Iterative decoding of differentially space-time coded multiple descriptions of images

We consider transporting images over wireless fading channels rather than the on-off channels considered in most works related to multiple description (MD) coding. The idea is to treat MD coding as a special case of distributed source coding with co-located sources, and use iterative (turbo) decoding techniques developed for serially concatenated coding systems to improve the performance of the receiver with successive source decoding iterations. MDs of an input image are generated by embedded coding plus unequal error protection. The proposed receiver consists of a maximum a posterior (MAP) differential space-time decoder, an MD source decoder, an interleaver and a deinterleaver. The two decoders exchange extrinsic values or a priori probabilities of transmitted bits between themselves in successive iterations. Experimental results show that our iterative scheme can effectively improve the system performance. Furthermore, most of the gain in PSNR is achieved with only two iterations.