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.
