低轨卫星网小区移动性对切换的影响

低轨卫星网络点波束覆盖布局与用户相对运动方向决定了用户在小区间的切换关系,并直接影响用户切换性能。该文针对两种典型的小区运动模式建立了移动模型,分析了驻留时间、切换概率和平均切换次数等移动性指标,并结合具体的信道分配策略分析比较了小区移动性对用户切换性能的影响。结果表明在小区低重叠度的条件下小区运动模式Ⅱ的用户切换性能优于模式Ⅰ,更适用于低轨卫星网络,为低轨卫星点波束的布局提供了参考。     

一种新的切换策略在LEO卫星系统中的应用

增强对数据业务等非话音业务的支持,是LEO(低地球轨道)卫星通信系统的一个重要发展方向。提出了LEO卫星通信系统中一种新的保护信道和强占优先相结合的信道分配策略,即为话音呼叫提供一定的强占数据业务的优先权。将该策略与单纯保护信道策略的各项主要性能指标进行比较,结果表明新策略以略微增加数据时延为代价换取了话音新呼叫阻塞概率和切换阻塞概率的极大改善。     

高空平台通信系统中重叠区辅助切换保证策略

为了确保高空平台通信系统提供通信业务的连续性,提出重叠区辅助切换保证策略(GHS-OA)。该策略在连接允许控制决策过程中,除利用高空平台和用户位置信息之外,还利用蜂窝之间的重叠区来协助判定并阻塞可能引起切换失败的新呼叫。建立多业务条件下基于时间的信道预留算法(TCRA)和GHS-OA的分析模型,推导上述2种策略在2类业务条件下新呼叫阻塞性能的数值解。通过仿真验证分析模型的有效性,与TCRA相比,在2类业务条件下GHS-OA可以极大地提升新呼叫阻塞性能,同时能够获得零切换掉话率,重叠区比例越大,利用重叠区的信道资源越多,GHS-OA的新呼叫阻塞性能越好。     

无线移动多媒体通信网的一种切换策略

该文提出了无线移动多媒体通信网中基于宽带呼叫业务和窄带呼叫业务的双向层间切换业务模型(BLHM)和单向层间切换业务模型(SLHM),分别研究了两种业务在模型中的新呼叫阻塞概率和切换呼叫失败概率,对由于层间切换机制带来的呼叫业务质量(QoS)下降的宽带切换呼叫进行了定量分析。另外,该文还提出了基于呼叫业务代价函数和呼叫业务QoS的信道分配算法。最后进行了计算机仿真,将两种模型的性能进行了比较。     

切换保留信道与新呼叫排队相结合的LEO星座通信系统信道分配方案研究

提出一种适用于LEO(低轨道)星座通信系统的信道分配方案。该方案为切换呼叫提供了保留信道,降低了切换呼叫的阻塞概率。同时,采取新呼叫排队策略抑制保留信道引起的新呼叫阻塞概率的恶化,如果正在进行的呼叫离开,队列中的新呼叫可以按照次序获得分配信道。结果表明,该方案可以显著降低切换呼叫阻塞概率,并使新呼叫阻塞概率得到改善。     

低轨卫星系统中的一种带优先级的信道预留策略

在卫星通信系统中,可能需要同时支持地面普通终端及一些快速移动特殊终端的通信,因此需要综合考虑不同类型终端的通信服务质量要求。该文从切换的角度考虑,针对两种不同用户终端及非均匀的业务分布,提出一种带优先级的信道预留策略。通过理论分析和仿真结果表明,该策略提高了特殊用户的切换性能,对低轨卫星通信系统的研究有一定的参考价值。     

高空平台通信系统中切换性能受限的呼叫允许控制策略

本文分析了高空平台通信系统中利用地理位置信息的呼叫密度受限和切换间隔时间受限的CAC(Call Admission Control,CAC)策略.设计了切换性能受限的CAC策略,该策略利用地理位置信息在每次新呼叫到达时计算可能引起的切换失败的概率,并且通过设置切换性能门限来约束切换性能,在满足切换性能的同时,能够尽量提高新呼叫阻塞性能.仿真结果表明,在相同切换掉话概率门限要求情况下,与新呼叫切换时间间隔受限的CAC策略相比,改进的切换时间间隔受限的CAC策略可提升新呼叫阻塞性能13.6%以上.在实际应用过程中,可以根据当前流量自适应地改变切换间隔时间门限,达到在满足切换性能的同时最小化新呼叫阻塞概率的目的.切换性能受限的CAC策略在业务量较高的条件下能够较好地保证了系统的切换掉话性能;比其它策略具有更好的呼叫阻塞性能,比呼叫密度受限的CAC至少提升25.3%,比切换时间间隔受限的CAC策略至少提升6.5%.     

