OFDM based low-complexity time of arrival estimation in active sonar

Estimation of bottom profile is one of the important geo-acoustic reversal problems in underwater acoustics that gives an idea about depth and structure of the sub-bottom layers of the ocean. Estimation of time of arrival (TOA) of bottom and sub-bottom reflections are the key to these estimations. To estimate TOAs from different bottom layers, an active sonar transmits a signal and receive its bottom reflections. In the literature, chirp, a frequency modulated signal is described as the best candidate for the transmitted signal. In this paper, it is shown that an orthogonal frequency modulated (OFDM) signal can also be used as a strong candidate for transmitted signal in active sonar. The proposed OFDM based TOA estimation technique is expected to give superior results in terms of complexity, parallelism, noise reduction and memory requirement compared to the existing chirp based technique.