Summary based on the input provided by ZTE Corporation, Sanechips in RP-220154.
This work item enables the transmission of small signalling and/or data packets whilst the UE remains in RRC_INACTIVE state. Prior to Rel-17, NR supports RRC_INACTIVE state and UEs with infrequent (periodic and/or non-periodic) data transmission are generally maintained by the network in the RRC_INACTIVE state. Until Rel-16, the RRC_INACTIVE state doesn't support data transmission. Hence, the UE has to resume the connection (i.e. move to RRC_CONNECTED state) for any DL (MT) and UL (MO) data. Connection setup and subsequently release to INACTIVE state happens for each data transmission however small and infrequent the data packets are. This results in unnecessary power consumption and signalling overhead.
Some examples of small and infrequent data traffic include Smartphone applications such as: traffic from Instant Messaging services; Heart-beat/keep-alive traffic from IM/email clients and other apps; Push notifications from various applications. Other examples are non-smartphone applications such as: traffic from wearables (periodic positioning information etc); sensors (Industrial Wireless Sensor Networks transmitting temperature, pressure readings periodically or in an event triggered manner etc); smart meters and smart meter networks sending periodic meter readings.
As noted in TR 22.891
, the NR system shall be efficient and flexible for low throughput short data bursts, support efficient signalling mechanisms (e.g. signalling is less than payload) and reduce signalling overhead in general.
Signalling overhead from INACTIVE state UEs for small data packets is a general problem and will become a critical issue with more UEs in NR not only for network performance and efficiency but also for the UE battery performance. In general, any device that has intermittent small data packets in INACTIVE state will benefit from enabling small data transmission in INACTIVE.
The key enablers for small data transmission in NR, namely the INACTIVE state, 2-step, 4-step RACH and configured grant type-1 have already been specified as part of Rel-15 and Rel-16. So, this work builds on these building blocks to enable small data transmission in INACTIVE state for NR.
The Small Data Transmission (SDT) feature allows data and/or signalling transmission while the UE remains in RRC_INACTIVE (i.e. without transitioning to RRC_CONNECTED state). SDT is enabled on a radio bearer basis and is initiated by the UE only if:
less than a configured amount of UL data awaits transmission across all radio bearers for which SDT is enabled, and;
the DL RSRP is above a configured threshold, and;
a valid SDT resource (either RACH or Configured grant) is available
SDT procedure is initiated with either a transmission over RACH (referred to as RA-SDT) or over Type 1 CG resources (referred to as CG-SDT). The SDT resources can be configured on initial BWP (for both RACH and CG). RACH and CG resources for SDT can be configured on either or both of NUL and SUL carriers. The initial PUSCH transmission during the SDT procedure includes at least the CCCH message. While the SDT procedure is ongoing, if data appears in a buffer of any radio bearer not enabled for SDT, the UE initiates a transmission of a non-SDT data arrival indication using UE assistance information message to the network and, if available, includes the resume cause. The network may configure UE to apply ROHC continuity for SDT either when the UE initiates SDT in the cell where the UE received RRCRelease and transitioned to RRC_INACTIVE state or when the UE initiates SDT in a cell of its RNA.
Details of RA-SDT-
For RA-SDT, the network may configure 2-step and/or 4-step RA resources. The UE in RRC_INACTIVE initiates RACH and requests RRC resume together with UL SDT data/signalling. If the UE accesses a gNB other than the last serving gNB, the UL SDT data/signalling is buffered at the receiving gNB, and then the receiving gNB triggers the XnAP Retrieve UE Context procedure. RA-SDT is supported with and without UE context relocation and these two mechanisms as depicted in Figure 7.1-1
and Figure 7.1-2
Details of CG-SDT
The CG-SDT resources are valid only within the cell the UE receives the previous RRCRelease (i.e. only for the no cell change case). When using CG resources for initial SDT transmission, the UE can perform autonomous retransmission of the initial transmission if the UE does not receive confirmation from the network. The network can schedule subsequent UL transmissions using dynamic grants or they can take place on the following CG resource occasions. The DL transmissions are scheduled using dynamic assignments. The UE can initiate subsequent UL transmission only after reception of confirmation for the initial PUSCH transmission from the network. For subsequent UL transmission, the UE cannot initiate re-transmission over a CG-SDT resource. CG-SDT can only be initiated with valid UL timing alignment. The UL timing alignment is maintained by the UE based on a SDT-specific timing alignment timer configured by the network via dedicated signalling and, for initial CG-SDT transmission, also by DL RSRP of configured number of highest ranked SSBs which are above a configured RSRP threshold. Upon expiry of the SDT-specific timing alignment timer, the CG resources are released.
