Coding and signal processing of an underwater electromagnetic communication system

Working in a narrowband channel with severe interference and noise is one of the challenges for communication under water with low frequency electromagnetic signals. It is found from experiments that the underwater electromagnetic channel is disturbed by time varying strong narrowband interference from various power systems. The channel acts as a sharp low pass filter that makes base band signaling suitable. We have developed a channel model with help from experimental data. We studied Trellis coded modulation, adaptive whitening of the interference components, interleaving and Viterbi decoding that together define the communication system. Trellis coded modulation is used for improving the reliability of a digital transmission system without increasing the transmitted power or the required bandwidth. At the receiver an interleaver against burst noise and a Viterbi decoder follows the adaptive whitening algorithm. We verified the properties of the communication system through extensive simulations. When the final simulation of the system was preformed we saw that our coded signal provided a result which was 7 times better than the uncoded signal at a SNR about 5 dB and at SNR about 9 dB the result is 10 times better than the uncoded signal.