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Proposed TGac Preamble

Proposed TGac Preamble. Date: 2010-01-20. Authors:. Outline. PPDU format VHT-SIG Legacy Rx state machine for VHT-SIG VHT-LTF 2 options Conclusion and future work. PPDU Format. VHT PPDU Format Design Considerations. Immediate (no symbol delay) detection Reliable

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Proposed TGac Preamble

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  1. Proposed TGac Preamble Date: 2010-01-20 Authors: Yung-Szu Tu, et al., Ralink Tech.

  2. Outline • PPDU format • VHT-SIG • Legacy Rx state machine for VHT-SIG • VHT-LTF • 2 options • Conclusion and future work Yung-Szu Tu, et al., Ralink Tech.

  3. PPDU Format Yung-Szu Tu, et al., Ralink Tech.

  4. VHT PPDU Format Design Considerations • Immediate (no symbol delay) detection • Reliable • Backward compatibility with 11a/n • Low PAPR Yung-Szu Tu, et al., Ralink Tech.

  5. Possible VHT PPDU Formats • All packet types present in MM-VHT network • Support for VHT-GF is optional Yung-Szu Tu, et al., Ralink Tech.

  6. Phase Rotation • 09/1174r0 [2] mentioned phase rotation over 4 sub-bands is required for low PAPR • Our simulation result on phase rotation agrees with 09/0847r1 [3] by Leonardo et al., i.e. 1 j 1 -j • We also found other sets of rotation that yield low PAPR Yung-Szu Tu, et al., Ralink Tech.

  7. VHT-SIG Yung-Szu Tu, et al., Ralink Tech.

  8. VHT Signal Field • Challenges for VHT-SIG design • Immediate and Reliable detection on first symbol after L-SIG • Minimize false detection • Backward compatibility • With 11a/n • Efficiency • Support enhanced features of TGac with no unnecessary fields Yung-Szu Tu, et al., Ralink Tech.

  9. Previously Proposed VHT Preamble Format • Proposed Signaling scheme allows MM/GF structure identical to 11n • Alternating subcarriers get 90-degree shift • “Orthogonal shift” compared to 0-degree and 90-degree Yung-Szu Tu, et al., Ralink Tech.

  10. 11n HT-SIG Field detection using 90 degree BPSK • 90 degree detector • Operate on 1st symbol following L-SIG • Detection: • Measure FEQ output • Compare I vs Q energy levels: High Q energy  HT packet • Legacy data symbols: low Q, or equal I and Q components Yung-Szu Tu, et al., Ralink Tech.

  11. Previously Proposed VHT-SIG modified 90 degree BPSK • Alternate 0/90 degree BPSK symbols on odd/even subcarriers • Will not be detected as 11n HT-SIG field Yung-Szu Tu, et al., Ralink Tech.

  12. Metric Data Symbol 11a L-SIG 11n HT-SIG 11ac VHT-SIG 11n 0 S -S 0 11ac 0 0 0 -S Previously Proposed VHT-SIG MM Detection Scheme Yung-Szu Tu, et al., Ralink Tech.

  13. Newly Proposed VHT-SIG with +45/+135 degree BPSK • Rotate VHT BPSK symbols +45 degrees • Alternate +45/-45 (+135) degree BPSK symbols on odd/even subcarriers • Will not be detected as 11n HT-SIG field • Even just a few subcarriers would detect equal I/Q energy Yung-Szu Tu, et al., Ralink Tech.

  14. Newly Proposed VHT-SIG MM Detection with Rotation • Detection metrics unchanged • More robust 11n spoofing • All subcarriers appear as QPSK to 11n detector (i.e., data symbol) • VHT detection on de-rotated symbols • Recovers original orthogonal 90-degree BPSK shift Yung-Szu Tu, et al., Ralink Tech.

  15. Orthogonal shift provides better backward compatibility • Both VHT-SIG1, 2 appear as QPSK data to 11n detector • All subcarriers contain both I/Q energy • Both VHT-SIG fields appear as data symbols under 11n detection • Delayed-90 shift could result in “false positive” 11n detection • Certain 11n implementations could trigger off either HT-SIG field to declare 11n packet • More efficient SIG field design • Open possibility to QPSK VHT-SIG2 • No need for VHT-SIG3 • Or, pack twice as much VHT descriptor info. by employing higher-order Modulation and Code Rate Yung-Szu Tu, et al., Ralink Tech.

