5G异构网络中基于熵权TOPSIS的小区预切换方法

为了减少5G异构网络中不必要的小区切换次数以及降低无线链路失败率,提出了一种基于熵权优劣解距离法(Technique for Order Preference by Similarity to an Ideal, TOPSIS)的小区预切换方案。熵权TOPSIS法将小区作为预切换对象,将下行信干噪比、预测驻留时间和移动角度均作为切换指标,分析并预测目标切换小区从而达到预切换目的。首先,根据邻小区的参考信号接收功率(Reference Signal Receiving Power, RSRP)值得到候选目标小区列表;然后,采用熵权法计算三个切换指标的权重;最后,使用TOPSIS法对候选小区进行排序,排序最高的小区即为目标切换小区。实验和仿真结果表明,与现有的切换方法比较,所提方案在一定程度上减少了小区切换次数和无线链路失败率。     

LTE系统中宏小区与femtocell的切换方法

3GPP LTE(长期演进)系统中部署大量femtocell后,在宏小区与femtocell之间将会存在不必要的频繁切换,针对这些不必要的切换,提出一种自适应切换方法。根据用户的位置及切换请求将用户分为四类,对前两种类型用户进行自适应功率控制,第三种类型用户以CAC(呼叫允许控制)算法为基础,自适应选择HOM(切换阈值),进行不同HOM的CAC切换,第四种类型用户进行简单的标准切换即可。通过与CAC算法和标准切换算法进行仿真对比,仿真结果表明,该算法明显降低了掉话率,减少了不必要的切换,提高了用户的平均吞吐量。     

一种适用于SC-FDMA多小区系统的协作调度和功率控制算法

该文针对长期演进(LTE)上行单载波频分多址(SC-FDMA)多小区系统的性能受限于小区间干扰的问题,提出一种综合考虑协作调度和功率控制的方案。该方法分步执行小区间的协作调度和功率控制,首先调度各小区中的用户,在此基础上优化用户的发射功率。调度时首先估计小区间的干扰信息并分配频率资源块给每个小区内的用户,在优化用户的发射功率时,同时考虑由于用户功率改变所造成的目标小区和其他干扰小区性能的变化。进一步提出一种低复杂度功率控制方案,在优化目标小区用户的功率时,只考虑受目标小区干扰影响最大的几个小区性能的变化,其他干扰小区性能的变化则通过引入补偿因子来估计。计算机仿真验证了该文所提方法在系统吞吐量和小区边缘吞吐量方面的性能优势显著。     

LTE切换自优化算法进展综述

LTE是新一代通信技术的代名词,它对现有3G系统的网络结构和无线接入方式都有较大改进.在简要介绍LTE系统的网络架构及切换功能的基础上,重点介绍并比较了2种LTE切换自优化算法：常见的用户速度的负载均衡算法有效地降低了系统的掉话率,使系统的整体性能得到提高,但没有考虑到目标小区资源变化的情况;基于RSRP/RSRQ负载均衡算法综合考虑了源小区和目标小区的RSRP（参考信号接收功率）和RSRQ（参考信号接收质量）,降低了系统的切换失败率,同时减少了不必要的切换,但没有考虑用户运动方向的影响.综合加权考虑多种因素,如用户的移动方向以及小区资源的变化等对切换的影响等方面均有待深入开展研究.     

超密集分簇网络中基于预测门限滞后余量可调的切换算法

在第五代移动通信(5G)系统中,大规模MIMO天线和超密集部署网络是实现高吞吐量的两种方式。针对超密集网络的切换管理的问题,该文基于网络分簇的思想提出了根据终端设备运动情况动态调节滞后余量的切换管理算法。在该算法中,基于小基站分簇化管理的前提,用户设备在小区间切换分为预切换和正式切换两个阶段,预切换阶段完成最佳目标小区选择、小区资源预留和预鉴权等操作,正式切换阶段根据预切换阶段监测的设备速度动态调节切换门限的滞后余量。仿真结果表明了该算法可以有效降低设备的切换时延和切换失败率。     

一种基于MRO的UE级乒乓切换解决方案

MRO是LTE系统中自组织网络里的一个重要功能。MRO通过识别异常切换场景,自动优化切换相关参数,以提高切换成功率和网络利用率。异常切换的场景通常包括过早切换、过晚切换、乒乓切换和错误切换。乒乓切换是异常切换的情况之一,它会导致UE短时间内的连续切换,造成不必要的网络资源占用。文中提出了两种方案,分别从UE在一段时间内的乒乓切换次数和乒乓切换前驻留小区的时间两个角度进行统计,并对切换参数进行相应的调整。该方案能够有效地终止UE乒乓切换,降低无线链路失败率、呼叫阻塞率,提高网络吞吐量。     

一种基于过渡区的小区间干扰协调方法

文章提出了一种基于过渡区的小区间干扰协调方法,通过小区的网络规划、时频资源划分和上行链路发射功率规划三个部分,详细阐述了该方案的实现。该方案能有效提高整个网络的平均用户吞吐量和小区边缘用户的吞吐量。     

