Broadcast operation, which disseminates information network-wide, is very important in multi-hop wireless networks. Due to the broadcast nature of wireless media, not all nodes need to transmit in order for the message to reach every node. Previous work on broadcast support can be classified as probabilistic (each node rebroadcasts a packet with a given probability) or deterministic approaches (nodes pre-select a few neighbors for rebroadcasting). In this paper, we show how network-coding can be applied to a deterministic broadcast approaches, resulting in significant reductions in the number of transmissions in the network. We propose two algorithms, that rely only on local two-hop topology information and makes extensive use of opportunistic listening to reduce the number of transmissions: 1) a simple XOR-based coding algorithm that provides up to 45% gains compared to a non-coding approach and 2) a Reed-Solomon based coding algorithm that determines the optimal coding gain achievable for a coding algorithm that relies only on local information, with gains up to 61% in our simulations. We also show that our coding-based deterministic approach outperforms the coding-based probabilistic approach presented in (C. Fragouli et al, 2006).

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 new paradigm of dynamic spectrum access (DSA) networks aims to provide opportunistic access to large parts of the underutilized spectrum. The majority of research in this area has focused on free-for-all, uncoordinated access methods common in ad-hoc military applications (Horne, W. 2003; Leaves, P. et al., 2002; Lehr, W. et al., 2002; Schafer, D.J.; To/spl uml/njes, R., 2002). We argue that a simpler pragmatic approach that offers coordinated, spatially aggregated spectrum access via a regional spectrum broker is more attractive in the immediate future. We first introduce two new concepts, coordinated access band (CAB) and statistically multiplexed access (SMA), to the spectrum. We describe their implementation in the new DIMSUMnet (dynamic intelligent management of spectrum for ubiquitous mobile-access network) architecture consisting of four elements: base stations; clients; a radio access network manager (RAN-MAN) that obtains spectrum leases; a per-domain spectrum broker that controls spectrum access. We also discuss in detail various issues in the design of spectrum brokers and spectrum allocation policies and algorithms.

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.

Mobile phones are quickly becoming one of the most ubiquitous wireless consumer devices. Separately, Internet services are growing by leaps and bounds. Thus, an interesting area of research is to see if and how the two can be married together to provide wireless ubiquitous access to the ever-growing Internet services. We highlight the challenges and issues in providing Internet services to mobile phones. As an example, we describe and examine a research prototype called Wireless Data Server, which provides, among other services, wireless email service to mobile phone users.