Objective In mobile underwater acoustic communication systems based on orthogonal chirp division multiplexing (OCDM), the coupling effects of multipath propagation and Doppler shifts can significantly degrade localization accuracy. To address this issue and overcome the limitation of conventional approaches that treat multipath components merely as interference, a joint delay–angle elliptic localization method is proposed for integrated sensing and communications (ISAC).
Methods First, a spatio-temporal signal reception model for Fourier-transform-precoded OCDM (FT-OCDM) signals received by a transducer array is established, and a three-dimensional steering vector incorporating delay, angle, and Doppler frequency is derived. The Doppler frequency is estimated and compensated in the Fresnel domain, after which super-resolution joint delay–angle estimation is performed using the multiple signal classification (MUSIC) algorithm. Subsequently, parameter pairing is achieved by exploiting the uniqueness of the Doppler frequency, and the channel parameters (delay and angle) are transformed into localization parameters (range and bearing). Finally, an elliptic localization scheme is developed by exploiting the geometric relationship between the line-of-sight path and single-bounce reflected paths, enabling the simultaneous estimation of the positions of the transmitter and reflectors from the receiver side.
Results Simulation results under dense-multipath and shallow-water conditions demonstrate that, at the specified high-speed conditions (i.e. v = 10, 13, 15 m/s), the proposed method reduces the relative root-mean-square error (RRMSE) of delay estimation by approximately 16.28 dB compared with orthogonal frequency-division multiplexing (OFDM). At a signal-to-noise ratio (SNR) of 0 dB, the localization resolution for both the transmitter and the reflectors in shallow-water conditions reaches approximately 1.00 m.
Conclusion The proposed method enables high-precision joint delay–angle estimation and localization in the presence of significant Doppler effects. By effectively exploiting multipath information, it provides a new technical approach to the design of integrated sensing and communications (ISAC) systems for underwater ship-cluster collaboration.
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