1. Introduction of OFDM System
指導老師:高永安
學 生:蘇家弘

2. Outline Why use OFDM? Advantage of OFDM OFDM Flow-chart
Problem in OFDM
1.Multipath
2.Carrier Frequency Offset
3. Samplin Clock Frequency Offset
Conclusion

3. Why use OFDM? Characterization 1.Orthogonality 子載波頻率為基頻的整數倍
相鄰子載波週期數相差”1週期”
2.Frequency Division
take use of multi-carrier

4. Advantage of OFDM
傳輸速率更快
有效使用頻寬
Fig. FDM System
Fig. OFDM System

5. Advantage of OFDM
有效解決ISI及ICI的問題
較不易失真

6. Flow Chart of OFDM System

7. Problem in OFDM 1.Multipath
More than one transmission path between Tx and Rx
Received signal is the sum of many versions of the transmitted signal with attenuation and delay

8. Fig. ISI(Inter-symbol Interference)
Effect of Multipath
Fig. ISI(Inter-symbol Interference)

9. Solve the Multipath problem
Data transmitted in parallel
Guard Interval

10. Problem in OFDM 2.Carrier Frequency Offset z(n) h(n) Channel
Transmitter
Receiver

11. Effect of Carrier Frequency Offset
ICI(Inter-carrier Interference)

12. Effect of Carrier Frequency Offset
Phase rotation of the coefficients because of frequency offset

13. Solve Carrier Frequency Offset
Using equalizer estimation to do compensation

14. Problem in OFDM 3.Sampling Clock Frequency Offset
Transmit Sampling Frequency =
Receive Sampling Frequency =

15. Effect of Sampling Clock Frequency Offset
OFDM Symbol Window Drift
sampling clock slow leads left drift
sampling clock fast leads right drift

16. Effect of Sampling Clock Frequency Offset
Subcarrier Symbol Rotation

17. Solve Sampling Clock Frequency Offset
Take use of algorithm to do estimation

18. Conclusion 更有效使用頻寬 解決ICI和ISI 應用 數位廣播系統（Digital Audio Broadcasting）
數位影視系統（Digital Video Broadcasting）
無線網路（IEEE a）