In mobile networks, the location of a mobile user needs to be traced for successful and efficient call delivery. In existing cellular networks, as a mobile user changes his/her location area (LA), a location registration request is sent to the home location register (HLR) to update the user profile to point to the new LA. With a large number of mobile subscribers, this conventional registration strategy will incur a high volume of signaling traffic. We propose a new location registration strategy, called Group Registration (GR), which efficiently reduces the location registration cost by reporting location changes to the HLR for multiple mobile terminals (MTs) in a single location update request message. Specifically, the IDs of the MTs newly moving into an LA are buffered and sent to the HLR for location update in the route response message of the next incoming call to any MT in the LA. An analytic model is developed and numerical results are presented. It is shown that the proposed GR strategy can achieve significant cost reductions compared to the conventional strategy and the local anchor strategy over a wide range of system parameters. Moreover, the GR strategy results in a much smaller call delivery latency than the local anchor strategy.

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.

In this paper, a new location registration strategy - group registrations for mobile networks is proposed, in which instead of sending a location registration request to the home location register (HLR) for each registration area (RA) change of a mobile terminal (MT), the identifications of the MTs newly moving into an RA are buffered and sent to the HLR for location registration when the next incoming call to the RA occurs, i.e., the buffered MT identifications are forwarded to the HLR in the route response message of the call. Upon RA change, a forwarding pointer is set up from the MT's local anchor to its new visitor location register (VLR), so that incoming calls to the MT can be delivered before the MT's local anchor is changed to its current VLR via the next group registration. An analytic model is developed and numerical results are presented. It is revealed that compared to the conventional RA-based location registration scheme, the group registration strategy can achieve a significant cost savings over a wide range of system parameters.

A user location information distribution strategy is proposed for mobile systems. Local anchors (LAs), replicated databases and forwarding pointers are applied in an integrated way that greatly reduces the location update rate and the call delivery cost incurred by location tracking. In particular, the visitor location registers (VLRs) associated with a user's home and workplace are selected as the user's LAs, which are connected by a forwarding pointer chain. When the user changes their registration area (RA) within a local signal transfer point (LSTP) region, the new location is reported to the home location register (HLR) and to the replicas. In the call delivery procedure, if a call orginates from one of the LAs or replicas, the HLR does not need to be queried. An analytic model is developed and numerical examples are given to compare the performance of the proposed scheme, the standard scheme, the replication scheme and the local anchoring scheme. The results show that the proposed strategy outperforms the other three strategies over a wide range of system parameters.

This paper introduces a distributed hierarchical database architecture for location management in global personal communications system (PCS) networks with the location-independent numbering plan. The proposed structure 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. Due to the localized nature of calling and mobility patterns, this scheme effectively reduces the database loads and signaling traffic incurred by the location update and call delivery procedures. Moreover, based on the flat numbering plan, two memory-resident access structures-the memory-resident direct file and the T-tree are proposed for the location databases to further improve the database throughput. Analytical models and numerical examples are presented to evaluate the response time and the storage capacity required for each location database. Results show that our method can produce a high-throughput database system, which is crucial for the deployment of high-capacity PCS systems in the future. In addition, modifications to the data structure, the insert algorithm, and the delete algorithm for the T-tree are proposed to enhance the performance of the T-tree.

Mobility tracking is to keep track of the users locations for call delivery. In standards, such as IS-41 and GSM, the two level hierarchy of location databases is used: the home location register (HLR) and the visitor location register (VLR). As the number of mobile subscribers increases, the HLR may become the system bottleneck. To alleviate the burden on the HLR, a number of auxiliary strategies based on the HLR-VLR architecture have been proposed. These strategies include the forwarding strategy (FS), the anchoring strategy (AS), the caching strategy (CS), and the replication strategy (RS). However, each of these strategies is only suitable for a certain type of users with a specific range of call to mobility ratios (CMRs). In reality, a user may change his/her mobility patterns frequently. To cope with such time-varying mobility patterns efficiently, an integrated strategy is proposed. In particular, the VLRs associated with a user's home and workplace, where the user spends considerable time periods, are selected as the user's local anchors (LAs), which are connected by a forwarding pointer chain. The VLRs from which relatively high call rates to the user originate are selected as the replicas. When the user changes registration area (RA) within a local signal transfer point (LSTP) region, the new location is updated at one of the LAs. Otherwise, the new location is reported to the HLR and the replicas. In the call delivery procedure, if a call originates from one of the LAs or replicas, the HLR does not need to be queried. An analytic model that can capture actual user mobility characteristics is used for performance evaluation. Results show that in terms of the end-to-end call setup delay and location update delay, the proposed strategy outperforms the standard scheme used in GSM and IS-41, the RS scheme, and the AS scheme over a wide range of system parameters.

This paper introduces a location-based locating strategy for Personal Communication Services (PCS) systems. In the proposed scheme, location updates are based on the value of a movement counter. The update of the movement counter is based on information on the locations visited by a mobile terminal (MT) since the last location update. In particular, the cell identifiers and the corresponding movement counter values are maintained in the MT for a part of the visited cells since the last location update. When the MT enters a cell whose identifier is not stored in the MT, the movement counter increases by one. If the movement counter reaches the update threshold, a location update is triggered; otherwise, the cell identifier and the corresponding movement counter value are stored in the MT. When the MT enters a cell whose identifier is in the MT, the movement counter is assigned with the counter value kept in the MT for this cell, and all cells with greater counter values in the MT are removed. The proposed scheme allows the dynamic selection of the update threshold according to each user's calling and mobility patterns. Analytical and simulation models have been developed to compare the proposed scheme with both the movement-based scheme and the distance-based scheme. Results demonstrate that when the call-to-mobility ratio (CMR) is low, the proposed scheme can achieve a significant cost reduction compared to the movement-based scheme. For example, when the CMR is 0.01, a savings of around 25% in the optimal total cost per call arrival is achieved with the proposed scheme. Moreover, the proposed scheme is easier to implement than the distance-based scheme.

This paper presents two location tracking strategies (LS-I and LS-II) for personal communications services (PCS) systems. In the proposed schemes, the movement history of a mobile terminal (MT) since the last location update is taken into account in making a location update decision. In particular, before reaching the update threshold the movement counter is increased only after the MT visits a new cell. When the MT revisits a cell since the last location update, in the LS-I scheme the counter remains unchanged, while in the LS-II scheme the counter is assigned with the old counter value when the MT visited this cell last time. Analytic and simulation results demonstrate that when the call-to-mobility ratio (CMR) is low, the proposed schemes can achieve a significant cost reduction compared to the movement-based scheme.