Analytical models for call blocking and dropping in sectorized cellular networks with fractional frequency reuse

In this paper, we construct mathematical models to analyze the probabilities of new call blocking and handoff call (HC) dropping for a sectorized cellular network with fractional frequency reuse (FFR). Because a sectorized FFR network (SFN) consists of two areas, the super group (SG) and the regular group (or sectors), three different types of HCs may happen when a mobile station (MS) moves from the SG to a sector, from a sector to the SG, or from one sector to another sector. To characterize three types of HCs, we first derive the area transition probability, which is defined as the reciprocal of MS's average residence time in an area (i.e., sector or SG). Moreover, we construct the model of Markov chains and derive the state transition rates. Then on the basis of the stationary probabilities of Markovian states, we derive the three types of blocking probabilities of new calls and two types of dropping probabilities of HCs. Finally, we conduct extensive numerical simulations. From the results of numerical simulations, we reveal two important rules for choosing the optimal radius of the SG, with which the system blocking and dropping probability can be effectively minimized. Copyright © 2014 John Wiley & Sons, Ltd.     

基于可行解及移动闭塞策略的新型逆变电路模型预测控制

电力电子电路是典型的混杂系统,文章建立了一种新型容错逆变电路的混杂系统模型,与开关函数模型相比,电路混杂系统模型能更好地描述电路的动态过程,有助于实现电路的精确控制.在此基础之上,将可行解及移动闭塞的思想用于电路的MPC,以电路可行解代替最优解,可有效减少电路控制序列总数、降低开关频率,实现电路MPC的快速求解,仿真和实验验证了控制方法的可行性与有效性.     

猫群算法求解阻塞流水车间调度问题

阻塞流水车间调度是现实生产调度中一类很重要的组合优化问题,其已被证明是典型的NP难问题。为了提高该问题的求解性能,文中提出了猫群算法（CSO）求解阻塞流水线调度问题。猫群算法是近几年来提出的群体智能算法,算法以一小部分猫执行跟踪模式,其余大部分猫执行搜寻模式,通过这两种模式同时进行局部搜索和全局搜索以达到优化目标。文中利用标准Car问题算例进行仿真实验,并与标准粒子群算法（PSO）和蝙蝠算法（BA）进行比较,结果表明猫群算法在求解生产调度问题的可行性和有效性。     

Tandem queue with group arrivals and no intermediate buffer

We study a system with two single-server stations in series. There is an infinite buffer in front of the first station and no buffer between the two stations. The customers come in groups; the groups contain random numbers of customers and arrive according to a Poisson process. Assuming general service time distributions at the two stations, we derive the Laplace transform and the recursive formula for the moments of the total time spent in the tandem system (waiting time in the system) by an arbitrary customer. From the Laplace transform, we conclude that the optimal order of the servers for minimizing the waiting time in the system does not depend on the group size.     

On the equivalence of three types of blocking in non-Markovian tandem queues

Definitions of blocking types for tandem queueing systems are given where each stage consists of multiple servers. Some of them are shown to be identical with respect to service initiation epochs at each stage. Such identical relationships are proved using sample path correspondence, and are therefore valid irrespective of the arrival process and the service time distributions.     

Semi-insulating InP grown by low pressure MOCVD

Fe-doped semi-insulating InP layers have been successfully grown in a vertical flow, low pressure metalorganic chemical vapor deposition (LPMOCVD) system, and used as current blocking layers in buried crescent (BC) laser structures emitting at 1.51 μm. Triethylindium ((C₂H₂)₃In), phosphine (PH₃) and iron pentacarbonyl (Fe(CO)₅) were used as the reactant gases. Process variables have been identified which produce high resistivity (10⁷ to 10₈ Ω-cm) InP having featureless surface morphology, and layer thickness and doping uniformity. There is optical and x-ray diffraction evidence for the presence of an unidentified In-Fe-P second phase associated with markedly degraded surface morphology under nonoptimized growth conditions. Early BC lasers incorporating LPMOCVD grown, Fe-doped InP blocking layers have operated CW with threshold currents as low as 12 m A and optical output > 18 mW.     

