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Deploying femtocells faces a major challenge of causing downlink interference to the existing macrocell. This paper proposes an intelligent spectrum sharing mechanism for a two-layer cellular network, which comprises macrocells and femtocells. Because users are scheduled to access the spectrum in time-domain according to their channel conditions, the usage of spectrum is predictable by tracing the channel conditions. Therefore, the femtocell can be managed, in time-domain, to reconfigure the antenna radiation pattern in order to suppress the interference to closely-located macrocell users who are expecting to access the spectrum. Simulation results show that user throughput at the macrocell edge can be boosted by 83%, compared to deploying femtocells with fixed omni-directional antennas.