无线ATM通信网的越区切换控制

论文研究无线ATM通信网的越区切换控制问题,提出不同的业务类型应采用不同的切换控制方法,从而使多媒体业务的服务质量(QoS)在越区切换时仍然可以得到保证。文中着重讨论了由于无线ATM通信的特点所引起的路由重建、QoS的保证与协商,信元次序的保证等关键问题,并提出了相应的解决办法。     

基于GSM-R铁路无线通信系统的越区切换分析研究

列车和无线闭塞中心在多数情况下通信处于正常状态,但是在实际通信过程中可能出现以下几种引发故障因素:传输数据出错、连接丢失、越区切换、端到端传输延时.主要考虑了高速列车在移动闭塞区间条件下GSM-R无线通信系统的越区切换的可靠性,采用计算机仿真的方法得到GSM-R通信系统在通信故障情况下的越区切换成功概率.结合随机Petri网理论对于铁路无线通信系统GSM-R中的越区切换事件进行了建模和分析,给出了随机Petri网表示的列车与无线闭塞中心通信的越区切换模型,并使用TimeNET仿真工具分析了GSM-R越区切换的可靠性.     

数字移动通信系统中越区切换的计算机模拟

切换技术是数字式蜂窝移动通信系统保证移动中用户通信质量的一个重要手段,本文在论述公用陆地移动网的越区切换功能基础上,提出了一种实现越区切换功能的计算机模拟方法。     

无线ATM越区切换中的路由重选

论文研究了目前无线ATM通信网越区切换中的路由重选问题,对目前主要的几种路由重选方案进行了详细的比较和分析。     

无线Mesh网在城市轨道交通车地通信系统中的研究

无线Mesh网因组网灵活、支持范围大和移动性强等特点,使其在城市轨道交通(城轨)中具有很好的应用前景。尝试将无线Mesh网技术应用于城轨车地通信系统中,针对车地通信存在的越区切换问题,提出了一种基于车载MMS(mobile Mesh station)位置触发的越区切换方案,利用OPNET对组网方案和切换方案进行了仿真。仿真结果表明,无线Mesh组网方案性能优于传统WLAN组网方案性能,切换方案能有效降低时延并避免了假切换和乒乓切换的发生。     

模糊技术在第三代移动通信越区切换中的应用

该文对蜂窝移动网的越区切换算法的模糊控制技术进行了介绍。蜂窝移动网中的越区切换是保证蜂窝网用户正常话的关键技术之一。从GSM的硬切换技术到CDMA的软切换技术,掉话率降低的同时也对应着更多的系统资源占用。而三代移动通信系统所能提供的频率资源得到了很大的提高,使得以前在2G时代提出的算法更无法适应新业务的要求和实的需要。该文就是对比第三代移动通信系统的越区切换算法,使用模糊控制技术,来提高CDMA系统的信道利用率,降越区切换的呼损率。     

位置功率联合判决的高铁通信越区切换算法

随着我国铁路运输现代化进程的加快,高铁列车对通信信息技术的需求日益提升。越区切换是高铁无线通信移动性管理的重要部分,对提高通信质量和运营效率、确保运营安全具有重要意义。针对高铁列车切换性能差、乒乓切换率高的问题,提出一种位置功率联合判决的越区切换算法。以切换阈值作为约束条件并借助信道模型和测量信息计算得到最佳切换带,利用高铁列车的单向移动特点简化位置信息并优化切换流程,以有效避免乒乓切换现象。考虑到车载多中继节点对切换触发位置的判决误差之间存在相关性,构建代价函数筛选最优的预测参数,采用加权统计线性回归方法预测判决误差并加以纠正,使得切换位置收敛于最佳切换点。仿真结果表明,相对A3算法、距离触发算法,该越区切换优化算法能有效降低乒乓切换率,在列车速度为350 km/h时越区切换成功率达到99.5%以上,其能够提高通信系统的可靠性,推动列车提速并保障行驶安全。     

移动IPv6越区切换算法的研究与仿真

分析移动IPv6中的TCP拥塞控制机制和移动检测技术,讨论一个改进的越区切换算法,并采用OPNET网络仿真软件对其进行仿真.仿真结果表明,该算法有效地抑制了由于移动节点的越区切换而导致的拥塞控制机制的启动,增强了移动网络的通信能力.     

