doc.: ieee 802.11-11/1255r0 submission sep.,2011 siyang liu, catrslide 1 dcf enhancements for large...
TRANSCRIPT
doc.: IEEE 802.11-11/1255r0
Submission
Sep.,2011
Siyang Liu, CATRSlide 1
DCF Enhancements for Large Number of STAs
Date: 2011-09-015
Name Affiliations Address Phone email
Siyang Liu CATR No.52 Huayuan Beilu，Beijing，100191
86-01-62300174
Zhendong Luo CATR No.52 Huayuan Beilu，Beijing，100191
86-01-62300171
Daning Gong CATR No.52 Huayuan Beilu，Beijing，100191
86-01-62300156
Authors:
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Sep.,2011
Slide 2
• For use case 1a “Smart Grid – Meter to Pole”, large number of STAs (up to 6000) should be supported in one AP [1].
• If 6000 STAs simultaneously contend for transmission opportunity, large time delay will be induced based on current DCFs scheme [2][3].
• In this contribution, we give our viewpoints on how to support large number of STAs efficiently.
Abstract
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Basic Idea
Sep.,2011
Slide 3
• When the network becomes congestion, the number of STAs which try to access the channel should be limited to reduce the collision rate.
• AP broadcasts some parameters to guide STAs’ contention process. These parameters can be provided in Beacon Frame.
• If STA can not satisfy the parameters, it should not contend for channel at a period of time.
• AP sets the parameters according to the current network utilization rate, the collision rate, and other factors. – For example, if AP finds the network becomes congestion, AP will change the
parameters to make only part of STAs can contend for channel.
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Introduce Contention Factor
• AP behavior: In Beacon Frame, a contention factor Q is provided. The value of Q is between [0,1].
• STA behavior: Before contending for channel via DIFS/backoff, each STA should firstly produce a random number r from a uniform distribution on the unit interval , and then compare r with Q . If r<= Q, STA can contend for channel; otherwise it is prohibited to contend for channel. – SIFS/PIFS does not apply the above scheme.
Sep.,2011
Slide 4
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Introduce Contention Factor (Cont’)
Sep.,2011
Slide 5
STARTS
AP
DIFS
backoff
SIFS
CTS
frame
ACK
SIFS SIFS DIFS
Satisfy: r<Q
SIFS
Again: Produce r
& Comapre with Q
• Special case: – If Q is set to 0, then STAs are prohibited to access channel.
– If Q is set to 1, then there is no difference for the proposed scheme with the current DCF function. STAs can just use the current DCF function.
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Further Introduce Prohibition Time
• AP behavior: In Beacon Frame, an prohibition time T is provided.
• STA behavior: If r> Q, STA is prohibited to contend for channel until the time T passed.
Sep.,2011
Slide 6
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Combination with Group
• STAs can be classified into several groups. Different group can also has different priority. Each group has its own {Qn,Tn}.
• By setting different {Qn,Tn} values for different groups, AP can control the mainly transmission groups at a period of time.
Sep.,2011
Slide 7
Group1
Group2
{Q1, T1} {Q2, T2}
T1 T2 T3
The time mainly used for Group1 STAs’ Transmission
The time mainly used for Group2 STAs’ Transmission
{Higher Q1, Lower T1}{Lower Q2, Higher T2}
All STA can contend for channel (same as current 802.11 DCF).
If AP finds that the network becomes congestion.
If AP finds that the network becomes free.
{Lower Q1, Higher T1}{Higher Q2, Lower T2}
{Q1=1, T1=0}{Q2=1, T2=0}
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
The value of {Qn,Tn}• AP can set {Qn,Tn} according to the current network utilization rate,
the number of STAs in group n and other factors (e.g., the priority of each group). Note: STA reports its group number in Association Request. – If the network is congestion, Qn can be set lower, and Tn can be set higher;
otherwise Qn can be set higher, and Tn can be set lower.
– For high priority group, Qn can be set higher, and Tn can be set lower; for low priority group, Qn can be set lower, and Tn can be set higher.
• Special case: – If Qn is set to 0, then STAs in group n is prohibited to access channel in the
time Tn.
– If Qn is set to 1, then STAs in group n use the current DCF scheme.
– If Tn is set to 0, then STAs in group n can contend for channel by enhanced DCF scheme in any DIFS.
Sep.,2011
Slide 8
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Sep.,2011
Slide 9
Conclusion
• To support large number of STAs in 802.11 ah, DCF scheme should be enhanced to reduce the collision rate and improve the transmission efficiency.
• Contention factor and prohibition time proposed in this contribution can be utilized to enhance the current DCF function, and thus support large number of STAs in 802. 11 ah efficiently.
• Similar idea can also be applied to EDCA.
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Sep.,2011
Slide 10
[1] 11-11-0457-00-00ah-potential-compromise-of-802-11ah-use-case-document
[2] 11-11-0985-01-00ah-performance-evaluation-of-multiple-stas-authentication-and-association-process
[3]11-11-1019-00-00ah-simulation-large-number-of-stas-support
References
doc.: IEEE 802.11-11/1255r0
Submission Siyang Liu, CATR
Sep.,2011
Slide 11
Thank you!