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DCF Enhancements for Large Number of STAs

DCF Enhancements for Large Number of STAs. Date: 2011-09-015. Authors:. Abstract. For use case 1a “ Smart Grid – Meter to Pole” , large number of STAs (up to 6000) should be supported in one AP [1].

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DCF Enhancements for Large Number of STAs

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  1. DCF Enhancements for Large Number of STAs Date:2011-09-015 Authors: Siyang Liu, CATR

  2. Abstract • 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. Siyang Liu, CATR

  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. Basic Idea Siyang Liu, CATR

  4. 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. Introduce Contention Factor Siyang Liu, CATR

  5. Special case: • If Qis set to 0, then STAs are prohibited to access channel. • If Qis 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. Introduce Contention Factor (Cont’) Siyang Liu, CATR

  6. 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. Further Introduce Prohibition Time Siyang Liu, CATR

  7. 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. Combination with Group Siyang Liu, CATR

  8. 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 Qnis set to 0, then STAs in group n is prohibited to access channel in the time Tn. • If Qnis set to 1, then STAs in group n use the current DCF scheme. • If Tnis set to 0, then STAs in group n can contend for channel by enhanced DCF scheme in any DIFS. The value of {Qn,Tn} Siyang Liu, CATR

  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. Siyang Liu, CATR

  10. References [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 Siyang Liu, CATR

  11. Thank you! Siyang Liu, CATR

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