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Open access is an efficient approach to reduce cross-tier interference in femtocell networks. In this paper, we study resource allocation in open access OFDMA femtocell networks to guarantee QoS of the neighboring macrocell user (MU) in Dead Zone and limit cross-tier interference to other MUs. A new resource allocation method is proposed to improve performance of both neighboring MU and femtocell users (FU). In specific, the subchannel set originally assigned to the MU may overlap the subchannel set occupied by FAP and cause cross-tier interference. The overlapped subchannel set is freed by macro base station (MBS) after MU resigns and joins the nearby femtocell. Then the subchannel and power resources in the femtocell are re-allocated. We leverage cognitive radio (CR) technology in femtocell networks and propose an asymptotically optimal resource allocation algorithm using dual decomposition methods. Simulation results show that the proposed algorithm for the open access scheme can achieve higher transmission rate in contrast to the closed access scheme.