全IP 4G无线网络中的关键问题

第四代移动通讯系统的特点是:多种接入网络和基于IP的传输技术.不同的接入技术使用户在选择服务时有了极大的灵活性,而服务也具有不同的QoS支持、商务类型和服务提供商.在考虑QoS和AAAC的同时,实现向最优网络进行无缝切换不仅要求无缝换手协议,而且要求智能换手决定策略.本文介绍了全IP结构的第四代移动通讯系统的特点和关键技术以及未来的问题和研究方向.     

A survey on applications of IEEE 802.21 Media Independent Handover framework in next generation wireless networks

Integration of various wireless access technologies is one of the major concerns in recent wireless systems in which multi-technology mobile devices are provided to users to roam between different access networks. Being an essential part in heterogeneous wireless systems, vertical handover is more complex than conventional horizontal handover. As IEEE 802.21 Media Independent Handover (MIH) is the standard addressing a uniform and media-independent framework for seamless handover between different access technologies, many works have been carried out in the literature to employ MIH services in handover management This paper presents a comprehensive survey of the proposed mobility management mechanisms that are using this framework. As a comparative view, the paper categorizes the efforts according to the layer of mobility management and evaluates some of the representative methods discussing about their advantages and disadvantages The paper also looks into recent handover decision and interface management methods that are exploiting MIH Moreover, the extensions and the amendments proposed on MIH are overviewed.     

A novel terminal-controlled handover scheme in heterogeneous wireless networks

In the next generation heterogeneous wireless networks, a mobile terminal (MT) with a multi-interface may have network access from different service providers using various technologies. In spite of this heterogeneity, seamless intersystem mobility is a mandatory requirement. One of the major challenges for seamless mobility is the creation of a vertical handover scheme, which is for users that move between different types of networks. In this article a seamless mobility handover scheme is presented. The novelty of the proposed scheme is that handover is fully controlled by the terminal. To improve the performance of the proposed handover scheme, a network discovery algorithm with fuzzy logic and a handover decision algorithm using multi criteria decision making (MCDM) based on vague sets are derived, which are both user-centric. With these algorithms, the handover scheme is power-saving, cost-aware, and performance-aware. Simulation results show that the novel handover scheme can perform network discovery in time to reduce handover dropping rate and present unnecessary activation of its interface to save the battery power, while effectively choose the optimum network through making trade-off among the user preference, network condition, and system performance.     

Implementation and performance study of IEEE 802.21 in integrated IEEE 802.11/802.16e networks

In this paper, we propose a framework for the implementation of the IEEE 802.21 Media Independent Handover (MIH) standard and evaluate its performance through experiments in integrated 802.11/802.16e networks. The IEEE 802.21 standard defines three types of MIH services (event, command, and information) that facilitate the mobility management and handover process in heterogeneous networks. To support MIH services, we develop a MIH-capable mobile node and the MIH information service server. Then, we introduce the Connection Manager (CM) which utilizes MIH services. Two main roles of CM are supporting seamless vertical handovers and efficient access point (AP) discoveries. From the experimental results in the real test-bed, we can know that the MIH services can be used to reduce packet losses during a vertical handover and to reduce the AP discovery time and energy consumption of mobile nodes.     

移动环境中多级网络安全切换策略设计

将异构移动网络抽象成多级网络模型,将多级安全引入切换过程,设计了基于MLS（Multilevel Security）的安全切换策略。该策略针对用户连续切换产生的信息泄露问题,规定保证安全等级不降低的约束条件,保证切换过程中用户与网络的安全,并且与其他方案相比,能够提供更全面的安全保护。经形式化证明,该策略是安全的。     

Optimized fast handover scheme in Mobile IPv6 networks to support mobile users for cloud computing

