A unity feedback system is a control system that has no component in the feedback path.
If W = V = 0:
E = R 1 + D G {\displaystyle E = {R \over {1 + DG}}}
General case:
E = R − ( V + G W + G u ) = R − ( V + G W ) 1 + D G {\displaystyle E = R - \left( {V + GW + Gu} \right) = {{R - \left( {V + GW} \right)} \over {1 + DG}}}