A distributed database architecture for global roaming in next-generation mobile networks

The next-generation mobile network will support terminal mobility, personal mobility, and service provider portability, making global roaming seamless. A location-independent personal telecommunication number (PTN) scheme is conducive to implementing such a global mobile system. However, the nongeographic PTNs coupled with the anticipated large number of mobile users in future mobile networks may introduce very large centralized databases. This necessitates research into the design and performance of high-throughput database technologies used in mobile systems to ensure that future systems will be able to carry efficiently the anticipated loads. This paper proposes a scalable, robust, efficient location database architecture based on the location-independent PTNs. The proposed multitree database architecture consists of a number of database subsystems, each of which is a three-level tree structure and is connected to the others only through its root. By exploiting the localized nature of calling and mobility patterns, the proposed architecture effectively reduces the database loads as well as the signaling traffic incurred by the location registration and call delivery procedures. In addition, two memory-resident database indices, memory-resident direct file and T-tree, are proposed for the location databases to further improve their throughput. Analysis model and numerical results are presented to evaluate the efficiency of the proposed database architecture. Results have revealed that the proposed database architecture for location management can effectively support the anticipated high user density in the future mobile networks.     

Performance analysis of cache strategy for signaling traffic management in a wireless ATM network

In a wireless ATM network for mobile multimedia services, conventional signaling protocols generate heavy traffic because the signaling load must be handled in a HLR (Home Location Register). This centralized structure of the wireless ATM network causes critical connection setup delays. Thus, distributed processing based on a reduction of the connection setup delays is needed in wireless ATM networks. A cache strategy for call delivery with cache updates of registration based on ATM multicasting is introduced with a comparison of the cost of cache scheme with the cost of a conventional scheme. Results show that the cache scheme has better performance than conventional methods when portable mobility is low with large traffic density. This revised version was published online in July 2006 with corrections to the Cover Date.     

TCP-Aware Call Admission Control in High Altitude Platforms Using Cross-Layer Design

In this paper, a new cross-layer design is proposed employing the predictability of rain faded channels to guarantee QoS requirements in High Altitude Platform (HAP) networks. Both a centralized and a distributed scheme are proposed for call admission control of packet-switched HAP wireless networks using a cross-layer approach aiming at keeping the call dropping probability below a predefined threshold. In both schemes, a new call is accepted if there are sufficient resources for the ongoing calls and for the new one to guarantee their QoS requirements for their whole connection. The performance of the proposed schemes is investigated using markov chain analysis and bounds of the call blocking probability are determined analytically.     

Channel Allocation Scheme for Handoff Control in Wireless Ad Hoc Network with Group Mobility

Because a wireless ad hoc network does not have a fixed backbone network and the mobile base station moves randomly, the conventional channel allocation scheme cannot efficiently predict group mobility and is not feasible to support a burst handoff traffic due to group mobility. In this paper, we propose an channel allocation scheme to solve this problem. Our scheme efficiently support burst handoff using guard channel and hello message in wireless ad hoc network with group mobility. We developed an analytical Markov model for the proposed scheme and evaluate our scheme in terms of new call and handoff blocking probability and channel utilization via simulation study. Simulation results show that our scheme offers better performance than the conventional schemes.     

Overflow control for cellular mobility database

In a cellular phone system, the service area is partitioned into several location areas (LAs). Every LA is associated with a mobility database called visitor location register (VLR). When a mobile user enters an LA, the user must register to the VLR before receiving any cellular service. If the VLR is full, the registration procedure fails and the system cannot deliver services to the user under the existing cellular technology. To resolve this problem, we propose a VLR overflow control scheme to accommodate the incoming mobile users during VLR overflow. Our scheme only requires minor modifications to the existing cellular mobility management protocols. Particularly, no modification is made to the mobile phones. An analytic model is proposed to investigate the performance of the overflow control scheme. When exercising the scheme, the call setup procedure for an “overflow” user is more expensive than that for a “normal” user. Under the range of input parameters considered in our study, we show that even if the VLR overflow situation is serious, the overhead for exercising the overflow control scheme is very low     

