Abstract
In orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems, the subcarriers occupied by the licensed users are deactivated to avoid interference with rental users, owing to which the portion of the active subcarriers can be used for transmission of data signals and pilot tones. Further, the position of the activated subcarriers may also be non-contiguous. In such a system, the conventional pilot design methods are no longer effective. In this paper, a new pilot design method for OFDM-based CR systems has been proposed. The pilot design is formulated as a new optimization problem, where a simple objective function related to the mean square error of the least squares channel estimation method is minimized. An efficient scheme based on hybrid of bacterial foraging and modified cuckoo search optimization has been proposed to solve the optimization problem. In comparison with the existing methods, the simulation results of the pilot sequence obtained by the proposed method have been shown to be far superior.
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