Doppler Shifts Estimation In Underwater Acoustic Communication

It is well known the speed of sound in the underwater acoustic communications is farless than the speed of electromagnetic waves in the land wireless communications. The lowvelocity of acoustic waves and the use of wide-band modulation result in several orders ofmagnitude greater than those experienced in EM transmission, and Doppler shifts estimationis an important research direction of underwater acoustic communications.The underwater acoustic communication system is a complex communication process,acoustic wave affects by the propagation loss, multipath delay, environmental noise andDoppler effect when it propagates in underwater. And in different regions and different depth,the acoustic velocity will be different. So the underwater acoustic channel is a complicatedand challenging channel. Relative motion of the transmitting and receiving elements isusually unavoidable, thus Doppler-effect will be caused. The relative motion and smallacoustic velocity (relative to the EM wave) determine the amount of Doppler extension orDoppler compressed, in other words Doppler should not be neglected. In order to ensure theaccuracy of the underwater communication and reduce the bit error rate, we need to take somesolutions to eliminate the influence of the Doppler. General approach is to estimate theDoppler factor and then compensate the Doppler shifts. In a word, Doppler estimation is avery important part of the underwater communications.This paper presents a based-on the training sequence Doppler estimation method. Firstly,construct the theory of noiseless received signal. Next obtain the minimum mean square errorof the theoretical received signal and the actual received signal, so we can establish atwo-objective optimization function which can be converted into single objective function.Through using the interval slope algorithm to solve the multimodal objective function withina limited range, then we can obtain the estimated value of the Doppler factor.The innovation point of this paper is the method of solving dual-objective function. Onepoint is the application of the interval slope algorithm, and another is converting thedual-objective function into a nested loop.