With the help of the discrete-time equivalent baseband system model we can now get insight into the two major impairments a signal incurs from the transmitter to the receiver, namely intersymbol interference and noise. For that purpose we separate the term for \(m=k\) from the sum in ( 1.40) and obtain $$\begin{aligned} q(k)=a(k)h(0)+\sum _{\begin{array}{c} m=-\infty \\ m\ne k \end{array}}^{\infty }a(m)h\left( k-m\right) +n(k) \end{aligned}$$ We see that the receive sample q(k) is composed of the transmit symbol a(k) multiplied by h(0) of the discrete-time impulse response h(k), the distortion term $$\begin{aligned} I(k)=\sum _{\begin{array}{c} m=-\infty \\ m\ne k \end{array}}^{\infty }a(m)h\left( k-m\right) \end{aligned}$$ and the noise n(k).