一种LTE与WLAN间垂直切换新算法

为提高用户在异构网络中的服务质量(QoS),减少切换产生的乒乓效应,文中提出了一种LTE和WLAN网络垂直切换新算法。该算法考虑了衰落对接收信号强度(RSS)的影响,基于RSS选出目标网络,根据用户移动速度并结合代价函数选出最佳网络,代价函数中采用了层次分析法来确定时延、资费和用户偏好等参数的权重。仿真结果表明,文中所提的垂直切换算法有效降低了“乒乓效应”,并提高了通信网络的服务质量。     

Optimal Joint Session Admission Control in Integrated WLAN and CDMA Cellular Networks with Vertical Handoff

This paper considers optimizing the utilization of radio resources in a heterogeneous integrated system consisting of two different networks: a wireless local area network (WLAN) and a wideband code division multiple access (CDMA) network. We propose a joint session admission control scheme for multimedia traffic that maximizes overall network revenue with quality of service (QoS) constraints over both the WLAN and the CDMA cellular networks. The WLAN operates under the IEEE 802.11e medium access control (MAC) protocol, which supports QoS for multimedia traffic. A novel concept of effective bandwidth is used in the CDMA network to derive the unified radio resource usage, taking into account both physical layer linear minimum mean square error (LMMSE) receivers and characteristics of the packet traffic. Numerical examples illustrate that the network revenue earned in the proposed joint admission control scheme is significantly larger than that when the individual networks are optimized independently with no vertical handoff between them. The revenue gain is also significant over the scheme in which vertical handoff is supported, but admission control is not done jointly. Furthermore, we show that the optimal joint admission control policy is a randomized policy, i.e., sessions are admitted to the system with probabilities in some states     

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.     

Efficient mobility management for vertical handoff between WWAN and WLAN

As we move toward next-generation all-IP wireless networks, we are facing the integration of heterogeneous networks, such as WWAN and WLAN, where vertical handoff is required. In vertical handoff between WWAN and WLAN, mobile hosts should be able to move freely across different networks while satisfying QoS requirements for a variety of applications. In order to achieve seamless handoff and maintain continuity of connection, we propose a novel mobility. management system that integrates a connection manager to detect network condition changes in a timely and accurate manner, and a virtual connectivity manager that uses an end-to-end principle to maintain a connection without additional network infrastructure support. A prototype system was built to test the effectiveness of the proposed system. Experiments show that seamless roaming between WLAN and WWAN can be achieved, and much better performance can be obtained than with the traditional scheme.     

Performance Analysis of an Improved Common Radio Resource Management Algorithm Based on Load Balance and Service Characteristics

In order to provide users with satisfactory quality of service and reduce service cost as much as possible, a key issue is how to manage radio resources reasonably and effectively in heterogeneous wireless networks (HWNs). Based on load balance and service characteristics, a common radio resource management (CRRM) algorithm for HWNs consisting of CDMA2000 and IEEE802.11 is proposed. The proposed algorithm selects appropriate access and handoff networks for new and handoff calls respectively, according to users’ mobility characteristic, location information, service type and network load. The performance of the proposed algorithm is analyzed based on a three-dimensional Markov chain model. Based on the HWNs model and handoff rate analysis, the model’s parameters are determined. In order to resolve the steady-state distribution of the three-dimensional Markov model, successive over-relaxation iteration method is adopted to work out steady state equations. According to the steady state probabilities of the Markov model, the closed formulas of HWNs performance metrics are given to evaluate the proposed CRRM algorithm, e.g. call blocking probability, handoff blocking probability, throughput, and service cost. For the purpose of illustrating advantages of the proposed algorithm, two other CRRM algorithms are employed for comparison. The simulation results show that the proposed algorithm can effectively reduce call blocking probability, and improve HWNs throughput.     

Heterogeneous Wireless Networks: Configuration and Vertical Handoff Management

Vertical handoff is one of the most important issues for the next generation heterogeneous wireless networks. However, in many situations, unbeneficial vertical handoffs occur across intersystem heterogeneous networks cause network performance degradation. Therefore, we propose a novel configuration architecture that can be deployed in the next generation of wireless networks. Second, we propose a predictive and adaptive Vertical Handoff Decision Scheme that optimizes the handoff initiation time as well as selection of the most optimal network. The proposed vertical handoff decision algorithm considers the technology type as well as the Signal to Interference Ratio (SIR), the Mobile Station (MS) velocity, the user preferences, the applications requirements and the terminal capabilities as the most important factors to make vertical handoff decision. In order to minimize handoff costs, the proposed decision algorithm uses the dwell timer concept. The handoff costs are analyzed in terms of unnecessary and unbeneficial handoffs rate.The simulation results show that the reduction of unnecessary handoffs proposed in our vertical handoff decision scheme reduces the handoff blocking probability, the packets loss rate and the handoff overhead     

异构网络中垂直切换的研究

在无线局域网WLAN和蜂窝网组成的异构网络中,切换方案是降低切换时延和数据丢失的一个重要因素.文中设计了一个基于不同接入技术的WLAN和GPRS/UMTS系统组成的异构网络,提出了移动台在这两个网络间切换的不同方案(移动台发起的小区重选和网络发起的切换).同时,针对WLAN的不足,为其增加了"在场检测"功能,仿真结果显示丢包率得到了明显的改善     

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.     