Predictive mobility support for QoS provisioning in mobile wirelessenvironments

With the proliferation of wireless network technologies, mobile users are expected to demand the same quality of service (QoS) available to fixed users. This paper presents a predictive and adaptive scheme to support timed-QoS guarantees in pico- and micro-cellular environments. The proposed scheme integrates the mobility model into the service model to achieve efficient network resource utilization and avoid severe network congestion. The mobility model uses a probabilistic approach to determine the most likely cluster to be visited by the mobile unit. The admission control is invoked when a new call arrives or an existing call performs a handoff to verify the feasibility of supporting the call. The performance of the proposed schemes is compared to the shadow cluster scheme. The performance of the proposed scheme under different traffic patterns is also presented     

Network issues for wireless communications

This article specifically focuses on wireless personal communications, i.e., wireless access, that provides either terminal or personal mobility. In particular, we discuss some important issues in networking, traffic, and performance. Although within radio and networking aspects there are significant commonalities between traditional cellular mobile communications and wireless personal communications, there exist distinct differences due to radio propagation and fading effects, interference environment, smaller cell sizes, type and pattern of mobility, and call delivery. Indeed, with respect to networking issues, a large set of system choices, characteristics of traffic to be carried, and important parameters have to be considered. These include the problems involved in selecting an appropriate multiaccess technology to efficiently handle the required subscriber service profile across a multiplicity of systems to complete a call. To present a meaningful discussion of these issues, we address in some detail radio resource assignment, mobility management, call control, and traffic aspect, which have significant impact on the network performance     

NonStop: continuous multimedia streaming in wireless ad hoc networks with node mobility

Guaranteeing continuous streaming of multimedia data from service providers to the users is a challenging task in wireless ad hoc networks, particularly when node mobility is considered. The topological dynamics introduced by node mobility are further exacerbated by the natural grouping behavior of mobile users, which leads to frequent network partitioning. Network partitioning poses significant challenges to the provisioning of continuous multimedia streaming services in wireless ad hoc networks, since the partitioning disconnects many mobile users from the centralized streaming service. In this paper, we propose NonStop, a collection of novel middleware-based run-time algorithms that ensures the continuous availability of such multimedia streaming services, while minimizing the overhead involved. The network-wide continuous streaming coverage is achieved by partition prediction and service replication on the streaming sources and assisted by distributed selection of streaming sources on regular mobile nodes and users. The proposed algorithms are validated by extensive results from performance evaluations.     

Quantitative analysis of a hybrid replication with forwarding strategy for efficient and uniform location management in mobile wireless networks

A location management scheme in wireless networks must effectively handle both user location update and search operations. Replication and forwarding are two well-known techniques to reduce user search and update costs, respectively, with replication being most effective when the call to mobility ratio (CMR) of the user is high, while forwarding is most effective when the CMR value is low. Thus, based on the user's CMR, the system can adopt a CMR threshold-based scheme such that if the user's CMR is lower than a threshold, then the system applies the forwarding scheme; otherwise, it applies the replication scheme. Applying different location management schemes based on per-user CMR values introduces undesirable high complexity in managing and maintaining location- related information stored in the system as different system support mechanisms must be applied to different users. In this paper, we quantitatively analyze a hybrid replication with forwarding scheme that can be uniformly applied to all users. The most striking feature of the hybrid scheme is that it can determine and apply the optimal number of replicas and forwarding chain length on a per-user basis to minimize the communication cost due to location management operations while still being able to use the same data structure and algorithm to execute location management operations in a uniform way for all users. We develop a stochastic Petri net model to help gather this information and show how the information obtained statically can be used efficiently by the system at runtime to determine the optimal number of replicas and forwarding chain length when given a use user's profile. We show that the proposed hybrid scheme outperforms both pure replication and forwarding schemes, as well as the CMR threshold-based scheme under all CMR values.     

Novel velocity and call duration support for QoS provision in mobile wireless networks

This article presents a novel mobility-based resource reservation and call admission control scheme that is applicable to any real wireless multimedia network. The scheme exploits three key mobility parameters - the position, direction, and speed of a mobile unit - together with the duration of a particular call to accurately estimate the cell visiting probability in order to identify a shadow cluster of cells the unit is most likely to visit. Each cell in the cluster reserves resources for an estimated time interval, which is adapted depending on the aggregated probability of all active units visiting a particular cell. Simulation results confirm the superiority of the new scheme over the existing predictive mobility support scheme in terms of three QoS parameters: call blocking rate, call dropping rate, and channel utilization.     

