异构无线网络垂直切换技术综述

垂直切换是多网融合的基础,是实现异构网络互通、支持不同接入方式无缝衔接的核心技术,目前正在受到业界的重点关注,并成为学术界研究的热点问题。随着无线移动通信技术向接入多元化、网络一体化和应用综合化的方向发展,各种蜂窝移动接入、宽带无线接入和固定接入将共同接入基于IP的统一核心网络,通过网络间的垂直切换,支持用户的移动性和移动过程中业务的连续性。首先给出了垂直切换的定义和基本概念,介绍了垂直切换的分类和基本流程,随后详细论述垂直切换的切换判决和切换执行2个环节。针对切换判决,总结了现有判决算法,重点评述各代表算法工作原理并剖析论其特点和存在的不足。针对切换执行,详述了现有垂直切换执行机制的工作原理和适用场景,并分析其优缺点。最后,对未来垂直切换技术的研究方向进行了展望。     

A constrained MDP-based vertical handoff decision algorithm for 4G heterogeneous wireless networks

The 4th generation wireless communication systems aim to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. To achieve this goal, the support of vertical handoff is important in mobility management. This paper focuses on the vertical handoff decision algorithm, which determines the criteria under which vertical handoff should be performed. The problem is formulated as a constrained Markov decision process. The objective is to maximize the expected total reward of a connection subject to the expected total access cost constraint. In our model, a benefit function is used to assess the quality of the connection, and a penalty function is used to model the signaling incurred and call dropping. The user’s velocity and location information are also considered when making handoff decisions. The policy iteration and Q-learning algorithms are employed to determine the optimal policy. Structural results on the optimal vertical handoff policy are derived by using the concept of supermodularity. We show that the optimal policy is a threshold policy in bandwidth, delay, and velocity. Numerical results show that our proposed vertical handoff decision algorithm outperforms other decision schemes in a wide range of conditions such as variations on connection duration, user’s velocity, user’s budget, traffic type, signaling cost, and monetary access cost.     

Signal threshold adaptation for vertical handoff in heterogeneous wireless networks

The convergence of heterogeneous wireless access technologies has been envisioned to characterize the next generation wireless networks. In such converged systems, the seamless and efficient handoff between different access technologies (vertical handoff) is essential and remains a challenging problem. The heterogeneous co-existence of access technologies with largely different characteristics results in handoff asymmetry that differs from the traditional intra-network handoff (horizontal handoff) problem. In the case where one network is preferred, the vertical handoff decision should be carefully executed, based on the wireless channel state, network layer characteristics, as well as application requirements. In this paper, we study the performance of vertical handoff using the integration of 3G cellular and wireless local area networks as an example. In particular, we investigate the effect of an application-based signal strength threshold on an adaptive preferred-network lifetime-based handoff strategy, in terms of the signalling load, available bandwidth, and packet delay for an inter-network roaming mobile. We present an analytical framework to evaluate the converged system performance, which is validated by computer simulation. We show how the proposed analytical model can be used to provide design guidelines for the optimization of vertical handoff in the next generation integrated wireless networks. This article is the extended version of a paper presented in IFIP Networking 2005 Ahmed H. Zahran is a Ph.D. candidate at the Department of Electrical and Computer Engineering, University of Toronto. He received both his M.Sc. and B.Sc. in Electrical Engineering from Electronics and Electrical Communication Department in the Faculty of Engineering, Cairo University in 2002 and 2000 respectively, where he was holding teaching and research positions. Since September 2003, he has been working as a research assistant in the Department of Electrical and Computer Engineering, University of Toronto under the supervision of Professor Ben Liang. His research interest is wireless communication and networking with an emphasis on the design and analysis of networking protocols and algorithms. Ben Liang received honors simultaneous B.Sc. (valedictorian) and M.Sc. degrees in Electrical Engineering from Polytechnic University in Brooklyn, New York, in 1997 and the PhD degree in Electrical Engineering with Computer Science minor from Cornell University in Ithaca, New York, in 2001. In the 2001–2002 academic year, he was a visiting lecturer and post-doctoral research associate at Cornell University. He joined the Department of Electrical and Computer Engineering at the University of Toronto as an Assistant Professor in 2002. His current research interests are in the areas of mobile networking and wireless multimedia systems. He is a member of Tau Beta Pi, IEEE, and ACM and serves on the organization and technical program committees of a number of major conferences each year. Aladdin Saleh earned his Ph.D. degree in Electrical Engineering from London University, England. Since March 1998, Dr. Saleh has been working in the Wireless Technology Department of Bell Canada, the largest service provider of wireless, wire-line, and Internet in Canada. He worked as a senior application architect in the wireless data group working on several projects among them the wireless application protocol (WAP) and the location-based services. Later, he led the work on several key projects in the broadband wireless network access planning group including planning of the IEEE 802.16/ Wimax, the IEEE 802.11/ WiFi, and the integration of these technologies with the 3G cellular network including Mobile IP (MIP) deployment. Dr. Saleh also holds the position of Adjunct Full Professor at the Department of Electrical and Computer Engineering of Waterloo University, Canada since January 2004. He is currently conducting several joint research projects with the University of Waterloo and the University of Toronto on IEEE 802.16-Wimax, MIMO technology, interworking of IEEE 802.11 WLAN and 3G cellular networks, and next generation wireless networks. Prior to joining Bell Canada, Dr. Saleh worked as a faculty member at different universities and was Dean and Chairman of Department for several years. Dr. Saleh is a Fellow of IEE and a Senior Member of IEEE.     

