analog d a converter 102 a transmission amplifier 104 a multimode fiber 106 and a receiver 108 an input bit sequence x n is provided to the d a converter 102 which converts the sequence to an input signal x t the transmission amplifier 104 transmits the input signal on the multimode fiber at the receiving end of the system the receiver 108 determines an output signal s t ideally the input bit stream x n can be unambiguously recovered from this output signal s t in practice however this is difficult due to the distorting effects of amplification by amplifier 104 propagation through fiber 106 and reception by receiver 108 of x t to determine a mathematical model of the transmission system it is convenient to group the effects of all distortion into one block in digital signal processing an abstract block known as a u201c channel u201d is used to model the distorting effects of the transmission system i e corresponding to the channel response discussed above fig1 b depicts such a mathematical model of the multimode optical transmission system 100 of fig1 a channel 106 replaces the amplifier fiber and receiver of the transmission system it is assumed that channel 106 introduces linear distortion only so that the channel can be completely characterized by the channel impulse response h t as discussed the channel impulse response may vary over time due to among other possible causes kinks in the fiber temporal variations of the fiber and fluctuations in power supply levels of the transmitter and or receiver.