Robust progressive image transmission over OFDM systems using space-time block code

A joint source-channel coding (JSCC) scheme for robust progressive image transmission over broadband wireless channels using orthogonal frequency division multiplexing (OFDM) systems with spatial diversity is proposed for the application environments where no feedback channel is available such as broadcasting services. Most of current research about JSCC focus on either binary symmetric channel (BSC) or additive white Gaussian noise (AWGN) channels. To deal with fading channels in most of previous methods, the fading channel is modeled as two state Gilbert-Elliott channel model and the JSCC is normally aimed at the BER of bad channel status, which is not optimal when channel is at good status. By using diversity techniques and OFDM, the frequency selective fading effects in broadband wireless channels can be significantly decreased and we show that subchannels in OFDM systems approach Gaussian noisy channels when the diversity gain gets large, as a result, the system performance can be improved in terms of throughput and channel coding efficiency. After analyzing the channel property of OFDM system with spatial diversity, a practical JSCC scheme for OFDM system is proposed. The simulation results are presented for transmit diversity with different number of antennas and different multipath delay and Doppler spread. It is observed from simulations that the performance can be improved more than 4 dB in terms of peak signal-to-noise ratio (PSNR) of received image Lena and the performance is not very sensitive to different multipath spread and Doppler frequency.