- 學位論文
Design and Implementation of A Wideband Video Transmission System based on 2x2 MIMO-OFDM
基於2x2多輸入多輸出正交分頻多工之寬頻視訊傳輸系統之設計與實作
摘要
本論文以歐規數位電視地面廣播(Digital Video Broadcast - Terrestrial)標準的發送機規格為基礎,設計多根天線4x4 MIMO-OFDM基頻發送機取代傳統單一天線系統,並提出新一代影像編碼技術H.264取代傳統 MPEG-2。在無線通訊環境中,有不少非理想效應存在,因此我們考慮了基頻等效通道模型來模擬無線傳輸通道,包含了多重路徑衰減效應(Multipath Fading)、加成性白高斯雜(Additive White Gaussian Noise, AWGN)與載波頻率漂移(Carrier Frequency Offset, CFO)等效應。再根據發送機架構與通道非理想特性,提出接收機架構之設計,其中主要包含同步、通道響應估測與補償、可適性階層調變與通道編碼解碼等四大部分。在同步的地方又分為初始估測、符元邊界估測以及載波頻率漂移估測與補償;通道響應估測中使用散佈領航碼在時域與頻域上做二維的估測,再利用 MIMO Detector 將通道效應補償;本論文提出了一個可適性階層調變機制,根據不同的通道狀況對應出不同的階層調變參數α、β,而階層調變技術將影像資料分級,使不同等級的影像受到不同的保護機制傳輸;最後通道編碼的解碼主要使用串接錯誤更正碼,包含維特比解碼器 (Viterbi Decoder)與里德所羅門解碼器(Reed-Solomon Decoder),將受到通道效應產生的錯誤更正。在硬體實現上,我們考慮了硬體面積與成本,將4x4 MIMO-OFDM System化簡為2x2 MIMO-OFDM System,並以兩塊FPGA版驗證發送機與通道模型、接收機。
並列摘要
In this thesis, based on transmitter specification of DVB-T, multi-antenna 4x4 MIMO-OFDM transmitter was designed to replace traditional single-antenna system. Furthermore, new generation image-coding technique H.264 was also presented to be an alternate for MPEG-2. In order to simulate the non-ideal effects of wireless communication environment, base-band channel model including Multi-path Fading effect, AWGN effect, CFO effect was took into account. Under such an environment and according to its structure and non-ideal characteristics, the receiver including four major sections was designed: synchronization, channel response estimation and compensation, adaptive modulation and channel decoding. First, in the synchronization section, initial estimation, symbol boundary estimation and CFO estimation/compensation were contained.Second, in the channel estimation, scattered pilots was estimated in two-dimensional time and frequency domain, and then compensated by the MIMO detector. Thirdly, adaptive modulation mechanism was proposed, with modulation variable α、β corresponded with different channel condition. The adaptive modulation technique classified the image data into different level, and then transmits each level through its corresponding protection mechanism. In the last, a concatenate error-correction decoder was used, where Viterbi Decoder and Reed-Solomon Decoder were corrected by the error of channel effect. In the hardware part, with the aim of reducing cost and size, 4x4 MIMO-OFDM system was reduced to 2x2 MIMO-OFDM system; the transmitter, channel model and receiver were verified by two FPGA board.