蜂窝网中基于位置预测的切换算法

为了满足未来移动网络蜂窝小、切换频繁、支持规模用户和多媒体应用的需求,对位置预测与越区切换进行深入分析,提出了基于位置预测的越区切换方案HDLP(Handover Decision based on Location Prediction),其基本思想是:(1)从移动用户的大量历史移动轨迹数据中挖掘频繁轨迹;(2)根据挖掘出的频繁轨迹集合生成运动规则;(3)将运动规则运用于判决蜂窝移动通信的越区切换中。对所提算法进行仿真的结果表明,与传统的切换方案相比较,本算法减少了不必要的越区切换次数,降低了错误切换率,提高了切换的准确率,进而在一定程度上降低了通信代价,提高了通信系统的容量以及QoS。     

CDMA2000-1X系统多业务复合越区切换策略

提出一种多业务综合越区切换策略,该策略同时支持实时业务和非实时业务;通过双队列模式解决了实时业务的虚拟切换问题,有效地利用资源、缓解呼叫和切换拥塞;并通过建立多维马尔科夫链越区切换策略模型,为请求越区切换的实时业务提供了抢占优先和排队相结合的策略。仿真结果表明,系统的呼损率、阻塞率、强制中断概率等系统性能指标得到明显改善。     

移动无线因特网中的一种基于QoS的切换支持机制*

研究了移动无线因特网中基于QoS的切换支持机制,该机制采用移动台辅助切换策略和基于底层信息的动态切换准则,软、硬切换有机结合,同时辅以重路由、频繁切换QoS控制与缓存等技术,为用户QoS保证提供支持。原型系统实现表明,该机制是可行和有效的。     

TEASE: A novel Tunnel-based sEcure Authentication SchemE to support smooth handoff in IEEE 802.11 wireless networks

With the growing popularity of WiFi-based devices, WiFi-based wireless networks have received a great deal of interest in the wireless networks community. However, due to the limited transmission range of WiFi-based networks, mobile users have to switch their associated access points constantly to maintain continuing communications during their movement. The process of switching access points is called handoff. Handoff management is a key service in mobile networks, because providing seamless roaming in wireless networks is mandatory for supporting real-time applications in a mobile environment, such as VoIP, online games, and eConference. Security is another important issue in network communications, and to prevent possible attacks, authentication is required during the handoff process to guarantee the reliability of mobile clients and access points. In this paper, we propose a novel authentication scheme to achieve a smooth handoff in WiFi-based networks, which we refer to as TEASE. A tunnel is introduced to forward data packets between the new access point and the original reliable access point. The processing of a complete secure authentication and the transmitting of data between mobile terminals and their correspondence nodes can go on simultaneously. The security of handoff is achieved without increasing overhead to authentication servers, and handoff latency can be minimized to support seamless roaming. Simulation results show that our proposed scheme reduces significantly the communication interruption time and generates low packet loss ratio, and our method is suitable to be used for secure handoff in real-time applications.     

移动IPv4切换时间特性的实验与分析

通过将切换过程进行小粒度解析总结出切换时延的组成,针对各类耗时在自行开发的系统上进行了实验。实验结果表明：目前移动IP切换时延主要取决于协议数据包的传输时间和在进行协议栈处理以前等待路由（代理）广告的时间,缩短这两部分时间是提高移动IP切换速度的关键。     

A bandwidth adaptation mechanism for Cloud Radio Access Networks

The Cloud Radio Access Network (C-RAN) is regarded as the possible implementation approach of the next-generation mobile networks. C-RAN splits a traditional base station into remote radio heads (RRHs) and the base band unit (BBU). Many BBUs are co-located into a centralized BBU pool. This enables the baseband resources to be managed in a centralized BBU pool and thus improves the efficiency. In this paper, a new bandwidth adaptation (BA) mechanism is designed for the C-RAN with the dual connectivity capability. The dual connectivity allows the bearer to be split so as to access more resources from RRHs simultaneously. The new BA mechanism is developed so as to dynamically allocate the resources to establish a new or a handoff bearer. The new BA mechanism is designed with a new downgrading index, which aims to fairly release the proportional resource from more RRHs and then aggregates the released resource to a new or a handoff bearer. Simulation and analysis results illustrate that the proposed BA mechanism reduces both the handoff bearer dropping and the bearer blocking probabilities.     

