Markov-based vertical handoff decision algorithms in heterogeneous wireless networks

In this paper, we propose a received signal strength (RSS)-based single-attribute handoff decision algorithm at first, and investigate handoff decision model based on connection lifetime, which can keep mobile terminals (MTs) staying long enough in the preferred network. Since the preferred quality of service (QoS) parameters may be distinct among different MTs, we then formulate the vertical handoff decision problem as a Markov decision process, with the objectives of maximizing the expected total reward and minimizing average number of handoffs. A reward function is constructed to assess the QoS during each connection, and the G1 and entropy methods are applied in an iterative way, by which we can work out a stationary deterministic handoff decision policy. Numerical results demonstrate the superiority of our proposed schemes compared with other existing algorithms.     

Investigation on MDP-based radio access technology selection in heterogeneous wireless networks

The new generation of wireless networks is characterized by heterogeneity i.e. the coexistence of two or more radio access technologies (RAT) in the same geographical area. While this coexistence of RATs offers various advantages, it also imposes many challenges for the network operator, whose aim is to maximize the generated revenue while satisfying the customers’ increasing demands. One important mechanism in heterogeneous wireless networks (HWN) is the RAT selection. It is normally triggered when a new call arrives, and provides the decision on whether the call can be admitted or not, and by which RAT it has to be served. Different approaches can be used to tackle the problem of RAT selection in HWNs. In this paper, we study Markov Decision Process (MDP)-based RAT selection in a cellular/WLAN heterogeneous network where the maximization of the revenue is considered as objective. An optimal RAT selection policy is therefore derived. The performance of the optimal scheme is evaluated in comparison with two other policies, namely Cellular-First policy and Load Balancing policy.     

Case study on handoff strategies for wireless overlay networks

One of the most challenging topics for next‐generation wireless networks is the process of vertical handoff since many of wireless technologies overlap each other and build a heterogeneous topology. Several parameters, pertaining to user/application requirements and network conditions, such as data rate, service cost, network latency, speed of mobile, and etc. must be considered in the handoff process of heterogeneous networks along with RSSI information. In this paper, adaptive fuzzy logic‐based vertical handoff decision‐making algorithms are presented for wireless overlay networks which consist of GSM/GPRS/Wi-Fi/UMTS/WiMAX technologies. The parameters data rate, monetary cost, speed of mobile and RSSI information are processed as inputs of the proposed fuzzy‐based systems. According to these parameters, an output value, which varies between 1 and 10, is produced. This output value is utilized to determine whether a handoff process is necessary or not and to select the best candidate access point in the vicinity. The results show that, compared to the traditional RSSI‐based algorithm significantly enhanced outcomes can be achieved for both user and network as a consequence of the proposed fuzzy‐based handoff systems. The simulation results are also compared with those of classical MADM (Multiple Attribute Decision Making) method, i.e. SAW (Simple Additive Weighting). According to the results obtained, the proposed vertical handoff decision algorithms are able to determine whether a handoff is necessary or not, properly, and select the best candidate access network considering the aforementioned parameters. Moreover, fuzzy‐based algorithm noticeably reduces the number of handoffs compared to SAW‐based algorithm.     

Dynamic RAT selection for multiple calls in heterogeneous wireless networks using group decision-making technique

Existing radio access technology (RAT)-selection algorithms for heterogeneous wireless networks (HWNs) do not consider the problem of RAT selection for a group of calls from a multimode terminal (MT). Multimode terminals (MTs) for next generation wireless networks have the capability to support two or more classes of calls simultaneously. When a new call is initiated on an MT already having an ongoing call in an HWN, the current RAT may no longer be suitable for the two calls (incoming call and the existing call). Thus, a new RAT may be more suitable for the two calls. The problem of RAT selection for two or more calls from an MT in an HWN is a group decision problem. This paper addresses the problem of RAT selection for a group of calls from an MT in an HWN by using the modified TOPSIS group decision-making technique. The paper proposes a dynamic RAT-selection algorithm that selects the most suitable RAT for a single call or group of calls from an MT in an HWN. The algorithm considers users’ preferences for individual RATs, which vary with each class of calls, in making RAT selection decisions in an HWN. A user’s preference for each of the available RATs is specified by weights assigned by the user to RAT selection criteria for different classes of calls. Based on the assigned weights, the proposed algorithm aggregates individual calls’ weights specified by the user to make a RAT-selection decision for a group of calls. In order to reduce the frequency of vertical handover, the proposed algorithm uses RAT preference margin in making RAT selection decisions. RAT preference margin is a measure of the degree to which the newly preferred RAT is better than the current RAT. Performance of the proposed algorithm is evaluated through numerical simulations. Results are given to show the effectiveness of the proposed RAT-selection algorithm.     

