Cooperative Access in Cognitive Radio Networks: Stable Throughput and Delay Tradeoffs

In this paper, we study and analyze fundamental throughput-delay tradeoffs in cooperative multiple access for cognitive radio systems. We focus on the class of randomized cooperative policies, whereby the secondary user (SU) serves either the queue of its own data or the queue of the primary user (PU) relayed data with certain service probabilities. The proposed policy opens room for trading the PU delay for enhanced SU delay. Towards this objective, stability conditions for the queues involved in the system are derived. Furthermore, a moment generating function approach is employed to derive closed-form expressions for the average delay encountered by the packets of both users. Results reveal that cooperation expands the stable throughput region of the system and significantly reduces the delay at both users. Moreover, we quantify the gain obtained in terms of the SU delay under the proposed policy, over conventional relaying that gives strict priority to the relay queue.Comment: accepted for publication in IEEE 12th Intl. Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 201

Cooperation and Underlay Mode Selection in Cognitive Radio Network

In this research, we proposes a new method for cooperation and underlay mode selection in cognitive radio networks. We characterize the maximum achievable throughput of our proposed method of hybrid spectrum sharing. Hybrid spectrum sharing is assumed where the Secondary User (SU) can access the Primary User (PU) channel in two modes, underlay mode or cooperative mode with admission control. In addition to access the channel in the overlay mode, secondary user is allowed to occupy the channel currently occupied by the primary user but with small transmission power. Adding the underlay access modes attains more opportunities to the secondary user to transmit data. It is proposed that the secondary user can only exploits the underlay access when the channel of the primary user direct link is good or predicted to be in non-outage state. Therefore, the secondary user could switch between underlay spectrum sharing and cooperation with the primary user. Hybrid access is regulated through monitoring the state of the primary link. By observing the simulation results, the proposed model attains noticeable improvement in the system performance in terms of maximum secondary user throughput than the conventional cooperation and non-cooperation schemes

Novi steroidni derivati sintetizirani iz 3betha-hidroksiandrosten-17-ona

In this study, we synthesized some new substituted steroidal derivatives using 3betha-hydroxyandrosten-17-one (dehydroepiandrosterone) as starting material. The synthesized steroidal derivatives 1-11 were evaluated for their androgenic-anabolic activities compared to testosterone as positive control. Details of the synthesis, spectroscopic data and toxicity (LD50) of synthesized compounds are reported.U radu je opisana sinteza novih steroidnih derivata 1-11 koristeći 3betha-hidroksiandrosten-17-on (dehidroepiandrosteron) kao početnu supstanciju. Androgeno-anaboličko djelovanje tih spojeva uspoređivano je s djelovanjem testosterona kao pozitivnom kontrolom. Navode se detaljni sintetski postupci, spektroskopska karakterizacija i podaci o toksičnosti (LD50)

Energy Efficient Multiuser Scheduling: Statistical Guarantees on Bursty Packet Loss

In this paper, we consider energy efficient multiuser scheduling. Packet loss tolerance of the applications is exploited to minimize average system energy. There is a constraint on average packet drop rate and maximum number of packets dropped successively (bursty loss). A finite buffer size is assumed. We propose a scheme which schedules the users opportunistically according to the channel conditions, packet loss constraints and buffer size parameters. We assume imperfect channel state information at the transmitter side and analyze the scheme in large user limit using stochastic optimization techniques. First, we optimize system energy for a fixed buffer size which results in a corresponding statistical guarantee on successive packet drop. Then, we determine the minimum buffer size to achieve a target (improved) energy efficiency for the same (or better) statistical guarantee. We show that buffer size can be traded effectively to achieve system energy efficiency for target statistical guarantees on packet loss parameters.Comment: Proc. Physcomnet in conjunction with WIOPT 201

Computer-aided transformer design capacity building

It is known that the deployment of highly efficient power transformers is crucial for the minimization of overall network losses. Hence, the curriculum of an elective senior-level course was developed for Cairo University students