1. July 2010
doc.: IEEE /0xxxr0
NR-U’s definition of success for LBT needs to be realigned with & European rules
1 July 2019
Authors:
Name
Company
Phone
Andrew Myles
Cisco
Andrew Myles, Cisco
Andrew Myles, Cisco

2. 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 and European rules
Executive Summary
European rules & IEEE 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

3. 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 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 are consistent with these European rules
IEEE 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 standard, such as broadcast frames and delayed block acks
However, they generally do not matter in practice; see BRAN(19) for more details
Andrew Myles, Cisco

4. … 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

5. 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

6. 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