I have the following summation: \begin{equation} f(k_1,k_2) = \sum_{l_1 = 0}^{k_1}\sum_{l_2 = 0}^{k_2} {\rho}^{l_1+l_2}\delta[k_1-k_2+l_2-l_1] \end{equation}
where $\rho$ is a constant and $\delta$ is Kronecker delta. I want to find a closed form of this summation but having difficulties. Can you help me out to simplify the equation?