Smart antennas are becoming one of the promising technologies to meet the rapidly increasing demands for more capacity of satellite communication systems. A main component in a smart antenna system is beamforming. Bec...
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Smart antennas are becoming one of the promising technologies to meet the rapidly increasing demands for more capacity of satellite communication systems. A main component in a smart antenna system is beamforming. Because of the limitations of analog beamforming, digital beamforming will be employed in future satellite communication systems. We evaluate the performance of various digital beamforming strategies proposed in the literature for satellite communications: 1) single fixed beam/single user, 2) single fixed beam/multiple users, 3) single adaptive beam/single user, and 4) single Chebyshev dynamic beam/multiple users. Multiple criteria including coverage, system capacity, signal-to-interference-plus-noise ratio (SINR), and computation complexity are used to evaluate these satellite communication beamforming strategies. In particular, a Ka-band satellite communication system is used to address the various issues of these beamforming strategies. For the adaptive beamforming approach, subarray structure is used to obtain the weights of a large 2D antenna array, and a globally convergent recurrent neural network (RNN) is proposed to realize the adaptive beamforming algorithm in parallel. The new subarray-based neural beamforming algorithm can reduce the computation complexity greatly, and is more effective than the conventional least mean square (LMS) beamforming approach. It is shown that the single adaptive beam/single user approach has the highest system capacity.
Based on the test information function of the item response theory (IRT), the high quality parallel test forms can be constructed far educational measurement, Many methods have been designed to construct a test that a...
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ISBN:
(纸本)0769506534
Based on the test information function of the item response theory (IRT), the high quality parallel test forms can be constructed far educational measurement, Many methods have been designed to construct a test that approximates the target test for containing the similar test information functions. In this paper;we propose a more effective method that can greatly reduce the error of the test information functions of parallel rests generated by other methods. Experimental results show that this method sharply reduces error with improvement ratios exceeding 96%. In addition, the computation complexity! of our method is the same as that of other methods. This method should greatly aid in the construction of parallel rest forms.
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