In the future cloud computing, users will heavily use mobile devices. Mobile networks for cloud computing should be managed efficiently as well as support seamless services to mobile users regardless of their locations and movements. Hence, in mobile networks for cloud computing, it is important to support seamless mobility management to mobile users who request real-time services such as VoIP, streaming, and interactive game playing. To support seamless mobility management for various wireless technologies in cloud computing, Mobile IPv6 (MIPv6) and fast handovers for MIPv6 (FMIPv6) have been studied. FMIPv6 has been emerged to reduce long handover latency and packet loss in MIPv6. FMIPv6 may provide seamless handover by minimizing the handover latency, and prevent packet loss through buffering and tunneling. FMIPv6 uses anticipation based on layer 2 trigger information, and consists of two operation modes such as the predictive mode and the reactive mode. Several works have been done to evaluate the performance of FMIPv6 in different network environments. However, the previous works did not consider the probability of predictive mode failure (PPMF) that distinguishes two operation modes. Even in the most previous work, two operation modes of FMIPv6 are evaluated separately. However, to accurately analyze the overall performance of FMIPv6, two operation modes should be analyzed altogether. In this paper, FMIPv6 combining two operation modes is analyzed considering the PPMF that is affected by the radius of a cell, velocity of mobile nodes, and the layer 2 triggering time. The effect of system parameters, such as the PPMF, the time required to process additional layer 3 signaling, and the layer 2 trigger time, is analytically investigated with respect to the signaling cost and the packet delivery cost. Analytical results show a trade-off between performance and system parameters. Then we show methods to optimize overhead of FMIPv6. Finally, mobile networks for cloud computing can be efficiently managed through the optimized FMIPv6.     

A simple and robust handover authentication between HeNB and eNB in LTE networks

There are two types of base stations in the Long Term Evolution (LTE) wireless networks, Home eNodeB (HeNB) and eNodeB (eNB). To achieve seamless handovers between the HeNB and the eNB is critical to support mobility in the LTE networks. A handover from an eNB/HeNB to a new eNB/HeNB, suggested by the third Generation Partnership Project (3GPP), requires distinct procedures for different mobility scenarios with a complex key management mechanism, which will increase the system complexity. Besides, it cannot achieve backward security in handover procedures. Furthermore, the existing handover schemes for other wireless networks are not suitable for the mobility scenarios in the LTE networks due to their inherent features. In this paper, we propose a fast and secure handover authentication scheme, which is to fit in with all of the mobility scenarios in the LTE networks. Compared with other handover schemes, our scheme cannot only achieve a simple authentication process with desirable efficiency, but also provide several security features including Perfect Forward/Backward Secrecy (PBS/PFS), which has never been achieved by previous works. The experimental results and formal verification by using the AVISPA tool show that the proposed scheme is efficient and secure against various malicious attacks.     

Optimization of QoS parameters using scheduling techniques in heterogeneous network

Multimedia applications in wireless communication have been increased in recent years. A variety of wireless access technologies is introduced for various needs. The abundant increase in mobile computing devices and different networking systems leads to the support of user’s mobility on heterogeneous network. In general, the roaming users migrate between two different wireless technologies and their service must be supported by vertical handover (HO). Since the roaming users expect a rapid handover experience while switching from one wireless network to another, the handover operation must be enhanced by the networks. Various wireless technologies such as wireless LAN, Worldwide Interoperability for Microwave Access (WiMAX), and the 3G Partnership Project (3GPP) are interlaced to support many wireless services in rural, urban, and global scenarios. Moreover, quality of service (QoS) has become more significant in many applications where wireless network resources are utilized. In this paper, a handover management scheme is proposed for QoS enhancement in roaming users between WiMAX and WLAN by subscribers of networks belonging to the 3GPP standards. The proposed algorithms genetic queuing, proportionally fair queuing, and WiMAX aware load balancing are analyzed in the scheduling process during handover. The simulation is implemented using NS–2 and the experimental results are obtained for the proposed algorithms and compared with the standard scheme.     

