LTE系统中切换优化算法的研究

3GPP提出了一种自组织,自配置,自愈合网络,即SON(Self-organizing Network)。SON的一个重要方面就是移动健壮性优化(Mobility Robust Optimization,MRO),其主要目的是通过基站自配置合适的切换参数,提高基站的切换性能。本文提出了一种基于SON的切换参数优化(Handover Parameter Optimization,HPO)算法,并且考虑了不同移动速度的UE对切换性能的影响,设置不同的迟滞参数,通过检测不同的场景动态调整切换参数。最后搭建了仿真平台,仿真结果表明,经过该算法优化后,切换性能大幅提高。     

基于拓扑控制的无线自组织网络TCP性能改进研究

针对无线自组织网络TCP性能不高的问题,在网络节点所处的平面上引入空间约束机制,通过加入位置信息和增大平面以降低网络节点间干扰的方法来减小网络总干扰。分析了网络源节点的广播成功率,计算了网络节点的空间位置下界,并分别就单TCP流和多TCP流的情况下网络的有效性加以讨论。通过实验仿真可见,这种新型的性能改进方法可以有效提高无线自组织网络的相关性能。     

高速客运通信系统中的动态资源预留

针对高速客运系统中用户频繁切换产生的大量资源开销,引入了组移动性概念,通过设置列车中继站,实现了车内用户的单用户切换方式.同时,针对大量用户同时切换至目标基站导致的基站拥塞,提出了基于基站协作的动态资源预留方案.即当前基站根据列车运行状态信息提前获知切换目标基站,并通告其资源需求,使其为车内用户预留资源.仿真结果表明列车业务量对系统性能产生了严重影响,采用动态资源预留方案,可以有效地提高列车用户的通信性能.     

基于RSS准则的CDMA软切换越区研究

硬切换技术中移动台在接收新基站信号之前中断与原基站的通信,通信中断的概率非常大。而软切换技术需要先建立与新基站之间的通信,等接收到原基站信号低于门限值时再切断与原基站的通信,故具有很高的可靠性。采用接收到的信号强度准则对软切换建立仿真模型,对两个小区之间的软切换进行了仿真,仿真结果表明,软切换的可靠性高于硬切换,采用软切换技术降低了系统的掉话率,提高了通信质量。然而,软切换也将使系统的复杂度和信道开销有所增加。     

使用EHN-HP机制提高移动切换中TCP性能

移动通讯技术的发展促使传统有线互联网向无线移动网络延伸.TCP协议是现在互联网上使用最为广泛的端到端可靠传输协议,但TCP协议是在有线链路基础上设计的,直接在无线移动网络上使用TCP协议会造成TCP性能的下降.本文详细分析了移动切换对TCP协议造成的影响,比较并分析现有的几种解决方案,针对切换对TCP造成的影响提出了EHN-HP机制.EHN-HP机制在现有的TCP协议上进行改进,增加了切换处理机制(Handoff Process),通过网络模拟器的模拟结果表明,EHN-HP机制有效的改善了TCP协议在切换过程中的性能.     

基于繁忙因子的VVSN自适应双簇头分簇算法研究

在WSN中,节点之间不平衡通信消耗大量能量,因此网络生存时间较短。为改善网络整体生存时间,提出一种基于网络繁忙因子的簇头自适应切换算法。首先,算法一次性选举双簇头,再根据网络实际情况自适应切换簇头。然后,在簇头选举完成后,节点通过当前簇头与基站通信,若当前簇头的能量低于门限值,则网络中的当前簇头将被切换到次级簇头,此时节点通过次级簇头与基站通信,从而降低节点能耗,减少节点的死亡率。双簇头切换机制缩短了整体通信距离,缓解簇头节点过早死亡,使网络生存时间增长。仿真结果表明,该算法通过缩短整体通信距离可显著降低整体网络的能量消耗,增加网络的生存时间。     

MobileIP切换时的TCP／UDP性能分析

这篇文章分析了ModbileIP的基本原理,讨论了移动主机的切换过程,详细分析了现有几种移动切换算法的性能,并在基础上提出利用链路层切换的信息及主动发送代理请求消息减小切换的时延,从而改善移动主机的切换性能的设想。计算机仿真结果表明这种算法能够有效地改善移动主机的TCP／UDP性能。     

LTE系统中基站内切换测试的自动化实现方案

为了更好的评估LTE系统中基站内切换性能,提出了一种基于LTE系统基站内切换测试的自动化实现方案。首先详细介绍了LTE系统基站内切换协议流程,接着设计了一套切换测试的硬件环境。并在公司Robot自动化测试平台上进行了测试用例的设计实现,在此基础上进行验证测试和实验结果的分析。最后提出了终端在高速移动中如何保持切换的高质量接续是一项值得深入研究的课题。     

一种基于最低能量保护的分簇CCLP算法

PEGASIS协议是一种基于链式结构的协议,链中总有一个节点被选为头节点,这个节点没有考虑到基站的位置,导致PEGASIS协议造成冗余数据的传送.提出了基于同中心簇中最低能量保护的算法.仿真结果表明,该算法能考虑到基站的位置和充分保护能量最小的节点,来增强它的性能和延长WSN的生命周期.     

