7 Cellular Internet of Things (IoT)

21.9163GPPRelease 16Release descriptionTS

7.1 Cellular IoT support and evolution for the 5G System

830043

Cellular IoT support and evolution for the 5G System

5G_CIoT

S2

SP-181118

 Sebastian Speicher

770038

Study on 5G_CIoT

FS_CIoT_5G

S2

SP-180614

Sebastian Speicher

820015

Stage 2 of 5G_CIoT

5G_CIoT

S2

SP-181118

Sebastian Speicher

830013

CT aspects of 5G_CIoT

5G_CIoT

ct

CP-111237

Mahmoud Watfa; Qualcomm

830038

CT1 aspects of 5G_CIoT

5G_CIoT

C1

CP-111237

Mahmoud Watfa; Qualcomm

830039

CT3 aspects of 5G_CIoT

5G_CIoT

C3

CP-111237

Mahmoud Watfa; Qualcomm

830040

CT4 aspects of 5G_CIoT

5G_CIoT

C4

CP-111237

Mahmoud Watfa; Qualcomm

830041

CT6 aspects of 5G_CIoT

5G_CIoT

C6

CP-111237

Mahmoud Watfa; Qualcomm

800033

Study on evolution of Cellular IoT security for the 5G System

FS_CIoT_sec_5G

S3

SP-180440

Noamen Ben Henda

760040

Study on MBMS User Services for IoT

FS_MBMS_IoT

S4

SP-170592

Cedric thienot, Expway

Summary based on the input provided by Qualcomm Incorporated in SP-200274.

Substantial E-UTRAN/EPC evolution has been achieved in 3GPP to enable the "Cellular Internet of Things" (CIoT). In particular, eMTC (WB-E-UTRAN) and NB-IoT have been designed in RAN WGs in Rel-13 and enhanced in Rel-14. The corresponding system architecture aspects have been designed for EPC in Rel-13 and Rel-14. These system architecture aspects apply to both NB-IoT and eMTC (WB-E-UTRAN).

The "Cellular IoT support and evolution for the 5G System" work item focused on enabling equivalent functionality for NB-IoT and eMTC connected to 5GC as what has been defined for NB-IoT and eMTC connected to EPC in earlier releases

This section summarizes the key system impacts resulting from the “Cellular IoT support and evolution for the 5G System” work item.

As documented in TS 23.501 [1] clause 5.31, the following CIoT features have been introduced in Rel-16:

– Control Plane CIoT 5GS Optimisation (CP CIoT 5GS Optimisation) is used to exchange user data between the UE and the SMF as payload of a NAS message in both uplink and downlink directions, avoiding the establishment of a user plane connection for the PDU Session (i.e. avoiding the need for Data Radio Bearer and N3 tunnel). Early Data Transmission (EDT), i.e. sending user data in RRC Message 3 is supported for mobile originated Control Plane CIoT 5GS Optimisation.

– User Plane CIoT 5GS Optimisation (UP CIoT 5GS Optimisation) supports transfer of user plane data from CM-IDLE without the need for using the Service Request procedure to establish an Access Stratum (AS) context in NG-RAN and UE. UP CIoT 5GS Optimisation is enabled by the Connection Suspend and Connection Resume in CM-IDLE with Suspend procedures. EDT is also supported for UP CIoT 5GS Optimisation.

– UE and network negotiate whether to use CP CIoT 5GS Optimisation and/or UP CIoT 5GS Optimisation as well as N3 data transport and header compression for CP CIoT 5GS Optimisation during the Registration procedure. The UE indicates its Preferred and Supported Network Behaviour, i.e. the UE indicates which of the aforementioned features the UE supports and whether it prefers to use CP CIoT 5GS Optimisation or UP CIoT 5GS Optimisation. In response, the network indicates which of those features it supports for this UE.

