A new constrained-send mechanism to enhance the performance of IEEE 802.11 DCF

In this paper, a modified access mechanism named Constrained-send DCF (CDCF) is proposed to improve the performance of IEEE 802.11 DCF protocol. It is found that, in DCF, the transmission probability is higher than the reasonable value when the node number is greater than 4 under basic access scheme or than 17 under RTS/CTS scheme, and it results in serious collision. To avoid collision of high access loading, a constrained-send probability is introduced at the end of each back off procedure for the station transmitting. The performance of this mechanism is analyzed based on a 2-Dimension Markov analytical model, after that the optimum constrained-send probability is derived. Numerical results show that the CDCF mechanism has much better performance than DCF with respect to both system throughput and average packet delay. And under RTS/CTS scheme, although CDCF slightly improve the throughput performance (due to the natural good throughput performance of RTS/CTS-scheme DCF), it leads to a much better average packet delay performance compared to DCF. The CDCF keeps all the features of the IEEE 802.11 DCF protocol and is quite easy to implement.     

CIMS环境下电子产品全面质量检验管理系统设计

近年来,基于Web的J2EE体系架构在管理信息系统中获得大量的成功应用。分析了电子类产品全面质量检验管理系统的业务过程与管理功能,设计了全面质量检验管理系统的功能结构、数据库E-R模型与逻辑模型以及基于模型-视图-控制器三层体系的软件系统总体架构,最后利用Flex、Hibernate与BlazeDS等相关技术实现了该系统的进货检验模块。实践表明,该质量检验系统具有易用性、图形化及可扩展性的特点,同时能降低系统开发的成本,易与CIMS、ERP等系统进行高效集成。     

一种用于移动自组控制网络的QoS路由

为更好地将移动自组网络用于网络控制系统（NCS）,结合NCS的网络特性,提出了一种基于链路信号质量的QoS路由算法。主要QoS机制包括根据接收信号强度选择较稳定的路由;用Hello报文广播节点的预留带宽;中间节点为所有受影响的数据流修复路由、目的节点向源节点广播路由修复报文进行路由修复。NS2仿真表明当节点移动性强时,该QoS路由算法可有效减少网络的平均端到端时延和丢包率,提高控制系统稳定性。     

基于VB编程的内存泄露检测

在计算机系统中,内存泄露常常容易诱发各种系统问题,比如系统宕机、重启等,给实际计算机应用系统造成非常严重的危害。在系统研发阶段,需要检测内存泄露是否存在,从而改进系统,进而提高系统的健壮性。为了有效地检测系统可能存在的内存泄露问题,运用基于Visual Basic编程的算法,通过对计算机进程的内存消耗数据进行数理统计,能够快速地寻找出发生内存泄露的进程。实验结果证明,本方法是切实可靠的,能够有效地预防计算机系统内存泄露,进而避免由于系统崩溃导致的损失。     

GSM和LTE互操作浅析

随着LTE(Long Term Evolution)的大规模建设,网络不仅要支持传统的语音业务,同时也需要满足各类数据业务。与此同时,GSM(Global System For mobile Communications)的技术成熟、设备稳定、性价比高,是目前语音业务的主要解决方案,在未来较长一段时间内仍有充足的发展空间。可以预计,GSM、LTE网络将在未来很长一段时间内共存,这种组网策略对于GSM和LTE系统之间的互操作提出了强烈需求。着重从GSM到LTE的小区重选以及CSFB(Circuit Switched Fallback)两方面分析了GSM和LTE之间的互操作。     

TD-LTE室内覆盖增强的灵活手段:中继

TD-LTE主要部署在高频段,传播损耗和穿透损耗较大,给未来网络室内深度覆盖带来严峻的挑战。在明确TD-LTE室外覆盖室内部署需求的基础上,结合现网测试验证,对中继(relay)增强室内覆盖的性能进行了深入分析。结果表明,针对一些暂时不具备有线回传条件的楼宇,引入中继并以室外覆盖室内方式进行部署,可提供快速、灵活、低成本的深度覆盖解决方案。     

S4开发及性能调优设计思想

文章对于实时流数据分析框架S4在开发和性能调优提出了新的设计思想，以便更适合在各种应用中进行整合和高效实现的探讨。     

TD-LTE网络上行CoMP方案研究与外场试验

TD-LTE采用同频组网,使得小区间干扰成为限制网络容量提升的主要瓶颈之一。TD-LTE规模试验的测试数据表明,终端有超过70%的概率会同时检测到多个小区的信号。多小区协作(CoMP)技术通过相邻多个小区对信号进行联合处理,可有效降低小区间干扰。介绍了几种上行CoMP的实现方案及仿真性能,并重点介绍在TD-LTE试验网络中开展上行CoMP外场试验的情况。测试结果表明,通过上行CoMP可将小区边缘用户上行吞吐率提升50%~100%,显著改善了用户体验。     

Improved modeling method to account for the kink effect of gaas phemts

Short gate-length High Electron Mobility Transistors (HEMTs) have been observed to exhibit kinks in their drain current-voltage (I–V) characteristics. To model this nonlinear effect, we present an effective approach that is easily incorporated into most existing empirical HEMT I–V models. This has been done by modifying the channel length modulation parameter (λ) to account for the kink effect. Moreover, the definitions of the left parameters in the original model will not be influenced, and the improved HEMT I–V model enhances its bias range of operation for which accuracy is maintained. The proposed modeling method is validated through DC/ Pulsed I–V as well as large-signal power measurements.