A vector set partitioning noisy channel image coder with unequal error protection
A vector enhancement of Said and Pearlman's set partitioning in hierarchical trees (SPIHT) methodology, named VSPIHT, has been proposed for embedded wavelet image compression. A major advantage of vector-based embedded coding with fixed length VQs over scalar embedded coding is its superior robustness to noise. We show that vector set partitioning can effectively alter the balance of bits in the bit steam so that significantly fewer critical bits carrying significant information are transmitted, thereby improving inherent noise resilience. For low noise channels, the critical bits are protected, while the degradation in reconstruction quality caused by errors in noncritical quantization information, can be reduced by appropriate VQ indexing, or designing channel optimized VQs for the successive refinement systems. For very noisy channels, unequal error protection to the critical and noncritical bits with either block codes or convolution codes are used. Additionally, the error protection for the critical bits is changed from pass to pass. A buffering mechanism is used to produce an unequally protected bit stream without sacrificing the embedding property. Extensive simulation results are presented for noisy channels, including bursty channels.