LEO卫星通信多优先级动态信道预留策略

针对低轨道(Low Earth Orbit,LEO)卫星通信系统包含不同层次业务的情况,提出一种动态多优先级信道预留策略。策略关键在于利用低轨卫星高速确定的运动特性进行呼叫业务预测,动态计算出最优的信道预留门限;进而建立了信道分配的马尔科夫模型;最终通过遗传算法获得该模型的解。在不需要对用户进行GPS定位的情况下,利用卫星运动预测动态获得最优预留门限,该策略有效降低了切换呼叫阻塞率,提高了信道利用率。仿真结果表明了该策略的有效性和优越性。     

准静止状态下的高空平台实时业务信道分配

受平台准静止状态的影响,高空平台（ HAPS)通信网络内存在大量的切换呼叫,且业务量动态变化。 HAPS网络可传输多种业务,其中实时业务在切换过程中具有较高的时延要求。通过为切换呼叫预留信道可降低平台不稳定对服务质量（ QoS)造成的影响。在基于服务优先级的多业务信道分配算法基础上,重点对实时业务的信道分配算法进行改进,提出了一种基于概率的预留信道借用策略。该算法可根据网络内业务量的实时统计数据控制新呼叫业务的准入。仿真结果表明：与固定预留信道算法和门限预留信道算法相比,该算法能够适应网络内业务量的动态变化,在保证切换呼叫掉线率满足期望值的条件下提升系统的整体性能,降低平台不稳定造成的性能损失。     

LEO卫星通信系统的呼叫接入性能分析

在均匀业务模型的基础上,根据LEO卫星通信系统自身特点,提出了一种简单有效的呼叫接入控制策略,这种策略能在非均匀业务下较好地工作,此时系统新呼叫阻塞率和切换呼叫失败率能达到更好的平衡。在分析随机接入（RANDOM）算法和预留保护信道（GC）算法的基础上,进行了计算机仿真,并给出了相应的仿真结果。     

Radio Resource Allocation for Scalable Video Services Over Wireless Cellular Networks

Good quality video services always require higher bandwidth. Hence, to provide the video services e.g., multicast/broadcast services (MBSs) and unicast services along with the existing voice, internet, and other background traffic services over the wireless cellular networks, it is required to efficiently manage the wireless resources in order to reduce the overall forced call termination probability, to maximize the overall service quality, and to maximize the revenue. Fixed bandwidth allocation for the MBS sessions either reduces the quality of the MBS videos and bandwidth utilization or increases the overall forced call termination probability and of course the handover call dropping probability as well. Scalable video coding (SVC) technique allows the variable bit rate allocation for the video services. In this paper, we propose a bandwidth allocation scheme that efficiently allocates bandwidth among the MBS sessions and the non-MBS traffic calls (e.g., voice, unicast, internet, and other background traffic). The proposed scheme reduces the bandwidth allocation for the MBS sessions during the congested traffic condition only to accommodate more calls in the system. Instead of allocating fixed bandwidths for the MBS sessions and the non-MBS traffic, our scheme allocates variable bandwidths for them. However, the minimum quality of the videos is guaranteed by allocating minimum bandwidth for them. Using the mathematical and numerical analyses, we show that the proposed scheme maximizes the bandwidth utilization and significantly reduces the overall forced call termination probability as well as the handover call dropping probability.     

