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doc.: IEEE 802.22-07/0050r0 Submission January 2007 Monisha Ghosh, PhilipsSlide 1 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. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at firstname.lastname@example.org@iee.org >
doc.: IEEE 802.22-07/0050r0 Submission January 2007 Monisha Ghosh, PhilipsSlide 2 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.
doc.: IEEE 802.22-07/0050r0 Submission January 2007 Monisha Ghosh, PhilipsSlide 3 Method For Generating Binary Preambles. General preamble structure in the frequency domain: [0 p 1 … p L 0 … 0 p L+1 … p 2L ] Problem: Determine the sequences [p 1..p L ] and [p L+1 … p 2L ] 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 x 10 +x 8 +x 7 + x 5 +1, and initialize the shift-register with all zeros, to generate a sequence a(n). Cyclically shift sequence a(n) by shift S 1 and let [p 1..p L ] = first L values of shifted sequence. Cyclically shift sequence a(n) by shift S 2 and let [p L+1..p 2L ] = first L values of shifted sequence. Form the preamble sequence [0 p 1 … p L 0 … 0 p L+1 … p 2L ]. Take IFFT of oversampled preamble and evaluate PAPR. Repeat for all combination of S 1 and S 2. Pick the combination (S 1, S 2 ) that minimizes PAPR.
doc.: IEEE 802.22-07/0050r0 Submission January 2007 Monisha Ghosh, PhilipsSlide 4 Example Assume L = 840 (1680 data+pilot carriers). Superframe/frame short: training symbol on every 4 th frequency. –Length 256 M-sequence: x 8 + x 7 +x 3 + x 2 + 1. –S 1 = 226, S 2 = 109; PAPR = 4.4292 dB Frame long: training symbol on every 2 nd frequency. –Length 512 M-sequence: x 9 + x 8 + x 7 + x 6 +x 4 +x 2 + 1 –S 1 = 256 S 2 = 492; PAPR = 4.7396 dB Superframe long: training symbol on every frequency. –Length 1024 M-sequence: x 10 +x 8 +x 7 +x 5 +1 –S 1 = 296, S 2 = 808; PAPR = 4.9868 dB If multiple preambles are required choose another generator, or another combination of (S 1,S 2 ).
doc.: IEEE 802.22-07/0050r0 Submission January 2007 Monisha Ghosh, PhilipsSlide 5 PAPR Of Random QPSK Data PAPR < 5 dB for the preamble sequences will be adequate.
doc.: IEEE 802.22-07/0050r0 Submission January 2007 Monisha Ghosh, PhilipsSlide 6 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.
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