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DFT spreading OFDM optional specification proposal for 11ah low rate PHY

DFT spreading OFDM optional specification proposal for 11ah low rate PHY. Date: 2012-11-15. Authors:. Slide 1. Background. TGah PHY supports 2 /4/8/16MHz signals based on the down clocked versions of 11ac 20/40/80/160 MHz, and an 1MHz signals based on 32FFT .

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DFT spreading OFDM optional specification proposal for 11ah low rate PHY

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  1. DFT spreading OFDM optional specificationproposal for 11ah low rate PHY Date: 2012-11-15 Authors: Slide 1

  2. Background • TGah PHY supports 2/4/8/16MHz signals based on the down clocked versions of 11ac 20/40/80/160 MHz, and an 1MHz signals based on 32FFT. • Both 2MHz and 1MHz signals are mandatory in TGah PHY. • DFT spreading OFDM (DFTs-OFDM) is adopted for the uplink in IMT-2000 LTE for battery operated mobile terminal. • DFTs-OFDM application to 11ah PHY was suggested in IEEE802.11-11/0753r0, and IEEE802.11-12/0349r2 in 2012/3. • The proposal of IEEE802.11-12/0349r2 was well-supported for its advantage of lower PAPR and lower ACPL (adjacent channel power leakage)in non-linear HPA operation. • Y 16 N 1 A 23 Slide 2

  3. Abstract • This contribution is a follow-up of IEEE802.11-12/0349r2. • We propose DFT-spreading OFDM based optional specification for 11ah low rate PHY, especially for 1MHz and 2MHz modes, aiming at sensor network applications which need high power efficiency. November 2012 Slide 3

  4. Review of advantages of 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 • Low transmission speed: 2 MHz mode and 1 MHz mode • Long battery life time • Low power consumption at wireless sensor terminals • Basic Requirements for the use cases • Lower PAPR and lower ACPL (adjacent channel power leakage) with higher energy efficiency, i.e. low output power back-off operation at HPA. • Less BER performance degradation in non-linear HPA operation. Slide 4

  5. Null DC sub-carrier DFTs-OFDM 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 neither “power of two” nor “even”. • 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. • DC offset error at modulator and demodulator can degrade BER performance in the conventional DFTs-OFDM.. • No BER performance degradation in OFDM since DC sub-carrier is not used. • DFTs-OFDM with null DC sub-carrier is proposed for 11ah low rate PHY optional specification, especially for sensor network applications where high power efficiency is required. • No BER performance degradation due to DC offset error in the proposed DFTs-OFDMsince DC sub-carrier is made null. Slide 5 Hongyuan Zhang, et. Al.

  6. January 2012 Block diagram of NDCS-DFTs-OFDM • DFT on the transmission side • 26 points DFT for 1MHz, 56 points DFT for 2MHz • IDFT and FDE on the reception side • 26 points IDFT for 1MHz, 56 points IDFT for 2MHz • FDE is performed using CSI. : Additional blocks required for NDCS-DFTs-OFDM Scrambler FEC Interleaver BPSK/QPSK mapper DFT IFFT GI & Window Analog & RF (a) Transmitter side of NDCS-DFTs-OFDM De-Scrambler FEC decoder De-interleaver BPSK/QPSK De-mapper FFT IDFT Frequency Domain Equalization Remove GI Analog & RF (b) Receiver side of NDCS-DFTs-OFDM Slide 6

  7. Details of DFT/IDFT in NDCS-DFTs-OFDM • M=56 and N=64 for 2MHz signals (52 Data tones, 4 Pilot tones, 7 Guard tones, and 1 DC tone) • M=26 and N=32 for 1MHz signals (24 Data tones, 2 Pilot tones, 5 Guard tones, and 1 DC tone) Spectrum splitting M M/2 M+1 N N S/P MOD DFT IFFT P/S GI windowing D/A ... Output Data ... ... 0 ... M/2 (1) Transmitter side M M/2 M+1 N N P/S IDFT FDE FFT S/P Remove GI A/D DEM … Data Input … … … … X … M/2 (2) Receiver side Slide 7

  8. Preamble and signal design for NDCS-DFTs-OFDM • DFTs-OMDF optional specification for 1MH/2MHz BPSK/QPSK signals. • No change in the preamble and basic signal design 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 … OFDM based DFT Spreading is applied in the data field only. Slide 8

  9. 2.0dB M=56 N=64 Modulated by random data. Comparison of PAPR Null DC subcarrier DFTs-OFDM (NDCS-DFTs-OFDM) achieves 2.0dB lower PAPR than OFDM, but 0.5dB higher than conventional DFTs-OFDM at CCDF=0.1%. Slide 9

  10. Rapp model Comparison of adjacent channel power leakage NDCS-DFTs-OFDM has almost the same adjacent channel power leakage as the conventional DFTs-OFDM, which is 3-4dB lower than that of OFDM when OBO=3dB. Slide 10

  11. 6dB (OFDM) 6dB 5dB 4dB Estimated PAE improvement DFTs-Spreading approach can reduce OBO from 6dB to 4.5dB to maintain ACLP. 1.5dB OBO reduction improves 20% in PAE (power-added-efficiency) from 15% to 18%. 5 56 sub-carriers / 2MHz mode / QPSK 0 -5 -10 Power Density [dB] -15 -20 -25 -30 0 1 2 3 Frequency (MHz) Jeonghu Han et al, “A Fully-Integrated 900-MHz CMOS Power Amplifier for Mobile RFID Reader Applications,”IEEE RFIC Symposium, 2006. Slide 11

  12. 50 45 : DFTs - OFDM 40 : NDSC-DFTs-OFDM - 35 30 EVM [%] 25 M=56 N=64 QPSK 20 15 10 5 0 0 2 4 6 8 10 DC offset error [%] EVM according to DC offset error in NDCS-DFTs-OFDM No EVM (Error Vector Magnitude)degradation due to DC offset error is observed in NDCS-DFTs-OFDM. Slide 12

  13. Signal processing complexity Estimation of required complex multiplications per OFDM symbol. (1) 1MHz mode Note: 26 point DFT is decomposed to 2X13 point DFT. (2) 2MHz mode Note: PFA (Prime Factor FFT algorithm) can be applied for 56 (8X7) points DFT. Slide 13

  14. Summary November 2011 • NDCS-DFTs-OFDM optional specification for 11ah low rate PHT is proposed. • 26 point DFT and 32 point FFT for 1MHz mode QPSK/BPSK. • 56 point DFT and 64 point FFT for 2MHz mode QPSK/BPSK. • DC sub-carrier is made null • Features of the proposed specification • No change in the preamble and basic signal design of OFDM signals. • Lower PAPR and lower ACPL than OFDM • No EVM degradation due to DC offset error • Less signal processing complexity by spectrum splitting Slide 14

  15. 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 [5] 11-12-0349-02-00ah-dft-spreading-OFDM-options-for-11ah-phy-enhancement

  16. Straw Poll Hongyuan Zhang, et. Al. • Do you support NDCS-DFTs-OFDM based optional specification in slide 7 and 8 for 11ah low rate PHY ? • Mainly for 1MHz/2MHz signals with BPSK/QPSK mode. • Y • N • A

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