– Non-IP Data Delivery (NIDD) refers to mobile originated (MO) and mobile terminated (MT) communication between UE and an Application Function (AF) where the user data is considered unstructured (also referred to as "non-IP"). NIDD is enabled using an unstructured PDU session between UE and NEF and the NEF’s NIDD API on the N33/Nnef reference point for data delivery from/to AF. Alternatively, non-IP data is delivered using an unstructured PDU session between UE and UPF and a Point-to-Point N6 tunnel between UPF and AF. The NEF also supports distribution of mobile terminated messages to a group of UEs based on the NIDD API.

– Reliable Data Service (RDS) may be used between UE and NEF or UPF, respectively, for unstructured PDU Sessions. RDS provides a mechanism for the NEF or UPF to determine if the user data was successfully delivered to the UE and for the UE to determine if the data was successfully delivered to the NEF or UPF. When a requested acknowledgement is not received, RDS retransmits the packet.

– Extended Discontinuous Reception (DRX) for CM-IDLE and CM-CONNECTED with RRC-INACTIVE enables the UE to reduce its power consumption while still being available for MT data and/or network originated procedures within a certain delay dependent on the negotiated DRX cycle value. In CM-IDLE state the following DRX cycles are supported: up to almost 44 minutes (for eMTC) and up to almost 3 hours (for NB-IoT). In CM-CONNECTED with RRC-INACTIVE, DRX cycles of up to 10.24 seconds are supported.

– Enhancements for the Mobile Initiated Connection Only (MICO) mode of rel.15:

– MICO mode with Extended Connected Time enables an AMF that is aware of pending or expected MT traffic to keep the UE in CM-CONNECTED state and to request the RAN to keep the UE in RRC-CONNECTED state for an Extended Connected Time period to ensure that the downlink data and/or signalling is delivered to the UE before the UE is released.

– MICO mode with Active Time is similar to the UE Power Saving Mode (PSM) defined for EPS [2], i.e. UE and AMF negotiate an Active Time value, which dictates for how long the UE is reachable for paging upon entering CM-IDLE. Once the Active Time has elapsed, the UE can enter MICO mode, i.e. become unreachable for paging.

– MICO mode and Periodic Registration Timer Control enables the network to align a UE’s Periodic Registration Updates with an expected DL communication schedule for the UE. This is achieved by the Strictly Periodic Registration Timer Indication which the network can provide to the UE to avoid that the Periodic Registration Timer is restarted by the UE when the UE enters CM-CONNECTED.

High latency communication refers to mechanisms that may be used to handle mobile terminated (MT) communication with UEs being unreachable while using power saving functions (e.g. extended DRX or MICO mode with Active or Extended Connected Time). High latency communication is supported by extended buffering of downlink data in the UPF, SMF or NEF when a UE is using power saving functions in CM-IDLE and is not reachable. Alternatively, high latency communication is supported through different AF notifications. An AF may for example subscribe to receive UE reachability notifications so that the AF then waits with sending the data until it gets a notification that the UE has become reachable.

Support for Monitoring Events enables AFs to acquire information such as whether a UE is roaming or to determine when a USIM is changed to a different ME. The complete list of monitoring events is documented in TS 23.502 [3] clause 4.15.3.1.

External parameter provisioning refers to functionality originally defined in Rel-15 already, which enables an AF to provision information such as Expected UE Behaviour parameters or other service parameters to the network (see TS 23.502 [3] clause 4.15.6.1). In Rel-16, additional Expected UE Behaviour parameters were introduced (e.g. an indication whether the UE is stationary or mobile), which can be used by the AMF and/or SMF for various purposes, e.g. by AMF for paging optimisations. In addition, an AF can provide Network Configuration parameters (e.g. Maximum Response Time) to the network, which in turn can be used to derive parameters for system procedures (e.g. to derive the Active Time or Extended Connected time for MICO mode). The complete list of Expected UE Behaviour parameters and Network Configuration parameters are documented in TS 23.502 [3] clause 4.15.6.3 and 4.15.6.3a, respectively.

PDU session handling during inter-RAT idle mode mobility to and from NB-IoT allows the SMF to maintain a PDU session, disconnect a PDU session with a reactivation request or to disconnect a PDU session without reactivation request when the UE moves between a "broadband" RAT (e.g. NR or WB-E-UTRAN) and a "narrowband" RAT (NB-IoT).

