Handover queuing strategies with dynamic and fixed channelallocation techniques in low Earth orbit mobile satellite systems

This paper deals with the performance evaluation of various resource management strategies that are suitable for low Earth orbit mobile satellite systems (LEO-MSSs). A user mobility model has been proposed and its statistical parameters have been derived. Both fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques have been considered. Moreover, in order to reduce the handover failure probability, we have assumed that interbeam handover requests which do not immediately obtain service can be queued. In particular, two different queuing disciplines have been compared: (a) the first input first output (FIFO) scheme and (b) a new technique called last useful instant (LUI) which is based on the knowledge of the maximum time within which the handover procedure must be accomplished. Implementation aspects for the LUI technique in a LEO-MSS have been discussed also in comparison with the measurement-based priority scheme (MBPS), previously proposed in the literature on this subject. The efficiency of the LUI queuing scheme as regards the FIFO technique has been investigated by simulations for both DCA and FCA techniques. An analytical approach has been also presented in order to allow the performance evaluation of the FCA scheme with different handover queuing disciplines     

A measurement-based prioritization scheme for handovers in mobilecellular networks

A method of improving the quality of service in mobile cellular systems based on prioritization of handover requests is presented. The objective is to improve perceived quality of cellular service by minimizing both the probability of forced termination of ongoing calls due to handover failures and the degradation in spectrum utilization. A model based on a multiple-priority nonpreemptive queuing discipline is developed. New calls are blocked if all channels are occupied. Handover requests are queued such that as soon as a channel is available, it is offered to the mobile subscriber with the measurement results closest to the minimum acceptable power level for communication. Service rate is given by channel occupancy time distribution and is assumed to be exponential. The performance of a cellular system employing the proposed handover policy is evaluated analytically and by simulation, and results are compared to those obtained when the cellular system employs nonprioritized call handling and first-in/first-out queuing discipline. This provides lower probability of forced termination and less call blocking, less reduction in traffic, and less delay     

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     

Mobility of queued call requests of a new call-queueing techniquefor cellular systems

A queueing algorithm for new call requests has been proposed to increase the system capacity of traditional fixed channel allocation (FCA) handoff channel reservation schemes. However, mobility of queued call requests was ignored in previous literature. In this paper, a detailed analysis on the effects of the mobility of queued call requests is included in the analytic model. This is important because we found that the mobiles with queued call requests are very likely to leave the cell before granted a free channel. Computer simulation is performed and the results are compared with the numerical ones. It is found that the mobility of the queued new call requests reduces the average queueing delay, but increases blocking probability generally     

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.     

QoS handover management for multimedia LEO satellite networks

Low earth orbit (LEO) satellite systems gained considerable interest towards the end of the previous decade by virtue of some of the appealing features that are endowed with, such as low propagation delay and the ability to communicate with handheld terminals. However, after the limited commercial success of the first networks of this kind, future satellite networks are now conceived as complementary rather than competitive to terrestrial networks. In this paper, we focus on one of the most influential factors in system performance, that is, the handover of a call. First, we provide a succinct review of the handover strategies that have been proposed in the literature. Then we propose two different satellite handover techniques for broadband LEO satellite systems that capitalize upon the satellite diversity that a system may provide. The proposed schemes cater for multimedia traffic and are based on the queuing of handover requests. Moreover, a deallocation scheme is also proposed according to which capacity reservation requests are countermanded when the capacity that they strive to reserve is unlikely to be used. Simulation studies further document and confirm the positive characteristics of the proposed handover schemes.     

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。     

On the performance analysis of dynamic channel allocation with FIFO handover queuing in LEO-MSS

The exact analysis of dynamic channel allocation (DCA) with first-in/first-out (FIFO) queuing of handover (QH) requests is highly complex, due to the dynamic nature of channel allocation to different cells. This letter presents an approximate but accurate analytical method to evaluate the performance of DCA in conjunction with FIFO-QH in low earth orbit mobile satellite systems. The accuracy of the proposed analysis has been verified by means of computer simulation.     

