doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 1 IEEE P Wireless RANs Date: Notice: This document has been prepared to assist IEEE 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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 Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at Authors: Modified CAZAC Sequences with Low PAPR as Preambles and Sounding Sequences
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 3 Background In Draft v0.1, frequency-domain sequences are proposed as channel sounding sequences (c.f. Section ) Design Requirements –Constant Amplitude Binary and polyphase sequences have been proposed –Low Peak-to-Average Power Ratio (PAPR) Reduce the backoff of the power amplifier –Low energy of the time-domain cross-correlation function for any two sequences in the set Reduce adjacent cell interference power Essentially the same requirements are suggested for preambles (Section 8.3) in Runcoms doc IEEE /0223r0, though the effect of adjacent cell interference on preambles was not considered in Draft v0.1.
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 4 Background Preambles in Draft v0.1 –Binary PN Sequences Only one sequence for one preamble of a type Rather high PAPR ( > 7.8dB for 2K FFT) Sounding Sequences in Current Draft –Binary Golay Sequences Length is restricted to the form of m*2 n After truncation, PAPR > 4.5 dB for 2K FFT mode with null subcarriers [L=160, DC, R=159] –Generalized Chirp Like (GCL) Sequence Sets A specific class of Constant Amplitude Zero Auto-Correlation (CAZAC) sequences Actually, only Chu sequence sets are used
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 5 Background –Generalized Chirp Like (GCL) Sequence Sets (cont.) Sets of Chu sequences of prime length are minimally truncated or extended to the required lengths Low PAPR (< 4 dB for 2K FFT mode, null subcarriers [L=160, DC, R=159] and set size (or #cells) = 114) Optimal peak cross-correlation level (but sub-optimal after truncation) Key Observation: Similar sequences with low PAPR can be used for preambles and sounding sequences.Key Observation: Similar sequences with low PAPR can be used for preambles and sounding sequences. In this proposal, we modify the CAZAC sequences to obtain individual and sets of sequences with very low PAPR for use as preambles and sounding sequences.
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 6 Choice & Modification of CAZAC Seq. In general, CAZAC sequence candidates with potentially better PAPR and cross- correlation properties can be chosen from the unified Perfect Root of Unity Sequence (PRUS) construction, which includes all known constructions of CAZAC sequences consisting of roots of unity (including the GCL sequences). Novel modification techniques are applied to selected CAZAC sequences to minimize their PAPR values Results are presented for the representative setting: –2K FFT mode, null subcarriers [L=160, DC, R=159] & 114 cells –Decimation separability mode (decimation factor = 4) is considered Here, all PAPR values are estimated for continuous-time waveforms using an oversampling factor of 4. Without oversampling, the computed PAPR values may be over-optimistic.
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 7 Modified CAZAC Sequences as Preambles The following table lists the PAPR values of the proposed modified CAZAC sequences, and the existing PN preambles in draft v0.1 When adjacent cell interference is not a concern, these individual (i.e. not a set) sequences can be used to replace preambles in the current draft with PAPR gain at least 6dB FFT Size = 2048 Null subcarriers [L=160, DC, R=159] Existing PN preambles (in draft 0.1, values from Runcoms ppt) Modified CAZAC (proposed) Frame Short Preamble (Decimation factor=4) 8.62 dB1.94dB Frame Long Preamble (Decimation factor = 2) dB1.75 dB Superframe Short Preamble (Deci. factor=4) 7.86 dB1.85 dB Superframe Long Preamble (Deci. factor=2) 9.42 dB1.83 dB
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 8 Modified CAZAC Sequence Sets with Low Cross- Correlation Energy as Preambles and Sounding Sequences When adjacent cell interference is a concern,When adjacent cell interference is a concern, we propose a set of modified CAZAC sequences with low PAPR and low cross-correlation levels as preambles and sounding sequences. Replacing Chu (or GCL) sounding sequences in current draft by sets of modified CAZAC sequences derived from the unified PRUS construction can lead to 0.4dB ~ 1.7dB gain depending on which sequence in the set. The peak (i.e. worst case) time-domain cross-correlation levels resulted are far from optimal. But the average energy of the time-domain cross-correlation functions is the same as that of the Chu set, leading to same adjacent cell interference power.
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 9 Modified CAZAC Sequence Set
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 10 CDF of PAPR of Sequence #114 in the Modified CAZAC Set PAPR value
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 11 CDF of PAPRs of the 114 Sequences in the Modified CAZAC Set
doc.: IEEE /0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 12 Summary We propose the use of modified CAZAC sequences as preambles and sounding sequences. 1.Modified individual CAZAC sequences can attain very low PAPR (<2dB for 2K FFT) 2.Sets of modified CAZAC sequences can attain very low PAPR (<2.2dB for 2K FFT & for all 114 cells), while having the same time-domain cross-correlation energy as that of the Chu set –These results are obtained at minor additional cost since the channel estimator/detector is similar to that for Chu (GCL) sequences described in the current draft.