Summary based on the input provided by MediaTek Inc., ZTE in RP-221544.
User experience is key to 5G/NR success, not only in terms of experienced data rates and latency but also importantly UE power consumption. UE Power saving enhancements are therefore vital to the success of 5G/NR. In Rel-17, additional enhancements are required to address outstanding issues in Rel-16, including idle/inactive-mode power consumption in NR SA deployments and connected-mode power consumption with traffic of more frequent packet arrivals, etc. Accordingly, the following new functionalities are developed and supported for NR:
Paging enhancements to reduce UE reception power consumption in idle/inactive mode
Enhancements for idle/inactive-mode UE power saving: Paging enhancements to reduce UE reception power consumption in idle/inactive mode and Provision of potential TRS/CSI-RS occasion(s) available in connected mode to idle/inactive-mode UEs
Enhancements for connected-mode UE power saving: Further PDCCH monitoring reduction, including enhanced search space set group (SSSG) switching and PDCCH skipping and Relaxation of UE measurements for RLM and/or BFD in connected mode
In order to reduce UE power consumption due to false paging alarms, the group of UEs monitoring the same PO can be further divided into multiple subgroups. With subgrouping, a UE shall monitor PDCCH in its PO for paging if the subgroup to which the UE belongs is paged as indicated via associated paging early indication (PEI). Since the false paging probability is reduced with subgrouping, UE reception power consumption in idle/inactive mode can be reduced accordingly. If the UE is unable to monitor the associated PEI occasion corresponding to its PO, it shall monitor the paging in its PO.
These subgroups have the following characteristics:
Provision of potential TRS/CSI-RS occasion(s) available in connected mode to idle/inactive-mode UEs
Subgrouping is either CN controlled or UE ID based:
For CN controlled subgrouping, AMF is responsible for assigning subgroup ID to the UE. The total number of subgroups for CN controlled subgrouping which can be configured e.g. by OAM is up to 8. It is assumed CN-based paging subgrouping support in an RNA is homogeneous.
For UE ID based subgrouping, the gNB and UE can determine the subgroup ID based on the UE ID and the total number of subgroups for UE ID based subgrouping in the cell. The total number of subgroups for UE ID based subgrouping is decided by the gNB for each cell and can be different in different cells.
Total number of subgroups allowed in a cell is up to 8 and represents the sum of CN controlled and UE ID based subgrouping configured by the network;
A UE with CN controlled subgroup ID shall apply CN controlled subgroup ID if there is a corresponding indication allocated in the PEI for the CN controlled subgroup; otherwise, it derives UE ID based subgroup ID if the cell supports only UE ID based subgrouping.
PEI associated with subgroups has the following characteristics:
If the PEI is supported by the UE, it shall at least support UE ID based subgrouping method;
PEI monitoring can be optionally limited via system information to the last used cell;
PEI monitoring is based on Type2A-PDCCH Common Search Space (CSS) set for a DCI format 2_7 with CRC scrambled by a PEI-RNTI on the primary cell of the MCG. Each bit of paging indication field of DCI format 2_7 indicates one UE subgroup of a paging occasion;
A PEI occasion (PEI-O) is a set of PDCCH monitoring occasions (MOs) and can consist of multiple time slots (e.g. subframe or OFDM symbol) where PEI can be sent. The number of PO(s) associated with one PEI -O is a factor of total PO number associated with up to two paging frames (PFs).
The time location of PEI-O for UE's PO is determined by a reference point and a symbol-level offset from the reference point to the start of the first PDCCH monitoring occasion of this PEI-O. The reference point is the start of a reference frame determined by a frame-level offset from the start of the first PF of the PF(s) associated with the PEI-O. The time location of PEI-O can be configured so that total UE reception power consumption in idle/inactive mode, including synchronization and RRM measurements, can be minimized.
In order to reduce UE power consumption due to synchronization for paging receptions, RS configuration of TRS occasion(s) for idle/inactive UE(s) can be provided via system information (SIB17). By exploiting TRS for synchronization, UE can reduce the number of wake-up for SSB before a paging reception and potentially achieve longer sleep. It is noticed that RS configuration in SIB17 does not affect the UE behaviour in CONNECTED mode and can be ignored by UE in CONNECTED mode.
The maximum number of TRS resource sets configured by higher layer is 64. If a TRS resource is configured, the L1 based availability indication is always enabled based on that configuration. A UE which acquired SIB17 with a TRS configuration but did not yet receive an associated L1-based availability indication considers the configured TRS as unavailable. The L1 availability indication is carried in a DCI format 2_7, if configured, and a DCI format 1_0 with CRC scrambled by P-RNTI. The TRS availability indication field in the DCI format(s) provides a bitmap for up to 6 groups of TRS resource sets where the configuration of each TRS resource set includes an association to a bit of the bitmap. The UE can be additionally provided a validity duration for TRS resource sets with indicated presence. UE considers the validity duration for all TRS resource set groups is ended when UE receives the changed TRS/CSI-RS configuration in the modification period following a SI change notification or until the validity time duration expires, whichever is earlier.
