Handover Failure Probability Research Articles

A new method for handover triggering condition estimation

It is desirable to maximize the WLAN usage in integrated heterogeneous network environment due to its high speed access and low access cost. We have modeled under geometry and mobility effects to dynamically estimate the distance of a mobile terminal from the access point at which the handover must be triggered to keep probability of handover failure within desired bounds while maximizing the WLAN usage. Monte-Carlo simulations are provided and they are in good conformance with our analytical findings.

Service characterization for cost/benefit optimization of enhanced UMTS

In this paper an all-IP Enhanced-Universal Mobile Telecommunications System (E-UMTS) is considered, where enhancements include link level behavior, high-speed downlink packet access (HSDPA) channel, resource management, Diffserv architecture, and Radio Resource Management schemes. An overview of E-UMTS deployment scenarios and service needs is presented based on the views of relevant players. Deployment and mobility scenarios are considered, including expected population density and usage of service mix for three environments, namely offices, urban/vehicular, and business city center. In addition, based on population and service penetration values, E-UMTS traffic generation and activity models are described and characterized. Based on these scenarios and characterizations, system level simulations are carried out and the enhanced service quality performance is demonstrated, including blocking probability, handover failure probability and end-to-end delay in each deployment scenario. By using system level simulations, services and environmental conditions can be mapped into deployment strategies (and supported system capacity) whose evaluation is essential prior to field trials and real implementation. On the one hand, costs depend on the prices of the spectrum, equipment, operation and maintenance, as well as on the number of cells which, in turn, depends on the cell radius. On the other, revenues depend on the price per MB and on the supported throughput. As the goal of operators and service providers is to maximize the profit, the profit in percentage was obtained for the three considered scenarios. Its optimum values are found for cell radii around 31, 257, and 310 m for offices, vehicular and business city center scenarios, respectively.

Admission control and handover management for high‐speed trains in vehicular geostationary satellite networks with terrestrial gap‐filling

AbstractFollowing a recent upgrade, the Digital Video Broadcasting—Return Channel Satellite (DVB‐RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite–terrestrial architecture for the provision of broadband services onboard high‐speed trains, in which terrestrial cellular networks are seen as viable gap‐fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB‐RCS‐cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high‐speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed‐point approximation, we show performance improvements with respect to stand‐alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2‐based DVB‐RCS packet‐level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly. Copyright © 2009 John Wiley & Sons, Ltd.

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

AbstractThis 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.

Modelling and simulation of B3G multi-service traffic in the presence of mobility

A multi-service traffic model is proposed, and its validation is achieved by using event-based simulation results which consider the burstiness of traffic. By considering the deployment scenarios and tele-traffic parameters from the Vehicular scenario of IST-SEACORN, a simulator was produced to extract conclusions about blocking and handover failure probabilities. Simulations, were performed for different cases, from single- to multi-service situations, and from absence to presence of mobility. Besides results for the quality of service in the air interface, including blocking and handover failure probabilities for several types of traffic, the simulator allows for extracting conclusions about the validation of the Bernoulli/Poisson/Pascal model for the computation of the on/off blocking probability, the ratio between the number of session rejected at the beginning of an on period and the total number of bursts generated during a session. In the single-service case, the theoretical and the experimental values of on/off blocking probability are close to each other. An almost perfect concordance between theoretical and simulation values is verified when the average sojourn time in cells is equal to the average holding time. In the multi-service case, although the results are not exactly coincident a coherent behaviour is achieved for an average traffic per user up to 0.06 Erl.

Performance Analysis and Improvement Methods for Channel Resource Management Strategies of LEO–MSS With Multiparty Traffic

A novel analytical framework for the accurate and efficient evaluation of the performance of channel resource management strategies for low Earth orbit mobile satellite systems (LEO-MSSs) supporting multiparty traffic is presented. By considering a fixed channel reservation (FCR) scheme as a benchmark, an efficient and accurate analytical approach is developed for obtaining the performance of multiparty traffic under various quality-of-service (QoS) performance measure criteria. The proposed approach is based on a Markovian queuing model, and its correctness and accuracy have been verified by means of computer simulations. To improve the overall performance of LEO-MSS, two novel resource management techniques are introduced and analyzed. The first one is an efficient adaptive channel reservation (ACR) scheme, which allows priority to be given to handover requests that are generated by multiparty traffic. The second one is a new call queuing (NCQ) policy, which efficiently reduces the new call blocking probability with little impact on other system performance measures, such as call dropping probability and unsuccessful call probability. Various performance results show that when ACR is used in conjunction with NCQ, extremely low blocking and handover failure probabilities can be achieved for multiparty traffic.

A Guard Code Scheme for Handover Traffic Management in WCDMA Systems

A key performance indicator of mobile wireless networks is failure probability of handover calls. In this paper, we propose a Call Admission Control policy which prioritizes handover calls over new calls in WCDMA systems. The OVSF code occupancy of the system is modeled by a Markov chain and the differentiation between handover and new calls is performed at the code level by introducing a “guard code” scheme. The scheme belongs to the well-known family of guard channel schemes and reserves some code capacity to favor the continuation of handover calls over the new calls. As the management of the general case is intractable, we solve certain numerical instances of the problem and manage to calculate several performance metrics like new call blocking and handover failure probabilities and code utilization. We complete our study with simulation results in the case of higher OVSF code tree capacity.

