Analysis and Comparison of Location Strategies for Reducing Registration Cost in PCS Networks

In mobile environments, a personal communication service (PCS) network must keep track of the location of each mobile user in order to correctly deliver calls. A basic scheme used in the standard IS-41 and GSM protocols is to always update the location of a mobile user whenever the mobile user moves to a new location. The problem with this approach is that the cost of location update operations is very high especially when the mobile user moves frequently. In recent years, various location management strategies for reducing the location update cost have been proposed. However, the performance issue of these proposed algorithms remains to be investigated. In this paper, we develop two Markov chains to analyze and compare the performance of two promising location update strategies, i.e., the two location algorithm (TLA) and the forwarding and resetting algorithm (FRA). By utilizing the Markov chain, we are able to quickly answer what-if questions regarding the performance of PCS networks under various workload conditions and also identify conditions under which one strategy can perform better than the others. Using the cost due to location update and search operations between two successive calls to a mobile user as a performance measure, we show that when the mobile user exhibits a high degree of locality and the mobile user's call-to-mobility ratio (CMR) is low, TLA can significantly outperform both FRA and IS-41. On the other hand, when CMR is high, FRA is the winner. Furthermore, unlike TLA which may perform worse than IS-41 at high CMR values, FRA at identified optimal conditions can always perform at least as good as IS-41, suggesting that FRA over TLA should be used as a generic scheme in reducing the location cost in the PCS network to cover all possible per-user CMR values.     

Performance Analysis of Location-Aware Mobile Service Proxies for Reducing Network Cost in Personal Communication Systems

We propose and analyze mobile service management schemes based on location-aware proxies with the objective to reduce the network signaling and communication cost in future personal communication systems (PCS). Under these schemes, a mobile user uses personal proxies as intelligent client-side agents to communication with services engaged by the mobile user. A personal proxy cooperates with the underlying location management system so that it is location-aware and can optimally decide when and how often it should move with the roaming user. We show that, when given a set of model parameters characterizing the network and workload conditions, there exists an optimal proxy service area size for service handoffs such that the overall network signaling and communication cost for servicing location and service operations is minimized. We demonstrate via Petri net models that our proposed proxy-based mobile service management schemes outperform non-proxy-based schemes over a wide range of identified conditions. Further, when the mobile user is concurrently engaged in multiple services, the per-service proxy scheme that uses a separate proxy for each service outperforms the aggregate proxy scheme that uses a single proxy to interface with multiple services taking their aggregate service characteristics into consideration. Baoshan Gu received the BS degree from University of Science and Technology of China, Hefei, China, in 1992 and the MS degree in computer science from Institute of Computing Technology, Chinese Academia of Science, Beijing, China, in 1995. From 1995 to 2000, he was a research and development engineer in Institute of Computing Technology, Chinese Academia of Science. He is currently pursuing his PhD degree in the Department of Computer Science, Virginia Tech, where he is a research assistant in the Systems and Software Engineering Laboratory. His research interests include next-generation wireless system architectures, design and evaluation of location and service management schemes in mobile computing environments, and mobile database systems. Ing-Ray Chen received the BS degree from the National Taiwan University, Taipei, Taiwan, and the MS and PhD degrees in computer science from the University of Houston, Texas. He is currently an associate professor in the Department of Computer Science at Virginia Tech. His research interests include mobile computing, pervasive computing, multimedia, distributed systems, real-time intelligent systems, and reliability and performance analysis. Dr. Chen has served on the program committee of numerous conferences, including being as program chair of 14th IEEE International Conference on Tools with Artificial Intelligence in 2002, and 3rd IEEE Symposium on Application-Specific Systems and Software Engineering Technology in 2000. Dr. Chen currently serves as an Associate Editor for IEEE Transactions on Knowledge and Data Engineering, The Computer Journal, and International Journal on Artificial Intelligence Tools. He is a member of the IEEE/CS and ACM.This revised version was published online in August 2005 with a corrected cover date.     

State-based paging/registration: a greedy technique

For a mobile unit moving according to some ergodic stochastic process, we show how to minimize the expected average cost of paging and registration based on system state information. Specifically, we assume that both the system and mobile unit (user) have access to or can derive the following: the user location probability distribution as a function of time given the last location known to the system, and the time elapsed since this last known location. We then derive methods by which the user decides whether to register based on the following: current location (x), the time elapsed since last contact with the system (t), the paging cost F(x_t,x₀,t) to be incurred by the system at time t given the current location x_t and the last known location x₀, i.e., the user knows the paging strategy to be used by the system for each time t. If x and t define the system state, the method can be called “state based”. Since the optimization is based only on the current expected cost rate and not that of all registration intervals, the method is “greedy”. The greedy method was compared to a timer-based method using a simple diffusive motion process. Reductions in the average paging registration cost of approximately 10% were observed. The more striking improvement was a reduction in the variability of paging/registration costs by a factor of three. Thus, taking both cost and variability reduction as a performance measure, even suboptimal inclusion of location information in the registration decision affords substantial improvement     

