IEEE 802.16m Synchronization Channel
IEEE 802.16 Presentation Submission Template (Rev. 9)
Document Number:
IEEE C802.16m-08/823r2
Date Submitted:
2008-07-09
Source:
Sungho Moon, Seunghee Han, Jin Sam Kwak
e-mail : {msungho; dondai; samji}@lge.com
Voice: +82-31-450-1935
LG Electronics
LG R&D Complex, 533 Hogye-1dong, Dongan-gu, Anyang, 431-749, Korea
Venue:
Call for Comments on 16m Preamble Related Document C80216m-08/634 and C8016m-08/636
Purpose:
For discussion in TGm (Preamble Rapporteur Group)
Notice:
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IEEE 802.16m Synchronization Channel
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Contents
 Synchronization Channel (SCH) Functionalities
 General Terms and Relationships
 Non-Hierarchical vs. Hierarchical
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SCH Functionality
 Synchronization
 Timing synchronization
 Symbol, frame, and super-frame
 Carrier frequency and frequency offset
 Cell Identification and Additional Information
 Cell or sector ID distinction
 Essential information for BCH decoding should be detected during cell search
 CP information
 # of transmit antennas for BCH
 Etc.
 Channel Estimation
 Allow estimation of channels for multiple transmit antennas
 Measurement Functions
 RSSI measurement
 Noise power estimation
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General Terms and Relationships
 Symbol Timing Detection Algorithms and Signal Forms
Signal Forms
Repeated Signal
Non-Repeated Signal
Auto-correlation based algorithm
Well-Matched
N/A
Cross-correlation based algorithm
Not recommended due to
ambiguous peaks
Well-Matched
Detection algorithm
 Hierarchy and Signal Forms
Signal Forms
Repeated Signal
Non-Repeated Signal
Hierarchical
(two symbols)
Matched
Well-Matched
Non-Hierarchical
(one symbols)
Well-Matched
Not recommended due to
complexity
Hierarchy
 Possible Structures



NH structure: (Non-Hierarchical, Repeated signal form, Auto-correlation based algorithm)
H structure 1 : (Hierarchical, Non-repeated signal form, Cross-correlation based algorithm)
H structure 2 : (Hierarchical, Repeated signal form for P-SCH, Auto-correlation based algorithm)
 Hybrid Type

Hierarchical with one symbol
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Non-Hierarchical Structure
 Definition
 Only a single type of 16m synchronization symbol which may be in addition to the
legacy 16e preamble
 No needs of 16e preamble as part of the SCH functionality
 Main Features




One OFDM symbol through multiple antennas (CDD, FSTD, or TSTD)
Every other subcarrier : Null  2x repeated signal in time
Auto-correlation based detection algorithm
Sector/cell-common allocation (due to maintain the 2x repeated signal in the celledge)
Super-Frame, 20 ms
 For Example,
5 ms
IFFT / FFT
Time
1 OFDM Symbol
CP
Tx. Ant 0
a
Frequency
5 MHz
-a
CP
...
A
-A
...
f
...
...
Circular
Shift
-5 -3 -1 1 3 5
Sector/Cell-Common
Allocation
From Other Sectors
CP
Tx. Ant Ntx-1
a'
...
-a'
...
-5 -3 -1 1 3 5
5 MHz
6
f
Hierarchical Structures
 Definition
 More than one type of SCH symbols exist within a super-frame.
 The may or may not use the legacy 16e preamble as one level of hierarchy.
 Main Features
 The P-SCH can be used for initial acquisition.
 Hierarchical structure 1 : Cross-correlation based detection algorithm
 Hierarchical structure 2 : Auto-correlation based detection algorithm
 The S-SCH can be used for fine synchronization, cell/sector identification
(ID), and channel measurements.
 The P-SCH may be used as a phase reference for S-SCH detection.
 16e preamble can be used for P-SCH or S-SCH.
 When P-SCH has a repeated signal form
- Need two symbols = doubled energy compared to the non-hierarchical structure
 When P-SCH has a non-repeated signal form
- Cross-correlation based detection (complexity)
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Problem of Hierarchical Structure 1
 Overhead
 Additional resource (secondary sync. channel) compared to the non-hierarchical
structure
 # of symbols for SCH (16e + 16m) in a super-frame
-
Total 8 symbols in the legacy-disabled mode
Total 12 symbols in the legacy-support mode without reusing of 16e preamble
 Complexity
 Cross-correlation based algorithm
 Sharpen peak in the condition of very small frequency offsets
 Require separate step only for updating correlation metric every sample
 Comparisons (# of multiplications and additions) [1]
 Replica-based detection (cross-correlation based)
 Auto-correlation based detection
 50,000 samples during a radio frame
M-part replica-based
Auto-correlation based
Ratio
# of complex multiplications
51,200,000
100,512
509 times
# of complex additions
51,150,000
100,511
509 times
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Problem of Hierarchical Structure 2
 Overhead
 Additional resource (secondary sync. channel) compared to the nonhierarchical structure
 # of symbols for SCH (16e + 16m) in a super-frame
 Total 8 symbols in the legacy-disabled mode
 Total 12 symbols in the legacy-support mode without reusing of 16e preamble
 Complexity
 The same as non-hierarchical one for coarse timing acquisition
 Performance
 Double energy should be required for the same performance as nonhierarchical one.
 With coherent detections of S-SCH using P-SCH, the performance will be
degraded due to the composite channel from adjacent cells at cell edge. 
The only benefit of coherent detection will disappear.
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Problem of Hybrid Structure
 Complexity
 With non-repeated P-SCH (cross-correlation based algorithm)
 Require separate steps only for updating correlation metrics every sample  large
complexity
 Three multiplexing may be possible; TDM, FDM, and CDM
 For TDM,
- In case that data channel is multiplexed with SCH,
» Twice transmission will be required (eg. 2*<256FFT+1*CP; for
SCH>+1*<512FFT+2*CP; for Data>)
» A number of guard subcarriers will be required due to orthogonality destruction.
 For FDM,
- Worse PAPR, short sequence
 For CDM,
- Worse PAPR, inter-code interference
 Performance of Time/Frequency Sync and Cell ID Detection
 The sequence length will become half in a given amount of information.  it
will result in an increase of detection error rate and false alarm rate.
 Similar problems to the previous Hierarchical 1 and 2 structure can be found.
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Text Proposal for IEEE802.16m SDD
============ Start of text proposal for C80216m-08/634 ==============
[Remove all options and sentences related to "hierarchical structure" though
the document, and adopt option 1 in Section 11.x.2.1.2.1.1.]
=================== End of text proposal ======================
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References
[1] IEEE80216m-08/478r3, Design on the Synchronization Channel for
IEEE802.16m.
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