RP-220153: Status Report TSG for WI: NR small data transmissions in INACTIVE state
Summary based on the input provided by Huawei, HiSilicon in RP-220530.
This Rel-17 work item introduced additional enhancements for NB-IoT and LTE-MTC based on features standardized in Rel-13 and enhancements performed from Rel-14 through Rel-16. Rel-17 adds features such as 16QAM for NB-IoT in downlink and uplink, 14 HARQ processes in downlink for HD-FDD Cat. M1 UEs, NB-IoT neighbour cell measurement and triggering before RLF, NB-IoT carrier selection based on coverage level, and a maximum DL TBS of 1736 bits for HD-FDD Cat. M1 UEs .
16-QAM for unicast in UL and DL for NB-IoT
From Rel-13 to Rel-16, an NB-IoT UE can use QPSK for unicast NPDSCH, and QPSK or BPSK for unicast NPUSCH.
This feature allows an NB-IoT UE to use 16-QAM for unicast NPDSCH with TBS up to 4968 bits for standalone and guard-band deployments and 3624 bits for in-band deployments; and allows an NB-IoT UE to use 16-QAM for unicast NPUSCH with TBS up to 2536 bits (which can be transmitted with up to half the time-domain resources with respect to QPSK). When 16-QAM for unicast NPDSCH is configured, an NB-IoT UE can report the channel quality report by reporting the recommended NPDCCH repetition and NPDSCH modulation and coding scheme.
Additional PDSCH scheduling delay for 14-HARQ processes in DL for LTE-MTC
With 10 HARQ processes, a HD-FDD Cat. M1 UE cannot use all available downlink subframes to transmit PDSCH. As shown in Figure 7.2-1
, the subframes #0, #1, #17, #18 cannot be scheduled to transmit PDSCH (as marked with an X).
This feature allows HD-FDD Cat. M1 UEs to use up to 14 HARQ processes in CE Mode A with an additional PDSCH scheduling delay to fully utilize the available BL/CE downlink and BL/CE uplink subframes, where the PDSCH scheduling delay can be indicated as 2 BL/CE DL subframes or a longer delay that consists of different subframe types. Two alternatives for the HARQ-ACK delay indication can be configured: either the HARQ-ACK delay consists of different subframe types, or the HARQ-ACK delay is indicated among sets of absolute subframes.
Neighbour cell measurements and measurement triggering before RLF for NB-IoT
This feature introduces measurements in RRC_CONNECTED for NB-IoT UEs to reduce the time taken for RRC connection reestablishment. The criteria to perform the measurements are signalled separately for intra- and inter-frequency measurements via broadcast signalling. Since dedicated measurements gaps are not supported, the UE may need to perform neighbour cell measurements during DL/UL idle periods that are provided by DRX or packet scheduling.
Carrier selection based on coverage level for NB-IoT
This feature introduces coverage-based paging in NB-IoT to reduce the latency and the resource usage in the network.
When coverage-based paging is enabled, up to two groups of paging carriers can be configured for lower levels of coverage enhancements. The eNB configures the UE during RRC connection release to use one of these groups of paging carriers. If configured, the UE selects a paging carrier in its assigned group if its NRSRP is suitable according to the paging carrier configuration. Coverage based paging is only applicable in the last cell where the coverage information was received.
