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介绍了异频方案在室内覆盖中的应用,包括在异频覆盖情况下空闲切换的实现,伪导频的配置方式,并介绍了异频待机、室内异频分层覆盖的方案及相关案例。 相似文献
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矿井机车无人驾驶系统面临的一个主要问题是车载移动节点MN在机车轨旁AP间进行切换产生的通信延时问题。传统切换机制扫描所有信道,时延过大,难以满足系统通信的实时性要求。因此建立井下802.11无线网络模型,提出基于信标同步及信道预测的井下无线网络切换机制,该机制通过同步AP信标帧的广播时间和维护AP邻接链表的方法减少切换延时。通过仿真实验验证该机制能够将切换时延降到实时通信系统的要求,对比传统硬切换机制可降低切换时延达70%以上。 相似文献
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The secondary usage of spectrum has been investigated in Cognitive Radio (CR) network to resolving the spectrum scarcity issue
in wireless communication. When Primary Users (PU) who own the spectrum appear, spectrum handoff is needed to maintain the
communications of Secondary Users. But the decision making of spectrum handoff is a challenge issue for CR network, because
the input of decision making, which obtain through spectrum sensing, is heterogeneous and inexact. In this paper we will use
fuzzy logic control theory to solve this issue and make use of new information for handoff operation: the probability of PU’s
occupancy at a certain channel. Our new algorithm can make more intelligent decision compared to simple traditional spectrum
handoff decision making and reduce the probability of spectrum handoff, also the performance of SU’s communication can be
enhanced. 相似文献
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Cognitive Radio (CR) is an emerging technology used to significantly improve the efficiency of spectrum utilization. Although some spectrum bands in the primary user’s licensed spectrum are intensively used, most of the spectrum bands remain underutilized. The introduction of open spectrum and dynamic spectrum access lets the secondary (unlicensed) users, supported by cognitive radios; opportunistically utilize the unused spectrum bands. However, if a primary user returns to a band occupied by a secondary user, the occupied spectrum band is vacated immediately by handing off the secondary user’s call to another idle spectrum band. Multiple spectrum handoffs can severely degrade quality of service (QoS) for the interrupted users. To avoid multiple handoffs, when a licensed primary user appears at the engaged licensed band utilized by a secondary user, an effective spectrum handoff procedure should be initiated to maintain a required level of QoS for secondary users. In other words, it enables the channel clearing while searching for target vacant channel(s) for completing unfinished transmission. This paper proposes prioritized proactive spectrum handoff decision schemes to reduce the handoff delay and the total service time. The proposed schemes have been modeled using a preemptive resume priority (PRP) M/G/1 queue to give a high priority to interrupted users to resume their transmission ahead of any other uninterrupted secondary user. The performance of proposed handoff schemes has been evaluated and compared against the existing spectrum handoff schemes. Experimental results show that the schemes developed here outperform the existing schemes in terms of average handoff delay and total service time under various traffic arrival rates as well as service rates. 相似文献
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In this article we present an optimal Markov Decision‐based Call Admission Control (MD‐CAC) policy for the multimedia services that characterize the next generation of wireless cellular networks. A Markov decision process (MDP) is used to represent the CAC policy. The MD‐CAC is formulated as a linear programming problem with the objectives of maximizing the system utilization while ensuring class differentiation and providing quantitative fairness guarantees among different classes of users. Through simulation, we show that the MD‐CAC policy potentially achieves the optimal decisions. Hence our proposed MD‐CAC policy satisfies its design goals in terms of call‐class‐differentiation, fairness and system utilization. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Chi‐Yuan Chang Hong‐Jie Wang Han‐Chieh Chao Jong Hyuk Park 《Wireless Communications and Mobile Computing》2008,8(9):1201-1213
Multimedia transmissions are delay‐sensitive Internet applications. Because mobile stations are in continual motion, handoff processes are necessary and unavoidable in wireless network environments. Because handoff processes tend to break the communication link, the research has been conducted on reducing the break time and arrival delay during Internet multimedia applications. In this paper, we propose an approach based on Fuzzy Logic to evaluate the average variation in signal strength received by a mobile station and produce a FitAP factor. This factor indicates the possible handoff access point that is suitable for the mobile station. According to the FitAP factor, a mobile station needs only to execute an active scan process once. Therefore, smaller handoff latency is expected. We compare the results from the current cell search scheme with that of the Fuzzy Logic approach. The statistical results show that the proposed method outperforms the current cell search scheme with an improved handoff latency performance. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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In the literature, there are two common assumptions for the tele‐traffic parameter in analyzing the wireless network performance, that is, the tele‐parameter follows a specific probability density function (pdf) and additionally the pdf exists closed‐form Laplace Transform (LT). However, taking into account the cell irregular shape, the specific pdf may be unavailable while only the measured statistical moments are available. Moreover, the pdf function may not exist a closed‐form LT, for example, lognormal distribution function. In this paper, based on the Central Limit Theorem and hyper‐Erlang universal approximation property, we propose an approximation method applicable in the situations when only the statistical moments are available or LT of pdf does not exist. We then employ the technique in diverse applications, including the performance analysis of wireless network and the cost evaluation of mobility management. Extensive numerical examples demonstrate the good approximation capability to the exact formula and the simulation results. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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在Ad Hoc网络中,如何基于多信道有效地利用网络中的频谱资源,提高网络的性能,已经成为近几年来研究的热点。在DSDV路由协议的基础上,提出了一种基于减少网络中的信道切换的路由算法——OLCH-DSDV,该算法采用最小切换时延的信道分配策略,尽量减少信道切换产生的时延,从而降低了网络时延,提高了吞吐量。该算法要求源节点通过自身维护的路由和信道使用信息,选择到达目的节点的最优路径,也就是需要最少信道切换的路径。仿真结果表明该路由改进算法在有效提高系统吞吐量的同时,也有效地减少了网络中的传输时延。 相似文献