Handover Performance of Priority Schemes in Cellular Networks

In this paper, we study the performance of three handover priority schemes - the pure guard channel method (GCM), GCM with first-in-first-out (GCM-FIFO), and dynamic priority queuing (DPQ) - and, for the first time, compare them for different scenarios and provide guidelines as to which scheme to use under which scenario. In the first scenario, the channel holding time is assumed to follow an exponential distribution. For this scenario, we derive new accurate formulas to evaluate the performance of GCM and GCM-FIFO schemes. Our results show that existing analytical frameworks for GCM and GCM-FIFO overestimate the handover failure probability. Recent field measurements have shown that the best fits to measured data for channel holding time are lognormal and mixed lognormal distributions rather than an exponential distribution. We quantify and compare the handover performance of GCM, GCM-FIFO, and DPQ for ideal (i.e., exponential channel holding time distribution) and for practical (i.e., lognormal and mixed lognormal channel holding time distributions) scenarios. Our results show that, depending on the cell type, the number of channels per cell, and the traffic load, the operator should use either DPQ or GCM. For example, for high handover traffic and high traffic load, the operator should use GCM-FIFO; for light-to-moderate traffic load and a high number of channels per cell (40 or more), DPQ seems to be the best option. To make the handover scheme adaptive, a switching mechanism can be used such that, depending on the time of the day, traffic load, number of channels per cell, and cell type, the handover scheme that provides the best performance is selected. The guidelines provided in our paper are, in most cases, valid for both exponential and pure/mixed lognormal distributions.

Performance Evaluation of CAC Schemes for Multi-service Traffic Environment in 3G Networks

The ever-growing mobile market and the number of services offered by the network providers, which are increasing with every passing day, has reinforced the need for optimized CAC schemes. The introduction of Code Division Multiple Access (CDMA) has resulted in extensive reuse of frequency and therefore the birth of microcells has increased the number of handovers especially in metropolitan cities. Consequently further stress is exerted on existing CAC schemes to maintain the Quality of Service (QoS). In this paper we present new CAC algorithms based on dynamic allocation of channels to multiple input traffic streams. In this context two CAC schemes are proposed; IPG (Independent DT Queue priority, Pre-emptable DS priority, Guard Channel priority) and ITPG (Independent DT Queue priority, Timeout handover DS queuing Priority, Pre-emptable DS priority, Guard Channel priority). This scheme provides differentiated admission to various delay sensitive (DS) and delay tolerant (DT) traffic streams for both handover request (HOR) and new call request (NCR) according to current load intensity. The scheme provides an effective pre-emption priority in order to decreases forced handover failure probability. Service nature and customer behavior was considered to lay down the different levels of priorities that were assigned at different stages of the CAC scheme in order to achieve optimal QoS for urban area (metropolitan) cell. The simulation results demonstrate the improved QoS under various traffic scenarios.

Dynamic Priority Queueing of Handover Calls in Wireless Networks: An Analytical Framework

In this paper, we present an analytical framework for dynamic priority queueing of handover calls in wireless networks. The framework employs a queueing discipline with two classes of priority for handover calls. Two queues, first priority and second priority, are employed for the two priority classes of handover calls. The priority of queued handover calls is not based only on the received signal strength, but also on the remaining time in the overlap region between two cells. We also incorporate a priority transition between handover calls in the queue; specifically, a second-priority handover call in the second-priority queue, based on certain criteria, can become a first-priority handover call and join the first-priority handover queue. In addition, the event that a handover call could finish its call while waiting in the queue is taken into account in the analysis. This event was not taken into consideration in previous related studies and, as a result, these previous studies overestimate handover failure probability. Our results also show that the predictions of the analytical framework developed in this paper are in very good agreement with simulation results. The developed analytical framework is comprehensive and can also cope with several priority schemes proposed by other researchers in the literature. For example, it is shown that, under certain conditions, the proposed framework converges to first-in-first-out queueing of handover calls. One can easily modify the proposed framework to incorporate priority schemes that use guard channels for handover calls. It is also shown that one could potentially use the framework developed in this paper in integrated voice/data networks, as well as for handover between different network types. The proposed analytical framework is anticipated to be a very useful tool in evaluating performance of present and future wireless networks employing dynamic priority queueing for handovers and in designing more efficient handover algorithms.

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

AbstractIn 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.

A time‐based reservation scheme for managing handovers in satellite systems

AbstractThis paper proposes a Time‐based Channel Reservation Algorithm (TCRA) suitable for managing 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 managing the channel through a reservation strategy in the cells to be crossed by the user. Based on the feature that the satellite motion is predictable and deterministic, the scheme tries to maximize the channel utilization and enables the system to handle the most important number of users. The performance of the TCRA scheme has been examined by simulations and compared to the Guaranteed Handover (GH) scheme. The results show the behaviour of the algorithm and its performance. Copyright © 2003 John Wiley & Sons, Ltd.

