preamble and cell search design for 802.16m system ieee 802.16 presentation submission template...
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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: [email protected]
Venue: IEEE 802.16 Session #55, Macao, ChinaBase Contribution:
IEEE C802.16m-08/470Purpose:
For discussion and approval by IEEE 802.16 Working GroupNotice:
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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