System aspects of the Enhanced Coverage RAN feature as specified in TS 36.300 [4], in particular storage of Paging Assistance Data for UEs supporting Enhanced Coverage and providing of Paging Assistance Data to RAN during paging has been introduced. Specific subscribers can also be restricted to use the Enhanced Coverage feature through Enhanced Coverage Restricted information that is stored in the UDM. Based on the latter, AMF informs UE, RAN and SMF about the use (or not) of the Enhanced Coverage feature.

– The rate of user data sent to and from a UE can be controlled in two ways:

– Serving PLMN rate control allows the serving network to protect its AMF and the Signalling Radio Bearers in the NG-RAN from the load generated by NAS Data PDUs by indicating a limit for the number of NAS Data PDUs per time unit to the UE and UPF/NEF.

– Small Data Rate Control allows HPLMN operators to offer customer services such as "maximum of Y messages per day" and is also based on indicating a number of packets per time unit limitation to UE and UPF/NEF for enforcement.

Congestion control for control plane data transfer enables the AMF to restrict, e.g. during high-load situations, the use of the control plane for data transmission (i.e. for Control Plane CIoT 5GS Optimisation). In particular, AMF may provide a Control Plane data back-off timer to the UE. While the Control Plane data back-off timer is running, the UE is not allowed to initiate any data transfer via Control Plane CIoT 5GS Optimisation.

Service Gap Control can be used to control the frequency at which UEs can access the network, e.g. to alleviate peak load situations. Service Gap control is realized by AMF indicating a Service Gap Time to a UE; the UE then stays in CM-IDLE mode for at least the whole duration of the Service Gap timer before triggering Mobile Originated user data transmission.

Inter-UE QoS for NB-IoT targets UEs that are using Control Plane CIoT 5GS Optimisation and are accessing the network via NB-IoT. The feature allows NG-RAN to prioritise resource allocation between those UEs based on the subscribed NB-IoT UE Priority that NG-RAN may retrieve from the AMF.

Differentiation of Category M UEs enables the network to identify traffic to/from Category M UEs, e.g. for charging differentiation and subscription based access control. This functionality is based on a Category M indication from UE to NG-RAN during RRC Connection Establishment and subsequently, an LTE-M Indication to the AMF in the Initial UE Message. Based on this, AMF considers the RAT type to be LTE-M and informs SMF, SMSF and PCF accordingly for subsequent use of the LTE-M RAT type, e.g. in CDRs. A subscription parameter for subscription based access restriction for LTE-M is also introduced.

Selection, steering and redirection between EPS and 5GS allows a network that supports CIoT features in both EPC and 5GC to steer UEs from the CN type that the UE is attempting to register with to the other CN type (e.g. from 5GC to EPC) due to operator policy, e.g., due to roaming agreements, Preferred and Supported Network Behaviour, load redistribution, etc. It is assumed that operators configure the steering policies in EPC and 5GC such that steering UEs back and forth between EPC and 5GC is avoided.

References

List of related CRs: select "TSG Status = Approved" in:
https://portal.3gpp.org/ChangeRequests.aspx?q=1&workitem=830043,770038,820015,830013,830038,830039,830040,830041,800033,760040

[1] TS 23.501, “System architecture for the 5G System (5GS)”

[2] TS 23.401, “General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access”

[3] TS 23.502, “Procedures for the 5G System (5GS)”

[4] TS 36.300, " Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2"

7.2 Additional enhancements for NB-IoT

800084

Additional enhancements for NB-IoT

NB_IOTenh3

R1

RP-200293

Huawei

800184

Core part: Additional enhancements for NB-IoT

NB_IOTenh3-Core

R1

RP-200293

Huawei

800284

Perf. part: Additional enhancements for NB-IoT

NB_IOTenh3-Perf

R4

RP-200293

Huawei

Summary based on the input provided by FUTUREWEI in RP-201229.