Optimisation of mobile broadband multi-service systems based in economics aspects

Multi-service traffic engineering has a strong impact in Mobile Broadband Systems (MBS) revenues, allowing one to obtain merit functions for optimisation purposes, a key aspect in cellular planning. A net cost model is presented for the design trade-offs between re-use pattern, K , coverage distance, R , and spectral efficiency, Sef (R). It allows for the determination of the revenue per basic channel, R384, that achieves a given value for the annual profit per kilometre. Fast terminal mobility has an important impact in handover failure probability, hence, in system capacity. While in the business city centre and other urban scenarios mobility has no significant effect, it strongly affects the supported traffic in main roads. Comparing the urban with the roads scenarios, a reduction up to 54% may come as a consequence, from (Sef)TOT = 32.2 to 15.2%, for R = 100 m and K = 2; R384 has to be 0.005 and 0.045 /min, respectively, i.e., the prices in the roads scenario have to be around one order of magnitude higher than in the urban one. As time goes by, and the use of MBS evolves, the operator will be able to choose different cell coverage distances, in order to support a different number of users, whilst maximising profit. In a medium term scenario, while the number of foreseen users is less than 70% of the number of users in the mature phase, cells with R = 200 m will be used.

A unified approach for improving QoS and provider revenue in 3G mobile networks

In this paper, we introduce a unified approach for the adaptive control of 3G mobile networks in order to improve both quality of service (QoS) for mobile subscribers and to increase revenue for service providers. The introduced approach constantly monitors QoS measures as packet loss probability and the current number of active mobile users during operation of the network. Based on the values of the QoS measures just observed, the system parameters of the admission controller and packet scheduler are controlled by the adaptive performance management entity. Considering UMTS, we present performance curves showing that handover failure probability is improved by more than one order of magnitude. Moreover, the packet loss probability can be effectively regulated to a predefined level and provider revenue is significantly increased for all pricing policies.

Channel management policies for handovers in cellular networks

A major criterion in evaluating a cellular system is the handover failure probability — the probability that a mobile call in progress will be forced to abort during a handover because it could not be allocated a radio channel in the new cell. One factor that influences the handover failure probability is the channel allocation policy within each cell. This policy is used to determine how to allocate the limited set of available channels in the cell to two kinds of calls: new calls originating within the cell, and handovers that migrate into the cell from neighboring cells. Two classes of such policies are explored in this paper — nonreserving and reservation-based. Nonreserving policies do not set aside resources for exclusive use by handover calls, whereas reservation-based policies do reserve resources. For the former class, this paper presents an optimal policy and, for the latter, an adaptive traffic-driven reservation policy that improves on static guard channel policies. Analytic and simulation results are provided for policies in each class.

Handover queuing strategies with dynamic and fixed channel allocation 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.

Fairness in wireless microcellular networks

In the design of cellular and microcellular telecommunication networks, it is common to consider service to subscribers in specific regions by more than a single base station. Although the service overlap provides certain advantages, such as performance improvement achieved in dynamic channel assignment, it results in a large variance in the quality of service across the cells. In this paper, we introduce channel restriction to achieve fairness in the network quality of service. We develop analytical and simulation models for network performance and examine the advantages gained in increased system throughput and reduced probability of handover failure. The numerical results indicate that restricting the number of available channels to users in the overlap region results in considerable improvement in the carried traffic and mean probability of blocking. Finally, we discuss the possibility of substituting or scaling down the guard channels with channel restriction to achieve the desired effect of reduced forced termination.

Teletraffic analysis and simulation for nongeostationary mobile satellite systems

The teletraffic performance parameters of a nongeostationary satellite system are estimated through analytical and simulation methods. In order to reduce the number of assumptions, the simulation tool that was developed emulates a mobile satellite system that is closer to the real thing. Parameters of interest include blocking, handover failure, noncompletion, and forced-termination probabilities. These are analyzed in terms of variations in satellite spot cells coverage, overlapping between cells, and in terms of a mobility factor. Additionally, the effect on the grade of service of different channel assignment strategies, for handover purposes, are investigated. The results show that the analytical work is in good agreement with the simulation outcome.

Handover scheme for mobile cellularcommunication systems

A new scheme for minimising handover failure probability in mobile cellular communication systems, by exchanging channels between two mobiles moving in opposite directions across the handover area of adjacent cells, is presented. The performance evaluation of the new scheme is carried out by computer simulation of a two cell model.

Call blocking performance for dynamic channel allocation technique in future mobile satellite systems

Different dynamic channel allocation (DCA) approaches based on the evaluation of a cost function are proposed. The scenario considered is low earth orbit and geostationary orbit mobile satellite systems. A suitable user mobility model has been defined to generate interbeam handover requests. Different alternatives to manage interbeam handovers have been investigated. Among them, the most promising solution seems to be the queuing of handover requests. The quality of service parameters that have been considered are: blocking probability for new call arrivals, handover failure probability and the probability of incompletely served call owing to the initial blocking or to the failure of a subsequent handover request. Comparisons among the proposed DCA techniques and the fixed channel allocation technique have been carried out to find a solution that represents a good trade-off between the blocking performance and the required signalling load.