this paper, we show that the use of WLD to resolve collisions of two simultaneously transmitted real- valued signals generated from two user equipments (UEs) enhances the capability of NB-IoT systems to facilitate massive connectivity. More specifically, to demonstrate the performance improvements, we analyze the uplink transmission reliability and the device density supported in NB-IoT systems with WLD in a grant-free scenario. The numerical results show that, for a 1% probability of decoding failure, the supported device density can be increased by one order of magnitude compared to that of conventional complex-valued signalling schemes.