January 2007

Monisha Ghosh, Philips

Slide 1

doc.: IEEE 802.22-07/0050r0

Submission

Low PAPR Binary Preamble Design

IEEE P802.22 Wireless RANs Date: 2007-01-17

Authors:

Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

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Name Company Address Phone email Monisha Ghosh Philips USA 914-945-6415 Monisha.Ghosh@philips.com

January 2007

Monisha Ghosh, Philips

Slide 2

doc.: IEEE 802.22-07/0050r0

Submission

Advantage Of Binary Preambles

• Binary preambles enable very simple channel estimation, with no multiplications required.– Significant complexity advantage for large FFT sizes, e.g 2K-FFT

systems.

• Storage requirements are minimal: 1 bit per preamble symbol.

• Generating the preambles with shift-registers eliminates the need for any storage of multiple sequences.

January 2007

Monisha Ghosh, Philips

Slide 3

doc.: IEEE 802.22-07/0050r0

Submission

Method For Generating Binary Preambles.

• General preamble structure in the frequency domain: • [0 p1 … pL 0 … 0 pL+1 … p2L]• Problem: Determine the sequences [p1..pL] and [pL+1 … p2L] to minimize

PAPR of 4-times oversampled signal in the time domain.• Let N = smallest power of 2 > L. For example, if L = 840, choose N = 1024.• Pick a maximal length sequence of length N. For example, for N = 1024,

choose x10 +x8 +x7 + x5 +1, and initialize the shift-register with all zeros, to generate a sequence a(n).

• Cyclically shift sequence a(n) by shift S1 and let [p1..pL] = first L values of shifted sequence.

• Cyclically shift sequence a(n) by shift S2 and let [pL+1..p2L] = first L values of shifted sequence.

• Form the preamble sequence [0 p1 … pL 0 … 0 pL+1 … p2L].• Take IFFT of oversampled preamble and evaluate PAPR.• Repeat for all combination of S1 and S2.• Pick the combination (S1, S2) that minimizes PAPR.

January 2007

Monisha Ghosh, Philips

Slide 4

doc.: IEEE 802.22-07/0050r0

Submission

Example

• Assume L = 840 (1680 data+pilot carriers).• Superframe/frame short: training symbol on every 4th frequency.

– Length 256 M-sequence: x8 + x7 +x3 + x2 + 1.– S1 = 226, S2 = 109; PAPR = 4.4292 dB

• Frame long: training symbol on every 2nd frequency.– Length 512 M-sequence: x9 + x8 + x7 + x6 +x4 +x2 + 1– S1 = 256 S2 = 492; PAPR = 4.7396 dB

• Superframe long: training symbol on every frequency.– Length 1024 M-sequence: x10 +x8 +x7 +x5 +1– S1 = 296, S2 = 808; PAPR = 4.9868 dB

• If multiple preambles are required choose another generator, or another combination of (S1,S2).

January 2007

Monisha Ghosh, Philips

Slide 5

doc.: IEEE 802.22-07/0050r0

Submission

PAPR Of Random QPSK Data

PAPR < 5 dB for the preamble sequences will be adequate.

January 2007

Monisha Ghosh, Philips

Slide 6

doc.: IEEE 802.22-07/0050r0

Submission

Conclusions

• Binary preambles for various decimation factors can be easily generated with low PAPR.

• Method presented leads to a very simple specification (generator + shifts) of sequences.