Experimental evaluation of power saving mode against powering down in an NB-IoT modem

Abstract

Narrowband Internet of Things (NB-IoT) is standardized by 3GPP to support low power devices that are deployed in locations that mandate requirements such as deep coverage and long battery life. This technology is adopted in applications such as smart water and gas metering, agriculture and many that require infrequent access to NB-IoT network. In such applications, the devices are in deep sleep more than 95% of the time. In deep sleep, the modems are expected to consume near zero currents. In order to support such applications 3GPP introduced power saving mode (PSM). During this deep sleep devices are not reachable for any downlink communication. Some NB-IoT modems such as one from Quectel provide an option to power down the modem, henceforth called as power down mode (PDM). This option looks more attractive as the modem consumes less current compared to PSM. This paper experimentally evaluates PDM and PSM using a Quectel modem. It is observed that even though current consumption in PDM is less than PSM for more than 95% of the time, still PSM is better than PDM when looked at holistically, i.e. cumulative of active, idle and sleep current consumption. Additionally, PDM generates additional signalling compared to PSM.