back-propagation frequency-response probability-density-function forward-propagation reflection-coefficient probability-density-estimation gauss-error-function probabolity-of-error signal-reflection impedance-mismatch power-line-cables cable-impedances termination-impedances speed-of-light gaussian-complementary-integral propagation-velocity-in-lines anticipate-quality-of-transmission digital-power-lines multiple-branched-lines three-inner-conductors