This Feature builds on the successful base NB-IoT feature in Rel-13, and enhancements in Rel-14 and Rel-15, and adds features such as DL/UL transmission efficiency improvement, UE power consumption improvement, scheduling enhancement, network management tool enhancement, latency improvement, enhancement on coexistence with NR and connection to 5GC.

Improved DL transmission efficiency and UE power consumption

Reduced UE power consumption and improved transmission efficiency are achieved through reduced downlink monitoring and reduced signalling, building on features introduced in earlier releases.

UE-group wake-up signals (GWUS) (FDD):

With the introduction of Rel-15 wake-up signalling (WUS), UE can skip the paging procedures if the wake-up signal is not detected to save power. This feature (UE-group WUS) allows eNB to transmit a UE-group WUS to instruct the UEs in the group that they must monitor NPDCCH for paging. This allows the UE to skip the paging procedures to save more power if eNB sends UE-group WUS to UEs in other groups. The UEs are grouped according to their paging probability and/or their UE ID based on system information configuration.

Mobile-terminated early data transmission (MT-EDT) (FDD):

Rel-15 Mobile Originating Early Data Transmission (MO-EDT) allows one uplink data transmission optionally followed by one downlink data transmission during the random access procedure, avoiding transition to RRC_CONNECTED mode. Rel-16 Mobile Terminating Early Data Transmission (MT-EDT) allows one downlink data transmission during the random access procedure triggered in response to a paging message. This feature allows the eNB to decide whether to initiate Mobile Terminated EDT procedures towards the UE based on the data size received from the core network. Mobile Terminating Early Data Transmission (MT-EDT) is only supported in EPC.

Support for Preconfigured uplink resources (PUR) in idle mode (FDD)

In Rel-15, signalling overhead and power consumption reductions were introduced by the (mobile-originated) early data transmission (EDT) feature, where data can be transmitted already in Msg3 during the random-access procedure.

In Rel-16, the earlier transmission of UL data payload has been further enhanced by introducing UL transmission using preconfigured uplink resources (PUR). This feature allows eNB to configure uplink resources, in which a UE in IDLE mode can send UL transmission without performing random access procedures. The UE can be potentially configured with a cyclic shift of DMRS, which allows sharing of the preconfigured resources under which up to two users can transmit NPUSCH simultaneously when the NPUSCH transmission is larger than or equal to 64ms for 12-tone allocation. By skipping the random access procedures, the uplink transmission efficiency can be improved and UE power consumption is reduced. Before performing a PUR transmission, the UE must evaluate the validity of the timing advance (TA) based on either individual or combined usage of any of the following attributes: a) serving cell change, b) TA timer, c) RSRP change. Additionally, it is possible to configure the TA as always valid within a given cell.

Scheduling of multiple DL/UL transport blocks with single DCI (FDD)

This feature allows the scheduling of up to two transport blocks (TB) with a single DCI for uplink or downlink unicast transmission, where the number of TBs is indicated by DCI. The transmission of multiple TBs can be configured to be contiguous or interleaved. And HARQ bundling can be potentially configured when transmission is configured as interleaved. It also allows the scheduling of up to eight transport blocks with a single DCI for SC-MTCH, where the number of TBs is indicated by DCI. The DCI overhead can be reduced for contiguous UL/DL transmissions.

Network management tool enhancements – SON (FDD and TDD)

Rel-16 introduces SON features: RACH report, RLF report and ANR for network resource optimisation. The ANR measurements are performed when the UE is in RRC_IDLE and reported next time the UE enters RRC_CONNECTED. The NPRACH configuration of the NB-IoT Cells are exchanged between neighbour eNBs for RACH optimization. And the RLF report from UE is forwarded to the old eNB to determine the nature of the failure.

SON features are only supported in EPC.

