Support of NR Industrial Internet of Things
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)”
