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

Flexural Strengthening Of Reinforced Concrete Beams Using Fabric Reinforced Cementitious Matrix Systems

This thesis is an experimental study performed to investigate the effectiveness of near surface embedded (NSE) and the hybrid near surface embedded externally bonded (NSE/EB) fabric reinforced cementitious matrix (FRCM) systems for flexural strengthening of reinforced concrete (RC) beams in flexure. A total of twenty beams were prepared with the consideration of three test parameters: (a) FRCM material (polyparaphenylene benzobisoxazole (PBO)/carbon/glass); (b) strengthening technique (externally bonded (EB), NSE and NSE/EB); and (c) the longitudinal reinforcement ratio (0.5% representing flexure-deficient beams and 1.28% representing typical under-reinforced beams). The results show that NSE strengthening provides improved bond behavior between FRCM composite and concrete substrate. The strengthening led to gains in ultimate flexural loads ranging between 30.1% and 108.6%. It was concluded that both NSE and NSE/EB are a valid strengthening alternative to the traditional EB strengthenin

Thrust and torque response for drilling titanium and carbon composite sandwich materials [abstract]

Abstract only availableExperiments were conducted based upon previous research conducted by El-Gizawy and Khasawneh [1] to determine the time response of thrust force and torque correlated to a simple drilling procedure through carbon fiber reinforced epoxy (IM7/997-3) composite material over 6Al-4V titanium alloy (AB1) sheets. The experiments measured the time response with a thrust and torque sensor, data acquisition system and CNC drilling machine. The research was used to locate points of interest among the previous statistical setup. Three-dimensional surfaces were analyzed to determine the drilling parameters that cause the highest force and torque in the CNC spindle (and, therefore, the drill bit) and the lowest force and torque, within the range available with the CNC used in the experimental setup. The experimental holes were also analyzed via surface profilometer and coordinate measurement probe to obtain surface roughness and dimensional accuracy measurements. The data indicates that the parameters that cause lower force and torque are preferable for dimensional accuracy in the titanium as well as for surface roughness, and tool life.College of Engineering Undergraduate Research Optio

Geophysical investigations of a geothermal anomaly at Wadi Ghadir, eastern Egypt

During regional heat flow studies a geothermal anomaly was discovered approximately 2 km from the Red Sea coast at Wadi Ghadir, in the Red Sea Hills of Eastern Egypt. A temperature gradient of 55 C/km was measured in a 150 m drillhole at this location, indicating a heat flow of approximately 175 mw/sqm, approximately four times the regional background heat flow for Egypt. Gravity and magnetic data were collected along Wadi Ghadir, and combined with offshore gravity data, to investigate the source of the thermal anomaly. Magnetic anomalies in the profile do not coincide with the thermal anomaly, but were observed to correlate with outcrops of basic rocks. Other regional heat flow and gravity data indicate that the transition from continental to oceanic type lithosphere occurs close to the Red Sea margin, and that the regional thermal anomaly is possibly related to the formation of the Red Sea