Seamless vertical handoff using modified weed optimization algorithm for heterogeneous wireless networks

In the global scenario, a variety of wireless access networks are available. Different types of applications such as real time, nonreal time, and high bandwidth availability are used for heterogeneous wireless networks. Therefore, it is necessary for a service provider to make an appropriate connection support. For better performance, connections are to be exchanged among the different networks using seamless vertical handoff (VHO). The proposed algorithm shows the effect of optimization technique, which involves handoff decision process using vertical handoff triggering and selection of the network. The handoff triggering is initiated by using the received signal strength (RSS). In traditional method, handoff triggering is initiated by using RSS only. This method, modified weed optimization (M-WO) algorithm, reduces the unnecessary handoff by considering both RSS and velocity of the mobile node in handoff triggering. The parameters such as battery lifetime, handoff call dropping rate, load, dynamic weights adaptation and so on are to be considered individually or combined to make an effective network selection process. This paper highlights a novel effect ofM-WOalgorithm for decision making during the VHO. Our effort is to essentially optimize the system load, so that it reduces the handoff call dropping rate and the battery power consumption of the mobile node (MN). Weight of each QoS metrics is adjusted along with the networks changing conditions to trace the M-WO. Therefore, the novel VHO decision-making algorithm is superior to the existing SSF and OPTG methods. The simulation results show that the performance ofM-WOalgorithm is far better than SSF andOPTGmethods in terms of load, handoff call dropping rate and battery lifetime of MN.     

Immune optimization algorithm for solving vertical handoff decision problem in heterogeneous wireless network

In heterogeneous wireless network environment, wireless local area network (WLAN) is usually deployed within the coverage of a cellular network to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. Vertical handoffs between the WLAN and the cellular network maybe occur frequently. As for the vertical handoff performance, there is a critical requirement for developing algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a mathematical model for vertical handoff decision problem, and propose a multi-objective optimization immune algorithm-based vertical handoff decision scheme. The proposed scheme can enable a wireless access network not only to balance the overall load among all base stations and access points but also maximize the collective battery lifetime of mobile terminals. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed scheme.     

Group vertical handoff management in heterogeneous networks

Traditional vertical handover schemes postulate that vertical handovers (VHOs) of users come on an individual basis. This enables users to know previously the decision already made by other users, and then the choice will be accordingly made. However, in case of group mobility, almost all VHO decisions of all users, in a given group (e.g., passengers on board a bus or a train equipped with smart phones or laptops), will be made at the same time. This concept is called group vertical handover (GVHO). When all VHO decisions of a large number of users are made at the same time, the system performance may degrade and network congestion may occur. In this paper, we propose two fully decentralized algorithms for network access selection, and that is based on the concept of congestion game to resolve the problem of network congestion in group mobility scenarios. Two learning algorithms, dubbed Sastry Algorithm and Q‐Learning Algorithm, are envisioned. Each one of these algorithms helps mobile users in a group to reach the nash equilibrium in a stochastic environment. The nash equilibrium represents a fair and efficient solution according to which each mobile user is connected to a single network and has no intention to change his decision to improve his throughput. This shall help resolve the problem of network congestion caused by GVHO. Simulation results validate the proposed algorithms and show their efficiency in achieving convergence, even at a slower pace. To achieve fast convergence, we also propose a heuristic method inspired from simulated annealing and incorporated in a hybrid learning algorithm to speed up convergence time and maintain efficient solutions. The simulation results also show the adaptability of our hybrid algorithm with decreasing step size‐simulated annealing (DSS‐SA) for high mobility group scenario. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

