The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Yang Xiao - One of the best experts on this subject based on the ideXlab platform.
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Optimal Utilization and Effects of Inaccurate Estimation in Mobile Database Failure Restoration
IEEE Transactions on Wireless Communications, 2007Co-Authors: Yang Xiao, Hui Chen, Hsiao-hwa Chen, C. Philip L. ChenAbstract:Mobility databases such as home location register and visitor location register are adopted to support mobility management in personal communications services networks. If a visitor location register fails or crashes, the subscribers' services will be seriously degraded due to the loss or corruption of location information. In this paper, we optimize utilization of demand re-registration messages for an adaptive p-persistent backoff database failure restoration scheme. An analytical model is developed and validated with simulations to obtain the optimal utilization using appropriate parameters so that the failed visitor location register is restored with the fastest speed. Some interesting aspects on the performance are studied and their deep insights are observed, such as effects of message sizes on choices of system parameters, effects of the inaccurate estimated number of stations, etc. One observation is that optimizations of utilization and successful transmission probability are two different goals, and a value to achieve the optimal successful transmission probability does not necessarily ensure optimal utilization. Furthermore, we also propose a scheme how to handle the problem with inaccurate (estimated) number of stations.
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A simulation study of overflow replacement policies for location management in mobile networks
International Journal of Mobile Communications, 2004Co-Authors: Jie Li, Yang XiaoAbstract:location management is one of the most important issues of mobile networking systems. Most current mobile systems employ a two-tier database structure to store mobile users' information. HLR (Home location register) is used to retrieve user's information, and VLR (visitor location register) is the temporal database for storing visitors' profiles. In the case when the number of users exceeds the capacity of the VLR due to mobility, database overflow occurs. To solve this problem, different replacement policies have been developed: random, most-idle, and inactive. In this paper, we propose a new policy, the least frequent replacement policy, which selects the least frequently accessed users as replacement candidates. Extensive simulation is carried out to predict the performance of the existing replacement policies and the proposed least frequent policy. Our simulation results show that the most idle and least frequent policies outperform the inactive and random replacement policies in most cases and the least frequent policy performs slightly better than the most idle replacement policy.
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Optimal location management for two-tier PCS networks
Computer Communications, 2003Co-Authors: Yang XiaoAbstract:Abstract One of the most important issues in Personal Communication Service (PCS) networks is location management, which keeps track of the Mobile Terminals (MTs) moving from place to place. In this paper, we analytically derive cost functions of location updates and paging for a dynamic movement-based location management scheme for PCS networks with two-tier mobility databases. We prove analytically that there is a unique optimal movement threshold that minimizes the total cost of Home location register location updates, visitor location register location updates, and paging, per call arrival. An effective algorithm is proposed to find the optimal movement threshold. Furthermore, we propose a hybrid location management scheme, in which when the call-to-mobility ratio is larger than a threshold, the optimal dynamic movement-based scheme is adopted. Otherwise, the static location update is adopted. The Newton approximation method is adopted to find this threshold. Our study shows that the proposed hybrid scheme outperforms both the dynamic movement-based scheme and the static location update scheme.
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A new overflow replacement policy for efficient location management in mobile networks
23rd International Conference on Distributed Computing Systems Workshops 2003. Proceedings., 2003Co-Authors: Jie Li, Yang XiaoAbstract:location management is one of the most important issues in mobile networking systems. Most current mobile systems employ a two-tier database structure to store mobile users' information. HLR (Home location register) is used to retrieve user's information, and VLR (visitor location register) is the temporal database for storing visitors' profile. In the case that the number of users exceeds the capacity of the VLR due to mobility, database overflow occurs. In this paper, we propose a new policy, the least frequent replacement policy, which selects the least frequently accessed users as replacement candidates. Extensive simulation is carried out for predicting the performance of the existing replacement policies and the proposed least frequent policy. Our simulation results show that the most idle and least frequent policies outperform the inactive and random replacement policies in most cases and that the least frequent policy performs slightly better than the most idle replacement policy.