一种无线异构网络的自适应垂直切换算法

针对移动节点在异构网络间切换性能不理想的问题,提出了一种自适应主动预测的垂直切换算法。采用一种面向当前应用程序的代价函数对可接入网络进行评估与选择;根据稳定周期、移动节点的运动速度及所处位置来自动调整切换执行时间,使移动节点能自适应地进行切换判决。仿真结果表明,该算法可以有效地减少切换延迟、分组丢失及切换次数,提高系统的切换性能,改善业务的QoS。     

一种支持IMS异构网络的垂直切换算法

为解决IMS异构无线网络的切换时延问题,设计一种IEEE 802.21定义的媒介无关切换标准与IMS架构相融合的方案,并在此基础上提出一种多路径冗余传输切换算法,采用马尔科夫决策过程实现在IMS异构网络中的无缝切换。NS-2仿真实验结果表明,该算法与传统垂直切换算法相比,在切换过程中的有效数据传输率、切换次数及切换稳定性均显示出一定优势。     

Interference aware vertical handoff decision algorithm for quality of service support in wireless heterogeneous networks

Next generation wireless networks concept aims at collaboration of various radio access technologies in order to provide quality of service (QoS) supported and cost efficient connections at anywhere and anytime. Since the next generation wireless systems are expected to be of heterogeneous topology, traditional handoff (horizontal handoff/handover) mechanisms are not sufficient to meet the requirements of these types of networks. More intelligent vertical handoff algorithms which consider user profiles, application requirements, and network conditions must be employed in order to provide enhanced performance results for both user and network. Moreover, frequency reuse of one (FRO) seems to be the strongest candidate of deployment options for next generation wireless networks; therefore, interference conditions gains a significant attention in vertical handoff decision making process. In this study, a fuzzy logic-based handoff decision algorithm is introduced for wireless heterogeneous networks. The parameters; data rate, received signal strength indicator (RSSI), and mobile speed are considered as inputs of the proposed fuzzy-based system in order to decide handoff initialization process and select the best candidate access point around a smart mobile terminal. Also, in contrast to the traditional fuzzy-based algorithms, the method proposed takes ambient interference power, which is referred to as interference rate, as another input to the decision process. The results show that the performance is significantly enhanced for both user and network by the method proposed.     

Network Selection Decisions for Multiple Calls Based on Consensus Level

Next generation multimode terminals have the capability to support different classes of calls simultaneously as well as the ability to connect to two or more radio access technologies (RATs), at the same time, in a heterogeneous wireless network. For a mobile terminal having multiple classes of simultaneous handoff calls (such as file download and video sessions), RAT selection decisions can be made independently for individual calls in the group or jointly for the entire group of calls. Both independent and group RAT selection decisions for multiple calls have advantages and disadvantages. Existing RAT selection algorithms have focused on RAT selection decisions for single calls. Therefore, this paper investigates independent call and group call RAT selection decisions for multiple calls in heterogeneous wireless networks, and proposes a scheme that makes RAT selection decisions for multiple calls based on a consensus level among the multiple calls to be admitted. When this consensus level is among multiple calls to be admitted into a particular RAT and is equal to or above a certain threshold value, a group decision is used. Otherwise, independent decisions are made. The performance of the proposed RAT selection scheme is evaluated in a three service three RAT heterogeneous network, supporting multihomed terminals. Simulation results are given to show the effectiveness of the proposed scheme.     