Improved multicarrier operations – Quality report in Msg3 and connected mode (FDD)

In cells with interference, the coverage level corresponding to the estimate RSRP may be mismatched with the channel quality. This feature allows the eNB to configure a UE in IDLE mode to report the downlink channel quality in Msg3 for non-anchor access. It also allows the UE to report the downlink channel quality in connected mode other than Msg3 for anchor and non-anchor carriers. This allows the eNB to schedule NPDCCH and NPDSCH more accurately, especially in cases with mismatch between coverage level and channel quality.

Presence of NRS on a non-anchor carrier for paging (FDD)

This feature allows eNB to transmit NRS in subframes on a non-anchor carrier for paging even when no paging NPDCCH is transmitted. The NRS are present in the first M subframes out of the 10 NB-IoT DL subframes before the Paging Occasion (PO), where the PO can be a subset of POs or a whole set of POs, and the values of M depend on the value of nB as defined in TS 36.304.

When NRS is present on a non-anchor paging carrier and the conditions for NRSRP measurement on non-anchor carrier are met as defined in TS 36.133, the UE may perform serving cell measurements on the non-anchor paging carrier.

Mobility enhancements – Idle mode inter-RAT cell selection to/from NB-IoT (FDD and TDD)

With this feature, NB-IoT can provide assistance information for inter-RAT cell selection to E-UTRAN/GERAN and E-UTRAN can provide assistance information for inter-RAT cell selection to NB-IoT. A UE may use the assistance information provided by the network for cell selection to/from NB-IoT.

Improved latency – UE Specific DRX (FDD and TDD)

Rel-16 introduces support for UE specific DRX to reduce paging latency. The eNB may broadcast a minimum UE specific DRX value shorter than the cell default DRX value. When UE specific DRX is configured by the upper layers and the minimum UE specific DRX value is broadcast, the UE monitors paging according to the longer of the two values.

Coexistence of NB-IoT with NR (FDD and TDD)

This feature allows the configuration of the DL/UL resource reservation in subframe/slot/symbol-levels on non-anchor carriers for unicast transmission to avoid resource overlapping with NR channels/signals. The configuration can be for 10ms or 40ms duration, with a periodicity from {10ms, 20ms, 40ms, 80ms, 160ms} and a start position in a granularity of 10ms, which is independent from legacy configurations. It also allows dynamic indication whether the resource reservation is applied or not.

Three system scenarios have been studied and captured in TR 37.824:

• For NB-IoT operation in NR in-band, RB alignment, power boosting and numerologies have been addressed.

• For NB-IoT operation in NR guard band, RF requirements will not be specified.

• For NB-IoT standalone operation, based on coexistence study, it is concluded that there is no issue for NB-IoT standalone coexistence with NR.

Connection to 5GC (FDD and TDD)

Rel-16 introduces support for connection to 5GC reusing eLTE as a baseline, including Unified Access Control (UAC). RRC_INACTIVE, NR SDAP and NR PDCP are not supported and a maximum of two PDU sessions mapped to two default DRBs is supported.

Rel-16 also introduces support for the CIoT 5GS optimisation, in particular extended DRX (eDRX) in RRC_IDLE, control plane and user plane CIoT optimisation, MO-EDT for the control plane and user plane CIoT optimisation, RRC Connection Reestablishment for the control plane and restriction of use of Enhanced Coverage.

Similar backhaul signalling to support control plane and user plane CIoT optimisation are introduced over NG interface (between ng-eNB and AMF) and over Xn interface (between ng-eNBs), including e.g. early UE radio capability retrieval from core network after msg3, NB-IoT CP relocation procedures to support connection reestablishment, Paging assistance information exchanging, UE differentiation information exchanging, etc.

References

List of related CRs: select "TSG Status = Approved" in:
https://portal.3gpp.org/ChangeRequests.aspx?q=1&workitem=800084,800184,800284

7.3 Additional MTC enhancements for LTE

800083

Additional MTC enhancements for LTE

LTE_eMTC5

R1

RP-191356

Ericsson

800183

Core part: Additional MTC enhancements for LTE

LTE_eMTC5-Core

R1

RP-190770

Ericsson

800283

Perf. part: Additional MTC enhancements for LTE

LTE_eMTC5-Perf

R4

RP-190770

Ericsson

Summary based on the input provided by Ericsson in RP-201276.

