In multibeam satellite communication systems it is important to improve the utilization efficiency of the power resources, due to the scarcity of satellite power resources. The interbeam interference between the beams must be considered in the power allocation; therefore, it is important to optimize the power allocated to each beam in order to improve the total system performance. Initially the power allocation problem is formulated as a nonlinear optimization, considering a compromise between the maximization of total system capacity and the fairness of the power allocation amongst the beams. A dynamic power allocation algorithm based on duality theory is then proposed to obtain a locally optimal solution for the optimization problem. Compared with traditional power allocation algorithms, this proposed dynamic power allocation algorithm improves the fairness of the power allocation amongst the beams, and, in addition, the proposed algorithm also increases the total system capacity in certain scenarios. 1. Introduction In satellite communication systems, a satellite may provide coverage of the entire region of the earth visible from the satellite, by using a single beam. In this case, the gain of the satellite antenna will be limited by the beamwidth, as imposed by the coverage. For instance, for a geostationary satellite, global coverage implies a 3？dB beamwidth of 17.5 and consequently an antenna gain of no more than 20？dB [1]. Therefore, each user must be equipped with a large aperture antenna to support the high traffic rate, which results in great inconvenience. In order to solve this problem, the multibeam technique has been widely applied in modern satellite communication systems. In multibeam satellite communication systems, the satellite provides coverage of only part of the earth, by means of a narrow beam. The benefit of a higher satellite antenna gain is obtained due to a reduction in the aperture angle of the antenna beam [1]. As a result, a user with a small aperture antenna can support a high traffic rate. Moreover, the multibeam technique supports the reuse of frequencies for different beams, in order to increase the total system capacity. When two beams utilize the same frequency, interbeam interference is introduced to the two beams, due to the nonzero gain of the antenna side lobe. It has been noted that when there is interbeam interference between the beams, the capacity allocated to each beam is determined not only by the power allocated to the beam, but also by the power allocated to the other beams. Due to the limitations of
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