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ICDCS Workshops - A new overflow replacement policy for efficient location management in mobile networks
23rd International Conference on Distributed Computing Systems Workshops 2003. Proceedings., 2003Co-Authors: Jie Li, Yang XiaoAbstract:location management is one of the most important issues in mobile networking systems. Most current mobile systems employ a two-tier database structure to store mobile users' information. HLR (Home location register) is used to retrieve user's information, and VLR (visitor location register) is the temporal database for storing visitors' profile. In the case that the number of users exceeds the capacity of the VLR due to mobility, database overflow occurs. In this paper, we propose a new policy, the least frequent replacement policy, which selects the least frequently accessed users as replacement candidates. Extensive simulation is carried out for predicting the performance of the existing replacement policies and the proposed least frequent policy. Our simulation results show that the most idle and least frequent policies outperform the inactive and random replacement policies in most cases and that the least frequent policy performs slightly better than the most idle replacement policy.
Jie Li - One of the best experts on this subject based on the ideXlab platform.
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Modeling and Cost Analysis of Movement-Based location Management for PCS Networks With HLR/VLR Architecture, General location Area and Cell Residence Time Distributions
IEEE Transactions on Vehicular Technology, 2008Co-Authors: Xian Wang, Jie LiAbstract:location management plays a central role in guaranteeing the effective operation of personal communication service (PCS) networks. In current PCS networks, a two-tier system of home location register (HLR) and visitor location register (VLR) databases is commonly used for location management. To improve the performance of PCS networks, several dynamic location management schemes have been proposed. Among the existing dynamic schemes, the movement-based location management may be the most practical due to its effectiveness and easy implementation under the framework of current PCS networks. To implement location management in PCS networks, cost analysis is a crucial aspect. However, most of the existing cost analyses for the movement-based scheme are too simple and not available for PCS networks with the HLR/VLR architecture. One reason for this is the complexity and the difficulty associated with the problem. Li et al. and Rodriguez-Dagnino et al. challenged this task by considering the HLR/VLR architecture. However, the cost analysis developed by Li et al. was carried out under the assumption that the cell and location area (LA) residence times are exponentially distributed. Rodriguez-Dagnino et al. furthered Li et al.'s work by assuming that the LA residence time follows a hyperexponential distribution and that the cell residence time is generally distributed. However, Li et al. and Rodriguez-Dagnino et al. failed to consider VLR location updates that are caused by terminal movements between LAs. In this paper, we relax the restrictions imposed on the distributions of the cell and LA residence times and propose an analytical model to study the movement-based scheme with HLR/VLR architecture. The issue of VLR location updates that are caused by movements between LAs is addressed carefully and successfully. Analytical formulas for the costs of HLR and VLR location updates are derived using a unified approach. Numerical study suggests that the total cost is a convex function of the movement threshold and is sensitive to the variances of the cell and LA residence times. The result presented in this paper can serve as a guideline for the system design and the implementation of the movement-based scheme for PCS networks.
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A simulation study of overflow replacement policies for location management in mobile networks
International Journal of Mobile Communications, 2004Co-Authors: Jie Li, Yang XiaoAbstract:location management is one of the most important issues of mobile networking systems. Most current mobile systems employ a two-tier database structure to store mobile users' information. HLR (Home location register) is used to retrieve user's information, and VLR (visitor location register) is the temporal database for storing visitors' profiles. In the case when the number of users exceeds the capacity of the VLR due to mobility, database overflow occurs. To solve this problem, different replacement policies have been developed: random, most-idle, and inactive. In this paper, we propose a new policy, the least frequent replacement policy, which selects the least frequently accessed users as replacement candidates. Extensive simulation is carried out to predict the performance of the existing replacement policies and the proposed least frequent policy. Our simulation results show that the most idle and least frequent policies outperform the inactive and random replacement policies in most cases and the least frequent policy performs slightly better than the most idle replacement policy.
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A new overflow replacement policy for efficient location management in mobile networks
23rd International Conference on Distributed Computing Systems Workshops 2003. Proceedings., 2003Co-Authors: Jie Li, Yang XiaoAbstract:location management is one of the most important issues in mobile networking systems. Most current mobile systems employ a two-tier database structure to store mobile users' information. HLR (Home location register) is used to retrieve user's information, and VLR (visitor location register) is the temporal database for storing visitors' profile. In the case that the number of users exceeds the capacity of the VLR due to mobility, database overflow occurs. In this paper, we propose a new policy, the least frequent replacement policy, which selects the least frequently accessed users as replacement candidates. Extensive simulation is carried out for predicting the performance of the existing replacement policies and the proposed least frequent policy. Our simulation results show that the most idle and least frequent policies outperform the inactive and random replacement policies in most cases and that the least frequent policy performs slightly better than the most idle replacement policy.
