July 2010 doc.: IEEE 802.11-10/0xxxr0 NR-U’s definition of success for LBT needs to be realigned with 802.11 & European rules 1 July 2019 Authors: Name Company Phone email Andrew Myles Cisco +61 418 656587 amyles@cisco.com Andrew Myles, Cisco Andrew Myles, Cisco

NR-U’s definition of success for LBT needs to be realigned with 802 NR-U’s definition of success for LBT needs to be realigned with 802.11 and European rules Executive Summary European rules & IEEE 802.11 base Contention Window (CW) updates in LBT on the success of transmissions at the start of a COT … … because only the success (or lack thereof) at the start of COT is relevant to collision detection for LBT Whereas, LAA/NR-U bases Contention Window (CW) updates on information later in the COT, contrary to the European rules It is time to align NR-U to focus success on start of transmission to enable compliance & fairness Cisco

European rules & IEEE 802.11 base CW updates in LBT on the success of tx’s at the start of a COT … The European 5 GHz rules (as currently documented in EN 301 893 v2.1.1) for updating the LBT Contention Window (CW) require … … at least one transmission that started at the beginning of the Channel Occupancy needs to be successful before CW can be reset, otherwise CW is doubled The CW update rules in for EDCA based access in IEEE 802.11 are consistent with these European rules IEEE 802.11 generally focuses on start of a TXOP to determine success or otherwise for the purposes of CW updates There are some interesting exceptions in the IEEE 802.11 standard, such as broadcast frames and delayed block acks However, they generally do not matter in practice; see BRAN(19)102015 for more details Andrew Myles, Cisco

… because only the success (or lack thereof) at the start of COT is relevant to collision detection for LBT Errors at the start of a COT indicate a collision for LBT; no errors at the start indicate a lack of a collision COT/TXOP 1 Errors later in a COT are not indicative of a collision Collision COT/TXOP 2 Note: An implicit assumption is that the start of transmissions align, which is true if one assumes successful use of hidden station mitigation mechanisms Andrew Myles, Cisco

Whereas, LAA/NR-U bases CW updates on information later in COT, contrary to the European rules It is understood that LAA/NR-U does not focus its evaluation of success at the start, possibly making it non-compliant with the European rules Rather, it evaluates the fraction of the COT that was rx’ed correctly to determine success, which may not include the start of the COT The situation is even worse if there is significant use of reservation signals at the start of a COT because this period is not evaluated at all The result is unfair access to LAA/NR-U, relative to Wi-Fi! Wi-Fi detects collision If 80% correct reception is threshold for success then this case might not be detected as a collision by LAA/NR-U; it should be! Wi-Fi TXOP Reservation signal NR-U COT Andrew Myles, Cisco

It is time to align NR-U to focus success on start of transmission to enable compliance & fairness Now would be a great time to fix NR-U so that collision detection focuses on the start of the COT The fix may require significant changes to the NR-U specification It may be less important to fix LAA, depending on one’s view of its market importance A fix is important to: Avoid future compliance issues for NR-U in Europe ... … and more importantly to promote fair access in a shared environment by aligning NR-U with the spirit of LBT based coexistence Andrew Myles, Cisco