A rate-distortion framework for information-theoretic mobility management

In this paper, we develop an analytical model of the signaling costs due to location update and paging for the radio interface in mobile communications networks. This model accounts for the effects that the savings brought by different algorithms have on the total Location Management (LM) costs. It also takes into account the trade-off between the location update and paging costs, showing that those strategies that achieve savings in the location update costs deliver a larger overall improvement in the total LM costs than those algorithms focusing on the minimization of the paging costs. Moreover, leveraging the factors studied to obtain this model, we also analyze the overall LM costs including the fixed network part.

In this paper, we propose two information-theoretic techniques for efficiently trading off the location update and paging costs associated with mobility management in wireless cellular networks. Previous approaches always attempt to accurately convey a mobile's movement sequence and hence cannot reduce the signaling cost below the entropy bound. Our proposed techniques, however, exploit the rate distortion theory to arbitrarily reduce the update cost at the expense of an increase in the corresponding paging overhead. To this end, we describe two location tracking algorithms based on spatial quantization and temporal quantization, which first quantize the movement sequence into a smaller set of codewords and then report a compressed representation of the codeword sequence. Although the spatial quantization algorithm clusters individual cells into registration areas, the more powerful temporal quantization algorithm groups sets of consecutive movement patterns. The quantizers themselves are adaptive and periodically reconfigure to accommodate changes in the mobile's movement pattern. Simulation study with synthetic and real movement traces for both single-system and multisystem cellular networks demonstrate that the proposed algorithms can reduce the mobile's update frequency to 3-4 updates/day with reasonable paging cost, low computational complexity, storage overhead, and codebook updates.

LOCATION MANAGEMENT AND COST PLANNING FOR PERSONAL COMMUNICATION SYSTEMS

Location management deals with how to track mobile users within the cellular network. It consists of two basic operations: location update and paging. The total location management cost is the sum of the location update cost and the paging cost. Location areas and reporting centers are two popular location management schemes. The motivation for the study is the observation that the location update cost difference between the reporting centers scheme and the location areas scheme is small whereas the paging cost in the reporting centers scheme is larger than that in the location areas scheme. The paper compares the performance of the location areas scheme and the reporting centers scheme under aggregate movement behavior mobility models by simulations. Simulation results show that the location areas scheme performs about the same as the reporting centers scheme in two extreme cases, that is, when a few cells or almost all cells are selected as the reporting cells. However, the location areas scheme outperforms the reporting centers scheme at the 100% confidence level with all call-to-mobility ratios when the reporting cells divide the whole service area into several regions.

Application of AI techniques for locating mobile terminals in mobile wireless cellular networks: A novel paging scheme

A location tracking scheme called as a group location tracking (GLT) is proposed to reduce the location update cost for terrestrial transportation systems (TSs) in personal communication networks. To provide user mobility in a TS, we introduce two new concepts, virtual visitor location register (VVLR) and representative identity (RID). A VVLR is used to provide current location of a TS and an RID of a TS is used to represent a TS and the group of all users on the TS. When a TS moves into a new registration area, the GLT scheme based on an RID of the TS and a VVLR updates location information by a group location update request message instead of individual location update request messages generated by each user in the TS. We analyze the performance of our proposed scheme in view of the signaling load and call delivery failure. Compared with the IS-41 location tracking scheme, the GLT scheme significantly reduces frequent location updates caused by the high mobility of a TS and a large number of users in a TS.

Many applications in vehicular ad hoc networks (VANETs) need to have the knowledge of vehicles' location information, such as location-aware routing, vehicle management, and emergency notifications. Therefore, how to provide efficient location services has become an important issue in VANETs. Three mechanisms must be considered when designing a location service protocol: namely the delegation of location servers, the location update and query mechanisms. Existing location service protocols for VANETs may either incur high location update cost or cause long location query latency. To improve existing works, we propose a cost-based location service protocol for VANETs. A set of cost functions are defined to evaluate the performance of the location service protocol. According to the evaluation results of these cost functions, we can delegate proper number of location servers at proper locations so as to reduce the cost of location update and query. Simulation results justify the efficiency of the proposed protocol.

A distributed mobility management scheme using a class of uniform quorum systems (UQS) is proposed for ad hoc networks. In the proposed scheme, location databases are stored in the network nodes themselves, which form a self-organizing virtual backbone within the flat network structure. The databases are dynamically organized into quorums, every two of which intersect at a constant number of databases. Upon location update or call arrival, a mobile's location information is written to or read from all the databases of a quorum, chosen in a nondeterministic manner. Compared with a conventional scheme [such as the use of home location register (HLR)] with fixed associations, this scheme is more suitable for ad hoc networks, where the connectivity of the nodes with the rest of the network can be intermittent and sporadic and the databases are relatively unstable. We introduce UQS, where the size of the quorum intersection is a design parameter that can be tuned to adapt to the traffic and mobility patterns of the network nodes. We propose the construction of UQS through the balanced incomplete block designs. The average cost, due to call loss and location updates using such systems, is analyzed in the presence of database disconnections. Based on the average cost, we investigate the tradeoff between the system reliability and the cost of location updates in the UQS scheme. The problem of optimizing the quorum size under different network traffic and mobility patterns is treated numerically. A dynamic and distributed HLR scheme, as a limiting case of the UQS, is also analyzed and shown to be suboptimal in general. It is also shown that partitioning of the network is sometimes necessary to reduce the cost of mobility management.