Two-level pointer forwarding strategy for location management in PCS networks

For a IPCS network to effectively deliver services to its mobile users, it must have an efficient way to keep track of the mobile users. The location management fulfills this task through location registration and paging. To reduce the signaling traffic, many schemes such as a local anchor (LA) scheme, per-user caching scheme and pointer forwarding scheme have been proposed in the past. In this paper, we present a new location management scheme which intends to mitigate the signaling traffic as well as reduce the tracking delay in the PCS systems. In this strategy, we choose a set of visitor location registers (VLRs) traversed by users as the mobility agents (MA), which form another level of management in order to make some registration signaling traffic localized. The idea is as follows: instead of always updating to the home location register (HLR), which would become the bottleneck otherwise, many location updates are carried out in the mobility agents. Thus, the two-level pointer forwarding scheme is designed to reduce the signaling traffic: pointers can be set up between VLRs as the traditional pointer forwarding scheme and can also be set up between MAs. The numerical results show that this strategy can significantly reduce the network signaling traffic for users with low CMR without increasing much of the call setup delay.     

A Novel Location Tracking Scheme for Reducing Location Updating Traffic in a Personal Communication System

How to reduce location updating traffic is a critical issue for tracking the current locations of users in a personal communication system. Traditional location management approaches usually bring about network overload or bottleneck of the HLR when a mobile user moves back and forth between adjacent location areas. So far, many works have focused on this research topic to solve the location updating rate or the location updating cost. In this paper, we shall employ both concepts of time stamp and virtual overlapping to propose a newly developed scheme for reducing both the location updating rate and the location updating cost. From the simulated results, our scheme can significantly reduce the location updating traffic.     

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     

A crossing-tier location update/paging scheme in hierarchical cellular networks

Location update/paging strategies have been widely studied in the traditional single-tier cellular networks. We propose and evaluate a novel crossing-tier location update/paging scheme that can be used in a hierarchical macrocell/microcell cellular network. Location update is proceeded only in the macrocell tier, where a location area (LA) is made up by larger macrocells. A mobile user will stay in such a LA for longer time. Therefore, the cost on location update can be reduced due to the decreased frequency of location update. To reduce the paging delay, the paged mobile user will be searched in the macrocell tier only when the paging load is not high. Otherwise, it will be searched in the microcell tier, where a sequential searching method is applied. The operation for the scheme is simple, as the macrocell/microcell cellular network has the advantage because a mobile user can receive a signal from both a microcell and the overlaid macrocell. Analytical models have been built for cost and delay evaluation. Numerical results show that, at relatively low cost, the crossing-tier scheme also achieves low paging delay.     

Hybrid TDOA/AOA mobile user location for wideband CDMA cellularsystems

This paper proposes a mobile user location scheme for wideband code-division multiple-access (CDMA) wireless communication systems. To achieve high location accuracy and low cost of the mobile receiver, the location scheme combines the time difference of arrival (TDOA) measurements from the forward link pilot signals with the angle of arrival (AOA) measurement from the reverse link pilot signal. High chip rates in wideband CDMA systems facilitate accurate TDOA measurements, and a smart antenna used at the home base station (BS) can provide accurate AOA measurement in a macrocell environment. A two-step least square location estimator is developed based on a linear form of the AOA equation in the small error region. Numerical results demonstrate that the proposed hybrid TDOA/AOA location scheme gives a much higher location accuracy than TDOA only location, when the number of base stations is small and/or when the TDOA measurements have a relatively poor accuracy     

Analysis of a mobility management scheme considering battery power conservation in IP-based mobile networks

Mobile hosts (MHs) in all IP-based mobile networks must update their current location to receive incoming packets. The MHs are idle for most of time. Both registration of approximate location information and paging can facilitate efficient power management for the idle MHs. Furthermore, the MHs can be in switch-off state for battery power conservation. Mobile IP, the current standard for IP-based mobility management, needs to be enhanced for use in all IP-based mobile networks. Mobility management in all IP-based mobile networks should consider idle and detached MH states as well as active MH state. A mobility management scheme for all IP-based mobile networks is introduced in this paper. This scheme includes management of communicating, attentive, idle, and detached states. We model MH behavior in the networks when the binding-lifetime-based registrations are utilized as a means of identifying that an MH is switched off. The steady-state probabilities for MH state transitions are derived, and an optimal rate of binding-lifetime-based registrations that results in minimum network cost is derived.     

