车联网环境下的4G和DSRC异构网络切换机制研究

面向车联网的实际应用需求,构建了一种高速公路环境下的基于4G和DSRC的异构网络通信场景。针对车辆在该场景下可能会在不同网络信道间频繁发生垂直切换导致较高的传输时延和丢包率的问题,在分析研究基于4G与DSRC的高速公路异构网络切换过程的基础上,引入网络跳数、连接次数和行驶轨迹作为切换判决条件,基于TREBOL路由协议设计了一种异构网络垂直切换算法。最后利用Veins仿真平台对提出的异构网络垂直切换算法的切换性能进行对比测试分析。测试结果表明,与基于RSSI的异构网络垂直切换方法相比,所提切换算法能增大车辆与DSRC网络连接的持续时间,并有效减少"乒乓效应"。     

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。     

一种基于模糊逻辑的预判决辅助垂直切换算法

针对全IP核心网络的不同无线接入技术,提出一种基于预判决模糊逻辑的垂直切换算法.引入预判决方法有效减少不必要的数据量和系统开销.采用前向差分预测能够较准确地预测出下一时刻的信号强度,提高了切换触发速度和切换判决精度.采用模糊逻辑的方法,以接收信号强度、预测信号强度及可用带宽作为网络参量设计模糊逻辑控制器,进而采用归一量化的方法改进模糊逻辑系统,得到网络的综合性能值进行垂直切换判决.仿真分析表明,本文提出的算法能够较准确做出切换判决,有效消除乒乓效应,提高系统性能.     

基于区间二型模糊神经网络的垂直切换算法

在超密集异构无线网络中,针对传统垂直切换算法无法同时描述网络状态的模糊性和随机性,导致网络性能得不到有效提升的问题,提出一种基于区间二型模糊神经网络的垂直切换算法.重构了两阶段判决算法:在网络预筛选阶段,定义了历史接入率,结合当前候选网络集的数目设置阈值.根据接收信号强度和剩余可用带宽,对用户接收范围内的所有网络进行初步筛选;再在垂直切换判决阶段,将剩余候选网络的时延,丢包率以及误码率作为区间二型模糊神经网络的输入,利用前馈神经网络的结构完成模糊逻辑推理,经训练之后计算得到输出判决值,从而选择最佳接入网络.实验结果表明,该算法能在保证时间开销较低的同时,有效降低切换决策的错误概率,减少切换失败和切换次数,提升网络总吞吐量.     

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.     

一种基于速度感知的垂直切换算法

 未来的4G网络不是由单一的接入方式构成,而是采用不同的无线接入技术的多种网络的融合.不同网络接入技术间的切换称为垂直切换.本文提出了一种基于速度感知的垂直切换算法,不需确切的节点坐标和速度信息,利用接收信号强度的历史测量数据来表征节点运动速度的影响,提高对切换触发时机的准确判断.该算法可以自动调整以适应不同的节点运动速度,有效提高垂直切换的效率.仿真试验表明该算法能有效提高垂直切换的性能.     

基于Matlab的LTE与Wi-Fi垂直切换多属性算法研究

随着数据业务的需求量日渐增长,通信面临巨大的压力.未来通信系统将是不同制式网络进行无缝融合的系统.异系统之间的垂直切换的正确性以及有效性将是系统能否无缝融合的决定性因素.本文研究了LTE与Wi-Fi异系统的多属性垂直切换算法,并基于Matlab进行了算法实现设计.设计结果表明,多属性垂直切换算法使得LTE与Wi-Fi融合系统能够成功进行垂直切换,并且切换发生的乒乓效应较弱.     

基于强化学习的异构网络垂直切换方法

网络切换技术不仅可以保证用户的网络连接,同时能够以较强的信号传输网络数据。网络切换技术的性能对网络服务质量(quality of service, QoS)的影响至关重要。然而,现有的切换算法多数存在严重的乒乓效应,这不仅造成网络资源的严重浪费,还会损害用户的QoS。为此,提出了一种基于强化学习的异构网络垂直切换方案,主要从触发切换、网络选择及判决切换等方面进行优化。在触发切换时将垂直切换考虑成必要切换和择优切换,通过Q-Learning（QL）算法在选择网络时优化垂直切换;然后以QoS为条件,在判决切换时加入驻留定时器,从多角度减少用户切换次数,降低乒乓效应对异构网络垂直切换的影响。仿真结果表明,基于强化学习的异构网络垂直切换方法可以在保证QoS的条件下有效减少用户切换网络的次数,短时间内频繁切换的情况也有所改善,降低了乒乓效应的影响。     

多网络共存下基于贝叶斯的垂直切换算法

针对目前的垂直切换技术普遍不能满足多网络下的切换问题,提出了一种改进的基于贝叶斯决策的垂直切换算法。首先根据接入终端网络的信号强度、网络负载、误码率和网络阻塞率以及用户业务对网络的实际需求偏好建立多条件相关的切换概率分布,计算出先验切换概率;然后通过贝叶斯决策算法计算出后验概率来进行判决比较,从而选取最优的接入网络。仿真结果表明,该算法不仅能有效地实现不同接入技术之间的垂直切换,从而减少不必要的切换,提高了切换成功的概率,而且还能在维持各网络平均负载达到30%~40%时减轻通信热点的阻塞情况,为用户提供更优的服务质量。     

无线异构网络的垂直切换

传统意义上的水平切换算法已经在同构网络中得到很好的研究和应用,而随着多种无线异构网络的出现,下一代网络必须支持垂直切换技术以保证用户从一种类型的网络切换到另一种类型的网络时仍然保持连接。由于切换算法所需考虑因素的多样性和算法本身的复杂性,有必要对现有文献中的网络切换类型、切换因素、切换算法进行了归纳总结,并对垂直切换算法进行比较,指出未来切换算法的研究方向。     

A trajectory-aware handoff algorithm based on GPS information

In this paper, we propose a trajectory-aware handoff algorithm based on position, velocity, signaling delay, and receive signal strength (RSS) of mobile terminal (MT). In order to provide seamless service in modern heterogeneous networks, handoff of the MT should be initiated with correct timing. In our algorithm, velocity of MT is divided into two parts as radial velocity and tangential velocity. For more precise handoff initiation, tangential velocity of MT is neglected, and only radial velocity of MT is considered in handoff decision making. Moreover, before handoff decision, least square line method is applied to RSS of MT to avoid unnecessary back-and-forth handoffs (ping-pong handoffs) between different services. A simulation is provided to compare the proposed algorithm with other various handoff methods, and the results prove this algorithm to have outperformed others.     

