4,815 research outputs found
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
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