| Accurate ranging and positioning between autonomous underwater vehicles(AUVs)have an irreplaceable role in accomplishing some important tasks,and is of great significance in achieving the synergy of multiple AUVs.However,in the face of extremely complex underwater acoustic channels,especially for shallow water AUVs,sonar-based ranging methods are susceptible to factors such as underwater acoustic multipath and time-varying,and the implementation principles are relatively complex.Therefore,this paper conducts research on underwater acoustic ranging technology in shallow sea multipath environments,focus on underwater acoustic signal synchronization,multipath delay detection,and underwater acoustic ranging using multipath delay.specific tasks include:Aiming at the problem of large amount of synchronization acquisition when msequences are used as transmission sequences in underwater acoustic ranging or communication systems,this paper proposes to use composite codes as synchronous transmission sequences in underwater acoustic ranging systems.at the same time,Aiming at the problem of multipath delay detection error caused by the three-valued autocorrelation characteristics of the composite code,a logical combination method is proposed to construct the regenerated composite code,It not only supports the receiving end to quickly and accurately synchronize the signals,but also supports the receiving end to more accurately extract the multipath delay using the regenerated composite code.Furthermore,under shallow sea multipath and noise environment,a simulation experiment was performed on the synchronous acquisition performance of the composite code using the sliding correlation method.The experimental results show that in shallow sea multipath and low signal-to-noise ratio(-10 d B)environment,the accuracy of synchronously capturing composite codes can reach 100%.In the process of synchronously capturing a composite code,the maximum number of correlation operations is the sum of the periods of each subcode.Compared with the synchronous acquisition process of m sequences of the same length,the correlation operation of system volume is greatly reduced.Aiming at the problem that the generalized cross-correlation multipath delay detection algorithm is susceptible to the noise of the shallow sea environment,this paper proposes an improved generalized cross-correlation multipath delay detection algorithm with improved weighting function,which improves the accuracy of the multipath delay detection in a low signal-to-noise environment.In addition,by introducing a matching function,a method of matching the multipath delay with the propagation path is proposed,and it is applied to the composite code underwater acoustic ranging method for shallow multipath delay to reduce the error of the ranging method.Furthermore,under shallow sea multipath and noise environment,simulation experiments are performed on the improved cross-correlation multipath time delay detection algorithm with improved weighting function and the composite code underwater acoustic ranging method based on shallow sea multipath time delay.Experimental results show that the improved generalized cross-correlation multipath delay detection algorithm with weighting function can suppress noise interference,sharpen correlation peaks,and improve the performance of multipath delay detection algorithm.Based on this,the performance of a composite code underwater acoustic ranging method based on shallow sea multipath delay under different environmental conditions is analyzed. |