Location Management in PCS Networks by Caching Two-Level Forwarding-Pointers

One of the challenging tasks in Personal Communication Services (PCS) is to efficiently maintain the location of PCS subscribers who move from one region to another (hereafter called mobile users). When a mobile user receives a call, the network has to quickly determine its current location. The existing location management scheme suffers from high signaling traffic in locating the mobile users. Two-level forwarding pointer scheme has been proposed from per-user forwarding pointer scheme to reduce the cost of signaling traffic. In this paper, we enhance the two-level forwarding pointer scheme. When a mobile user moves from its current Registered Area (RA), which is served by Mobile Switching Center (MSC), to another RA the local switch that acts as a parent of those two MSCs maintains this movement in its memory (hereafter called cache entry). A cache entry is used to locate rapidly the mobile user instead of querying the Home Location Register (HLR) and waiting for its reply. HLR is centralized in the network and far away from the mobile users so that the signaling traffic crossing it is expensive. Sometimes the cache entry may be failed to reach the mobile user then a two-level forwarding pointers will be created from the corresponding Visitor Location Register (VLR), attached to its MSC, through a correct path to locate the mobile user. Thus, there is a saving in cost of querying the underlying HLR. The analytical results indicate that such proposal efficiently reduces the signaling traffic cost for all values of Call to Mobility Ratio (CMR), this is especially considerable when CMR ≥1, without any increase in the call setup delay. Salah M. Ramadan (samohra@yahoo.com) received the BS and MS degrees from Computers Engineering Department, Al-Azhar University, Cairo, Egypt, in 1995 and 2002, respectively. From 2002, he was a Ph.D. student in Computers Engineering Department at Al-Azhar University and is currently pursuing the Ph.D. degree, where he is a research assistant in the Wireless Networks Branch. His research interests include traffic management in ATM networks, routing protocols, mobility management in PCS networks, and mobile computing. He is currently an instructor in Cisco Academy, Egypt. Ahmed M. El-Sherbini (Sherbini@mcit.gov.eg) received the Ph.D. in Electrical and Communication Engineering, Case Western University, U.S.A. March 1983 and M.Sc. in Communication Engineering, Cairo University, Giza, Egypt, June 1980. (M. Sc. Research Studies at the Ecole Nationale Superieure des Telecommunications (ENST), Paris, France). He is the Director, National Telecommunication Institute – Ministry of Communications and Information Technology, Egypt and Professor of Electrical and Communication Engineering Dept. Faculty of Engineering, Cairo University, Egypt. M. I. Marie received his B.Sc., M.Sc. and Ph.D. in electronic and communication engineering from Cairo University on 1972, 1981, 1985, respectively. Now he is a professor of communications at Computer and System Engineering department Al-Azhar University, Cairo, Egypt. His fields of interest includes digital communication, computer networks and protocols development. M. Zaki (azhar@mailer.scu.eun.eg) is the professor of software engineering, Computer and System Engineering Department, Faculty of Engineering, Al-Azhar University at Cairo. He received his B.Sc. and M.Sc. degrees in electrical engineering from Cairo University in 1968 and 1973 respectively. He received his Ph.D. degrees in computer engineering from Warsaw Technical University, Poland in 1977. His fields of interest include artificial intelligence, soft computing, and distributed system.     

Agent-Based Forwarding Strategies for Reducing Location Management Cost in Mobile Networks

An important issue in location management for dealing with user mobility in wireless networks is to reduce the cost associated with location updates and searches. The former operation occurs when a mobile user moves to a new location registration area and the network is being informed of the mobile user's current location; the latter operation occurs when there is a call for the mobile user and the network must deliver the call to the mobile user. In this paper, we propose and analyze a class of new agent-based forwarding schemes with the objective to reduce the location management cost in mobile wireless networks. We develop analytical models to compare the performance of the proposed schemes with existing location management schemes to demonstrate their feasibility and also to reveal conditions under which our proposed schemes are superior to existing ones. Our proposed schemes are particularly suitable for mobile networks with switches which can cover a large number of location registration areas.     

