Carrier Frequency Offset Estimation and Correcting of DAB Receiver

[[abstract]]非對稱數位用戶迴路(ADSL)及數位語音廣播(DAB)皆是應用正交分頻多工(orthogonal frequency-division multiplexing OFDM)的調變技術，OFDM技術在無線通道傳輸環境中可以有效地克服多重路徑衰落，然而，在OFDM系統中最大的問題在於信號的同步方面，特別是對於載波頻率同步非常的敏感且必須要求非常準確，因為頻率偏差會破壞次載波間的正交性，進而對系統接收品質造成負面的影響。造成頻率偏差的原因主要由接收機移動所造成都卜勒效應以及接收機本地振盪的不準度產生，本論文主要是在於探討OFDM應用於數位語音廣播系統中，當有頻率偏差產生時對DAB系統所造成的不良影響及其更正方法。我們利用前人文獻[9]所提出的一個觀念，設計出頻率偏差更正(Frequency Error Detection FED)系統，在頻率偏差發生時且小於1/2次載波的情況下，系統皆能把頻率錯誤偏差值給更正回來，降低接收端的位元錯誤率。 在本論文模擬系統研究中，我們選用四種數位廣播系統模式中的第三種模式，只針對頻率偏差對系統的影響做為研究方向，且在一開始假設無載波相位干擾(Phase noise)以及時序(Timing)的問題。我們在AWGN通道上給予頻率偏差0 1~0 5的情況下，觀察接收端位元錯誤率的情況，並和訊號經過FED系統後的位元錯誤率相比較，確定訊號受到頻率偏差的干擾後經過我們所設計的FED系統，其位元錯誤率降低了許多。[[abstract]]Asymmetric digital subscriber line (ADSL) and digital audio broadcast (DAB) are applications of the technique of orthogonal frequency-division multiplexing (OFDM) OFDM system is also an effective way to solve the multi-path fading in wireless chann- el However the disadvantage of OFDM system is the synchronization problem Its rec- eiver is very sensitive to carry frequency offset Frequency offset is caused by Doppler shift and tuning oscillator inaccuracy in transmission channel It makes the sub- carry become non-orthogonal with each other therefore the performance of receiver will deg- rade largely In this thesis research the frequency offset problem in OFDM DAB system is addressed We cope with this problem by design a frequency error detection (FED) sub-system When the frequency offset is smaller than 1/2 sub-carry Our proposed method can detect and correct the frequency offset then the bit error rate (BER) is reduced in the receiver In this thesis we use the third kind of DAB system and analyze the effect of the frequency offset The phase noise and timing problem is not considered We assume the value of frequency offset is between 0 1 and 0 5 in AWGN channel By applying our proposed FED scheme it is shown that the BER can be reduced recursivel