Intelligent environments rely on context information for providing services to their users. Among various existing platforms for context recognition, smart phones are one of the most widely used. However, despite numerous advantages, smart phones exhibit limited energy resources. To mitigate this there exist approaches for energy efficient context recognition for smart phones but these approaches are usually fine-tuned for specific types of context. As a result their applicability to other context types is limited. In this paper, we present an energy efficient context recognition system for smart phones which provides generalized applicability of four generic energy efficiency techniques which have been described in the literature and applied to location sensing using mobile phones. These four techniques as termed by authors include Suppression, Substitution, Adaptation and Piggybacking. Our system provides their generalized applicability by modelling context recognition applications using a state machine abstraction. Consequently the resulting applications are structured as combinations of states and transitions. To aid rapid prototyping our system is equipped with an off-line development tool which allows the creation and (code) generation of state machines using a graphical editor. We evaluate our system by creating a test application. Using a precise hardware set up, we perform energy measurements to demonstrate the energy savings of these different techniques.

Online collaboration tools such as Google+, Face-book or Dropbox have become an important and ubiquitous mediator of many human interactions. In the virtual world, they enable secure interaction by controlling access to shared resources. Yet relying on them to support synchronous direct interactions, such as face-to-face meetings, might be suboptimal as they require reliable online connectivity and even then often introduce delays. A much more efficient way of co-located resource sharing is the use of local communications, such as ad-hoc WiFi. Yet setting up the necessary encryption and authentication mechanisms is often cumbersome. In this paper, we present PIKE, a key exchange protocol that minimizes this configuration effort. PIKE piggybacks the exchange of keys on top of an existing service infrastructure. To support encryption or authentication without Internet connection, PIKE relies on triggers for upcoming personal interactions and exchanges keys before they take place. To evaluate PIKE, we present two example applications and we perform an experimental as well as an analytical analysis of its characteristics. The evaluation indicates that PIKE is broadly applicable, scales well enough to support larger events and provides a level of security that is (at least) comparable to the one provided by the underlying service.

Existing context recognition applications for personal mobile devices are usually fine-tuned to recognize the set of characteristics required to support a particular user task. Outside of a laboratory environment, however, users are often involved in multiple tasks at a time which requires the simultaneous execution of several applications. Yet, due to the energy constraints of most personal mobile devices this approach is inherently limited in scale. In this paper, we show how this problem can be avoided by applying a component-based approach to application development and execution. We present a component system that enables developers to build individual applications in isolation without compromising runtime efficiency. When applications are executed simultaneously, the component system applies a novel technique called configuration folding to automatically remove redundancies. Our experimental evaluation of configuration folding shows that it can save up to 48 percent of energy when applied to a music and a speech detection application, thus, amortizing energy costs after a few seconds of execution.

The Proxy Mobile IPv6 (PMIPv6) is a network based mobility management protocol standard that was ratified recently by the Network-based Localized Mobility Management (NetLMM) working group of the Internet Engineering Task Force (IETF). PMIPv6 is a protocol that uses the same concepts as used in Mobile IPv6 (MIPv6), but modified to operate in the network part only instead of involving the Mobile Node (MN) as well. PMPv6 is claimed to posses a number of advantages over the host based mobility management protocols in use today, above all MIPv6. The main advantage of using PMIPv6 is the freeing up of the mobile host in doing any mobility related activities and thereby saving its resources. The saving of resources may result in their usage for other purposes or even enable otherwise capabilities restricted devices to operate in the PMIPv6 domains. Other advantages include reduced signaling traffic volume and no tunneled packets in the access network. These aspects become very important since the access networks in mobile networks usually are air interfaces. Further, PMIPv6 is also becoming a very attractive mobility management protocol for mobile network operators as seen by its inclusion in current 3rdGeneration Partnership Project (3GPP) standardization as a possible alternative mobility management protocol for the Long Term Evolution (LTE) technologies. In addition to qualitative analyses and comparisons, the work attempts to quantify these advantages to show the achieved benefits. The quantifications are done through measurements in a real test-bed which is installed with a PMIPv6 implementation developed as part of this work.