Seamless handover support over heterogeneous networks using FMIPv6 with definitive L2 triggers

Various wireless communication systems have been developed and will be integrated into an IP-based network to offer end users the Internet access anytime and anywhere. In heterogeneous multi-access networks, one of main issues is to manage nodes’ mobility with session continuity and minimal handover latency. In order to support the mobility of mobile nodes, MIPv6 has been proposed by IETF. Even though MIPv6 provides a solution to handling nodes’ mobility in IPv6 networks, there is a significant problem due to its inability to support a seamless handover caused by long latency and high packet losses during a handover. FMIPv6 has been proposed to reduce MIPv6 handover latency by using an address pre- configuration method with the aid of L2 triggers. Current research defines a general L2 trigger model for seamless handover operation, but it does not address the exact timing and definitive criteria of L2 triggers which causes a significant effect on the handover performance of FMIPv6. This paper considers the available timing and accurate criteria of L2 triggers. With the definitive L2 triggers, we present a practical handover scenario to integrate L2 and L3 layers for low handover latency and low number of packet losses during a handover. We also study the impact of definitive L2 triggers on the handover performance of the FMIPv6 protocol in real testbeds and prove that the FMIPv6 protocol performs its handover operation prior to the L2 handover and obtains a seamless handover.     

Satellite-UMTS traffic dimensioning and resource managementtechnique analysis

The universal mobile telecommunications system (UMTS) will consist of space UMTS (S-UMTS) and terrestrial UMTS (T-UMTS) components. An algorithm for predicting the traffic capacity in terms of the number of subscribers for the satellite component of UMTS is presented. The algorithm takes into account the takeup characteristics of new products, the growth of gross domestic product (GDP), the projection of population, the tariff of the service, and price fall over the forecast period. The predicted traffic is used to generate a traffic grid in terms of Erlang of dimension 36×72 in steps of 5° in both the latitude and longitude directions. The traffic grid is used to evaluate the performance of a dynamic channel allocation (DCA) technique as, well as a fixed channel allocation (FCA) technique. Both channel allocation techniques have been considered with the queuing of handover (QH) requests. In order to compare the respective techniques' performance, a low-earth orbit mobile satellite system (LEO-MSS) mobility model is developed to take into account the effect of satellites' motion during interbeam handovers. A theoretical model for obtaining the values of blocking probabilities for low-traffic loads is presented. Finally, the performance of the DCA-QH technique is compared with the FCA-QH technique under suitably defined traffic and mobility conditions     

A Generic Analytical Modelling Approach for Performance Evaluation of the Handover Schemes in Heterogeneous Environments

In recent years, there has been an increased interest in the integration of different technologies in heterogeneous environments. Modelling heterogeneous systems is a complex task and handover schemes should consider issues such as network coverage, mobility, and Quality of Service (QoS). Analytical models are useful to deal with this complexity. This paper presents a generic framework to model handover in heterogeneous environments for performance evaluation of different handover schemes. The model developed considers mobility of the users, coverage radius of the networks as well as decision making probabilities about handover between the two networks. The interaction between cellular mobile technologies is considered and handover between a WLAN and a cellular system is analysed using the proposed model. Two stage open networks can be used to model this kind of integrated systems. The cellular mobile technologies are modelled as a multi-channel queuing system while the WLAN is depicted as a single channel queuing system, both with finite buffers. The exact spectral expansion method is employed to solve the models. Simulation is also employed for the proposed systems and used for validation of the accuracy of the proposed models. Numerical results are presented for mean queue length and blocking probabilities for each system. The results of this study show that QoS measures of such systems can be evaluated efficiently and accurately, using the proposed analytical model and its solution. In addition, it can be used as a framework in heterogeneous environments and can also be adapted to various types of networks in interaction.     

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.     

IMS-Based Centralized Service Continuity

The IP Multimedia Subsystem (IMS) has been selected as a telecommunication industrial standard for the signal processing in the heterogeneous access networks. It is also brought up to handle the mobility management. However, the mobility of the user equipment (UE) may disrupt or even intermittently disconnect an ongoing real-time session, which heavily affects the satisfaction of the users. Therefore, how to reduce the service disruption time gets more and more important. This paper first proposes a centralized service continuity scheme, abbreviated as CSC, in IMS-based networks. The CSC treats handover as a service in the IMS network. Its architecture and operation are based on service invocation. The service continuity procedure is performed by an application server called CSC AS. The CSC AS can carry out the third-party call control for fast session re-establishment by initiating two INVITE requests concurrently. In addition, a variant of the CSC, denoted by CSC*, is derived by adopting the E-IMS AKA with one-pass authentication for achieving the acceleration of IMS registration during the handover. Analytical results show that both schemes could shorten the handover latency significantly, as compared with the standard IMS-based service continuity.     