Exploiting mobility patterns for inter-technology handover in mobile environments

Mobile terminals with multi-radio devices have become increasingly prevalent. This makes it possible for Internet applications to be supported by heterogeneous wireless networks while the terminal is on the move. As the user is constantly moving, it is highly desirable that the terminal connects to the best network and retains high performance of network connections. Handovers can be made within the same type of network (horizontal handover) or different types of networks (vertical handover). This paper focuses on link-layer inter-technology vertical handovers. Vertical handovers present several great challenges, such as user mobility randomness, high handover overhead and optimality requirement. Existing work often focuses only on the current network condition when making handover decisions, ignoring future performance of the terminal. As a result, a handover decision good for the current moment may soon become poor when the user moves to another place. This paper is motivated by the observation that users in a given mobile environment, such as university or enterprise campus, exhibit clear mobility patterns. We propose an approach for making handover decisions, which explicitly exploits user mobility patterns. This approach can produce high-performance handover decisions in the long run. Employing a comprehensive framework for preference customization, the approach supports user customization caring for different user preferences. Extensive real trace driven simulations and comparative study show our algorithm is better than the conventional vertical handover algorithms.     

Fuzzy based multi-criteria vertical handover decision modeling in heterogeneous wireless networks

Vertical handover gain significant importance due to the enhancements in mobility models by the Fourth Generation (4G) technologies. However, these enhancements are limited to specific scenarios and hence do not provide support for generic mobility. Similarly, various schemes are proposed based on these mobility models but most of them are suffered from the high packet loss, frequent handovers, too early and late handovers, inappropriate network selection, etc. To address these challenges, a generic vertical handover management scheme for heterogeneous wireless networks is proposed in this article. The proposed scheme works in three phases. In the first phase, a handover triggering approach is designed to identify the appropriate place for initiating handover based on the estimated coverage area of a WLAN access point or cellular base station. In the second phase, fuzzy rule based system is designed to eliminate the inappropriate networks before deciding an optimal network for handover. In the third phase, a network selection scheme is developed based on the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) decision mechanism. Various parameters such as delay, jitter, Bit Error Rate (BER), packet loss, communication cost, response time, and network load are considered for selecting an optimal network. The proposed scheme is tested in a mobility scenario with different speeds of a mobile node ranging from very low to very high. The simulation results are compared with the existing decision models used for network selection and handover triggering approaches. The proposed scheme outperforms these schemes in terms of energy consumption, handover delay and time, packet loss, good put, etc.     

基于移动用户位置预测的垂直切换算法

针对异构无线网络环境中现有垂直切换算法存在难以实现移动用户接入网络的无缝切换,无法向用户提供稳定通信服务的问题,提出一种基于移动用户位置预测的垂直切换算法。首先利用用户移动轨迹的相似性,使用用户轨迹数据离线训练LSTM模型以学习各用户普遍具有的移动规律;然后在线加载LSTM模型进行用户位置预测,从而使用模糊逻辑分析计算下一时刻用户对应候选网络的回报值,并选取回报值最高的网络进行切换。实验结果表明,该算法与已有垂直切换算法相比,在不同的用户移动速度和用户规模条件下的切换次数、切换失败次数和切换时延均有明显下降,内存消耗较低,能够实现无缝切换。     

Cognitive vertical handover engine for vehicular communication

Always best connected (ABC) communication is an essential requirement for intelligent transportation system. In this paper, we propose a cognitive vertical handover (CVHO) engine to ensure seamless connectivity on the move. Analytic hierarchy process and artificial neural network are used for the development of the algorithm and MATLAB is used as simulation platform. The CVHO engine, which is knowledge based context aware system, takes into account multiple relevant criteria and previous experiences. This system is capable of performing both voluntary and reflex actions. A detailed literature review is presented to compare this work with the conventional methods of vertical handover. A case study, considering the network selection in a typical highway traffic scenario, which consists of both peer-to-peer (P2P) and mobile networks, is presented for the validation of the design. Three radio access technologies, WLAN (P2P), UMTS and WiMAX (mobile networks), are considered for simulation. The results show that the presented model not only realistically optimizes the best available network on the move but also avoids unnecessary handovers. This algorithm is specific to vehicular communication system and hence variation in network selection with vehicle speed is shown.     

