1. Jing Sun, Qualcomm Incorporated Rapporteur of Rel.16 NR-U Work Item
2019 July IEEE Coexistence Workshop
Vienna, Austria, 17th, July, 2019
Status Report for Rel.16 NR-U
Jing Sun, Qualcomm Incorporated
Rapporteur of Rel.16 NR-U Work Item

2. History: 3GPP & unlicensed band
LTE-based
LTE-based access into unlicensed bands first presented in
Licensed Assisted Access (LAA) Study approved in
LAA introduced in the 3GPP specifications in Rel-13
Supports only downlink in unlicensed band: Secondary cell (sCell) aggregated with a licensed primary cell (pCell)
eLAA evolves the feature in Rel-14
Introduces uplink operation in unlicensed band
FeLAA further evolves it in Rel-15
Introduces “autonomous” uplink
5GHz defined as a 3GPP band (Band 46)
Set of base station coexistence tests for LAA documented in a RAN4 Technical Report
3GPP TR
Identification of traffic carried over unlicensed spectrum also covered to cater to certain regulatory requirements
USOS: Unlicensed Spectrum Offloading System-enhancements

3. History: 3GPP & unlicensed band
NR-based
NR (New Radio) is a 3GPP Rel-15 feature
NR-U study item approved in March 2017
On hold during the rest of 2017 as core NR design was prioritized
The study was carried out mostly during 2018
NR-U work item approved in December 2018
Scope includes Licensed Assisted Access (LAA) & Standalone (NR access in unlicensed without a licensed anchor)

4. 3GPP NR-U work-plan and schedule
2018
2019
2020 Q1 Q2 Q3 Q4
Rel.15 NR-U Study Item
Rel.16 NR-U Work Item
Now
Core part complete
Performance part complete

5. From work item description (WID)
Scope of NR-U work
From work item description (WID)
This work item will specify NR enhancements for a single global solution framework for access to unlicensed spectrum which enables operation of NR in the 5GHz and the 6GHz (e.g., US 5925 – 7125 MHz, or European 5925 – 6425 MHz, or parts thereof) unlicensed bands taking into account regional regulatory requirements. The core technology should be band agnostic as much as possible. To allow for an efficient design, the enhancements should reuse the features of NR as much as possible.

6. Status Report for Rel.16 NR-U on Channel Access Related Design

7. Types of LBT supported in NR-U
Cat 4 LBT – LBT with exponential random back-off with a contention window of variable size
Cat 2 LBT – LBT without random backoff
Only defined for two lengths (25µs and 16µs)
25µs Cat 2 LBT reuse LTE-LAA definition, while 16µs Cat 2 LBT to be defined
gNB scheduler ensures gaps between 16µs and 25µs are not scheduled
Cat 1 immediate transmission – Used when gap is no more than 16µs
Maximum limits of the duration of the UL burst other than those already derived from the MCOT duration limits are being discussed

8. NR-U channel occupancy structure design considerations
In NR-U (like in licensed NR), UL transmissions are always granted (with a DCI) or configured (through RRC configuration)
A Channel Occupancy (CO) in NR-U can start with a DL transmission, followed by other UL or DL transmissions
The follow up UL/DL transmissions can be in the initial gNB CO
UL transmission can be granted outside gNB CO
A UE can start a CO as well with a grant out of the gNB CO, with an RRC configured UL transmission, or for initial access
In some cases, the UE initiated CO can be shared with gNB for some DL transmission
The detailed conditions for the CO sharing is still being discussed

9. Channel occupancy structure
As in NR, DL or UL burst of NR-U is composed of slots and mini-slots
Each slot is 0.5ms for 30KHz subcarrier spacing and 1ms for 15KHz subcarrier spacing
Each slot contains 14 OFDM symbols
The slot/symbol boundaries are on a fixed grid for NR-U system
NR-U can start a DL burst or UL burst at slot boundary or symbol boundary
NR already supports PDSCH/PUSCH starts at any symbol (35 µs granularity with 30KHz SCS)
A gap (DLUL, ULUL, or UL DL) of a specific duration is created using one or more of:
Timing Advance
CP extension (Max value of not more than one OFDM symbol)
Shortening of DL or UL transmission duration by one or more OFDM-symbol(s) by puncturing or rate matching
Details not finalized yet

