In our thesis, we investigate the detection of malicious behavior in cooperative networks. Our model contain one source, one destination and two relays where relays adopt Orthogonal Space Time Block Code (OSTBC) to achieve spatial diversity. Cooperative communication takes two phases to forward signal to the destination. During first phase, source broadcasts data symbols to relay and destination, and a few tracing symbols are inserted randomly in data symbols. The values and positions of tracing symbols are known at source and destination. The random placement of tracing symbols is to prevent relays evade the detection of malicious behavior. In second phase, relays adopt orthogonal space time block code to forward the received signals after decoding source message successfully. We consider two scenarios based on the decoding capability at relays. The first scenario assumes perfect source¡Vrelay links. So, relays can always decode symbols correctly. Second scenario considers decoding failures at relays. In both scenarios, relays have a certain probability to perform maliciously. After receiving symbols at destination, the destination extracts and detect the tracing symbols. The malicious behavior of relay is detected depending on the value of the correlation between detected and exact tracing symbols. Moreover, depending on the average received energy, we can distinguish whether relays behaves as in outage. Through computer simulation, we can verify that our proposed tracing algorithm and decoding strategy reduce bit error rate.

This study uses a quasi-experimental, nonequivalent control group design and aims to investigate the effects of the application of cooperative learning to visual arts curriculum on the creativity and drawing performance of the the lower graders. Subjects are students from two second grade classes in an elementary school in Tainan City. One class represents the experimental group, while the other one is the control group. Each of the classes is given instruction for twenty sessions of classes in ten weeks. The experimental group receives cooperative learning based on STAD. The control group receives seperate learning. This study incorporates quantitative and qualitative approaches. Two assessment tools are conducted, which include ¡§New Creativity Test for Use with Students in Taiwan¡¨ developed by Dr. Ching-Chi Wu, and the ¡§Rating Scale for the drawing performance of the the lower graders ¡¨ designed by the author. Quantitative data are analyzed by ANCOVA and MANCOVA. Qualitative data processed by content analysis are gathered from teacher's classroom anecdotes, student works of curriculum, student feedback about the instruction , and vedio records of teaching process. The results of this study indicate that in the aspect of creativity, application of cooperative learning to visual arts curriculum increases the lower grader¡¦s verbal creativity in terms of flexibility as well as the figural creativity regarding fluency, flexibility and elaboration. In the aspect of drawing performance, application of cooperative learning to visual arts curriculum significantly improved the lower grader¡¦s drawing performance on ¡§content¡¨, ¡§illustrate¡¨, ¡§image ¡¨and ¡¨ color¡¨. The possibility of applying cooperative learning to the visual arts curriculum for the lower grade in the elementary school is recognized.students in the experimental group show positive acknowledgement and feedbacks to the whole instruction. Conclusions for practical application and suggestions for further research are discussed.

Thesis (doctoral)--Universität Basel, 1935. / Includes bibliographical references.

Thesis--Uppsala. / Includes bibliographical references (p. 172-177).

Thesis (M.A.)-University of KwaZulu-Natal, Durban, 2009. / Full text also available online. Scroll down for electronic link.

Cooperative services--a term which includes any system that relies on the resources and participation of its clients to function--have proven to be a popular, naturally scalable means to disseminate content, distribute computational workloads, or provide network connectivity. However, because these services critically depend on participants that are not controlled by a single administrative domain, these services must be designed to function in environments where no participant--because of failure or selfishness--will necessarily follow the specified protocol. This thesis addresses the challenge of establishing and maintaining cooperation in cooperative services by (1) advancing our understanding of the limits to what our services can guarantee in the presence of failure, (2) demonstrating the critical role that correct participants can play in the incentives provided by the service, and (3) proposing a new notion of equilibrium that, unlike traditional notions, provides both rigorous yet practical guarantees in the presence of collusion. Furthermore, we demonstrate that our ideas can be applied to practice by designing and implementing Seer, a system that provides a scalable, reliable, and robust method for disseminating content even if participants may fail arbitrarily or deviate selfishly as a coalition. / text

