Using wireless devices to provide location-based services is an emerging area, which leads to increasing demand and diverse requirements on the services including those in asset tracking, social networking, mobile commerce and advertising, and physical security. This thesis focuses on providing accurate and secure location-based services in mobile wireless networks including developing accurate and low cost device-based and device-free localization system, achieving efficient and effective data access and retrieval, and facilitating secure communication among mobile devices .;First of all, location information plays a key role enabling these applications in location-based services. To ensure the accuracy of localization, we design and develop accurate and low-cost localization system by using multi-frequencies and multi-powers. We focus on designing and developing techniques that characterize the multipath effect on localization algorithms when multiple sets of RSS data (via different frequency and power level) can be selected and used in the system.;Furthermore, although device-based localization have attracted much attention in location-based services, device-free passive localization is an emerging technology that enables locating targets without carrying any radio devices or actively partic- ipating in the wireless localization process. We demonstrate that our framework is flexible to work with any device-free localization method using signal strength and provides significant performance improvement under dynamically changing speed of the target. .;To provide effective location-based services, besides the localization accuracy, efficient data access and retrieval needs to be achieved in fully distributed wireless networks. The development of data-centric storage has enabled efficient data dissem- ination of wireless networks. We propose mechanisms to predict near likely nodes to achieve efficient data storage and retrieval in mobile wireless networks.;In addition to provide effective and efficient localization-based services, we explore to facilitate secure mobile devices while providing the location-based services. We thus propose a fully decentralized key management framework by utilizing the cryptography-based secret sharing method for mobile wireless devices. We develop the Transitive Prediction (TRAP) protocol that helps to maximize the chances of successful key share reconstruction and minimize the communication overhead, and in the meanwhile avoiding the degradation of the security guarantee of data access.
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