异构分层无线网络中基于业务QoS保证的切换策略研究

针对异构分层无线网络提出了一种保证业务QoS的切换策略。该策略在层间呼叫双向溢出基础上,为实时业务切换设置了保护信道,为非实时业务切换设置了缓冲队列。为了进一步降低实时业务切换的掉线率,还使用了信道侵占技术,原理是实时业务切换呼叫可以侵占数据业务正在使用的信道资源。仿真结果表明,提出的切换方法能够显著降低各类切换业务的掉线率,同时整个异构分层系统的信道利用率也略有提高。     

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。     

可避免数据包乱序的网络层软切换方法及其性能分析

随着异构无线网络的融合和全IP网络的推广,网络层软切换方法不断演进,用以提高垂直切换的性能.但是,现有的软切换方法在下行垂直切换过程中会造成严重的数据包乱序.为此,文中在讨论下行垂直切换时数据包乱序的原因之后,提出了一种新型网络层软切换方法——SHORDER.该方法根据移动终端与其家乡代理之间的交互信令对终端所收数据包进行适当的缓存,能有效避免移动终端因下行垂直切换接收到乱序的数据包.该方法所具有的网络层独立性使其能与各种传输层协议及其改进协议相兼容.此外,文中还从理论上定量地分析了所提方法对TCP应用的切换时延、有效吞吐量及拥塞窗口的影响,并与现有的典型网络层软切换方法进行了比较.通过比较,得出了SHORDER机制的适用条件,并基于此,进一步改进了SHORDER方法.最后,在原型系统上的实验显示出了所提机制便于部署的优点以及该机制在其适用条件下的良好性能.此外,实验结果还显示出与数值分析结果的一致性.     

Performance analysis of a novel architecture to integrate heterogeneous wireless systems

Current wireless world witnesses multiple heterogeneous systems such as Bluetooth, IEEE 802.11, UMTS, and satellite networks. These systems are envisioned to coordinate with each other to provide ubiquitous communications to mobile users. A novel architecture, Architecture for ubiquitous Mobile Communications (AMC), is introduced in this paper that integrates these heterogeneous wireless systems. AMC eliminates the need for direct Service Level Agreements (SLAs) among service providers by using a third party, Network Inter-operating Agent (NIA). Instead of developing a new architecture, AMC extends the existing infrastructure to integrate heterogeneous wireless systems. It uses IP as the inter-connection protocol to provide transparency to the heterogeneities of individual systems. Third-party-based authentication and billing algorithms are designed for AMC. New handoff management protocols are also designed to support seamless vertical handoffs between different wireless systems in AMC. Performance analysis is carried out to determine the latency associated with vertical handoffs and the load on the NIA that arises because of these vertical handoffs. Toward this, a network deployment scenario that consists of three types of wireless systems: WLAN, 3G, and satellite networks is considered. Moreover, the number of SLAs required in AMC is also determined for a given number of network operators. It is also shown that by using hierarchical structure, AMC can realize the integration of heterogeneous wireless systems around the globe.     

Optimization model for handoff-aware channel assignment problem for multi-radio wireless mesh networks

Optimal channel assignment (CA) in multi-radio wireless mesh networks is an NP-hard problem for which solutions usually leave several links interfering. Most of these solutions usually consider the overall throughput as the main optimization objective. However, other objectives have to be considered in order to provide better quality wireless connections to non stationary users. In this paper, we propose a multi-objective optimization model that, besides maximizing throughput, improves fairness and handoff experience of mesh clients. In this model, we use the Jain’s index to maximize users’ fairness and we allow same-channel assignments to links involved in the same high handoff traffic, thus reducing handoff-triggered re-routing characterized by its high latency. Then, we propose a centralized variable neighborhood search and a Tabu search heuristics to efficiently solve our model as an offline CA process. Moreover, in order to adapt to traffic dynamics caused especially by user handoffs, we propose an online CA scheme that carefully re-assigns channels to interfaces with the purpose of continuously minimizing the re-routing overhead/latency during user handoffs. We further improve this online scheme using load balancing. Simulation results show the good performance of our proposed approach in terms of delay, loss rate, overall throughput and fairness. Particularly, performance results of our online handoff-aware CA show the effectiveness of handoffs not involving path re-routing in decreasing the delay, especially when considering load balancing.     

