无线异构网络的垂直切换

传统意义上的水平切换算法已经在同构网络中得到很好的研究和应用,而随着多种无线异构网络的出现,下一代网络必须支持垂直切换技术以保证用户从一种类型的网络切换到另一种类型的网络时仍然保持连接。由于切换算法所需考虑因素的多样性和算法本身的复杂性,有必要对现有文献中的网络切换类型、切换因素、切换算法进行了归纳总结,并对垂直切换算法进行比较,指出未来切换算法的研究方向。     

无线异构网络的垂直切换算法研究

以通用移动通信系统(UMTS)与无线局域网(WLAN)融合为例,研究无线异构网络的垂直切换算法。由于垂直切换算法应考虑因素的复杂性以及不同网络性能的各异性,有必要对现有算法作出归纳总结比较,并据此提出新的垂直切换算法。该算法以代价函数为基础,将稳定周期与切换目标网络和当前服务网络的效用函数联系起来,实现移动节点自适应的切换判决。提出的算法能有效减少不必要的切换,增强异构网络的适应性。     

车联网中基于贝叶斯决策的垂直切换方法研究

车辆需要在车联网的异构无线网络环境下进行垂直切换,针对垂直切换技术普遍不能支持 WAVE, WiMAX和3G cellular间的垂直切换这一问题,提出了一种基于贝叶斯决策的垂直切换算法。首先,根据接入网络的信号强度、传输速率、误码率和网络阻塞率以及车辆终端的速度和运动趋势建立多条件相关的切换概率分布,计算出切换先验概率;然后通过贝叶斯决策算法计算后验概率并进行决策分类,从而选取最优网络接入。仿真实验结果表明,该算法不仅有效地实现WAVE,WiMAX和3G cellular无线接入技术之间的垂直切换,而且避免了乒乓效应,保证了网络及时更新。     

车辆异构网络中预测垂直切换算法

在车辆异构网络中,针对垂直切换决策时刻之后网络状态的动态变化,提高切换性能问题,提出一种基于马尔可夫过程的预测垂直切换(M-VHO)算法。算法考虑了切换决策后网络状态的动态变化对车辆终端服务质量(QoS)的影响。其基本思路是:在需要垂直切换时,利用马尔可夫过程的转移概率预测未来网络状态的变化;另外,采用模糊逻辑方法确定评价属性参数权重;最后,比较切换决策、切换执行和切换之后时刻的总收益来优化选择最佳切换网络。仿真结果证明,该算法在确保较高负载均衡的情况下,可有效改进车辆终端的平均阻塞率及丢包率,降低乒乓效应,确保了车辆终端的QoS。     

一种基于速度感知的垂直切换算法

 未来的4G网络不是由单一的接入方式构成,而是采用不同的无线接入技术的多种网络的融合.不同网络接入技术间的切换称为垂直切换.本文提出了一种基于速度感知的垂直切换算法,不需确切的节点坐标和速度信息,利用接收信号强度的历史测量数据来表征节点运动速度的影响,提高对切换触发时机的准确判断.该算法可以自动调整以适应不同的节点运动速度,有效提高垂直切换的效率.仿真试验表明该算法能有效提高垂直切换的性能.     

基于分段式PPP协商的快速网络接入算法

多网融合是当今无线通信网络发展的必然趋势,垂直切换是网络融合的关键技术之一。对现有3G网络的终端接入信令流程进行分析,提出了一种基于分段式PPP协商的快速接入算法。通过在现网环境中测试,证明该算法有效地缩短了切换执行时延,对垂直切换过程中"切换执行"阶段的研究做出了贡献。     

车联网环境下的4G和DSRC异构网络切换机制研究

面向车联网的实际应用需求,构建了一种高速公路环境下的基于4G和DSRC的异构网络通信场景。针对车辆在该场景下可能会在不同网络信道间频繁发生垂直切换导致较高的传输时延和丢包率的问题,在分析研究基于4G与DSRC的高速公路异构网络切换过程的基础上,引入网络跳数、连接次数和行驶轨迹作为切换判决条件,基于TREBOL路由协议设计了一种异构网络垂直切换算法。最后利用Veins仿真平台对提出的异构网络垂直切换算法的切换性能进行对比测试分析。测试结果表明,与基于RSSI的异构网络垂直切换方法相比,所提切换算法能增大车辆与DSRC网络连接的持续时间,并有效减少"乒乓效应"。     