A novel software‐defined networking approach for vertical handoff in heterogeneous wireless networks

We propose a novel vertical handoff scheme with the support of the software‐defined networking technique for heterogeneous wireless networks. The proposed scheme solves two important issues in vertical handoff: network selection and handoff timing. In this paper, the network selection is formulated as a 0‐1 integer programming problem, which maximizes the sum of channel capacities that handoff users can obtain from their new access points. After the network selection process is finished, a user will wait for a time period. Only if the new access point is consistently more appropriate than the current access point during this time period, will the user transfer its inter‐network connection to the new access point. Our proposed scheme ensures that a user will transfer to the most appropriate access point at the most appropriate time. Comprehensive simulation has been conducted. It is shown that the proposed scheme reduces the number of vertical handoffs, maximizes the total throughput, and user served ratio significantly. Copyright © 2016 John Wiley & Sons, Ltd.     

A new handoff management system for heterogeneous wireless access networks

In heterogeneous wireless access networks, each mobile terminal may frequently need to change its base station (BS); this change is called a ‘handoff’. BSs have static parameters, which are related to their radio access technologies (RATs); however, they also contain dynamic parameters such as load and signal quality. Therefore, the problem of handoff decision includes two subproblems of RAT selection and BS selection. In this paper, first a ‘heterogeneous handoff management system’ for gathering all different required parameters is proposed. Second, a RAT Selection algorithm based on analytic hierarchy process and a BS Selection algorithm based on data envelopment analysis are designed. Finally, by means of ‘weight restriction’ technique, we develop a method for studying the impact of RAT Selection parameters on the performance of the network. Simulation results indicate that RAT Selection parameters have significant impact on the bandwidth utilization, energy consumption and the whole satisfaction of the users in heterogeneous wireless access networks.Copyright © 2012 John Wiley & Sons, Ltd.     

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。     

一种新的无线异构网络的自适应垂直切换算法

针对当前无线异构网络融合技术中的垂直切换机制,提出了一种以平均接收信号强度为评价指标,并由此指标判断可能的运动趋势的自适应垂直切换算法。仿真结果表明:相比于传统的固定门限的平均接收信号强度垂直切换算法,提出的方法能较好地预测并提前触发该发生的切换,改善切换性能。     

异构网中一种能效最优的垂直切换算法

针对传统垂直切换算法中未能考虑能效这一关键因素,提出了一种能效最优的垂直切换算法,算法核心是移动终端检测并计算来至不同候选网络中的接收信号强度以及各候选小区中的系统容量,以候选小区中每单位能量所能提供的容量作为判决准则切入到最佳网络,同时结合传统的网络因子对多属性判决算法进行能效扩展。仿真结果表明,基于单位能量容量的切换算法较传统的切换算法节省10%左右的能量,扩展的多属性判决算法较传统的切换算法节省7%左右的能量,同时减少了“乒乓效应”,提高了用户的通信体验质量。     

Network selection based on multiple attribute decision making and group decision making for heterogeneous wireless networks

One of the key issues for radio resources management is network selection strategy in heterogeneous scenarios.In order to provide ubiquitous service,the paper puts forward a network selection algorithm based on multiple attribute decision making(MADM) and group decision making(GDM).Firstly,the proposed algorithm acquires attribute weights’ vectors of the subjective and objective decision makers based on MADM,and then the two attribute weights’ vectors are synthesized to be a new attribute weights’ vector by using GDM.Considering that the results of GDM should be reasonable and convincible,the criterion of consistency is adopted for judging the compatibility of group judgments.More specifically,the algorithm takes into account not only objective attributes of networks but also the preference of subscribers and traffic class.Hence it guarantees that the subscribers can not select the networks with poor performance depending on their preference.The simulation results show that the proposed algorithm can effectively reduce the handoff number and provide subscribers with satisfactory quality of service(QoS).     