802.11无线局域网链路层切换机制研究

首先介绍了目前基于802．1l无线局域网的各种切换算法，对其在切换延迟和丢包率等方面进行了分析。在此基础上提出了一种多点预先转发的切换模式，并对其切换原理和特征进行了阐述，另外也对其相关问题进行了说明。     

Dynamically adaptive channel reservation scheme for cellular networks

In personal communications networks (PCN) supporting network-wide handoffs, new and handoff requests compete for connection resources in both mobile and backbone networks. Forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. In general, most of the previously proposed schemes for radio channel allocation in cellular networks reduce handoff call blocking probability substantially at the expense of increasing the new call blocking probability by giving higher priority to handoff calls over new calls in admission control. This reduces the total admitted traffic and results in inefficient utilization of wireless channels. The tradeoff between the new and handoff calls blocking probabilities should be defined on importance basis. In this paper, we propose a performance metric equation that makes a trade off between the two probabilities depending on the network preferences. Using this equation, we study the performance of various proposed channel reservation schemes. Also in this paper, a new dynamically adaptive channel reservation scheme (DACRS) is developed and compared with other schemes proposed in the literature. The DACRS assigns handoff-reserved channels to new calls depending on the locality principle in which the base station with the help of location estimation algorithms in the mobile location center predicts the position of the mobile terminal. Eventually, the DACRS is designed to improve channel utilization while satisfying the QoS of the calls. As will be shown analytically and through simulation, the DACRS outperforms current reservation schemes and results in more statistical gain, and powerful channel utilization.     

移动IP中一种基于双链路的切换协议

移动IP技术中的切换延时是阻碍移动IP技术广泛应用的关键问题。该文提出了一种基于双链路的切换协议,该协议在提前触发等机制的保障下采用链路冗余的方式,实现了移动节点的无缝切换。另外,对该协议在切换性能上的改进进行了分析,并对该协议下切换过程中的通信性能进行了测试。     

Simulation studies of the effects of user mobility on the handoff performance of mobile communications

The performance of soft handoffs of code division multiple access (CDMA) mobile communication systems is determined by several factors. Due to the importance of handoffs in mobile communications, several handoff methods have been proposed and evaluated through computer simulations. However, the credibility of simulation results depends on the objectivity of the assumptions made by the simulations. This paper presents a new soft handoff method that controls handoff drop timer based on a mobile station’s speed, and compares it with the current method of CDMA systems. A computer program has been developed to simulate the handoff methods under a variety of conditions. The simulation results showed that the new method is much more efficient for mobile stations that are free in their moving direction and space than for those restricted in their moving direction and space. In addition, the results showed that even the same handoff method may produce different simulation results depending on whether a service area is modeled as two-dimensional space or three-dimensional space. These results indicate the importance of suitable models of user mobility, especially the movement types and space allowed for mobile stations, which have been neglected in simulation studies of mobile communications.     

QoS-aware radio resource management scheme for CDMA cellular networks based on dynamic interference guard margin (IGM)

Efficient radio resource management (RRM) for CDMA-based cellular communication systems using the interference guard margin (IGM) scheme is investigated in this work. Two important concepts, i.e., the guard channel (GC) and the load curve (LC), are integrated to derive IGM. The resulting call admission control (CAC) scheme gives preferential treatment to higher priority handoff calls by pre-reserving a certain amount of resource in terms of IGM. A radio resource estimation (RRE) function is implemented in each base station (BS) to assist RRM module to adjust the level of IGM dynamically. RRE in each BS estimates the amount of IGM by considering traffic load in its current cell as well as traffic conditions in neighboring cells. A service model is adopted to support quality of service (QoS) demand of multiple services, which includes mobile terminal’s data rate, different levels of priorities, mobility and rate adaptivity characteristics. Simulations are conducted by OPNET to study performance of the proposed IGM scheme in terms of a defined cost function, new call blocking probability, handoff dropping probability and system utilization, under different traffic conditions.