This letter considers the optimum transmission power allocation strategy for maximizing the aggregate communication rate of a desired tier in a multi-tier network for a multi-carrier scenario. Users of the tier of interest form a multiple access channel with their base station. They share the same resources with other tiers, and cause inter-tier interference. Optimal power control for users of the tier of interest is found by maximizing their sum data rate while limiting the power transmitted per user and interference caused per tier. The power allocation is found to be a power and interference regulated water-tilling solution which is a combination of conventional power-filling with interference-filling. The superiority of our proposed algorithm over orthogonal frequency division multiple access and equal power allocation schemes is demonstrated.