Causality Condition of a Discrete-Time LTI System As xi[n]*x2[n] for n>no the only way the condition ∑k]x[-k]=∑hk]x2{To-k] k will hold if both sums are equal to zero which is satisfied if h[k]=o for k<0 Copyright C 2001, S K MitraCopyright © 2001, S. K. Mitra 9 Causality Condition of a Discrete-Time LTI System • As for the only way the condition will hold if both sums are equal to zero, which is satisfied if x [n] x [n] 1 2 n no − =− − =− − = − 1 2 1 1 k o k o h[k]x [n k] h[k]x [n k] h[k] = 0 for k < 0