10. How to indicate the CO structure
GC-PDCCH will be used to indicate the CO structure, including both time domain and frequency domain structure
Time domain CO structure indication
The functionality is considered as an extension to the GC-PDCCH with DCI format 2_0 in Rel-15 NR
Frequency domain CO structure indication
The GC-PDCCH will inform the UE that one or more carriers and/or LBT bandwidths are not available or available for DL reception, at least for slot(s) that are not at the beginning of DL transmission burst
Whether and how to support the mechanism at the beginning of the DL transmission burst is still being discussed
DCI signaling design details are TBD

11. LBT requirements for gNB initiated CO
To initiate a CO by gNB, Cat 4 LBT is typically used (except some DRS transmissions with details later)
The channel access priority class depends on the priority of data carried in the DL and UL portion
UL grant can carry an indication on the LBT type and channel access priority class
For additional DL burst within a gNB CO (allowed in cases where there is no gap larger than 25µs between any two transmissions in the CO):
Cat 1 immediate transmission is used when the gap from the end of the scheduled UL transmission to the beginning of the DL burst is up to 16 µs
Cat 2 LBT is used when the gap from the end of the scheduled UL transmission to the beginning of the DL burst is larger than 16 µs but not more than 25 µs
For UL burst within a gNB CO:
Cat 1 immediate transmission can be used when the gap from the end of the DL transmission to the beginning of the UL burst is no more than 16 µs
Cat 2 LBT is used when
The gap between any two successive scheduled/granted transmissions in the CO 16 µs or 25 µs, or
The UL transmission is not followed by a DL transmission in the same CO

12. Scenarios when gNB can initiate CO w/ Cat 2 LBT
gNB can use Cat 2 LBT (25 µs Cat 2 LBT) to initiate a CO only when:
gNB is transmitting DRS alone or multiplexed with non-unicast data (e.g. OSI, paging, RAR), and the DRS duty cycle ≤ 1/20, and the total transmission duration is up to 1 ms
Still pending further discussion
Maximum number of Cat 2 LBT attempts for DRS transmission in the DRS transmission window

13. LBT requirements for UE initiated CO
UE can initiate CO for
Dynamically granted UL data/control transmission with grant received in a previous CO
RRC configured UL transmission, including configured grant UL, SRS, PUCCH, RACH
Only Cat 4 LBT is used by UE to initiate CO
For UL burst with user plane data, channel access priority class depends on the multiplexed data
For UL burst with control information only, the highest priority class can be used

14. CWS adjustment
In addition to aspects considered in LTE LAA, CWS adjustment procedure in NR-U may additionally consider at least the following aspects:
CBG based HARQ-ACK operation,
NR scheduling and HARQ-feedback delays and processing times
wideband (>20 MHz) operation including BWPs
Configured grant operation
In case of CBG-based HARQ and LBT category 4, enhancements for defining how to adjust the contention window size (CWS) based on TB-level HARQ-ACK and CBG-level HARQ-ACK would be beneficial.

15. Multi-carrier LBT Multi-carrier or multi-subband channel access
Use LTE-LAA multi-carrier channel access as baseline
If NR-U carrier is wide band (multiple of 20MHz), apply the multi-carrier channel access to the set of all LBT subbands
Multi-carrier channel access schemes that are applicable to multiple carriers with a single LBT sub-band per carrier that is the same as the carrier bandwidth are also applicable to multiple LBT sub-bands within a carrier when such carriers are used either as a single wideband carrier or as part of carrier aggregation of a set of carriers.

16. LBT requirements for FBE mode of operation
Fixed frame period as defined by ETSI harmonized standard EN
CO is at the beginning of the FFP and occupies at most 95% of the FFP
Idle period is at the end of the FFP and occupies at least 5% of the FFP with a minimum of 100 µs
gNB acquires CO with Cat2 LBT immediately prior to the fixed frame period
Within the gNB acquired CO, if a gap is ≤16 µs, Cat 1 immediate transmission is used by the gNB and associated UEs to start a DL/UL burst
Within the gNB acquired CO, if a gap is > 16 µs, Cat 2 LBT is used by the gNB and associated UEs to start a DL/UL burst

17. Backup slides: Waveform changes introduced

18. Waveform changes for NR-U
NR-U supports legacy NR contiguous UL resource allocation and new interlaced waveform while complying with regulations
Interlaced waveform for PUCCH and PUSCH
PRB interlace with 5 interlaces for 30KHz SCS and 10 interlaces for 15KHz SCS
Waveform for PRACH
Legacy NR PRACH waveform with 139 REs are still supported
Satisfies the 2MHz temporary OCB requirement
New wider bandwidth PRACH waveform is being discussed
Example with 30KHz SCS (5 interlaces)
Each interlace is formed by a set of distributed RBs (same color in the figure)
Applies to PUCCH and PUSCH