Support of NR Industrial Internet of Things

Support of NR Industrial Internet of Things

  November 07, 2020    Mr. Standards

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The Tdoc RP-192590 on Support of NR Industrial Internet of Things (IoT) [2] aimed at evolving NR system to better support use cases of various vertical markets such as factory automation or electrical power distribution. It introduced transmission reliability enhancements, NR support for Time Sensitive Communications (as defined in 3GPP TS 23.501 [4]), and addressed efficiency of the system where UEs handle a mixture of URLLC and eMBB traffic. This article focuses mainly on Layer 2/3 protocols aspects while PHY layer enhancements for URLLC is explained in "Physical Layer Enhancements for NR URLLC"

The following enhancements are introduced:

1. PDCP packet duplication enhancements – a possibility of multiplication of the packets related to signalling or data radio bearer over three or four logical channels has been specified for the increased reliability of the transmission over the air interface. This is possible for both Carrier Aggregation based packet duplication where the packet is sent over up to four different serving cells of a single gNB and for Dual Connectivity based packet duplication where the packet is sent over serving cells belonging to two different gNBs (e.g. two serving cells in Master Node and two serving cells in Secondary Node or three serving cells in Master Node and one serving cell in Secondary Node etc.). The network dynamically controls which of the configured logical channels are active for duplication at a certain time by utilizing a dedicated MAC CE command.

2. RAN support for higher layer multi-connectivity - The feature introduces also higher reliability for the end to end transmission by using duplication of a PDU session. This functionality allows NG-RAN to ensure the data of the PDU session and its redundant one to utilize two independent transmission paths. The NG-RAN may, for example, use dual connectivity principles with one PDU session delivered through the master node and the redundant one via the secondary node, or the NG-RAN may use independent paths within the same NG-RAN node. Besides, the feature offers the possibility to provide redundancy over N3 tunnel between the UPF and the NG-RAN node on a per QoS flow basis.

3. Support for accurate reference timing delivery – to support strict synchronization accuracy requirements of TSC applications, the delivery of time reference information from the gNB to the UE using unicast or broadcast RRC signalling with a granularity of 10 ns was introduced. UE Assistance Information procedure was extended to allow the UE to indicate its preference to receive such information.

4. Scheduling enhancements – support for up to eight simultaneously active semi-persistent scheduling (SPS) configurations for a given BWP of a UE was specified. Work Item introduced also new logical channel restriction based on physical layer priority level of the grant and a list of Configured Grant (CG) configurations allowed to be utilized by a certain logical channel (support of up to twelve simultaneously active CG configurations in a BWP of a UE was introduced as part of WI on Physical Layer Enhancements for NR Ultra-Reliable and Low Latency Communication (URLLC) [3]). UE can now be configured with CG and SPS periodicities of any integer multiple of a slot with maximum periodicity of 640 ms. These enhancements allow, e.g., to more efficiently support, deterministic traffic with a wide range of different periodicities.

5. Time Sensitive Communication Assistance Information (TSCAI): Core Network may provide a gNB with an information about TSC traffic characteristics such as Burst Arrival Time, traffic flow direction and periodicity, to allow for a more efficient scheduling at the gNB.

6. Ethernet Header Compression (EHC): since TSC traffic is often carried over Ethernet frames with a short size (e.g. 20-50 bytes), EHC protocol was specified within PDCP sublayer to increase efficiency of Ethernet frames transmission over the NR air interface. EHC allows to avoid transmission of Ethernet header fields such as DESTINATION ADDRESS, SOURCE ADDRESS, 802.1Q TAG, and LENGTH/TYPE, between the gNB and the UE. EHC was specified for both NR and EUTRA PDCP.

7. Prioritization between overlapping uplink resources of one UE: when multiple UL grants provided to a single UE overlap in time on a serving cell, the UE is now able to consider the priority of the grant and/or the priority of the logical channel that can be carried over the grant when making a decision about which grant to utilize. Similarly, the UE may consider the priority of a scheduling request (SR) as well as priority of the logical channel which triggered the SR when deciding whether to transmit PUSCH or SR when they overlap in time. Furthermore, if two PUCCHs of different PHY priorities or a PUCCH and a PUSCH of different PHY priorities are overlapping in time on a serving cell, the UE is able to cancel the lower priority transmission with the specified cancellation behaviour and related timeline to allow for transmission of the PUSCH or PUCCH of higher PHY priority. 

Thanks to the introduced enhancements it is possible to support Industrial IOT applications and Time Sensitive Communications in a more efficient way, allow for extra reliability for URLLC traffic as well optimize handling of a mixture of applications with various priorities and QoS requirements by a single UE.

