Yunus Durmus

Cooperative Density Estimation in Random Wireless Ad Hoc Networks

Density estimation is crucial for wireless ad hoc networks for adequate capacity planning. Protocols have to adapt their operation to the density since the throughput in an ad hoc network approaches asymptotically to zero as the density increases. A wireless node can estimate the global density by using local information such as the received power from neighbors. In this paper, we propose a cross layer protocol to compute the density estimate. The accuracy of the estimate can be enhanced and its variance can be reduced through cooperation among the nodes. Nodes share the received power measurements with each other. Based on the collected observations, the maximum likelihood estimate is computed. It is shown that cooperative density estimation has better accuracy with less variance than the individual estimation. When nodes share received power measurements from further away neighbors, the variance of the estimate is further reduced.

Wifi authentication through social networks — A decentralized and context-aware approach

With the proliferation of WiFi-enabled devices, people expect to be able to use them everywhere, be it at work, while commuting, or when visiting friends. In the latter case, home owners are confronted with the burden of controlling the access to their WiFi router, and usually resort to simply sharing the password. Although convenient, this solution breaches basic security principles, and puts the burden on the friends who have to enter the password in each and every of their devices. The use of social networks, specifying the trust relations between people and devices, provides for a more secure and more friendly authentication mechanism. In this paper, we progress the state-of-the-art by abandoning the centralized solution to embed social networks in WiFi authentication; we introduce EAP-SocTLS, a decentralized approach for authentication and authorization of WiFi access points and other devices, exploiting the embedded trust relations. In particular, we address the (quadratic) search complexity when indirect trust relations, like the smartphone of a friends kid, are involved. We show that the simple heuristic of limiting the search to friends and devices in physical proximity makes for a scalable solution. Our prototype implementation, which is based on WebID and EAP-TLS, uses WiFi probe requests to determine the pool of neighboring devices and was shown to reduce the search time from 1 minute for the naive policy down to 11 seconds in the case of granting access over an indirect friend.

Event-Driven MAC Protocol for Dual-Radio Cooperation

One of the sources of the energy waste in wireless sensor networks is idle listening, the time in which a node monitors the free channel. In applications where the events occur sporadically, energy consumption due to idle listening can be further reduced by dual-radio cooperation. In dual- radio cooperation, nodes in the network have two stacks. One stack makes use of a low-power wake-up radio for event-driven communication over the main radio. The other stack may employ any sensor networking medium access control protocol only over the main radio. One of the two stacks can be dynamically operational depending on the rate of the events or the packet arrival rate. When the event rate becomes small, the event-driven stack takes over the operation. If the event rate increases, it could be more efficient to operate the legacy single radio stack. In this paper, we investigate the performance of the dual-radio cooperation in wireless sensor networks. A medium access control protocol is proposed for the dual- radio cooperation to maximize the energy efficiency of the wireless network. We define the critical event rate as the event rate threshold above which the single-radio stack performs better than the dual- radio stack. We analyzed and validated the critical event rate by simulations. We show that 70-97% energy conservation is possible by employing the dual-radio cooperation.

Imitation as the simplest strategy for cooperation

Ad hoc networks comprise independent cooperative nodes which work together to constitute a system having a value greater than the sum of the values of the individual components. The nodes cooperate to gain access to the medium or to establish a messaging infrastructure by relaying foreign packets. However, when nodes in an ad hoc network operate autonomously without a central authority, they tend to defect, e.g., do not forward each others packets following the game theoretic analysis. External mechanisms may preserve and enforce cooperation in network in return of additional operational costs or security overheads. However, low power devices may lack computational power that is required to implement the system. Recent works in evolutionary game theory have shown that cooperation may survive in a lattice structured biological network without any enforcement. The spatial structure of the network may allow the survival of the cooperative nodes when they imitate the dominant surrounding strategy. Imitating strategy helps low power devices adapt dynamically to the environment rather than giving deterministic and static decisions. In this work, we apply the imitation strategy to ad hoc networks which have geometric random network structure different from the lattice structured networks. Simulations show that simple imitation strategy allows cooperation to be spread over the network.

Collaborative and Cognitive Network Platforms: Vision and Research Challenges

In this paper, we present a visionary concept referred to as Collaborative and Cognitive Network Platforms (CCNPs) as a future-proof solution for creating a dependable, self-organizing and self-managing communication substrate for effective ICT solutions to societal problems. CCNP creates a cooperative communication platform to support critical services across a range of business sectors. CCNP is based on the personal network (PN) technology which is an inherently cooperative environment prototyped in the Dutch Freeband PNP2008 and the European Union IST MAGNET projects. In CCNP, the cognitive control plane strives to exploit the resources to better satisfy the requirements of networked applications. CCNP facilitates collaboration inherently. Through cognition in the cognitive control plane, CCNP becomes a self-managed substrate. The self-managed substrate, in this paper, is defined as cognitive and collaborative middleware on which future applications run without user intervention. Endemic sensor networks may be incorporated into the CCNP concept to feed its cognitive control plane. In this paper, we present the CCNP concept and discuss the research challenges related to collaboration and cognition.

Semantic edge caching and prefetching in 5G

Recent popularity of mobile devices increased the demand for mobile network services and applications that require minimal delay. 5G mobile networks are expected to provide much lesser delay than the present mobile networks. One of the conventional ways for decreasing the latency is caching the content closer to the end user. However, currently deployed methods are not effective enough. In this work-in-progress paper, we propose a new astute caching strategy that is able to smartly predict subsequent user requests and prefetch necessary contents to remarkably decrease the end-to-end latency in 5G systems. We employ semantic inference by mobile edge computing, deduce what the end-user may request in the sequel and prefetch the content.

Cooperative networks: the mobile tethering game

We propose an analysis of cooperation for data sharing and the behavioral aspects involved in the process of decision making. Starting with the tethering capabilities of recent devices we apply game theoretical principles and models, inquire what makes the cooperation work, and what are the economical implications required to build a cooperative network. Aggregating the game theory with the results of the market inquiry of a questionnaire and with a developed android application, will give us an idea of why and how people share.