Implementation of a real-time time-varying channel simulator for the verification test of underwater acoustic communication modems and network algorithms

Generally, sea trials for performance test of acoustic communication modems and network algorithms are time-consuming and expensive process, because we need to verify the system performance for various underwater channels and operating conditions. A Doppler shift channel environment due to the relative modem movement, a time-varying stochastic channel with time-varying environment, and various types of channels according to depth and locations are some examples. For this reason, we developed a real-time channel simulator that can simulate time-varying channels including Doppler shift in various marine environments and test conditions, which brings the effect of reducing test time and cost. In the simulator the Doppler shift was implemented using the change of the impulse response function according to the movement of the modem. Similarly, the time-varying stochastic channel is simulated by random change of each impulse in magnitude and time delay according to a given probability distribution function over time. The simultaneous sampling frequency of the eight-channel input and output module is 1 MHz, which covers operating frequency of eight modems up to several hundred kHz. It also has the simulation capability of delay time more than 25 s which corresponds to 37.5 km distance. For the system verification performance test was conducted and verified the key performances.