Maximum DL TBS of 1736 bits for eMTC
From Rel-13 to Rel-16, the max DL TBS size for LTE-MTC Cat. M1 UEs is 1000 bits.
This feature allows HD-FDD Cat. M1 UEs to use a DL TBS of up to 1736 bits in CE Mode A, and the soft channel bits for UE supporting this feature is 43008 bits.
RP-220528: Status report for WI: Additional enhancements for NB-IoT and LTE-MTC; rapporteur: Huawei
Summary based on the input provided by Nokia, Nokia Shanghai Bell in Nokia, Nokia Shanghai Bell.
In order to extend the NR applicability in various verticals with tight latency and reliability requirements, Release 16 IIoT work item has introduced transmission reliability enhancements for Time Sensitive Communications (TSC) and addressed efficiency of the system where UEs handle a mixture of URLLC and eMBB traffic. In TSG SA enhancements for the support TSC have been studied (see TR23.700-20) with normative work followed accordingly for Release 17. This Release 17 work item introduced the following enhancements in RAN:
Physical Layer feedback enhancements for HARQ-ACK and CSI reporting:
Intra-UE multiplexing and prioritization of traffic with different priority:
For HARQ-ACK feedback enhancements, SPS HARQ-ACK deferral was introduced to prevent excessive SPS HARQ-ACK dropping for PUCCH on TDD cells. Besides, to reduce latency, PUCCH cell switching is supported between the PCell, PSCell, PUCCH-SCell and an additional PUCCH-sSCell for TDD cells. Furthermore, PUCCH repetition enhancements over multiple slots/subslots, HARQ-ACK codebook enhancements and triggered HARQ-ACK codebook retransmissions were introduced to improve the HARQ-ACK feedback reliability.
For CSI reporting, enhanced 4-bit sub-band CQI report with absolute values was introduced targeting URLLC services with high reliability requirements and tight latency constraints.
To improve UL and DL efficiency and reduce PHY latency for high priority traffic, enhancements on intra-UE multiplexing and prioritization were introduced for overlapping dynamic grant and CG PUSCH of different PHY priorities, multiplexing HARQ-ACK on a PUCCH or PUSCH of a different PHY priority, and simultaneous PUCCH and PUSCH transmissions of different PHY priorities on different cells for inter-band carrier aggregation (CA).
Uplink enhancements for URLLC in unlicensed controlled environments:
Enhancements for support of time synchronization with propagation delay compensation:
URLLC services can be supported in shared spectrum where LBT failures are assumed to be not frequent. For this scenario, semi-static channel occupancy initiated by the UE was introduced.
Besides, autonomous retransmissions for UL configured grant (CG) and enhanced intra-UE overlapping resource prioritization mechanisms may be enabled simultaneously to harmonize the NR-U and URLLC CG operation.
To improve the absolute time synchronization accuracy of a UE being essential for Time-Sensitive Network (TSN)/TSC operation, two propagation delay compensation (PDC) enhancements are introduced to compensate for time synchronization errors caused by the propagation delay between gNB and UE: PDC based on round-trip-time (RTT) measurements and PDC based on timing advance (TA), which can be performed at the UE or gNB side.
RAN enhancements based on new QoS related parameter (survival time):
In addition to the TSC traffic characteristics introduced in Release 16 as TSC Assistance Information (TSCAI), the Core Network may provide survival time as part of the TSCAI to allow for efficient scheduling at the gNB while satisfying the performance requirements of periodic deterministic communication.
To support uplink periodic traffics of services with survival time requirement, configured grant resources can be used such that the mapping relation between the service and the configured grant is known to both gNB and UE. The gNB can use configured grant retransmission scheduling grant to trigger survival time state entry for a DRB which activates all the RLC entities configured for PDCP duplication of the corresponding DRB to prevent failure of subsequent messages.
RP-220151: Status report for WI Enhanced Industrial Internet of Things (IoT) and ultra-reliable and low latency communication (URLLC) support for NR; rapporteur: Nokia