IEEE 802.11-16/0353r2 TWT Function in 11ax SFD
Explore the IEEE 802.11-16/0353r2 document discussing the Target Wake Time (TWT) function as agreed in the 11ax SFD. Learn about TWT protection rules based on the 11ah(S1G) standard, including details on Solicited TWT and Broadcast TWT negotiations and mechanisms. Dive into the elements of TWT, Wake Time, Wake Interval, Triggered and Implicit TWT, and more for a comprehensive understanding of this important aspect of wireless communication standards.
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March 2016 doc.: IEEE 802.11-16/0353r2 MU-RTS/CTS for TWT Protection Date: 2016-03-16 Authors: Name Hanseul Hong Affiliations Address Yonsei Univ. Phone email hhs0811@yonsei.a c.kr gumgoki@yonsei.a c.kr woozzas@yonsei.a c.kr ronnykim@ut.ac.kr Jinsoo Ahn Yonsei Univ. Woojin Ahn Yonsei Univ. Ronny Yongho Kim Korea National University of Transportation Submission Slide 1 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 Introduction TWT function is agreed in the 11ax SFD[1]: The spec shall include a mechanism that allows a target transmission time for a Trigger frame to be indicated. The mechanism is based on implicit TWT operation and additionally enables: Broadcast triggered TWT by including a TWT element in the Beacon Solicited triggered TWT by using implicit TWT negotiation procedure When the broadcast triggered TWT is enabled, STA and AP may exchange TWT request/response to indicate the target Beacon frame to be monitored by the PS STA. Multiple TWTs can be indicated in the TWT IE in the Beacon frame by allowing multiple TWT parameter sets in the same TWT IE. In this presentation, TWT protection rule is discussed based on that of 11ah(S1G) Submission Slide 2 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 Recap: Target Wake Time(TWT) Solicited TWT: negotiates for TWT parameter Inclusion of Trigger frame in TWT SP is indicated in TWT element Indicated in Triggered subfield AP M- BA UL PS-Poll/Data TWT Resp. Trigger UL or DL Data transmission UL PS-Poll/Data TWT Req UL PS-Poll/Data UL PS-Poll/Data Target Wake Time Broadcast TWT: negotiates for First TBTT Each TWT SP information is indicated in TWT element in Beacon frame TWT3 TWT2 TWT1 AP B e a c o n TWT Resp. Trigger Trigger UL or DL DL transmission UL or DL TWT Req TWT IE STA(s) TBTT Submission Slide 3 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 Recap : TWT element NDP Paging Indicator Responder PM Mode Broadcast Reserved Bits: 1 1 1 5 Nominal Minimum Wake Duration Target Wake Time TWT Wake Interval Mantissa NDP Paging (optional) Element ID Request Type TWT Group Assignment TWT Channel Length Control Octets: 1 1 1 2 8 or 0 9 or 3 or 0 1 2 1 0 or 4 TWT Flow Identifier Wake Interval Exponent TWT Request TWT Setup Command Flow Type TWT Triggered Implicit Protection Bits: 1 3 1 1 1 3 5 1 Broadcast: indicates the use of broadcast TWT[3] TWT Flow Identifier: For Broadcast TWT, indicates flow type in TWT SP Triggered: According to [2], [3] set if trigger frame is sent at the start of TWT SP According to [4], set if trigger frame is sent at least once during the TWT SP Implicit In SFD: The mechanism is based on implicit TWT operation TWT Protection: not defined in 11ax Submission Slide 4 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 TWT protection field in 11ah-RAW TWT protection field in 11ah: indicates the protection of TWT SP using Restricted Access Window(RAW) A TWT requesting STA sets the TWT Protection subfield to 1 to request the TWT responding STA to provide protection of the set of TWT SPs corresponding to the requested TWT flow identifier by allocating RAW(s) that restrict access to the medium during the TWT SP(s) for that(those) TWTs. When transmitted by a TWT responding STA that is an AP, the TWT Protection subfield indicates whether the TWT SP(s) identified in the TWT element will be protected. Submission Slide 5 