qi wang july 3rd, 2008 389.075 mobile communication seminar
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Synchronization Aspects in LTEQi WangJuly 3rd, 2008
389.075 Mobile Communication Seminar
Outline
LTE PHY Synchronization in OFDMFrom WiMAX to LTE
Synchronization in WiMAXLTE Frame Structure
Conclusion
2
LTE Physical LayerNew Features to Cellular Application
Orthogonal Frequency Division Multiplexing (OFDM)
Multiple Input Multiple Output (MIMO)OFDMA on downlinkSC-FDMA on uplinkFrequency domain scheduling
3
LTE Physical Layer
4
slot
Outline
LTE PHY Synchronization in OFDMFrom WiMAX to LTE
Synchronization in WiMAXLTE Frame Structure
Conclusion
5
Carrier Frequency Error in OFDM
6
Received signal:Nnjenr /2 CFO)( )(nr
CFO : Carrier Frequency Offset normalized in subcarrier spacing
N: FFT size
e.g. subcarrier spacing = 15kHz, 10ppm.Osc at 2.5GHz,
667.115/25ˆCFO kHzkHz
CFO
Fractional Frequency Offset (~0.665) + Integer Frequency Offset (1) + Residual Frequency Offset (~0.002)
FFOIFORFO
Carrier Frequency Offset (~1.667)
OFDM Synchronization
7
1. Frame Start Detection
Frequency Offset
Correction
2.Fractional Frequency Offset Estimation
3.Integer Frequency Offset Estimation
4. Residual Frequency Offset Tracking
Remove CP
FFT
Outline
LTE PHY Synchronization in OFDMFrom WiMAX to LTE
Synchronization in WiMAXLTE Frame Structure
Conclusion
8
9
WiMAX Frame Structure1st Preamble:frame start detection, fractional frequency offset estimation
0
13
255
freq
uenc
y
time
000
0
0
0
0
0 0
0 00
0 000
0
0
0
0
8 pilots on subcarriers {13 38 63 88 114 139 164 189}:Residual frequency offset tracking
2nd Preamble:Integer frequency offset estimation
1. Frame Detection
10
1. Frame Start Detection
Frequency Offset
Correction
2.Fractional Frequency Offset Estimation
3.Integer Frequency Offset Estimation
4. Residual Frequency Offset Tracking
Remove CP
FFT
preamble
preamble
pilot tones
1. Frame Detection
11
264
0
264
0
64
0
*
gg
g
|)192(||)(|
)192()()(
N
k
N
k
N
k
knrknr
knrknrnM
CP 64 64 64 64
1st Preamble in time domain:
NgN
|)(| nM
Estimated Frame Start
2. Fractional Frequency Offset
12
1. Frame Start Detection
Frequency Offset
Correction
2.Fractional Frequency Offset Estimation
3.Integer Frequency Offset Estimation
4. Residual Frequency Offset Tracking
Remove CP
FFT
preamble
preamble
pilot tones
Calculate the phase difference:
2. Fractional Frequency Offset
13
1st Preamble in time domain:
gN N
N
enrenrg Nnj
NnjN
n
12821
)128()(arg1
ˆ
FFO
128
0
*FFO }{ )(
)128(22
1. Frame Start Detection
Frequency Offset
Correction
2.Fractional Frequency Offset Estimation
3.Integer Frequency Offset Estimation
4. Residual Frequency Offset Tracking
Remove CP
FFT
3. Integer Frequency Offset
14
preamble
preamble
pilot tones
15
3. Integer Frequency Offset
k k ikik
k kkikik
XX
PPXXiM
22,2
22,1
**,2,1
*2,22,1
||||
|)(|)2(
|)2(| iM
Estimated integer frequency offset
Received Preamble shifted by 2i
Defined Preamble
Defined Preamble:
Received Preamble:
4. Residual Frequency Offset
16
1. Frame Start Detection
Frequency Offset
Correction
2.Fractional Frequency Offset Estimation
