Notification on Change of BW & Rx Nss Date: 2010-11-08 Authors: Joshua Zhao, Atheros

Motivation STA may change BW for performance or power save Notify Channel Width frame was defined in 11n STA may shut down some RF chains for PS AP needs to know how many spatial streams the STA can receive A new action frame needs to be defined AP may ask whole BSS to change channel/BW Simply extend Channel Switch Announcement frame Joshua Zhao, Atheros

Concerns AP may have frames queued for this STA before the action frame is processed The AP may transmit to the STA while the STA is in process of changing operating mode and thus unable to receive Unnecessary re-transmissions may occur Packet loss may result It takes time for STA to change operating BW (or RF chains) After receiving ACK from AP, the STA may not be quick enough to switch mode within PIFS interval (shortest time before an AP may transmit) STA may want to wait a bit before making the change (to avoid packet loss) AP can not predict when the STA will be ready to receive Suggestion: Use operating mode notification with the existing PS behavior AP holds packets for STAs in PS AP HW doesn’t need to do special processing on action frames Joshua Zhao, Atheros

Operating Mode Notification Sequence STA AP Mode change notification with PS on STA in mode change AP holds up tx to STA in sleep Turn PS off Packet delivery The STA sends operating mode notification frame with PS bit set. After the STA is done switching modes, it sends a frame to the AP with PS bit cleared. Optional to STA if it has no worry on packet loss during mode transition. Joshua Zhao, Atheros

Notification frame format Define a new frame for operating mode change for 11ac Leave existing Notify Channel Width frame unchanged for 11n devices Define a new action type: avoid confusion between HT and VHT actions Use this new action type for both BW and Rx Nss STA may want to adjust both BW and RF chains simultaneously Or a STA can change one and keep the other same as before B0-B1 B2-B3 B4-B6 B7 BW Reserved Nss Joshua Zhao, Atheros

BSS Channel/BW change Extended Channel Switch Announcement frame will automatically support wider BW options as operating class definition is extended. But some old devices may not support it. For better compatibility, legacy Channel Switch Announcement frame might still be used. We can either extend bits definitions in Secondary Channel Offset element or define new elements for wider BW options. Details are to be decided in BSS Channel Specification discussion. Joshua Zhao, Atheros

Pre-Motion #1 Do you support to update TGac spec frame work to define a new VHT action frame for operating mode change as defined in Slide 5? Joshua Zhao, Atheros

Pre-Motion #2 Do you support to update TGac spec framework to add the concept of optionally using Power Save mode in the “operating mode notification” frame exchange sequence as described in slide 4? Joshua Zhao, Atheros