1 / 36

CFO Estimation with ICI Cancellation for OFDM Systems

CFO Estimation with ICI Cancellation for OFDM Systems. 吳宗威. Outline. Motivations Background knowledge Conventional CFO estimation strategies Modified CFO estimation strategies Simulation results Conclusions. Outline. Motivations Background knowledge

red
Download Presentation

CFO Estimation with ICI Cancellation for OFDM Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CFO Estimation with ICI Cancellation for OFDM Systems 吳宗威

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

  3. Outline • Motivations • Background knowledge • Conventional CFO estimationstrategies • Modified CFO estimationstrategies • Simulation results • Conclusions

  4. 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.

  5. Outline • Motivations • Background knowledge • Conventional CFO estimationstrategies • Modified CFO estimationstrategies • Simulation results • Conclusions

  6. 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 Signal Demapper FFT ADC 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

  7. OFDM System Model • The nth sample of an OFDM block generated by IFFT : N: number of subcarriers Ng: length of cyclic prefix

  8. Signal strength Time 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]

  9. Outline • Motivations • Background knowledge • Conventional CFO estimation strategies • Modified CFO estimationstrategies • Simulation results • Conclusions

  10. 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 Signal Demapper FFT ADC • is the ratio of the actual frquency offset to the sub-carrier spacing

  11. Sensitivity for Carrier Frequency Offset • The n-th received sample of the m-th symbol is given by FFT

  12. Sensitivity for Carrier Frequency Offset • . • Amplitude reduction: • Phase shift: • .

  13. R1 R2 Rm Rm+D Pilot3 (n3) Pilot2 (n2) Pilot1 (n1) t 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

  14. Outline • Motivations • Background knowledge • Conventional CFO estimationstrategies • Modified CFO estimation strategies • Simulation results • Conclusions

  15. Matrix form of R(k)

  16. A math property • A(k) , k=0…N-1 is the DFT of a(n) , n=0,…,N-1

  17. The Problem • Can we find a matrix B, such that

  18. B is in fact a matrix that does Gaussian Reduction to

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

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

  21. However, is zero when k=0 . 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

  22. 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.

  23. Outline • Motivations • Background knowledge • Conventional CFO estimationstrategies • Modified CFO estimationstrategies • Simulation results • Conclusions

  24. Different Modulation BPSK

  25. QPSK

  26. 8PSK

  27. 16PSK

  28. Recursive Recursive

  29. Random initial condition Random initial condition =0.5 Delta_f=0.1

  30. Outline • Motivations • Background knowledge • Conventional CFO estimationstrategies • Modified CFO estimationstrategies • Simulation results • Conclusions

  31. 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: N*Np multiplier .

  32. Thank you ~

  33. 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. (ICASSP’04), vol. 4, pp. 365-368, 17-21 May 2004.

More Related