3.Integer Frequency Offset Estimation
4. Residual Frequency Offset Tracking
Remove CP
FFT
preamble
preamble
pilot tones
17
4. Residual Frequency Offset
: received pilot in th OFDM symbol : pre-defined pilot in th OFDM symbol
}{ **,,1
*,,1RFO )(arg
2
1ˆ
l k
klklklklg
PPXXNN
N
klX , k
klP ,
l
FFT size
Cyclic Prefix length
average over l OFDM symbols
average over k pilot subcarriers
0
13
255
freq
uenc
y
time
000
0
0
0
0
0 0
0 00
0 000
0
0
0
0
kl
Outline
LTE PHY Synchronization in OFDMFrom WiMAX to LTE
Synchronization in WiMAXLTE Frame Structure
Conclusion
18
LTE Frame Structure
19
Resource Block
Resource Element
Primary Synchronization Signals • identical in slot 0 and 10• mapped to 72 centre subcarriersSecondary Synchronization Signals • Different in slot 0 and 10 • Mapped to 62 centre subcarriers
Synchronization Signals
20
72 s
ubca
rrie
r
Reference Signals
21
1 Subframe 1ms 2 ResourceBlocks
Antenna Port 0Antenna Port 1Antenna Port 1
Reference Signals
22
Antenna Port 0Antenna Port 1
Antenna Port 2Antenna Port 2
Reference Signals
23
Antenna Port 0Antenna Port 1
Antenna Port 3Antenna Port 2Antenna Port 3
Reference Signals
24
Antenna Port 0Antenna Port 1Antenna Port 2Antenna Port 3
06modcellIDshift Nv 16modcellIDshift Nv
2.Fractional Frequency Offset Estimation
1. Frame Start Detection
Frequency Offset
Correction
3.Integer Frequency Offset Estimation
4. Residual Frequency Offset Tracking
Remove CP
FFT
Primary & Secondary Synchronization
Signals
Primary Synchronization
Signals
Primary & Secondary Synchronization
Signals
Reference Signals
Conclusion: Synchronization in LTE DL
25
Reference 3GPP TS 36.211 V8.2.0 3rd Generation Prtnership Project; Technical Specification
group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8), March 2008
Freescale, ”Overview of the 3GPP Long Term Evolution Physical Layer,” 2007. E. Dahlman, S. Parkvall, J. Sköld, P. Beming: “3G Evolution: HSPA and LTE for Mobile
Broadband“, Elsevier 2007. M. Morelli, C.-C Jay Guo, M. Pun: “Synchronization Techniques for Orthogonal
Frequency Division Multiple Access (OFDMA): A Tutorial Review“, Proc. IEEE, vol. 95, No.7, July 2007.
T. M. Schmidl, D. C. Cox: “Robust Frequency and Timing Synchronization for OFDM“, IEEE Tran. Comm. Vol. 45, No. 12, Dec. 1997.
Y. Yan, M. Tomisawa, Y. gong, Y. Guan, G. Wang, C. Law, Joint timing and frequency synchronization for IEEE 802.16 OFDM systems, Mobile WiMAX Symposium, 2007. IEEE
26
Thanks!
27
Simulation Result
28
WiMAX SISO throughput with Timing Offset = 89, Carrier Frequency Offset = pi, in the Pedestrian B Channel, 500 frame simulation
Perfect synchronized
Both Timing Offset and Frequency Offset Corrected
Only Timing Offset Corrected
Only Frequency Offset Corrected
Simulation Result
29/17
WiMAX SISO throughput, Carrier Frequency Offset = = 3.1416, Pedestrian B Channel, 500 frames simulation
Perfectly Corrected
Frame-wise Residual Frequency Offset Estimation
Symbol-wise Residual Frequency Offset Estimation
Without Residual Frequency Offset Correction
Without Carrier Frequency Offset Correction
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