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

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

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

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

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

Flow Chart of OFDM System

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

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

Solve the Multipath problem Data transmitted in parallel Guard Interval

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

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

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

Solve Carrier Frequency Offset Using equalizer estimation to do compensation

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

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

Effect of Sampling Clock Frequency Offset Subcarrier Symbol Rotation

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

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 802.11a）