Joint Source and Channel Coding for Wireless Networks

无线网络设计带来了有线网络中不存在的几个挑战。无线介质具有随机时变、无线信号的广播性造成干扰、无线频谱有限以及移动终端电池较小等特点。对于无线多媒体和低功率传感器网络等应用，这些功能变得特别有限，在这些应用中，在给定特定系统资源的情况下，很难保持端到端的信号质量。本研究概述了应用层和物理层之间的跨层方法来解决这些问题。目标是设计联合信源和信道编码技术以最小化端到端的信源失真。无线网络中一般的信源和信道分离定理并不存在；Shannon的信源和信道分离编码设计的最优性对于非遍历衰落信道或多用户通信系统是不成立的。另一方面，即使在信源和信道分离不是最佳的情况下，也希望在信源和信道编码器之间仅具有松散耦合以简化设计。该研究针对无线网络的基本构建块，即单用户(点对点)、多路接入、广播和干扰信道，进行联合信源和信道编码。系统模型通常涵盖不同的通信场景：允许源信号之间的相关性，接收器可能具有相关的边信息，信道可以是时不变的或可能存在衰落，链路可以具有多个自由度，例如多个天线或多个衰落块。该项目研究了最优联合信源和信道编码策略的设计，以及当源和信道编码器之间允许最小交互时的性能改进。目标是发现在哪些情况下分离是最佳的，或者接近最佳的。信息理论结果将得到无线信道上视频传输的分析和实验研究的补充。

Wireless network design poses several challenges that do not exist in wired networks. The wireless medium suffers from random time variations, the broadcast nature of wireless signals causes interference, the wireless spectrum is limited and mobile terminals have small batteries. These features become especially limiting for applications such as multimedia over wireless and low power sensor networks, where maintaining the end-to-end signal quality given the specific system resources is difficult. This research outlines a cross-layer approach between the application layer and the physical layer to address these problems. The objective is to design joint source and channel coding techniques to minimize the end-to-end source distortion. A general source and channel separation theorem for wireless networks does not exist; optimality of Shannon's separate source and channel code design fails for non-ergodic fading channels or for multiuser communication systems. On the other hand, even when source and channel separation is not optimal, it is desirable to have only a loose coupling between the source and channel coders to simplify the designs. The research addresses joint source and channel coding for the fundamental building blocks of a wireless network, namely single user (point-to-point), multiple access, broadcast and interference channels. The system model is general to encompass different communication scenarios: Correlation among the source signals is allowed, the receivers may have correlated side information, the channel can be time-invariant or fading may be present, links can have multiple degrees of freedom such as multiple antennas or multiple fading blocks. This project investigates the design of optimal joint source and channel coding strategies, and performance improvements when minimal interaction among the source and channel coders is allowed. The goal is to discover scenarios under which separation is optimal, or close to optimal. The information theoretic results will be complemented by analytical and experimental studies for video transmission over wireless channels.