CFO Estimation with ICI Cancellation for OFDM Systems

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CFO Estimation with ICI Cancellation for OFDM
Systems

• ???

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Outline

• Motivations
• Background knowledge
• Conventional CFO estimation strategies
• Modified CFO estimation strategies
• Simulation results
• Conclusions

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Outline

• Motivations
• Background knowledge
• Conventional CFO estimation strategies
• Modified CFO estimation strategies
• Simulation results
• Conclusions

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Motivations

• Motivations
• Every OFDM model has a specific form in the
  carrier frequency offset system.
• When we estimate the frequency offset by
  pilot,the ICI still exists. It is intuitive to
  decrease the ICI first , then estimate it.

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Outline

• Motivations
• Background knowledge
• Conventional CFO estimation strategies
• Modified CFO estimation strategies
• Simulation results
• Conclusions

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OFDM System Model

• The OFDM system model

• C is pilot sequence
• h is time domain channel impulse response
• w is additive white Gaussian noise.
• N data information S(k) which have been
  modulated with N modulation values X(k) on
  every sub-carrier

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OFDM System Model

• The nth sample of an OFDM block generated by IFFT
  

N number of subcarriers Ng length of cyclic
prefix
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UWB Channel Model
cluster decay factor path decay
factor cluster arrival rate the
arrival rate of path within each cluster

• Four environments in this UWB channel model
• CM1 model is based on LOS (0-4m) channel
  measurements in 2

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Outline

• Motivations
• Background knowledge
• Conventional CFO estimation strategies
• Modified CFO estimation strategies
• Simulation results
• Conclusions

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Sensitivity for Carrier Frequency Offset

• The OFDM system model with CFO

S ( k )
X ( k )
x(n)
Adding Cyclic Prefix P/S
S/P
Signal Mapper
Adding Pilots C(n) IFFT
x ( t )
DAC
Channel h ( t)
z (t )
AWGN w ( t)
Remove Cyclic Prefix S/P
r (t )
P/S
FFT
Signal Demapper
ADC

• is the ratio of the actual
  frquency offset to the sub-carrier spacing

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Sensitivity for Carrier Frequency Offset

• The n-th received sample of the m-th symbol is
  given by

FFT
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Sensitivity for Carrier Frequency Offset

• .

• Amplitude reduction
• Phase shift

• .

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Pilot tone - aided CFO Estimation

• PTA with weighting (PTAW) CFO estimation

• Let P denote the set of indexes of the Np
  pilot carriers

f
Q
I
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Outline

• Motivations
• Background knowledge
• Conventional CFO estimation strategies
• Modified CFO estimation strategies
• Simulation results
• Conclusions

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Matrix form of R(k)

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A math property

• A(k) , k0N-1 is the DFT of
• a(n) , n0,,N-1

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The Problem

• Can we find a matrix B, such that
• 
  

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• B is in fact a matrix that does Gaussian
• Reduction to

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• The term is the key point
  .Because if the ratio between each term is
  irrelevant to , then we can definitely
  finish the matrix B.

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• The numerator of
  is actually .
• And the denominator
  because
• So, we can regard as
  
• Thus, the ratio between each term is
  irrelevant to .

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• However, is zero when k0 . So
  we need a estimate for the denominator of
  
• Choose the PTAW estimate for the denominator of
  
• B is the matrix does Gaussian reduction to the
  cyclic matrix
• composed of

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The Procedure

• Step1 Estimate the frequency offset by PTAW
• Step2 Substitute the estimate into the
  denominator of
• Step3 multiply the matrix B with the incoming
  symbol and the previous symbol
• Step4 Apply the PTAW again, then we have a more
  accurate estimate.

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Outline

• Motivations
• Background knowledge
• Conventional CFO estimation strategies
• Modified CFO estimation strategies
• Simulation results
• Conclusions

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Different Modulation
BPSK
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QPSK
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8PSK
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16PSK
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(No Transcript)
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Recursive
Recursive
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Random initial condition
Random initial condition 0.5 Delta_f0.1
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Outline

• Motivations
• Background knowledge
• Conventional CFO estimation strategies
• Modified CFO estimation strategies
• Simulation results
• Conclusions

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Conclusions

• Advantages
• The key advantages of our proposed algorithms is
  to provide more accurate frequency
  synchronization .
• Estimate the frequency offset without knowing the
  channel response first.
• Complexity NNp multiplier .

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• Thank you

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Reference

• 1 J. R. Foerster, Ed., Channel Modeling
  Sub-committee Report Final, IEEE P802.15 SG3a
  contribution.
• 2 H. Chen and G.J. Pottie, "A Comparison of
  Frequency Offset Tracking Algorithms for OFDM",
  GLOBECOM '03, vol.2, pp. 1069-1073, Dec. 2003.
• 3 K. Shi, E. Serpedin, and P. Ciblat,
  Decision-directed fine synchronization for coded
  OFDM systems, in Proc. IEEE International Conf.
  on Acoustics, Speech, and Signal Processing.
  (ICASSP04), vol. 4, pp. 365-368, 17-21 May 2004.