中頻解調在數位傳輸系統上之探討

Abstract

藉由中頻取樣及數位解調以取代數位接收器中的第三個震盪器, 將 得到一高密度取樣的數列以用作等化。 為了 充分利用此高密度取樣數列, 分數間 距式等化器被選擇作為信號等化以對抗傳輸過程中之通道失真。分數間距 式等化器的優點在於取樣時基誤差對其影響很小, 因此只需要 一簡單的時基恢復電路即可, 區段同步信號 也可省略以提高傳輸效率。 With bandpass sampling and digital demodulation to remove the 3rd oscillator in the digital receiver, an oversampled sequence is obtained for equalization. To make good use of this oversampled sequence, a fractionally-spaced decision feedback equalizer is chosen for signal equalization to combat the channel distortion during transmission. The advantage to use the fractionally-spaced equalizer is that the effect of the symbol timing error on the performance of the equalizer can be made minimum. Therefore, the clock recovery circuit can be made very simple. The segment syncs can also be omitted to increase the transmission efficiency.