Comparison of two underwater acoustic frequency-hopping communication schemes under low sound energy condition

Underwater acoustic(UWA) channel is a complex channel that is time-varying,space-varying and frequency-varying.UWA communications suffer from interferences due to multi-path,ambient noise and Doppler shift.Frequency hopping spread-spectrum(FH-SS) provides good performance to UWA communi-cations that require strict security and interference immunity.In a simulation environment,correlation,ba-lance,power spectrum and multi-address of m-sequence and chaotic sequence based on two-dimension mapping have been studied.An UWA communication framework utilizing FH-SS under low sound energy condition is proposed.Implemetation of coding and decoding has been presented.The system is composed of activated signal,synchronization signal,time delay signal and three groups of(15,11) Hamming code.Dual diversity is employed both in time and frequency for decoding and error correction.System security is improved and error rate reduced.Field experiments show that both m-sequence and chaotic sequence are feasible in UWA FH-SS communications.Comparison has also been made.As the number of chaotic sequences is enormous and they perform excellently in terms of correlation,they are suitable to be applied to multi-access communications and UWA communications requiring high security.Therefore chaotic sequences have good prospects in UWA communication.