1. A method of initializing an Orthogonal Frequency Division Multiplex (OFDM) data transmission in which OFDM symbols including an orthogonality interval of length N having N samples and a guard interval of length L with L samples are transmitted over a physical link, the method comprising: synthesizing, based on an estimated link transfer function of the physical link, an input filter at a modem connected to the physical link; selecting a number L sel of samples of the guard interval based on an Impulse Response (IR) of a communication channel comprising the physical link and the synthesized input filter; estimating a channel quality of the physical link; and selecting the number L sel of samples of the guard interval based on the estimated channel quality.