Simple channel sounders for underwater acoustic communications in the presence of double selective channel environments

This paper proposes channel sounders suitable for time and frequency selective channels, i.e., double selective channels, inevitable in underwater acoustic communications (UWAC). As double selective channels in UWAC are highly dependent on their times and places, it is difficult for UWAC to define typical channel models. This paper proposes channel sounders, which transit maximum-length (M) sequence and detect channel impulse response (CIR) using cyclic correlation of M sequence. The proposed channel sounders with cyclic correlator can precisely detect time-varying CIR sets with small time interval. This is because the proposed cyclic correlator derives CIR sets using the received signals with the same time span. Finally, this paper reports field evaluation results of CIR in shallow environments of Lake Biwa, assuming water depth of around 3m.