CUDA架構下針對低密度奇偶校驗碼為基礎之分散式編碼的近即時解碼設計

Abstract

Wyner-Ziv (或簡稱WZ) 視訊編碼為分散式視訊編碼 (或簡稱DVC) 的一種實作，它基於Wyner-Ziv 的理論，主要針對視訊資料之間的資料相關性進行失真壓縮。這種新的壓縮方式，在計算複雜度上因為擁有簡單的編碼器和極複雜的解碼器特性而受到重視，其解碼器的複雜度來自於Slepian–Wolf解碼。雖然近年來，許多能有效改進WZ 視訊編碼壓縮效率的方法被提出，目前大部分被提出的WZ視訊編碼，其解碼端的時間延遲都非常的長，這對於即時性要求較高的應用裡，WZ 視訊編碼失去了其實用價值。在這篇論文中，我們使用CUDA架構，針對低密度奇偶校驗碼（目前壓縮效能最好的Slepian–Wolf解碼器）中的sum-product 演算法(或簡稱SPA)，提出一個高度平行化的設計。再者，我們在CUDA上提出的收斂偵測機制，能消除CPU和GPU之間的傳輸延遲。實驗結果顯示，在QCIF大小下，（監控）影片格式能夠被即時解碼，其他格式也有至少每秒五張的解碼速率。影片在解壓縮的過程中，和平行化之前相比，都能維持非常高的壓縮比以及極低的失真率。

Wyner-Ziv (WZ) video coding – a particular case of distributed video coding (DVC), is based on the Wyner-Ziv theorem for lossy coding of correlated video sources. This new coding paradigm is well known for its low-complexity encoding and high-complexity decoding characteristics, where the high decoding complexity is mainly due to the intricate procedures of Slepian–Wolf decoding. Although some works have been made in recent years, especially for improving the coding efficiency, most reported WZ codecs have high time delay in the decoder, which hinders its practical values for applications with critical timing constraint. In this paper, a fully parallelized sum-product algorithm (SPA) for low density parity check accumulate (LDPCA) codes is applied through Compute Unified Device Architecture (CUDA) based on General-Purpose Graphics Processing Unit (GPGPU). Furthermore, we proposed a novel early stop detection mechanism, implemented on CUDA, which substantially eliminates the communication latency between CPU and GPU. Experimental results show that, through our work, QCIF (surveillance) videos can be decoded in real-time and videos in other formats can reach to at least 5.01 frames per second in terms of decoding speed. All videos are decoded with extremely high quality and negligible rate-distortion (RD) loss.