H.263無線傳輸之誤差控制

Abstract

這篇論文主要是提出一些方法來對付在無線通道上傳輸H.263編碼的視訊 影像所會遇到的雜訊問題. 其中, 我們使用一種稱為抗誤熵編碼 (EREC) 的方法來降低因使用可變長度編碼所造成的錯誤蔓延. 另外, 針對無法藉 由檢查編碼內容來偵誤的DC係數, 我們提出了一恢復DC值的演算法來處理 之. 我們並提出一個方法來偵測到並更正發生錯誤的運動向量. 此方法在 編碼端使用一匹配運動向量的演算法, 在解碼端則使用一對應的檢查及恢 復運動向量的演算法. 利用上述這些方法, 我們可以避免因錯誤蔓延而導 致畫面上出現條條黑帶的現象, 亦可減少因錯誤的DC值而在畫面上產生綠 色與粉紅色塊的情形, 並降低因運動向量受損而導致的錯誤的運動補償所 造成的不良影響. This thesis presents some methods to combat the error effects whentransmitting H.263 video sequences over a wireless channel. We useerror-resilient entropy coding (EREC) to reduce the error propaga-tion caused by using variable-length codewords in the bitstreams.Besides, corrupted DC coefficients which cannot be detected by checking the bitstream syntax are concealed by a DC recoveryalgorithm. We also propose a method to detect and correct corruptedmotion vectors which uses a motion-vector pairing technique in theencoder and a corresponding motion- vector checking and recoveryalgorithm in the decoder. By these methods, corrupted strips in theimages caused by error propagation from loss of synchronization areavoided. The annoying "green/pink" block artifacts caused byerroneous DC coefficients and the effects of incorrect motioncompensation caused by corrupted motion vectors are also alleviated.