Cross-Layer Approach for Reliable Transmission of Wavelet Coded Images over Portable Multimedia Devices

Transmission of compressed images over portable multimedia devices is a challenging task due to high error rate wireless channels, fluctuating and limited bandwidth availability and low energy requirements. Wavelet-based embedded (or progressive) image coders are most suited to cope with time varying channel bandwidth of wireless networks. These coders have excellent rate-distortion performance but they are extremely sensitive to channel errors. Several error resilient image coding techniques have been proposed in order to minimize the effects of transmission errors. Among these, unequal error protection (UEP) of coded image bitstream is one of the most successful techniques, where important bits have a higher protection than the rest of the bitstream. Conventionally, the forward error correction (FEC) based UEP is applied at the application layer. Alternatively, UEP can also be provided using hierarchical modulation approach at the physical layer. In this chapter, we discuss the cross-layer design methodology for UEP that rely on interaction between the application layer and the physical layer to achieve reliable and high quality end-to-end performance in wireless environments. The discussion is mainly focused on set partitioning in hierarchical trees (SPIHT) image coder, but it is applicable to other progressively coded bitstreams as well.