Identification Research On Modulation Method And Parameters Of Underwater Acoustic Communication Signal

Automatic modulation identification and parameter estimation of communication signals have always been a research hotspot in the field of underwater acoustic communication.In non-cooperative communication,there is no prior knowledge,the time-space variability of underwater environment,the serious multipath effect and doppler effect of underwater acoustic channel,so it is very difficult to intercept the information carried by the unknown signal.Aiming at the non-cooperative communication in the field of underwater acoustic communication,this paper overcomes the influence brought by underwater channel and under the condition of lacking prior knowledge,extracts the recognition characteristic parameters of received signals to realize the blind recognition of unknown signals.The innovation and main research contents are as follows:1.In non-cooperative communication,carrier frequency estimation,symbol width estimation and modulation mode identification are theoretically analyzed and experimentally researched based on measured ocean channels and noise.And pool and sea experiments were carried out.2.This paper proposes a code-width estimation algorithm based on Hilbert transform,and verifies the feasibility of this algorithm through the derivation of formula and the high accuracy of simulation.Compared with the algorithm based on Haar wavelet transform in the underwater acoustic channel with gaussian white noise,the estimation accuracy of this algorithm is higher under AWGN condition.3.The paper extracts the ratio of the maximum frequency coefficient to the length and the instantaneous frequency to classify the MASK signal,MFSK signal and MPSK signal.The MASK signal is identified by the amplitude compactness index,the number of the peak values of the spectrum and the average coefficient of the envelope are used as the characteristic parameter of MFSK signal recognition.4.The paper proposes the modulation recognition algorithm based on the quadratic spectrum of MPSK signal,and the ratio of the maximum spectrum coefficient of the quadratic spectrum to the spectrum length is obtained as the identification parameter to distinguish 2PSK signal from 4PSK signal.Compared with the recognition algorithm based on high-order cumulant,this algorithm has better robustness and anti-noise performance.5.For the proposed algorithm of parameter estimation and modulation recognition,and considering the transmission characteristics of underwater channel,the pool experiment shows that the estimation error of carrier frequency is less than 0.1%,and the modulation recognition accuracy can reach 94.7%.And the robustness of the proposed algorithm is verified by sea trial data.