Variable Modulation and Bit Energy Optimization for Transmission of Compressed Images

Efficient image transmission over wireless networks is challenged with the limited bandwidth and time-varying nature of the underlying channels. In this paper, we propose a joint variable modulation and power allocation scheme for transmission of compressed images. In our scheme, the modulation level and allocated power are jointly optimized to minimize the mean square error (MSE) of the reconstructed image. We investigate fixed level 16-QAM modulations as well as variable M-QAM with adaptive power allocation. We also introduce an off-line iterative algorithm that finds the optimum combination of modulation and power allocation. Simulation results show that significant improvements in the MSE (in the order of 2~4 dB) and bandwidth efficiency have been achieved when compared to fixed power and modulation level schemes.