Modeling and Management of Location and Mobility

Location modeling represents inclusive mobile objects and their relationship in space, dealing with how to describe a mobile object’s location. The goal of mobility modeling, on the other hand, is to predict or statistically estimate the movement of mobile objects. With the increasing demand for multimedia applications, location-aware services, and system capacity, many recognize that modeling and management of location and mobility is becoming critical to locating mobile objects in wireless information networks. Mobility modeling and location management strongly influence the design and performance of wireless networks in many aspects, such as routing, network planning, handoff, call admission control, and so forth. In this chapter, we present a comprehensive survey of mobility and location models, and schemes used for location-mobility management in cellular and ad hoc networks, which are discussed along with necessary, but understandable, formulation, analysis, and discussions.

Broadcast Data Placement over Multiple Wireless Channels

The advances in computer and communication technologies made possible an ubiquitous computing environment were clients equipped with portable devices can send and receive data anytime and from anyplace. Due to the asymmetry in communication and the scarceness of wireless resources, data broadcast is widely employed as an effective means in delivering data to the mobile clients. For reasons like heterogeneous communication capabilities and variable quality of service offerings, we may need to divide a single wireless channel into multiple physical or logical channels. Thus, we need efficient algorithms for placing the broadcast data into these multiple channels so as to reduce the client access time. The present chapter discusses algorithms for placing broadcast data to multiple wireless channels, which cannot be coalesced into a lesser number of high-bandwidth channels, assuming that there are no dependencies among the transmitted data. We give an algorithm for obtaining the optimal placement to the channels and explain its limitation since it is computationally very demanding and thus unfeasible. Then, we present heuristic schemes for obtaining suboptimal solutions to the problem of reporting on their implementation cost and their relative performance.

Data Broadcasting in a Mobile Environment

The advances in mobile devices and wireless communication techniques have enabled anywhere, anytime data access. Data being accessed can be categorized into three classes: private data, shared data, and public data. Private and shared data are usually accessed through on-demand-based approaches, while public data can be most effectively disseminated using broadcasting. In the mobile computing environment, the characteristics of mobile devices and limitations of wireless communication technology pose challenges on broadcasting strategy as well as data-retrieval method designs. Major research issues include indexing scheme, broadcasting over single and parallel channels, data distribution and replication strategy, conflict resolution, and data retrieval method. In this chapter, we investigate solutions proposed for these issues. High performance and low power consumption are the two main objectives of the proposed schemes. Comprehensive simulation results are used to demonstrate the effectiveness of each solution and compare different approaches.

Extensible Platform for Location-Based Services Deployment and Provisioning

Location-based services can be considered the most rapidly expanding field of the mobile communications sector. The proliferation of mobile-wireless Internet, the constantly increasing use of handheld, mobile devices and position-tracking technologies, and the emergence of mobile computing prepared the grounds for the introduction of this new type of services with an impressively large application domain and use range. The combination of position-fixing mechanisms with location-dependent, geographical information can offer truly customised, personal communication services through the mobile phone or other type of devices. In this chapter, motivated by the technology advances in the aforementioned areas, we present a generic platform for delivering Location-based services (LBSs) to the nomadic user. The platform features a modular architecture, which can be easily extended. Although the overall architecture of the platform is discussed, the focus is on the technical specifications, the design, the functionality, and the prototype implementation of its central component, the kernel. The kernel is responsible for coordinating communication with the various pluggable components in order to provide the full range of operations involved in the LBS delivery chain (i.e., from initial deployment to invocation, execution, and delivery of results).

Service Discovery in Wireless and Mobile Networks

Service discovery is an important component of wireless and mobile network systems. An efficient service discovery mechanism would ensure high availability of services to users and applications, and high utilization of services. In this chapter, we discuss various issues and challenges facing the design and selection of a proper service discovery mechanism. This chapter also investigates service discovery mechanisms such as SLP, Jini, Salutation, and others, and assesses their suitability for applications in wireless and mobile environments.

Mobility Management in Mobile Computing and Networking Environments

This chapter analyzes and proposes some mobility management models and schemes by taking into account their capability to reduce search and location update costs in wireless mobile networks. The first model proposed is called the built-in memory model; it is based on the architecture of the IS-41 network and aims at reducing the home-location-register (HLR) access overhead. The performance of this model was investigated by comparing it with the IS-41 scheme for different call-to-mobility ratios (CMRs). Experimental results indicate that the proposed model is potentially beneficial for large classes of users and can yield substantial reductions in total user-location management costs, particularly for users who have a low CMR. These results also show that the cost reduction obtained on the location update is very significant while the extra costs paid to locate a mobile unit simply amount to the costs of crossing a single pointer between two location areas. The built-in memory model is also compared with the forwarding pointers’ scheme. The results show that this model consistently outperforms the forwarding pointers’ strategy. A second location management model to manage mobility in wireless communications systems is also proposed. The results show that significant cost savings can be obtained compared with the IS-41 standard location-management scheme depending on the value of the mobile units’ CMR.

Indexing and Clustering of Wireless Broadcast Data

This chapter describes some data management issues that are necessary for wireless data broadcasting. The major topics we include in this chapter are (a) broadcast data indexing and (b) broadcast data clustering. Mobile clients can access the wireless data in an energy-efficient way with the index on the broadcast channel, and the well-clustered broadcast data enables mobile clients to access the wireless data in a short latency.

Mobile Cache Management

This chapter introduces advanced client-side data-caching techniques to enhance the performance of mobile data access. The authors address three mobile caching issues. The first is the necessity of a cache replacement policy for realistic wireless data-broadcasting services. The authors present the Min-SAUD policy, which takes into account the cost of ensuring cache consistency before each cached item is used. Next, the authors discuss the caching issues for an emerging mobile data application, that is, location-dependent information services (LDISs). In particular, they consider data inconsistency caused by client movements and describe several location-dependent cache invalidation schemes. Then, as the spatial property of LDISs also brings new challenges for cache replacement policies, the authors present two novel cache replacement policies, called PA and PAID, for location-dependent data.

Push and Pull Systems

Data broadcasting has emerged as an efficient way for the dissemination of information over asymmetric wireless environments where the needs of the various users of the data items are usually overlapping. In such environments, data broadcasting stands to be an efficient solution since the broadcast of a single information item is likely to satisfy a possibly large number of users. Communications asymmetry is due to a number of facts, the most important being equipment, network, and application asymmetry. This chapter starts with a discussion of preliminary issues and terminology for asymmetric environments for data broadcasting. The chapter then discusses broadcast schedule construction for systems employing a single broadcast channel, schedule construction for systems employing multiple broadcast channels, and schedule construction for systems that take into account the effect of reception errors. It then presents an algorithm that tries to provide better support for clients whose access patterns deviate a lot form the overall access pattern of the client population. It also presents algorithms for environments where item requests by clients are dropped if not served in a certain time period. Brief comments on issues that affect performance of the discussed data broadcasting methods are also made.

Indexing Mobile Objects

Mobile computing emerged as a new application area due to recent advances in communication and positioning technology. As David Lomet (2002) notices, a substantial part of the conducted work refers to keeping track of the position of moving objects (automobiles, people, etc.) at any point in time. This information is very critical for decision making, and, since objects’ locations may change with relatively high frequency, this calls for providing fast access to object location information, thus rendering the indexing of moving objects a very interesting as well as crucial part of the area. In this chapter we present an overview on advances made in databases during the last few years in the area of mobile object indexing, and discuss issues that remain open or, probably, are interesting for related applications.