A Handover Strategy in the LEO Satellite-Based Constellation Networks with ISLs

A new handover strategy named minimal-hops handover(MHH) strategy for the lowearth orbit(LEO) satellite constellations networks equipped with inter-satellite links(ISLs) is proposed.MHH strategy,which is based on the hops of the end-to-end connection paths and makes good use of theregularity of the constellation network topology,can appropriately combine the handover procedure withrouting and efficiently solve the inter-satellite handover issue.Moreover,MHH strategy can providequality of services(QoS) guarantees to some extent.The system performances of the MHH strategy,suchas time propagation delay and handover frequency,are evaluated and compared with that of otherprevious strategies.The simulation results show that MHH strategy performs better than other previoushandover strategies.     

New spray and wait protocol with node activity in heterogeneous delay tolerant networks

The spray and wait protocol is a classic copy-limited spraying protocol in delay tolerant networks, in which, the binary spray mode can be improved for heterogeneous delay tolerant networks. In this article, a new conception of node activity was defined to weigh the importance of nodes in aspect of message dissemination in the whole network. A new spray and wait protocol with node activity was proposed to improve the performance in heterogeneous delay tolerant networks. A mathematical model used under varieties of the spraying protocols was also proposed to analyze the expected delay of the protocol. Simulations show that the spray token proportion with node activity is optimal and the new protocol is of better performance than other related protocols. Therefore, this protocol has high efficiency and good scalability.     

Quality of Service Improvement for High-Speed Railway Communications

With the fast development of highspeed railways, a call for fulfilling the notion of communication at ＂anytime, anywhere＂ for high-speed train passengers in the Train Operating Control System is on the way. In order to make a realization of that, new railway wireless communication networks are needed. The most promising one is the Long Term Evolution for Railway which will provide broadband access, fast handover, and reliable communication for high mobility users. However, with the increase of speed, the system is subjected to high bit error rate, Doppler frequency shift and handover failure just like other system does. This paper is trying to solve these problems by employing MIMO technique. Specifically, the goal is to provide higher data rate, higher reliability, less delay, and other relative quality of services for passengers. MIMO performance analysis, resource allocation, and access control for handover and various services in a two-hop model are proposed in this paper. Analytical results and simulation results show that the proposed model and schemes perform well in improving the system performances.     

垂直交换管理的集合架构

Recent advances in hardware technology have made it possible for mobile devices to interface with multiple networks of different types. In this paper, an IEEE 802.21 Media Independent Handover (MIH) based handover management architecture containing four modules is proposed and the multihoming technology is adopted to achieve Make-Before-Break vertical handover. Then the paper presents the performance analysis of the architecture and simulation in ns-2. The results substantiate the effi cacy of the architecture in improving the handover performance signifi cantly compared with the traditional Mobile IPv6 (MIPv6) based vertical handover. Besides, we design and implement this handover management architecture in our test-bed. The experimental results in a real network environment show that our proposed architecture can not only support the Make-before-break handover, but also guarantee the scalability because of the modulized design.     

Performance analysis of multicast replication mechanism in shared-memory switch with speedup

A multicast replication algorithm is proposed for shared memory switches. It uses a dedicated FIFO to multicast by replicating cells at receiver and the FIFO is operating with shared memory in parallel. Speedup is used to promote loss and delay performance. A new queueing analytical model is developed based on a sub-timeslot approach. The system performance in terms of cell loss and delay is analyzed and verified by simulation.     

Manageable Fast Handover at Access Point in WLAN

The handover speed is always vital for the further development of Wireless Local Area Network (WLAN), which is enjoying a fast growth. Based on the handover technology specified in IEEE 802.11 WLAN, Manageable Fast Handover (MFHO) mechanism is proposed to speed up handover at the Access Point (AP), meet handover demands of services with different Quality of Service (QoS), and ensure service continuity. Adopting a handover policy named "Make-before-break", this mechanism enables wireless APs to control and manage handover between two stations based on improving Inter-Access Point Protocol (IAPP). Tests have been carried out to compare functions and performance of MFHO and IAPP-based handover technology. The test results prove that MFHO provides a higher successful handover ratio and better handover performance than IAPP-based handover technology.     

