The Friis equation is as follow.
$$P_r = P_tA_rA_t(\lambda/(4\pi d))^\alpha$$
where $d$ is distance between terminals, $P_r$ is received power, $P_t$ is transmission power, $A_r, A_t$ are the rx, tx antenna gains, respectively, and $\lambda$ is wavelength.
If $d$ is 0, the $P_r$ must be $P_t$. But in this equation, the $P_r$ is infinity.
How can I find $P_r$ in this situation? What formula is needed?