Femtocells have been considered as a costeffective solution to unload traffic from already overburdened macrocell networks in 4G cellular networks. The severe interference in spectrum-sharing macro and femto networks may cause User-equipment(UE) to experience outage. We derive an utmost isotropic Spatial Poisson point process(SPPP) density for Femtocell access points(FAPs) under the UEs’ outage constraints. Based on the derived isotropic SPPP density, we propose a distributed transmit probability self-regulation scheme for an FAP to adapt its transmit probability per Transmission time interval(TTI). The scheme adjusts the homogeneous distributed FAPs in practice deployment to the proposed isotropic one. Simulation results show that the derived density can fulfill the outage probability constraints of UEs while accommodating the maximum femtocells. The selfregulation scheme can adapt the femtocell transmit probabilities to provide reliable downlink service, for even a large number of femtocells per cell site. Femtocells have been considered as a costeffective solution to unload traffic from already overburdened macrocell networks in 4G cellular networks. The severe interference in spectrum-sharing macro and femto networks may cause User-equipment (UE) to experience outage. We derive an utmost isotropic Spatial Based on the derived isotropic SPPP density, we propose a distributed transmit probability self-regulation scheme for an FAP to adapt its transmit probability per Transmission time (FAPs) under the UEs’ outage constraints The scheme adjusts the homogeneous distributed FAPs in practice deployment to the proposed isotropic one. Simulation results show that the derived density can fulfill the outage probability constraints of UEs while accommodating the maximum femtocells. The selfregulation scheme can adapt the femtocell transmit probabilities to provide reliable downlink service, for even a large number of fe mtocells per cell site.