Joint Source and Channel Coding for Wireless Networks

无线网络设计提出了有线网络中不存在的几个挑战。无线介质受到随机时间变化的影响，无线信号的广播性质引起干扰，无线频谱有限，移动终端的电池小。对于无线多媒体和低功耗传感器网络等应用来说，这些特性尤其受到限制，因为在这些应用中，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。目标是设计联合源和信道编码技术，以最大限度地减少端到端源失真。一般的无线网络源信道分离定理不存在；对于非遍历衰落信道或多用户通信系统，香农分离源信道码设计的最优性失效。另一方面，即使源和信道分离不是最优的，也希望源和信道编码器之间只有松散耦合以简化设计。该研究解决了无线网络基本构建块的联合源和信道编码，即单用户（点对点）、多址、广播和干扰信道。系统模型是通用的，以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侧信息，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。本项目研究了最优联合源和信道编码策略的设计，以及在允许源和信道编码器之间最小交互时的性能改进。目标是发现分离是最优或接近最优的情况。信息理论的结果将被无线信道视频传输的分析和实验研究所补充。

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.