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FEC Frame Formats for 802.11a. John M. Kowalski Sharp Laboratories USA Camas, Washington (360) 817-7520 kowalskj@sharplabs.com. Outline. Motivation General Requirements Tradeoff of Where Coding is done Timing Issues with 802.11a PHY Conclusions Proposed Coding. Motivation.

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fec frame formats for 802 11a

FEC Frame Formats for 802.11a

John M. Kowalski

Sharp Laboratories USA

Camas, Washington

(360) 817-7520

kowalskj@sharplabs.com

John M. Kowalski, Sharp

outline
Outline
  • Motivation
  • General Requirements
  • Tradeoff of Where Coding is done
  • Timing Issues with 802.11a PHY
  • Conclusions
  • Proposed Coding

John M. Kowalski, Sharp

motivation
Motivation

Adding an outer code option with the 802.11e/802.11a PHY would:

  • Greatly expand the market for 802.11 devices
  • Allow existing infrastructure networks to perform more reliably
  • Address competition from other wireless home network solutions
  • Facilitate delay/jitter management for QoS

John M. Kowalski, Sharp

general requirements
General Requirements
  • Provide less than 1 frame (PSDU) error in 10 hours ( or P[error] < 1.15X10-9 for 1000 octet packets.)
  • Minimal overhead
  • Be compatible with OFDM symbol sizes
  • Be consistent with 802.11/802.11a SIFS timing rules
  • Be friendly to known AV formats
  • Be friendly to any aggregation proposals.

John M. Kowalski, Sharp

tradeoff of where coding is done 2
Tradeoff of Where Coding is Done (2)

1

1. P[PLCP Header Failure]  3.15 X10-4 at specified MDSL

at 6 Mbps. At higher rates, (due to higher MDSL)

this falls of drastically.

John M. Kowalski, Sharp

timing issues in 802 11a 1
Timing Issues in 802.11A (1)
  • In 11a, aMACProcessingDelay < 2ms to do:
    • FCS
    • Check control field and address field to decide whether to ACK.
  • Cannot be done before PHY-RXEnd.indicate
  • Must be done in time to issue PHY-TXStart.request for ACK so that beginning of ACK preamble reaches transmit antenna within ±10% of SIFS time.

John M. Kowalski, Sharp

timing issues in 802 11a 2
Timing Issues in 802.11A (2)
  • Issue: it may not be feasible to use a decoder that decodes within aMACProcessingDelay
  • However we can use delayed ACK/Unacknowledged frames
    • Can this be used in enhanced DCF?

John M. Kowalski, Sharp

a proposed coding format
A Proposed Coding Format
  • IV=initialization vector
  • ICV= integrity check vector
  • RS coding assumed

John M. Kowalski, Sharp

proposed coding format
Proposed Coding Format
  • Other codes, e.g., RS(204, 188) work well, but are do not have small least common multiples of 48.
  • Codes that are multiples of 48 work well with MPEG-2, DVD (k can be any fixed number on which the group agrees, e.g., RS(64,48)).
  • This format has benefits for aggregated MPDU’s with TS packets: higher layers can selectively retry.
  • Smaller code sizes for smaller PDU sizes can improve channel efficiency.

John M. Kowalski, Sharp

conclusions
Conclusions
  • For AV applications, delayed ACK/unacknowledged service OK.
  • Requirements can be met at high data rates, (higher MDSL), where they would be used anyway.
  • We would prefer this ASAP (i.e., in the MAC), but we want to make sure any potential issues are addressed.

John M. Kowalski, Sharp