  16. Detection Timeline with and without Rotation of VHT-SIG1 • With VHT-SIG1 rotation, 11ac devices can recognize 11ac packets at FEQ output immediately after VHT-SIG1 Yung-Szu Tu, et al., Ralink Tech.

  17. Straightforward Extension to Greenfield • Allows highly efficient all-GF operation • Eventual phase-out of 11a devices: all 11n/ac network Yung-Szu Tu, et al., Ralink Tech.

  18. Rx State Machine Yung-Szu Tu, et al., Ralink Tech.

  19. 11a PLCP Rx State Machine Yung-Szu Tu, et al., Ralink Tech.

  20. 11n PLCP Rx State Machine Yung-Szu Tu, et al., Ralink Tech.

  21. Legacy Rx State Machine • 11a devices can recognize L-SIG but not the following VHT-SIG, so it will wait LENGTH indicated in L-SIG • 11n devices cannot recognize VHT-SIG, so three ways at “RX HT-SIG” are all possible • Carrier lost • HT-SIG, but CRC will fail • Claimed as 11a/g, but can’t be decoded wait LENGTH • 1 and 2 will return to IDLE state when the PPDU is over, just as invalid and corrupted 11n PPDU All legacy devices are not affected Yung-Szu Tu, et al., Ralink Tech.

  22. Summary • Use “orthogonal shift” to signal new VHT packet format • Take advantage of OFDM property to expand signaling space • More robust detection VHT-SIG1,2 appear as QPSK to 11n detector • More efficient SIG field design • Open possibility to QPSK VHT-SIG2 • No need for VHT-SIG3 • Additional user data • GF compatibility • Extends gracefully to VHT-GF operation Yung-Szu Tu, et al., Ralink Tech.

  23. VHT-LTF Yung-Szu Tu, et al., Ralink Tech.

  24. CSD Q IFFT Channel Estimation by P Matrix Yung-Szu Tu, et al., Ralink Tech.

  25. Generation of the New P matrixfor More Tx Antenna • Requirement of generating P • P must be a unitary matrix ( ) • The element of P must be +1 or -1 • Ensures the Tx and Rx power the same as payload. • The 2x2 P must be a sub-matrix of 3x3 P Yung-Szu Tu, et al., Ralink Tech.

  26. NSTS NDLTF 1 1 2 2 3 4 4 4 5 8 6 8 7 8 8 8 Compatible with 11n P Matrix • The size of the P matrix must be even. • There exists no 6x6 P matrix which is also compatible with the 11n P matrix(4x4) Yung-Szu Tu, et al., Ralink Tech.

  27. MIMO Channel Estimation by FDM LTF (1) Yung-Szu Tu, et al., Ralink Tech.

  28. MIMO Channel Estimation by FDM LTF (2) Yung-Szu Tu, et al., Ralink Tech.

  29. Channel B Channel D Mean Square Error for 6x6 Yung-Szu Tu, et al., Ralink Tech.

  30. Channel B Channel D Mean Square Error for 6x8 Yung-Szu Tu, et al., Ralink Tech.

  31. Channel B Channel D Mean Square Error for 8x8 Yung-Szu Tu, et al., Ralink Tech.

  32. Comparison • FDM is more efficiency • For FDM, No. of symbols = No. of streams • For P matrix, No. of symbols = 8 for 5~7 streams • At the expense of worse MSE • P matrix method is compatible with 11n and has lower MSE Yung-Szu Tu, et al., Ralink Tech.

  33. Conclusion and Future Work • VHT-SIG is refined with extra 45 degree rotation, compared with 09/1258r0 • VHT-SIG is backward compatible with legacy Rx state machine • Two options of VHT-LTF are proposed • Future work: • Simulation of VHT-SIG • More PHY designs Yung-Szu Tu, et al., Ralink Tech.

  34. References • [1] Yug-Szu Tu, et. al., Proposal for TGac VHT Format , IEEE 802.11-09/1258r0, Nov. 19, 2009 • [2] Hongyuan Zhang , et. al., 802.11ac Preamble, IEEE 802.11-10/0070r0, Jan. 19, 2010 • [3] Leonardo Lanante , et. al., IEEE802.11ac Preamble with Legacy 802.11a/nBackward Compatibility, IEEE 802.11-09/0847r1, Nov. 16, 2009 Yung-Szu Tu, et al., Ralink Tech.

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