References

[1] 3GPP TR 38.825: “Study on NR industrial Internet of Things (IoT)”

[2] RP-192590: ”Revised WID: Support of NR Industrial Internet of Things (IoT)”

[3] RP-190726: “New WID: Physical Layer Enhancements for NR Ultra-Reliable and                                   Low Latency Communication (URLLC)”

[4] 3GPP TS 23.501: “System architecture for the 5G System (5GS)”

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Physical Layer Enhancements for NR URLLC (Ultra-Reliable and Low Latency Communication)

Physical Layer Enhancements for NR URLLC (Ultra-Reliable and Low Latency Communication)

  November 07, 2020    Mr. Standards

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In Release 15 the basic support for URLLC was introduced with TTI structures for low latency as well as methods for improved reliability. However, use cases with tighter requirements, e.g. higher reliability up to 1E-6 and short latency in the order of 0.5 to 1ms, have been identified as important areas for NR.

In R16 there have been enhancements to PDCCH, UCI, PUSCH, inter UE TX prioritization/multiplexing and UL configured grant transmission.

The following are key functionalities:

DCI format 0_2 and DCI format 1_2

DCI format 0_2/1_2 with configurable sizes for most of the DCI fields are introduced, which provides the possibility to improve the reliability by decreasing the DCI size (e.g. ~24 bits) with appropriate RRC configuration of the DCI fields. Details of DCI format 0_2/1_2 can be found in [4].    

Enhanced PDCCH monitoring capability 

Rel-16 span-based PDCCH monitoring capability is introduced mainly for achieving low latency. A UE can indicate a capability to monitor PDCCH according to one or more of the combinations (X, Y) = (2, 2), (4, 3), and (7, 3) per SCS configuration of μ=0 and μ=1. A span is a number of consecutive symbols in a slot where the UE is configured to monitor PDCCH. If a UE monitors PDCCH on a cell according to combination (X,Y), the UE supports PDCCH monitoring occasions in any symbol of a slot with minimum time separation of X symbols between the first symbol of two consecutive spans, and the number of symbols of a span is up to Y. For each reported combination (X, Y), the UE supports the limit M_PDCCH^(max,(X,Y),μ) on the maximum number of monitored PDCCH candidates per PDCCH monitoring span as defined in Table 10.1-2A in [5] and the limit C_PDCCH^(max,(X,Y),μ) on the maximum number of non-overlapped CCEs for channel estimation per PDCCH monitoring span as defined in Table 10.1-3A in [5]. An example of PDCCH monitoring according to combination (4, 3) is as shown in Figure 1.  

Fig. 1. An example of PDCCH monitoring using Rel-16 span based PDCCH monitoring capability.

Sub-slot based HARQ-ACK feedback  

Sub-slot based HARQ-ACK feedback is introduced to support more than one PUCCH for HARQ-ACK transmission within a slot, which  is mainly beneficial for achieving low latency.  An UL slot consists of a number of sub-slots. No more than one PUCCH carrying HARQ-ACKs starts in a sub-slot. A UE can indicate the supported sub-slot configuration among the candidate values of {7-symbol*2, 2-symbol*7 and 7-symbol*2} for normal CP or { 6-symbol*2, 2-symbol*6 and 6-symbol*2} for extended CP. 

Two HARQ-ACK codebooks constructed simultaneously   

This work item specifies the support of two HARQ-ACK codebooks with different priorities to be simultaneously constructed, which is mainly beneficial for improving reliability for service with higher priority. Each of the two HARQ-ACK codebooks can be either slot-based HARQ-ACK codebook or sub-slot-based HARQ-ACK codebook. Separate PUCCH configurations are supported for different HARQ-ACK codebooks. The feature supports two priority levels for HARQ-ACK. Rules are defined for the UE to resolve collisions between UL channels/signals with different priorities. 

PUSCH enhancements    

This work item specifies PUSCH repetition type B and PUSCH repetition type A for PUSCH enhancements. PUSCH repetition type B is mainly beneficial for achieving low latency. PUSCH repetition type A can improve the spectral efficiency. 

For PUSCH repetition type B, for a transport block, one dynamic UL grant or one configured grant schedules two or more PUSCH repetitions that can be in one slot, or across a slot boundary in consecutive available slots. Examples of PUSCH repetition type B are given in Figure 2. Inter-slot frequency hopping and inter-repetition frequency hopping are specified for PUSCH repetition type B. Interaction with DL/UL directions is specified as in Clause 6 in [6].   

Fig. 2. Examples of PUSCH repetition type B.

PUSCH repetition type A corresponds to PUSCH transmission with Rel-15 behavior with or without slot aggregation. With slot aggregation, the number of repetitions can be dynamically indicated in Rel-16. 

Enhanced inter UE Tx prioritization/multiplexing

This work item specifies UL cancellation scheme and enhanced UL power control scheme for enhanced inter UE Tx prioritization/multiplexing, which are mainly beneficial for achieving low latency.

