Mda simulation study mdaop stretching and other concerns
Download
1 / 18

MDA Simulation Study: MDAOP Stretching and Other Concerns - PowerPoint PPT Presentation


  • 63 Views
  • Uploaded on

MDA Simulation Study: MDAOP Stretching and Other Concerns. Date: 2007-09-18. Authors:. Abstract.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'MDA Simulation Study: MDAOP Stretching and Other Concerns' - camdyn


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Mda simulation study mdaop stretching and other concerns
MDA Simulation Study: MDAOP Stretching and Other Concerns

Date: 2007-09-18

Authors:

Ye Chen, Motorola


Abstract
Abstract

  • This document investigates challenges involved in restricting channel access to occur during deterministic intervals (e.g. an MDAOP), and explores the benefits of adding flexibility. Results from simulation experiments are presented to illustrate the issues involved. Additionally, modification to MDA channel access to address these issues are reviewed.

Ye Chen, Motorola


Comments received
Comments Received

  • Comments received about the deterministic channel access mechanism specified in MDA include:

    • Concerns about restriction that MDA TXOPs are not allowed to cross MDAOP boundaries, and how these restrictions complicate retransmission procedures

    • Concerns about needing to reserve excess time so every MDAOP can accommodate one or more retransmissions

    • Questions raised about whether time taken to access the channel should count towards the MDAOP length

    • Questions about whether the use of a single set of channel access parameters both within and after the MDAOP should be prohibited

Ye Chen, Motorola


What have we done
What have we done?

  • Started looking into the details of MDA channel access using a simulation scenario to better understand

    • Do the start of MDA TXOPs frequently get delayed?

    • Do MDA TXOPs generally finish in time (e.g. before the end of the reserved MDAOP)?

    • If we were to enforce the rule that MDA TXOPs must finish in time, how much excess time should each MDAOP include

      • Note: this is not a question for which we would expect to find a simple answer

Ye Chen, Motorola


How did we do it

Mesh AP1

Mesh AP3

Mesh AP6

Mesh AP2 / Mesh Portal

Mesh AP7

Wired DS

How did we do it?

  • Started with MDA simulation model described in 11/07-356r0

  • Modified the model to collect some new MDA statistics

  • Collected results for mixture of MDA and station traffic

Ye Chen, Motorola


New statistics

Delayed Start Time

TxOP

MDAOP

Delayed Start Time

Delayed in Completion time

TxOP

MDAOP

Delayed Start Time

TxOP

Delayed in Completion time

MDAOP

New Statistics?

  • Looking at two error cases:

Normal MDAOP

Case 1: Stretched MDAOP

Case 2: Missed MDAOP

Ye Chen, Motorola


Results
Results

  • Delayed Start Time

  • Percentage of Missed/Stretched MDAOPs

  • Delay in Completion Time

Ye Chen, Motorola


Delayed start time portal ap2
Delayed Start Time (Portal AP2)

  • Even at low loads (e.g. 5 VoIP STA), the MDAOP is often stretched; issue for delay sensitive traffic

Each MDAOP contains 90 µs (10 slots) of extra time

If Start Delay > 90 µs, then it’s a stretched MDAOP

Reserved MDAOP = 340 µs

If Start Delay > 340 µs, then it’s a missed MDAOP

Ye Chen, Motorola


Missed stretched mdaops ap2 portal
Missed/Stretched MDAOPs (AP2 Portal)

  • A significant number of the TXOPs do not complete on time; issue for delay sensitive traffic

Ye Chen, Motorola


Delay in completion time ap2 portal
Delay in Completion Time (AP2 Portal)

  • Numbers shown are averages; size of MDAOP would need to be lengthened even more to keep losses low

  • Completion time can get pushed out due to:

  • Delays in start time

  • Hidden terminals

  • Retransmissions

Ye Chen, Motorola


Discussion
Discussion

  • Results suggest issues with current MDA specification

    • Start times and completion times are frequently delayed

    • A significant percentage of MDAOPs are either stretched or missed

  • Factor preventing on-time completion include

    • STA traffic, congestion, hidden terminals, retransmissions

  • Changes recommended

    • Recommend modifying MDA channel access to accommodate and work around conditions that prevent on-time completion

Ye Chen, Motorola


Proposal
Proposal

  • Continue Negotiating MDAOP times with neighbors

    • Use existing MDAOD setup and advertisement signaling

    • Creation of schedule reduces collisions between mesh points that might be hidden from one another

  • Modify MDA contention mechanism

    • Restriction to complete transmissions within an MDAOP were in place to

      • Avoid misuse of the MDA contention parameters

      • Avoid fairness issues with nodes not deploying MDA

      • Avoid contending for channel during the neighbors’ MDAOP

    • Largest gain in performance due to scheduling, not specialized contention parameters

    • Revert to utilizing EDCA during and after MDAOP

Ye Chen, Motorola


Details of proposed changes
Details of Proposed Changes

  • Modify 9.21 and specifically 9.21.10 to

    • Transmit using EDCA channel access parameters associated with each frame instead of employing a special set of MDA parameters

    • Replace restriction that

      • (old) TXOP must complete within an MDOP, with

      • (new) if MDAOP stretching or a missed MDAOP occurs then channel access is suspended during any neighbor’s MDAOPs

    • Reuse EDCA retransmit procedures to recover from channel errors, subject to restriction above

  • Continue to use existing MDAOD setup and advertisement signaling with enhanced access scheme

  • Document 11-07/2536r0 describes suggested changes to the 802.11s draft 1.06 to address comments 1045, 1300, and 1538

Ye Chen, Motorola


Questions

Questions?

Ye Chen, Motorola


Backup
Backup

Ye Chen, Motorola


Case study
Case Study

MDAOP Schedule

MDAOP1

MDAOP2

MDAOP3

  • The MP with missed/stretched MDAOP can finish the MDA transmission if possible instead of waiting for the next MDAOP

  • The same contention parameters within/outside the MDAOP simplifies the transition in/out MDAOP (no sudden contention parameter changes)

Current MDAOP Definition

Dstart1

Dstart2

Channel busy

Tx 3

Tx2

Time

Tstart1

Tstart2

Channel error

Modified MDAOP Definition

Dstart1

Dstart2

Channel busy

Tx 1

Tx2

Tx 3

reTx

Time

Channel error

Ye Chen, Motorola


Cdf of delayed start time ap2 portal

8 Voice STAs

13 Voice STAs

CDF of Delayed Start time (AP2 Portal)

For 8 voice STAs, 5% of the frames have a delayed start time that exceeds 340 µs (missed MDAOP)

For 13 voice STAs, 20% of the frames have a delayed start time in excess of 340 µs. (missed MDAOP)

340 µs

ms

Ye Chen, Motorola


Cdf of delayed completion time ap2 portal

8 Voice STAs

13 Voice STAs

CDF of Delayed Completion Time (AP2 Portal)

  • These trends can impact delay sensitive traffic

For 8 voice STAs, 10% of the frames have a completion time delay time that exceeds 400 us.

For 13 voice STAs, 10% of the frames have a completion time that exceeds 1.5 ms

The maximum delay in completion time for 8 voice STAs loading is about 2 ms. For 13 voice STAs loading it could be a long as 8 ms

ms

Ye Chen, Motorola


ad