认知网络下TCP协议性能分析

首先在无线环境下的基础上搭建认知平台,当主用户想要占次用户信道时,通过基站的频谱监测,频谱分配,分配次用户到其他空闲信道继续通信.其次,在此平台下分析TCP Reno,TCP Newreno,TCP Sackl和TCP vegas协议的性能,包括拥塞窗口、吞吐量.最后定量分析主用户活跃程度、切换后信道带宽和信道误比特率...     

A comparison of congestion control and time slot algorithms in Internet transmission performance

The characteristics of TCP and UDP lead to different network transmission behaviours. TCP is responsive to network congestion whereas UDP is not. This paper proposes two mechanisms that operate at the source node to regulate TCP and UDP flows and provide a differential service for them. One is the congestion‐control mechanism, which uses congestion signal detected by TCP flows to regulate the flows at the source node. Another is the time‐slot mechanism, which assigns different number of time slots to flows to control their flow transmission. Based on the priority of each flow, different bandwidth proportions are allocated for each flow and differential services are provided. Simulation results show some insights of these two mechanisms. Moreover, we summarize the factors that may impact the performance of these two mechanisms. Copyright © 2001 John Wiley & Sons, Ltd.     

Using multiple per egress burstifiers for enhanced TCP performance in OBS networks

Burst assembly mechanism is one of the fundamental factors that determine the performance of an optical burst switching (OBS) network. In this paper, we investigate the influence of the number of burstifiers on TCP performance for an OBS network. The goodput of TCP flows between an ingress node and an egress node traveling through an optical network is studied as the number of assembly buffers per destination varies. First, the burst-length independent losses resulting from the contention in the core OBS network using a non-void-filling burst scheduling algorithm, e.g., Horizon, are studied. Then, burst-length dependent losses arising as a result of void-filling scheduling algorithms, e.g., LAUC-VF, are studied for two different TCP flow models: FTP-type long-lived flows and variable size short-lived flows. Simulation results show that for both types of scheduling algorithms, both types of TCP flow models, and different TCP versions (Reno, Newreno and Sack), TCP goodput increases as the number of burst assemblers per egress node is increased for an OBS network employing timer-based assembly algorithm. The improvement from one burstifier to moderate number of burst assemblers is significant (15–50% depending on the burst loss probability, per-hop processing delay, and the TCP version), but the goodput difference between moderate number of buffers and per-flow aggregation is relatively small, implying that an OBS edge switch should use moderate number of assembly buffers per destination for enhanced TCP performance without substantially increasing the hardware complexity.

Using TCP rate control for queue input‐output rate matching

In explicit TCP rate control, the receiver's advertised window size in acknowledgment (ACK) packets can be modified by intermediate network elements to reflect network congestion conditions. The TCP receiver's advertised window (i.e. the receive buffer of a TCP connection) limits the maximum window and consequently the throughput that can be achieved by the sender. Appropriate reduction of the advertised window can control the number of packets allowed to be sent from a TCP source. This paper evaluates the performance of a TCP rate control scheme in which the receiver's advertised window size in ACK packets are modified in a network node in order to match the generated load to the assigned bandwidth in the node. Using simulation and performance metrics such as the packet loss rates and the cumulative number of TCP timeouts, we examine the service improvement provided by the TCP rate control scheme to the users. The modified advertised windows computed in the network elements and the link utilization are also examined. Copyright © 2002 John Wiley & Sons, Ltd.     

TCP transmission rate control mechanism based on channel utilization and contention ratio in AD hoc networks

In ad hoc networks, both contention and congestion can severely affect the performance of TCP. In our work, we first show that the over-injection of conventional TCP window mechanism results in severe contentions, and medium contentions cause network congestion. Furthermore, introducing two metrics, channel utilization (CU) and contention ratio (CR), we characterize the network status. Then, based on these two metrics, we propose a new TCP transmission rate control mechanism based on Channel utilization and Contention ratio (TCPCC). In this mechanism, each node collects the information about the network busy status and determines the CU and CR accordingly. The CU and CR values fed back through ACK are ultimately determined by the bottleneck node along the flow. The TCP sender controls its transmission rate based on the feedback information. Simulation results show that the proposed TCPCC mechanism significantly outperforms the conventional TCP mechanism and the TCP contention control mechanism in terms of throughput and end-to-end delay.     