基于模糊逻辑的呼叫允许控制研究

无线频谱资源的缺乏以及用户的移动性使无线网络的服务质量的供给成为一个日益严峻的问题。为了满足服务质量的需要,该文提出蜂窝移动通信系统的一种模糊呼叫允许控制方案。它自动搜寻基站中保护信道数量的最优值,使资源得到合理的利用并保证服务质量的供给。对提出的模糊方案和一种动态信道预留方案进行了仿真比较,仿真结果表明模糊方案具有较强的鲁棒性,方案的呼叫阻止率、切换掉线率和信道利用率等性能参数都优于自适应方案。     

User mobility pattern scheme for location update and paging in wireless systems

The user mobility pattern (UMP) scheme is introduced for location update and paging in wireless systems where mobile terminals (MTs) maintain their history data in a database called user mobility history (UMH). During a location update, a UMP is derived from UMH and registered to the network. Unless the MT detects that it has moved out of the registered UMP, it does not perform any other location update. On the other hand, cells are paged selectively according to the cell entry times in the registered UMP upon a call arrival for the MT. The related data structures and the protocols for the UMP scheme are presented in the paper. The experimental results show that the UMP scheme outperforms the time-based and movement-based location update schemes as well as the blanket, selective, and velocity paging schemes.     

A distributed paths migration scheme for IEEE 802.6 based personalcommunication networks

Wireless personal communications will be provided via the usage of microcells in urban areas. The current centralized architecture may be unsuitable with the increased processing load and handoff rate associated with microcells. Some distributed architectures based upon interconnected IEEE 802.6 MAN'S for wireless personal communications have been proposed recently. The IEEE 802.6 MAN is attractive since it also provides isochronous services which are quite suitable for voice communications. In such a network, a communication path between two mobile terminals may be inefficient due to the lack of better paths when the path is established or become inefficient due to the mobility of terminals, e.g., the path elongates and consumes too much isochronous channels. In this paper, a distributed paths migration scheme is proposed for the IEEE 802.6 based personal communication networks. This distributed scheme automatically recognizes inefficient paths and migrates them to better ones, if any. During the migration, the property of isochronous services is also preserved. The performance of this scheme is evaluated by simulations. Simulation results show that the proposed paths migration scheme dramatically reduces the number of isochronous channels consumed per path. As a result, the call blocking rate is reduced and the number of successful established paths is increased significantly     

Aggregate History of User Mobility Pattern for QoS Provisioning in Multimedia Wireless Networks

Multimedia traffic is expected to be included in the next generation of wireless networks. As in wireline networks, the wireless network must also be capable of providing guaranteed quality-of-service (QoS) over the lifetime of mobile connections. In this paper, a bandwidth reservation scheme incorporating a user mobility prediction is proposed to manage the QoS of the networks. The mobility prediction scheme is developed based on the aggregate history of mobile users. Based on the mobility prediction, bandwidth is reserved to guarantee the uninterrupted handoff process. Simulation results demonstrate that the proposed scheme can guarantee the required QoS requirements in terms of handoff call dropping probability and new call blocking probability while maintaining efficient bandwidth utilization.     

Impact of Mobility on CDMA Call Admission Control

Interference is the key parameter in a code-division multiple access (CDMA) network. As users move around, the interference will flow with the movement. The objective of this paper is to study the impact of the moving interference (mobility) on systems' performance and design parameters. In this paper, we develop a detailed CDMA interference model with soft handoff, power-control errors, and shadowing effect. We combine this interference model with a Markov model to study the performance of CDMA systems under various mobility and traffic conditions. We also present a call admission control (CAC) scheme that sets aside some interference cushion for handling mobility and compare this scheme with other CAC schemes in terms of the effectiveness of mitigating the negative impact of mobility on system capacity     

