Comparison of energy conservation strategies for 5G NR RedCap service in industrial environment

Abstract

The recently standardized reduced capability (RedCap) type of user equipment (UE) for 5G New Radio (NR) systems offers a useful option for energy-constrained devices. By utilizing a combination of discontinuous reception (DRX), wake-up signal (WUS), and radio resource management (RRM) relaxation functions, RedCap UE may provide excellent power efficiency for a large set of applications. In this study, we investigate power efficiency and battery lifetime for RedCap UEs for different types of applications and various combinations of energy conservation mechanisms. We utilize extended virtual reality (X-VR) and web browsing as applications of interest. To this aim, we develop a versatile mathematical framework representing the sought metrics as a function of time, accounting for specifics of millimeter wave (mmWave) propagation, micro- and macro-mobility of UEs, human body blockage, and type of application. Numerically, we show that higher micro- and macro-mobility speeds lead to worse power efficiency and the loss can be quite substantial amounting up to 30%. Antenna arrays with worse directivity show better performance in the presence of micro- and macro-mobilities when RRM Relaxation is utilized, with a difference between $15\times 15$ and $4\times 4$ arrays reaching 1.5 bit/J/KHz, which is approximately 40%. The energy conservation mechanisms produce no noticeable impact on the power efficiency and battery lifetime for rate-greedy applications such as X-VR. Low-data-rate applications with long pauses between transmission cycles, such as web browsing, may benefit from utilizing WUS and RRM Relaxation in addition to conventional DRX. However, their impact is rather small at a scale of 5%–10%.