Subcarrier Mapping for Underwater Video Transmission Over OFDM

We study the transmission of high-quality video underwater. The underwater acoustic medium pathloss attenuation depends not only on transmission distance but also on the frequency occupied by the signal, where lower frequencies have lower attenuation for a given distance. We propose cross-layer design algorithms that exploit this frequency-dependent attenuation by connecting channel reliability to the structure of the compressed video. The video data are categorized based on their importance. Orthogonal frequency-division multiplexing is adopted as the modulation technique, such that different data can be sent on different frequencies. The underlying communications system accompanied with a noise analysis is developed in this article. The signal and noise statistics are used in the simulations to represent the underwater channel. We propose three new techniques and compare them to three baseline techniques. In the proposed techniques, important video information is transmitted on the least attenuated frequencies while less important data are transmitted through higher frequencies. Simulation results show that at least one of our proposed techniques can achieve significant improvements in the peak signal-to-noise ratio in comparison to the baseline techniques.