LEO网络中卫星切换的动态概率路由优化策略

在LEO卫星网络中，卫星切换方案需要在保证最小切换延时的同时，合理地使用网络资源，因此应该合理选择卫星切换中路由优化的触发条件。本文在综合考虑卫星切换中消耗的网络资源，包括带宽资源和信令资源的前提下，提出动态概率路由优化方案。指出在卫星切换中，为了达到对网络资源的有效使用，路由优化概率应该随LEO星座结构，呼叫带宽，业务分布等网络参数不同而动态变化。     

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。     

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。     

低轨星座卫星通信系统中多业务条件下的非充分保证切换策略

该文提出了一种适用于低轨星座卫星通信系统多业务条件下的非充分保证切换策略。该策略在小于一个小区最大驻留时间的时间间隔内为到达小区的呼叫安排和预定信道,在呼叫结束环节作为补充策略对存在切换失败风险的信道进行调整。提出了策略在多业务条件下具体的实施方法,根据实时的切换呼叫性能调整策略的非充分程度。通过仿真,分析比较了不同程度非充分保证切换策略的QoS性能,验证了动态自适应调整非充分程度值的IGH策略的有效性。仿真结果表明,相对于保证切换策略,新策略以存在微小切换失败概率为代价,换取了新呼叫阻塞概率的显著降低,是一种适用于多业务低轨卫星通信系统的信道分配策略。     

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。     

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。     

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。     

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,...     

低轨卫星移动通信系统接入方案

在低轨卫星移动通信系统中,由于卫星和移动用户间的相对运动使得呼叫切换频繁发生.为了降低星间切换请求到达率,减小系统切换开销,本文在距离优先接入方案基础上进一步提出了两种接入策略:覆盖时间优先方案和仰角加权的覆盖时间优先方案.构造了非均匀分布全球话务密度模型.并参照某实际系统参数,对不同接入方案准则下的全球话务服务进行了系统仿真,得到了相应的系统性能参数.     

LEO卫星IP网中的低延时切换

提出了一种由覆盖全球的无星际链路的低轨(LEO)星座构成卫星IP网,首次提出了一种按信关站来划分网络的策略,并着重讨论了卫星IP网中的星间切换技术,提出用邻站广播技术来实现低延时切换的策略。仿真结果表明,本文提出的策略能大大减少信令交换量和降低切换延时,有效保障了卫星网中实时多媒体业务的QoS。     

低轨卫星通信网络中改进的综合加权接入算法

针对用户终端有效与可靠接入低轨卫星通信网络的需求,基于现有的接入算法,综合考虑了卫星对用户终端的覆盖时间、卫星空闲信道数以及卫星接收信号的信噪比因素,提出了一种改进的综合加权接入算法,对该算法的目标函数和参数进行了设计与计算.仿真结果表明,采用改进的综合加权接入算法,新呼叫阻塞率和强制中断率等性能都得到了明显的改善.     

Q-Win – A New Admission and Handoff Management Scheme for Multimedia LEO Satellite Networks

Low Earth Orbit (LEO) satellite networks are deployed as an enhancement to terrestrial wireless networks in order to provide broadband services to users regardless of their location. In addition to global coverage, these satellite systems support communications with hand-held devices and offer low cost-per-minute access cost, making them promising platform for Personal Communication Services (PCS). LEO satellites are expected to support multimedia traffic and to provide their users with the negotiated Quality of Service (QoS). However, the limited bandwidth of the satellite channel, satellite rotation around the Earth and mobility of end-users makes QoS provisioning and mobility management a challenging task. One important mobility problem is the intra-satellite handoff management. The main contribution of this work is to propose Q-Win, a novel call admission and handoff management scheme for LEO satellite networks. A key ingredient in our scheme is a companion predictive bandwidth allocation strategy that exploits the topology of the network and contributes to maintaining high bandwidth utilization. Our bandwidth allocation scheme is specifically tailored to meet the QoS needs of multimedia connections. The performance of Q-Win is compared to that of two recent schemes proposed in the literature. Simulation results show that our scheme offers low call dropping probability, providing for reliable handoff of on-going calls, good call blocking probability for new call requests, while maintaining bandwidth utilization high.     

Call admission control for CDMA mobile communications systems supporting multimedia services

The call admission control (CAC) belongs to the category of resource management. Since the radio spectrum is very scarce resource, CAC is one of the most important engineering issues for mobile communications. In this paper, we propose a CAC scheme for direct sequence code-division multiple-access cellular systems supporting mobile multimedia communications services. There are multiple call classes in multimedia services and the required signal-to-interference ratio (SIR) varies with call classes. Call admission decision in the proposed scheme is based on SIR measurement. We take account of the traffic asymmetry between uplink and downlink, which is the most important characteristic of multimedia traffic. In addition, the proposed scheme guarantees the priority of handoff call requests over new call requests. We evaluate the performance of the proposed scheme using Markov analysis. The performance measures which we focus on are the system throughput and the blocking probabilities of handoff calls and new calls. The outage probability of a call in progress is also calculated, which is the probability that the measured bit energy-to-noise density ratio of the call is smaller than the required value for maintaining adequate transmission quality. We present some numerical examples with practically meaningful parameter values and, as a result, show that the proposed CAC scheme can operate well in the mobile multimedia systems such as the International Mobile Telecommunications-2000 (IMT-2000) systems.     