TCRA: a time‐based channel reservation scheme for handover requests in LEO satellite systems

In this paper, we propose a time‐based channel reservation algorithm (TCRA) suitable for handover and call admission control procedures in future mobile satellite systems. These systems are characterized by a high rate of handover attempts which can degrade significantly their performance. Therefore, we propose TCRA, a scheme which guarantees a null handover failure probability by using a channel reservation strategy in the cells to be crossed by the user. The performance of TCRA has been compared to the guaranteed handover (GH) scheme. The TCRA reservation method has the advantage of a better channel utilization by locking the resources only for their expected time of use. A mathematical model has been developed for both schemes, and its results have been validated through simulations. Copyright © 2003 John Wiley & Sons, Ltd.     

Handover authentication between different types of eNBs in LTE networks

There are two types of base stations in the long term evolution (LTE) wireless networks, home eNodeB (HeNB) and eNodeB (eNB). It is critical to achieve seamless handovers between the HeNB and the eNB in order to support mobility in the LTE networks. A handover from an eNB/HeNB to a new eNB/HeNB, suggested by the third generation partnership project (3GPP), requires distinct procedures for different mobility scenarios, which will increase the system complexity. Besides, the existing handover schemes for other wireless networks are not suitable for the mobility scenarios in the LTE networks due to their inherent vulnerabilities. In this paper, we propose a fast and secure handover authentication scheme, which is to fit in with most of the mobility scenarios in the LTE networks. Compared with other handover schemes, our scheme cannot only achieve a simple authentication process with desirable efficiency, but also provide several security features including perfect forward/backward secrecy (PFS/PBS), which have never been achieved by the previous works. The experiment results and formal verification by using the automated validation of internet security protocols and applications (AVISPA) tool show that the proposed scheme is efficient and secure against various malicious attacks.     

Efficient dynamic channel allocation techniques with handoverqueuing for mobile satellite networks

Efficient dynamic channel allocation techniques with handover queuing suitable for applications in mobile satellite cellular networks, are discussed. The channel assignment on demand is performed on the basis of the evaluation of a suitable cost function. Geostationary and low Earth orbit (LEO) satellites have been considered. In order to highlight the better performance of the dynamic techniques proposed, a performance comparison with a classical fixed channel allocation (FCA) has been carried out, as regards the probability that a newly arriving call is not completely served. It has also been shown that a higher traffic density, with respect to GEO systems, is manageable by means of LEO satellites     

Integration of wide-band service in time division multiplex systems

The authors present a TDM (time division multiplexing) channel access concept based on narrowband and wideband traffic requests which are queued in separated parallel queues. The system may be regarded as a part of a wideband integrated services digital network (ISDN). The channel access strategy follows the premise of allocating that type of customer first into service which fits best (fills out best) the nonoccupied channels. A Poisson arrival process and exponentially distributed service times for both are assumed for both traffic types, but they may have different bit rate requirements. The model involves four characteristic random variables; its joint probability is obtained by means of balance equations. Since it is difficult to determine the solution analytically, the authors develop the transition rate matrix and suggest a procedure for the numerical solution of the balance equations. Several numerical results are presented and discussed     

Reactive Handover Optimization in IPv6-Based Mobile Networks

In recent years, there has been a rapid growth in the need to support moving hosts and moving networks in IPv6-based mobile networks. As the number of such hosts and networks grows, so will the demand for delay sensitive real-time applications, such as voice over IP (VoIP), that require seamless handover. Two well-known approaches to reduce the handover latency have been proposed in the literature: proactive and reactive approaches. While proactive handover is known to generally outperform reactive handover, its reliability and practicality are still questionable since it basically depends on predictive information which may be unreliable in some cases. In this paper, based on the standard specification for IPv6 mobility support, we analyze the existing movement detection and address configuration procedures which are the main components of reactive handover approach. We also propose a novel reactive handover procedure which employs our optimized movement detection and address configuration schemes. The proposal is simple and robust because it does not need any predictive information and it requires a minimum number of signaling messages. The performance evaluation shows that the proposal substantially reduces the signaling load on wireless/wired networks and its handover latency is reduced enough to support seamless services.     

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.     

WLAN中基于MIPv6的移动VoIP切换性能仿真分析

移动IP是一个在Internet上基于网络层提供移动性支持功能的要求较高的VoIP业务,切换延迟将直接影响到话音质量,严重时甚至会中断正在进行的会话.文章借助ns2网络模拟器仿真分析了WLAN中基于MIPv6的移动VoIP切换性能.结果表明,MIPv6及其扩展协议的切换性能优劣顺序依次为:F-HMIPv6、FMIPv6、HMIPv6、MIPv6.尤其是F-HMIPv6协议,无论端到端延迟还是切换延迟,都得到了最大的改善.所得结论能为网络切换性能的进一步优化提供重要依据.