无线异构网络的垂直切换判决算法

传统上的水平切换处理方法已经应用在同一接入技术的网络中（如无线蜂窝网络）。随着多种异构无线网络的出现,下一代网络必须支持垂直切换技术以保证用户从一个网络切换到内一个网络时仍然保持连接,垂直切换作为多网融合的基础,受到了学术界和工业界的广泛关注。对使用层次分析法进行垂直切换技术的工作原理及应用环境进行了分析,提出同时使用多种切换技术以解决不同环境下的切换问题。     

基于半马尔可夫链的WLAN/CDMA联合呼叫接入控制

下一代网络（NGN）将融合多种异构无线接入网络。为了在满足QoS限制下,最大化网络收益,在对WLAN／CDMA等效带宽的研究基础上,提出一种基于SMDP（半马尔可夫决策规划）的最优的联合呼叫接入控制（JCAC）方案,方案考虑了WLAN和CDMA网络间的相互影响,并将网络连接的联合呼叫控制问题等效成一个半马尔可夫决策过程,仿真表明方案相对于离散时间的MDP和在MDP基础上的JCAC算法具有明显的优势。     

基于运动趋势的模糊逻辑垂直切换算法

随着无线异构网络的融合,移动性管理技术成为其关键问题,而切换管理又是移动性管理的重要部分。针对垂直切换管理提出了一种基于运动趋势的模糊逻辑垂直切换算法。算法分为预判定、模糊逻辑控制及切换判决3个过程。首先,在预判定阶段根据MN的运动趋势及接收信号强度滤除掉不适宜接入WLAN的网络信息,从而有效减少不必要的数据量和系统开销;其次,将接收信号强度、网络的可用带宽和网络开销送入模糊逻辑控制器,通过参数的归一量化最终得到网络综合性能值(VCPN);最后,通过综合考虑VCPN和驻留时间来进行网络切换判决。仿真结果显示,该算法能够有针对性地做出切换判决,有效消除乒乓效应,提高网络切换性能。     

Load balancing for cellular/WLAN integrated networks

The interworking between heterogeneous third-generation cellular networks and wireless local area networks is one promising evolution approach to fourth-generation wireless networks, which can exploit the complementary advantages of the cellular network and WLANs. Resource management for the 4G-oriented cellular/WLAN integrated network is an important open issue that deserves more research efforts. In this article we present a policy framework for resource management in a loosely coupled cellular/WLAN integrated network, where load balancing policies are designed to efficiently utilize the pooled resources of the network. A two-phase control strategy is adopted in the load balancing policies, in which call assignment is used to provide a statistical quality of service guarantee during the admission phase, and dynamic vertical handoff during the traffic service phase is used to minimize the performance variations. Numerical results are presented to demonstrate that the proposed load balancing solution achieves significant performance improvement over two other reference schemes     

SIP-based vertical handoff between WWANs and WLANs

Future-generation wireless networks have been envisioned as the integration of various wireless access networks, including both wireless wide area networks and wireless local area networks. In such a heterogeneous network environment, seamless mobility support is the basis of providing uninterrupted wireless services to mobile users roaming between various wireless access networks. Because of transparency to lower-layer characteristics, ease of deployment, and greater scalability, the application-layer-based session initiation protocol has been considered the right candidate for handling mobility in heterogeneous wireless networks. However, SIP entails application-layer transport and processing of messages, which may introduce considerable delay. As a case study of the performance of mobility management protocols in the heterogeneous wireless networks, we analyze the delay associated with vertical handoff using SIP in the WLAN-UMTS internetwork. Analytical results show that WLAN-to-UMTS handoff incurs unacceptable delay for supporting real-time multimedia services, and is mainly due to transmission of SIP signaling messages over erroneous and bandwidth-limited wireless links. On the other hand, UMTS-to-WLAN handoff experiences much less delay, mainly contributed by the processing delay of signaling messages at the WLAN gateways and servers. While the former case requires the deployment of soft handoff techniques to reduce the delay, faster servers and more efficient host configuration mechanisms can do the job in the latter case.     

