We consider the problem of Downlink (DL) power allocation at a Femtocell Base Station (FBS) in a macro-cell/femtocell coexisting system based on OFDMA transmission. To mitigate the interference to macrocell users, many conventional methods rely on the information of the interference channel states and macrocell user allocation provided by a control channel, causing large overhead increase. Instead, in our proposed method, each FBS is able to predict the subchannel allocation of macrocell users based on partially overheard Channel State Information (CSI) from the macrocell users to the Macrocell Base Station (MBS). Based on this estimation, the FBS performs subchannel and power allocation to femtocell users. With this procedure, the proposed method can mitigate the interference to macrocell users without largely increasing the control overhead. Simulations show the validity of the proposed method, providing sum-rate gains for both femtocells and macrocell users compared to reference schemes. © 2012 IEEE.