多网络共存下基于贝叶斯的垂直切换算法

针对目前的垂直切换技术普遍不能满足多网络下的切换问题,提出了一种改进的基于贝叶斯决策的垂直切换算法。首先根据接入终端网络的信号强度、网络负载、误码率和网络阻塞率以及用户业务对网络的实际需求偏好建立多条件相关的切换概率分布,计算出先验切换概率;然后通过贝叶斯决策算法计算出后验概率来进行判决比较,从而选取最优的接入网络。仿真结果表明,该算法不仅能有效地实现不同接入技术之间的垂直切换,从而减少不必要的切换,提高了切换成功的概率,而且还能在维持各网络平均负载达到30%~40%时减轻通信热点的阻塞情况,为用户提供更优的服务质量。     

3G-WLAN融合网络中一种新的双模终端设计

设计了一种能够在3G与WLAN融合网络中智能切换的双模终端模型.为了实现两种网络之间的无缝切换,提出了网络接口选择算法.该算法通过提前注册和认证机制减少了垂直切换时延,并采用提前切换的方法减少了垂直切换时数据包丢失.仿真结果验证了设计和算法具有良好性能.     

基于Matlab的LTE与Wi-Fi垂直切换多属性算法研究

随着数据业务的需求量日渐增长,通信面临巨大的压力.未来通信系统将是不同制式网络进行无缝融合的系统.异系统之间的垂直切换的正确性以及有效性将是系统能否无缝融合的决定性因素.本文研究了LTE与Wi-Fi异系统的多属性垂直切换算法,并基于Matlab进行了算法实现设计.设计结果表明,多属性垂直切换算法使得LTE与Wi-Fi融合系统能够成功进行垂直切换,并且切换发生的乒乓效应较弱.     

Two-state pattern-recognition handoffs for corner-turningsituations

Handoff algorithms are used in wireless cellular systems to decide when and to which base station to handoff. Traditional handoff algorithms generally cannot keep both the average number of unnecessary handoffs and the handoff decision delay low. They do not exploit the relative constancy of path loss and shadow fading effects at any given location around a base station. However, handoff algorithms with both a negligible number of unnecessary handoffs and a negligible decision delay can be realized by exploiting this information. One example is the set of handoff algorithms using pattern-recognition introduced in previous work. In this paper, we describe how pattern-recognition handoff algorithms can be applied to the problem of turning a corner. This can be used as part of an integrated pattern-recognition handoff algorithm or together with a traditional handoff algorithm, in which case the pattern-recognition handles only the special cases like turning a corner     

移动通信系统中的越区切换技术研究

针对切换策略和算法是决定3G网络性能好坏的关键因素之一,文章简单介绍了越区切换的原因,对越区切换的策略进行相关的论述,最后主要介绍了几种典型的越区切换算法,着重对资源预留和呼叫请求排队联合切换算法做了详细的分析.     

在DWCS中的位置和方向辅助切换算法

DWCS(分布式无线通信系统)中的切换可分成两类:单天线切换和天线组切换。对选择固定虚拟小区大小方式的DWCS系统,天线组切换方式有较好的性能。为进一步提高切换的性能,一种位置和方向信息辅助的切换算法被提出,而且经过仿真研究其在不同定位精度下的性能,发现在20m以内精度下,该算法将能保持良好的稳定性,从而保证了其在DWCS中的可行性。     

An Adaptive Hard Handoff Algorithm for Mobile Cellular Communication Systems

In this letter, we propose an adaptive hard handoff algorithm with a dynamic hysteresis value based on the received signal strength from the serving base station, for mobile cellular communication systems. A discrete‐time method is presented to evaluate handoff algorithms analytically. Performance is evaluated in terms of the average number of handoffs, the probability of link degradation, and the average handoff delay. Numerical results and simulations demonstrate that the proposed algorithm outperforms the handoff algorithm with fixed hysteresis values and the handoff algorithm using both threshold and hysteresis.     

