Movement-based location update and selective paging for PCSnetworks

This paper introduces a mobility tracking mechanism that combines a movement-based location update policy with a selective paging scheme. Movement-based location update is selected for its simplicity. It does not require each mobile terminal to store information about the arrangement and the distance relationship of all cells. In fact, each mobile terminal only keeps a counter of the number of cells visited. A location update is performed when this counter exceeds a predefined threshold value. This scheme allows the dynamic selection of the movement threshold on a per-user basis. This is desirable as different users may have very different mobility patterns. Selective paging reduces the cost for locating a mobile terminal in the expense of an increase in the paging delay. We propose a selective paging scheme which significantly decreases the location tracking cost under a small increase in the allowable paging delay. We introduce an analytical model for the proposed location tracking mechanism which captures the mobility and the incoming call arrival patterns of each mobile terminal. Analytical results are provided to demonstrate the cost-effectiveness of the proposed scheme under various parameters     

Mobile user location update and paging under delay constraints

Wireless personal communication networks (PCNs) consist of a fixed wireline network and a large number of mobile terminals. These terminals are free to travel within the PCN coverage area without service interruption. Each terminal periodically reports its location to the network by a process calledlocation update. When a call for a specific terminal arrives, the network will determine the exact location of the destination terminal by a process calledterminal paging. This paper introduces a mobile user location management mechanism that incorporates a distance based location update scheme and a selective paging mechanism that satisfies predefined delay requirements. An analytical model is developed which captures the mobility and call arrival pattern of a terminal. Given the respective costs for location update and terminal paging, the average total location update and terminal paging cost is determined. An iterative algorithm is then used to determine the optimal location update threshold distance that results in the minimum cost. Analytical results are also obtained to demonstrate the relative cost incurred by the proposed mechanism under various delay requirements.     

Derivation of Moving Distance Distribution to Enhance Sequential Paging in Distance-Based Mobility Management for PCS Networks

The total signaling cost of distance-based location management scheme, which is the lowest among dynamic location management schemes for PCS networks, can be further reduced by a sequential paging strategy that pages first the cells in which the mobile is most likely located. To enable this strategy, we derive the probability distribution of a mobile's moving distances between the last location update and the next call arrival. An efficient and effective sequential paging scheme is presented, which guarantees that a mobile can be located during the first paging step with a probability equal to or better than a predefined value. The features of the proposed model include flexible cell topologies, general cell residence time, and full use of mobile's moving pattern     

Paging strategy optimization in personal communication systems

Mobility tracking is concerned with finding a mobile subscriber (MS) within the area serviced by the wireless network. The two basic operations for tracking an MS, location updating and paging, constitute additional load on the wireless network. The total cost of updating and paging can be minimized by optimally dividing the cellular area into location registration (LR) areas. In current systems broadcast paging messages are sent within the LR area to alert the MS of an incoming call. In this paper we propose a selective paging strategy which uses the MS mobility and call patterns to minimize the cost of locating an MS within an LR area subject to a constraint on the delay in locating the MS. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Combination of Optimal Partitioning and Location Prediction to Assist Paging in Mobile Cellular Networks

The correlated both in space and time user mobility behavior can aid significantly in the localization of a moving terminal in the network coverage area. However, there is always some uncertainty in mobile user position and a network-wide search cannot be done. Therefore, a predictive paging scheme must always be combined with a location update strategy and a compatible algorithm to conduct the search. In this paper, we introduce a new strategy that combines an optimal partitioning of the location area (LA) with a model to predict user movements, based on the additional information of the cell where the last interaction between the network and the terminal took place. We study the performance of the strategy under delay bounds and different mobility and call arrival characteristics. It is found that the new scheme further minimizes signaling costs and enhances previous sequential paging algorithms.     

Location update optimization in personal communication systems

Mobility tracking is concerned with finding a mobile subscriber (MS) within the area serviced by the wireless network. The two basic operations for tracking an MS, location updating and paging, constitute additional load on the wireless network. The total cost of updating and paging can be minimized by optimally dividing the service area into location registration (LR) areas. There are various factors affecting this cost, including the mobility and call patterns of the individual MS, the shape, size and orientation of the LR area, and the method of searching for the MS within the LR area. Based on various mobility patterns of users and network architecture, the design of the LR area is formulated as a combinatorial optimization problem. The objective is to minimize the location update cost subject to a constraint on the size of the LR area. This revised version was published online in July 2006 with corrections to the Cover Date.     

