Doc.: IEEE 802.22-07/0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 1 IEEE P802.22 Wireless RANs Date: 2006-12-14 Notice: This

doc.: IEEE 802.22-07/0002r0

Slide 1Submission

December 2006

Soo-Young Chang, Huawei Technologies

IEEE P802.22 Wireless RANs Date: 2006-12-14

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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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 Chair Carl 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 [email protected].

Name Company Address Phone email

Wai Ho Mow HKUST Hong Kong, China 852-2358-7070 [email protected]

Vincent K. N. Lau HKUST Hong Kong, China 852-2358-7066 [email protected]

Roger S. Cheng HKUST Hong Kong, China 852-2358-7072 [email protected]

Ross D. Murch HKUST Hong Kong, China 852-2358-7044 [email protected]

Khaled Ben Letaief HKUST Hong Kong, China 852-2358-7064 [email protected]

Linjun Lu Huawei Technologies Shenzhen, China 0086-755-28973119 [email protected]

Soo-Young Chang Huawei Technologies Davis, CA, U.S. 1-916 278 6568 [email protected]

Jianwei Zhang Huawei Technologies Shanghai, China 86-21-68644808 [email protected]

Lai Qian Huawei Technologies Shenzhen, China 86-755-28973118 [email protected]

Jianhuan Wen Huawei Technologies Shenzhen, China 86-755-28973121 [email protected]

Authors:

Modified CAZAC Sequences with Low PAPR as Preambles and Sounding Sequences

doc.: IEEE 802.22-07/0002r0

Slide 2Submission

December 2006


Name Company Address Phone email

Jianhua Sun HKUST Hong Kong, China 852-2358-7086 [email protected]

Edward K. S. Au HKUST Hong Kong, China 852-2358-7086 [email protected]

Zhou Wu Huawei Technologies Shenzhen, China 86-755-28979499 [email protected]

Jun Rong Huawei Technologies Shenzhen, China 86-755-28979499 [email protected]

Jian Jiao Huawei Technologies Beijing, China 86-10-82882751 [email protected]

Meiwei Jie Huawei Technologies Shenzhen, China 86-755-28972660 [email protected]

Co-Authors:

doc.: IEEE 802.22-07/0002r0

Slide 3Submission

December 2006


Background

• In Draft v0.1, frequency-domain sequences are proposed as channel sounding sequences (c.f. Section 8.10.5.4.4)

• 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 Runcom’s doc IEEE802.22-06/0223r0, though the effect of adjacent cell interference on preambles was not considered in Draft v0.1.

doc.: IEEE 802.22-07/0002r0

Slide 4Submission

December 2006


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*2n

• 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

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Slide 5Submission

December 2006


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 ObservationKey Observation: Similar sequences with low PAPR can be used for : Similar sequences with low PAPR can be used for preambles and sounding sequences. 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 802.22-07/0002r0

Slide 6Submission

December 2006


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 802.22-07/0002r0

Slide 7Submission

December 2006


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 Runcom’s ppt)

Modified CAZAC

(proposed)

Frame Short Preamble (Decimation factor=4)

8.62 dB 1.94dB

Frame Long Preamble

(Decimation factor = 2)10.78 dB 1.75 dB

Superframe Short Preamble (Deci. factor=4)

7.86 dB 1.85 dB

Superframe Long Preamble (Deci. factor=2)

9.42 dB 1.83 dB

doc.: IEEE 802.22-07/0002r0

Slide 8Submission

December 2006


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 802.22-07/0002r0

Slide 9Submission

December 2006


Modified CAZAC Sequence Set

0 20 40 60 80 1001.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8FFT Size = 2048, Decimation Factor = 4

sorted sequence index

PA

PR

(dB

)

Chu SetModified CAZAC Set

doc.: IEEE 802.22-07/0002r0

Slide 10Submission

December 2006


CDF of PAPR of Sequence #114 in the Modified CAZAC Set

-2 -1.5 -1 -0.5 0 0.5 1 1.5 20.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1FFT Size = 2048, Decimation Factor = 4

Pro

babili

ty

PAPR in dB

PAPR value

doc.: IEEE 802.22-07/0002r0

Slide 11Submission

December 2006


CDF of PAPRs of the 114 Sequences in the Modified CAZAC Set

1.9 1.95 2 2.05 2.1 2.15 2.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

PAPR (dB)

CD

F

FFT Size = 2048, Decimation Factor = 4

doc.: IEEE 802.22-07/0002r0

Slide 12Submission

December 2006


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.

Documents

Doc.: IEEE 802.22-07/0002r0 Submission December 2006 Soo-Young Chang, Huawei Technologies Slide 1 IEEE P802.22 Wireless RANs Date: 2006-12-14 Notice: This