多小区毫米波系统中无人机基站飞行姿态优化及性能分析

为了提高多小区毫米波系统中无人机基站覆盖区域内用户的通信质量,本文提出了一种无人机基站的飞行姿态优化方案。该方案首先在无人机基站天线数量趋于无穷大的情况下对吞吐量进行优化,得到最大吞吐量的渐近表达式,然后将吞吐量优化问题进一步细化为天线倾斜角优化问题,最后通过穷举搜索算法来获得使吞吐量最大的天线阵列倾斜角,进一步通过调整天线倾斜角以优化无人机飞行姿态。数值仿真结果表明,所提出的优化方案能够有效提高系统性能,对于多小区无人机毫米波通信系统的性能优化具有理论指导意义。      

多小区边缘用户集中式资源分配策略

针对传统频率复用方案无法适应小区边缘负载变化的问题,提出一种多小区边缘用户集中式调度策略,可以在避免产生干扰的同时动态适应每个小区的负载分布情况,并结合一种基于匈牙利算法的资源分配算法来保证用户的速率要求和系统吞吐量。仿真证明,该方案相较其他方案在用户满意度和吞吐量上都有较大的提升。     

机器学习在5G超密集网络切换中的应用

超密集网络（Ultra-dense Network,UDN）作为5G网络架构的关键技术,其切换时延及无效切换等已成为网络发展的巨大挑战。提出了一种基于集成策略的机器学习算法,并结合用户的移动性数据,进行较高精确度的切换预测,减少切换时延及非必要切换等目标。仿真结果表明,采用结合改进机器学习算法的切换策略,不必要切换率降低了40.2%,平均时延降低了28.6%。     

Vertical Handover Over Intermediate Switching Framework: Assuring Service Quality for Mobile Users

Ensuring quality of service (QoS) for the mobile users during vertical handover between IEEE 802.11 wireless local area networks (WLAN) and data network provided by Ultramodern Telecommunication Systems (UMTS) is one of the key requirements for seamless mobility and transfer of existing connections from one network to another. QoS fulfillment is a complex problem and requires participation of both the mobile users as well as the connection networks. The QoS assurance criteria for existing connections can be affected by fluctuations of data rates when a user moves from the high speed WLAN network to the low speed UMTS network, even in the presence of another WLAN network in its vicinity. This can happen if the alternate WLAN network is highly loaded. Therefore handover from a high speed network to a low speed network should be avoided, whenever possible. This paper proposes a QoS based handover procedure that prioritizes the existing connection over the new connections so that rate fluctuations due to handover can be avoided if there exist another WLAN network in the range of the mobile user. Whenever the possibility of handover is detected, a pre-handover bandwidth reservation technique is used to reserve bandwidth at the alternate WLAN networks to avoid QoS degradation. The proposed scheme is implemented in Qualnet network simulator and the performance is analyzed and compared with traditional handover techniques.     

Handover Ranging Power Adjustment Using Uplink Channel Information in IEEE 802.16e/m

This letter proposes a handover ranging power adjustment scheme to improve handover performance. Incorrect ranging power can degrade handover performance due to the increased handover latency; therefore, the proposed scheme exploits the uplink channel information to adjust the uplink handover ranging power. Simulation results demonstrate that the proposed scheme reduces call outage probability by 33% compared to that of the conventional scheme. It also improves the number of users who satisfy the system requirements for handover interruption time.     

LTE中关于冲突避免的切换参数动态优化

In order to achieve dynamical optimization of mobility load balancing, we analyze the conflict between mobility load balancing and mobility robustness optimization caused by the improper operation of handover parameters. To this end, a method of Handover Parameters Adjustment for Conflict Avoidance (HPACA) is proposed. Considering the movement of users, HPCAC can dynamically adjust handover range to optimize the mobility load balancing. The movement of users is an important factor of handover, which has a dramatic impact on system performance. The numerical evaluation results show the proposed approach outperforms the existing method in terms of throughput, call blocking ratio, load balancing index, radio link failure ratio, ping-pong handover ratio and call dropping ratio.     

Effective resource scheduling scheme considering scheduling relevancy for downlink joint transmission system

Coordinated multi-point(CoMP) transmission is a promising technique to improve both cell average and cell edge throughput for long term evolution-advanced(LTE-A).For CoMP joint transmission(CoMP-JT) in heterogeneous scenario,if joint transmission(JT) users are firstly scheduled,other non-JT users will not be allocated sufficient resources,i.e.,scheduling relevancy exists in the users under different cells in the same coordination cluster.However,the CoMP system throughput will decline remarkably,if the impact of scheduling relevancy is not considered.To address this issue,this paper proposes a novel scheduling scheme for CoMP in heterogeneous scenario.The principles of the proposed scheme include two aspects.Firstly,this scheme gives priority to user fairness,based on an extended proportional fairness(PF) scheduling algorithm.Secondly,the throughput of the coordination cluster should be maintained at a high level.By taking the non-CoMP system as a baseline,the proposed scheme is evaluated by comparing to random PF(RPF) and orthogonal PF(OPF) scheme.System-level simulation results indicate that,the proposed scheme can achieve considerable performance gain in both cell average and cell edge throughput.     

