Abstract: A joint subcarrier usage ratio and power allocation method, the system and base station, and a controller using the same are proposed. The method is adapted for a femtocell base station using OFDMA technology to jointly select transmission power and subcarrier usage ratio. The method includes a first adjustment process, which simultaneously, dynamically and jointly adjusts the transmission power and the subcarrier usage ratio so as to quickly satisfy capacity requirement and link reliability requirement. The method also includes a second adjustment process for slowly adjusting the transmission power and the subcarrier usage ratio after the capacity requirement and the link reliability requirement are both met in the first adjustment process for stability duration. The second adjustment process helps the femtocell base station achieve maximal power efficiency. An outer-loop control might be used in the method to relax the capacity requirement of one femtocell for quickly achieving a stable situation.