异构无线网络中基于马尔可夫决策过程的区分业务接纳控制的研究

对异构无线网络中区分业务类型的接纳控制机制进行研究.分析了语音和数据2种典型业务在CDMA蜂窝网络和WLAN中的容量区域.基于马尔可夫决策过程理论,提出异构无线网络中区分业务类型的接纳控制理论模型,规定了不同类型业务的接纳控制行为并推导了系统状态转移概率.而且,进一步从用户角度对不同类型业务QoS要求和网络状态之间关系进行分析,提出一种基于模糊逻辑的接纳效用评估机制,在保证各类业务接入和切换成功率的基础上,推导出接纳效用最大的最优接纳控制策略.仿真表明,基于模糊逻辑的接纳效用评估能够有效反映网络状态动态变化对接纳控制的影响,最优接纳控制策略在平均接纳效用方面明显优于不考虑业务区分和用户移动性2种接纳控制机制,并且能严格保证各类业务的接入和切换成功率.     

Learning with handoff cost constraint for network selection in heterogeneous wireless networks

In heterogeneous wireless networks, network selection algorithms provide the user with the optimum network access choice. The optimal network is evaluated according to network parameters. Considering that the network parameters are dynamic and unavailable for the user in realistic heterogeneous wireless network environments, most existing network selection algorithms cannot work effectively. Learning‐based algorithms can address the problem of uncertain network parameters, while they commonly need considerable network handoff, resulting in unbearable handoff cost. In order to tackle the uncertainty of network parameters, we formulate the network selection problem as a multi‐armed bandit problem. Moreover, two online learning‐based network selection algorithms with a special consideration on reducing network handoff cost are proposed. By updating in a block manner, both algorithms achieve optimal logarithmic‐order regret and limited network handoff cost. The simulation indicates that the two algorithms can significantly reduce the network handoff cost and improve the transmission performance compared with existing algorithms, simultaneously. Copyright © 2014 John Wiley & Sons, Ltd.     

Improving TCP performance for vertical handover in heterogeneous wireless networks

The incorporation of wireless local area networks (WLANs) into existing cellular networks as supplementary access technologies has become an issue of great interest. However, vertical handover (VHO), which allows users to roam between a WLAN and a cellular network, causes an abrupt change in certain link characteristics such as the round trip time and data rate. Owing to such changes, reordering problem and premature timeout occur and trigger unnecessarily fast retransmission during VHO, causing throughput degradation. Thus, we propose a new transmission control protocol (TCP) mechanism, which resolves the reordering problem by suppressing unnecessary retransmission caused by spurious duplicate acknowledgments (dupacks) incurred because of the reordering problem, and prevents premature timeout by employing an adaptive retransmission timer. We analytically investigate the throughput of our proposed TCP scheme. The numerical and simulation results show that our proposed TCP performs better in terms of throughput than other schemes appearing in the literature. Copyright © 2009 John Wiley & Sons, Ltd.     

Vertical handoff decision in 4G wireless networks using multi attribute decision making approach

Multi-interface terminal in heterogeneous wireless networks will have network access from diverse access technologies. Multiple attribute for decision making including user preference will increase the complexity of handoff process. Various approaches have been proposed to solve the complexity problem of handoff decision. In this paper, multi attribute decision making algorithms Analytic Hierarchy Process (AHP) method, Simple Additive Weighting (SAW), Total Order Preference by Similarity to the Ideal Solution (TOPSIS), and Grey Relational Analysis (GRA) methods have been proposed for handoff decision in a WiMAX–WLAN environment to facilitate user with better quality of service. AHP has been used for calculation of weights of decision parameters. Numerical results show that SAW, TOPSIS and GRA provide almost similar performance. SAW is very simple to implement but probability of error is less in GRA because values of decision attribute are directly used for ranking of alternatives. TOPSIS is sensitive to the attribute with high score.     

一种基于上下文感知的垂直切换技术研究

未来网络的发展趋势是各种无线接入网络共存的异构网络环境,而垂直切换技术是融合多个异构接入网络的关键技术之一,垂直切换包括三个阶段,即系统发现、切换决策和切换执行。文中主要研究了基于上下文感知的垂直切换判决策略,并与移动垂直切换技术相结合,实现了WLAN/UMTS网络间的垂直切换,通过仿真表明该方法在吞吐量和切换时延方面都得到改善。     

异构网络中基于终端决策的通用垂直切换算法

垂直切换是异构网络中的关键技术,目前已有的垂直切换算法大多是针对特定的网络或切换过程的某个环节,提出一种与网络类型无关的通用垂直切换算法,仿真结果表明该算法在支持多任务,有效利用能量方面比传统方法有很大的改进.