Dictionary-Theory-Based Orthogonal Chirp Division Multiplexing Signal for Integrated Sonar and Communication System

The integrated sonar and communication (ISC) system plays an important role in smart ocean engineering, owing to its convenience in environmental perception and communication. The characteristics of the integrated signal and the signal processing methods are critical to the ISC system's performance. Orthogonal chirp division multiplexing (OCDM) signal is considered as a potential integrated signal due to its robustness in communication as well as excellent detection performance. However, insufficient bandwidth and subcarrier spacing can significantly degrade the performance of OCDM-based ISC system due to the severe Doppler expansion of the underwater acoustic (UWA) channel. In this paper, we introduce the dictionary theory into the multicarrier signal design and propose a new Dictionary-theory-based orthogonal chirp division multiplexing (Dic-OCDM) signal. We consider the chirp signal as the basis function. The geometric transformation in structure dictionary design is implemented to rearrange the basis function, resulting in the dictionary-theory-based discrete Fresnel transform (Dic-DFnT) matrix. The Dic-DFnT matrix is regarded as the modulation matrix of Dic-OCDM and provides a larger subcarrier spacing without requiring additional bandwidth. Besides, a Dic-OCDM based ISC system is designed, and corresponding signal processing methods for detection and communication are given. Simulation and lake experiment results attest to the effectiveness of our proposed Dic-OCDM-based ISC system for underwater active detection and communication.