1. 1 OFDM Synchronization Speaker:

2. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 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. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 3 OFDM System Block S/PIFFT P/S channel P/SFFT S/P

4. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 4 OFDM System Description An OFDM symbol structure CP Symbol interval Cyclic prefix interval x i,0,x i,1,……………………………,x i,N-1 copy

5. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 5 Signal Model FFT IFFT

6. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 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. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 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 s n, then the complex baseband model of the passband signal y n is Then the received complex baseband signal r n is

8. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 8 Received Signal Transmitted signal Received signal Symbol interval Cyclic prefix interval

9. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 9 CP ith OFDM symbol CP

10. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 10 CP ith OFDM symbol CP

11. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 11 CP ith OFDM symbol CP

12. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 12 CP ith OFDM symbol CP

13. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 13 Synchronization task Data-aided method Non-data-aided method

14. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 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. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 15 Non-data-aided Method (Maximum likelihood)

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

17. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 17 Non-data-aided Method (Maximum likelihood)

18. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 18 Non-data-aided Method (Maximum likelihood)

19. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 19 Non-data-aided Method (Maximum likelihood)

20. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 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. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 21 Non-data-aided Method (BPSK-OFDM case) Signal model in BPSK-OFDM system

22. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 22 Non-data-aided Method (BPSK-OFDM case)

23. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 23 Non-data-aided Method (BPSK-OFDM case)

24. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 24 Non-data-aided Method (BPSK-OFDM case)

25. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 25 Non-data-aided Method (BPSK-OFDM case) CP

26. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 26 Non-data-aided Method (BPSK-OFDM case) CP

27. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 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. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 28 Non-data-aided Method (BPSK-OFDM case) - Using angle CP

29. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 29 Non-data-aided Method (BPSK-OFDM case) - Using angle CP

30. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 30 Non-data-aided Method (BPSK-OFDM case) - Using correlation CP

31. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 31 Non-data-aided Method (BPSK-OFDM case) - Using correlation CP

32. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 32 Performance Analysis

33. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 33 CP

34. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 34 Solution Real part Image part : A pair of sample which has symmetry characteristic in noise free case

35. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 35 Solution Real part Image part : A pair of sample which has symmetry characteristic in noise free case

36. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 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. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 37 Non-data-aided Method (Via oversampling)

38. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 38 Non-data-aided Method (Via oversampling)

39. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 39 Non-data-aided Method (Via oversampling)

40. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 40 Non-data-aided Method (Via oversampling)

41. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 41 Non-data-aided Method (Via oversampling)

42. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 42 Non-data-aided Method (Via oversampling)

43. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 43 Non-data-aided Method (Via oversampling) Perfect recovery of carrier frequency offset in the absence of noise

44. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 44 Non-data-aided Method (Via oversampling) Frequency offset estimation in the present of noise

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

48. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 48 A timing metric is defined: Data-aided Method (Special training-symbol-block)

49. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 49 Data-aided Method (Special training-symbol-block)

50. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 50 Data-aided Method (Special training-symbol-block)

51. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 51 Data-aided Method (Special training-symbol-block)

52. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 52 Data-aided Method (Special training-symbol-block)

53. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 53 Data-aided Method (Special training-symbol-block)

54. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 54 Data-aided Method (Special training-symbol-block)

55. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 55 After acquisition, if the remaining carrier frequency offset exceeds the tracking range, tracking algorithm will not work correctly, and this is called Missing Lock. For usable SNR, if N is large enough, the probability of Missing Lock is negligible. Data-aided Method (Special training-symbol-block)

56. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 56 After acquisition, the remaining frequency offset needs to be further corrected. Data-aided Method (Special training-symbol-block)

57. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 57 Data-aided Method (Special training-symbol-block)

58. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 58 Data-aided Method (Special training-symbol-block)

59. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 59 Data-aided Method (Special training-symbol-block)

60. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 60 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)

61. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 61 Non-data-aided Method (Exploiting second order cyclostationarity)

62. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 62 Non-data-aided Method (Exploiting second order cyclostationarity)

63. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 63 Non-data-aided Method (Exploiting second order cyclostationarity)

64. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 64 Non-data-aided Method (Exploiting second order cyclostationarity)

65. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 65 Non-data-aided Method (Exploiting second order cyclostationarity)

66. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 66 Non-data-aided Method (Exploiting second order cyclostationarity)

67. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 67 Non-data-aided Method (Exploiting second order cyclostationarity)

68. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 68 Non-data-aided Method (Exploiting second order cyclostationarity)

69. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 69 Non-data-aided Method (Exploiting second order cyclostationarity)

70. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 70 Non-data-aided Method (Exploiting second order cyclostationarity)

71. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 71 Non-data-aided Method (Exploiting second order cyclostationarity)

72. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 72 Non-data-aided Method (Exploiting second order cyclostationarity)

73. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 73 Reference 1) J.J. van de Beek, M. Sandell and P. O. Börjesson, ML estimation of time and frequency offset in OFDM systems, IEEE Trans. Signal Processing, vol. 45, no. 7, pp. 1800-1805, July 1997. 2) B. Chen, H. Wang, Blind OFDM carrier frequency offset estimation via oversampling, 2001 IEEE, vol. 2, pp. 1465 – 1469, Nov. 2001. 3) Z. Zhang, M. Zhao, H. Zhou, Y. Liu, J. Gao, Frequency offset estimation with fast acquisition in OFDM system, IEEE Communications Letters, vol. 8, no. 3, pp. 171 – 173, Mar. 2004. 4) B. Park, H. Cheon, E. Ko, C. Kang, D. Hong, A blind OFDM synchronization algorithm based on cyclic correlation, IEEE Signal Processing Letters, vol. 11, no. 2, pp. 83 – 85, Feb. 2004.

74. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. 74