Transcript 11-15-0878

July 2015
doc.: IEEE 802.11-15/0878r0
Issues on Trigger Frame Retransmission
Date: 2015-07-12
Authors:
Name
Affiliations
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]
Slide 1
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Introduction
• UL-OFDMA and UL-MU-MIMO are key enabling
technologies to enhance the performance in dense
environment in 11ax
• Trigger Frame was adopted in SFD to initiate UL-OFDMA
transmission[1]
• The acknowledgement of Trigger Frame was discussed in
the last meeting[2]
– UL MPDU/A-MPDU could be the acknowledgement of the trigger
frame
Submission
Slide 2
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Trigger Frame based UL-OFDMA procedure
Trigger
Frame
STA1 UL PPDU
BA
5
MBA
STA2 DL PPDU
STA2 UL PPDU
STA3 UL PPDU
BA
2
STA5 UL PPDU
• Trigger frame could be transmitted with contention based
access scheme (similar to RTS frame)
• UL PPDU could be the acknowledgement of trigger frame
• M-BA is the acknowledgement of UL PPDUs
• Conventional EDCA procedure follows UL OFDMA
transmission
Submission
Slide 3
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Trigger Frame based UL-OFDMA procedure
What kind of
CW is applied?
What kind of
AIFS is applied?
Trigger
Frame
No Response
No Response
What kind of
procedure follows
Trigger Frame
failure?
No Response
• Access Category(AC) of Trigger frame should be defined
– To determine Trigger Frame’s AIFS, CW, etc.
– Not only fixed values but also variable values could be considered
• Absence of some or all UL PPDUs after Trigger Frame
might mean a failure of trigger frame exchange
– At least, absence of all UL PPDUs after trigger frame means a failure
of trigger frame exchange
– What is the next procedure of the trigger frame failure?
Submission
Slide 4
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Retransmission of Trigger Frame
• Conventional retransmission of trigger frame
AP considers the
transmission failed and
retransmits Trigger
Frame
Trigger
Frame
AP will contend with
other stations
Longer CW is applied
due to tx failure
BA
2
No Response
No Response
No Response
EIFS
Trigger
Frame
Retransmitted Trigger
Frame
STA 1 UL PPDU
MBA
No Response
STA2 UL PPDU
STA 3 UL PPDU
STA2 already transmitted
its UL PPDU before UL
OFDMA
– Due to large retransmission delay, original UL OFDMA scheduling
might be invalid
• UL STA could transmit its PPDU before TF retransmission
• Channel availability could be changed
Submission
Slide 5
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Retransmission of Trigger Frame
• Conventional retransmission of trigger frame
– Trigger frame retransmission with conventional contention based
retransmission could degrade 11ax system performance due to
invalidity of UL OFDMA scheduling
• We need to consider other type of retransmission
procedure in case of trigger frame failure
– Criteria for retransmission
– Contention based retransmission or not
– Behavior of AP after retransmission failure
Submission
Slide 6
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Retransmission of Trigger Frame
• Fast retransmission of Trigger Frame
AP considers the
transmission failed and
retransmits Trigger
Frame immediately
Trigger
Frame
No
Response
No
Response
No
Response
Trigger
Frame
AP will contend with
other stations with initial
CW
STA 1 UL PPDU
BA
5
MBA
STA 2 UL PPDU
STA 3 UL PPDU
STA5 UL PPDU
Preamble
Duration
Original TXOP
– AP retransmits its trigger frame after sensing absence of UL-PPDU(s)
• If AP cannot detect UL OFDMA PPDU and the channel is idle, AP
immediately retransmit its trigger frame
• Retransmission number or duration might be limited
Submission
Slide 7
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Retransmission of Trigger Frame
• Fast retransmission of Trigger Frame
– In fast retransmission scheme, conventional retransmission scheme on
trigger frame is not allowed
– Fast retransmission could sustain its reliability on UL OFDMA
scheduling
– Original TXOP is not accessible in conventional 802.11 system
• AP get TXOP only if Downlink PPDU transmission and cannot detect
collision
• Therefore, fast retransmission may not cause severe interferences than
conventional 802.11
Submission
Slide 8
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Fast retransmission failure
• Initial CW for next frame
AP considers the
transmission failed and
retransmits Trigger
Frame immediately
Trigger
Frame
No
Response
No
Response
No
Response
Preamble
Duration
Trigger
Frame
AP will contend with
other stations with initial
CW
BA
5
No
Response
No
Response
No
Response
Preamble
Duration
Retransmission duration
Trigger
Frame
STA 1 UL PPDU
MBA
STA 3 UL PPDU
STA2 UL PPDU
STA 4 UL PPDU
Fast Retransmission
Failure would delete
Trigger Frame in Buffer
– AP could transmit a next frame after fast retransmission failure
– The next frame could be a new trigger frame or DL data frame(s)
– Initial CW is applied to next frame because CW doubling is applied
only on retransmission in conventional 802.11 system
Submission
Slide 9
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Fast retransmission failure
• Doubled CW for next frame
AP considers the
transmission failed and
retransmits Trigger
Frame immediately
Trigger
Frame
No
Response
No
Response
No
Response
Preamble
Duration
Trigger
Frame
AP will contend with
other stations with
doubled CW
BA
2
No
Response
No
Response
No
Response
Preamble
Duration
Trigger
Frame
STA 1 UL PPDU
MBA
STA 3 UL PPDU
STA2 UL PPDU
STA 4 UL PPDU
Fast Retransmission
Failure would delete
Trigger Frame in Buffer
Retransmission duration
– Although conventional retransmission rule is not applied to trigger
frame, trigger frame failure could be considered as congestion situation
– To avoid congestion, CW doubling could be applied upon trigger frame
failure
– Doubled CW is applied to the next frame
Submission
Slide 10
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Conclusion
• We need to discuss access category parameters of trigger
frame
• Next procedure of trigger frame failure need to be defined
• Conventional retransmission has some problems(issues) on
trigger frame
• Fast retransmission could be considered instead of
conventional retransmission
Submission
Slide 11
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
Straw Poll
• Do you agree with trigger frame is not allowed to follow
conventional retransmission procedure?
• Y
• N
• A
Submission
Slide 12
Jinsoo Ahn, Yonsei University
July 2015
doc.: IEEE 802.11-15/0878r0
References
[1] IEEE 802.11-15/0132r4 "Specification Framework for TGax"
[2] IEEE 802.11-15/0615r1 “UL OFDMA Bandwidth"
Submission
Slide 13
Jinsoo Ahn, Yonsei University