以探测功能为主的雷达通信一体化(Dual Function Radar and Communication, DFRC)系统发射一体化信号,能够在保证探测性能的条件下,尽可能高效地与合作目标通信,使其在设备集约化要求高的电磁对抗环境中占有一席之地。因此,探通一体化...以探测功能为主的雷达通信一体化(Dual Function Radar and Communication, DFRC)系统发射一体化信号,能够在保证探测性能的条件下,尽可能高效地与合作目标通信,使其在设备集约化要求高的电磁对抗环境中占有一席之地。因此,探通一体化信号设计是以探测功能为主DFRC系统研究的关键科学问题之一。但电磁对抗环境复杂多变,可能存在非均匀、多变和强独立散射的散射体与雷达探测信号相互作用,使DFRC系统接收的回波中含有在空间上呈现非均匀特性的杂波分量,从而给雷达目标检测带来挑战。针对杂波环境中DFRC系统探测性能下降的问题,本文采用认知系统架构,获取空间非均匀杂波先验知识,以信干噪比(Signal Interference to Noise Ratio, SINR)为准则,保障雷达的探测性能。引入发射方向图主瓣和旁瓣约束,使天线方向图具有低旁瓣特性同时集中探测能量在目标所在的方位,进一步保障探测性能。此外,考虑信号变模约束平衡雷达系统发射机功放的非线性失真和优化自由度。采用了一种空间合成信号频谱置零的方法实现信息传输,构建了通信调制约束。为求解上述多约束高维非凸优化问题,研究了一种联合序列块增强(Sequential Block Enhancement, SBE)、丁克尔巴赫(Dinkelbach’s Iterative Procedure, DIP)、凸序列逼近(Sequential Convex Approximation, SCA)和内点法(Interior Point Method, IPM)的迭代求解算法。理论分析了该算法的收敛性和计算复杂度。仿真结果表明,所设计的波形能够在信号相关旁瓣杂波下,同时实现探测和多用户通信。展开更多
Temperate regions of the world are characterized by seasonal warm and cool temperature. Cool temperature enables the plant to undergo physiological processes essential for flowering and fruit bearing in the following ...Temperate regions of the world are characterized by seasonal warm and cool temperature. Cool temperature enables the plant to undergo physiological processes essential for flowering and fruit bearing in the following season. Failure of environments to provide chilling conditions required for the fruit cultivar results in deformed leaves, fruits, or barren trees. The present study was conducted to assess production and distribution of chilling hours in Kentucky environments. Weather data were provided by Kentucky Mesonet system for 50 counties over a 5-year period. A chilling unit is defined as a clock hour in which air temperature is between 0°C and 7.2°C. Temperature readings in this range were recorded from September through April. Average number of chilling hours observed in the study was 1556 overall, and ranged from 1463-1680 for sites, and 1473-1842 for years. Estimated chilling hours were more variable for years than for sites. Consistency of chilling results was high when measured by linear correlation and relative standard deviation statistical procedures. Accumulated chilling hours at the sites reached approximately 1000 by mid-January thereby meeting the requirements for many fruit crops. At that point, plants would be ready for bud break and become subject to freezing damage. The results indicated that chilling exceeded requirements for most Kentucky crops. This margin of excess has both negative and positive value. First, the plants become more vulnerable to freezing damage before winter weather is completed. The higher risk could be mitigated by growing cultivars with longer chilling requirements. Second, since warming has been shown to decrease chilling production, the margin of chilling hours could provide time for adjusting horticultural enterprises in Kentucky to global warming. Additional understanding of relationships between environments and chilling will contribute to perennial fruit production in temperate regions of the world.展开更多
文摘Temperate regions of the world are characterized by seasonal warm and cool temperature. Cool temperature enables the plant to undergo physiological processes essential for flowering and fruit bearing in the following season. Failure of environments to provide chilling conditions required for the fruit cultivar results in deformed leaves, fruits, or barren trees. The present study was conducted to assess production and distribution of chilling hours in Kentucky environments. Weather data were provided by Kentucky Mesonet system for 50 counties over a 5-year period. A chilling unit is defined as a clock hour in which air temperature is between 0°C and 7.2°C. Temperature readings in this range were recorded from September through April. Average number of chilling hours observed in the study was 1556 overall, and ranged from 1463-1680 for sites, and 1473-1842 for years. Estimated chilling hours were more variable for years than for sites. Consistency of chilling results was high when measured by linear correlation and relative standard deviation statistical procedures. Accumulated chilling hours at the sites reached approximately 1000 by mid-January thereby meeting the requirements for many fruit crops. At that point, plants would be ready for bud break and become subject to freezing damage. The results indicated that chilling exceeded requirements for most Kentucky crops. This margin of excess has both negative and positive value. First, the plants become more vulnerable to freezing damage before winter weather is completed. The higher risk could be mitigated by growing cultivars with longer chilling requirements. Second, since warming has been shown to decrease chilling production, the margin of chilling hours could provide time for adjusting horticultural enterprises in Kentucky to global warming. Additional understanding of relationships between environments and chilling will contribute to perennial fruit production in temperate regions of the world.