个人通信系统中的用户登记认证

个人通信系统(PCS)的智能网络层上每个结点的数据库采用全分布式结构。根据PCS的智能层数据库结构特点以及X.509目录认证架构,提出了一种移动用户登记认证方案。此方案克服了X.509所具有的“静态”特性,使其能够满足PCS用户移动性及终端移动性的要求。在进行用户登记认证的同时,用户与本地的访问网络之间还建立起一个秘密数据。基于这一秘密数据,用户与网络之间可以在呼叫建立阶段进行相互认证。这就避免了现有的移动通信系统(如GSM,IS-41等)呼叫建立阶段的认证受归属网位置登记数据库(HLR)控制的缺陷。因此,用于位置修订和查询的信令负荷大大减小;同时,有关骨干网络(如PSPDN或共路信令网)安全的假定也可以被取消。     

Handoff priority scheme with preemptive, finite queueing and reneging in mobile multiservice networks

A scheme supporting voice and data calls with some grade of service (GoS)¹ guarantee in mobile multiservice networks is proposed. In this system, voice calls have preemptive priority over data calls. Preempted data calls can wait in a queue for a random patience time after which they leave the queue. A data call can be preempted only if there is space left in the finite size queue. To assess the performance of this system, an analytical model is given and performance metrics such as call blocking, call dropping and call non‐completion probabilities are investigated. Although this scheme is a generic model, it can be easily adapted to take into account the specific definitions of practical and commercial data service standards in wireless mobile networks such as GPRS or DECT. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Framework for Seamless Roaming Across Heterogeneous Next Generation Wireless Networks

In the future, wireless and mobile users will have increased demands for seamless roaming across different types of wireless networks, quality of service guarantees and support of different types of services. This awareness has led to research activities directed towards inter-system and global roaming and can be noticed in the numerous products like multimode handsets, inter-working gateways and some ongoing standards and research work on signaling protocols for inter-system roaming. This article proposes a global mobility management framework. The framework is like an overlay network comprising of Inter-System Interface Control Units IICU to support inter-network communication and control for Location Management. The protocols and functions of this framework will be distributed and exist partly within the wireless networks and partly within the core-network. A hierarchy introduced among the IICUs will accommodate for the varying mobility coverage required by the mobile user. The IICU may be configured to perform various functions depending on its placement in the hierarchy of the framework. This approach aims to optimize across call set up delays, signaling traffic, database processing, handoff facilitation for seamless roaming and QoS mapping and negotiations as the user moves across different wireless networks. It avoids centralized database dependency with its associated single-point bottleneck and failures. We restrict our analysis of the framework to a 2-network and a 3-network roaming scenario. The presentation has been further restricted to cost and delay analysis of the location update and call delivery procedures. We have taken into account the signalling requirements when the mobile user roams across networks with and without an active call. Nirmala Shenoy is Associate Professor at the Information Technology department at RIT. She has several years of teaching and research experience while working in Germany, Singapore and Australia before she moved to USA. She is an avid researcher in the wireless networks area and has technically led several wireless network projects to success. She holds a Ph.D. in computer science from the University of Bremen, Germany, Masters in Applied Electronics and Bachelors in Electronics and Telecommunications Engineering both from Madras University in India. Professor Shenoy is interested in research in the area mobility management and modeling for wireless networks, Quality of service in wireless networks and the Internet.     

Dynamic hierarchical database architecture for location managementin PCS networks

This paper introduces a dynamic hierarchical database architecture for location management in personal communications service (PCS) networks. The proposed scheme allows the dynamic adjustments of user location information distribution based on the mobility and calling patterns of the mobile terminals (MTs). A unique distribution strategy is determined for each MT, and location pointers are set up at selected remote locations which indicate the current location of the MTs. This method effectively reduces the signaling and database access overhead for location registration and call delivery. Besides, the required processing is handled by a distributed network of directory registers and centralized coordination is not necessary. The functions of the other network elements, such as the home location register (HLR) and the visitor location registers (VLRs), remain primarily unchanged. This greatly facilitates the deployment of this scheme in current PCS networks     

Performance Evaluation of Non-prioritized and Prioritized Call Admission Control Schemes in Wireless Cellular Networks

In cellular wireless networks, the choice of Call Admission Control scheme impacts the performance of the system, particularly as how calls are managed when a mobile user is handed off from one cell to another. Non-prioritized schemes treat handoff calls and new calls equally, while, prioritized schemes give higher priority to handoff calls. In this paper, some of the popular non-prioritized and prioritized Call Admission Control schemes were investigated and their behavior was simulated and analyzed. They are evaluated based on call dropping probability, call blocking probability and system utilization parameters.