In satellite mobile communication system, relative movement of the satellite and the terminal will cause a large Doppler offset. Timing advanced estimation with Zadoff-Chu sequence is sensitive to the frequency offset...In satellite mobile communication system, relative movement of the satellite and the terminal will cause a large Doppler offset. Timing advanced estimation with Zadoff-Chu sequence is sensitive to the frequency offset. When the frequency offset is larger than one times subcarrier spacing, the value of peak cannot be detected at the receiving end. To suppress the larger Doppler frequency shift, this paper proposes a novel timing advanced estimation scheme(TAE-MCD) for satellite communication system. In this algorithm, t r a n s m i t t e d s i g n a l i s d i v i d e d i n t o Z C sequence and its conjugate sequence. Using multiplication and DFT operation to find the estimated peak at the receiving end, and make subtraction with the obtained sequences at last. The scheme can not only inhibit the adverse effects of large Doppler frequency shift in timing estimation effectively, but also reduce the computational complexity at the receiving end and improve the work efficiency of the hardware. Simulations results show that TAEMCD outperform the existing timing advanced estimation methods, on the condition of no additional time and frequency resource are needed.展开更多
文摘低表面亮度星系(Low Surface Brightness Galaxy,LSBG)的特征对于理解星系整体特征非常重要,通过现代的机器学习特别是深度学习算法来搜寻扩充低表面亮度星系样本具有重要意义.LSBG因特征不明显而难以用传统方法进行自动和准确辨别,但深度学习确具有自动找出复杂且有效特征的优势,针对此问题提出了一种可用于在大样本巡天观测项目中搜寻LSBG的算法---YOLOX-CS(You Only Look Once version X-CS).首先通过实验对比5种经典目标检测算法并选择较优的YOLOX算法作为基础算法,然后结合不同注意力机制和不同优化器,构建了YOLOX-CS的框架结构.数据集使用的是斯隆数字化巡天(Sloan Digital Sky Survey,SDSS)中的图像,其标签来自于α.40-SDSS DR7(40%中性氢苜蓿巡天与第7次数据发布的斯隆数字化巡天的交叉覆盖天区)巡天项目中的LSBG,由于该数据集样本较少,还采用了深度卷积生成对抗网络(Deep Convolutional Generative Adversarial Networks,DCGAN)模型扩充了实验测试数据.通过与一系列目标检测算法对比后,YOLOX-CS在扩充前后两个数据集中搜索LSBG的召回率和AP(Average Precision)值都有较好的测试结果,其在未扩充数据集的测试集中的召回率达到97.75%,AP值达到97.83%,在DCGAN模型扩充的数据集中,同样测试集下进行实验的召回率达到99.10%,AP值达到98.94%,验证了该算法在LSBG搜索中具有优秀的性能.最后,将该算法应用到SDSS部分测光数据上,搜寻得到了765个LSBG候选体.
文摘巡天观测与高能物理、黑洞天文等领域均有密切的联系.基于星系-超新星二分类问题,研究光谱数据预处理,结合余弦相似度改善PCA(Principal Component Analysis)光谱分解特征提取方法,用SDSS(the Sloan Digital Sky Survey)、WISeREP(the Weizmann Interactive Supernova data REPository)组成的5620条光谱数据集训练支持向量机,可以得到0.498%泛化误差的识别模型和新样本分类概率.使用Neyman-Pearson决策方法建立NPSVM(Neyman-Pearson Support Vector Machine)模型可进一步降低超新星的漏判率.
基金supported by the Science and Technology on Information Transmission and Dissemination in Communication Networks Laboratory (ITD-U13007/ KX132600014)the National Natural Science Foundation of China (No. 9143810063)the Fundamental Research Funds for the Central Universities (2014RC0202)
文摘In satellite mobile communication system, relative movement of the satellite and the terminal will cause a large Doppler offset. Timing advanced estimation with Zadoff-Chu sequence is sensitive to the frequency offset. When the frequency offset is larger than one times subcarrier spacing, the value of peak cannot be detected at the receiving end. To suppress the larger Doppler frequency shift, this paper proposes a novel timing advanced estimation scheme(TAE-MCD) for satellite communication system. In this algorithm, t r a n s m i t t e d s i g n a l i s d i v i d e d i n t o Z C sequence and its conjugate sequence. Using multiplication and DFT operation to find the estimated peak at the receiving end, and make subtraction with the obtained sequences at last. The scheme can not only inhibit the adverse effects of large Doppler frequency shift in timing estimation effectively, but also reduce the computational complexity at the receiving end and improve the work efficiency of the hardware. Simulations results show that TAEMCD outperform the existing timing advanced estimation methods, on the condition of no additional time and frequency resource are needed.