Utility aware network selection in small cell

In fifth generation heterogeneous network, small cell is developed to compensate the growing demand for mobile data services. Due to the smaller size of cell, users have a short duration of connection, however, the user may also have the need of handoff frequently. At the time of handoff, different networks are available with different data rate and different other parameters. So, there is the need of frequent selection for the optimal network. In this paper, a utility-aware optimization algorithm has been proposed for network selection in a heterogeneous environment of Wi-Fi, WiMAX, WLAN, LTE, UMTS, and GPRS network. The weight factor is proposed for modified Jaya algorithm which is calculated by the analytical hierarchical process, standard deviation, and entropy method. Different applications are considered such as video, voice, web browsing and email transfer in which available bandwidth, packet jitter, packet loss, cost per byte are taken as dominant attributes, respectively. According to the dominant factor, different networks are selected for different applications because the requirement of all applications cannot be fulfilled by one network. Finally, the proposed algorithm is compared with multi-attribute decision making algorithms and game theory and accuracy of the proposed algorithm is calculated. The accuracy of proposed algorithm is higher as compared to the other algorithms and at the same time, this algorithm requires less computation which can further reduce the handoff latency and failure probability. Hence, the performance of handoff can be improved by using modified Jaya algorithm.

     

Power-Efficient Spatial Reusable Channel Assignment Scheme in WLAN Mesh Networks

Interference has strong effect on the available bandwidth of wireless local area network (WLAN) based mesh networks. The channel assignment problem for multi-radio multi-channel multihop WLAN mesh networks is complex NP-hard, and channel assignment, routing and power control are tightly coupled. To mitigate the co-channel interference and improve capacity in multi-channel and multi-interface WLAN mesh networks, a power-efficient spatial reusable channel assignment scheme is proposed, which considers both channel diversity and spatial reusability to reduce co-channel interference by joint adjusting channel, transmission power and routing. In order to assign channel appropriately, an efficient power control scheme and a simple heuristic algorithm is introduced to achieve this objective, which adjust the channel and power level of each radio according to the current channel conditions so as to increase the opportunity of channel spatial reusability. The proposed channel assignment scheme also takes load, capacity and interference of links into consideration. Simulation results show the effectiveness of our approach and demonstrate that the proposed scheme can get better performance than other approaches in terms of throughput, blocking ratio, energy consumption and end-to-end delay.     

无线异构网络中带有动态权值的新型垂直切换算法

In order to enhance the quality of vertical handoff in an overlay wireless network, multiple attributes are taken into account when optimizing the vertical handoff decision including user-based and network-based QoS factors. In this paper, we develop a novel vertical handoff algorithm in an integrated 3G cellular and Wireless LAN networks. The proposed algorithm can adjust the weight of each QoS attribute dynamically as the networks change, trace the network condition and choose the optimal access point at transient regions. Simulation results show that this algorithm is able to provide accurate handoff decision, resulting in small unnecessary handoff numbers, good performance of throughput and handoff delay in heterogeneous environments.     

CDMA增强型软切换探讨

文章介绍了增强型软切换算法,并通过引用相关文献和分析商用网实验结果,证实该算法能够有效控制软切换比例,最后给出的参数设置方法可作为工程人员实用参考.     

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.     

A simple algorithm for adjusting cell-site transmitter power inCDMA cellular systems

Traditional downlink power control methods for code-division multiple-access (CDMA) cellular systems allocate individual power levels to the different users of a given cell according to their relative needs, while assuming the amount of total power transmitted by each base to be constant. If this amount is not controlled, it is impossible to reduce unnecessary interference and, as a result, to achieve an optimal power control performance. In this paper, we address rather a simple convergent algorithm for adjusting the total power as well as allocating it for each user. The objective of this algorithm is to allocate the available power of each base to as many mobiles as possible that can enjoy sufficient transmission quality. In the appendix, we also provide an extended version of the algorithm, which relaxes an ideal assumption on soft handoff pertaining to existing works. Numerical results show that the proposed algorithm can be an alternative for CDMA downlink power control     

Seamless Handoff Scheme Based on Pre-registration and Pre-authentication for UMTS–WLAN Interworking

Interworking issues between Universal Mobile Telecommunication System (UMTS) and Wireless Local Area Network (WLAN) have become a great matter of interest as an increasing number of mobile internet users require broadband wireless access to IP services in the wide area. In this paper, we present a practical UMTS–WLAN interworking architecture based on 3GPP standards and propose a seamless handoff scheme that guarantees low delay and low packet loss during UMTS–WLAN handoff. For low handoff delay, the proposed handoff scheme performs pre-registration and pre-authentication processes before layer 2 handoff. Moreover, it uses packet buffering and forwarding functions in order to reduce packet loss during the handoff period. On the above basis, detailed signaling procedures are presented, together with system requirements when a mobile terminal moves from UMTS to WLAN and vice-versa. Numerical results show that the proposed scheme performs well with respect to signaling cost, handoff delay, and packet loss compared with conventional schemes.