A distributed QoS routing based on ant algorithm for LEO satellite network

Low Earth Orbit (LEO) satellites provide short round-trip delays and are becoming in- creasingly important. One of the challenges in LEO satellite networks is the development of specialized and efficient routing algorithms. To satisfy the QoS requirements of multimedia applications, satellite routing protocols should consider handovers and minimize their effect on the active connections. A distributed QoS routing scheme based on heuristic ant algorithm is proposed for satisfying delay bound and avoiding link congestion. Simulation results show that the call blocking probabilities of this al- gorithm are less than that of Shortest Path First (SPF) with different delay bound.     

多业务LEO卫星网络中最优呼叫允许控制及切换管理策略

该文针对多业务条件下的LEO(Low-Earth-Orbit)卫星网络,提出了一种新的基于最优多门限信道预留(OMTCR)的呼叫允许控制(CAC)及切换管理策略,建立了评价LEO卫星网络连接级QoS性能的理论分析模型框架。借鉴经济学收益函数的概念分别建立了无QoS约束和有QoS约束的系统收益目标优化模型,求解在给定系统参数和输入业务条件下OMTCR的最优门限参数矢量。仿真结果表明OMTCR能够在不同用户QoS要求和系统收益目标的多业务环境下获得比传统CS(Completely Sharing)策略及GC(Guard Channel)策略更好的性能。     

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.     

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。     

Variable-target admission control for nonstationary handover traffic in LEO satellite networks

Handover management is of great importance in a low Earth orbit (LEO) satellite system. However, the blocking performance of handover traffic in an LEO satellite system is not easily formulated with an acceptable level of accuracy because of the nonstationary nature of handover traffic, which causes difficulty in quantitatively making optimal decisions for channel assignment to meet a given quality-of-service requirement. Even though many challenging schemes have been proposed to dynamically determine the number of guard channels, most either use heuristic methods or are based on simplifying assumptions, causing invalid decision results. As an alternative, we suggest a quantified method to minimize the fraction of the number of blocked calls out of the number of total calls under nonstationary handover traffic. We develop new mathematical formulations of those fraction and optimization models with efficient exact solution algorithms. Performance analysis shows that the proposed method improves the blocking probabilities of handovers and new calls; this improvement results from a highly adaptive and reactive characteristic to the fluctuating handover traffic condition.     

Satellite selection scheme for reducing handover attempts in LEO satellite communication systems

Low earth orbit (LEO) satellite communication systems perform frequent intersatellite handovers for both fixed and mobile users. This paper proposes a satellite selection scheme for new/handover call requests when two or more satellites can be seen simultaneously. Each satellite in this scheme has a non-uniform transmitter antenna gain according to its relative position inside the coverage area. The antenna gain is proportional to the residual distance in the satellite's direction of movement and it compensates for the difference in path losses between satellite links. The residual distance distribution of the selected satellite and the mean number of intersatellite handovers during a call connection are calculated and compared with the results based on conventional methods. The proposed scheme can reduce the intersatellite handover call attempt rate without increasing system load and terminal complexity. Furthermore, this scheme can be extended to reduce both intersatellite and interbeam handover call attempt rates in a multiple spot beam environment. Especially, the average number of intersatellite and interbeam handovers during a call can be significantly reduced by using a hybrid algorithm with the proposed non-uniform power transmission scheme. © 1998 John Wiley & Sons, Ltd.     

Footprint handover rerouting protocol for low Earth orbit satellite networks

Low Earth Orbit (LEO) satellite networks will be an integral part of the next generation telecommunications infrastructures. In a LEO satellite network, satellites and their individual coverage areas move relative to a fixed observer on Earth. To ensure that ongoing calls are not disrupted as a result of satellite movement, calls should be transferred or handed over to new satellites. Since two satellites are involved in a satellite handover, connection route should be modified to include the new satellite into the connection route. The route change can be achieved by augmenting the existing route with the new satellite or by completely rerouting the connection. Route augmentation is simple to implement, however the resulting route is not optimal. Complete rerouting achieves optimal routes at the expense of signaling overhead. In this paper, we introduce a handover rerouting protocol that maintains the optimality of the initial route without performing a routing algorithm after intersatellite handovers. The FHRP makes use of the footprints of the satellites in the initial route as the reference for rerouting. More specifically, after an optimum route has been determined during the call establishment process, the FHRP ensures that the new route due to handover is also optimum. The FHRP demands easy processing, signaling, and storage costs. The performance results show that the FHRP performs similar to a network without any handovers in terms of call blocking probability.     

