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OFDM Synchronization

OFDM Synchronization. Speaker: 官雯彗. Outline. OFDM System Description Synchronization What is Synchronization? Symbol Synchronization Non-data-aided Method (Maximum likelihood, BPSK-OFDM case) Frequency Synchronization Non-data-aided Method (Via oversampling)

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OFDM Synchronization

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  1. OFDM Synchronization Speaker: 官雯彗

  2. Outline • OFDM System Description • Synchronization • What is Synchronization? • Symbol Synchronization • Non-data-aided Method (Maximum likelihood, BPSK-OFDM case) • Frequency Synchronization • Non-data-aided Method (Via oversampling) • Data-aided Method (Special training-symbol-block) • Joint Symbol and Frequency Synchronization • Non-data-aided Method (Exploiting second-order cyclostationarity)

  3. OFDM System Block P/S S/P IFFT channel S/P P/S FFT

  4. OFDM System Description • An OFDM symbol structure Cyclic prefix interval Symbol interval CP xi,0,xi,1,……………………………,xi,N-1 copy

  5. Signal Model FFT IFFT

  6. OFDM System Description • Synchronization • What is Synchronization? • Symbol Synchronization • Non-data-aided Method (Maximum likelihood, BPSK-OFDM case) • Frequency Synchronization • Non-data-aided Method (Via oversampling) • Data-aided Method (Special training-symbol-block) • Joint Symbol and Frequency Synchronization • Non-data-aided Method (Exploiting second-order cyclostationarity)

  7. What is Synchronization? • Symbol synchronization • Symbol Synchronization refers to the task of finding the precise moment of when individual OFDM symbols start and end. • Frequency synchronization • Let the transmitted signal be sn, then the complex baseband model of the passband signal yn is • Then the received complex baseband signal rn is

  8. Received Signal • Transmitted signal • Received signal Cyclic prefix interval Symbol interval

  9. CP ith OFDM symbol CP

  10. CP ith OFDM symbol CP

  11. CP ith OFDM symbol CP

  12. CP ith OFDM symbol CP

  13. Synchronization task • Data-aided method • Non-data-aided method

  14. OFDM System Description • Synchronization • What is Synchronization? • Symbol Synchronization • Non-data-aided Method (Maximum likelihood, BPSK-OFDM case) • Frequency Synchronization • Non-data-aided Method (Via oversampling) • Data-aided Method (Special training-symbol-block) • Joint Symbol and Frequency Synchronization • Non-data-aided Method (Exploiting second-order cyclostationarity)

  15. Non-data-aided Method (Maximum likelihood)

  16. Non-data-aided Method (Maximum likelihood) Observation interval Symbol i-1 Symbol i Symbol i+1 2N+CP 1

  17. Non-data-aided Method (Maximum likelihood)

  18. Non-data-aided Method (Maximum likelihood)

  19. Non-data-aided Method (Maximum likelihood)

  20. OFDM System Description • Synchronization • What is Synchronization? • Symbol Synchronization • Non-data-aided Method (Maximum likelihood, BPSK-OFDM case) • Frequency Synchronization • Non-data-aided Method (Via oversampling) • Data-aided Method (Special training-symbol-block) • Joint Symbol and Frequency Synchronization • Non-data-aided Method (Exploiting second-order cyclostationarity)

  21. Non-data-aided Method (BPSK-OFDM case) • Signal model in BPSK-OFDM system

  22. Non-data-aided Method (BPSK-OFDM case)

  23. Non-data-aided Method (BPSK-OFDM case)

  24. Non-data-aided Method (BPSK-OFDM case)

  25. Non-data-aided Method (BPSK-OFDM case) CP

  26. Non-data-aided Method (BPSK-OFDM case) CP CP

  27. Non-data-aided Method (BPSK-OFDM case) • There are three kinds of useful property can be employed as follows: • The first group of symmetry relationship. • The second group of symmetry relationship. • The cyclic prefix copied from the tail of OFDM symbol.

  28. Non-data-aided Method (BPSK-OFDM case)- Using angle CP CP

  29. Non-data-aided Method (BPSK-OFDM case) - Using angle CP CP CP

  30. Non-data-aided Method (BPSK-OFDM case) - Using correlation CP CP

  31. Non-data-aided Method (BPSK-OFDM case) - Using correlation CP CP CP

  32. Performance Analysis

  33. CP CP CP

  34. Solution Image part Real part : A pair of sample which has symmetry characteristic in noise free case

  35. Solution Image part Real part : A pair of sample which has symmetry characteristic in noise free case

  36. OFDM System Description • Synchronization • What is Synchronization? • Symbol Synchronization • Non-data-aided Method (Maximum likelihood, BPSK-OFDM case) • Frequency Synchronization • Non-data-aided Method (Via oversampling) • Data-aided Method (Special training-symbol-block) • Joint Symbol and Frequency Synchronization • Non-data-aided Method (Exploiting second-order cyclostationarity)

  37. Non-data-aided Method (Via oversampling)

  38. Non-data-aided Method (Via oversampling)

  39. Non-data-aided Method (Via oversampling)

  40. Non-data-aided Method (Via oversampling)

  41. Non-data-aided Method (Via oversampling)

  42. Non-data-aided Method (Via oversampling)

  43. Non-data-aided Method (Via oversampling) • Perfect recovery of carrier frequency offset in the absence of noise

  44. Non-data-aided Method (Via oversampling) • Frequency offset estimation in the present of noise

  45. OFDM System Description • Synchronization • What is Synchronization? • Symbol Synchronization • Non-data-aided Method (Maximum likelihood, BPSK-OFDM case) • Frequency Synchronization • Non-data-aided Method (Via oversampling) • Data-aided Method (Special training-symbol-block) • Joint Symbol and Frequency Synchronization • Non-data-aided Method (Exploiting second-order cyclostationarity)

  46. Data-aided Method (Special training-symbol-block) • At the transmitter, the training-symbol-block contains two equal-length training symbols in time domain, and the second training symbol is the inverse repeat of the first one.

  47. Data-aided Method (Special training-symbol-block) • At receiver, without considering of the channel attenuation and additive AWGN, the relationship between corresponding samples in a received training-symbol-block is :

  48. Data-aided Method (Special training-symbol-block) • A timing metric is defined:

  49. Data-aided Method (Special training-symbol-block)

  50. Data-aided Method (Special training-symbol-block)

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