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IEEE802.11ac Preamble with Legacy 802.11a/n Backward Compatibility

Date: 2009-07-14. IEEE802.11ac Preamble with Legacy 802.11a/n Backward Compatibility . Authors:. Introduction Proposed Preamble Format Preamble Waveform PAPR Preamble Efficiency. Outline. Functional requirements for TGac. System Performance Shall operate in 5GHz frequency band

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IEEE802.11ac Preamble with Legacy 802.11a/n Backward Compatibility

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  1. Date: 2009-07-14 IEEE802.11ac Preamble with Legacy 802.11a/n Backward Compatibility Authors:

  2. Introduction • Proposed Preamble Format • Preamble Waveform • PAPR • Preamble Efficiency Outline

  3. Functional requirements for TGac. • System Performance • Shall operate in 5GHz frequency band • At least 1Gbps at MAC SAPs utilizing 80MHz • At least 500Mbps for Single STA • Spectral efficiency at least 7.5 bps/Hz • Shall ensure backward compatibility with IEEE 802.11a/n. • Enable coexistence and spectrum sharing with IEEE 802.11a/n. • Compliance to PAR I. Introduction Doc.IEEE802.11-09/0304r0 March 2009

  4. Main Features • Uses 80MHz channel and meets all functional requirements for a VHT preamble • Three preamble modes to minimize overhead • Seamless upgrade from 802.11n preamble • Almost identical PAPR characteristics with 802.11n • Comparable Preamble Efficiency to 802.11n II. Proposed Preamble

  5. Mixed 11a/n Mode • 56us duration • Backward compatible with 802.11a/n • Mixed 11n Mode • 44us duration • Backward compatible with 802.11n • VHT Greenfield Mode • 36us duration • VHT only mode Proposed Preamble Modes

  6. A) Mixed 11a/n Mode Frame Format Proposed Mixed 11a/n mode: Backward compatible with IEEE802.11a/n 8μs 8μs 4μs 8μs 8μs 4μs 4μs per LTF 4/3.6μs per Data L-STF L-LTF L-SIG HT-SIG VHT-SIG VHT STF VHT LTF1 VHT LTF4 Data Data Duration=56μs * A New SIG field is defined to accommodate changes in VHT while maintaining compatibility 802.11n Mixed Mode Preamble 8μs 8μs 4μs 8μs 4μs 4μs per LTF 4/3.6μs per Data L-STF L-LTF L-SIG HT-SIG HT STF HT LTF1 HT LTF4 Data Data Duration=48μs * * 4 spatial streams

  7. Proposed Phase Rotation for 80 MHz Channel to Maintain Low PAPR -128 -64 0 64 127 Proposed scheme for 80Mhz S = subcarrier pattern for 802.11a system -64 0 63 802.11n 40Mhz case -This phase rotation scheme is used for all preamble symbols -The phases were chosen to give lowest PAPR

  8. L-STF L-LTF L-SIG HT-SIG VHT-SIG VHT STF VHT LTF1 VHT LTF4 Data Data Legacy – Short Training Field L-STF 20MHz -128 127 -64 0 64 Subcarriers #

  9. L-STF L-LTF L-SIG HT-SIG VHT-SIG VHT STF VHT LTF1 VHT LTF4 Data Data Legacy - Long Training Field L-LTF 20MHz -128 127 -64 0 64 Subcarriers #

  10. L-STF L-LTF L-SIG HT-SIG VHT-SIG VHT STF VHT LTF1 VHT LTF4 Data Data Legacy - SIGNAL Field L-SIG 20MHz -128 127 -64 0 64 Subcarriers # GI L-SIG 0.8 m m 3.2 m m s s s s

  11. VHT – SIGNAL Field BW BW MSB LSB STBC LENGTH should be increased by one bit to maintain preamble efficiency lost with the use of 80MHz channel Reserved one STBC Short GI • 64 options of MCS. • 131072 octet of data LENGTH = 2 X 802.11n. • CRC protected.

  12. B) Mixed 11n Mode Frame Format HT mode: Backward compatibility with IEEE802.11n 8μs 8μs 8μs 8μs 4μs per LTF 4/3.6μs per Data HT-STF HT-LTF HT-SIG VHT-SIG VHT LTF2 VHT LTF4 Data Data Duration=44μs * The difference with 802.11n greenfield preamble is the additional SIG symbol 802.11n Greenfield Preamble 8μs 8μs 8μs 4μs per LTF 4/3.6μs per Data HT-STF HT-LTF1 HT-SIG HT LTF2 HT LTF4 Data Data Duration=36μs * * 4 spatial streams

  13. C) VHT Greenfield Mode Frame Format Greenfield mode: No backward compatibility with IEEE802.11a/n 8μs 8μs 8μs 4μs per LTF 4/3.6μs per Data VHT-STF VHT-LTF1 VHT-SIG VHT LTF2 VHT LTF4 Data Data Duration=36μs* -Same purpose as the 802.11n greenfield format preamble

  14. III. Preamble Waveform VHT- LTF2 VHT- LTF4 L- SIG HT- SIG1 HT- SIG2 VHT- SIG1 VHT- SIG2 VHT- STF VHT- LTF1 VHT- LTF3 L-STF L-LTF Time ( ) m s

  15. V. Preamble Efficiency The preamble efficiency is defined as 95.29 48 96.43 36 131072 94.26 230 56 131072 44 95.43 230 131072 230 96.23 36

  16. IV. PAPR

  17. We have been developing an 80MHz BW WLAN preamble which has backward compatibility with IEEE802.11a/n system. The proposed preamble has comparable efficiency compared to IEEE802.11n’s preamble. The proposed preamble has comparable PAPR with IEEE802.11n’s preamble. Conclusion

  18. E. Perahia, ”IEEE P802.11 Wireless LANs: VHT below 6GHz PAR Plus 5C’s”, doc.:IEEE 802.11-08/0807r4. • ”Supplement to IEEE STANDARD for Information Technology – Telecommunications and Information Exchange between Systems - Local and Metropolitan Area Networks - Specific Requirements”, IEEE Std 802.11a- 1999(R2003), June 2003. • ”Draft STANDARD for Information Technology – Telecommunications and Information Exchange between Systems - Local and Metropolitan Area Networks - Specific Requirements”, IEEE P802.11n./D9.0, March 2009. • Peter L and Minho C, ”TGac Functional Requirements Rev.0”, doc.:IEEE 802.11-09/0304r0. • Rolf de V, ”802.11ac Usage Models Document”, doc.:IEEE802.11- 09/0161r2. • Minho C and Peter L, ”Proposal for TGac Evaluation Methodology”, doc.:IEEE802.11-09/0376r1. References

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