Transcript 11-15/0612

May 2015
doc.: IEEE 802.11-15/0612r1
Multi Channel Availability
for UL-OFDMA
Date: 2015-05-12
Authors:
Name
Affiliations
Woojin Ahn
Yonsei Univ.
[email protected]
Jinsoo Ahn
Yonsei Univ.
[email protected]
Ronny Yongho
Kim
Korea National
University of
Transportation
[email protected]
Submission
Address
Slide 1
Phone
email
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Introduction
• In dense BSS environment, STAs in the same BSS
might be influenced by transmissions from different
OBSSs[1], [2]
• Considering wider band operation, STAs might belong
to radio ranges of different OBSS STAs and see
channel (idle/busy) differently (different channel
availability)
• UL-OFDMA procedure might suffer from the different
channel availability between AP and UL-STAs
Submission
Slide 2
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Hidden node & Channel availability
STA1
STA2
STA4
STA3
AP
Transmitting
Busy channel
Idle channel
•
•
STA1
Channel 1
Channel 2
Channel 3
Channel 4
STA2
Channel 1
Channel 2
Channel 3
Channel 4
AP
Channel 1
Channel 2
Channel 3
Channel 4
STA3
Channel 1
Channel 2
Channel 3
Channel 4
STA4
Channel 1
Channel 2
Channel 3
Channel 4
STA1(CH1, 2) & STA4(CH3, 4) are transmitting data
•
Since STA1 and STA4 is hidden from AP, AP sees channel 1 to 4 idle.
•
STA2 sees CH1, 2 busy and (STA3-> CH3, 4)
STA1,2 and AP have different channel availability(CA)
Submission
Slide 3
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
MU-UL motion in the previous meeting
•
Acknowledge
frame
Trigger frame
STA1
UL MU PPDU
STA2
UL MU PPDU
STA3
UL MU PPDU
STA4
UL MU PPDU
Frequency/
Spatial domain
AP
The spec shall define the following mode of operation:
An UL MU PPDU (MU-MIMO or OFDMA) is sent as an immediate response
(IFS TBD) to a Trigger frame (format TBD) sent by the AP. [3]
• UL STAs have to transmit UL data immediately after
the trigger frame
• Every control information for UL data transmission must be
delivered to UL-STAs within the trigger frame
Submission
Slide 4
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
UL-OFDMA procedure
• Considering UL-OFDMA with multiple channels
• AP must decide which STAs to participate on which channels
• AP requires STAs’ buffer status and CA
• Buffer status information might be gathered periodically or implicitly
within ongoing transmissions
• CA cannot be obtained with the same manner
• much more sensitive to time
• CA of past time is not valid for current transmission
• AP might assign (sub-)channels to UL-STAs with trigger frame
• There have been no considerations on CA yet
• AP will assign STAs to its available channels based on its discretion
• Simply using previous CSI or random assignment
Submission
Slide 5
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Necessity of channel availability
on UL-OFDMA procedure (1)
Assigned to STA1
Trigger
xIFS
Assigned to STA2
Second 2
Trigger
xIFS
Assigned to STA3
Trigger
xIFS
Assigned to STA4
Second 3
xIFS
Second 1
Primary
Trigger
Transmission from
OBSS STA (STA1 side)
Transmission from
OBSS STA (STA4 side)
•
4 channels are idle on AP side
•
AP assigns 4 UL STAs
•
Two nodes of different OBSSs, close to STA1 and STA4, were
transmitting data (hidden from AP)
Submission
Slide 6
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Necessity of channel availability
on UL-OFDMA procedure (2)
Trigger
SIFS
Assigned to STA2
Second 2
Trigger
SIFS
Assigned to STA3
Trigger
SIFS
Assigned to STA4
Transmission from
OBSS STA (STA4 side)
PIFS
Transmission from
OBSS STA (STA1 side)
Second 1
Assigned to STA1
Transmission from
OBSS STA (STA1 side)
Primary
SIFS
Second 3
Trigger
Second 1
Primary
STA1 couldn't hear
trigger frame
No UL data sent
Trigger
xIFS
Assigned to STA1
Trigger
xIFS
UL Data (STA2)
STAs cannot perform CCA
• STA2 receives TF well from primary or secondary 1
•
Successful UL transmission occurs
•
TF structure on multiple channel(duplicate or not) and STAs channel sensing policy
(full channel or just primary) need to be defined
• STA1 cannot transmit UL data as it couldn’t hear the trigger frame
•
AP didn’t notice that the primary channel was busy for STA1
•
Assigned channel will be wasted
Submission
Slide 7
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Necessity of channel availability
on UL-OFDMA procedure (3)
PIFS
Trigger
SIFS
Assigned to STA2
Second 2
Trigger
SIFS
Assigned to STA3
Trigger
SIFS
Transmission from
OBSS STA (STA4 side)
•
Assigned to STA4
Second 3
SIFS
Second 3
Second 1
Trigger
PIFS
•
Assigned to STA1
Second 2
Primary
Transmission from
OBSS STA (STA1 side)
Transmission from
OBSS STA (STA4 side)
STAs cannot perform CCA
STA cannot
perform CCA
Trigger
xIFS
UL Data (STA3)
Trigger
xIFS
UL Data (STA4)
STA4 heard
trigger frame
STA4 could hear the trigger frame
STA4 overrides and
interferes the
transmission of OBSS
•
In 802.11, It is generally assumed that STAs are sensing only primary channel before they transmit data
•
STA4 might hear the trigger frame from the primary channel