A delay based backoff scheme for WLAN with QoS guarantee and its performance

Based on the Distributed Coordination Function (DCF) and the Enhanced DCF (EDCF) mechanisms in IEEE 802.11 and 802.11e, a novel backoff scheme for Wireless Local Area Network (WLAN) is proposed. The scheme is to solve the problem of the packet loss and the decrease of performance due to the increasing Contention Window (CW) when there are continuous collisions. In the proposed scheme, the CW of the packet will change dynamically with different delay for the different traffics. Mathematic formulas are presented to indicate the relationship between the CW and the delay character. The performance of the new scheme is also discussed with simulation results. The results show that it helps WLAN system handle multimedia simultaneously.     

PERFORMANCE OF CODED OFDM VIA VARIABLE GUARD INTERVAL

This letter presents the principles of Coded Orthogonal Frequency Division Multiplexing (COFDM) system and focuses on the effect of the Guard Interval (GI) on the system performance. The role of the GI parameter period to solve the problem of interferences that occur at the receiver is discussed. A new COFDM concept with a Variable GI (VGI) is proposed in order to improve the Bit Error Rate (BER) performance in the presence of multipaths with variable delays. A series of simulations have been carried out on the BER performance as a function of GI, maximum delay spread, and Signal-to-Noise Ratio (SNR), with QPSK as modulation scheme over multipath fading and Additive White Gaussian Noise (AWGN). The results show that the optimum values of the GI parameter approximately equal to the maximum delay spread, and the proposed system with VGI provides a better performance compared with the fixed length GI.     

Study and enhancement on buffer management for smooth handover in MIPv6

For improving Transfer Control Protocol (TCP) performance in mobile environment,smooth handover with buffer management has been proposed to realize seamless handovers. However in our simulation, even if smooth handover in Mobile IPv6 (MIPv6) is implemented, TCP can not always achieve better performance due to packets forwarding burst. Based on the study of buffer management for smooth handover, this paper proposes an enhanced buffer management scheme for smooth handover to improve TCP performance. In this scheme, a packet-pair probing technology is adopted to estimate the available bandwidth of the new path from Previous router (Prtr) to Mobile Node (MN), which will be used by Prtr to control the buffered packets forwarding. The simulation results demonstrate that smooth handover with this scheme can achieve better TCP performance than the original scheme.     

A Mobility Management Solution Based on ID/Locator Separation

Current mobility management solutions based on ID/Locator separation are not easily deployed and cannot solve routing scalability and mobility problems. This paper proposes a novel network architecture based on ID/Locator separation and suggests a new mobility management solution. This solution solves the problem of scalability in the network and also provides better support for mobility. It can be easily deployed because no modification of the mobile host’s protocol stack is required. The identifier contains some routing information; so the solution provides intrinsic interworking with traditional mobile hosts. Because the mapping systems are distributed to the edge networks, robustness of the whole system is enhanced and handover delay is decreased.     

低轨卫星星座网的切换研究

提出了一种适用于装备有星际链路的低轨卫星星座网的切换策略——最小跳数切换策略。该策略以端到端连接的跳数为基础,充分利用了低轨星座网的特点,将切换过程与路由有机地结合为一体,有效解决了不同卫星之间的切换问题。仿真结果表明,同已有的切换策略相比,该策略能够提供一定程度的QoS保障,获得较好的系统性能,如较低的传播延时和较小的切换频率,具有很好的实用价值。     

移动IPv6切换时延优化新方法

移动IPv6中,移动节点(MN)在不同子网间移动时,既不中断与通信对端(CN)的通信,也不用改变其本身的IP地址.但是当MN与其家乡代理(HA)之间相距较远时,移动IPv6切换时延较大,对于实时性要求较高的业务无法适用.本文分析比较了目前移动IPv6常用的切换时延优化方法,提出了一种自适应快速层次移动IPv6切换时延优化方法,减小了移动IPv6切换时延,提高了网络的性能.     

