# Design and Development of an SVM-Powered Underwater Acoustic Modem
## 2 Materials and Methods
### Hardware Setup  
The core of the experimental setup is a Lattice Semiconductors ICE5 LP1K FPGA, which was used for signal modulation and processing. This FPGA was selected for its low power consumption and sufficient logic element capacity to handle the required processing tasks. The FPGA was programmed in Verilog to perform the FSK modulation. This involved generating precise control signals to drive the high-voltage oscillator, which, in turn, excited the PZT4 ultrasonic transducer for signal transmission. Custom-designed PCBs facilitated the integration of the FPGA with other hardware components, including the high-voltage signal generator for the transmitter and a specialized filter and amplifier circuit for the receiver. Then, the data source for the experiments was an FSK modulator, which consisted of a 200 kHz PZT4 transducer equipped with a high-voltage oscillator for the excitation. The choice of these transducers was based on their frequency response, aligning with the target communication frequencies. The control of this oscillator was mediated through high-power MOSFET transistors governed by the FPGA programmed to produce the required FSK modulation. An example of the resultant modulated signal is shown in Figure 1a. The experimental setup was constructed to mimic the constraints of an underwater communication channel. The signal transmission was conducted through a 6 m waveguide, which served as a controlled medium to replicate the acoustic properties of an underwater environment. This approach allowed for the precise manipulation and measurement of the acoustic signals, thus ensuring the reliability of the data for subsequent digital processing. Data acquisition and signal monitoring were performed using a Fluke 190-504 (FLUKE, Everett, WA, USA) Scopemeter Series III and a Rigol MSO5354 (RIGOL, Gilching, Germany) digital oscilloscope, which ensured high-fidelity capture of the transmitted and received signals. To capture the transmitted signals, the oscilloscopes were set at both the transmitter and receiver ends. The Fluke and Rigol oscilloscopes used in the experiments were capable of high-resolution measurements, capturing the signal at a rate of 8 GSPS, which was then decimated to 2 MSPS to suit the system's requirements. The oscilloscopes facilitated an accurate data acquisition process that was fed into MATLAB scripts for further processing and analysis. To maintain the integrity of the signals and to negate the influences of variable laboratory conditions, such as temperature fluctuations and extraneous noise, stringent controls were imposed. While acknowledging the deviation from open-sea trials, these laboratory conditions offered a rigorous and stable testing environment for ascertaining the performance of the underwater modem system. The fidelity of these conditions to actual underwater scenarios was anticipated to provide a robust indication of the system's operational efficacy in situ. The system was set up as follows:  
* The FPGA board was connected to the transmission board via a board-to-board connector. * The transmission board was linked to the ultrasonic transducer PZT4. * The Fluke 190-504 CH1 was connected to the signal input from the FPGA in the transmission board. * The Fluke 190-504 CH2 was connected to the PZT4 transmission transducer to monitor the exact transmitted signal. * The Rigol MSO5354 CH1 was connected to the output of the filter + amplifier block. * The Rigol MSO5354 CH3 was connected to the PZT4 receiver transducer for system troubleshooting. For the system setup and verification, the CH1 and CH3 channels of the Rigol oscilloscope were enabled. The trigger was set to CH3, AC coupled, and given a rising edge in normal mode, resulting in a sampling rate of 2 GSPS. For the signal gathering, only CH1 was enabled, with the trigger set to CH1, AC coupled, given a rising edge, and in SINGLE mode. The acquisition memory depth was set to 200 Mpts, enabling the scope to sample at 8 GSPS. In Figure 0(b), a closeup of the scope (Fluke) with three signals is shown.