# Design of an Underwater Acoustic Waveform and Integrated System for Communication and Detection
## 1 Introduction
A multi-function RF architecture based on linear frequency modulation (LFM) was proposed by [PERSON] [19]. In this system, up-LFM is used for communication while down-LFM is used for radar detection. These waveforms are superimposed and occupy the same frequency band, but separate receivers are used for communication and detection. The second category is based on communication waveforms. With this approach, a communication waveform is modified or directly used for detection. An integrated radar-communication waveform based on minimum shift keying (MSK) direct sequence spread spectrum was proposed by [PERSON] [20]. The spread spectrum is used to improve the autocorrelation of the digital baseband signal. It also has excellent ambiguity to meet detection requirements. The third category is based on radar waveforms. In this case, the data are modulated onto the radar waveform. A multi-input multi-output (MIMO) design was proposed by [PERSON] that embeds data onto an MIMO radar waveform using frequency hopping [21]. Phase shift keying (PSK) is used to modulate the data in each frequency hopping interval. The data rate is a function of the number of transmit antennas and the pulse repetition frequency. The superposed shared waveform features simple modulation, but the straightforward superposition of communication and detection signalsleads to significant interference between the two types of signals, making signal separation and information processing difficult. The shared waveform based on the communication waveform ensures the system's data transmission rate, yet its non-constant modulus and high peak-to-average power ratio (PAPR) characteristics constrain the system's detection performance [22]. Additionally, the non-constant modulus characteristic poses challenges for the design of power amplifiers, potentially causing waveform distortion and low power efficiency. On the other hand, the shared waveform based on the detection waveform guarantees the system's detection performance but limits the data rate. Compared to radar, sonar has a much smaller frequency band, smaller aperture arrays, and slower propagation rate, due to the underwater acoustic environment. Therefore, time division, frequency division, and beam division multiplexing for underwater acoustics are not practical. Time division results in large detection blind zones, frequency division imposes high bandwidth requirements, and beam division reduces the energy available for communication and detection. Consequently, the full sharing system is more appropriate for underwater acoustics. The application of underwater autonomous underwater vehicles (AUVs) primarily focuses on detection, where the capability to detect targets is critical. Therefore, integrated systems based on detection waveforms represent a significant developmental direction. The mainstream shared waveform is based on the linear frequency modulation (LFM) signal. [PERSON] proposes a minimum shift keying-linear frequency modulation (MSK-LFM) approach, which exhibits robust multi-target detection capabilities [23]. [PERSON] introduces an integrated signal based on fractional Fourier transform (FRFT) and OFDM-LFM, demonstrating enhanced range resolution and reduced bit error rates under frequency-selective fading conditions [24]. [PERSON] designed an integrated waveform of high order radar communication combining an 64 QAM signal and LFM pulse [25]. This shows that the waveform has a higher frequency band utilization rate than the integrated signal of BPSK-LFM and MSK-LFM. [PERSON] et al. proposed a sector-modulated linear frequency modulation (SM-LFM) signal for an integrated system of underwater detection and communication (ISUDC). They divided the Fresnel domain into sectors of equal length and improved the maximum unambiguous velocity by calculating the relative radial velocity in the Fresnel domain instead of the frequency domain [26].