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Access Control Enhancement

Access Control Enhancement. Date: 2013 -11 -08. Authors:. Abstract. This contribution shows that time limitation for low rate frames improve aggregate throughput in a BSS. Recap.

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Access Control Enhancement

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  1. Access Control Enhancement • Date:2013-11-08 Authors: Katsuo Yunoki, KDDI R&D Labs.

  2. Abstract • This contribution shows that time limitation for low rate frames improve aggregate throughput in a BSS. Katsuo Yunoki, KDDI R&D Labs.

  3. Recap • Even high rate communication degrades its throughput performance when low rate communication exists in parallel. This issue was explained in doc. 13/0801r1(NTT) and 13/1073r0(KDDI). • TDMA like access control mechanism may mitigate this performance degradation by restricting longer time occupation of low rate frames on WLAN. • Performance evaluation in densely STAs deployed BSS is shown in the following slides: Katsuo Yunoki, KDDI R&D Labs.

  4. Time occupation of a 802.11 frame When a STA transmits 1500B IP packet, time occupations at each data rate are: • Assumptions: • 11n • 1X1 SISO, 20MHzBW • Not considering frame aggregation. Apparently, lower rate frames occupy much time. Calculation detail is on Slide 13. Katsuo Yunoki, KDDI R&D Labs.

  5. Assumed Throughput Considering 10STAs communicating under each MCS, assumed throughputs are: Not considering retry, conflicts or losses. Results are just derived from time occupation in the previous slide. When transmission opportunities among STAs are equal, data amounts per unit time are equal also. So assumed throughputs are equal. Katsuo Yunoki, KDDI R&D Labs.

  6. Consideration • Throughputs on each STA are equalized regardless of link data rate. Because transmission opportunities are equally given to each STA at CSMA/CA mechanism. • High rate link can’t perform its available throughput due to lack of transmission opportunities. Do you think it’s a proper manner? • How about equalizing time resource occupancies among STAs instead of equal transmission opportunities? • Next slide Katsuo Yunoki, KDDI R&D Labs.

  7. Assumed Throughputby equal time allocation for each link Katsuo Yunoki, KDDI R&D Labs.

  8. Throughput Comparison(Current stds. vs. Equal time allocation) Katsuo Yunoki, KDDI R&D Labs.

  9. Summary • Time limitation for low rate frames will improve aggregated throughput on a BSS. It’s equivalent to raise proportion of high rate frames. • However, this consideration showed just an aspect for efficiency improvement. It’s just from simple mathematical evaluations. Katsuo Yunoki, KDDI R&D Labs.

  10. Issues • Mechanism to increase proportion of higher rate frames • Reduction of retry frames • Many implementations lower data rate when re-transmission increases due to frame errors or losses. It’s conflicting behavior against increasing higher rate frames. • Low rate transmissions at cell edge • Coexistence with current standard’s devices • Suppressing low rate frames of legacy devices may be needed. • Considerations of OBSS environment • Integration with existing mechanisms • RTS/CTS, PCF, HCCA, frame aggregation,,, • etc. Katsuo Yunoki, KDDI R&D Labs.

  11. Possible function for HEW • Control for increasing higher rate frames’ proportion Katsuo Yunoki, KDDI R&D Labs.

  12. References • IEEE 11-13/0801r1: Issues of low rate transmission (NTT) • IEEE 11-13/1073r0: Access control enhancement (KDDI) Katsuo Yunoki, KDDI R&D Labs.

  13. Annex: Occupied time calculation Data frame SIFS 8us 8us 4us 8us 4us 4us 16us L-STF L-LTF L-SIG HT-SIG HT- STF HT- LTF Data ACK frame 36us Data length (us) = roundup((service + MAC header + LCP header + Data(1500B)+ FCS + tail)/OFDM symbol)*4 ACK frame DIFS CW 8us 8us 4us 8us 4us 4us 34us L-STF L-LTF L-SIG HT-SIG HT- STF HT- LTF ACK Next frame 36us ACK length (us) = roundup((service + ACK + FCS + tail)/OFDM symbol)*4 Ave. CW (us) = Cwmin * slot time /2 = 15*9/2 = 64.5 Katsuo Yunoki, KDDI R&D Labs.

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