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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom 32FFT STF/LTF Sequences Date: 2012-01-16 Authors: Slide 1

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom Authors continued: Slide 2

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom Outline Contribution 11/1482r2 describes the 1MHz (32FFT) preamble structure We propose here specific STF and LTF sequences for the 32FFT preamble Slide 3

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom STF Sequence Recall from 1482r2 the STF signal is boosted by 3dB for MCS0 rep2 to allow robust packet detection at low SNR Hence low PAPR sequence is of paramount importance to minimize clipping distortion when power boosted for MCS0 rep2 We propose the following sequence –Tone index=[-12 -8 -4 4 8 12] –Values: [0.5, -1, 1, -1, -1, -0.5]x(1+j)x where is a normalization factor – = 2.4 for MCS0 rep2, 1.7 otherwise The sequence uses power tapering at the band edge to reduce time domain PAPR The resulting PAPR is 0.45dB. Slide 4

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom Cont. – Time Domain Plot Slide 5

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom LTF Sequence Recall from 1482r2 the requirement for the 32FFT LTF sequence to be orthogonal to each half of the 64FFT LTF sequence to allow 1 vs. 2MHz mode detection. In addition, in order to aid packet detection an important feature of the LTF sequence is to maximize the speed of autocorrelation drop after the STF field The third important attribute of the LTF sequence is lower PAPR than the PAPR of DATA symbols Slide 6

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom Cont. We propose the following sequence: –Tone index is [-16 -15 -14 …. -1 0 1 ….. 14 15] =[0 0 0 1 -1 1 -1 -1 1 -1 1 1 -1 1 1 1 0 -1 -1 -1 1 -1 -1 -1 1 -1 1 1 1 -1 0 0] –Sequence achieves zero cross correlation with each half of the 64FFT LTF sequence –Maximizes speed at which STF autocorrelator drops (aiding timing recovery) –PAPR=3.7dB, which is lower than that of DATA Slide 7

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom Summary 32FFT STF and LTF sequences that meet the design criteria are proposed Slide 8

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom Straw Poll Do you support the proposed STF and LTF sequences? Y N A Slide 9

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doc.: IEEE 802.11-12/0115r0 Submission January 2012 Ron Porat, Broadcom Appendix A - LTF Orthogonality Metric The orthogonality metric used for searching for an optimal 32FFT LTF sequence is – are the LTF sequences for 32FFT and the upper and lower portions of the 64FFT –The index k is limited to indices [-16:-1 1:15] (skipping 32FFT DC) The metric enables a frequency domain cross correlation to be performed Where y(k) is the final received and averaged LTF value (used for channel estimation), p(k) is the transmitted LTF sequence belonging to a 64FFT or 32FFT. Slide 10

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doc.: IEEE 802.11-12/0115r0 Submission Cont. Cross correlation with the transmitted sequence finds the most likely transmitted sequence and autocorrelation of successive tones removes the effect of the channel –For the correct sequence we get a large positive number –For the incorrect sequence we get a small number – the sum of random numbers Slide 11 Ron Porat, Broadcom January 2012

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doc.: IEEE 802.11-12/0115r0 Submission Appendix B – Autocorrelation Drop Slide 12 Ron Porat, Broadcom January 2012

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