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Aligning 802.11e HCF and 802.11h TPC Operations

Aligning 802.11e HCF and 802.11h TPC Operations. Amjad Soomro, Sunghyun Choi, and Javier del Prado Philips Research-USA Briarcliff Manor, New York sunghyun.choi@philips.com. Outline. Introduction Transmit Power Control under HCF Proposed rules to improve TPC under HCF. References.

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Aligning 802.11e HCF and 802.11h TPC Operations

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  1. Aligning 802.11e HCF and 802.11h TPC Operations Amjad Soomro, Sunghyun Choi, and Javier del Prado Philips Research-USA Briarcliff Manor, New York sunghyun.choi@philips.com

  2. Outline • Introduction • Transmit Power Control under HCF • Proposed rules to improve TPC under HCF

  3. References • IEEE 802.11e QoS draft D1.0 • IEEE 802.11-01/169r2: “DFS and TPC Joint Proposal for 802.11h” by S. Choi, et al • IEEE 802.11-01/373r0:“NAV Operation Rules under HCF” by J. del Prado, S. Choi, and A. Soomro

  4. Transmit Power Control (TPC) • Mechanism to reduce energy consumption and co-channel interference • Adapt the radio transmit power to the minimum level required to ensure correct reception of a frame

  5. Baseline • TGh is working on Transmit Power Control (TPC) • 01/169r2 (baseline of .11h) is assuming per-STA power control during CFP and CFB under the HCF operation • But...

  6. TPC under HCF • TPC may not be very efficient under the current rules of HCF: • HC needs to “hear” (i.e., CCA busy) all the frames within its QBSS. Otherwise, it will reclaim the channel after sensing the medium idle for DIFS • HC needs to “receive” certain frames for the correct operation of the QBSS (e.g., to update TC queue sizes) Inefficiency: in ESTA-to-ESTA communications, the transmit power may not be as low as it could be

  7. ESTA2 ESTA2 HC HC ESTA1 ESTA1 Example • Under current rules of HCF, TxOP holder, i.e., ESTA 1, will need to transmit frames so that they can be received by ESTA 2 and at least heard (and preferably received) by the HC. But the HC need to hear the frames ESTA-to-ESTA communication: ideal case Transmission range of ESTA1 CCA busy range of ESTA1

  8. Proposed HCF Rules for TPC

  9. Goal • Reduce the energy consumption: • Increase TPC efficiency for direct ESTA-to-ESTA transmissions under HCF

  10. ESTA2 HC ESTA1 For the First Frame in a Granted TxOP ... • The TxOP holder shall transmit the first frame in a granted TxOP at a high enough power so that the HC can hear it and the destination ESTA can receive it • Use the best power/data rate combination with the above constraint • The HC needs to hear the first frame to determine whether the polled ESTA received the QoS CF-poll frame correctly or not CCA busy range of ESTA1 Transmission range of ESTA1

  11. ESTA2 HC ESTA1 For the Subsequent Frames …. • The TxOP holder may transmit at the best power/data rate combination so that the destination ESTA can receive the frame correctly • To update the TC queue size, or update or request a new TxOP, the TxOP holder should transmit at a power/data rate combination so that both the destination ESTA and the HC can receive the frame correctly Transmission range of ESTA1

  12. ESTA2 HC ESTA1 For Last Frames in a Granted TxOP... • An ESTA should transmit at least the following types of frames at a power/data rate combination to be received by both the HC and the destination ESTA: • QoS data frame with NF=0 • QoS CF-ACK responding to the QoS frame with NF=0. • Desirable to save bandwidth, especially when the TxOP holder finishes earlier than the originally granted TxOP Transmission range of ESTA1

  13. HC Reclaim Operation Rules • The HC can reclaim the channel only in the following situations: • When the CCA stays idle for PIFS time immediately after the end of the QoS CF- Poll frame • Upon reception of a frame from the TxOP holder with NF=0 and a relevant QoS CF-ACK frame if the normal ACK policy is used • The granted TxOP expires • Note that the HC cannot reclaim the channel after sensing the medium idle for DIFS unconditionally • The first difference from 802.11e D1.0

  14. Recovery Rules • During a TxOP, only the TxOP holder is responsible for recovery from the absence of an expected reception. • The second difference from 802.11e D1.0 • The recovery can be done by: • Retransmiting the frame • Sending a frame to another ESTA • Sending a QoS Null Data to the HC with the NF bit equal to 0 (In this manner, the TxOP ends and the HC can reclaim the channel) • All other ESTAs, including the HC, shall not initiate channel recovery since they cannot determine if the TXOP holder is transmitting/receiving a frame or not

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