The length of xIFS might influence the following behavior of STA4
•
Assuming xIFS less than PIFS
•
Since STA4 is not possible to measure CCA within the xIFS duration, it must transmit UL-data regardless of
the CA
•
UL data of STA4 might cause interference to ongoing transmissions of OBSS STAs
Submission
Slide 8
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Necessity of channel availability
on UL-OFDMA procedure (4)
SIFS
Second 2
Second 3
Transmission from
OBSS STA (STA4 side)
Trigger
xIFS
UL Data (STA3)
Trigger
xIFS
Assigned to STA4
STA 4 is not allowed to
transmit UL data
UL STAs can perform CCA
• With increased xIFS (up to PIFS), it is possible for UL STAs to
measure CCA before they transmit UL data
• Assigned STAs(STA4) may decide not to participate UL-transmission
• STA4 won’t make any interference to OBSS, but assigned channel will
still be wasted
• PIFS sensing for secondary channels may collide with existing
PIFS based mechanism (e.g., beacon)
Submission
Slide 9
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Necessity of channel availability on ULOFDMA procedure (5)
Primary
Transmission from
OBSS STA (STA1 side)
Trigger
SIFS
Assigned to STA1
STA6
SIFS
Assigned to STA2
Second 2
Trigger
SIFS
Assigned to STA3
Trigger
SIFS
Assigned to STA4
Second 3
Second 1
STA5
Trigger
Transmission from
OBSS STA (STA4 side)
PIFS
STAs cannot perform CCA
STA1
STA4
AP
STA2
STA6
STA5
STA3
STA1
STA4
AP
STA2
STA3
• If AP could exploit channel availability of STAs
• Avoiding selecting inappropriate UL STAs
• STA1 and STA4 might interfere OBSS transmission or not transmit any UL data
• Assigning other STAs without CA issues
• STA5, STA6 don’t belong to OBSS interference range
• Assigning more channels to STA2, STA3
• Overall contention isolation gain or channel utility can be maintained
Submission
Slide 10
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Hidden node protection
with existing RTS/CTS
• Using RTS/CTS for multiple STAs
•
RTS/CTS are supposed to reserve and protect channel from hidden nodes
•
For UL-OFDMA case, each UL-STA might have different hidden node
•
RTS/CTS must be exchanged on by one for each UL STA
•
CTS can be regarded as CA feedback
CTS
Trigger
CTS
Trigger
RTS
CTS
RTS
Slide 11
STA2
Trigger
RTS
CTS
RTS
RTS
Submission
...
Trigger
RTS
RTS
RTS
...
STA1
AP
RTS
RTS
...
CTS
RTS
• Advanced channel availability feedback
or channel protection mechanism is
required
RTS
Other potential problems exist (backup slides)
Second 3
•
...
Second 2
Overhead of multiple STAs RTS/CTS is too large
AP
Second 1
•
AP
Primary
• RTS/CTS is not apt for solving CA
problem
STA n
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Conclusion
• In dense BSS and STA environment, STAs in the same BSS might
have different channel availability due to ongoing transmissions of
OBSSs
• Channel availability might not only reduce the channel utility and
contention isolation gain of UL-OFDMA but also interfere ongoing
transmissions of OBSSs
• It is necessary to take the effect of channel availability into account
for developing the procedure of UL-OFDMA
• Advanced sensing or channel reservation mechanism
• Channel availability feedback
• Relevant channel protection mechanism
Submission
Slide 12
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
References
[1] 11-15-0091-01-00ax-ul-ofdma-procedure-in-ieee-80211ax
[2] 11-15-0378-02-00ax-channel-sensing-in-ul-ofdma
[3] 11-15-0365-00-00ax-ul-mu-procedure
Submission
Slide 13
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Strawpoll
• UL-OFDMA procedure should consider the effect of
different channel availability between AP and UL STAs
• Y:
• N:
• A:
Submission
Slide 14
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Hidden node protection
with existing RTS/CTS - backup
• Channel will be over protected
CTS
RTS
CTS
RTS
CTS
RTS
...
CTS
RTS
Slide 15
...
CTS
Submission
...
CTS
OBSS STAs may start transmission during RTS/CTS
period
...
CTS
•
CTS
• For OBSS STAs only exposed to specific
UL-STA, RTS/CTS duration could be seen
idle
RTS
OBSS STAs of STA1 side have to defer for unused
channels
RTS
•
Channel is idle for OBSS STAs
only exposed to STA1
AP
RTS
Secondary 1~3 didn’t have to be protected for STA1
RTS
•
Second 3
STAs will send CTS for every available channel
Second 2
•
Second 1
STAs don’t know which channel will be assigned
Primary
•
Trigger
Trigger
Trigger
Trigger
UL Data (STA1)
UL Data (STA2)
UL Data (STA3)
UL Data (STA4)
STA1
Woojin Ahn, Yonsei Univ.
May 2015
doc.: IEEE 802.11-15/0612r1
Hidden node protection
with existing RTS/CTS - backup
Slide 16
CTS
Submission
...
RTS
Overall UL-OFDMA procedure might become
heavier due to channel allocation
Trigger
CTS
•
...
RTS
OBSS STAs may start transmission during
RTS/CTS period still
Trigger
CTS
•
RTS
Channel overprotection problem is no longer exist
...
Second 3
•
Trigger
Second 2
RTS/CTS will be exchanged only on the assigned
channel for each UL-STA
...
Second 1
•
AP
Primary
• Assuming the channel allocation is
performed prior to the trigger
Trigger
STA1
Woojin Ahn, Yonsei Univ.