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Suggested Criteria for High Throughput Extensions to IEEE 802.11 Systems

This paper discusses suggested criteria for high throughput extensions to IEEE 802.11 systems, including considerations for backward compatibility and upgrade paths. It also explores the scope of changes at the PHY, MAC, and beyond levels, as well as potential directions for extensions.

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Suggested Criteria for High Throughput Extensions to IEEE 802.11 Systems

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  1. Suggested Criteria for High Throughput Extensions to IEEE 802.11 Systems Sean Coffey Wireless Networking Business Unit Texas Instruments 141 Stony Circle, Suite 210 Santa Rosa, CA 95401 coffey@ti.com Sean Coffey, Texas Instruments

  2. Overview • Recap of current context in high data rate extensions in IEEE 802.11 • Throughput, Rate, Range: suggested criteria • Backwards compatibility and upgrade path issues • PHY, MAC, and beyond: suggested scope Sean Coffey, Texas Instruments

  3. Recap of higher rates & 802.11 • 11b and 11a completed in September 1999 • March 2000 – present: Task Group G, charged with developing a PHY with rate > 20 Mbps in the 2.4 GHz band (ongoing) • Ordinarily, next logical step would be analogous effort in the 5 GHz band, but … • … tentative 11g solution complicates the situation Sean Coffey, Texas Instruments

  4. “g = b + a” • Current draft combines aspects of 11b and 11a in the 2.4 GHz band • 11a PHY taken as is, and placed in 2.4 GHz band • Draft also allows for PBCC-22 & -33 (b extension) and CCK-OFDM (b-to-a-in-packet format) • Compatibility possible due to functionality of the common 802.11 MAC • Provides a path to dual-band devices Sean Coffey, Texas Instruments

  5. Possible directions for extensions • Extend rates simultaneously in both bands • Preserves dual-band convergence from g • Places extra requirements on performance OR • Extend rates only at 5 GHz • No 2.4 GHz issues to be considered • Similar barrier to adoption as existing 11a-only Sean Coffey, Texas Instruments

  6. Suggested direction • Set criteria in terms of “extensions to wireless LANs” • Keep our options open! Sean Coffey, Texas Instruments

  7. Spectral efficiency vs. “Rate” • Can immediately get higher numbers by “channel bonding” • This is a poor idea • Always an option with any system • Criteria should be set up in terms of rates per channel • I.e., spectral efficiency Sean Coffey, Texas Instruments

  8. Rates, throughput and range Current 11a, 1000 byte packets: Sean Coffey, Texas Instruments

  9. Rates, throughput and range One possible future: X Sean Coffey, Texas Instruments

  10. Rates, throughput and range A more interesting goal: . . . Sean Coffey, Texas Instruments

  11. Throughput vs. Rate • Net throughput must account for various types of overhead • Header (20 us) • SIFS time (16 us) • Acknowledgement (incl. header) (24 us) • DIFS time (34 us) • Backoff, etc. • Note that top “rate” does not even appear on previous graphs Sean Coffey, Texas Instruments

  12. Overhead reduction: Initial examples • Packet aggregation: ensure maximum data payloads • 1500 bytes @ “54” Mbps -> 37 Mbps • 420 bytes @ “54” Mbps -> 21 Mbps • 420 bytes @ “100” Mbps -> 26 Mbps • Was in 11e, but has been removed • Burst acks: reduce acknowledgement traffic • 11e currently provides for this Sean Coffey, Texas Instruments

  13. Range extension • Target should be higher effective throughputs at ranges that at least match current top rates Sean Coffey, Texas Instruments

  14. Overhead constraints • Constellation affects required preamble length • Code changes affect required SIFS time • Bit loading requires more channel measurement information • Challenge is to introduce changes that do not require increase in overhead elsewhere Sean Coffey, Texas Instruments

  15. Suggested criterion • Criterion can be set up in terms of higher throughput • E.g., “must have 2x throughput advantage over existing systems” • This implies increased spectral efficiency • Allows invention in terms of how overall system is used Sean Coffey, Texas Instruments

  16. Backwards compatibility • Backwards compatibility comes with many constraints … • … however, it is vital for the success of any communications protocol • A possible approach: require backwards compatibility, but in the “wide sense” • Proposals would have wide latitude in how they achieve the required backwards compatibility Sean Coffey, Texas Instruments

  17. PHY, MAC, and beyond: suggested scope • In the past, study groups have been classified informally at the outset: e.g., PHY or MAC • This is unnecessary and has the potential for problems • Study group should be empowered to recommend all appropriate changes at every layer • This is not the same as saying that proposals can ignore the OSI model Sean Coffey, Texas Instruments

  18. Summary • Study group should emphasize high performance (throughput/rate) WLANs in general • SG should emphasize overall performance • Backwards compatibility is vital • SG should have broad scope and the authorization to recommend all necessary changes Sean Coffey, Texas Instruments

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