A speed-adaptive strategy for location management cost reduction in cellular networks

A speed adaptive location management scheme will greatly reduce the cost of tracking mobile stations, because mobile stations can travel at a wide range of speeds. Recently, an elegant distance- and time-based scheme has been proposed. The scheme uses a look-up table which describes the relationship between the distance and the time: the distance decreases while the time increases. In the scheme, the paging area for a mobile station will be automatically reduced if the mobile station does not update its location over a certain time period. Therefore, the scheme performs well when a mobile station travels at a low speed. However, it does not perform well when the incoming call arrival rate is high or when the speed of a mobile station is high. To overcome those drawbacks, a novel speed-adaptive scheme is proposed in this paper. The proposed scheme uses an enhanced look-up table that consists of two parts: the distance in the first part increases while the time increases; in the second part, the distance decreases with the increasing time. By introducing the first part, the proposed scheme reduces the paging cost for a call arriving shortly after a location update, and adapts to the speed range of a mobile station. To reduce the paging cost further, a paging angle is introduced for high-speed mobile stations. Numerical simulations using various activity-based models and random walk models show that the proposed scheme performs well for mobile stations traveling at both high and low speeds. Zhijun Wang is a Ph.D. candidate in the Department of Computer Science at the University of Alabama. He received his M.S. in computer science from the University of Alabama in 2002. He also had a formal training in physics and obtained his B.S. in physics from Tianjin University in 1993 and his M.S. in physics from Yale University in 1998. His current research interests include location management in cellular networks and routing in ad hoc networks. Jingyuan Zhang received the bachelor’s degree from Shandong University in 1984, the master’s degree from Zhejiang University in 1987, and the doctoral degree from Old Dominion University in 1992, all in computer science. He is currently an assistant professor with the Department of Computer Science at the University of Alabama. Prior to joining the University of Alabama, he was an instructor with Ningbo University, an assistant professor with Elizabeth City State University, and a principal computer scientist with ECI Systems and Engineering. Dr. Zhang’s current research interests include wireless networks and mobile computing, single display groupware, graphics, and parallel processing. He is a member of the IEEE.     

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.     

Dynamic periodic location area update in mobile networks

In mobile communications networks, periodic location area update (PLAU) is utilized to detect the presence of a mobile station (MS). In the 3GPP Technical Specifications 23.012 and 24.008, a fixed PLAU scheme was proposed for the Universal Mobile Telecommunications System (UMTS), where the interval between two PLAUs is of fixed length. We observe that MS presence can also be detected through call activities and normal location area update (NLAU). Therefore, we propose a dynamic PLAU scheme where the PLAU interval is dynamically adjusted based on the call traffic and NLAU rate. An analytic model is developed to investigate the performance of dynamic and fixed PLAU schemes. This paper provides guidelines to select parameters for dynamic PLAU.     

An intra-LA location update strategy for reducing paging cost

The blanket paging strategy in current mobile networks may waste a lot of wireless bandwidth. While keeping the standard location area (LA) based location update (LU) strategy unchanged, we propose an intra-LA LU scheme to reduce the paging cost. While a mobile terminal (MT) is residing in an LA with a cell called anchor cell, where the MT usually stays for a significant period, an intra-LA LU is performed whenever the MT changes its location between the anchor cell and the rest of cells in the LA. For an incoming call, either the anchor cell or the rest of cells in the LA is paged to locate the MT. Thus the paging cost is greatly reduced, especially when the called MT is located in its anchor cell.     

Modeling and analysis of the dynamic location registration andpaging in microcellular systems

A 0-1 integer programming model is considered to determine the most appropriate dynamic location registration (LR) area of each subscriber in microcellular systems. The minimization model of the LR area updating and paging signal costs is examined. The model is based on the subscriber characteristics, such as the call arrival rate and the velocity, as well as the regional information. The control channel blocking probabilities are considered as constraints to meet the service level of subscribers. A dynamic scheme which adaptively updates the size and shape of the LR area is developed by solving the minimization problem. Paging and location updating procedures are presented based on the dynamic procedure. The superiority of the proposed scheme is demonstrated with various computational results     

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.     

