Bandwidth efficient and error resilient image coding for Rayleigh fading channels

Abstract

The transmission of still images over wireless channels is an exercise in tradeoffs. For bandwidth efficiency, a high source compression rate is required. However, the transmission must be robust towards channel errors since wireless channels are subject to fading. These are conflicting requirements. High source compression rates result in images that are very vulnerable to any single bit error. Low-rate channel coding to protect highly compressed images from channel errors drastically reduces the bandwidth efficiency. The combinations of set partitioning in hierarchical trees (SPIHT) wavelet based source coding and list Viterbi (1971) algorithm (LVA) for channel decoding allows for bandwidth efficient, error resilient image transmission over wireless channels. SPIHT offers compression superior to existing DCT and fractal based algorithms. LVA decoding outperforms conventional Viterbi decoding at the expense of an increase in complexity. We construct a system model to transmit raw images over AWGN and narrowband Rayleigh fading channels with SPIHT source coding and LVA decoding using rate compatible punctured convolutional (RCPC) codes. We also propose a method of unequal error protection over the channel. We show that this scheme is superior to equal error protection under the premise that there is a minimum acceptable level of image quality below which the received image has no utility.