SUMMARY This letter proposes an improved timer-based location management scheme for packet-switched (PS) mobile communication systems. Compared to the conventional timer-based scheme with a single timer threshold, a new timer-based scheme with two timer thresholds is proposed to accommodate the bursty data traffic characteristics of PS service. The location update and paging costs of the proposed scheme are analyzed and compared with those of the conventional scheme. We show that the proposed scheme outperforms the conventional scheme in terms of total cost of both location update and paging with an appropriate selection

To accommodate the growth in the user population and network size in mobile environments, hierarchical architectures of location databases have been proposed. Recent studies showed that the signaling traffic and processing overhead of location updates is expected to grow tremendously, leading to poor performance. The authors present a Profile based Hierarchical location management Scheme (PHS) that focuses on reducing the cost of updates while keeping the lookup cost low. Our proposal is motivated by the observation that users follow repetitive patterns that can be profiled and predicted with reasonable cost, allowing users to send updates occasionally and not on every move. Further, it deploys a simple prediction technique that reduces the uncertainty of a user's location. We quantify the costs and benefits of PHS for several mobility patterns and show that it can result in up to 60% reduction in the update cost with minimal increase (7%) in lookup cost.

Cellular mobile systems provides access to a wide range of services and allow mobile terminals (MTs) to move randomly from one place to another within a well-defined geographical area. Due to the growing number of mobile users, global connectivity, and the small size of cells, one of the most critical issues regarding these networks is location management. The challenging task in a cellular system is to track the location of the mobile users effectively so that the connection establishment cost and delay is low. In recent years, several strategies have been proposed to improve the performance of the location management procedure in cellular networks. In this paper, we propose an intelligent approach by taking the User Profile History (UPH); to reduce the location update cost by combining Back-Propagation Algorithm and Cascaded Correlation Neural Network. The implementation of this strategy has been subject to extensive tests. The results obtained confirm the efficiency of UPH in significantly reducing the costs of both location updates and call delivery procedures when compared to the various other strategies well-known in the literature.

Managing location information of mobile hosts is an important issue in mobile computing systems. There is a trade-off between location update and search, when a mobile host moves. This paper proposes a simple quorum-based distributed dynamic location management method using location registers. The cost of location updates and searches is reduced by our method because the location information of mobile hosts is managed efficiently in a subset of location registers instead of in all location registers. In our method, the subset of location registers is dynamically changed, and the load of each location register is balanced by considering query rate for mobile hosts. The performance of the proposed algorithm is evaluated in terms of the total cost of a location update and a location search, and is compared with Prakash's algorithm.

The paper proposes an integrated location management scheme, based on our previously proposed novel rule-based paging scheme (RBPS) for reducing the cost of terminal paging in a cellular wireless environment. We extend that scheme to propose a complete location management scheme. This requires application of RBPS together with a judicious movement based location update (LU) scheme. Numerical results show that the proposed integrated location management scheme, called RBPS*, not only attempts to resolve the issue of inherent tradeoff between the cost components, comprised of paging and LU cost, but also does reduce the total cost for location management compared to the other schemes. RBPS* significantly outperforms RBPS and the GSM-adopted blanket paging scheme along with movement based LU. When compared with the popular shortest distance first (SDF) scheme, results are again encouraging. The proposed scheme, RBPS*, is a generic one and can be deployed on-line. It has the potential for use in next generation wireless networks, irrespective of any standards.

On the problem of location update and terminal paging, many schemes using ring-paging strategies have been proposed. However, sequentially paging the rings surrounding the mobile user's last updated location may cause large paging cost. We propose a direction-based location update (DBLU) scheme using a line-paging strategy to reduce the paging cost. A moving direction identification mechanism using only simple computations detects the change of moving direction and updates the mobile's location. The numerical results show that our DBLU scheme achieves good performance when the paging cost is high.

Future personal communication service (PCS) networks consider smaller cells to accommodate continuously growing population of subscribers. Frequently performed location updates caused by such an infrastructure incur extensive signaling and consequently higher cost. Thus, new strategies are demanded to locate mobile users more efficiently. Among several proposals, the direction-based location update (DBLU) scheme uses a dynamic strategy such that the mobile users update their locations only when a change of direction occurs. To locate users, the system pages cells along the direction of initial move. The scheme works well when the change of direction is infrequent and the ratio of location update cost to paging cost is low. Otherwise, the location update, and consequently the overall cost increase significantly. To attack this problem, we propose an enhanced direction-based location update (EDBLU) scheme, which takes into account both the moving distance and the moving direction. We analyze the performance of the EDBLU under different mobility patterns and call-to-mobility ratios based on a 2D Markov walk model. The numerical results demonstrate that the proposed scheme augments the performance reported by the distance-based and the direction-based methods.