Transmission of multimedia signals over wireless networks poses several challenges that do not exist in wired networks. Bandwidth limitations of the wireless channel, interference from multiple users operating in the same band and channel variations due to fading become bottlenecks for typical multimedia applications that require high bandwidth and an error resilient communication medium.
This research outlines a cross-layer approach between the application layer and the physical layer to maintain desired end-to-end signal quality for multimedia transmission over bandwidth and power limited multiuser wireless channels. 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.
This project addresses joint source and channel coding for the fundamental building blocks of a wireless network, including single user (point-to-point), multiple access and relay 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.
Our project also considers practical applications, in particular unicast and multicast wireless video. The emphasis is on cross-layer design to improve the quality of wireless video transmission using cooperative networking.
One of our papers in this area, “Minimum expected distortion in Gaussian joint source-channel layered broadcast coding with successive refinement,” was selected for the Student Paper Award at ISIT 2007.
This research is partly funded by NSF through grants #0093163, #0430885, #0635177.