Downlink Control Channel Scheduling for 3GPP Narrowband-IoT

Narrowband Internet of Things (NB-IoT) is a recent feature introduced by 3rd Generation Partnership Project (3GPP). It is a low power wide area network technology that will enable cellular service to a massive number of low throughput IoT devices. The NB-IoT is a derivative of existing 3GPP Long Term Evolution (LTE) that has to be delay tolerant with low cost devices. In LTE, the decoding of Physical Downlink Control Channel (PDCCH) consumes a significant amount of user equipment's (UE) battery power because of its high computational complexity and complicated search space design. Hence, the existing downlink control channel scheduling schemes for LTE cannot be reused for NB-IoT. The reduction in available bandwidth and introduction of repetitions for achieving wider coverage makes the Narrowband PDCCH (NPDCCH) search space design and its allocation even more challenging. In this paper, we first explain the NPDCCH in detail and present its design rationale. We propose several novel downlink control channel scheduling schemes for 3GPP NB-IoT and compare their performance through extensive Monte Carlo simulations.