A new phenomenon observed in connection with determining the FEQ of DMT transceivers with insufficient guard interval

Working with wireline communication systems and spatial long transmission loops in the range of 10-20 km for telecontrol applications, we discovered a non-linear effect whose mean value does not equal to zero and thus would lapse all common assumptions like modeling noise as AWGN, estimate SNRs and many more. Simulation shows that the phenomenon discovered is a superposition of two independent errors where the only critical step is channel estimation. If this step is performed in the absence of non-linear distortion like interference, the situation is not critical.