This work item builds on the LTE features for Machine-Type Communications (MTC) introduced in earlier releases (e.g. low-complexity UE categories M1 and M2, and Coverage Enhancement Modes A and B) by further improving network operation and efficiency in a range of areas.

The following sections describe the new MTC features for LTE in Rel-16. All features are optional for the UE and can be supported by Cat-M1 and Cat-M2 and by normal LTE UEs supporting CE mode unless otherwise stated. All features are applicable to both CE modes (A and B) in all duplex modes (HD-FDD, FD-FDD, and TDD) unless otherwise stated.

Improved DL transmission efficiency and UE power consumption

Reduced UE power consumption is achieved through reduced downlink monitoring and reduced signalling, building on features introduced in earlier releases.

• UE-group wake-up signals (GWUS): Reduced UE power consumption in idle mode was enabled in Rel-15 by the introduction of the wake-up signal (WUS), a compact signal transmitted a configurable time before the paging occasion (PO) when a UE is being paged, allowing the UE to maximize its sleep time during periods when there is no paging. In Rel-16, an enhancement is introduced that allows a WUS to wake up a configurable group of UEs rather than all UEs that happen to monitor the same PO. This helps reduce the power consumption even further. The mapping of GWUS in the time and frequency domains is highly configurable.

• Mobile-terminated early data transmission (MT-EDT): For scenarios where the UE only needs to transmit a small amount of data, the early data transmission (EDT) feature in Rel-15 enables the UE to transmit up to (slightly more than) 100 bytes of data already in Msg3 during the random-access procedure, and to receive data already in Msg4. If needed, eNB can order fallback to legacy random-access procedure during the EDT procedure. In Rel-16, an enhancement is introduced that allows not only mobile-originated (MO) EDT access but also mobile-terminated (MT) EDT. When the MME triggers MT-EDT, an indication is included in the paging message, after which the UE triggers random access to resume the connection (in case the UP CIoT EPS optimization is used) or initiate MO-EDT (in case the CP CIoT EPS optimization is used). MT traffic is received in Msg4. MT-EDT is only supported when UE is connected to EPC (not 5GC).

• Improved DL quality reporting: Legacy CE mode A supports both periodic and aperiodic CSI reporting which can be used to assist PDSCH link adaptation. In Rel-16, a new type of DL quality reporting is introduced which reflects MPDCCH quality rather than PDSCH quality. The report represents the required number of MPDCCH subframe repetitions for reliable MPDCCH reception. It can be sent in connected mode, but it can also be sent already in Msg3 during the random access procedure, which means that the report can be used for guiding the UE-specific MPDCCH configuration, which helps optimize power consumption, latency, and spectral efficiency.

• MPDCCH performance improvement: In legacy LTE-MTC, MPDCCH demodulation is DMRS-based. With this feature, the UE can use a combination of DMRS and CRS for MPDCCH demodulation to improve the MPDCCH performance. The feature takes the configured DMRS-to-CRS power ratio into account. The feature can be used for transmissions in idle mode and/or connected mode. In idle mode, the DMRS-to-CRS mapping is based on precoder cycling, whereas in connected mode, it can be configured to be precoder cycling based, CSI-based, or (in case of TDD) reciprocity-based.

Beside the features listed above, the features described in sections 2.2, 2.3 and 2.6 can also improve UE power consumption and/or transmission efficiency in DL and/or UL.

Preconfigured uplink resources (PUR)

In Rel-15, signalling overhead and power consumption reductions were introduced by the (mobile-originated) early data transmission (EDT) feature, where data can be transmitted already in Msg3 during the random-access procedure.

In Rel-16, the earlier transmission of UL data payload has been further enhanced by introducing UL transmission using preconfigured uplink resources (PUR). When the feature is configured, both the random-access preamble transmission (Msg1) and the random-access response (Msg2) can be omitted, and the data transmission can be completed in only two messages (i.e., Msg3 and Msg4).

