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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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slide1

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
Outline
  • Introduction
  • Transmit Power Control under HCF
  • Proposed rules to improve TPC under HCF
references
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
transmit power control tpc
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
baseline
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...
tpc under hcf
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

example

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

slide9
Goal
  • Reduce the energy consumption:
    • Increase TPC efficiency for direct ESTA-to-ESTA transmissions under HCF
slide10

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

slide11

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

slide12

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

hc reclaim operation rules
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
recovery rules
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