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IEEE 802.16m Synchronization Channel

IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number:

IEEE C802.16m-08/823r3Date Submitted:

2008-07-09Source:

Sungho Moon, Seunghee Han, Jin Sam Kwak, Young-Hyoun Kwon Voice: +82-31-450-1935 e-mail : {msungho; dondai; samji; wishwill}@lge.com

LG Electronics LG R&D Complex, 533 Hogye-1dong, Dongan-gu, Anyang, 431-749, Korea

Venue:Call for Comments on 16m Preamble Related Documents C80216m-08/634 and C8016m-08/636

Purpose:For discussion in TGm (Preamble Rapporteur Group)

Notice:This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who 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 802.16.

Patent Policy:The contributor is familiar with the IEEE-SA Patent Policy and Procedures:

<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>.Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.

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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

Hierarchy and Signal Forms

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

Signal FormsDetection algorithm

Repeated Signal Non-Repeated Signal

Auto-correlation based algorithm

Well-Matched N/A

Cross-correlation based algorithm

Not recommended due to ambiguous peaks &

complexityWell-Matched

Signal FormsHierarchy

Repeated Signal Non-Repeated Signal

Hierarchical (two symbols)

Matched Well-Matched

Non-Hierarchical (one symbol)

Well-MatchedNot recommended due to

complexity

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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 cell-edge) For Example,

Super-Frame, 20 ms

Tx. Ant 0

Tx. Ant Ntx-1

a -aCP

...

a' -a'CP

Circu

lar S

hift

1 OFDM Symbol

A -ACP

IFFT / FFT

Time Frequency

-1 1 3 5

... ...

-3-5

5 MHz

f

... ...

5 MHz

f

From Other Sectors

5 ms

-1 1 3 5-3-5

Sector/Cell-Common Allocation

...

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Hierarchical Structures

Definition More than one type of SCH symbols exist within a super-frame. This 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 can be used as a phase reference for S-SCH detection.

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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 in Timing Detection 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

Cross-correlation 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

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

Performance Double energy should be required for the same performance as

non-hierarchical one. With coherent detections of S-SCH using P-SCH, the

performance will be degraded due to Frequency offsets in practical environments Composite channel from adjacent cells at cell edge

The only benefit of coherent detection will disappear.

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Reuse of 16e Preamble in Hierarchical Structures 16e preamble can be used for hierarchical

structures: When P-SCH reuses 16e preamble,

Ambiguity problem in the cell edge When P-SCH has a non-repeated signal form (H structure

1) Cross-correlation based detection (complexity)

When P-SCH has a repeated signal form (H structure 2) Need two symbols in the Greenfield mode = double energy

compared to the non-hierarchical structure

No need to reuse 16e preamble for any combinations

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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

Multiplexing of Data Channel with SCH Separate processing for multiplexing will be required (e.g. 2

times of 256FFT for SCH and a single 512FFT for data in the 5MHz)

A number of guard subcarriers will be required due to orthogonality destruction.

Performance Degradation in 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 performance degradation to the previous Hierarchical 1 and 2 structures

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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" throughout 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.