Teletraffic performance evaluation of microcellular personalcommunication networks (PCN's) with prioritized handoff procedures

Evaluates four handoff priority-oriented channel allocation schemes. These give priority to handoff calls by reserving channels exclusively for handoff calls. The measurement-based handover channel adaptive reassignment scheme (MHAR-A) exclusively uses reserved handover channels for newly originated calls if a certain criterion is satisfied. All four schemes studied differ from the conventional guard channel-based handover priority-oriented channel allocation scheme. To study the schemes, a personal communication network (PCN) based on city street microcells is considered. A teletraffic simulation model accommodating a fast moving vehicle is developed, and the performance parameters are obtained. The performances of all four schemes are compared with the nonpriority scheme and the conventional guard channel-based handover priority-oriented channel allocation scheme. It was found that some of the channel allocation algorithms studied improved the teletraffic capacity over the nonpriority and the conventional guard case. Also, the probability of new call blocking and carried traffic was improved for three of the schemes when compared to the conventional guard scheme. The MHAR-A scheme did not perform up to expectation. Nevertheless, it can be used to finely control the communication service quality equivalent to the control obtained by varying the number of handoff channels in a fraction of one. Increasing the number of reserved handover channels in fraction of one can never be achieved in the conventional guard channel-based handover priority-oriented channel allocation scheme     

基于优先级信道预留的快速动态信道分配算法

针对TD-SCDMA系统现有快速动态信道分配算法的不足,提出了一种基于优先级信道预留的快速动态信道分配算法.该算法根据接力切换用户的移动台属性设定不同的优先级,为接力切换呼叫预留信道,结合小分组借用算法,增加了可移动边界动态信道分配(MB DCA)策略的灵活性.仿真结果表明,此算法相对于混合数据速率、小分组借用(MRG,mixed-data rate grouping borrowed)MB DCA算法,实现了VIP和快速移动切换用户的优先接入,有效地降低了切换呼叫的阻塞率,提高了数据业务性能和系统的信道利用率.     

基于信道预留和强占优先的接力切换策略

提出了一种适用于TD-SCDMA(Time Division Synchronous Code Division Multiple Access)移动通信系统综合业务(语音/数据)的接力切换策略.该策略为语音切换预留信道,根据语音用户属性设置不同切换优先级,赋予语音切换和语音新呼叫对数据服务信道的强占优先权.仿真表明,...     

Handover prioritizing scheme for reducing call failure probability in cellular wireless network

This paper proposes a scheme suitable for managing handover in wireless cellular network. The main objective of the proposed scheme is to reduce the probability of forced termination of ongoing call due to handover failure. The scheme employs a queuing discipline, and the priority of queued is based on the residual time of the mobile user in the overlap region between two adjacent cells, assuming that the user's location and speed can be determined, then we applied the ascending priority; it means that the users having a shorter residual time join the head of the queue (i.e., high priority) while those having longer residual time at the end of the queue (i.e., low priority). Fixed channel allocation strategy (FCA) is employed and simulation results obtained concern: call blocking probability (CBP), handover failure probability, and average waiting time in the queue. Also simulation results are compared to those obtained by: non‐prioritized scheme (FCA), and FCA queuing with FIFO discipline. Results show that our proposed method decreases significantly handover failure probability compared with other two schemes. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance Evaluation and Resource Management of Hierarchical MACRO-/MICRO Cellular Networks using MOSEL-2

The paper presents a performance evaluation and resource management of hierarchical MACRO-/MICRO cellular networks using the new Modeling and Evaluation Language (MOSEL-2). MOSEL-2 with new constructs has the ability to find the performance and reliability modeling and evaluation of systems with exponential and non-exponential distributions. A MACRO/MICRO cell structure is solved numerically and mathematically in this paper to handle the handoff calls. Additionally, a simulation program is written to validate these results. In order to reduce the loss probability, a guard channels are introduced at the MICRO cell and channel reservation at the MACRO cell. Additionally, the concept of queuing is introduced where there is a possibility for the handoff calls from both MACRO and MICRO layers to be queued when all the resources are occupied. MOSEL-2 is used to find the numerical solution for this problem with both exponential and general exponential (GE) distribution. The performance analysis show the efficiency of the proposed scheme to manage the handoff calls and the ability of the suggested scheme to reduce the blocking probability of handover calls and the loss probability as the main objective is to block the new connection rather than terminating the ongoing connection as well as balancing the load all over the whole network. It is shown in this paper that there are a set of important factors that affect the performance, such as: reservation policy, channel allocation, handover ratio, capacity of the queue and the variation of the inter-arrival times. These factors are discussed via some important performance measures, such as: new call blocking probability, blocking probability of handover calls, loss probability, utilization and the average delay of the queue.     

