Preamble and Cell Search Design for 802.16m System

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

IEEE S802.16m-08/470r1Date Submitted: 2008-05-05Source:

Mingyang Sun, Yunsong Yang, Xueqin Gu, Chongli Liu, Xin Chang E-mail: xin.chang@huawei.comHuawei

Venue: IEEE 802.16 Session #55, Macao, ChinaBase Contribution:

IEEE C802.16m-08/470Purpose:

For discussion and approval by IEEE 802.16 Working GroupNotice:

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 >.

Outline

• Requirements for Cell Search

• Proposed preamble features

• Structure of the super-frame header• Synchronization Sequences Design• Simulation Results

Requirements for Cell Search

• Fast system access, support fast cell select and reselect;• Good cell detection performance;• Low overhead;• Low complexity;• Support large cell average;• Large cell ID set to support femto cell and Relay station;• Support multi-bandwidth;• Support CP detection;• Low PAPR;• Support multi-carrier fast handover;• Assistant channel measure;• Assistant channel estimation;• Support MIMO;

Why do we need new preamble?

• System access latency– 16e preamble can not support fast system access

• System access latency: 300ms• B3G system desired value: 20-80ms and below

• Cell coverage– 16e preamble PAPR is not enough low

• 3.65~4.36dB– 16e preamble cross-correlation is not enough good– Sector specific 16e preamble sequence limit cell edge MS system access

performance• In cell edge the property of repetition of 3 is destroyed

• MS capability support– 16e preamble can not support different capability MS access

• pure 16m system support• MIMO support

Proposed preamble features

• Low PAPR sequence and larger cell coverage– PAPR is almost 0 dB– Good cross correlation

• Large cell ID set than 16e to support femto cell and Relay station• 16e: 114 • Proposed scheme: 417

• Low cell search time and complexity– 300ms->20ms– Simple cell detection algorithm and one FFT operation can detect multiple cell

IDs– Proposed sequence provide better cell detection performance– Same OFDM waveform on P-SCH in all cells– Coarse time synchronization in time domain– Hierarchical SCH structure

• P-SCH and S-SCH

16m super frame header location

P-SCH

S-SCH

P-BCH

S-BCH

16e preambl e

FCH &MAP

DL data

UL data

16e zone 16m zone

16m super frame header location

• The super frame header is transmitted one or more times every 20 ms super frame– The transmission period of SCH and BCH may be different

• Different level of error protection

– preamble is placed in DL last sub frame• The interval between 16m preamble and 16e preamble is fixed

• The SCH and BCH is transmitted only in the central part of the overall transmission band of the cell– Enable bandwidth Identification– Enable multi-bandwidth MS access

• Fixed CP length on P-SCH and S-SCH and specific preamble structure– Enable CP Identification

Multiplexing of SCH and BCH

• The multiplexing of P-SCH and S-SCH is TDM– The design provides enough power to guarantee cell search

performance

• The multiplexing of SCH and BCH is TDM • The multiplexing of P-BCH and S-BCH is TDM

– If the system bandwidth is big enough, the retaining bandwidth may carry other data or control channel

Purposes of the 16m preamble

• P-SCH– Same OFDM waveform in all cells– Used for SCH symbol timing and frequency acquisition

• S-SCH– Cell specific OFDM waveform – Used for determining the cell ID

• P-BCH– network-wide common and Static system parameter and information to

decode S-BCH– CP length, DL/UL FFT size, S-BCH frequency reuse indication, S-

BCH location, S-BCH hopping seed, antenna configuration information• S-BCH

– Cell specific system parameter

CP Identification

• CP length is fixed for the OFDM symbols carried P-SCH and S-SCH– Enable CP Identification

– After decoding P-SCH and S-SCH, P-BCH is decoded and CP length information is acquired

S-SCHP-SCHP-BCH

fi xed CP l engthnormal CP l ength

. . . . . . . . . . . .

Transmit diversity for SCH and BCH transmission

• P-SCH and S-SCH– the CSD transmission interval is same as the CP length

• P-BCH

• Default: STBC/SFBC/Co-STBC/Co-SFBC (Matrix A)

• Optional: CDD 、 PSD 、 TSTD 、 FSTD

• S-BCH• Default: STBC/SFBC/Co-STBC/Co-SFBC (Matrix A)

• Optional: CDD 、 PSD 、 TSTD 、 FSTD

Synchronization Sequences Design

Preamble Transmission Structure

• After P-SCH sequences and S-SCH sequences are generated, P-SCH and S-SCH sequences firstly are processed with DFT operation and then are mapped on sub-carriers.

