G’day all,
The Coexistence SC has been discussing various aspects of a mechanism currently specified in EN 301 893 (the European Harmonised Standard for 5 GHz) that allows each device to access the medium for
short control signalling without using any LBT for about 5% of the time.
There is a concern by some people that this mechanism could be misused or overused. There is less concern about overuse by 3PPP LAA for DRS frames (like Beacons) because only eNBs (like an AP) use this mechanism and there are unlikely to
many eNBs in a particular area/channel, given eNBs will typically owned and operated by SPs (who also own the paired licensed spectrum). There is concern about overuse by 3GPP NR-U for DRS frames (and possibly other frames) because it is more likely that multiple
gNBs (like an AP) will be operating in an area/channel, given NR-U is very similar to Wi-Fi in its deployment model. It should be noted that both LAA and NR-U do not actually use
no LBT access but rather use short LBT access (like PIFS). If n independent gNBs were operating in a channel then
n x 5% of the medium could be accessed using this super high priority short LBT access mechanism. A
presentation at the Coex Workshop asserted the 5% threshold would have significant adverse effects on Wi-Fi, with
n as low as 4.
The IEEE 802.11 WG has previously sent both ETSI BRAN and 3GPP RAN1 liaisons supporting changing the threshold for the use of this mechanism from 5% to 1% (possibly with use by LAA grandfathered). The discussion in both organisations has
failed to reach any consensus on the IEEE 802.11 WG propoal. 3GPP RAN1 is unlikely to make any change to the
status quo unless forced to do so. The discussion continues in ETSI BRAN in the context of the 5 GHz band (EN 301 893) and is likely to start soon in the context of the 6 GHz band (EN 303 687). In this discussion in ETSI BRAN, it has been asserted that
some/many Wi-Fi devices do not follow the IEEE 802.11 standard when accessing the medium for Beacons. Rather than using normal EDCA style access, it is asserted some/many Wi-Fi APs are using PIFS access. If PIFS access for Beacons is widespread then it diminishes
the argument that NR-U should not use short LBT access too.
So I have some questions for the IEEE 802.11 WG community:
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Do products you manufacture/sell use PIFS access for Beacons? If so, how often?
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Do you know of products manufactured by others that use PIFS access for Beacons? If so, how often?
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Do you believe the use of PIFS access for Beacons is widespread (or not)? On what basis do you have this belief?
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Assuming the use of PIFS access for Beacons is not widespread, should its use be further discouraged by ETSI BRAN reducing the threshold for using
short control signalling without any LBT to 1%?
Please send answers to these questions to me as soon as possible.
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Andrew Myles Manager, Cisco Standards
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Andrew Myles |
Cisco Systems Limited |
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