排序方式: 共有14条查询结果,搜索用时 15 毫秒
1.
The standardized IEEE ,802. II distributed coordination function ( DCF) provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters. 相似文献
2.
探讨了IEEE 802.11 DCF的特点和NS2的结构、功能和仿真原理.通过NS2对无线网络传榆性能进行仿真测试,并提出了改善无线网络效能异常现象的有效方法. 相似文献
3.
论述了利用DCF估价模型测算公司未来价值的基本方法,同时阐述了对该方法所计算出的未来价值需要修正的原因以及修正方法. 相似文献
4.
孙博 《连云港职业技术学院学报》2007,20(4):31-33,36
随着便携式计算机(包含笔记本和PDA)的快速普及,无线局域网IEEE 802.1 1成为目前短距离无线通讯技术的主流.无线局域网IEEE 802.11中采用DCF、PCF的接入机制,IEEE802.11e中采用EDCF、HCF的接入机制.对这四种接入机制的接入效率和服务质量 (QoS)进行分析,在此基础上提出了两种改进接入效率的方式,即碰撞导向工作模式与工作站数量导向工作模式.通过这两种方式使网络资源的分配更具有弹性,并满足具有不同优先级的工作站对效率的需求. 相似文献
5.
林正祥 《深圳职业技术学院学报》2010,9(6):3-8,45
同时考虑市场经济波动及随机地震风险等因素,利用折现现金流法(discounted cash flow method)的指标——净现值(net present value,NPV),提出一个量测不动产投资报酬率的架构,并以蒙第卡罗仿真技术(Monte Carlo simulation technique)模拟净现值及其超越概率之关系。此关系提供投资者在投资决策过程中,有关报酬及风险的基本讯息。分析时,不动产的潜在租金收入以随机过程(stochastic process)模拟,地震损坏之年修复成本(annual cost to repair earthquake damages)以年损失量测,并且考虑为随机变量。 相似文献
6.
基于期权定价理论的R&D投资决策思想 总被引:16,自引:1,他引:15
当今竞争激烈的市场要求企业重视R&D投资。本文在探讨了单纯运用系统DCF方法进行R&D投资决策的局限性后,将R&D投资与金融期权进行类比,提出了R&D投资决策的期权定价方法 相似文献
7.
8.
实物期权理论在实际应用中的偏差 总被引:2,自引:0,他引:2
实物期权是期权理论的一个新型应用。实物期权理论突破了传统的投资方法瓶颈,比传统的投资方法更能适用于风险投资决策。但是,实物期权理论也存在缺陷,不仅体现在实物期权定价模型本身的不足,更多的是人们运用实物期权理论于项目投资决策时存在认识误区,从而导致像因特网和其他高科技投资泡沫的破灭。 相似文献
9.
Jázef LUBZCZ 《浙江大学学报(A卷英文版)》2008,9(10):1309-1317
This paper presents an analytical saturation throughput model of IEEE 802.11DCF (distributed coordination function) with basic access in ad hoc mode. The model takes into account freezing of the backofftimer when a station senses busy channel. It is shown that taking into account this feature of DCF is important in modeling saturation throughput by yielding more accurate and realistic results than models known from literature. The proposed analytical model also takes into account the effect of transmission errors. All essential features of the proposed analytical approach are illustrated with numerical results. The presen- tation of the model is proceeded by an overview of approaches to IEEE 802.11 network performance evaluation presented in the literature. 相似文献
10.
DCF方法的局限性研究 总被引:11,自引:0,他引:11
20世纪60年代以后,资本市场理论、资产组合理论突飞猛进地发展,为人们能精确估计企业资本化比率创造了有利条件。粗糙的DCF方法日臻完美,逐渐成为人们普遍认同的企业价值评估的主流方法。然而,基于对不确定风险处理的内在逻辑缺陷,导致DCF方法在使用过程中存在很大的局限性。 相似文献