Acoustical Frequency Hopping Communication Method Resisting Multipath in Shallow Water

Intersymbol interference(ISI) due to shallow water multipath seriously influences underwater acoustical communication. To resist multipath and ISI in acoustical communication, a single filter receiving method and a new method, namely preprocessing frequency hopping filtering method, were adopted simultaneously. A controlled preprocessing frequency hopping filter was added before mixing frequencies of signal receiving system to strengthen resistance against multipath and ISI. The method was simulated respectively on two frequency hopping sequences of PN code and increasing sequence. Simulation results show that the bit error rate(BER) can be decreased by using the increasing frequency hopping sequence. The BER reaches 10^-4 when signal noise ratio(SNR) is greater than 10 dB and energy ratio of series interference signal to direct arrival signal is litter than 0.6.