Slides S802.16m-08/470r1
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Transcript Slides S802.16m-08/470r1
Preamble and Cell Search Design for 802.16m System
IEEE 802.16 Presentation Submission Template (Rev. 9)
Document Number:
IEEE S802.16m-08/470r1
Date Submitted:
2008-05-05
Source:
Mingyang Sun, Yunsong Yang, Xueqin Gu, Chongli Liu, Xin Chang
Huawei
Venue:
IEEE 802.16 Session #55, Macao, China
Base Contribution:
IEEE C802.16m-08/470
Purpose:
For discussion and approval by IEEE 802.16 Working Group
Notice:
E-mail: [email protected]
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Outline
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Requirements for Cell Search
Proposed preamble features
Structure of the super-frame header
Synchronization Sequences Design
Simulation Results
Requirements for Cell Search
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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
16e zone
16m zone
P-SCH
P-BCH
16e preamble
DL data
S-SCH
S-BCH
FCH &MAP
UL data
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 PSCH and S-SCH
– Enable CP Identification
– After decoding P-SCH and S-SCH, P-BCH is decoded
and CP length information is acquired
... ...
P-BCH
P-SCH
S-SCH
normal CP length fixed CP length
... ...
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 subcarriers.
P-SCH Senquence
Generator
Subcarrier
Mapping
DFT
IFFT
TDM
S-SCH Senquence
Generator
Scrambler
DFT
Subcarrier
Mapping
IFFT
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:
k
P k exp j 4
N
G
The S-SCH sequences are defined:
k
Su k exp j 2u
NG
k 0, , NG 1
u 3,..., N G 1
NG is desired sequence length
The integer “u” is referred to as class index
– A different “u” will also act as a cell ID
k 0,..., NG 1
SCH sequence sub-carrier mapping
• 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/2
N/2
DC subcarrier
Scramble for SCH and BCH
•
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.
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:
uˆ NG nmax
The identified u is the integer closest to û calculated by the above
formula;
System Acquisition Procedure
Cell Search Procedure
Stage 1
Decode P-SCH
FFT Timing &Fractional
freq. offset
auto correlation in time
domain
PASS
Stage 2
Integer freq. offset
Correlation with PSC in
frequency domain
PASS
Stage 3
Fine Timing
Correlation with PSC in
time domain
PASS
Stage 4
Decode S-SCH
Acquire Cell ID
PASS
Decode P-BCH
detection with SSC in
frequency 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
PAPR
-12
6
Their PAPRs of all 417
sequences are almost 0dB,
i.e. almost constant
amplitude.
new sequence
5
4
PAPR(dB)
Noted the sequence index is
the number of sequences.
x 10
3
2
1
0
0
50
100
150
200
250
sequence index
300
350
400
450
Coarse Search with proposed sequence
VA30
30
coarse search
Samples error
25
20
15
10
5
0
1
2
3
4
5
SNR
6
7
8
9
10
Decimal FO Estimation with proposed sequence
VA30
0.014
decimal FO
0.012
frequency offset
0.01
0.008
0.006
0.004
0.002
0
0
1
2
3
4
5
SNR
6
7
8
9
10
frequency offset≤2% of the sub-carrier spacing at 0 dB in the case of no power boost
Integer FO Estimation with proposed sequence
VA30
0.03
integer FO
FO estimation error rate
0.025
0.02
0.015
0.01
0.005
0
0
1
2
3
4
5
SNR
6
7
8
9
10
Fine Search with proposed sequence
VA30
18
fine search
16
Samples offset
14
12
10
8
6
4
2
0
1
2
3
4
5
SNR
6
7
8
9
10
VA30, SNR=-2dB, proposed sequences cell detection
performance (200 Monte-Carlo simulation)
Cell Identification
1
0.9
0.8
Normalized Power/dB
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Sequence Elenment Index
One FFT can separate multiple cells ID
120
140
PB3, SNR=-2dB, proposed sequences cell detection
performance (200 Monte-Carlo simulation)
Cell Identification
1
0.9
0.8
Normalized Power/dB
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
Sequence Elenment Index
120
140
False alarm probability
VA30 channel (1024 FFT Size)
0.04
0.035
False Alarm Probability
0.03
0.025
0.02
0.015
0.01
0.005
-4
-3
-2
-1
0
SNR/dB
1
2
3
4