University of Konstanz
Graduiertenkolleg / PhD Program
Computer and Information Science

Guest Talks


Intelligent Multimedia Coding over Oblivious Networking Protocols: A Case for a Cross Layer Multimedia Architecture


Dr. Syed Ali Khayam, NUST School of Electrical Engineering and Computer Science
Islamabad, Pakistan

date & place

Thursday, 01.10.2009, 14:00 h
Room C 252


Packets transmitted over wireless channels experience unpredictable and time-varying errors due to attenuation, interference, noise, contention and mobility. Multimedia content contains some inherent resilience against errors and losses. Moreover, recent multimedia coding standards support intelligent error concealment and resilience options designed to mitigate the affect of channel errors on multimedia quality at a wireless receiver. However, the underlying protocols in an IP stack are completely oblivious of these error recovery features and continue to drop all corrupted packets without regard to the number and location of errors in such packets. It has been shown that distortion in the multimedia quality at a wireless receiver can be substantially decreased if corrupted packets, instead of being dropped, are relayed to the receiver's multimedia application. The application can then decide to retain, drop or recover these packets.

In this talk, I will present a receiver-based cross-layer wireless multimedia framework that makes the lower layer networking protocols aware of the constraints of multimedia communication and relays corrupted packets to the application layer. This framework, generically referred to as Header Estimation, ignores packet payload errors at the receiver and estimates transmitted headers to relay corrupted packets to the receiver's multimedia application. These corrupted packets are then recovered using Forward Error Correction (FEC). For performance evaluation of the header estimation framework, I will focus on two important classes of MAC-layer wireless channels, namely High-order Markov and Multifractal Wavelet (MWM) channels. From a protocol perspective, I will compare performance with two prominent multimedia transport protocols, namely UDP and UDP-Lite. We will first discuss FEC redundancy lower bounds on UDP, UDP-Lite and ideal header estimation. Comparison of these bounds reveals that for any realistic wireless system, the minimum expected FEC redundancy required by header estimation is always lower than UDP and UDP-Lite. Then I will present a practical estimation-theoretic methodology to achieve near-ideal header estimation. Trace-driven video simulations at varying data rates of an 802.11b LAN will be used to demonstrate that the proposed methodology provides significantly better throughput and multimedia quality than UDP and UDP-Lite.