Further PDCCH monitoring reduction, including enhanced SSSG switching and PDCCH skipping
In order to reduce UE power consumption on PDCCH monitoring, enhanced PDCCH monitoring adaptation mechanisms within an active BWP and triggered by scheduling DCI formats are provided. The adaptation applies to Type3-PDCCH CSS sets or USS sets on the active DL BWP of the serving cell. The adaptation is triggered according to the PDCCH monitoring adaptation indication field, if present, in DCI format 0_1/0_2/1_1/1_2. With the fast adaptation mechanisms, UE can be indicated to perform reduced PDCCH monitoring at the end of or after a duration of data scheduling, thereby achieving UE power saving with minimum impact to data scheduling.
UE power saving can be achieved through Rel-17 SSSG switching mechanism when Rel-17 SSSG configuration is configured. UE can be indicated to switch to a target SSSG via the indication of a scheduling DCI. If search space switch timer is also configured, UE switches to the SSSG of the lowest group index after timer expiration if no detected DCI format with CRC scrambled by C-RNTI/CS-RNTI/MCS-C-RNTI for the configured timer duration. The switch delay is at least Pswitch symbols, and Pswitch depends on the numerology of the serving cell. For Rel-17, UE can be configured with up to 3 SSSGs.
UE power saving can also be achieved through PDCCH skipping mechanism when PDCCH skipping duration configuration is configured. UE can be indicated to skip PDCCH monitoring for a duration, starting from next slot after the indication, and shall resume PDCCH monitoring after the indicated duration. For Rel-17, UE can be configured with up to 3 skipping durations. In the following cases, UE ignores PDCCH skipping:
on all serving cells of the corresponding Cell Group when SR is sent and is pending;
on SpCell while contention resolution timer is running;
on SpCell during monitoring of the RAR/MsgB window.
UE can be configured with both Rel-17 SSSG configuration and PDCCH skipping durations. In this case, UE performs either SSSG switching or PDCCH skipping based on the PDCCH monitoring adaptation indication field in a detected DCI format 0_1/0_2/1_1/1_2.
Relaxation of UE measurements for RLM and/or BFD in connected mode
UE power saving can be enabled by UE relaxing measurements for RLM/BFD. When configured, UE determines whether its serving cell radio link quality is better than a threshold and, if criterion is configured, whether it is in low mobility state. The configuration for good serving cell quality criterion and, if included, low mobility criterion is provided through dedicated signalling.
RLM and BFD relaxation may be enabled/disabled separately. Additionally, RLM relaxation may be enabled/disabled on per-CG basis while the BFD relaxation may be enabled/disabled on per serving cell basis.
The UE is only allowed to perform RLM and/or BFD relaxation when relaxed measurement criterion for good serving cell quality and, if configured, for low mobility is met. If configured to do so, the UE shall trigger reporting of its RLM and/or BFD relaxation status through UE assistance information if the UE changes its respective RLM and/or BFD relaxation status while meeting the UE minimum requirements specified.
RP-221543: "Revised WID_UE Power Saving Enhancements for NR", MediaTek Inc.
RP-220747: "Status report for WI_UE Power Saving Enhancements for NR", MediaTek Inc.
RP-212972: "Introduction of UE power savings enhancements in NR", RAN1
RP-220256: "Rel-17 maintenance of UE power savings enhancements in NR", RAN1
RP-220483: "RAN2 CRs to UE power saving enhancements for NR", RAN2
RP-220960: "Introduction of UE power saving enhancements in 38.300", Huawei, HiSilicon
RP-220961: "Introduction of ePowSav in TS 38.331", CATT
RP-220235: "RAN3 CRs for UE power saving enhancements for NR", RAN3
RP-220366: "RAN4 CRs for Open REL-17 NR or NR+LTE WIs - Batch 23", RAN4
Summary based on the input provided by Ericsson in SP-210326.
This work item addresses Energy Efficiency (EE) of 5G networks from two angles: 1) define EE KPIs and 2) specify solutions to optimize EE via Energy Saving (ES) techniques.
Similar work items addressing 3G and 4G were launched and completed in the past.
Overall concepts for EE in 5G networks have been described (see );
New EE KPIs have been defined at various granularity levels of 5G networks: Virtualized Network Function (VNF), 5G Core network function, 5G Core network, NG-RAN, network slice of various types (eMBB, URLLC, MIoT) (see );
Use cases, requirements and solutions for saving energy in NG-RAN have been described (see );
5G NRM (Network Resource Model), representing the management perspective of 5G networks, has been augmented with attributes capturing customer's expectations in terms of energy efficiency of the network slice being ordered (see ), in relation with GSMA NG.116 attributes.
: "Management and orchestration; Energy efficiency of 5G"
: "Management and orchestration; 5G end to end Key Performance Indicators (KPI)"
: "Management and orchestration; 5G Network Resource Model (NRM); Stage 2 and stage 3"