Signal Strength Ratio Based Vertical Handoff Decision Algorithms in Integrated Heterogeneous Networks

In this paper, we propose the signal strength ratio (SSR) based vertical handoff (VHO) algorithms and the averaged received signal strength (ARSS) based VHO algorithms for integrated networks of wireless local area network (WLAN) and 3G network. The performance of our proposed VHO algorithms with hysteresis and dwell timer approaches has been investigated for two different topologies of integrated heterogeneous network. Two different network topologies consider two different types of radio cell arrangement. A mobile terminal (MT) is moving within the coverage area of WLAN and 3G with constant velocity. The received signal strength at the MT of interest is measured at different sampling instant. The received signal strength with other additional parameters is used to determine the condition of VHO. We evaluate the decision delay, and the number of vertical handoffs between WLAN and 3G network using the proposed VHO algorithms. We compare the performance of our proposed VHO algorithms with existing RSS based VHO algorithm. Our proposed SSR and ARSS based VHO algorithms provide less decision delay as compared to existing RSS based VHO algorithm. Further, ARSS with dwell timer based VHO algorithm provides better performance than other VHO algorithms.     

Performance Improvements of Mobile SCTP in Integrated Heterogeneous Wireless Networks

The complementary characteristics of cellular networks and wireless local area networks (WLANs) make it attractive to integrate these two technologies. In this integrated heterogeneous environment, mobile stream control transmission protocol (MSCTP) is ideal to support vertical handover (VHO) between them by enabling a mobile client to freely switch between IP addresses acquired in different networks. In this paper, we show that the MSCTP-based VHO scheme suffers from poor throughput performance during WLAN to cellular forced VHOs. We propose a novel error recovery scheme called Sending-buffer Multicast-Aided Retransmission with Fast Retransmission (SMART-FRX) to improve performance during VHO by multicasting the buffered and new data over both WLAN and cellular links when handover losses occur. In addition, we propose a new analytical model for SCTP that takes into account the congestion window, the round trip time, the slow-start and congestion avoidance processes. By comparing numerical results from the proposed analytical model with simulation results, we demonstrate that our analytical model is able to predict the SCTP throughput accurately, with or without the SMART-FRX scheme. The analytical model provides a useful tool that can be extended to study the performance of SCTP in other applications. Analytical and simulation results show that the proposed SMART-FRX scheme can improve the SCTP throughput performance significantly in WLAN to cellular forced VHO situations.     

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.     

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。     

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.     

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.     

异构无线网络中基于SINR和层次分析法的SAW垂直切换算法研究

B3G或者4G无线网络体系致力于集成各种异构无线接入网络,其中一个主要的设计课题是支持垂直切换的研究。该文将多属性QoS考虑在内,针对各业务特点,提出一种基于SINR(信干噪比)和层次分析法(AHP)的SAW(简单加权法)垂直切换算法(SASAW)。它综合考虑SINR的影响以及要获得同等数据速率情况下,目标网络需要的等效SINR数值、用户通信代价、网络可用带宽等来构造属性矩阵做切换判决。为了评估性能,考虑3GPP定义的4类业务,利用层次分析法中的特征向量法来决定各个QoS属性之间的权重关系,构造比较判决矩阵并检验其一致性;根据判决矩阵,利用特征根法获得权重向量;最后根据属性矩阵和权重向量,利用SAW垂直切换算法进行判决。通过对算法的通过率、丢话率、垂直切换次数、平均用户代价等的性能比较,结果表明该文提出的算法能够根据各业务特点综合考虑各属性间关系,获得优良的系统性能。     

Effect of mobile terminal heterogeneity on call blocking/dropping probability in cooperative heterogeneous cellular networks

It is envisaged that next generation wireless networks (NGWN) will be heterogeneous, consisting of multiple radio access technologies (RATs) coexisting in the same geographical area. In these heterogeneous wireless networks, mobile terminals of different capabilities (heterogeneous terminals) will be used by subscribers to access network services. We investigate the effect of using heterogeneous mobile terminals (e.g. single-mode, dual-mode, triple-mode, etc.) on call blocking and call dropping probabilities in cooperative heterogeneous wireless networks. We develop analytical models for heterogeneous mobile terminals and joint radio resource management in heterogeneous wireless networks. Using a two-class three-RAT heterogeneous wireless network as an example, the effect of using heterogeneous terminals in the network is evaluated. Results show the overall call blocking/dropping probability experienced by subscribers in heterogeneous wireless networks depends on the capabilities of mobile terminals used by the subscribers. In the worst case scenario, when all subscribers use single-mode mobile terminals, each subscriber is confined to a single RAT and consequently, joint radio resource management in heterogeneous wireless network has no improvement on new call blocking and handoff call dropping probabilities. However, in the best case scenario, when all subscribers use three-mode terminals, new class-1 call blocking probability decreases from 0.37 (for 100% single-mode terminals) to 0.05, at the arrival rate of 6 calls per minute. New class-2 call blocking probability also decreases from 0.8 to 0.52. Similarly, handoff class-1 call dropping probability decreases from 0.14 to 0.003, and handoff class-2 call dropping probability decreases from 0.44 to 0.09.     