The UE is configured with PUR via dedicated RRC signaling while in connected mode. Configuring a UE with PUR can be triggered by the network or requested by the UE. Before performing a PUR transmission, the UE must evaluate the validity of the timing advance (TA) based on either individual or combined usage of any of the following attributes: a) serving cell change, b) TA timer, c) RSRP change. Additionally, it is possible to configure the TA as always valid within a given cell.

There are two schemes for transmitting using PUR, dedicated PUR and shared PUR, the latter allows up to two users to transmit simultaneously when the number of PUSCH repetitions is greater than or equal to 64 for full-PRB allocation.

Scheduling of multiple transport blocks

In legacy LTE-MTC operation, each DCI carried by MPDCCH schedules a single PDSCH or PUSCH transport block (TB). In Rel-16, a possibility to schedule multiple TBs using a single is introduced. This can help improve the resource utilization by reducing the number of physical resource blocks (PRBs) spent on MPDCCH transmission and the number of subframes spent on guard time for DL-to-UL and UL-to-DL transition (in half-duplex FDD operation).

• Unicast multi-TB scheduling: When the feature is configured, a single DCI can schedule multi TBs for PDSCH or PUSCH (up to 8 TBs in CE mode A, or up to 4 TBs in CE mode B). The number of TBs is dynamically controlled by the DCI. The TBs can be configured to be transmitted consecutively or subframe interleaved (in case of subframe repetition). For PDSCH multi-TB scheduling, HARQ-ACK bundling can optionally be used to improve the resource utilization further for UEs in good coverage. For PUSCH multi-TB scheduling, early termination of the PUSCH transmission is supported through indication of positive HARQ-ACK in the DCI.

• Multicast multi-TB scheduling: When the feature is configured a single DCI can schedule up to 8 TBs for PDSCH for a SC-MTCH, with configurable time gaps between the TBs if desired. The number of TBs is dynamically controlled by the DCI.

CE mode improvements for non-Cat-M UEs

The features in this work item can be supported both by Cat-M UEs and non-Cat-M UEs that support CE mode A or B. In addition, the following features have been specified specifically for non-Cat-M UEs that support CE mode A or B.

• Enhancements to idle mode mobility: A possibility is introduced for a non-Cat-M UE in a non-standalone LTE-MTC cell to use enhanced coverage functionality to camp in the cell even if the S-criterion indicates that the UE is in normal coverage. This functionality is enabled/disabled by a configuration provided in SIB1. (This is the default behavior for the standalone LTE-MTC case described in the next section in this document.)

• CSI feedback based on CSI-RS: In legacy CE mode A, periodic and aperiodic CSI feedback is based on up to 4 CRS antenna ports. This feature introduces support for periodic CSI feedback based on 8 CSI-RS antenna ports in TM9 for non-Cat-M UEs in CE mode A. The feature can help improve the DL link adaptation and hence the DL performance. As a separate UE capability, the feature can also optionally be supported in combination with codebook subset restriction.

• ETWS/CMAS in connected mode: In legacy LTE-MTC, ETWS/CMAS notification indication is supported using DCI format 6-2 in MPDCCH common search space Type-1 in idle mode. This feature introduces ETWS/CMAS notification indication using DCI format 6-1A/B in MPDCCH common search space Type-0 in connected mode for non-Cat-M UEs in CE mode A/B. This means that a UE can be notified without releasing the UE to idle mode.

Stand-alone deployment

In legacy LTE-MTC operation, the first few OFDM symbols in each DL subframe are unused by LTE-MTC since they are assumed to be occupied by LTE control channels for normal LTE UEs (PCFICH, PDCCH, PHICH). This feature enables transmission of MPDCCH and/or PDSCH to UEs in CE mode A/B in the “LTE control channel region” on carriers that are not used for normal LTE. The feature can be used for transmissions in idle mode and/or connected mode. The potential DL transmission efficiency gain is about 14% (corresponding to 2 out of 14 OFDM symbols) for 1.4 MHz carriers and about 7% (corresponding to 1 out of 14 OFDM symbols) for wider carriers.