Performance of CAC strategies for multimedia traffic in wireless networks

Call admission control (CAC) strategies for multimedia traffic in wireless networks is studied. A wireless network cell serving two types of customers; narrowband customers, which require one channel and wideband customers, which require b/sub w//spl ges/1 channels is considered. Two CAC strategies; reserve channels strategy (RCS) and threshold strategy (TS) are applied to the wireless cell and their performances are compared. The results show that in most operating conditions, the RCS has a lower blocking probability and probability of handoff call dropping than the TS. Only in the case when the wideband traffic is higher than the narrowband traffic that the weighted probability of handoff call dropping becomes higher for the RCS. Mean server utilization is lower for the threshold CAC than for the reserve channels CAC strategy at most operating conditions.     

A dynamic call admission policy with precision QoS guarantee usingstochastic control for mobile wireless networks

Call admission control is one of the key elements in ensuring the quality of service in mobile wireless networks. The traditional trunk reservation policy and its numerous variants give preferential treatment to the handoff calls over new arrivals by reserving a number of radio channels exclusively for handoffs. Such schemes, however, cannot adapt to changes in traffic pattern due to the static nature. This paper introduces a novel stable dynamic call admission control mechanism (SDCA), which can maximize the radio channel utilization subject to a predetermined bound on the call dropping probability. The novelties of the proposed mechanism are: (1) it is adaptive to wide range of system parameters and traffic conditions due to its dynamic nature; (2) the control is stable under overloading traffic conditions, thus can effectively deal with sudden traffic surges; (3) the admission policy is stochastic, thus spreading new arrivals evenly over a control period, and resulting in more effective and accurate control; and (4) the model takes into account the effects of limited channel capacity and time dependence on the call dropping probability, and the influences from nearest and next-nearest neighboring cells, which greatly improve the control precision. In addition, we introduce local control algorithms based on strictly local estimations of the needed traffic parameters, without requiring the status information exchange among different cells, which makes it very appealing in actual implementation. Most of the computational complexities lie in off-line precalculations, except for the nonlinear equation of the acceptance ratio, in which a coarse-grain numerical integration is shown to be sufficient for stochastic control. Extensive simulation results show that our scheme steadily satisfies the hard constraint on call dropping probability while maintaining a high channel throughput     

A call admission control scheme for packet data in CDMA cellular communications

In wireless cellular communication systems, call admission control (CAC) is to ensure satisfactory services for mobile users and maximize the utilization of the limited radio spectrum. In this paper, we propose a new CAC scheme for a code division multiple access (CDMA) wireless cellular network supporting heterogeneous self-similar data traffic. In addition to ensuring transmission accuracy at the bit level, the CAC scheme guarantees service requirements at both the call level and the packet level. The grade of service (GoS) at the call level and the quality of service (QoS) at the packet level are evaluated using the handoff call dropping probability and the packet transmission delay, respectively. The effective bandwidth approach for data traffic is applied to guarantee QoS requirements. Handoff probability and cell overload probability are derived via the traffic aggregation method. The two probabilities are used to determine the handoff call dropping probability, and the GoS requirement can be guaranteed on a per call basis. Numerical analysis and computer simulation results demonstrate that the proposed CAC scheme can meet both QoS and GoS requirements and achieve efficient resource utilization.     

A New Connection Admission Control for Spotbeam Handover in LEO Satellite Networks

Frequent spotbeam handovers in low earth orbit (LEO) satellite networks require a technique to decrease the handover blocking probabilities. A large variety of schemes have been proposed to achieve this goal in terrestrial mobile cellular networks. Most of them focus on the notion of prioritized channel allocation algorithms. However, these schemes cannot provide the connection-level quality of service (QoS) guarantees. Due to the scarcity of resources in LEO satellite networks, a connection admission control (CAC) technique becomes important to achieve this connection-level QoS for the spotbeam handovers. In this paper, a geographical connection admission control (GCAC) algorithm is introduced, which estimates the future handover blocking performance of a new call attempt based on the user location database, in order to decrease the handover blocking. Also, for its channel allocation scheme, an adaptive dynamic channel allocation (ADCA) scheme is introduced. By simulation, it is shown that the proposed GCAC with ADCA scheme guarantees the handover blocking probability to a predefined target level of QoS. Since GCAC algorithm utilizes the user location information, performance evaluation indicates that the quality of service (QoS) is also guaranteed in the non-uniform traffic pattern.