1. 3GPP RAN1 status on NR-Unlicensed
Month Year
doc.: IEEE yy/xxxxr0
January 2019
3GPP RAN1 status on NR-Unlicensed
Date:
Authors:
Name
Affiliations
Address
Phone
Shubhodeep Adhikari
Broadcom
Sindhu Verma
John Doe, Some Company

2. Month Year
doc.: IEEE yy/xxxxr0
January 2019
Abstract
This presentation provides updates from the latest 3GPP RAN1 meeting (RAN1#95) on the standardization of NR-Unlicensed, with a focus on fair coexistence with
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3. Month Year
doc.: IEEE yy/xxxxr0
January 2019
Outline
The presentation discusses the following topics, as captured in the NR-U Technical Report V ( ) [1]:
25us LBT for transmission of control messages
No-LBT for UL transmissions within a COT with a gap of 16 us
Adoption of a preamble by NR-U
Multicarrier channel access
Multiple LBT attempts by UL within a shared COT
UE to gNB COT sharing
Shared COT for AUL transmissions
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4. January 2019
RAN1: NR-Unlicensed
Topic: 25us LBT for transmission of control messages
Status:
25us LBT for transmission of DRS up to 5% of the airtime per gNB
Proposals for 25us LBT for a host of other transmissions including “control messages related to initial/random access, mobility, paging, reference signals only, and PDCCH-only transmissions, e.g. "RACH message 4", handover command, GC-PDCCH, or short message paging transmitted either alone or when multiplexed with DRS” [1].
Observation:
25us LBT lacks any backoff procedure; it cannot react to collisions between transmissions by randomizing the subsequent set of transmissions after the collision. So, 25us LBT will lead to poor performance in a congested network. In a less loaded network where collisions are rare, the latency achieved by 25us LBT and CAT4 LBT with the highest priority (AC_VO) are about the same. For this reason, 25us LBT is a poor design choice. It will also harm performance of co-channel Wi-Fi. Note that Wi-Fi too can be made to use 25us LBT to match any purported performance gains in NR-U. However, doing this would lead to poor performance for both NR-U and Wi-Fi in a congested network and so Wi-Fi should desist from making such a change.

5. January 2019
RAN1: NR-Unlicensed
Topic: No-LBT for UL transmissions within a COT with a gap of 16 us
Status:
Allowed. Proposals on limiting the length of UL transmissions can be considered in the working group meeting.
Observation :
ETSI-BRAN allows such transmissions.
Wi-Fi allows this only for short transmissions.
11ac: ACKs with a max duration of 60us.
11ax: Transmissions <= 128us in most cases and <= 584us in some special cases including preamble.
In presence of hidden nodes, transmissions without LBT will lead to increased collision and poor network performance. This is aggravated by the fact that a NR-U + Wi-Fi network will have higher incidence of hidden nodes than a Wi-Fi network.
PD at -82dBm (or lower) in a Wi-Fi network compared to ED at -72dBm or -62dBm in a NR-U + Wi-Fi network
Wi-Fi has many other schemes to mitigate collisions due to hidden nodes which are absent in NR-U
However, if NR-U adopts a Wi-Fi based preamble the incidence of hidden nodes in a NR-U + Wi-Fi network may be similar to a Wi-Fi only network.

6. RAN1: NR-Unlicensed Topic: Adoption of 802.11a preamble by NR-U
January 2019
RAN1: NR-Unlicensed
Topic: Adoption of a preamble by NR-U
Status:
In RAN1 #95, 12 companies supported the use of an based preamble for NR-U while 1 company opposed it. This is captured in the feature lead summary.
12 companies (Charter Communications, Qualcomm, Broadcom, Cisco, Intel, Apple, CableLabs, Panasonic, AT&T, Sony, ORANGE, Blackberry, Comcast) think that the a preamble can be used for coexistence between NR-U and Wi-Fi networks.
1 company (Ericsson) thinks that NR-U networks in the unlicensed band can coexist well with Wi-Fi networks in both indoor and outdoor scenarios without the introduction of an a preamble.
The NR-U WID finalized in RAN#82 specifies that extensions on top of an ED-only scheme will be discussed during the work item.
Extensions are to be discussed in line with the framework on channel access as captured in the TR , Section (i.e., WiFi 11a/11ax preamble, existing NR signal with potential enhancements, existing NR channel with potential enhancements)

7. RAN1: NR-Unlicensed Topic: Multicarrier channel access
January 2019
RAN1: NR-Unlicensed
Topic: Multicarrier channel access
Status: To be discussed in the working group meetings
Observation: Multi-carrier channel access in NR-U should follow the multi-carrier channel access schemes specified in section of ETSI-BRAN EN
Topic: Multiple LBT attempts by UL within a shared COT
Observation: There are two different interpretations on the number of one-shot LBT attempts that are allowed in ETSI-BRAN EN for a Responding device within a shared COT. According to one interpretation only a single one-shot LBT is allowed. According to another interpretation, multiple one-shot LBT attempts are allowed, but the number of such one-shot LBT attempts is limited to the total consecutive time in ms granted to the Responding device for transmission within a shared COT.

8. RAN1: NR-Unlicensed Topic: UE to gNB COT sharing
January 2019
RAN1: NR-Unlicensed
Topic: UE to gNB COT sharing
Status: To be discussed in the working group meetings
Observation:
If UE to gNB COT sharing is allowed without restrictions it can be used to circumvent the principles of fair channel access. Some of the examples are as follows:
The ED threshold used for CAT4 LBT to win a COT is proportional to the maximum transmit power of a device. However, if UE-gNB COT sharing is allowed without restrictions, a COT that is won with a lower ED threshold due to the lower maximum transmit power of a UE can be used by a gNB which has a much higher transmit power.
It can be used by a gNB to circumvent congestion in its neighbourhood by directing a UE that experiences the least congestion to win the COT and then handover the COT to the gNB for its own transmission.
So, a procedure similar to AUL UE to eNB COT sharing as agreed in RAN1#92 can be considered as a starting point also keeping in mind the restrictions due to differences in the maximum transmit power between the UE and the gNB.

9. RAN1: NR-Unlicensed Topic: Shared COT for AUL transmissions
January 2019
RAN1: NR-Unlicensed
Topic: Shared COT for AUL transmissions
Status: To be discussed in the working group meetings
Observation: The shared COT feature in ETSI-BRAN EN is intended to allow only those transmissions that cannot happen without an explicit grant from the Initiating device within the same COT and so, autonomous UL transmissions which can proceed without any grant from the Initiating device should not use a shared COT. Such autonomous UL transmissions are allowed as an Initiating device with CAT4 LBT.

10. Month Year
doc.: IEEE yy/xxxxr0
January 2019
References
[1] 3GPP TR V ( ), Study on NR-based access to unlicensed spectrum (Release 16)
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