514 research outputs found
On Spectrum Sharing Between Energy Harvesting Cognitive Radio Users and Primary Users
This paper investigates the maximum secondary throughput for a rechargeable
secondary user (SU) sharing the spectrum with a primary user (PU) plugged to a
reliable power supply. The SU maintains a finite energy queue and harvests
energy from natural resources and primary radio frequency (RF) transmissions.
We propose a power allocation policy at the PU and analyze its effect on the
throughput of both the PU and SU. Furthermore, we study the impact of the
bursty arrivals at the PU on the energy harvested by the SU from RF
transmissions. Moreover, we investigate the impact of the rate of energy
harvesting from natural resources on the SU throughput. We assume fading
channels and compute exact closed-form expressions for the energy harvested by
the SU under fading. Results reveal that the proposed power allocation policy
along with the implemented RF energy harvesting at the SU enhance the
throughput of both primary and secondary links
Power-Optimal Feedback-Based Random Spectrum Access for an Energy Harvesting Cognitive User
In this paper, we study and analyze cognitive radio networks in which
secondary users (SUs) are equipped with Energy Harvesting (EH) capability. We
design a random spectrum sensing and access protocol for the SU that exploits
the primary link's feedback and requires less average sensing time. Unlike
previous works proposed earlier in literature, we do not assume perfect
feedback. Instead, we take into account the more practical possibilities of
overhearing unreliable feedback signals and accommodate spectrum sensing
errors. Moreover, we assume an interference-based channel model where the
receivers are equipped with multi-packet reception (MPR) capability.
Furthermore, we perform power allocation at the SU with the objective of
maximizing the secondary throughput under constraints that maintain certain
quality-of-service (QoS) measures for the primary user (PU)
Optimal Spectrum Access for a Rechargeable Cognitive Radio User Based on Energy Buffer State
This paper investigates the maximum throughput for a rechargeable secondary
user (SU) sharing the spectrum with a primary user (PU) plugged to a reliable
power supply. The SU maintains a finite energy queue and harvests energy from
natural resources, e.g., solar, wind and acoustic noise. We propose a
probabilistic access strategy by the SU based on the number of packets at its
energy queue. We investigate the effect of the energy arrival rate, the amount
of energy per energy packet, and the capacity of the energy queue on the SU
throughput under fading channels. Results reveal that the proposed access
strategy can enhance the performance of the SU.Comment: arXiv admin note: text overlap with arXiv:1407.726
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
Energy-aware cooperative wireless networks with multiple cognitive users
In this paper, we study and analyze cooperative cognitive radio networks with arbitrary number of secondary users (SUs). Each SU is considered a prospective relay for the primary user (PU) besides having its own data transmission demand. We consider a multi-packet transmission framework that allows multiple SUs to transmit simultaneously because of dirty-paper coding. We propose power allocation and scheduling policies that optimize the throughput for both PU and SU with minimum energy expenditure. The performance of the system is evaluated in terms of throughput and delay under different opportunistic relay selection policies. Toward this objective, we present a mathematical framework for deriving stability conditions for all queues in the system. Consequently, the throughput of both primary and secondary links is quantified. Furthermore, a moment generating function approach is employed to derive a closed-form expression for the average delay encountered by the PU packets. Results reveal that we achieve better performance in terms of throughput and delay at lower energy cost as compared with equal power allocation schemes proposed earlier in the literature. Extensive simulations are conducted to validate our theoretical findings
Mechanisms of damage tolerance and repair during DNA replication
Accurate duplication of chromosomal DNA is essential for the transmission of genetic information. The DNA replication fork encounters template lesions, physical barriers, transcriptional machinery, and topological barriers that challenge the faithful completion of the replication process. The flexibility of replisomes coupled with tolerance and repair mechanisms counteract these replication fork obstacles. The cell possesses several universal mechanisms that may be activated in response to various replication fork impediments, but it has also evolved ways to counter specific obstacles. In this review, we will discuss these general and specific strategies to counteract different forms of replication associated damage to maintain genomic stability
Evaluation of the population growth and fatty acid composition of Copepoda, Oithona nana, fed on different diets
The marine Copepoda species Oithona nana, is considered as one of the most Copepoda species that successfully mass cultured in marine hatcheries. This study investigated the effects of four feed diets (soybean, yeast, rice bran, and corn starch) on the population growth, growth rate, population composition, fecundity, and fatty acid composition of Copepoda, O. nana. The experiment was continued for 15 days and the copepods were fed on four feed diets with concentration of 1 g/106 individual/day. The results found that O. nana fed on corn starch showed the highest significant population growth (9067 Individual/L) and population growth rate (0.735). For nutritional value, copepods fed on rice bran were detected to have the highest content of monounsaturated fatty acid (MUFA), polyunsaturated fatty acids (PUFA), the lowest saturated fatty acids/unsaturated fatty acids ratio (SFA/UFA ratio) and the lowest SFA. More importantly, the rice bran diet was the only diet that showed eicosapentaenoic acid (EPA; C20:5ω3). Moreover, copepods fed on rice bran showed the highest significant female fecundity (8.33 egg/female), copepodite and nauplii percentages (33.27 and 32.65%, respectively). Finally, regarding to the quantity, corn starch is the most suitable diet for mass culturing O. nana, while, regarding to the quality, rice bran enhances the nutritional value and fecundity of the Calanoida Copepoda O. nana
Assessment of Pile Group Response under Lateral Load
Assessment of the response of a laterally loaded pile group based on soil-pile interaction is presented in this paper. The behavior of a pile group in uniform and layered soil (sand and/or clay) is predicted based on the strain wedge (SW) model approach that has been developed to predict the response of a flexible pile under lateral loading. The pile group is characterized in terms of three-dimensional soil-pile interaction and then transformed into its one-dimensional beam on elastic foundation equivalent with associated parameters (modulus of sugrade reaction). Therefore, the interference among the piles in a group is determined based on the geometry of the mobilized passive wedge of soil in front of the pile in addition to the pile spacing. The overlap of shear zones among the piles in the group varies along the length of the pile and changes from one soil to another in the soil profile. Also, the interference among the piles grows with the increase in lateral loading. The modulus of subgrade reaction determined will account for the additional strains (i.e. stresses) in the adjacent soil due to pile interference within the group
Effect of the Non-Linear Behavior of Pile Material on the Response of Laterally Loaded Piles
The main purpose of this study is to assess the lateral response of piles/shafts and the p-y curves for different soil-pile combinations while introducing the effect of the moment-curvature (M - Φ) relationship of the pile into the soil-pile interaction. Therefore, the equilibrium among soil reaction, pile deflection pattern, pile-head load, and flexural stiffness distribution should be satisfied at any level of loading. The influence of the nonlinear behavior of the pile/drilled shaft material on the nature of the associated p-y curve is presented through strain wedge (SW) model analysis. The SW model allows the assessment of the (soil-pile) modulus of subgrade reaction (i.e. the p-y curve) based on soil and pile properties which includes the pile bending stiffness. Therefore, the assessed modulus of subgrade reaction will be affected by changes in the bending stiffness of the pile or drilled shaft at any pile cross section (via the M-Q relationship). The reduction in pile bending stiffness will affect the pile-head stiffness under varying static or dynamic loading
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