Signal Processing for High Speed Underwater Acoustic Transmission of Image (March 2007)

In this paper, a signal processing method for high-speed underwater acoustic transmission of image is presented. It has two parts. Part 1 is underwater acoustic coherent communication signal processing. Part 1 includes 3 technical points. 1. Doppler shift compensation. Chirp signals are inserted between data packages. A correlation process between two copy correlation results gives more accurate estimation of the mean Doppler shift. Resample the data to compensate it. In feedback adaptive equalizer an adaptive phase compensator with fast self-optimized least mean square (FOLMS) adaptation algorithm is utilized resulting in better motion tolerance than compensators with 2nd order PLL algorithm. The performance of the combination of mean Doppler shift compensation and adaptive phase compensator is quite good. 2. A combiner is used in advance of equalizer. Both combiner and feedback adaptive equalizer are based on FOLMS adaptation algorithm and have reduced computation complexity and good performance. 3. Cascaded equalizer and Turbo-TCM decoder and the iteration algorithm. A new bit-symbol converter based on Soft Output Viterbi Algorithm (SOVA) is studied. Comparing with the traditional decision, coding and mapping algorithm, new converter can reduce BER by nearly 2 orders. Part 2 is a robust image compression algorithm. In high-speed underwater acoustic image transmission, there are always some error bits. Ordinary image compression algorithms, for example, JPEG and JPEG2000, are sensitive to error bits. One error bit may destroy whole image. So they are not suitable for high-speed underwater acoustic image transmission.