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ICDCS Workshops - A new overflow replacement policy for efficient location management in mobile networks
23rd International Conference on Distributed Computing Systems Workshops 2003. Proceedings., 2003Co-Authors: Jie Li, Yang XiaoAbstract:location management is one of the most important issues in mobile networking systems. Most current mobile systems employ a two-tier database structure to store mobile users' information. HLR (Home location register) is used to retrieve user's information, and VLR (visitor location register) is the temporal database for storing visitors' profile. In the case that the number of users exceeds the capacity of the VLR due to mobility, database overflow occurs. In this paper, we propose a new policy, the least frequent replacement policy, which selects the least frequently accessed users as replacement candidates. Extensive simulation is carried out for predicting the performance of the existing replacement policies and the proposed least frequent policy. Our simulation results show that the most idle and least frequent policies outperform the inactive and random replacement policies in most cases and that the least frequent policy performs slightly better than the most idle replacement policy.
Chi-chun Lo - One of the best experts on this subject based on the ideXlab platform.
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Diminishing capacity requirement for mobility database in wireless ATM
Journal of Circuits Systems and Computers, 2004Co-Authors: Chi-chun LoAbstract:In wireless ATM, visitor location register (VLR) is the database that supports mobility management. In case the number of roaming users exceeds the VLR supports, the arriving users cannot receive any service. To solve the problem, the Random Replacement (RR) policy randomly selects a victim record in VLR to be replaced with the record of the arriving user. The quality of services for the victim user will certainly drop. Therefore, the proportion of affected users is not allowed to exceed a tolerable threshold. Apparently, VLR size is the key factor of the threshold. The cost for maintaining a VLR increases significantly as its size grows. So, how to utilize the capacity efficiently is an important issue in VLR planning. We propose a Second Chance Replacement (SCR) policy to reduce the requirements for VLR capacity. As compared with the RR policy, the discrete-event simulation results show that the SCR policy can save 2.5% to 28% VLR size under various QoS thresholds.
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N-class replacement policy for resolving mobility database overflow
International Conference on Communication Technology Proceedings 2003. ICCT 2003., 2003Co-Authors: Chi-chun LoAbstract:visitor location register (VLR) may overflow due to the limited capacity. By replacing an existing record, the overflow users can still receive services. The most-idle replacement (MR) policy was proposed to improve the performance of the random replacement (RR) policy. The MR policy seems to be optimum and outperforms the RR policy significantly. However, the MR policy has potential limitations. Accordingly, we propose the N-class replacement (NR) policy to overcome the drawbacks. Moreover the simulation results show that the NR policy outperforms the MR policy in most scenarios investigated in our study. As N increases, the improvement becomes more considerable.
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Overflow control in mobile communication using N-class replacement
Electronics Letters, 2003Co-Authors: Chi-chun LoAbstract:A strategy called N-class replacement (NR) policy is proposed to overcome visitor location register (VLR) overflow in a mobile communication system. The NR policy requires only few bits in the VLR record. It is feasible for separated VLR databases in real mobile networks. For the rate of excellent replacement, the simulation results show that the NR policy outperforms currently proposed policies.
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GLOBECOM - Second chance replacement policy for mobile database overflow
Global Telecommunications Conference 2002. GLOBECOM '02. IEEE, 2002Co-Authors: Chi-chun LoAbstract:The visitor location register (VLR) is used to store temporary records for roaming users. Due to the limited capacity, the VLR may be full. This phenomenon is called VLR overflow. By replacing an existing record, the incoming user can still receive services. The most-idle replacement (MR) policy was proposed to improve the random replacement (RR) policy. The MR policy is almost the optimum method and outperforms RR policy significantly. However, the MR policy requires global information to find the most-idle user. It needs considerable extra cost and is unfeasible due to the separated VLR databases in the real mobile network. Therefore, we propose the second chance replacement (SCR) policy to overcome these drawbacks. The SCR policy needs only an additional bit in the record. Partial information is sufficient for our method, so it is feasible in the real mobile network. Moreover, the simulation results show that the SCR policy outperforms the MR policy in most scenarios investigated in our study.
