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DFT spreading OFDM options for 11ah PHY enhancement

DFT spreading OFDM options for 11ah PHY enhancement. Date: 2012-3-15. Authors:. Abstract. This presentation proposes DFT spreading OFDM options for 11ah PHY enhancement. Overview.

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DFT spreading OFDM options for 11ah PHY enhancement

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  1. DFT spreading OFDM options for 11ah PHY enhancement Date: 2012-3-15 Authors:

  2. Abstract • This presentation proposes DFT spreading OFDM options for 11ah PHY enhancement.

  3. Overview • TGah decided to support 2/4/8/16MHz signals based on the down clocked versions of 11ac 20/40/80/160 MHz, and an 1MHz signal based on 32FFT. • Both 2MHz and 1MHz receptions are mandatory in TGah PHY. • DFT spreading OFDM (DFTS-OFDM) is adopted for the uplink in IMT-2000 LTE, and the concept of DFTS-OFDM was presented in IEEE 802.11-11/0753r0. • We propose DFTS-OFDM options for 11ah PHY enhancement for 1MHz and 2MHz signals, especially for the purpose of sensor applications in this presentation. • Advantage of DFT-spreading OFDM • Proposal of DFT spreading OFDM option.

  4. Why DFTS-OFDM ? • Battery driven wireless terminals are used for sensor network applications • Basic Requirements for the use cases of 1a/1f and 2d/2e/2f • Relatively low transmission speed • Long battery life time • Reduced power consumption at wireless sensor terminals • Higher efficiency at HPA, i.e. low output back-off operation • Computer simulation results on PAPR, Power spectrum after HPA and BER are shown in the following slides. • 56 points DFT spreading is assumed. Slide 4

  5. 0 10 -1 10 -2 10 -3 10 Cumulative Probability -4 10 -5 : OFDM 10 : DFTS-OFDM -6 10 0 2 4 6 8 10 Instantaneous Power [dB] Comparison of PAPR DFTS-OFDM achieved lower PAPR than OFDM. 56 subcarriers 56 point DFT spreading 64 point IFFT QPSK 2.5dB @0.1% Slide 5

  6. Comparison of output spectrum after HPA • DFTS-OFDM achieved less ACL (adjacent channel power leakage) when output backoff is small. • DFTS-OFDM is more suitable for low output backoff operation. Note: 1/To=Subcarrier spacing 0 : OFDM -5 : DFTS-OFDM -10 -15 OBO=0dB PSD [dB] -20 -25 OBO=3dB -30 OBO=6dB -35 Rapp model (smooth factor=2) -40 0 32 64 96 128 Normalized Frequency [1/To] Slide 6

  7. : QPSK Theory : OFDM 0dB : OFDM 3dB : OFDM 6dB : DFTS-OFDM 0dB : DFTS-OFDM 3dB : DFTS-OFDM 6dB 0 5 10 15 Eb/N0 [dB] BER performance • DFTS-OFDM achieved better BER performance, when OBO=0dB-3dB. 100 QPSK Uncoded AWGN 10-1 10-2 BER 10-3 10-4 10-5 10-6 Slide 7

  8. Transmission flow for DFTS-OFDM options (1) • DFTS-OMDF options will be useful for 1MH/2MHz BPSK/QPSK signals. • It is desirable not to change the basic signal design and preamble of OFDM signals. • 1MHz (32 FFT) • 24 Data tones, 2 Pilot tones, 5 Guard tones, and 1 DC tone • 2MHz(64 FFT) • 52 Data tones, 4 Pilot tones, 7 Guard tones, and 1 DC tone AH-STF AH-LTF AH-SIG AH-LTF1 DFTS-OFDM 1 DFTS-OFDM 2 DFTS-OFDM n … DFT Spreading is applied in the data field only. Slide 8

  9. January 2012 Transmission flow for DFTS-OFDM options (2) • DFT on the transmission side • 26 or 27 points DFT for 1MHz, 56 or 57 points DFT for 2MHz • IDFT and FDE on the reception side • 26 or 27 points IDFT for 1MHz, 56 or 57 points IDFT for 2MHz • FDE is performed using CSI : Additional functions for DFTS-OFDM enhancement Scrambler FEC Interleaver BPSK/QPSK mapper DFT IDFT GI & Window Analog & RF (a) Transmission side for DFTS-OFDM enhancement De-Scrambler FEC decoder De-interleaver BPSK/QPSK De-mapper DFT IDFT Frequency Domain Equalization GI & Window Analog & RF (b) Reception side for DFTS-OFDM enhancement Slide 9 Hongyuan Zhang, et. Al.

  10. Discussions November 2011 • 57 DFT/IDFT is the simplest approach for DFTS-OFDM, howeverFFT algorithm can not be applied for DFT/IDFT implementation since 57 is not power of two. • It needs large amount of signal processing for DFT/IDFT. • 56 DFT/IDFT is another simple approach for DFTS-OFDM. • 56 DFT/IDFT needs less amount of signal processing than 57 DFT/IDFT. • DC tone is replaced with one data tone. • Though 57/56 DFT/IDFT needs large amount of signal processing, it is worth employingDFTS-OFDM for 1MHz/2MHz signals for sensor network applications where low PAPR is strongly desired. • Direct DFT/IDFT will be possible because of its low symbol rate. • Other DFTS-OFDM based approaches can be employed based on the trade-off between PAPR and signal processing. Slide 10 Hongyuan Zhang, et. Al.

  11. Straw Poll Hongyuan Zhang, et. Al. • Do you support DFTS-OFDM based options for 11ah PHY enhancement for its advantage of low PAPR and better BER performance in non-linear HPA operation ? • Applied only for 1MHz/2MHz signals with BPSK/QPSK mode. • Needs further considerations on other approaches based on trade-off between PAPR and signal processing.

  12. Hongyuan Zhang, et. Al. References [1] 011-11-0753-00-00ah-dft-spread-ofdm-optimized-for-802-11ah [2] 11-11-1482-00-00ah-preamble-format-for-1-MHz [3] 11-11-1483-00-00ah-11ah-preamble-for-2MHz-and-beyond [4] 11-11-1484-06-00ah-11ah-phy-transmission-flow

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