DFEC: Dynamic Forward Error Control for DVB-H

DVB-T (數位電視廣播-地面廣播)已經逐漸普及，歐洲電信標準協會(ETSI)正在發展DVB-H (數位電視廣播-手持系統)，其特點為低功率消耗、高位元錯誤率容忍度，以及使用者可以在各網路細胞間以不同速率自由地移動。要達到這樣的目標，DVB-H提供了額外之理德-所羅門碼，以增進對行動需求的支援。 我們提出了一個適應性錯誤更正系統的方案，結合了DVB-H上的互動回饋頻道及理德-所羅門碼，在傳輸端根據目前的頻道環境，調整額外之理德-所羅門碼的位元組數，以達到即時反應環境變化的目標。此外，因應逐漸增加的資訊服務，我們也提供不同的演算法，分別適合錯誤容忍度高的多媒體資料與錯誤容忍度低的程式資料類別這二種需求。 實驗結果顯示我們所提出的DFEC系統，僅需要增加些許系統之複雜度，就能在持續變化的頻道環境中，獲得較大的流量，並且維持在很低的位元錯誤率。DVB-H is a terrestrial digital TV standard which consumes less power and allows user to move freely when receiving signals. Additional Reed-Solomon codes are also included as an option to cope with higher channel error rate in mobile environment. However, it is designed with fix-valued link layer parameters, such as coding rates and error rates. In mobile networks, channel conditions change from time to time, thus code rates that behave well in one case may become inadequate in another. On the other hand, to implement static and highly protective codes results in low throughput. In this thesis, we propose Dynamic Forward Error Control Scheme (DFEC) that adapts to different channel conditions. Depending on the content carried, DFEC provides suitable error control for channels under various conditions. Simulations show that it offers better throughput, which could translate to power saving for the system.Abstract...................................................................................................................... i Acknowledgement...................................................................................................... iii Table of Contents........................................................................................................... iv Chapter 1 Introduction................................................................................................ 1 1.1 Introduction to DVB-H..................................................................................... 1 1.2 Motivation......................................................................................................... 4 1.3 Related Works................................................................................................... 5 1.4 Thesis Organization.......................................................................................... 6 Chapter 2 Preliminaries........................................................................................... 8 2.1 Overview of Forward Error Correction............................................................ 8 2.2 Reed-Solomon Code......................................................................................... 10 2.2.1 Encoder....................................................................................................... 11 2.2.2 Decoder...................................................................................................... 12 2.3 Convolutional Code.......................................................................................... 15 2.4 Return Channel................................................................................................. 16 Chapter 3 System Architecture................................................................................ 18 3.1 Overview........................................................................................................... 18 3.2 Multimedia Content.......................................................................................... 20 3.3 Program Data.................................................................................................... 22 3.4 Channel Model.................................................................................................. 24 3.5 Assumptions for Multiple Receivers................................................................. 25 Chapter 4 Improved Simulation Model….............................................................. 27 4.1 Original Model.................................................................................................. 27 4.2 Improved Model................................................................................................ 28 Chapter 5 Simulation Results.................................................................................. 31 5.1 Environment Sets.............................................................................................. 31 5.2 Multimedia Content.......................................................................................... 33 5.3 Program Data.................................................................................................... 35 5.4 Robustness in Noisy Channel........................................................................... 37 5.5 System Tuning.................................................................................................. 39 Chapter 6 Conclusion and Future Works........................................................................... 42 Bibliography........................................................................................................................... 4