  This paper proposes two interference mitigation strategies that adjust the
maximum transmit power of femtocell users to suppress the cross-tier
interference at a macrocell base station (BS). The open-loop and the
closed-loop control suppress the cross-tier interference less than a fixed
threshold and an adaptive threshold based on the noise and interference (NI)
level at the macrocell BS, respectively. Simulation results show that both
schemes effectively compensate the uplink throughput degradation of the
macrocell BS due to the cross-tier interference and that the closed-loop
control provides better femtocell throughput than the open-loop control at a
minimal cost of macrocell throughput.