Mobility enhancements

In Rel-15, two new LTE-MTC signals were introduced, the resynchronization signal (RSS) and the wake-up signal (WUS), and in Rel-16 the following mobility enhancements are introduced which make use of the Rel-15 signals.

• RSS-based measurements: In Rel-15, support for a resynchronization signal (RSS) was introduced and its configuration is provided by the serving cell. In Rel-16, signaling of RSS configurations for neighbor cells is introduced. Both broadcasted and dedicated signaling can be used to provide the configurations. The primary purpose of RSS is to improved synchronization performance, but with the Rel-16 signaling, the UE may also use RSS for improved measurement performance for intra-frequency RSRP measurements for neighbor cells in both idle and connected mode.

• RRM measurement relaxation: The legacy LTE-MTC UE behavior requires the UE to measure on the serving cell and evaluate the cell selection criterion at least every DRX cycle. The wake-up signal (WUS) introduced in Rel-15 would allow the UE to sleep for multiple paging cycles and wake up to receive paging after a configurable time duration, but the UE power saving gain from WUS cannot be fully utilized since the UE is still required to wake up for measurements. Therefore, an RRM measurement relaxation is introduced in Rel-16, which allows the UE meet the requirements using a longer measurement cycle to save power, where the cycle is configurable under certain conditions.

Performance improvement for NR coexistence

Spectrum sharing with legacy (Rel-13/14/15) LTE-MTC is already supported in Rel-15 NR, and the RF coexistence aspects described in TR 37.823. The following features are introduced in Rel-16 LTE-MTC in order to further improve the performance of the coexistence with NR.

• DL/UL resource reservation: Legacy LTE-MTC supports configuration of invalid DL/UL subframes, which can be used in order to avoid mapping LTE-MTC transmissions to subframes that are needed for NR transmissions. Rel-16 takes a step further by introducing finer-granularity LTE-MTC resource reservation in both the time domain (with subframe, slot, or symbol level granularity) and the frequency domain (with LTE RBG level granularity) for unicast MPDCCH/PDSCH/PUSCH/PUCCH transmissions in connected mode in CE mode A/B. The resource reservation patterns are configurable using parameter combinations based on bitmaps, periodicities and offsets. For PDSCH/PUSCH, the DCI can indicate that the resource reservation should be overridden, in which case the PDSCH/PUSCH transmission becomes continuous.

• DL subcarrier puncturing: In order to achieve PRB alignment between LTE-MTC and NR, a possibility to puncture 1 or 2 DL subcarriers at the lower or higher edge of each 6-PRB narrowband is introduced. The puncturing affects MPDCCH/PDSCH transmissions in connected mode in CE mode A/B. The performance loss from the puncturing should typically be insignificant.

Connection to 5GC

In Rel-16, support for connecting LTE-MTC UEs to 5GC is introduced. It resembles the Rel-15 functionality for connecting LTE UEs to 5GC. The RRC_INACTIVE state is supported and additionally the User Plane CIoT 5GS optimisation is supported in RRC_IDLE (similar to the corresponding EPC feature). Some features, such as EDT and PUR are supported only in RRC_IDLE using the UP-optimisation solution and are not supported in RRC_INACTIVE. Long extended DRX in RRC_IDLE is supported, and RAN paging cycles of 5.12 s and 10.24 s are supported in RRC_INACTIVE.

References

List of related CRs: select "TSG Status = Approved" in:
https://portal.3gpp.org/ChangeRequests.aspx?q=1&workitem=800083,800183,800283

[1] RP-192875, Rel-16 LTE-MTC work item description

[2] RP-201275, Rel-16 LTE-MTC work item status report

[3] RP-192647 & RP-192648 & RP-200196 & RP-200698, RAN1 CR packs

[4] RP-200360 & RP-201192 & RP-201193, RAN2 CR packs

[5] RP-201086 & RP-201087, RAN3 CR packs

[6] RP-193023 & RP-200418 & RP-200962, RAN4 CR packs