Wireless networks based on 802.11a/b/g protocols have gained wide-spread acceptance in both enterprise as well as home networks. However, these devices lack native support for many advanced features such as service differentiation, etc., that are required in specific application domains. In this paper, we propose Covenant, a software based cooperative scheduling framework to provide a rich set of features for applications that require nodes to cooperate with each other to satisfy system-wide objectives. We propose a novel 2 1/2-stage pipeline architecture as an efficient mechanism to implement cooperative scheduling among multiple nodes. We demonstrate how Covenant can be easily implemented in software, thus requiring absolutely no hardware or firmware changes to the already widely installed base of 802.11a/b/g based wireless devices. We also evaluate, using a real Linux based test-bed with Covenant drivers, the efficacy of the approach on two different scheduling disciplines: proportional priority and strict priority. We demonstrate that these scheduling disciplines are effective in providing service guarantees to multimedia applications even in the presence of other competing traffic.

Wireless access networks scale by replicating base stations geographically and then allowing mobile clients to seamlessly "hand off" from one station to the next as they traverse the network. However, providing the illusion of continuous connectivity requires selecting the right moment to handoff and the right base station to transfer to. Unfortunately, 802.11-based networks only attempt a handoff when a client's service degrades to a point where connectivity is threatened. Worse, the overhead of scanning for nearby base stations is routinely over 250 ms - during which incoming packets are dropped - far longer than what can be tolerated by highly interactive applications such as voice telephony. In this paper we describe SyncScan, a low-cost technique for continuously tracking nearby base stations by synchronizing short listening periods at the client with periodic transmissions from each base station. We have implemented this SyncScan algorithm using commodity 802.11 hardware and we demonstrate that it allows better handoff decisions and over an order of magnitude improvement in handoff delay. Finally, our approach only requires trivial implementation changes, is incrementally deployable and is completely backward compatible with existing 802.11 standards.

We present a location detection system for tracking multimedia appliances and users within a wireless local area network (WLAN) enabled home environment. Multimedia appliances communicate with a central gateway via low cost network interface devices called buddies. The gateway can locate the users and appliances within the accuracy of a room and use the location information to automatically redirect media streams to user's presence. We call this paradigm as a media cloud. This paper presents the scheme for collecting proximity information from the buddies and effective techniques to determine their location. We have implemented the location detection system and present an experimental performance evaluation.