With reference to 5G NR, what do you understand by Wake-up signal? and what is it used for?
WUS (Wake Up Signal) is a type of power saving mechanism introduced in NR release 16. WUS tries to save power by letting UE to continue to sleep (i.e, No Wake up) even for DRX OnDuration period when there is no data for the UE and gNB notifies the UE of ‘No Wake Up’. When there is any data for the UE, gNB would notify the UE of ‘Wake Up’ so that UE wakes up and receive data during OnDuration time.
Most UEs can be configured for discontinuous reception (DRX) — remaining in an idle state for a certain period, waking up periodically to check for traffic on the PDSCH. Currently, when configured for a long DRX period, the UE will wake up at the scheduled time and stay awake for the entire duration of the configurated “on” period. Release 16 introduces a new downlink control information (DCI) format that can be read by the UE before the long DRX wakeup time. This short DCI can inform the UE if there is no relevant downlink traffic on the PDSCH, enabling it to return immediately to an idle state through the next “on” duration.
The wakeup signal may have only minimal impact on the power a phone’s consumption. It will, however, have a much more significant effect on the power consumption of non-smartphone UEs such as IoT devices and sensors, many of which by design remain in an idle state for long periods — weeks, months, or even years — waking up only to transmit or receive information only when an event occurs
-Enhanced cross-slot scheduling:
Release 16 adds the concept of enhanced cross-slot scheduling, which enables a UE to go into a microsleep state, rather than performing some non-essential decoding tasks, if applicable. A new bit field in some DCI formats informs the UE in advance if the time between the uplink or downlink control information slot and data slots is sufficient to enable microsleep, an intermediate low-power state that reduces current draw without impacting performance
-Adaptive MIMO layer reduction:
Adaptive MIMO layer reduction in Release 16 creates the ability to adaptively reduce the number of downlink MIMO layers in a transmission, saving the UE a significant amount of power by allowing the UE to reduce the number of antennas in use. For example, the initial bandwidth part — set of contiguous common physical resource blocks (PRBs) — can be configured for a single MIMO layer, while other bandwidth parts could use a higher number of MIMO layers. The adaption of the maximum number of downlink MIMO layers is done on a per-bandwidth part basis.
