Robust Video Communication Over Wireless Packet Networks

by

Gubbi R. Rajugopal

1997 Ph. D. Thesis

Abstract

This thesis is an investigation of a high performance universal video communication system for mobile (indoor or outdoor) environment with an ATM backbone network. This work is in line with the upcoming MPEG-4 proposals which is being planned for future systems. Channel and Bandwidth constraints in mobile environment limit the achievable data rate. However, the end users demand a good quality video and would prefer gracefully degrading video quality with decrease in available Bandwidth. The two main issues addressed are video compression and channel adaptation of the system.

A good source coder is required to provide high compression gain and gracefully degrading video quality with decrease in the available Bandwidth. Also it is known that variable bit rate (VBR) source coders outperform constant bit rate source coders under network transport conditions. Hence investigation of combination of wavelet transform, multi-resolution motion estimation and zero tree coder is a good choice for VBR video compression at low bit rates. Robust design of zero tree coder is proposed to make the source coder error resistant under hostile environment.

We suggest two stages of channel coding, with unequal error protection at the inner stage to better protect the data of higher importance. Varying channel conditions demand dynamically changing error protection for better use of bandwidth. A source level rate controller is proposed to enable adaptation to the channel conditions and to provide VBR video. The rate controller needs to efficiently analyze the channel conditions and adjust the system parameters for the best performance. It is suggested to sense the channel at the receiver and send it as a feedback. This information is further processed and used by the rate controller to dynamically adapt the system. Outer channel coding is suggested to be as per standard air interface specifications such as in CODIT, DECT, etc.

Another important system requirement fulfilled is the requirement of low overhead when the source coder robustness or the channel adaptation are not required. This will be the case at low BER (or CLR) environments. The Robust design of source coder and dynamic channel adaptation of the system without much overhead enables its application in a variety of channel conditions like narrowband, broadband, indoor and outdoor.

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