Detection of Communications Channels in VHF Band for Enhanced Maritime Surveillance

This work aimed to develop and evaluate a real-time communication channel detection system in the Very High Frequency (VHF) band using software-defined radio (SDR). For this purpose, an FFT based spectral analyzer with 32,768 points was designed, capable of converting signals from the time domain to the frequency domain, ensuring efficient characterization of a 3 MHz bandwidth with updates every 0.5 s. Three detection algorithms were developed and compared: Energy Detection (ED) and two Waveform-Based Detection methods supported by machine learning models, SVM and KNN. ED stood out for its low computational requirements, suitable for low-cost systems, but had a limited probability of detection (Pd) at short distances, with zero detection beyond 500 m. KNN showed superior performance at longer distances, achieving 23% Pd at 700 m but insufficient for real-time applications. The SVM model proved to be the most effective, achieving a Pd of 80% at 1000 m and maintaining a low false positive rate of around 1%. It is concluded that the SVM model is the most suitable for real-time detection systems in the VHF band, offering a balance between accuracy and usability. The extrapolation of the results demonstrates the system's potential for coverage greater than 2 km with higher-powered marine radios, around 25 W.