In Fifth-Generation (5G) New Radio (NR), satisfying a scenario called Ultra-Reliable and Low-Latency Communication (URLLC) is one of main goals. URLLC requires very high reliability with low latency, 1 ms user plane latency and 99.999% reliability. In Long Term Evolution-Advanced (LTE-A) system, however, latency requirement required by URLLC cannot be satisfied because resource allocation process increases latency. In this paper, we propose DRaMA, a grant-free uplink transmission scheme for low latency required in URLLC. With its own preamble and repetition pattern, a device repeatedly transmits the same packet using different frequency resources across consecutive mini- slots right after sending the preamble. We develop a mathematical model of collision probability to design repetition patterns, which determine the device- specific frequency resources. We demonstrate that DRaMA satisfied URLLC requirements in most cases by using system level simulation.

Energy awareness of mobile devices with limited battery capacity can be achieved by embedding battery drain rate monitoring capability into the devices. With Li-ion battery, battery drain rate varies with temperature and battery aging, since they affect battery characteristics such as capacity and internal resistance. We develop BattTracker, an algorithm to estimate battery drain rate without knowing the exact capacity and internal resistance by incorporating the concept of effective resistance. BattTracker tracks the instantaneous battery drain rate with up to 0.5 second time granularity. Extensive evaluation with smartphones demonstrates that BattTracker accurately estimates the battery drain rate with less than 5% estimation error, thus enabling energy-aware operation of smartphones with finegrained time granularity. To the best of our knowledge, this is the first effort to estimate the instantaneous battery drain rate by considering both temperature and aging effects on the battery characteristics.