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Hi all,
This is to initiate a discussion on the contribution 11-23/0034 “Non-primary channel utilization” which I presented in the UHR SG meeting last Monday. Below are detailed responses to some of the questions that were raised in the meeting (as captured in the minutes of the meeting). Please send any other comments and questions.
How do you deal with legacy smaller bandwidth devices?
>>This proposal for non-primary channel usage allows a transmitter to transmit on non-primary channels only if the primary channel is occupied by an OBSS. This naturally respects legacy and smaller bandwidth devices in the following ways:
If the legacy devices detect OBSS, they would not be transmitting to the non-primary transmitter during the period.
If the legacy devices do not detect OBSS and attempt to transmit to the non-primary transmitter during the period, the non-primary transmitter even if present on the primary to would have not responded with CTS or not been able to decode the transmission.
What if the non-AP STA is the hidden node?
>>Hidden nodes will need to be handled using RTS/CTS as applicable also to legacy cases. Transmissions on non-primary channels initiated with RTS/CTS will ensure that even if the intended receiver is unavailable to receive on the non-primary channel due to not detecting OBSS on the primary channel or detecting OBSS on the non-primary channel, the error scenario is gracefully resolved.
For the anchor channels, need to understand the preamble.
>> Yes. In Operating Mode Option 1, the anchor channels agreed are those which the receiver can decode preambles on and also be able to receive any data following it.
Did you have some research on the below issue, there is BSS1 and BSS2. Also have BSS3. BSS3 is only the OBSS of BSS2. If AP1 gets P80, AP2 jumps to S80, AP3 cannot hear AP1, AP2 is actively operating on secondary channel of AP3. It may interrupt BSS3’s transmission. If AP3 wants to contend the channel, he may think the whole 160MHz is available, if they don’t do packet detection on S80. Not necessarily a hidden node. It is recommend to align the primary channel. Now the proposal is like to not align the primary channel.
>>In your example, are you assuming AP1 to be of only 80MHz bandwidths while AP2 and AP3 are 160MHz? Otherwise, you are assuming another BSS which occupies only S80 and so, the underlying assumption of aligned primary 20MHz channels is not true.
Going with the former assumption, in case of non-primary channel utilization, it is possible for both AP2 and AP3 to operate in S80. In your example when AP2 is on S80, AP1 and AP3 can operate simultaneously on P80. AP2 transmits on S80 only as long as AP1 is on P80. AP3 transmits on P80 but it also needs to perform CCA for S80. Note that the CCA for secondary channels in Wi-Fi is more conservative in that an OFDMA signal needs to be detected at a threshold of approximately -72dB/20MHz or even lower in some cases. Additionally, RTS/CTS used by APs and their receivers will enhance the protection in such situations. Importantly, even in your example, S80 which would have otherwise gone unoccupied would be usable for data exchange. We can definitely evaluate and enhance coexistence for multi-BSS scenarios considering a typical topology and traffic configuration. The proposal does not recommend not aligning primary 20MHz channels.
Regards,
Sindhu
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