Analysis of handover characteristics in shadowed LEO satellite communication networks

In the near future, low earth orbit (LEO) satellite communication networks will partially substitute the fixed terrestrial multimedia networks especially in sparsely populated areas. Unlike fixed terrestrial networks, ongoing calls may be dropped if satellite channels are shadowed. Therefore, in most LEO satellite communication networks more than one satellite needs to be simultaneously visible in order to hand over a call to an unshadowed satellite when the communicating satellite is shadowed. In this paper, handover characteristics for fixed terminals (FTs) in LEO satellite communication networks are analysed. The probability distribution of multiple satellite visibility is analytically obtained and the shadowing process of satelites for FTs are modelled. Using the proposed analysis model, shadowing effects on the traffic performance are evaluated in terms of the number of intersatellite and interbeam handovers during a call. Copyright © 2001 John Wiley & Sons, Ltd.     

QoS Handover Management in LEO/MEO Satellite Systems

Low Earth Orbit (LEO) satellite networks are foreseen to complement terrestrial networks in future global mobile networks. Although space segment topology of a LEO network is characterized by periodic variations, connections of mobile stations (MSs) to the satellite backbone network alter stochastically. As a result the quality of service delivered to users may degrade. Different procedures have been proposed either as part of a resource allocation mechanism or as part of an end-to-end routing protocol to manage transitions of MSs from one satellite to another (handover). All of these techniques are based on the prioritization of requested handovers to ease network operation and therefore enhance provision of service. This paper proposes a new handover procedure that exploits all geometric characteristics of a satellite-to-MS connection to provide an equable handover in systems incorporating onboard processing satellites. Its performance is evaluated by simulations for a variety of satellite constellations to prove its general applicability. This revised version was published online in July 2006 with corrections to the Cover Date.     

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。     

A Novel Probability-Based Handoff Strategy for Multimedia LEO Satellite Communications

A novel bandwidth allocation strategy and a connection admission control technique arc proposed to improve the utilization of network resource and provide the network with better quality of service （QoS） guarantees in multimedia low earth orbit （LEO） satellite networks. Our connection admission control scheme, we call the probability based dynamic channel reservation strategy （PDR）, dynamically reserves bandwidth for real-time services based on their handoff probability. And the reserved bandwidth for real-time handoff connection can also be used by new connections under a certain probability determined by the mobility characteristics and bandwidth usage of the system. Simulation results show that our scheme not only lowers the call dropping probability （CDP） for Class I real-time service but also maintains the call blocking probability （CBP） to certain degree. Consequently, the scheme can offer very low CDP for rcal-time connections while keeping resource utilization high.     

CAC-RD: an UMTS call admission control

The third wireless network generation (3G) aims to provide fast Internet access with quality of service (QoS) guarantees, especially to multimedia applications. UMTS (Universal Mobile Telecommunication System) is a kind of 3G networks. To provide QoS, the network must use an efficient admission control mechanism. This mechanism needs to prioritize network access to critical classes of applications. This work proposes an UMTS admission control mechanism, called CAC-RD (Call Admission Control—based on Reservation and Diagnosis). It is based on network diagnosis and on channel reservation for handovers. These techniques are associated with new calls blocking when the network reaches utilization thresholds. CAC-RD is a tool that prioritises handovers and conversational applications. The main CAC-RD goals are the handovers blocking reduction and the acceptable performance levels guarantee. Simulation results show that the CAC-RD channel reservation and the diagnosis techniques associated with the intrinsic network signal power control effectively reduces blockings while guarantying performance levels. Due to computational resource limits, simulations cannot answer related to admission control in big networks with thousands of users. This work presents a method to extrapolate scientific questions like CAC’s behavior with thousands of users and many antennas. An artificial neural network approach for CAC-RD in UMTS 3G networks is presented as an extension of the work.     

