Unit impulse sequence and unit step signal

Unit Impulse Sequence

It is denoted as δ(n) in discrete time domain and can be defined as;

δ(n)={1,0,forn=0Otherwise$$\delta (n)=\{\begin{array}{ll}1,& forn=0\\ 0,& Otherwise\end{array}$$

Unit Step Signal

Discrete time unit step signal is defined as;

U(n)={1,0,forn≥0forn<0$$U(n)=\{\begin{array}{ll}1,& forn\ge 0\\ 0,& forn<0\end{array}$$

The figure above shows the graphical representation of a discrete step function.