Fresnel Domain Sector Modulation LFM Signal for Underwater Integrated Communication and Detection

The Internet of Underwater Things (IoUT) technology has been gaining importance in smart ocean investigation in recent years. The integrated system for underwater detection and communication (ISUDC) is considered a crucial technique for IoUT due to its potential to decrease equipment size and power consumption. The linear frequency modulation (LFM) signal has the characteristics of large time-bandwidth product and has great advantages in detection. However, it has high complexity and low robustness of communication in ISUDC. To address this issue, this article proposes a sector-modulated LFM (SM-LFM) signal for ISUDC. In terms of communication, it divides Fresnel domain into equal length sectors. Then, data is loaded by activating different sector. At the communication receiver, by establishing a relationship between the Dirac function in the Fresnel domain and the channel impulse response (CIR) in the time domain, data is demodulated by finding CIR’s main path without channel estimation or equalization. In terms of detection, SM-LFM has an improvement in the maximum unambiguous velocity by calculating relative radial velocity in the Fresnel domain instead of the frequency domain. Numerical simulations and lake experiments have confirmed that the SM-LFM signal can deliver superior robustness and easy-to-use advantages for underwater active detection and communication.