自适应门限的异构无线网络预切换机制

以无线局域网（WLAN）和WiMAX网络融合构成的异构网络为研究对象,研究了多模移动终端基于FMIPv6机制完成异构无线网络之间垂直切换的操作流程。针对垂直切换过程中使用固定门限值预切换机制存在的不足,提出了一种自适应门限预切换机制,并详细分析了垂直切换过程中目标网络接入时延,从而为所提出的自适应门限值预切换机制提供了理论依据。在仿真部分,扩充了NS2仿真平台上已有的功能模块,从而验证了所提出的自适应门限预切换机制的性能。     

Scanless fast handoff technique based on global Path-Cache for WLANs

Wireless LANs (WLANs) have been widely adopted and are more convenient as they are interconnected as wireless campus networks and wireless mesh networks. However, time-sensitive multimedia applications, which have become more popular, could suffer from long end-to-end latency in WLANs. This is due mainly to handoff delay, which in turn is caused by channel scanning. This paper proposes a technique called Global Path-Cache (GPC) that provides fast handoffs in WLANs. GPC properly captures the dynamic behavior of the network and mobile stations (MSs), and provides accurate next-AP (access point) predictions to minimize the handoff latency. Moreover, the handoff frequencies are treated as time-series data, thus GPC calibrates the prediction models based on short-term and periodic behaviors of mobile users. Our simulation study shows that GPC virtually eliminates the need to scan for APs during handoffs and results in much better overall handoff delay compared to existing methods.     

An Efficient Handoff Decision Algorithm for Vertical Handoff Between WWAN and WLAN

Vertical handoff is one significant challenge for mobility management in heterogeneous wireless networks. Compared with horizontal handoff, vertical handoff involves different wireless network technologies varying widely in terms of bandwidth, delay, coverage area, power consumption, etc. In this paper, we analyze the signal strength model of mobile node and present a new vertical handoff decision algorithm. This algorithm can adapt to the change of mobile node＇s velocity and improve the handoff efficiency significantly. We analyze the algorithm＇s performance and the effect of different parameters on handoff triggering. In addition, we propose three performance evaluation models and verify the algorithm＇s feasibility and effectiveness in simulations.     

异构分层无线网络中基于业务和逗留时间的动态流量均衡算法

在异构分层无线网络中使用有效的流量均衡技术,可以给更多的移动用户提供服务。现有的流量均衡算法主要针对同种无线网络,因而不能直接用于异构无线网络。本文提出了一种适用于异构无线网络的基于业务和逗留时间的动态流量均衡算法,该算法首先根据移动模型计算移动用户在小区内的逗留时间,然后基于小区呼叫到达率和重叠覆盖小区的流量状态来确定一个周期内转移的非实时性呼叫数量,最后依据逗留时间门限值将重负载小区中满足条件的呼叫转移到轻负载的重叠覆盖小区中。为降低切换呼叫掉线率,还对异构网间的呼叫切换策略做了改进。仿真实验结果表明．本算法在新呼叫阻寒率和切换呼叫掉线率等性能指标上比传统方法有显著提高．     

基于运动趋势的自适应垂直切换算法及其性能评价

采用不同的无线接入技术的多种网络的融合可以提高无线传输性能,为移动用户提供随时随地的网络连接.垂直切换是异构无线网络相互融合的基础.在垂直切换过程中,切换判定是一个非常重要的环节,直接决定切换性能.文中给出了常用的迟滞电平算法和驻留定时器算法中切换判定条件的形式化表达,并对其进行了性能分析.在此基础上,提出了一种自适应的垂直切换算法,通过分析节点的运动趋势,自适应地调节切换触发条件,有效提高垂直切换性能.所涉及的运算均为初等计算,算法简单,适用于低能量、低运算能力的移动设备.仿真实验表明,该算法的综合性能优于迟滞电平算法和驻留定时器算法.     

分层蜂窝网络中基于移动速度、方向的流量均衡

在异构无线网络中,使用有效的流量均衡可以服务更多的移动用户。文章为异构分层无线网络提出了一种基于移动速度、方向和位置的流量均衡算法,其原理是选择逗留时间较长的移动用户执行垂直切换,从负载较重的小区转移到负载较轻的重叠覆盖小区。同时,快速切换呼叫在一定条件下可以接入到微小区,慢速切换呼叫也可以切换进入宏小区。仿真实验结果表明,该算法改善了新呼叫阻塞率和切换呼叫掉线率等方面的性能。     

异构无线网中面向QoS的马尔可夫选择策略

针对移动终端在异构网络环境下,需要在垂直切换过程中进行网络选择的问题,提出一种面向QoS的马尔可夫选择决策算法,通过对算法模型合理化构建过程与异构环境特点的紧密结合、报酬函数的正确定义与求解,可以为用户选择合适的接入网络,最大程度地满足在异构网络环境中用户QoS的长期效益。仿真结果表明,该算法可以有效提高判决水平,改善业务的QoS。