Impact of Modulation Signals on Digital Self-Interference Cancellation in Amplitude Modulation Systems

Many critical infrastructure radio systems (such as air traffic control or maritime radio) still use analog modulation formats in the VHF band. Whereas analog radio systems utilize conventional half-duplex communication, this study investigates the use of in-band full-duplex communication in amplitude modulation systems, focusing on the influence of the modulation signal on the achievable digital self-interference cancellation. Evaluations of the interference cancellation ratio for different values of the modulation index (identical to different loudness levels) show that a low modulation index allows more digital cancellation, since the modulated signal in this case has a simpler shape and is far from its full saturation. The comparison of the achievable cancellation for EBU database files reveals that simpler modulation signals can be canceled more effectively in the simulations, whereas in the measurements the effects of nonlinearities near the full saturation dominate the results.