基於疊代解碼效能的可變長度碼設計

Abstract

本論文主要探討可變長度碼在疊代訊源通道解碼機制上的設計與應用。首先針對可變長度碼在位元層級上的籬柵結構，推導其軟性訊源解碼演算法，並將其整合運用於疊代訊源通道解碼機制。主要是針對具特定機率分佈的訊源，利用其可變長度編碼所得的殘餘冗息，再基於渦輪碼原則在疊代解碼過程中相互交換訊源及通道解碼器輸出的額外訊息。另外探討各種不同的可變長度編碼方式，並以額外資訊轉換圖加以理論分析。最後提出基於額外資訊轉換特性的可變長度碼設計，實驗証實能有效對抗通道雜訊干擾，進而提昇系統的強健性。

This thesis focuses on the variable‐length code (VLC) design using the performance of iterative source‐channel decoder (ISCD). Our work starts with a soft‐bit source decoding algorithm based on the bit‐based trellis. According to the source distribution, VLC can exploit the residual redundancy between source‐encoder indexes to enhance the robustness of the ISCD system. Then we analyze the performance of different VLC schemes, in terms of the extrinsic information transfer chart (EXIT chart). To further improve the reliability of ISCD system, we propose a new approach to VLC based on the EXIT chart. Simulation results show that the proposed VLC scheme can improve the error robustness of ISCD system.