以快速富立葉轉換為基礎之DPSK犁耙式接收機

Abstract

本論文提出一種新的犁耙式接收機架構，以及一種新的展頻碼時脈修正法。不同於一般犁耙式接收機在時域處理信號，此新的犁耙式接收機將利用快速富立葉轉換在頻域做信號處理。系統所使用之調變方式為DPSK，因此發射端不需傳送額外的領航信號或領航幅元作通道量測。在接收端可以直接利用其調變特性得到所傳送之訊息位元，或是利用DPSK信號的特性先作通道估計決定DPSK信號，然後再用差分解碼的方式得到訊息位元。在作通道估計時，接收機也利用了決定導向的方法以提升系統性能。在展頻碼時脈修正方面，我們利用了FFT及通道具有最小相位移的特性回復展頻碼時脈。我們以電腦模擬的方式評估接收機及時脈修正法的性能表現。由模擬結果可以證明，不論在靜態通道或衰變通道下，此新的犁耙式接收機與展頻碼時脈修正法均能有良好的表現。

This thesis describes a new RAKE receiver architecture and a new timing correction method of spreading code. Unlike general RAKE receiver that processes signals in time domain, this new RAKE receiver will use Fast Fourier transform (FFT) to process signals in frequency domain. The modulation scheme used by the system is differential phase shift keying (DPSK), so transmitter does not need to transmit extra pilot signal or pilot symbol for channel sounding. Receiver can obtain information data from its modulation characteristic directly or can estimate the channel impulse response to make decision of DPSK signal and then use differential decoding method to obtain information data. In order to improve system performance, this new RAKE receiver also adopts decision-directed method for channel estimation. About correcting the timing of spreading code, we assume the channel is a minimum phase system and take advantage of the characteristic of FFT to recover the timing of spreading code. Monte Carlo simulation is used to evaluate the performance of our RAKE receiver and the timing correction method. Simulation results can show that this new RAKE receiver and timing correction method will work well in both a static channel and a mobile radio channel.