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In this paper, we investigate adaptive resource allocation in downlink transmission of orthogonal frequency division multiple access (OFDMA) networks. A block-level resource allocation scheme is developed to maximize the overall throughput of the networks by appropriately allocating resource blocks (RB's) and power to different users. We focus on application in long term evolution (LTE) systems where all RB's allocated to the same user must use the same modulation and coding scheme (MCS). Unfortunately, the complexity of solving such an optimization problem is prohibitively high in general. In order to reduce the complexity, we divide the original joint optimization problem into two subproblems. We first allocate appropriate RB's to users with the best channel condition and then perform power allocation. Then, a more effective MCS is selected in our scheme, which not only ensures the block-error rate (BLER) of the RB with the worst channel condition but also makes full use of the RB's with better channel conditions. Simulation results show that the proposed resource allocation scheme can improve the overall throughput of the network by 20% compared with the existing scheme when the number of users is 4 and the signal-to-interference-plus-noise ratio (SINR) is 10 dB.