doc.: IEEE 802.22-07/0002r0
December 2006
Modified CAZAC Sequences with Low PAPR as
Preambles and Sounding Sequences
IEEE P802.22 Wireless RANs
Date: 2006-12-14
Authors:
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]
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Submission
Slide 1
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
December 2006
Co-Authors:
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]
Submission
Slide 2
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
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.
Submission
Slide 3
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
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
Submission
Slide 4
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
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 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.
Submission
Slide 5
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
December 2006
Choice & Modification of CAZAC Seq.
• In general, CAZAC sequence candidates with potentially better PAPR and crosscorrelation 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.
Submission
Slide 6
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
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
Submission
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
Slide 7
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
December 2006
Modified CAZAC Sequence Sets with Low CrossCorrelation Energy as Preambles and Sounding Sequences
•
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.
Submission
Slide 8
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
December 2006
Modified CAZAC Sequence Set
FFT Size = 2048, Decimation Factor = 4
3.8
Chu Set
Modified CAZAC Set
3.6
3.4
PAPR (dB)
3.2
3
2.8
2.6
2.4
2.2
2
1.8
0
20
60
40
80
100
sorted sequence index
Submission
Slide 9
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
December 2006
CDF of PAPR of Sequence #114 in the Modified CAZAC Set
FFT Size = 2048, Decimation Factor = 4
1
0.9
PAPR value
0.8
Probability
0.7
0.6
0.5
0.4
0.3
0.2
0.1
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
PAPR in dB
Submission
Slide 10
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
December 2006
CDF of PAPRs of the 114 Sequences in the Modified CAZAC Set
FFT Size = 2048, Decimation Factor = 4
1
0.9
0.8
0.7
CDF
0.6
0.5
0.4
0.3
0.2
0.1
0
1.9
1.95
2
2.05
2.1
2.15
2.2
PAPR (dB)
Submission
Slide 11
Soo-Young Chang, Huawei Technologies
doc.: IEEE 802.22-07/0002r0
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.
Submission
Slide 12
Soo-Young Chang, Huawei Technologies