Optimizing TCP forwarder performance

A TCP forwarder is a network node that establishes and forwards data between a pair of TCP connections. An example of a TCP forwarder is a firewall that places a proxy between a TCP connection to an external host and a TCP connection to an internal host, controlling access to a resource on the internal host. Once the proxy approves the access, it simply forwards data from one connection to the other. We use the term TCP forwarding to describe indirect TCP communication via a proxy in general. This paper characterizes the behavior of TCP forwarding, and illustrates the role TCP forwarding plays in common network services like firewalls and HTTP proxies. We then introduce an optimization technique, called connection splicing, that can be applied to a TCP forwarder, and report the results of a performance study designed to evaluate its impact. Connection splicing improves TCP forwarding performance by a factor of two to four, making it competitive with IP router performance on the same hardware     

Applications of network coding to improve TCP performance over wireless mesh networks: a survey

There is growing interest in the use of wireless mesh network (WMN) as a last‐mile option for Internet access. Despite the many benefits of WMNs, the performance of Internet access may not be ideal. One of the main issues is the interaction of transmission control protocol (TCP) with the underlying network. The poor performance of TCP over multi‐hop networks is well‐documented, and extensive research exists, which addresses TCPs foible and enhance TCP performance for multi‐hop environments. This paper provides a thorough survey of TCP performance issues over WMNs and the available solutions to address these issues. Among the existing methods, we focused on network coding (NC) and the ways that TCP interacts with network coded systems. NC is a technique that encodes the received packets in each node before forwarding them towards the destination. The use of NC in the transport layer to address performance issues raised by wireless access is a recent research topic. This paper presents a detailed study of TCP interaction with NC. Some open research areas in this field are suggested. Copyright © 2012 John Wiley & Sons, Ltd.     

Dropping Policy with Burst Retransmission to Improve the Throughput of TCP Over Optical Burst-switched Networks

A major concern in optical burst-switched (OBS) networks is contention, which occurs when more than one bursts contend for the same data channel at the same time. Due to the bufferless nature of OBS networks, these contentions randomly occur at any degree of congestion in the network. When contention occurs at any core node, the core node drops bursts according to its dropping policy. Burst loss in OBS networks significantly degrades the throughput of TCP sources in the local access networks because current TCP congestion control mechanisms perform a slow start phase mainly due to contention rather than heavy congestion. However, there has not been much study about the impact of burst loss on the performance of TCP over OBS networks. To improve TCP throughput over OBS networks, we first introduce a dropping policy with burst retransmission that retransmits the bursts dropped due to contention, at the ingress node. Then, we extend the dropping policy with burst retransmission to drop a burst that has experienced fewer retransmissions in the event of contention at a core node in order to reduce the number of events that a TCP source enters the slow start phase due to contention. In addition, we propose to limit the number of retransmissions of each burst to prevent severe congestion. For the performance evaluation of the proposed schemes, we provide an analytic throughput model of TCP over OBS networks. Through simulations as well as analytic modeling, it is shown that the proposed dropping policy with burst retransmission can improve TCP throughput over OBS networks compared with an existing dropping policy without burst retransmission.     

对TCP/IP计算机网络拥塞控制的研究

为提升计算机的网络性能,更好地避免拥塞现象的发生,需要对其进行必要的技术控制。鉴于此,对基于TCP/IP协议的网络拥塞控制方法进行分析。在TCP拥塞控制中主要采用TCP Tahoe,TCP Reno,TCP New Reno以及TCP Sack四种方法,其中TCP New Reno对快速恢复算法进行了改进,通过对TCP协议中的Reno进行可视化处理,实行对网络拥塞的有效管理。而IP拥塞控制方法则分为FIFO,FQ和WFQ,RED以及ECN四种类型,通过队列调度管理方式实现了对网络拥塞的有效管理。     

Rate Control Algorithm Considering Mobility in Mobile Ad Hoc Networks

For reducing the loss of data packet due to network congestion and mobility, rate control algorithm is effective means for ensuring the fair allocation of network resource among communication flows and alleviating network congestion. The Transport Control Protocol (TCP) was originally designed for wire-line networks, where the links are assumed to be reliable and with fixed capacities. However, the performance of TCP becomes very poor when it is directly used in ad hoc networks. Some optimization-based congestion control schemes have been proposed to improve TCP performance in ad hoc networks, but the mobility of hosts and route change frequently are not considered for designing rate control algorithm. In this paper, we propose rate control algorithms in a more practical way by taking into account link congestion and node movement. Numerical results show that the rate control algorithms can approach the globally optimal value and show the effect of the node mobility on the algorithms.     

TCP Window-Based Flow-Oriented Dynamic Assembly Algorithm for OBS Networks

In transport control protocol (TCP) over optical burst switching (OBS) networks, TCP window size and OBS parameters, including assembly period and burst dropping probability, will impact the network performance. In this paper, a parameter window data dropping probability(WDDP), is defined to analyze the impact of the assembly and the burst loss on the network performance in terms of the round trip time and the throughput. To reduce the WDDP without introducing the extra assembly delay penalty, we propose a novel TCP window based flow-oriented assembly algorithm dynamic assembly period (DAP). In the traditional OBS assembly algorithms, the packets with the same destination and class of service (CoS) are assembled into the same burst, i.e., the packets from different sources will be assembled into one burst. In that case, one burst loss will influence multiple TCP sources. In DAP, the packets from one TCP connection are assembled into bursts, which can avoid the above situation. Through comparing the two consecutive burst lengths, DAP can track the variation of TCP window dynamically and update the assembly period for the next assembly. In addition, the ingress node architecture for the flow-oriented assembly is designed. The performance of DAP is evaluated and compared with that of fixed assembly period (FAP) over a single TCP connection and multiple TCP connections. The results show that DAP performs better than FAP at almost the whole range of burst dropping probability.