TDM

P-SCH SenquenceGenerator

S-SCH SenquenceGenerator

Subcarri erMappi ng

Subcarri erMappi ngDFT

I FFT

I FFTScrambl er

DFT

Non-CAZAC SCH sequence

• The proposed synchronization sequences are based on a particular sequences

• The proposed sequences have very low PAPR (lower than the PN sequence based 16e preambles) and better cross correlation in frequency domain between any pair of the sequences

• Specific and simple cell detection algorithm to provide better cell detection performance

Sequence definition

The P-SCH sequence is defined:

The S-SCH sequences are defined:

NG is desired sequence length The integer “u” is referred to as class index

– A different “u” will also act as a cell ID

exp 4 0, , 1GG

kP k j k N

N

1,...,0 1,...,3 2exp

GG

Gu NkNu

N

kujkS

• The P-SCH and S-SCH are transmitted only on the central part of the overall transmission band of the cell

• Because sequence inherent characteristic, SCH time domain sequence is composed of two repeated sequences though SCH is transmitted on continuous subcarriers

• Better performance because longer sequence

• Larger cell ID set

• Low cell search time

• Coarse time synchronization in time domain

CP N/ 2N/ 2

DC subcarri er

SCH sequence sub-carrier mapping

• S-SCH

– Scrambled by 2 bits LSBs of frame index and P-SCH sequence

• Determine the superframe boundary

• Determine the frame in which P-BCH is carried in despite of transmission period of SCH and BCH

• P-BCH carries all the bits of system time

• These two bits can also be used to seed PHY algorithms like hopping/scrambling etc

• P-BCH

– P-BCH is scrambled by SFN ID

• S-BCH

– Scrambled by Cell ID

• P-SCH

– when only P-SCH is present, P-SCH is scrambled by 2 bits LSBs of frame index.

Scramble for SCH and BCH

Fast cell search process

Obtain time and frequency synchronization;

Take N-point FFT to the receives data to get the frequency domain data

at NG sub-carriers; denote the NG frequency data with Y(m), m=1,…,

NG;

The peak position nmax of Y(m) gives information about u:

The identified u is the integer closest to calculated by the above formula;

maxˆ nNu G u

System Acquisition Procedure

Decode P-SCHFFT Timing &Fractional

freq. offset

Integer freq. offset

Fine Timing

Decode S-SCHAcquire Cell ID

Decode P- BCH

Cell Search Procedure

PASS

PASS

PASS

PASS

Stage 1

Stage 2

Stage 3

Stage 4

auto correlation in timedomain

Correlation with PSC infrequency domain

detection with SSC infrequency domain

Correlation with PSC intime domain

Simulation Assumptions

• This section provides several simulations to illustrate the performance of the proposed synchronization sequences. The simulation parameters are set as in Table 1.

Carrier frequency 2.5GHz

Sub-carrier spacing 10.94kHz

Channel model PB3, VA30

System bandwidth 10MHz

P-SCH bandwidth 5MHz (420 sub-carriers)

S-SCH bandwidth 5MHz (420 sub-carriers)

Power boost no

CP length 128

Cell ID number 417

0 50 100 150 200 250 300 350 400 4500

1

2

3

4

5

6x 10

-12

sequence index

PA

PR

(dB

)

new sequenceTheir PAPRs of all 417 sequences are almost 0dB, i.e. almost constant amplitude.

Noted the sequence index is the number of sequences.

PAPR

0 1 2 3 4 5 6 7 8 9 105

10

15

20

25

30VA30

SNR

Sam

ples

err

or

coarse search

Coarse Search with proposed sequence

0 1 2 3 4 5 6 7 8 9 100

0.002

0.004

0.006

0.008

0.01

0.012

0.014

SNR

VA30

freq

uenc

y of

fset

decimal FO

frequency offset≤2% of the sub-carrier spacing at 0 dB in the case of no power

boost

Decimal FO Estimation with proposed sequence

0 1 2 3 4 5 6 7 8 9 100

0.005

0.01

0.015

0.02

0.025

0.03

SNR

VA30

FO

est

imat

ion

erro

r ra

te

integer FO

Integer FO Estimation with proposed sequence

0 1 2 3 4 5 6 7 8 9 102

4

6

8

10

12

14

16

18

SNR

VA30

Sam

ples

off

set

fine search

Fine Search with proposed sequence

0 20 40 60 80 100 120 1400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Cell Identification

Sequence Elenment Index

Nor

mal

ized

Pow

er/d

B

One FFT can separate multiple cells ID

VA30, SNR=-2dB, proposed sequences cell detection performance (200 Monte-Carlo simulation)

0 20 40 60 80 100 120 1400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Cell Identification

Sequence Elenment Index

Nor

mal

ized

Pow

er/d

B

PB3, SNR=-2dB, proposed sequences cell detection performance (200 Monte-Carlo simulation)

-4 -3 -2 -1 0 1 2 3 40.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

SNR/dB

Fal

se A

larm

Pro

babi

lityVA30 channel (1024 FFT Size)

False alarm probability