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.     

Adaptation of CDMA Soft Handoff Thresholds Using Fuzzy Inference System

This paper proposes a new procedure to adjust soft handoff thresholds dynamically by using fuzzy inference system. This algorithm is compared with IS-95A and IS-95B/cdma2000 soft handoffs. The aims are to increase the thresholds at high traffic loads in order to release the traffic channel for supporting more carried traffic, and to decrease the thresholds at low traffic loads in order to give high quality of traffic channel. The inputs of the proposed algorithm are the number of remaining channels of each base station and the number of active pilots in active set of each mobile station. The output is the new soft handoff thresholds. In the fuzzy inference module, the triangular membership function, the max-min composition, and the weighted average formula defuzzification are selected. By comparison of all performance indicators among three algorithms, soft handoff using fuzzy inference tends to give higher performance than those of IS-95A and IS-95B/cdma2000 soft handoffs at high traffic loads and at lower soft handoff thresholds while the quality of traffic channel is still acceptable. Moreover, the wider soft handoff window size of the proposed algorithm gives high carried traffic and low blocking probability but lower quality of traffic channels. In addition, the adaptive soft handoff window size can give lower blocking probability while still keep acceptable quality of traffic channels.     

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.     

一种基于模糊逻辑的切换算法

针对蜂窝移动系统的越区切换,提出了一种基于模糊逻辑的切换判决算法.通过仿真与只以信号强度为指标的传统切换算法进行了性能比较,结果表明:采用多指标判决的模糊逻辑切换算法能够有效降低系统的掉话率和切换数量,提高服务等级.     

Microcellular handoff using fuzzy techniques

In order to manage the high call density expected in future cellular systems, microcell must be used. The size of the microcell will cause a dramatic increase in the number of handoffs. In addition, the small size of the microcell will require handoff algorithms to respond faster than those in todays systems. The problems are further exacerbated by the corner effect phenomenon which causes the signal level to drop by 20–30 dB in 10–20 m. Thus, in order to maintain reliable communication in a microcellular system new and better handoff algorithms must be developed. The use of hysteresis and averaging window in classical handoff techniques reduces unnecessary handoffs, but causes delays which may result in the calls being dropped. A fuzzy based handoff algorithm is proposed in this paper as a solution to this problem. The performance of fuzzy based handoff algorithm was also compared to that obtained using the classical handoff algorithms.     

CDMA系统基于多业务的软切换优化算法

文中利用剩余容量的概念,提出了CDMA系统中基于多业务的软切换优化算法,并对其进行了仿真.此算法综合考虑了传播衰耗和负载均衡两个因素,达到了各小区之间负载平衡和资源合理利用的目的.通过仿真结果可以看出,相对于传统的软切换算法,新算法降低了切换中断率,提高了系统性能,显示出较大的优越性,具有一定的价值.     

Soft handoff algorithms for CDMA cellular networks

This paper discusses the design of soft handoff algorithms for cellular communication systems. The handoff process is modeled as a hybrid system and handoff design is cast as an optimization problem based on such a model. Performance is evaluated in terms of call quality, average number of active base stations, average number of active set updates, and average amount of interference. A soft handoff algorithm, which achieves a tradeoff between these performance criteria, is obtained using principles of dynamic programming. One key feature of the algorithm is that it incorporates the effects of mobility and shadow fading in the handoff decision. Different diversity combining schemes are considered including selective combining, equal gain combining (EGC), and various optimized combining (OC) methods in the soft handoff mode. For EGC and OC, Wilkinson's and Schwartz and Yeh's methods are used to compute the statistics for the power sum of the signals. Simulation results indicate that the performance of the handoff algorithm is a function of the different combining schemes and of the different methods used to compute the statistics of the power sum. Moreover, it is observed that interference cancellation is important in order for the algorithm to be viable for cellular systems which experience interference due to using nonorthogonal multiple access.     

An Adaptive Hard Handoff Algorithm for Mobile Cellular Communication Systems

In this letter, we propose an adaptive hard handoff algorithm with a dynamic hysteresis value based on the received signal strength from the serving base station, for mobile cellular communication systems. A discrete‐time method is presented to evaluate handoff algorithms analytically. Performance is evaluated in terms of the average number of handoffs, the probability of link degradation, and the average handoff delay. Numerical results and simulations demonstrate that the proposed algorithm outperforms the handoff algorithm with fixed hysteresis values and the handoff algorithm using both threshold and hysteresis.     

多载波蜂窝移动通信系统中的多业务切换算法

提出一种用于多载波蜂窝移动通信系统的子信道合并切换算法。采用多维Markov链对子信道合并切换算法进行系统建模分析,得到了呼叫阻塞率、切换阻塞率等关键系统性能参数的解析结果。与切换保护信道算法相比,子信道合并切换算法在对其他类型呼叫性能影响很小的前提下,改善了对带宽要求较高的业务的切换性能。该算法还可以与其他资源预留切换算法相结合,改善其性能。