A resource allocation problem of maximizing total achievable rates for multi-user DFT-precoded orthogonal frequency division multiplexing (OFDM) uplink systems is investigated in this paper. A suboptimal subcarrier allocation scheme is proposed, which uses a proposed spectral efficiency enhancement parameter as an index to assign subcarriers to users. The proposed scheme has a lower computational complexity than that of the existing scheme which is shown to be close to the multiuser waterfilling solution. The simulation results show the proposed suboptimal scheme outperforms the existing scheme. Besides, an iterative subcarrier allocation scheme is proposed to improve the performance.Index Terms-Orthogonal frequency division multiplexing (OFDM), orthogonal frequency division multiple access (OFDMA), resource allocation, subcarrier allocation.
An evolutionary strategy (ES) scheme is proposed to solve the subcarrier, bit, and power allocation problem in this paper. By the property of the real-valued representation in the evolutionary strategy, the difficulties in coding with the geneticbased algorithms (GA) are conquered. This paper utilizes the method of the binary integer programming to perform the bit loading to overcome the limitation met in the water-filling algorithm. A fuzzy logic controller (FLC) is introduced to adjust the mutation probability in the iteration process. A simple subcarrier assignment modification step is also introduced to speed up the convergence rate and improve the performance. Simulation results are conducted to verify the features of better convergence rates with the proposed schemes, and the performance is improved.
The capacity maximisation problem of the secondary user subject to an interference constraint in orthogonal frequency division multiplexing-based cognitive radio systems is studied in this paper. A novel constant interference strategy to allocate power to subcarriers is derived, where all selected subcarriers are subject to the same interference constraint. It means all subcarriers have the same interference power. This strategy ensures the original interference constraint satisfied. The capacity loss of the proposed methods compared with the optimal solution is also analysed. An upper bound of the capacity loss is derived. Its value can determine the potential benefit of the proposed methods even if the optimal solution is not obtained. Therefore an advanced strategy to select subcarriers to allocate power becomes important, which affects the performance of the proposed methods and the upper bound. By using a proposed indicator, two novel power allocation methods were presented with a lower complexity to select subcarriers for allocating power, which outperforms the existing methods. Performances of the proposed methods are very near that of the optimal solution.
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