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 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.     

泛在网络中的等效频谱带宽概念及其在异构网络切换中的应用

未来无线通信系统将融合多种异构无线接入网络以提供泛在业务。为了表达用户在不同系统中占用的资源,为异构无线网络提出了等效带宽的概念,在此基础上将等效带宽用到异构网络切换控制中,同时将马尔科夫决策过程引入切换算法。仿真结果表明本算法相对于门限切换法有较好的期望收益。     

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。     

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.     

基于模糊语言变量的动态目标无线网络选择技术

Even though various wireless Net-work Access Technologies (NATs) with dif-ferent specifications and applications have been developed in the recent years, no single wireless technology alone can satisfy the any-time, anywhere, and any service wire-less-access needs of mobile users. A real seamless wireless mobile environment is only realized by considering vertical and horizontal handoffs together. One of the major design issues in heterogeneous wireless networks is the support of Vertical Handoff (VHO). VHO occurs when a multi-interface enabled mobile terminal changes its Point of Attachment (PoA) from one type of wireless access technology to another, while maintaining an active session. In this paper we present a novel multi-criteria VHO algorithm, which chooses the target NAT based on several factors such as user preferences, system parameters, and traffic-types with varying Quality of Service (QoS) requirements. Two modules i.e., VHO Necessity Estimation (VHONE) module and target NAT selection module, are designed. Both modules utilize several “weighted” users’ and system’s parameters. To improve the robustness of the proposed algorithm, the weighting system is designed based on the concept of fuzzy linguistic variables.     

Artificial Neural Network Based Vertical Handoff Algorithm for Reducing Handoff Latency

One of the most challenging topics for next generation wireless networks is vertical handoff concept since several wireless technologies are assumed to cooperate. Plenty of parameters related to user preferences, application requirements, and network conditions, such as; data rate, service cost, network latency, speed of mobile, battery level, interference ratio and etc. must be considered in vertical handoff process along with traditional RSSI information. In this study, a new artificial neural network based handoff decision algorithm is proposed in order to reduce the handoff latency of smart terminal deployed in aforementioned wireless heterogeneous infrastructures. The prominent parameters data rate, monetary cost and RSSI information are taken as inputs of the developed vertical handoff decision system. Performance results of the proposed system are also compared with those of classical Multiple Attribute Decision Making method Simple Additive Weighting, and of some other artificial intelligence based algorithms. According to the results obtained, the proposed neural network based vertical handoff decision algorithm is able to determine whether a handoff is necessary or not properly, and selects the best candidate access network considering the abovementioned parameters. The results also show that, the neural network based algorithm developed significantly reduces the handoff latency while the number of handoffs, which is another vital performance metric, is still reasonable.     

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。     

A context‐aware handover decision based on user perceived quality of service trigger

Growing demands for pervasive and ubiquitous services over wireless mobile networks and evolution of such networks towards heterogeneous solutions have emphasized the necessity of more intelligent handoff decisions. The existing handoff management methods in the literature are mostly using signal strength measurements and other link quality evaluations not addressing the knowledge about context of mobile devices, users and networks. Recently, context‐aware handoff management has been considered as a novel candidate for fourth generation (4G) wireless technology. In this paper, user perceived quality of service has been considered in addition to traditional contexts such as user preferences, application requirements, network parameters and link quality for decision making. User perceived quality (UPQ) has been employed as a trigger source, in addition to link layer triggers which are emerged using media independent handover (MIH) event service. This paper presents a policy based mechanism for handoff decision making where fuzzy petri nets (FPNs) have been utilized as its evaluation algorithm. A case study has been provided by simulations to show the usability and user level satisfaction. Simulation results show superior performance in terms of UPQ, jitter and packet delivery measures. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance Comparison of Two Channel Allocation Strategies in Cellular Networks

Channel allocation plays an important role in increasing the throughput and assuring fairness to users not only in traditional cellular networks but also in cognitive radio networks and mesh networks. In this paper, we study the effect of pre-allocating channels to cells with respect to a distributed and fault-tolerant channel allocation algorithm. Results from our extensive performance evaluation indicate that distributed channel allocation algorithms that pre-allocate all channels to cells can have lower call failure rate, call blocking rate, and handoff drop rate compared to algorithms that partially pre-allocate channels or does not pre-allocate channels.     

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.     

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。