A New Enhanced Fast Handover Algorithm in Hierarchical Mobile IPv6 Network

1　Introduction　MobileIPv6requirestheMobileNode (MN)toregisterwiththeHomeAgent (HA)andtheCorre spondentNode (CN)whenitchangesitspointofattachmentintheInternet[1～ 3] .Therefore ,thiscauseMobileIPv6toincurlongdelayintheregis tration process,andaddsignalingtraffictothebackbonenetworkespeciallywhentheHAandCNarefarawayfromtheMN .Inordertominimizethisdelay ,andthesignalingoverhead presentinMobileIPv6,literatures[4～7] proposeHierarchicalMobileIPv6(HMIPv6)architectureandafasthan dover…     

基于协作检测的频谱移动技术

频谱移动的目的是使网络状态变化尽可能快地平滑进行,以确保频谱切换中对通信性能的影响最小。采用基于协作检测的协同频谱感知方法,研究频谱移动的策略,分析频谱池容量对系统性能的影响,设计合适的跨层策略,减小切换延迟,最小化频谱切换对各层的影响。     

On the fast BSS transition algorithms in the IEEE 802.11r local area wireless networks

Handover performance is critical to support multimedia services that are becoming increasingly available over the wireless devices. The high transition delay can be unaccepted for such services or can be a source of disruption on the session. On the other side, IEEE 802.11 standard is being extended with new functionalities. Security and QoS features, included in recent IEEE 802.11-2007 standard, add management frames that are exchanged during the transition process. In consequence the handover delay is increased. IEEE 802.11r-2008 amendment introduces Fast BSS Transition (FT) that simplifies the handover process. The authors propose the new handover algorithms based on FT protocol and compare them with existing solution. Additionally, simulation experiments are conducted to answer the question if multimedia services can be properly supported in IEEE 802.11r networks. The authors prove that handover delay can be reduced to 13 ms in the average case.     

Traffic performance analysis of handover in GMPCS systems

This paper presents an analysis of handover process and its effect on the traffic performance in global mobile personal communications by satellite (GMPCS) systems. With the nongeostationary satellite used for the system, the handover scheme needs to be applied to make calls completed without any interruption. An analytical model is developed for the analysis of the handover process. We derive the mean number of handovers and handover delay with various satellite antenna patterns and different settings of handover parameter. A suitable traffic model of the whole system is also derived after due considerations of the handover process. The system performance measures include new call blocking probability, call dropping probability, and mean number of handovers per call. A computer simulation is developed and used. We also analyze the system performance with a number of handover priority schemes applied. Based on the study results, the handover parameters are selected to maximize the traffic performance. It is shown that we can improve the overall traffic performance of GMPCS system by setting handover parameters properly and using the handover priority scheme     

Handover signalling for microcellular environments

A new strategy for routing handover signalling in microcellular environments is proposed. Simulation results show that time delay for handover packets travelling across the fixed network could be reduced by diverting the signalling through the air interface between the serving and the candidate base station (BS)     

mSCTP协议异构网络切换性能评估

在RFC 5061中,提出了一种对SCTP协议的扩展,采用地址动态重配置的方法,解决了现在网络设备IP地址不断变化的问题。RFC 5061的推出促进了SCTP协议在移动网络无缝漫游解决方案中的应用。在本文中,测试了SCTP和mSCTP协议的切换时延,验证了mSCTP在无缝切换中应用的可行性。切换的场景包括移动终端的慢速移动和快速移动两种情况。     

快速层次移动IPv6切换性能分析及优化

移动IPv6技术中切换延时对实时应用影响很大。介绍了目前移动IPv6常用的快速移动和层次移动切换技术,描述其切换原理和过程。结合2种技术的优缺点,给出了一种新的快速层次移动IPv6的切换方案。利用NS-2对这3种切换方法进行仿真得到的结果表明,快速层次移动IPv6切换延时要小于快速移动IPv6和层次移动IPv6的切换延时,且降低了数据包丢失率,提高了网络的性能。