Call Blocking Performance Study for PCS Networks under More Realistic Mobility Assumptions

In the micro-cell-based PCS networks, due to the high user mobility, handoffs occur more frequently. Hence, the classical assumptions, such as the exponential assumptions for channel holding time and call inter-arrival time, may not be valid. In this paper, we investigate the call blocking performance for PCS networks using a semi-analytic and semi-simulation approach. We first construct a simulation model as the base for our performance study, using which the handoff traffic is studied. Then we present a few possible approximation models from which analytical results for call blocking performance metrics can be obtained and compared with the simulation results. We show that for a certain parameter range, such approximations may provide appropriate results for call blocking performance. Finally, using the simulation model, we investigate how various factors, such as the high moments, the variance of cell residence time, mobility factors and the new call traffic load affect the call blocking performance. Our study shows that all these factors may have a significant impact on call blocking performance metrics such as call blocking probability, call incompletion probability and call dropping probability. This research provides a strong motivation for the necessity of reexamining the validity of analytical results obtained from classical teletraffic theory when dealing with the emerging wireless systems.     

Modeling iCAR via Multi-Dimensional Markov Chains

iCAR is a new wireless system architecture based on the integration of cellular and modern ad hoc relaying technologies. It addresses the congestion problem due to limited channel access in a cellular system and provides interoperability for heterogeneous networks. The iCAR system can efficiently balance traffic loads and share channel resource between cells by using ad hoc relaying stations (ARS) to relay traffic from one cell to another dynamically. Analyzing the performance of iCAR is nontrivial as the classic Erlang-B formula no longer applies when relaying is used. In this paper, we build multi-dimensional Markov chains to analyze the performance of the iCAR system in terms of the call blocking probability. In particular, we develop an approximate model as well as an accurate model. While it can be time-consuming and tedious to obtain the solutions of the accurate model, the approximate model yields analytical results that are close to the simulation results we obtained previously. Our results show that with a limited number of ARSs, the call blocking probability in a congested cell as well as the overall system can be reduced.     

基于同波长光纤延迟线集光突发交换结构及其性能分析

由于光突发交换机制本身就避免了光缓存的使用，但是现实中，光突发包之间竞争以及提供优先级服务又依靠光纤延迟线来解决。为此，我们设计了应用光纤延迟线的光突发交换网络核心节点结构。为了避免光纤延迟线色散引起的突发包输入排队缓存偏移，在该结构中设计了同波长光纤延迟线集。采用了空分交换矩阵，避免了波长转换的需要。为了有效运行该交换结构，我们提出了输入排队与自适应光缓存调度算法，而该算法不仅仅适用于光突发交换，也适合于光纤延迟线得到普遍应用的光分组交换。该调度算法能够提供优先级服务，避免队头阻塞，对该调度算法建立了严格的理论分析模型，并进行了仿真。仿真结果表明，与传统的延迟线竞争解决方案相比，这一调度算法能够改善交换性能1到2个数量级，是利用光纤延迟线解决光突发交换中竞争问题的一个较佳方案。     

一种有源加性复合干扰的对抗算法研究

针对雷达有源加性复合干扰对抗的情况,传统的抗干扰算法只针对单一样式干扰进行抑制,很难做到有效权衡。由于有源复合干扰噪声功率高、欺骗性强的特点,为此提出了一种基于相位扰动的有源加性复合干扰对抗算法,该算法在斜变线性调频信号（SV LFM）信号的基础上,先对发射雷达信号的前后沿脉冲附加上一个扰动的相位,再通过与前一脉冲的匹配滤波,限幅处理和逆匹配,最后与当前脉冲进行匹配滤波处理,附加扰动的相位和限幅处理减弱了距离假目标信号的增益,而经过三次匹配滤波的作用,同样有效的削弱了大部分压制性干扰信号的成分,从而恢复出比较纯净的目标回波信号。通过实验仿真手段验证了相位扰动抗干扰算法的有效性,与传统直接匹配滤波的抗干扰算法相比,接收信号的信噪比提升了约25dB。