一种基于CSMA/CA的VLC系统多用户接入方法研究

针对可见光的通信距离较短和带宽有限的特点,提出了一种多终端组网的可见光网络模型,对于室内可见光通信(VLC)系统多用户接入碰撞问题,我们分析了这种网络模型的特点,提出了一种基于载波侦听多路访问/冲突避免(CSMA/CA)的多用户接入方法,给出了多用户接入时碰撞概率和系统吞吐量的表达式,并进行了相应的仿真。仿真结果表明模型和接入方法合理有效。     

琥珀酸酯为内给电子体的新型MgCl2载体催化剂用于丙烯聚合

A novel MgCl2-supported Ziegler-Natta catalyst containing diethyl diisopropylsuccinate donor was prepared and propylene polymerizations with the combination of such catalyst and four external donors were investigated in detail. The catalyst was compared with a commercial one with phthalate as internal donor in terms of catalytic activity, hydrogen sensitivity and stereospecificity in propylene polymerization. The molecular weight, molecular weight distribution and microstructure of the produced polypropylenes were compared also. It was found that the novel catalyst containing succinate internal donor showed higher activity and higher stereospecificity than those with phthalate as internal donor. Consequently, polypropylenes obtained by the succinate-based catalyst showed high molecular weight, high melting temperature, high isotactic index and broad molecular weight distribution than those obtained with the commercial catalyst.     

基于D2D中继的异构网络负载均衡策略

提出了一种基于设备间数据直传(D2D)中继的异构网络负载均衡策略,通过设备之间的直接数据传输,将满载大基站的数据分流到其覆盖范围内的空闲小基站中。具体提出了频谱资源和发射功率的联合资源分配算法,深入研究了在异构网络中利用D2D通信进行数据中继的传输速率最大化问题。仿真结果显示,提出的方法在保证原有用户的通信性能的前提下,增加了系统的可接入用户数和总体吞吐率,从而提升了自组织异构网络的整体性能。