Adaptive region-based location management for PCS systems

The personal communications services (PCSs) systems can provide ubiquitous and customized services. The key issue, which affects the performance of the whole system, is the location management. We propose a region-based location strategy by taking advantage of the user's movement behavior to improve the performance of the conventional systems. Each mobile user is associated with a set of regions, which are derived from the user's movement patterns. The registration processes in the same region can be eliminated such that the cost of location management can be significantly reduced. Several design issues are studied by considering the workload balance and the call-to-mobility ratio for a user. The proposed strategy can be dynamically adjusted based on different system parameters and user behavior. A performance analysis on the signaling cost and the database access cost is given to justify the benefits of this approach     

一种基于状态的动态位置管理方法

在蜂窝移动通信系统中,用户位置管理方法性能的好坏直接影响系统的服务质量.本文提出了一种基于运动状态的动态位置管理方法.系统根据用户不同的运动状态动态地决定其位置区的大小.其性能较传统方法有显著提高,接近基于个体移动特征的方法;同时,它保持了传统算法实现简单的特点,不增加任何系统负担,不改变现有的信令流程,较好地兼顾了性能与工程实用性两方面的要求,适合3G系统的应用要求,具有很好的工程应用前景.     

A Time and Location Information Assisted OTP Scheme

As the mobile networks are springing up, mobile devices become a must gadget in our daily life. People can easily access Internet application services anytime and anywhere via the hand-carried mobile devices. Most of modern mobile devices are equipped with a GPS module, which can help get the real-time location of the mobile device. In this paper, we propose a novel authentication scheme which exploits volatile passwords—One-Time Passwords (OTPs) based on the time and location information of the mobile device to transparently and securely authenticate users while accessing Internet services, such as online banking services and e-commerce transactions. Compared to a permanent password base scheme, an OTP based one can prevent users from being eavesdropped. In addition to a memoryless feature, the scheme restricts the validness of the OTP password not only in a certain time period but also in a tolerant geometric region to increase the security protection. However, if a legitimate user is not in the anticipated tolerant region, the user may fail to be authenticated. Hence, a Short Message Service based mutual authentication mechanism is also proposed in the article to supplement the unexpected misjudgement. The proposed method with a volatile time/location-based password features more secure and more convenient for user authentication.     

The User-level Security of Mobile Communication Systems

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On Integrated Location and Service Management for Minimizing Network Cost in Personal Communication Systems

We investigate the notion of per-user integrated location and service management in personal communication service (PCS) networks by which a per-user service proxy is created to serve as a gateway between the mobile user and all client-server applications engaged by the mobile user. The service proxy is always colocated with the mobile user's location database such that whenever the MU's location database moves during a location handoff, a service handoff also ensues to colocate the service proxy with the location database. This allows the proxy to know the location of the mobile user all the time to reduce the network communication cost for service delivery. We investigate four integrated location and service management schemes. Our results show that the centralized scheme performs the best when the mobile user's SMR (service to mobility ratio) is low and CMR (call to mobility ratio) is high, while the fully distributed scheme performs the best when both SMR and CMR are high. In all other conditions, the dynamic anchor scheme is the best except when the service context transfer cost is high, under which the static anchor scheme performs the best. Through analytical and simulation results, we demonstrate that different users with vastly different mobility and service patterns should adopt different integrated location and service management methods to optimize system performance. Further, the best integrated scheme always performs better than the best decoupled scheme that considers location and service managements separately and management schemes that do not use any service proxy.     

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.     

LTE/SAE系统中用户移动性管理的研究与分析

文章首先介绍了LTE网络下的移动性管理功能,然后对用户的移动性管理状态进行了描述,并用图形法描述了LTE移动状态之间的转移,最后分别对空闲状态、连接状态和3GPP无线接入系统之间的移动性管理进行研究与分析,分析表明,提出的移动性管理机制能够解决移动通信网络的安全性、可靠性和端到端的QoS保证。     

Handover with resource pre-allocation in the OFDMA systems

This article proposed a new handover algorithm for beyond the third generation (B3G) systems with an orthogonal frequency division multiple access (OFDMA) downlink. In the proposed algorithm, handover mobile termination (MT) chooses a subchannel set in the candidate cells by a subchannel booking rule, based on the terminal speed and the subchannel's channel state information (CSI). Moreover, the handover decision is made after analyzing if at least one candidate cell can reserve the subchannel set for the handover user. Simulation results show that the algorithm reduces the number of handovers and guarantees the quality of service (QoS) for the handover users. It yields better system performance in the OFDMA systems.     

Dynamic Location Management for Mobile Computing

This paper presents a dynamic and individualized location update scheme that considers each user's mobility patterns. The mobility patterns are used to create individualized location areas for each user. The proposed scheme is flexible and can be used in network with arbitrary cell topologies. The scheme, along with other existing schemes is simulated using realistic users' mobility and call arrival patterns, and network topology. The simulated environment consists of 90 cells representing the geographical area of the San Francisco bay, and 66,550 mobile users representing the typical classes of users that are normally present in a real cellular network. Results show the proposed scheme gives lower overall signaling costs, resulting in savings on the limited radio bandwidth that may have otherwise been used for location updates and paging.