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31.
Natalia Vassileva Yevgeni Koucheryavy 《Wireless Communications and Mobile Computing》2015,15(4):666-684
The adaptive modulation and coding (AMC) technique, which has been adopted by advanced mobile telecommunication systems, supports a flexible response to the random radio behaviour. As a result, the attained transmission rate over a wireless link is time varying. Hence, resource demands are not deterministic but fluctuating even for calls with constant bit rate service requirements. Consequently, constant bit rate calls are susceptible to a forced call termination because of insufficient resources not only in a target cell during inter‐cell handoffs but also in a serving cell during radio link deterioration. Furthermore, call blocking and dropping probabilities depend on radio propagation conditions among other factors and therefore they are dissimilar throughout a service area. The latter leads to unfairness problems. We analytically measure the impact of AMC on fixed‐rate service with hard delay constraints such as voice for different signal, mobility and traffic conditions. We consider a reference case (call requests are admitted into the system provided there are enough free resources) and two classes of admission control approaches: traditional (only inter‐cell handoffs are prioritised) and modified (all ongoing calls are prioritised). The reported results reveal conditions for which AMC affects voice call performance and can serve as guidelines on admission control design. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
32.
Tsang‐Ling Sheu Chia‐Nan Lin Jenq‐Neng Hwang 《Wireless Communications and Mobile Computing》2015,15(12):1589-1605
This paper presents a channel reservation and preemption (CRP) model using overlapping regions in a cellular network with multiple sectors. To fully exploit and reuse the frequencies, directional antennas are installed on base stations (BSs) to divide the coverage into a number of equal‐sized sectors. When traffic is unevenly distributed across the sectors in a BS, channel utilization in every sector may become very different; low‐traffic sectors may be underutilized while high‐traffic sectors may be overutilized. A CRP scheme is thus proposed to more efficiently utilize free channels among sectors. CRP aims at reducing the dropping probabilities of handoff calls. Specifically, when free channels in a sector are not available, a handoff call, instead of being dropped, is allowed to preempt an ongoing call residing in the overlapping region of two adjacent sectors or two neighbor cells. Under CRP, the preempted ongoing call will not be disconnected, because it can switch over its service to the BS of a neighbor cell or to another directional antenna of an adjacent sector. For the purpose of evaluation, we build an analytical model for the proposed CRP using six‐tuple Markov chains. Analytical results show that the proposed CRP can significantly reduce the dropping probabilities of inter‐sector handoff calls, particularly when traffic between two sectors is not evenly distributed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
33.
Several analytical models have been proposed to study the blocking probability for personal communications service networks or mobile phone networks. These models cannot accurately predict the blocking probability because they do not capture two important features. First, they do not capture the busy-line effect. Even if a cell has free channels, incoming and outgoing calls must be dropped when the destination portable is already in a conversation. Second, they do not capture the mobility of individual portables. In these models, mobility is addressed by net hand-off traffic to a cell, which results in traffic with a smaller variance to a cell compared with the true situation. We propose a new analytic model which addresses both the busy-line effect and individual portable mobility. Furthermore, our model can be used to derive the portable population distribution in a cell. The model is validated against the simulation experiments. We indicate that the previously proposed models approximate a special case of our model where the number of portables in a cell is 40 times larger than the number of channels. 相似文献
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35.
计算机接警指挥调度系统的设计 总被引:1,自引:0,他引:1
介绍分局级公安指挥和接处警系统的设计思想和实现方法.该系统利用语音卡得到报警信息,以自动拨号方式同相关单位建立联系,通过电话召开临时会议,帮助指挥人员迅速、准确地作出决策和部署警力. 相似文献
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37.
超分子结构水杨酸根插层水滑石的组装及结构与性能研究 总被引:26,自引:0,他引:26
以锌铝水滑石ZnAl-CO3 LDHs为前体(主体),以乙二醇为分散介质,用离子 交换法组装了水杨酸根(客体)插层水滑石ZnAl-[o-HO(C6H4)COO]LDHs,并用XRD ,FT-IR,TG-DTA等手段对样品进行了表征。结果表明,能过控制离子交换条件, 水杨酸根阴离子可取代锌铝水滑石前体层间的CO3^2-离子,组装得到晶体结构良好 的水杨酸根插层水滑石。通过研究发现,主体水滑石层板与客体以静电力和氢键相 互作用,得到的超分子结构材料紫外阻隔作用增强并具有较好的稳定性,从而成为 一种集屏蔽和吸收双重功能的新型无机-有机得合紫外阻隔材料。 相似文献
38.
The experimental one-, three-, and five-quasiparticle bands in ~(177)Lu are analyzed by the particle-number conserving (PNC) method for treating the cranked shell model with pairing interaction, in which the blocking effects are taken into account exactly. The experimental moments of inertia are reproduced very well by PNC calculations with us free parameter. 相似文献
39.
提出了一种多媒体呼叫中心在IMS核心网架构下的部署方案,并介绍了各网元的作用,最后给出了呼叫中心注册流程和终端到呼叫中心会话流程。 相似文献
40.
介绍武进呼叫服务中心的框架结构以及对用户来电的流程处理,介绍新建呼叫服务中心时应如何选择和培训呼叫服务人员,总结武进呼叫服务中心在运营管理方面注重的几个要点,并对呼叫服务中心的未来发展提出设想。 相似文献