Hybrid coupling scheme for UMTS and wireless LAN interworking

We propose a hybrid coupling scheme to support interworking between UMTS and WLAN networks. Under the Tight-coupled system, it is expected that WLAN users can also use UMTS services with guaranteed QoS and seamless mobility. However, the interworking is problematic. The capacity of UMTS core network nodes cannot accommodate the bulky data traffic from WLAN, since the core network nodes are designed to handle the small-sized data of circuit voice calls or short packets. The proposed coupling scheme differentiates the data paths according to the type of the traffic and can accommodate traffic from WLAN efficiently, with guaranteed QoS and seamless mobility. We compare the handover procedures of the proposed coupling strategy with those of the loose and tight coupled schemes. In addition, we analyze the delay based on signaling costs during vertical handover. It is shown that the handover latency decreases when the UMTS and WLAN are coupled in the proposed way.     

异构无线网络中基于业务转移和接入控制的混合负载均衡

 针对现有异构无线网络负载均衡方法未能综合考虑重载网络业务转移和新业务接入控制的问题,提出了一种混合负载均衡算法.该算法首先根据各小区负载水平和终端移动性,将重载小区的适量业务向重叠覆盖的轻载小区转移;其次通过资源预留和强占优先的接入控制策略,为不同优先级的新到业务提供有差别的服务.仿真结果表明,本文算法在保证系统资源利用率的同时,保障了实时与非实时业务的QoS,并相对于参考算法有效降低了系统阻塞率和业务切换概率.     

Priority-determined multiclass handoff scheme with guaranteed mobile QoS in wireless multimedia networks

The provision of multiclass services is gaining wide acceptance and will be more ubiquitous in future wireless and mobile systems. The crucial issue is to provide the guaranteed mobile quality of service (QoS) for arriving multiclass calls. In multimedia cellular networks, we should not only minimize the dropping rate of handoff calls, but also control the blocking rate of new calls at an acceptable level. This paper proposes a novel multiclass call-admission-control mechanism that is based on a dynamic reservation pool for handoff requests. In this paper, we propose the concept of servicing multiclass connections based on priority determination through the combined analysis of mobile movement information and the desired QoS requirements of multimedia traffic. A practical framework is provided to determine the occurrence time of handoff-request reservations. In our simulation experiments, three kinds of timers are introduced for controlling the progress of discrete events. Our simulation results show that the individual QoS criteria of multiclass traffic such as the handoff call-dropping probability can be achieved within a targeted objective and the new-call-blocking probability is constrained to be below a given level. The proposed scheme is applicable to channel allocation of multiclass calls over high-speed wireless multimedia networks.     

An adaptive measured-based preassignment scheme withconnection-level QoS support for mobile networks

This paper presents a new adaptive bandwidth allocation scheme to prevent handoff failure in wireless cellular networks, known as the measurement-based preassignment (MPr) technique. This technique is particularly useful in micro/pico cellular networks which offers quality-of-service (QoS) guarantee against call dropping. The proposed MPr scheme distinguishes itself from the well-known guarded channel (GC) based schemes in that it allows the handoff calls to utilize a prereserved channel pool before competing for the shared channels with new call arrivals. The key advantage of the proposed MPr scheme is that it enables easy derivation of the number of channels that needs to be reserved for handoff based on a predetermined handoff dropping probability, without the need for solving the often complex Markov chain required in GC schemes, thus, making the proposed MPr scheme simple and efficient for implementation. This is essential in handling multiple traffic types with potentially different QoS requirements. In addition, the MPr scheme is adaptive in that it can dynamically adjust the number of reserved channels for the handoff according to the periodical measurement of the traffic status within a local cell, thus completely eliminating the signaling overhead for status information exchange among cells mandated in most existing channel allocation schemes. Numerical results and comparisons are given to illustrate the tradeoff