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Jing Sun, Qualcomm Incorporated Rapporteur of Rel.16 NR-U Work Item

This status report outlines the history and advancements of NR-U in unlicensed bands, focusing on channel access design, LBT types supported, channel occupancy structure considerations, and CO structure indication methods. It provides insights into the core technology, performance aspects, and scope of NR enhancements in accessing unlicensed spectrum. The report summarizes the key features, timelines, and planned enhancements for an efficient design of NR in the 5GHz and 6GHz bands, considering regional regulatory requirements.

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Jing Sun, Qualcomm Incorporated Rapporteur of Rel.16 NR-U Work Item

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  1. Jing Sun, Qualcomm Incorporated Rapporteur of Rel.16 NR-U Work Item 2019 July IEEE 802.11 Coexistence Workshop Vienna, Austria, 17th, July, 2019 Status Report for Rel.16 NR-U

  2. History: 3GPP & unlicensed band LTE-based • LTE-based access into unlicensed bands first presented in 12- 2013 • Licensed Assisted Access (LAA) Study approved in 09-2014 • 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 36.789 • 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 Rel.15 NR-U Study Item Rel.16 NR-U Work Item Now Core part complete Performance part complete

  5. 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 301 893 • 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

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