# Low-Power Wake-Up Receivers for Resilient Cellular Internet of Things
## 2 Motivation and Scope of Cellular WURs  
Over the past several 3 GPP releases, there has been a trend towards reducing device complexity to enable cost-effective deployment of IoT devices, as well as allowing for feature removal when the use case will not benefit. RedCap (reduced capability) devices were introduced in Rel-17, with a 50% to 65% reduction in complexity at a lower data rate still suitable for the most demanding broadband IoT use cases [14]. The introduction of NB-IoT served a similar purpose. Implementing these types of modifications that address a wide range of device capabilities leads to a single standard-based ecosystem and eliminates the choice of radio access technology when planning new IoT deployments or consolidating existing applications to a single technology. Figure 3 provides an illustration of device types for 4G and 5G, with lower data rates corresponding to a distinct reduction in complexity. In each case, a simplified WUR enables a decrease in idle power.  
Figure 2: Side-by-side comparison of a traditional eDRX node vs. a node with a WUR. (**a**) Traditional IoT node structure and power consumption model in eDRX mode. (**b**) IoT node equipped with WUR and its power consumption model (assuming a duty-cycled WUR).  
The 3 GPP RAN1 group has identified target use cases of WUR under the following three categories: IoT, wearables, and eMBB (enhanced mobile broadband) [5].  
The forecasted IoT use cases are notable because they serve functions that should be nearly invisible to the user in the context of Smart Cities. Industrial wireless sensors, controllers, and actuators are all latency-critical. Typically, form factors and power sensitivity will be a function of desired mobility. For example, a static device may be located near existing power infrastructures, excluding the need for energy efficiency. On the other hand, highly mobile cases face power, size, and weight constraints.  
Wearable devices including smart watches, rings, and medical monitoring devices benefit from the same overall weight and power reduction, with a somewhat higher target throughput. A similar category, eMBB, is assumed to have a relatively relaxed form factor and comprises personal devices such as smartphones and smart glasses.  
Mobile devices used for communication between humans need to check frequently for incoming messages, whereas industrial sensors may only initiate communication when abnormal conditions are detected, such as fire detectors and extinguishers in a building. For the former case, the period may be configured to optimize the user experience. In the latter case, however, eDRX operation is not a good solution. The infrequency of messages calls for very long duty-cycling periods, but in the rare case that a message is sent, it will be very urgent. Another use case, asset tracking, may have a daily or hourly schedule where it regularly reports its current location and status. However, the user may want to reach the device on an infrequent basis, and therefore, it must always be reachable. By employing a WUS, the device can follow its normal behavior with significantly reduced latency as needed.  
In general, the addition of wake-up capability provides a highly adaptable technique to adjust latency and simultaneously reduce power consumption compared to the legacy methods based on straightforward UE duty cycling.