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 Restricted Access Window(RAW) RAW TIM STAs see RPS(Raw Parameter set) element to determine whether they are allowed paeameter set B e a c o n AP UL or DL procedure Allowed STA Not allowed to contend RAW duration RAW allows AP to restrict access for specified duration by group of STAs or types of traffic to improve medium utilization, by reducing collision STAs which awake to receive Beacon frame are indicated RAW information and restrict their contention in RAW duration Submission Slide 6 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 Limitation to use RAW in TWT Protection Legacy STAs which cannot decode RAW Parameter Set (RPS) element in beacon may transmit packets in RAW duration Differ from 11ah (operates under 1GHz), there are legacy STAs in 11ax scenario TWT SP is not protected RPS IE B e a c o n RAW duration including TWT SP is set TWT SP is not protected AP UL or DL procedure Allowed STA Collision Data packet Legacy STA Cannot decode the RPS element TWT SP(RAW duration) Submission Slide 7 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 MU-RTS/CTS procedure in TWT SP In SFD, MU-RTS/CTS frame exchange may be used for protection of MU transmissions during that TXOP This MU-RTS/CTS procedure can be used to protect DL Data and Block Ack from hidden node in TWT SP AP TWT Resp. MU- RTS UL or DL Data transmission Simu- CTS TWT Req STA(s) NAV (Simu-CTS) NAV (MU-RTS) NAV TWT SP Submission Slide 8 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 TWT Protection using MU-RTS/CTS Intra-BSS STA Intra-BSS STA OBSS STA OBSS STA AP indicates to use MU- RTS in TWT SP STA requests to protect TWT SP using MU-RTS As in 11ah, the indication of TWT protection in TWT element is needed In case of many OBSS STAs near intra BSS STA, TWT requesting STA can indicate to request the protection of TWT SPs TWT responding STA which is AP can indicate that MU-RTS will be sent at the start of TWT SP Submission Slide 9 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 TWT Protection using MU-RTS/CTS TWT requesting STA which is indicated the use of MU-RTS/CTS by TWT element may wait for MU-RTS at the start of TWT SP AP TWT Resp. MU- RTS UL or DL Data transmission TWT Req Simu- CTS STA(s) NAV (Simu-CTS) NAV (MU-RTS) NAV TWT SP Waits for MU RTS at the beginning of TWT SP In broadcast TWT, the use of TWT protection in each TWT SP is indicated in TWT element in Beacon frame TWT2 (No protection indicated) TWT1 (Protection indicated) AP B e a c o n TWT Resp. MU- RTS UL or DL UL or DL Simu- CTS TWT Req TWT IE STA(s) TBTT Submission Slide 10 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 Conclusion Protection of TWT SP is needed as in 11ah RAW operation is not enough because of legacy STAs which cannot decode RAW information TWT SP can be protected by MU-RTS/CTS procedure In 11ax, MU-RTS is agreed for protection Indication of TWT protection in TWT element is needed Using TWT element, TWT requesting STA can indicate to request the protection of TWT SPs TWT responding STA can indicate that MU-RTS will be sent at the start of TWT SP Submission Slide 11 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 Straw Poll 1 Do you agree to add to the TG Specification Framework document? Spec shall define a mechanism to protect TWT SP. A TWT requesting STA sets the TWT Protection subfield to 1 in TWT Request frame to request the AP to provide protection of the set of TWT SPs using a NAV protection mechanism defined in 802.11ax (e.g., (MU- )RTS/CTS or CTS-to-self, etc.). Y N A Submission Slide 12 Hanseul Hong, Yonsei University
March 2016 doc.: IEEE 802.11-16/0353r2 References [1] 11-15-0132-15-00ax-spec-framework [2] 11-15-0880-02-00ax-scheduled-trigger-frames [3] 11-15-1319-00-00ax-scheduled-trigger-frames-follow-up [4] 11-16-0024-00-00ax-proposed-draft-specification Submission Slide 13 Hanseul Hong, Yonsei University