垂直切换过程中TCP协议的RTT和RTO分析

随着网络技术的发展，终端可以通过多种接入方式与网络连接，并在不同种网络之间漫游．这导致了垂直切换的产生。本文简述了垂直切换的概念和带来的问题，详细分析了TCP协议中的RTT和RTO参数在垂直切换过程中的变化情况，以及对TCP在切换过程中性能的影响，最后给出结论和一些想法，为优化TCP在移动网络中的性能，设计适用于移动网络的传输协议提供参考。     

Mobility management for m-commerce requests in wireless cellular networks

Increasing number of sophisticated services provided by the current wireless communication systems have caused a significant transition from E-commerce to M-commerce. Enterprises have provided considerable new opportunities to promote their businesses accessible from small mobile devices such as personal digital assistant (PDA) or mobiles phones. These facilities are envisioned as the most convenient way of using M-commerce. Using such services from mobile phones or PDAs equipped with GSM/GPRS involve effective mobility management mechanisms in cellular networks—a popular architecture for wireless networks. Success of such systems will largely depend on the reliable connection for the roaming users. Consequently, Quality of Service (QoS) provision is one of the most challenging issues in the heterogeneous wireless network-based m-commerce systems. Such m-commerce systems enable users to roam between different wireless networks operators and geographical areas while providing interactive broadband services and seamless connectivity. This paper presents an analytical framework to model scarce channels in any cell for maximizing channel utilization and efficient handling of handover requests. Typical numerical experiments are presented to validate the analytical solution against simulation to study the effect of bursty traffic upon the performance of the cell in any cellular networks.     

Performance evaluation of e-commerce requests in wireless cellular networks

Recent technological advances in mobile devices and wireless networks enable mobile users to order goods in an anywhere and anytime fashion. Quality of Service (QoS) provision is one of the most challenging issues in the heterogeneous wireless network-based e-commerce systems. Such e-commerce systems enable users to roam between different wireless networks operators and geographical areas while providing interactive broadband services and seamless connectivity. Due to movement of users during e-commerce requests, one of the most important QoS factors for successful completion of users' requests is related to handover of request from one cell to another. A handover could fail due to unavailability of sufficient bandwidth in the destination cell. Such failure of ongoing e-commerce requests is highly undesirable and can cause serious problems to the e-commerce users and the service providers. This paper proposes an enhanced priority queuing based handover scheme in order to ensure a seamless connectivity of e-commerce requests. It focuses on the performance anaylsis of the proposed scheme. Experimental study demonstrates that the proposed scheme provides QoS with low connection failure and mean response time for handover of e-commerce requests.     

An enhanced framework for providing multimedia broadcast/multicast service over heterogeneous networks

Multimedia broadcast multicast service （MBMS） with inherently low requirement for network resources has been proposed as a candidate solution for using such resources in a more efficient manner. On the other hand, the Next Generation Mobile Network （NGMN） combines multiple radio access technologies （RATs） to optimize overall network performance. Handover performance is becoming a vital indicator of the quality experience of mobile user equipment （UE）. In contrast to the conventional vertical handover issue, the problem we are facing is how to seamlessly transmit broadcast/multicast sessions among heterogeneous networks. In this paper, we propose a new network entity, media independent broadcast multicast service center （MIBM-SC）, to provide seamless handover for broadcast/multicast sessions over heterogeneous networks, by extensions and enhancements of MBMS and media independent information service （MIIS） architectures. Additionally, a network selection scheme and a cell transmission mode selection scheme are proposed for selecting the best target network and best transmission mode. Both schemes are based on a load-aware network capacity estimation algorithm. Simulation results show that the pro- posed approach has the capability to provide MBMS over heterogeneous networks, with improved handover performance in terms of packet loss rate, throughput, handover delay, cell load, bandwidth usage, and the peak signal-to-noise ratio （PSNR）.     

Call Admission and Handover in Heterogeneous Wireless Networks

Today's mobile communication networks support not just simple mobile voice and data services but also access to mobile Internet-based services with varying bandwidth and quality-of-service requirements. The work presented in this article addresses this issue by proposing a management architecture for mobile user roaming based on efficient call admission and handover control in heterogeneous wireless access networks. Our proposed architecture consists of databases that hold profile and policy information, a roaming controller with two main elements (namely, call admission control for new and handover traffic), and intersystem handover control