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     

一种适应微蜂窝的移动性管理策略

在微蜂窝系统中,移动性管理是一个很重要的课题。如果采用传播蜂窝的位置登记的管理方式将会产生大量的系统资源浪费,降低系统的效率。本文提出一种基于用户移动特性（例如呼叫到达率、移动速度和移动位置等特点）的动态位置区的管理方案。在论文中对方案的寻呼代价和位置区修改代价进行分析和讨论,并与传统位置区管理方式〖１〗〖２〗做了比较。     

A dynamic anchor-cell assisted paging with an optimal timer for PCS networks

An intra location area (intra-LA) location update (LU) scheme is proposed to increase paging accuracy for PCS networks. In the proposed scheme, each mobile terminal (MT) has a valid/invalid anchor-cell, which may be dynamically changed. A MT updates its anchor-cell information only when the status is changed, i.e., from the valid to the invalid or vice versa. Therefore, the intra-LA LU cost is minimized. Whenever the MT enters a cell, a timer is set. The MT realizes that the entered cell is its current anchor-cell if the timer expires before leaving the cell. An analytical model is proposed, and the optimal time threshold is derived explicitly.     

Non-Blocking Pipeline Paging with Known Location Probabilities for Wireless Systems

Paging schemes for wireless systems have been well studied in the literature. However, most schemes are considered on per user basis. In these schemes, when an incoming call arrives at a mobile terminal (MT), a paging request (PR) is put in a queue. PRs are served in an FIFO manner. When a PR is served, a search process is carried out to find the corresponding MT in a location area (LA). Most schemes study how to achieve a better performance in terms of cost with/without delay constraints per PR, and totally ignore other PRs in the queue until the MT is found or all the cells in the LA have been paged. In this paper, we propose a non-blocking pipeline probability paging scheme, which assumes known knowledge on location probabilities of individual MTs, under a paging delay constraint, where the location probability of an MT in a cell is the probability that the MT is in the cell. The proposed scheme is independent of the number of PRs in the queue and the arrival rate of PRs. Our study shows that the proposed scheme outperforms both the sequential probability paging scheme with known knowledge on location probabilities of individual MTs and the blanket paging scheme in terms of discovery rate and the total delay. Finally, we study several optimization problems with quality of service constraint for the pipeline probability paging scheme.     

A cost effective distributed location management strategy for wireless networks

The mobility feature of mobile stations (MSs) imposes a large burden on network traffic control as a result of location management. Design issues of location management include MS registration (updating) and call setup (paging). Previous approaches introduced several network topologies for updating and paging procedures, but most of them focused on a single problem: either updating optimization or paging optimization. In this paper, we design and integrate two mechanisms, distributed temporary location caches (TLCs) and distributed home location registers (HLRs), to reduce database access delay and to decrease network signaling traffic in both updating and paging for low power, low tier micro cellular systems. By using TLCs, our approach can improve the performance of updating and paging in comparison with previous approaches. Experimental results based on our analytic model show that our location management procedures have lower HLR access rate, lower registration cost, and lower call setup cost than other approaches.     

Optimal fractional movement-based scheme for PCS location management

In this letter, we propose a fractional movement-based location update scheme for personal communication service networks. Similar to the well-known fractional guard channel scheme for channel assignments, in our proposed scheme, the movement threshold is a real number with a fraction instead of an integer. We prove analytically that there is a unique optimal fractional movement threshold that minimizes the total cost of location updates and paging per call arrival.     

Location area planning and cell-to-switch assignment in cellular networks

Location area (LA) planning plays an important role in cellular networks because of the tradeoff caused by paging and registration signalling. The upper boundary for the size of an LA is the service area of a mobile services switching center (MSC). In that extreme case, the cost of paging is at its maximum but no registration is needed. On the other hand, if each cell is an LA, the paging cost is minimal but the cost of registration is the largest. Between these extremes lie one or more partitions of the MSC service area that minimize the total cost of paging and registration. In this paper, we seek to determine the location areas in an optimum fashion. Cell to switch assignments are also determined to achieve the minimization of the network cost. For that purpose, we use the available network information to formulate a realistic optimization problem, and propose an algorithm based on simulated annealing (SA) for its solution. Then, we investigate the quality of the SA-based technique by comparing it to greedy search, random generation methods, and a heuristic algorithm.     

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.