Control Period Adaptation and Resource Allocation for Joint Uplink and Downlink in NB-IoT Networks

Narrowband Internet of Things (NB-IoT) offers three coverage enhancement (CE) levels to serve massive machines in a large area. For each CE level, the base station configures control periods to determine the number of allocatable radio resources for signal and data transmissions. Both uplink (UL) and downlink (DL) communications use the same control periods, but UL and DL machines need different period lengths. In general, a control period suitable for the UL is longer than that for the DL. Then, the base station assigns UL and DL resources in control periods to each machine. To this end, we study how to choose a suitable length of control periods and allot radio resources to UL and DL machines to minimize resource consumption, thereby improving NB-IoT performance. Two efficient algorithms are thus proposed. Based on the CE level, the control period adaptation algorithm flexibly adjusts control periods using a scale factor. The joint UL and DL resource allocation algorithm distributes radio resources in each control period among machines to increase utilization. Simulation results demonstrate that our algorithms can efficiently decrease the consumption of UL and DL subframes, especially for machines with bad channel qualities.