Single stream pilots for 11ah
This presentation is the property of its rightful owner.
Sponsored Links
1 / 16

Single Stream Pilots for 11ah PowerPoint PPT Presentation


  • 96 Views
  • Uploaded on
  • Presentation posted in: General

Single Stream Pilots for 11ah. Authors:. Date: 2012-01-16. Authors continued:. Slide 2. Abstract. This presentation proposes pilot waveform designs for 11ah. In [1][2], we proposed preamble formats for 1MHz, and >=2MHz SU/MU.

Download Presentation

Single Stream Pilots for 11ah

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Single stream pilots for 11ah

Single Stream Pilots for 11ah

Authors:

Date: 2012-01-16

Hongyuan Zhang, et. Al.


Single stream pilots for 11ah

Authors continued:

Hongyuan Zhang, et al

Slide 2


Abstract

Abstract

This presentation proposes pilot waveform designs for 11ah.

Hongyuan Zhang, et. Al.


Preamble overview

In [1][2], we proposed preamble formats for 1MHz, and >=2MHz SU/MU.

In multi-stream cases, LTF1 and LTF2 are placed much further way, compared with 11n/11ac—due to (1) downclocking and (2) the “green-field type” preambles.

Example of 2SS:

Preamble Overview

2MHz SU:

STF

LTF1

SIG

LTF2

DATA

120us

2MHz MU:

STF

LTF1

SIGA

MU-STF

MU-LTF1

MU-LTF2

SIGB

DATA

40us

STF

LTF1

SIG

LTF2

DATA

1MHz SU:

(Assume 6-symb SIG)

280us

Hongyuan Zhang, et. Al.


Phase shift issues

  • 11n defines pilot tones per-stream, and HTLTF does not have specific pilot tones.

    • Receiver has to equalize multiple streams to track the pilots, during data portion.

  • 11ac uses single stream pilots in VHTLTFs, SIGB and Data.

    • Due to larger phase drift with up to 8 VHTLTFs

  • The LTF phase drift issue is exaggerated in 11ah:

    • Example: residue [email protected] (after the LTF1 fine CFO acquisition) still leads to a ~9o phase shift between LTF1 and LTF2 in 1MHz (assume 6 symbol SIG field).

    • Typical worst case residue ppm could be much larger than 0.1ppm (e.g. 0.5ppm).

    • Besides residue CFO, there is also phase noise that contributes to phase differences between LTFs.

    • Large phase shift between LTFs distorts the MIMO receiver—see equation below.

  • Therefore LTF phase tracking is then essential for multi-stream PPDUs in 11ah.

January 2012

Phase Shift Issues

Received two LTFs

Hongyuan Zhang, et. Al.


Simulation set1

  • 2x2, 2SS, MCS5, DNLOS.

  • 0.5ppm residue CFO, and 0.1ppm residue CFO, fc=900MHz

  • 2MHz, and 1MHz packets.

  • Legends:

    • “LTF2 and LTF1 1-symbol apart” mimics 2MHz MU.

    • “LTF2 and LTF1 3-symbol apart” mimics 2MHz SU.

    • “LTF2 and LTF1 7-symbol apart” mimics 1MHz SU.

  • By doing LTF tracking, we assume single stream pilot tones in LTFs mapped by the first column of P matrix.

Simulation Set1

Hongyuan Zhang, et. Al.


2mhz residue 0 5ppm

2MHz, Residue 0.5ppm

Hongyuan Zhang, et. Al.


2mhz residue 0 1ppm

2MHz, Residue 0.1ppm

Hongyuan Zhang, et. Al.


1mhz residue 0 1ppm

1MHz, Residue 0.1ppm

Hongyuan Zhang, et. Al.


Simulation set2

  • 1MHz SU, 2x2, 2SS, 6-symbol SIG field.

  • fc=900MHz , 40ppm raw CFO, estimate CFO by STF (coarse) and LTF1 (fine) in each packet.

    • Different from Sims set1, now we do actual CFO acquisitions at beginning of packet

  • By doing LTF tracking, we assume single stream pilot tones in LTFs mapped by the first column of P matrix.

Simulation Set2

Hongyuan Zhang, et. Al.


1mhz mcs6

1MHz, MCS6

Hongyuan Zhang, et. Al.


Residue cfo histogram at snr 40db 1000 samples

Residue CFO Histogram at SNR=40dB (1000 samples)

Worst case ~0.17 ppm

Hongyuan Zhang, et. Al.


Discussions

  • Significant performance hit with a small ppm such as 0.1ppm, especially for 1MHz.

  • Simulations did not cover some real case impairments that may further affect CFO estimations, e.g. timing error, oscillator drift, etc.

  • Average PER may not reflect the whole picture: once a device hits a bad channel (static) with large residue CFO, the MIMO traffic may not be able to work.

    • While for 11n GF, this issue was not as serious, except a 1~2dB performance hit. Because data portion still has pilots and the MIMO CE phase impact was much smaller.

  • Rather than betting on a super accurate CFO estimation on receiving each packet, introducing a single stream pilot turns out to be a trivial DSP add-on that rules out all these analog uncertainties.

    • 11ac receivers already implemented the same scheme.

Discussions

Hongyuan Zhang, et. Al.


Discussions cont d

  • To facilitate 1M/2M classification during LTF1 [1][2][3], suggest to use 1st column of P matrix to map the single stream pilot across the PPDU—no phase jump from adjacent data tones in LTF1.

    • Note that all data tones in LTF1 are also mapped using 1st column of P mat.

  • LTF sequence design should be based on the above proposed single stream pilot—e.g. to optimize PAPR, as well as get low cross-correlation between 1M and 2M LTF signs in the overlapping tones [3].

Discussions—Cont’d

Hongyuan Zhang, et. Al.


Straw poll single stream pilots

  • Do you agree that 11ah defines single stream pilots in the LTF, SIG and Data fields of SU packets, using the first column of P matrix for multi-stream mapping, as below?

    • For MU packets, the same single stream pilot is applied starting from MU-LTF1.

Straw Poll: Single Stream Pilots

The transmitted pilot tone signals, in the k-th tone and n-th OFDM symbol is expressed as:

Hongyuan Zhang, et. Al.


References

[1] 11-11-1482-00-00ah-preamble-format-for-1-MHz

[2] 11-11-1483-00-00ah-11ah-preamble-for-2MHz-and-beyond

[3] 11-12-0115-00-00ah-32FFT-STF-LTF-Sequences

References

Hongyuan Zhang, et. Al.


  • Login