Doc.: IEEE 802.22-07/0050r0 Submission January 2007 Monisha Ghosh, PhilipsSlide 1 Low PAPR Binary...

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:

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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.