歐規數位電視地面廣播基頻接收機之設計

Abstract

本論文依據歐規數位電視地面廣播（DVB-T）標準的傳送機架構和系統規格，提出基頻等效通道模型，並設計及實作一基頻接收機。基頻等效通道模型包括多路徑衰減通道（Multipath Fading Channel）、加成性白色高斯雜訊（Additive White Gaussian Noise，AWGN）、載波頻率漂移（Carrier Frequency Offset，CFO）、取樣時脈漂移（Sampling Frequency Offset，SCO）和相位雜訊（Phase Noise）等效應。而因為DVB-T在系統規格上，可以選擇2種快速傅立葉轉換（Fast Fourier Transform，FFT）大小和4種保護區間比例（Guard-Interval Ratio，GR）大小，所以在接收機的架構演算法設計上，一開始就必須偵測傳送機所使用的FFT模式及GR模式。本論文設計提出了一兩階段模式偵測演算法來實現接收機一開始所需的模式偵測功能，並結合符元時間偵測、載波頻率漂移及取樣時脈漂移之擷取、補償和追蹤、2k-8k FFT處理器、相位調整、通道估測與補償、軟性輸出解映射器（Soft-Out De-Mapper）及軟性輸入維特比解碼器（Soft-In Viterbi Decoder）等演算法來實現整個DVB-T基頻接收機系統。在硬體電路方面，本論文也提出使用輸出訊噪比（Output SNR）取代位元錯誤率（Bit Error Rate，BER）來做為取最佳位元數的指標，並在演算法可容忍些微誤差下，為了節省硬體，提出了分段線性近似的演算法。經過系統效能模擬與全系統RTL Verilog的實作驗證，說明了本論文所提出的DVB-T基頻接收機是可以良好工作的。

This thesis proposes a baseband receiver and a baseband equivalent channel model according to the transmitter and system specification of Euporean DVB-T standard. The baseband equivalent channel model includes effects of multipath fading channel, Additive White Gaussian Noise (AWGN), Carrier Frequency Offset (CFO), Sampling Frequency Offset (SCO), and phase noise. DVB-T system has two choices in Fast Fourier Transform (FFT) size and four choices in Guard-Interval Ratio (GR) size, so a DVB-T reciever should detect FFT mode and GR mode used in the transmitter in the beginning. This thesis proposes a two-stage mode detection algorithm to perform the function, and combines algorithms of symbol timing detection, CFO acquisition, compensation, and tracking as well as SCO, 2k-8k FFT processor, phase modification, channel estimation and compensation, soft-out demapper, and soft-in Viterbi decoder to implement the whole system of DVB-T receiver. In hardware circuit design, this thesis also proposes to use output SNR instead of Bit Error Rate (BER) as the metric of optimum wordlength and use piecewise linear approximation algorithm to save hardware cost with tolerable approximation error. Through system performance simulation and verification of whole system RTL Verilog, the proposed DVB-T baseband receiver is proven to work well.