A Simple and Robust Vertical Handoff Algorithm for Heterogeneous Wireless Mobile Networks

Wireless networking is becoming an increasingly important and popular way of providing global information access to users on the move. One of the main challenges for seamless mobility is the availability of simple and robust vertical handoff algorithms, which allow a mobile node to roam among heterogeneous wireless networks. In this paper, motivated by the facts that vertical handoff procedure is done on mobile nodes and battery power may be one crucial parameter for certain mobile nodes, a simple and robust two-step vertical handoff decision algorithm is proposed for heterogeneous wireless mobile networks. To the best of our knowledge, this is the first vertical handoff algorithm that takes the classification of mobile nodes into consideration, one is resource-poor mobile nodes, and the other is resource-rich mobile nodes. This new feature makes it more applicable in the real world. In addition, dynamic new call blocking probability is firstly introduced by this paper to make handoff decision for wireless networks. The experiment results have shown that the proposed algorithm outperforms traditional algorithms in bandwidth utilization, handoff dropping rate and handoff rate.     

Signal-based evaluation of handoff algorithms

We propose a new framework, based on signal quality, for performance evaluation and comparison between existing handoff algorithms. It includes new call quality measures and an off-line cluster-based computationally-simple heuristic algorithm to find a near optimal handoff sequence used as a benchmark. We then compare existing handoff algorithms and identify the trade-off between signal quality and number of handoffs.     

Hierarchical optimization of microcellular call handoffs

In this paper, we present a novel hierarchical optimization handoff algorithm (HOHA) which has superior performance over the conventional one- and two-threshold handoff algorithms. Our proposed algorithm scans through layers of call handoff options and determines the best candidate based on a heuristic that synchronizes reciprocal handoffs in adjacent cells and maximizes the spare channel capacity in the destination cells. Computer simulation results show that under a unity normalized load condition, the HOHA achieves a gain of about 55% and 11% in the probability of handoff failure as compared to the one- and two-threshold handoff algorithms, respectively. In addition, the total effective load carried is also improved by about 13% and 4%, respectively     

集成Ad Hoc和移动蜂窝网络系统的切换算法

传统切换算法不能适应多准则切换的要求,基于多准则切换算法的实现越来越重要,必须发展新的技术来提高切换算法的有效性,在用户满意度和网络效率间形成平衡。智能和优化切换算法对像集成自组网(Ad hoc)和蜂窝网络结构的混合网络具有很好的适应性和鲁棒性,能够根据未来混合网络中的各种业务类型的服务质量需求、网络状态以及移动节点条件等多种因素的变化进行自适应切换,可以运用这些智能优化算法来进行更加有效的切换判决,从而提高系统的性能。更进一步的研究方向是在集成Ad hoc和蜂窝网络的环境下,使用智能或优化技术设计垂直切换算法来提高系统整体性能。     

Variations on optimal and suboptimal handoff control for wirelesscommunication systems

The design of handoff algorithms for cellular communication systems based on signal-strength measurements is addressed. The system is modeled using a hybrid framework: a mixture of continuous state and discrete event systems. The handoff problem is formulated as an optimization problem to control the switchings within the discrete event system. Performance is evaluated as a function of the expected number of handoffs, the expected handoff delay, and the expected number of signal degradations. A signal degradation occurs when the signal level falls below a threshold. The cost of handoff delay is explicitly specified, in contrast to prior work. Various optimization problems are posed to trade off between these quantities. Based on the optimal solutions which are obtained through dynamic programming, suboptimal versions are proposed for ease of implementation. The performance of the suboptimal algorithm which trades off between the expected number of handoffs and the expected number of signal degradations is improved through the use of signal averaging; however, this algorithm suffers from excessive handoff delay. Therefore, the tradeoff between handoff delay and number of handoffs is considered. The corresponding suboptimal algorithm provides nearly one handoff and almost no delay, which is ideal if call quality is also good. Finally, an algorithm which is a combination of the two previous algorithms is explored     

Adaptive vertical handoff algorithm in heterogeneous networks

The integration of cellular network (CN) and wireless local area network (WLAN) is the trend of the next generation mobile communication systems, and nodes will handoff between the two kinds of networks. The received signal strength (RSS) is the dominant factor considered when handoff occurs. In order to improve the handoff efficiency, this study proposes an adaptive decision algorithm for vertical handoff on the basis of fast Fourier transform (FFT). The algorithm makes handoff decision after analyzing the signal strength fluctuation which is caused by slow fading through FFT. Simulations show that the algorithm reduces the number of handoff by 35%, shortens the areas influenced by slow fading, and enables the nodes to make full use of WLAN in communication compared with traditional algorithms.