應用於無線視訊傳輸之可變長度解碼器

Abstract

可變長度編碼在近來的視訊及影像編碼當中一直被廣泛的應用。然而，傳統的解碼方式可能會因為傳輸的錯誤而產生非同步的解碼，甚至產生錯誤傳遞的情況。而為了改善其容錯的能力，越來越多的研究者投入心力在聯合訊源與通道編碼的設計領域上。一種新型的可變長度解碼器已經慢慢的浮現出來，他能夠在頻寬有限和廣播的系統當中抵抗傳輸的錯誤。而這樣的解碼方式通常需要保留許多的狀態，尤其是當編碼表格很大的時候。因此，這種新型的解碼方式在實作的時候，會產生很高的複雜度和需要很大的記憶體容量。 為了減少表格的大小和記憶體讀取的次數，我們提出了一種低複雜度和低記憶體使用量的方式。甚者，我們更提出一種 ”Symbol-alias” 的量測方法來提高對於解碼效能的猜測。利用我們所提出的 Black-Box 模型，我們可以在效能以及複雜度上取得最佳的平衡點。 最後，利用我們所提出的效能模型，一個高效能、低複雜度的可變長度解碼器已被我們實現。在可允許的效能損失之下，它不只減低了記憶體的使用量，更減少了表格的大小。而整個系統的模擬是在 MPEG-4/UDP- Lite/UEP/AWGN 的平台上所實現。無論是跟傳統的解碼或者是擁有錯誤更正能力的RVLC解碼的比較上，我們平均可以提昇畫面的品質 0.4~2.9dB ，並且提供更好的主觀品質。

Variable Length Codes (VLCs) are extensively used in recent video and image coding standard. However, traditional table look-up hard decoding may lose synchronization and induce error propagation over a noisy channel. To improve the error resilience of VLC, more and more researchers pay lots of attention about the joint source and channel design. The soft VLC decoding method has emerged to resist the channel disturbances on the environment of band-limited and broadcasting system. Such design generally needs to maintain many states when the table size grows. Hence, soft VLC decoders have problems of high complexity and high memory access. To reduce the table size and the number of memory access, we propose a soft VLC decoder with low memory access and low complexity approach. Further, a novel measurement of “symbol-alias” is presented to provide more accurate performance estimation. With the proposed Black-Box model, we can achieve the optimal trade-off between performance and complexity. Finally, a memory-efficient and low-complexity soft VLC decoder using performance modeling is proposed. It exploits not only modified sorting scheme to reduce the memory access, but also table redundancy to reduce the table size at the cost of minor performance loss. The system evaluation is achieved in the model of MPEG-4/UDP-Lite/UEP/AWGN. We averagely improve the PSNR by 0.4~2.9dB (i.e. 40~80% improvement) and offer better subjective quality compared with the traditional VLC decoding and standard-support RVLC decoding.