For every Gaussian network, there exists a corresponding deterministic network called the discrete superposition network . We show that this discrete superposition network provides a near-optimal digital interface for operating a class consisting of many Gaussian networks in the sense that any code for the discrete superposition network can be naturally lifted to a corresponding code for the Gaussian network, while achieving a rate that is no more than a constant number of bits lesser than the rate it achieves for the discrete superposition network. This constant depends only on the number of nodes in the network and not on the channel gains or SNR. Moreover the capacities of the two networks are within a constant of each other, again independent of channel gains and SNR. We show that the class of Gaussian networks for which this interface property holds includes relay networks with a single source-destination pair, interference networks, multicast networks, and the counterparts of these networks with multiple transmit and receive antennas. The code for the Gaussian relay network can be obtained from any code for the discrete superposition network simply by pruning it. This lifting scheme establishes that the superposition model can indeed potentially serve as a strong surrogate for designing codes for Gaussian relay networks. We present similar results for the K ×K Gaussian interference network, MIMO Gaussian interference networks, MIMO Gaussian relay networks, and multicast networks, with the constant gap depending additionally on the number of antennas in case of MIMO networks.

The Web has become the host platform for interactive and collaborative applications that usually consist of multiple Web services. This transition is pushing the browsers to perform operating system like functionalities for better resource utilization. Unfortunately, there exists limited support for resource management on current Web platforms. This problem is further aggravated on mobile devices because of their limited resources. If current Web communication APIs were used as-is, mobile users would suffer from low responsiveness, battery drainage, and expensive charges.

We present PAN-on-Demand, a self-organizing wireless personalarea network (PAN) that balances performance and energy concerns by scaling the structure of the network to match the demands of applications. PAN-on-Demand autonomously organizes co-located mobile devices with one or more commodity radios

We observe that the modularity of current power management algorithms often leads to poor results. We propose two new interfaces that pierce the abstraction barrier that inhibits device power management. First, an OS power manager allows applications to query the current power mode of I/O devices to evaluate the performance and energy cost of alternative strategies for reading and writing data. Second, we allow applications to disclose ghost hints that enable better power management in the presence of multiple devices. Adaptive applications issue ghost hints to device power managers when they are forced to use a poor I/O path because a device is not in an ideal power mode; such hints allow devices to implement proactive power management strategies that do not depend upon passive load observation. Using these new interfaces, we implement a middleware layer that supports adaptive disk cache management. On an iPAQ handheld running Linux, our cache manager reduces interactive response time for a Web browser by 27% and decreases total energy usage by 9%. For a mail reader, the cache manager decreases response time by 42% and energy use by 5%.

Current wireless network power management often substantially degrades performance and may even increase overall energy usage when used with latency-sensitive applications. We propose self-tuning power management (STPM) that adapts its behavior to the access patterns and intent of applications, the characteristics of the network interface, and the energy usage of the platform. We have implemented STPM as a Linux kernel module---our results show substantial benefits for distributed file systems, streaming audio, and thin-client applications. Compared to default 802.11b power management, STPM reduces the total energy usage of an iPAQ running the Coda distributed file system by 21% while also reducing interactive file system delay by 80%. Further, STPM adapts to diverse operating conditions: it yields good results on both laptops and handhelds, supports 802.11b network interfaces with substantially different characteristics, and performs well across a range of application network access patterns.

We discuss our approach to constructing a dynamic and secure smart home environment and tackling the challenges associated with it. We envision a smart home as an active environment populated with smart, dynamically configurable consumer devices capable of interacting with humans and other smart devices. In such a dynamic and active environment, there is a great need for an agile, lightweight, distributed security mechanism. This security mechanism needs to be programmable and able to evolve as rapidly as the environment itself. Yet, this mechanism should be able to adapt to environments with scarce resources. We present Tiny SESAME to meet these challenges while utilizing Jini/sup TM/ technology from Sun Microsystems to handle the common parts of distributed devices. Tiny SESAME is a lightweight component-based, Java-implementation of a subset of SESAME. SESAME is an extension to Kerberos that supports public key technologies, access control, and delegation of access rights. We discuss our Tiny SESAME and how it could be integrated with handheld and consumer devices.