Transcript 11-16/0353

March 2016
doc.: IEEE 802.11-16/0353r2
MU-RTS/CTS for TWT Protection
Date: 2016-03-16
Authors:
Name
Affiliations
Hanseul Hong
Yonsei Univ.
Jinsoo Ahn
Yonsei Univ.
Woojin Ahn
Yonsei Univ.
Ronny Yongho
Kim
Korea National
University of
Transportation
Submission
Address
Phone
email
[email protected]
c.kr
[email protected]
c.kr
[email protected]
c.kr
[email protected]
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
TWT
Resp.
TWT
Req
MBA
UL PS-Poll/Data
Trigger
UL or DL Data transmission
UL PS-Poll/Data
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.
TWT
Req
Trigger
Trigger
UL or DL
DL transmission
UL or DL
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
1
1
1
5
Bits:
Element
ID
Length
1
1
Octets:
TWT Wake
Interval
Mantissa
TWT
Channel
NDP
Paging
(optional)
1
2
8 or 0
9 or 3 or 0
1
2
1
0 or 4
TWT Setup
Command
Triggered
Implicit
Flow
Type
TWT
Flow
Identifier
Wake
Interval
Exponent
TWT
Protection
1
3
1
1
1
3
5
1
TWT Flow Identifier: For Broadcast TWT, indicates flow type in TWT SP
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
–
•
Nominal
Minimum
Wake
Duration
Triggered:
–
–
•
TWT Group
Assignment
Broadcast: indicates the use of broadcast TWT[3]
–
•
Target
Wake
Time
TWT
Request
Bits:
•
Control
Request
Type
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)
AP
RAW
paeameter set
B
e
a
c
o
n
TIM STAs see RPS(Raw Parameter set)
element to determine whether they are
allowed
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
RAW duration including
TWT SP is set
AP
B
e
a
c
o
n
TWT SP is not protected
UL or DL procedure
Allowed STA
ion
Collis
Data packet
Legacy STA
Cannot decode
the RPS element
Submission
TWT SP(RAW duration)
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
Req
TWT
Resp.
MURTS
SimuCTS
UL or DL Data transmission
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
STA requests
to protect
TWT SP using
MU-RTS
AP indicates
to use MURTS in TWT SP
• 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 elementAPmay wait for MU-RTS at the start of TWT SP
TWT
Req
TWT
Resp.
MURTS
SimuCTS
UL or DL Data transmission
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.
TWT
Req
MURTS
SimuCTS
UL or DL
UL or DL
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