This Letter proposes a novel tractable solution for the average rate in cellular networks. Specifically, the authors derive a closed-form solution based on bipolar point processes to simplify the computational complexity, which may be conveniently applied to the analysis of actual base station (BS) deployment. Proved by simulation, the results of closed-form solution are consistent with the numerical results. Furthermore, they analyse the BS activation effect under noisy Rayleigh fading channel conditions in 2D and 3D cases, respectively. Simulation shows that turning off the inactive BS can be used as an effective interference mitigation solution, and the interference of the system is mainly limited by the density of active users.