Download Transmission probability for RA-BSR

January 2016
doc.: IEEE 802.11-16/0085r1
Congestion control
for UL MU random access
• Date: 2016-01-19
Authors:
Name
Affiliations
Woojin Ahn
Yonsei
University
Yonsei
University
Korea National
University of
Transportation
Jinsoo Ahn
Ronny Yongho
Kim
Submission
Address
Phone
email
[email protected]
[email protected]
[email protected]
Slide 1
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Abstract
• Discussing performance boundary UL MU random
access
• Proposing to use transmission probability as a
congestion control parameter (included in TF-R) for
random access
• Providing simulation results that shows the effect of the
transmission probability in terms of network
throughput
Submission
Slide 2
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Random Access (RA) for MU transmission
• A STA with OBO decremented to 0 randomly selects
any one of the assigned RUs for random access and
transmits its frame.
− [MU Motion 27, September 17, 2015, see [1]]
• RA prevents excessive overhead caused by point-topoint transmission control for UL MU
− Expected to be used for many applications such as Buffer Status
Report (BSR), control frame, UL data
Submission
Slide 3
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Acceptance rate of RA
• The acceptance rate of RA has analytical boundary
•
•
Resemblance with slotted ALOHA
Defined by the number of active STAs (OBO=0, Nt.STA) & assigned RUs
(NRU)
• Maximum rate: ≈ 37%
•
When Na.STA = NRU
The performance of RA keeps decreasing
from the maximum value as the number of
active STAs increases
•
•
Submission
3.5
Assigned RUs are occupied by collisions
RA has the same RU utilization with SU
when Na.STA is near 30
Slide 4
Acceptance rate
•
20 MHz, 9 RUs
4
3
2.5
2
1.5
1
0.5
5
10
15
20
25
30
Number of transmitting STAs
35
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Throughput analysis with
Random Access BSR (RA BSR) [2]
RA BSR
MBA
Trigger
STA 5, 8, 9, 10
Throughput (Mbps)
18
16
14
12
10
8
•
Measuring network throughput (1 BSS, 20 MHz)
•
Repeating RA BSR, UL MU transmission
−
RA-BSR
SU
20
MBA
Trigger
5
Col
Col
10
8
Col
Col
9
lmin: 0.5KB, lmax : 1KB
22
6
5
10
15
20
25
Number of Active STAs
30
35
lmin: 2KB, lmax : 5KB
42
RA-BSR
SU
40
Simple integer RU allocation without frequency selectivity
−
•
Comparing to basic access SU transmission
MU transmission with RA shows better throughput when
congestion level is low
Throughput (Mbps)
38
36
34
32
30
•
HOWEVER, MU throughput drops much faster than SU
•
The network throughput of SU is maintained by congestion
control (exponential backoff)
Submission
Slide 5
28
26
5
10
15
20
25
Number of Active STAs
30
Woojin Ahn, Yonsei Univ.
35
January 2016
doc.: IEEE 802.11-16/0085r1
Congestion control parameter for RA
• An HE AP is allowed to broadcast a TBD parameter in
the trigger frame to the STAs so that STAs can initiate
the random access process after the trigger frames.
− [MAC Motion 41, September 17, 2015, see [3]]
• The TBD parameter can be used for enhancing the
efficiency of RA
− Congestion control
− E.g., CWOmin or CWOmax, transmission probability
• We prefer transmission probability
Submission
Slide 6
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Transmission probability pt for RA
• AP broadcasts pt with trigger frame for RA
− Format is TBD
− Optimal pt*: min(NRU, Na.STA)/Na.STA
• Active STAs attempt a Bernoulli trial with pt
− Only STAs with 0 OBO value (after OBO decrement) attempt the
trial, and if fail, do not transmit (regarded as collision)
Pt
FCS
...
Per STA
info n
Per STA
info 1
Common
info field
TA
(RA)
Duration
Frame
Control
5
Col
STA1
STA2
STA3
STA4
STA5
STA6
STA7
STA8
STA9
STA10
...
STA20
STA 5, 8, 9, 10
MBA
Trigger
MBA
Trigger
10
8
Col
Col
9
Bernoulli trial with probability pt
Submission
Slide 7
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Comparison between CWO control and pt
• CWO control
− CWO cannot be applied to STAs that already have OBO
• Once a STA draws its OBO, it won’t be affected by following CWO
controls
− Most of the effect will be shown from the latter TF-Rs
• impossible to control the number of access attempts immediately
• pt
− Currently delivered pt is used for the following immediate
response
• pt instantaneously affects current access behavior
− pt can be applied to every active STAs every time AP broadcasts
it
• We find pt is more immediate and fairer
Submission
Slide 8
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Calculating pt
• In order to calculate pt, AP requires the number of active STA (Na.STA)
• Finding the approximated Na.STA
− Tracing event history
•
# of collision, success, no-access
− Measuring RSSI level of RA or simultaneous CTS
− Moving average of pt
• Several solutions can be applied for implementation
Submission
Slide 9
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Performance analysis with pt
Submission
Slide 10
lmin: 0.5KB, lmax : 1KB
22
20
18
Throughput (Mbps)
• Measuring throughput enhancement of
pt, and observing the effect of Na.STA
estimation error
• Repeating the same simulation on slide 5
with different pt values
• pt = min(NRU, α∙Na.STA)/ α∙Na.STA
α: error scaling
• pt helps to maintain the throughput of
MU RA near maximum regardless of
increase of the number of active STAs
• pt still enhances the throughput of MU
RA even with large amount of estimation
error
1.4Na.STA
16
1.2Na.STA
Na.STA
14
0.8Na.STA
12
0.6Na.STA
10
8
6
5
10
15
20
25
Number of Active STAs
30
Woojin Ahn, Yonsei Univ.
35
January 2016
doc.: IEEE 802.11-16/0085r1
Conclusion
• In order to fully take advantage of UL MU random
access, a proper congestion control mechanism is
necessary
• ‘a TBD parameter’ in TF can be used for congestion
control of RA
• Simulation results shows that transmission probability
successfully control the network congestion
Submission
Slide 11
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Strawpoll
• Do you agree to add to the TG Specification Frame
work document?
• 4.5 UL OFDMA-based random access
− An HE AP is allowed to broadcast transmission probability, pt,, in
the trigger frame to the STAs so that STAs can initiate the random
access process after the trigger frames.
− After OBO decrement, each STA with zero OBO value chooses a
random number [0, 1]. If the chosen number is smaller than pt, the
STA transmits its frame. Otherwise, the STA shall not transmit its
frame, and the STA shall reselect its OBO.
Submission
Slide 12
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
References
• [1] 15/1105r0 UL OFDMA-based Random Access
Procedure
• [2] 15/1369r1 Random access based buffer status report
• [3] 15/1137r1 Triggered OFDMA Random Access
Observations
• [4] 15/0843/r0 UL MU OFDMA analysis
Submission
Slide 13
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Appendix
Submission
Slide 14
Woojin Ahn, Yonsei Univ.
January 2016
doc.: IEEE 802.11-16/0085r1
Simulation setting
• MCS7
• Uniformly distributed MPDU size
− [0.5KB, 1KB], [2KB, 5KB]
•
•
•
•
•
PIFS access for TF-R
All other IFSs are SIFS
BSR duration: 128us [4]
Trigger duration: 112us[4]
MBA duration: 150us
Submission
Slide 15
Woojin Ahn, Yonsei Univ.