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Time-sensitive applications that are also CPU intensive like video games, video playback, eye-candy desktops etc. are increasingly common. These applications run on commodity operating systems that are targeted at diverse hardware, and hence they cannot assume that sufficient CPU is always available. Increasingly, these applications are designed to be adaptive. When executing multiple such applications, the operating system must not only provide good timeliness but also (optionally) allow co-ordinating their adaptations so that applications can deliver uniform fidelity. In this work, we present a starvation-free, fair, process scheduling algorithm that provides predictable and low latency execution without the use of reservations and assists adaptive time sensitive tasks with achieving consistent quality through cooperation. We combine an event-driven application model called cooperative polling with a fair-share scheduler. Cooperative polling allows sharing of timing or priority information across applications via the kernel thus providing good timeliness, and the fair-share scheduler provides fairness and full utilization. Our experiments show that cooperative polling leverages the inherent efficiency advantages of voluntary context switching versus involuntary pre-emption. In CPU saturated conditions, we show that the scheduling responsiveness of cooperative polling is five times better than a well-tuned fair-share scheduler, and orders of magnitude better than the best-effort scheduler used in the mainstream Linux kernel.

Wireless Sensor Networks (WSNs) are networks of small devices, called motes, designed to monitor resources and report to a server. Motes are battery-powered and have very little memory to store data. To conserve power, the motes usually form clusters to coordinate their activities. In heterogeneous WSNs, the motes have different resources available to them. For example, some motes might have more powerful radios, or larger power supplies. By exploiting heterogeneity within a WSN can allow the network to stay active for longer periods of time. In WSNs, the communications between motes draw the most power. By choosing better clusterheads in the clusters to control and route messages, all motes in the network will have longer lifespans. By leveraging heterogeneity to select better clusterheads, I have developed Heterogeneous Clustering Control Protocol (HCCP). HCCP is designed to be highly robust to change and to fully utilize the resources that are currently available.

Cooperative driving holds the potential to considerably improve the level of safety and efficiency on our roads. Recent advances in in-vehicle sensing and wireless communication technology have paved the way for the development of cooperative traffic safety applications based on the exchange of data between vehicles (or between vehicles and road side units) over a wireless link. The access to up-to-date status information from surrounding vehicles is vital to most cooperative driving applications. Other applications rely on the fast dissemination of warning messages in case a hazardous event or certain situation is detected. Both message types put high requirements on timeliness and reliability of the underlying communication protocols. The recently adopted European profile of IEEE 802.11p defines two message types,periodic beacons for basic status exchange and event-triggered hazard warnings, both operating at pre-defined send rates and sharing a common control channel. The IEEE 802.11p Medium Access Control (MAC) scheme is a random access protocol that doesnot offer deterministic real-time support, i.e. no guarantee that a packet is granted access to the channel before its deadline can be given. It has been shown that a high number of channel access requests, either due to a high number of communicating vehicles or highdata volumes produced by these vehicles, cannot be supported by the IEEE 802.11p MAC protocol, as it may result in dropped packets and unbounded delays. The goal of the work presented in this thesis has therefore been to enhance IEEE 802.11p without altering the standard such that it better supports the timing and reliability requirements of traffic safety applications and provides context-aware andefficient use of the available communication resources in a vehicular network. The proposed solutions are mapped to the specific demands of a set of cooperative driving scenarios (featuring infrastructure-based and infrastructure-free use cases, densely and sparsely trafficked roads, very high and more relaxed timing requirements) and evaluated either analytically, by computer simulation or by measurements and compared to the results produced by the unaltered IEEE 802.11p standard. As an alternative to the random MAC method of IEEE 802.11p, a centralized solution isproposed for application scenarios where either a road side unit or a suitable dedicated vehicle is present long enough to take the coordinating role. A random access phase forevent-driven data traffic is interleaved with a collision-free phase where timely channel access of periodic delay-sensitive data is scheduled. The ratio of the two phases isdynamically adapted to the current data traffic load and specific application requirements. This centralized MAC solution is mapped on two cooperative driving applications: merge assistance at highway entrances and platooning of trucks. Further,the effect of a context-aware choice of parameters like send rate or priority settings based on a vehicle’s position or role in the safety application is studied with the goal to reduce the overall number of packets in the network or, alternatively, use the available resources more efficiently. Examples include position-based priorities for the merge assistance use case, context-aware send rate adaptation of status updates in anovertaking warning application targeting sparsely-trafficked rural roads and an efficient dissemination strategy for warning messages within a platoon. It can be concluded that IEEE 802.11p as is does not provide sufficient support for the specific timing and reliability requirements imposed by the exchange of safety-criticalreal-time data for cooperative driving applications. While the proper, context-awarechoice of parameters, concerning send rate or priority level, within the limits of the standard, can lead to improved packet inter-arrival rates and reduced end-to-end delays,the added benefits from integrating MAC solutions with real-time support into the standard are obvious and needs to be investigated further.