Self‐optimization of handover parameters for dynamic small‐cell networks

Seamless handover is an essential feature of cellular networks. For small‐cell networks, effective handover becomes particularly challenging. If some cells may be activated and deactivated dynamically, effective handover handling will become even more difficult. A key factor of good handover performance is “handover timing,” that is, making handover decision at a right time. If handover is executed too early or too late, users will experience temporary link disconnection, called radio link failure (RLF). Handover timing is controlled by handover parameters, which are set by the network. RLF prevention is directly related to the proper configuration of these parameters. In this paper, we propose a self‐optimization scheme that adjusts the handover parameters to minimize RLFs for dynamic small‐cell networks. Our scheme first detects the types of RLF and then adjusts the handover parameters according to the types of RLF. Unlike most existing schemes, our scheme adjusts both system common parameters and cell‐specific parameters together. In certain situations, such as when two adjacent cells do not have sufficient coverage overlap, RLFs may not be reduced to a satisfactory level by the handover parameter adjustment alone. To deal with such a case, our scheme adjusts the cell coverage in conjunction with the handover parameter optimization. The simulation results show that the proposed scheme can virtually eliminate RLFs. Copyright © 2013 John Wiley & Sons, Ltd.     

An efficient handover decision in heterogeneous LTE-A networks under the assistance of users’ profile

The increasing demand for wireless networks calls for the use of heterogeneous networks in order to fulfil user requirements. Mobility management is considered one of the important entities for such networks. The handover is one of the main features of mobility management in regard to the long term evolution advanced (LTE-A) system, which depends purely on the hard handover. The vertical handover decision is a significant component of heterogeneous networks; it authorizes the user equipment (UE) to migrate between the two-tier LTE-A wireless networks. Femtocell, or also known as the home-evolved nodeB (HeNB), has turned out to be a promising arrangement, as it enhances the coverage and the quality of service for users on one hand, and offloads the eNB on the other hand. In this paper, an advanced handover technique is presented, in terms of adding new and critical parameters, as well as combining between the present UE trajectory and the HeNB cell location. A polynomial function is used to predict the future UE position while the cosine function along with distance are used for the selection of an appropriate target cell. The proposed algorithm is evaluated and then compared to the present work based on the handover number, number of signaling measurements, packet delay ratio, packet loss ratio, and system throughput. Simulation of the LTE-Sim demonstrates that the proposed algorithm significantly reduces the number of handovers, the transmission measurement number, the packet delay ratio, and the packet loss ratio and increases system throughput.     

一种减少移动IPv6切换延时的新方法

切换问题是移动计算环境中最基本的问题。理想的切换是指同时具备快速切换和平滑切换能力的无缝切换;快速切换就是要求系统具有最小的切换时延,平滑切换则要求系统具备最低的丢包率。现提出一种基于组播的平滑切换框架模型,该模型的基本思想是让移动节点本身携带途经的接入路由器绑定更新队列,每当移动节点到达一个新的链路并获得该链路的转交地址,就向家乡代理和队列成员进行组播。该模型有效地减少了数据包的丢失率,减少了延时,并与现有的快速切换/IPv6路由优化技术能很好地结合起来。     

Dynamic inter-domain MDS approach with secure seamless handover based on IEEE 802.21 MIH

The accessibility of available wireless access technologies with increasing demand for real time multimedia application becomes an essential part for mobile communication. Mobile users resourcefully utilize the heterogeneous environment for best quality of service (Qos) anywhere and anytime. Efficient handover optimization and intelligent mobility management is a key requirement for designing next generation wireless networks. Therefore, a novel IEEE 802.21 media independent handover (MIH) standard is adopted to provide an associated service for intelligent handover procedures. In addition, dynamic mobility management decision server (MDS) and IEEE 802.21a security extension for MIH services are also integrated in the proposed architectures to support fast, seamless and secure handover optimization in inter-domain mobility. Simulation results prove that the presented work resourcefully minimizes the packet loss, unnecessary handover probability and vertical handover delay by avoiding time consuming scanning process for target network discovery. The system thus achieves Qos guarantee by balancing the network load and throughput improvement for different applications with Proxy MIPv6 mobility management protocol.     

A utility‐based load‐balancing scheme with guarantee of users' rate for LTE self‐organization networks

Mobility load balance is becoming increasingly crucial in the design of self‐organization networks for LTE (long‐term evolution), especially under dynamic scenarios. In this paper, we study the problem of load balance with guarantee of users' rate and formulate a general optimization model, where the weighted sum of the first‐order and second‐order statistics of load distribution (load variance and total load level) are considered directly. We prove the convexity of the model and derive the optimal user‐station association scheme in different weights. Based on analysis of the optimization model, a dynamic admission and handover scheme is proposed. Mobile users with rate requirement select a base station based on the load utility in a distributed way and handover to the selected station (if handover is triggered). Furthermore, a simulation platform with seven cells is developed to evaluate the dynamic admission and handover scheme. It is demonstrated that our proposed scheme outperforms the conventional counterpart. Copyright © 2013 John Wiley & Sons, Ltd.