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Second chance replacement policy for mobile database overflow
Global Telecommunications Conference 2002. GLOBECOM '02. IEEE, 2002Co-Authors: Chi-chun LoAbstract:The visitor location register (VLR) is used to store temporary records for roaming users. Due to the limited capacity, the VLR may be full. This phenomenon is called VLR overflow. By replacing an existing record, the incoming user can still receive services. The most-idle replacement (MR) policy was proposed to improve the random replacement (RR) policy. The MR policy is almost the optimum method and outperforms RR policy significantly. However, the MR policy requires global information to find the most-idle user. It needs considerable extra cost and is unfeasible due to the separated VLR databases in the real mobile network. Therefore, we propose the second chance replacement (SCR) policy to overcome these drawbacks. The SCR policy needs only an additional bit in the record. Partial information is sufficient for our method, so it is feasible in the real mobile network. Moreover, the simulation results show that the SCR policy outperforms the MR policy in most scenarios investigated in our study.
N.h. Vaidya - One of the best experts on this subject based on the ideXlab platform.
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SRDS - Tolerating visitor location register failures in mobile environments
Proceedings Seventeenth IEEE Symposium on Reliable Distributed Systems (Cat. No.98CB36281), 1998Co-Authors: S. Biaz, N.h. VaidyaAbstract:For mobile users who move frequently but receive relatively rare calls, a forwarding scheme has been shown to outperform the normal IS-41 location management scheme. But the forwarding scheme is more vulnerable to failure of intermediate visitor location registers (VLRs) than the IS-41 scheme. We propose two simple variations to the forwarding scheme to address the fault tolerance weakness. One is based on the idea of maintaining two paths from the home location server to the last VLR. The second scheme is based on the knowledge of the neighbors of the faulty VLR. We evaluate and compare the performance of these location management schemes.
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Tolerating visitor location register failures in mobile environments
Proceedings Seventeenth IEEE Symposium on Reliable Distributed Systems (Cat. No.98CB36281), 1998Co-Authors: S. Biaz, N.h. VaidyaAbstract:For mobile users who move frequently but receive relatively rare calls, a forwarding scheme has been shown to outperform the normal IS-41 location management scheme. But the forwarding scheme is more vulnerable to failure of intermediate visitor location registers (VLRs) than the IS-41 scheme. We propose two simple variations to the forwarding scheme to address the fault tolerance weakness. One is based on the idea of maintaining two paths from the home location server to the last VLR. The second scheme is based on the knowledge of the neighbors of the faulty VLR. We evaluate and compare the performance of these location management schemes.
Wen-nung Tsai - One of the best experts on this subject based on the ideXlab platform.
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location tracking with distributed HLR's and pointer forwarding
IEEE Transactions on Vehicular Technology, 1998Co-Authors: Wen-nung TsaiAbstract:location tracking operations in a personal communications service (PCS) network are expensive. A location tracking algorithm called pointer forwarding has been proposed to reduce the location update cost. The key observation behind forwarding is that if users change PCS registration areas (RAs) frequently, but receive calls relatively infrequently, it should be possible to avoid registrations at the home-location register (HLR) database by simply setting up a forwarding pointer from the previous visitor-location register (VLR). Calls to a given user will first query the user's HLR to determine the first VLR, which the user was registered at, and then follow a chain of forwarding pointers to the user's current VLR. To reduce the "find" cost in call delivery, the PCS provider may distribute HLR databases in the network. This paper integrates the concept of distributed HLRs with pointer forwarding, and the new scheme is referred to as the pointer forwarding with distributed HLR (PFDHLR). Since no registration to the HLR is performed in the pointer forwarding scheme when a user moves to the new locations, the cost of updating multiple HLRs is eliminated in PFDHLR. Our study indicates that PFDHLR may significantly reduce the mobility management cost compared with the single HLR approach.
