| Unequal error protection (UEP) for multimedia communications relies on transmitting more important data through the sub-channels experiencing lower bit error rates (BERs). In radio broadcasting, UEP is implemented by deploying multiresolution (MR) modulations which allow support for receivers close to the transmitter with higher perceived recovered image quality, while receivers farther away experience acceptable quality.;In addition, we also investigate new alternative 2-D constellation designs which, unlike the MR modulation schemes discussed earlier, are 'semi-multiresolutional' in nature. We analyze the performance of several such semi-multiresolutional constellations and conclude on their effectiveness in image broadcasting from the results obtained.;This research proposes a new approach to design MR modulations for such an image broadcasting scenario that optimizes the near receiver quality by exploiting the inherent scalability in image compression and UEP flexibility in 2-D modulation schemes. Specifically, MR modulation parameters are investigated for optimized system performance by (i) allocating different percentage of priority bits to sub-channels created through bit-to-symbol mappings with different UEP and (ii) adjusting the minimum distances in the superimposed constellations. This new framework for the design of MR modulations proposed in this thesis effectively integrates constellation distances and priority bit assignments, resulting in optimized joint source-channel coding for near and far receivers. We present the simulation results for near and far receivers' image quality in two-tier radio broadcasting system with additive white Gaussian noise (AWGN). The results show clear variations in the optimum set of modulation parameters obtained following an adopted cost criterion. The results are obtained for different carrier to noise ratios, and different cost factors in our cost criterion. Thus, the optimization strategy for channel modulation utilized in this research leads to a solution to problem of designing efficient modulation schemes given the input parameters or constraints in the communication system. |
