Dft spreading ofdm options for 11ah phy enhancement Date: 2012-3-15

DFT spreading OFDM options for 11ah PHY enhancement

• Date: 2012-3-15

Abstract

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

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.

• 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.

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.

Comparison of PAPR

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.

BER performance

• DFTS-OFDM achieved better BER performance, when OBO=0dB-3dB.

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

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

57 DFT/IDFT is the simplest approach for DFTS-OFDM, however FFT algorithm can not be applied for DFT/IDFT implementation since 57 is not power of two.

• 57 DFT/IDFT is the simplest approach for DFTS-OFDM, however FFT 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 employing DFTS-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.

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 ?

• 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.

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