A traditional approach to indoor tracking utilizes non-RF ranging techniques, such as infrared or ultrasound. The problem with these non-RF ranging techniques is that they do not work well when the tracking devices are buried in users' wallets or bags. As a result, there has been considerable interest in using only RF techniques for indoor tracking. Existing RF-only techniques, however, typically require a costly site survey and a floor-plan. In this paper, we present the MERIT system that we designed, implemented, and evaluated. MERIT is significantly different from existing systems in that it is pure RF-based yet it does not require a site survey nor a floor-plan. MERIT tracks users to a room granularity, and it can disambiguate neighboring rooms. This disambiguation is challenging because RF signals can traverse through walls. Also, because of indoor multipath interference, it is difficult to correlate signal strength with distance. In this work, we proposed two techniques for accurate disambiguation: spatial diversity and RF reflector. In our evaluation MERIT achieved an accuracy of 98.9%. MERIT was first conceived for a telecommunication application - intelligent telephone call routing, but it can also be used for other location-aware services

The third-generation (3G) wide area wireless networks and 802.11 local area wireless networks possess complementary characteristics. 3G networks promise to offer always-on, ubiquitous connectivity with relatively low data rates. 802.11 offers much higher data rates, comparable to wired networks, but can cover only smaller areas, suitable for hot-spot applications in hotels and airports. The performance and flexibility of wireless data services would be dramatically improved if users could seamlessly roam across the two networks. In this paper, we address the problem of integration of these two classes of networks to offer such seamless connectivity. Specifically, we describe two possible integration approaches - namely tight integration and loose integration and advocate the latter as the preferred approach. Our realization of the loose integration approach consists of two components: a new network element called IOTA gateway deployed in 802.11 networks, and a new client software. The IOTA gateway is composed of several software modules, and with cooperation from the client software offers integrated 802.11/3G wireless data services that support seamless intertechnology mobility, Quality of Service (QoS) guarantees and multiprovider roaming agreements. We describe the design and implementation of the IOTA gateway and the client software in detail and present experimental performance results that validate our architectural approach.

This paper addresses a bottleneck problem in mobile file systems: the propagation of updated large tiles from a weakly-connected client to its servers. It proposes an efficient mechanism called operation shipping or operation-based update propagation. In the new mechanism, the client ships the user operation that updated the large files, rather than the files themselves, across the weak network. (in contrast, existing file systems use value shipping and ship the files.) The user operation is sent to a surrogate client that is strongly connected to the servers. The surrogate replays the user operation, regenerates the files, checks whether they are identical to the originals, and, it so, sends the files to the servers on behalf of the client. Care has been taken such that the new mechanism does not compromise correctness or server scalability. For example, we show how forward error correction (FEC) can restore minor reexecution discrepancies and, thus, make operation shipping work with more applications. Operation shipping can be further classified into two types: application-transparent and application-aware. Their feasibilities and benefits have been demonstrated by the design, implementation, and evaluation of a prototype extension to the Coda File System. In our controlled experiments, operation shipping achieved substantial performance improvements-network traffic reductions from 12 times to nearly 400 times and speedups in the range of 1.4 times to nearly 50 times.