This is an echo cancelling system used in modems and other communication devices. Some have single echo cancel, better ones have two like this problem.
This was the main reason for old phone modem connection speed limits due to noise caused by echoes, not hiss or hum.
Now the same is true with WiFi, similar in forward direction, we call it Rician Fading Loss due to deadspots caused by reflected echo cancellation of signal of same amplitude burst out of phase. This limits Wifi range and speed.
But for this...
Imagine each successive echo response n is declining in amplitude An and create opposite polarity echo to match.
But read book and solve with math.