Rel 16 Feature – UE Power Saving in NR

UE Power saving in NR: To improve power efficiency of UEs.

UE battery life is an important aspect of the user’s experience. The RAN1 study of the Rel-16 UE power saving had shown substantial power saving gain comparing to considered Rel-15 NR features such as DRX operation, with UE adaptation in frequency domain, time domain, antenna domain, tight control of DRX operations, and reducing PDCCH monitoring with different traffic types.

The work item of UE power saving in NR includes the power saving techniques, such as DRX adaptation, cross-slot scheduling, and maximum MIMO layer adaptation in CONNECTED state, fast transition out of CONNECTED state, and reduced RRM measurements in idle/inactive states. The UE assistance information is part of the work to enable the UE to feedback its preferred configuration to achieve desired power saving.

1. Reduced RRM measurements –

3GPP companies have developed a mutually-agreed device power model that captures the relative powers associated with different active operations, in relation to the lowest power, deep sleep mode. Clearly, reducing the fraction of time for the device to perform unnecessary PDCCH monitoring and enabling the device to be in a sleep state instead offers a high potential for energy conservation.

Figure (below) presents the accumulated energy consumption profile of a typical eMBB device operating in a variety of states in a mix of traffic events over 24 hours. The left-hand bar graph shows, starting from the top, the fraction of energy consumed while performing control channel monitoring, data reception, periodic activities in connected and inactive modes, and deep sleep. The right-hand bar graph indicates the fraction of total time spent performing the respective operations.

• Improved cross-slot scheduling:

The network can inform the device that a guaranteed minimum time interval of K0 slots exists between the downlink control channel PDCCH and the data packet it schedules. The device can thereby omit unnecessary radio frequency (RF) operation to buffer the data channel if no data is scheduled. It may also be able to use a more efficient receiver configuration for PDCCH reception. The signaling is dynamic so the reception mode may be adapted to match the instantaneous data traffic pattern. The resulting connected-mode energy reduction can be up to 15 to 20 percent, depending on the use case. Figure 2 illustrates device receiver processing for K0=2 slot.