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In wireless communication systems, traditionally, the physical, medium access layer, network/transport and application layers have been designed in isolation. In other words, no interaction between such layers have been taken into account in the design. This “layered” optimization leads to a simple, independent implementation, but clearly results in sub-optimal multimedia service performance. Alternatively, wireless systems may optimally adapt their multimedia compression (application layer), transmission (physical layer and network layer) and resource allocation (medium access layer) strategies jointly across the protocol stack in order to satisfy a given QoS requirement across the user population, while maintaining spectral efficiency over the wireless channel. Such a design is called a cross-layer design. We firmly believe that cross-layer design is a requirement for efficient wireless air interface design for a specific multimedia service [1,2,6]. A T\”{u}bitak Career Award has been received on cross-layer design for wireless multimedia networks in 2005.

Cross-Layer Design for Wireless Video

The state-of-the-art video coding technique, H.264, enables the encoder to adjust the rate-distortion point of operation through a number of quantities, such as the group of pictures (GOP) size, video frame rate, intra period, and quantization parameters. Various error concealment techniques have been proposed for the H.264 codec as well. Traditionally, the physical and MAC layers of wireless systems are tuned to operate at the 1\% packet error rate. This value is inherited from the voice-centric designs of yesteryears. We propose a cross-layer design where the physical layer error correction algorithms, H.264 encoding parameters as well as the wireless system packet error rate operating point are jointly selected to achieve maximum QoS across the user population and maximum network capacity simultaneously using a multiple-objective optimization framework.