For UL cancellation scheme, DCI format 2_4 is introduced for notifying the PRB(s) and OFDM symbol(s) where UE cancels the corresponding UL transmission from the UE. An indication by DCI format 2_4 for a serving cell is applicable to a PUSCH transmission or an SRS transmission on the serving cell.

For UL power control scheme, open-loop power control parameter set indication is included in DCI format 0_1/0_2 to indicate the P0 value for PUSCH scheduled dynamically as defined in [5].

Multiple active configured grant configurations for a BWP 

Up to 12 configured grant configurations can be configured in a BWP of a serving cell, which is mainly beneficial for achieving high reliability. Separate RRC parameters can be configured for different configured grant configurations. Separate activation/release can be used for different configured grant Type 2 configurations. In addition, joint release for two or more configured grant Type 2 configurations for a given BWP of a serving cell is also supported.

References

[1] RP-191584, “Revised WID: Physical Layer Enhancements for NR Ultra-Reliable and Low Latency Communication (URLLC)”, Newport Beach, CA, June 3-6, 2019.

[2] TR 38.824 v16.0.0.

[3] TR 38.825 v16.0.0.

[4] TS 38.212 v16.2.0.

[5] TS 38.213 v16.2.0.

[6] TS 38.214 v16.2.0.

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Enhancement of URLLC support in the 5G Core network

Enhancement of URLLC support in the 5G Core network

  November 07, 2020    Mr. Standards

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The main functionalities introduced here are the support of redundant transmission, QoS monitoring, dynamic division of the Packet Delay Budget, and enhancements of the session continuity mechanism.

Redundant transmission for high-reliability communication

Some URLLC services request very high reliability that hardly can be supported in an economical way by a single transport path. To support such services, a redundant transmission mechanism is specified. User packets are duplicated and simultaneously transferred to the receiver via two disjoint user plane paths. The redundant packets are then eliminated at the receiver side. With this, service failure can be avoided even in case the packet transmission via one path occasionally fails or exceeds the delay requirement.

Different options are specified to support redundant transmission at different layers:

-    Dual-connectivity-based end-to-end redundant user plane paths. Two redundant PDU Sessions with independent user plane paths are established between UE and DN . Packet replication and elimination are performed by the upper layer of UE and DN, which are not specified in 3GPP.

-    Support of redundant transmission on N3/N9 interfaces. For a PDU Session used for URLLC services, two redundant N3/N9 tunnels with independent user plane paths are established between UPF and NG-RAN to transfer the duplicated user packets. Packet replication and elimination are performed by NG-RAN and UPF.

-    Support of redundant transmission at transport layer. This approach assumes that the backhaul provides two disjoint transport paths between UPF and RAN. The redundancy functionality within NG-RAN and UPF makes use of the independent paths at transport layer, which is not specified in 3GPP.

QoS Monitoring

QoS Monitoring is defined in this release for the measurement of packet delay between UE and PSA UPF. The NG-RAN is required to provide the QoS Monitoring of UL/DL packet delay at the Uu interface. The QoS Monitoring of UL/DL packet delay between NG-RAN and PSA UPF can be performed at different levels of granularities, i.e. per QoS flow level, or per GTP-U path level.

Dynamic division of Packet Delay Budget

The Packet Delay Budget (PDB) of URLLC services is typically more stringent than for traditional services. To obtain a more accurate delay budget for NG-RAN, SA WG2 decided to allow a dynamic value for the core network PDB (CN PDB), so that the SMF or NG-RAN can dynamically calculate delay budget of NG-RAN based on the CN PDB.

Enhancements of session continuity

When a UE moves, the user plane path of low latency services need to be optimized to reduce the latency and to guarantee session continuity.

PSA relocation for Ethernet PDU Session is specified in this release. The target UPF will assist in the update of Ethernet forwarding tables of Ethernet switches in the DN, so that UL/DL traffics will switch to the target UPF once the UE moves.

For ULCL relocation, a forwarding tunnel between the old and new UL CLs is introduced to avoid packet loss during relocation.

AF-influenced traffic routing mechanism is further enhanced to allow flexible coordination between SMF and AF when user plane change events happen.

References

The redundant transmission and QoS monitoring mechanisms are specified in TS 23.501[1], Clause 5.33. Dynamic division of Packet Delay Budget is specified in TS 23.501 [1], Clause 5.7.3.4. Enhancements of session continuity mechanisms are mainly in TS 23.501 [1], Clause 5.6.7, and TS 23.502 [2], Clause 4.3.5 and Clause 4.3.6.

[1] 3GPP TS 23.501: "System Architecture for the 5G System; Stage 2".

[2] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".

[3] 3GPP TR 23.725: "Study on enhancement of Ultra-Reliable Low-Latency Communication (URLLC) support in the 5G Core network"

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