Performance analysis for a guaranteed handover service in an LEOconstellation with a “satellite-fixed cell” system

It is anticipated that the satellite component of the future universal mobile telecommunications system (UMTS) will be based (partly or totally) on non-geostationary (nonGEO) constellations of satellites to serve mixed populations of users, each category being treated through different contracts stipulating different quality of service (QoS). In particular, we envisage a high-quality premium service which guarantees the success of each handover procedure, called guaranteed handover (GH) service, and a low-cost lower quality service called regular service, where handover failures are accepted provided that the probability of a call being unsuccessful does not exceed a given value. This paper proposes a strategy which eliminates forced call terminations due to handover failures, thus allowing the GH service. This procedure applies to low Earth orbit (LEO) constellations using the satellite-fixed cell technique. An analytical model has been derived to calculate QoS parameters for a mixed population of GH and regular users. Providing both GH service to some users and regular service to other users requires an increased satellite capacity with respect to the case where all the users are served with the regular service; this capacity increase has been evaluated as a function of the percentage of GH users, the traffic load per cell, and the considered satellite mobility environment. The GH approach has been validated through the comparison with another scheme which envisages the queuing of handover requests for privileged users     

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     

A distributed adaptive guard channel reservation scheme for cellular networks

In this paper, a distributed adaptive guard channel reservation (DAGCR) scheme is proposed to give priority to handoff calls. This scheme is built upon the concept of guard channels and it uses an adaptive algorithm to search automatically the optimal number of guard channels to be reserved at each base station. The quality‐of‐service (QoS) parameters used are the new and handoff call blockings. Simulation studies are performed to compare the present algorithm with the static guard channel policy. Simulation results show that this proposed algorithm guarantees the handoff call blocking probability to remain below the targeted threshold up to a substantially high offered load with a minimal blocking to new calls up to a moderate offered load and also shows significantly high channel utilization in all offered load conditions. This scheme is examined over a wide range of offered load. Thus, it seems the proposed scheme is very useful in controlling the blocking performances in wireless cellular networks. Copyright © 2006 John Wiley & Sons, Ltd.     

A seamless soft handover management scheme in NGEO satellite networks

Satellite networks can provide extensive geographic coverage to diverse user population, but handovers of active communications should be controlled considering the satellites' high speed. Mobile IP and many other handover algorithms have been proposed for terrestrial wireless networks. However, the satellite network exhibits several unique features compared with the terrestrial wireless networks, such as the long delay. This paper proposes a seamless soft handover scheme (S2H) for satellite networks. S2H designs an identity locator split addressing to solve the multihoming problem and applies the network coding scheme during handover. This manner is able to reduce the interference opportunity, save transmissions, and achieve low handover delay, short queue length, and high throughput. Relying on the simulation results, S2H is able to achieve better performance compared with the proposed handover algorithms in the satellite environment when there are multiple traffic flows. Copyright © 2013 John Wiley & Sons, Ltd.     

低中轨道双层卫星光网络的分时切换半实物仿真演示系统

为精确模拟验证低中轨道（LEO／MEO）双层卫星光网络及其关键技术,按1：30的比例设计了分时切换双层卫星光网络半实物实验演示系统。系统包括计算机仿真环境和硬件平台两部分,通过SITL模块互联而成。软件部分由虚拟网络组成,实现灵活、可扩展的配置;硬件平台由1个圆形往复转台、6个伺服机构、6个无线激光通信终端和6组自动追...     

Hybrid channel adaptive handover scheme for non-GEO satellitediversity based systems

This article presents an improved hybrid handover scheme, which is proposed for the satellite component of UMTS. The scheme is channel adaptive and is generic as it can operate in soft and hard handover. The handover algorithm uses different power thresholds to add/drop a highest and second highest satellite and uses dual satellite diversity only under critical channel conditions. The analysis includes the simulation of a LEO constellation and the elevation-dependent satellite channel. Based on the channel time series the hybrid scheme shows improved performance when compared to existing handover schemes and is less bandwidth demanding than continuous diversity     

Satellite handover techniques for LEO networks

Low earth orbit satellite constellations could play an important role in future mobile communication networks due to their characteristics, such as global coverage and low propagation delays. However, because of the non‐stationarity of the satellites, a call may be subjected to handovers, which can be cell or satellite handovers. Quite many techniques have been proposed in the literature dealing with the cell handover issue. In this paper, a satellite handover procedure is proposed, that investigates and exploits the partial satellite diversity (namely, the existing common coverage area between contiguous satellites) in order to provide an efficient handover strategy, based always on a tradeoff of blocking and forced termination probabilities for a fair treatment of new and handover calls. Three different criteria were examined for the selection of a satellite. Each one of them could be applied either to new or handover calls, therefore we investigated nine different service schemes. A simulation tool was implemented in order to compare the different service schemes and simulation results are presented at the end of the paper. Copyright © 2004 John Wiley & Sons, Ltd.