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- 저자 : M. Ejaz Ahmed (검색결과 3 건)
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Ahmed, M. Ejaz,Ju Bin Song,Zhu Han,Doug Young Suh IEEE 2014 IEEE TRANSACTIONS ON MOBILE COMPUTING Vol.13 No.9
<P>In cognitive radio networks, the main objective of spectrum sensing is to exploit spectrum holes left by the primary users (PUs). Different PUs' traffic patterns might provide different opportunities for second user (SU) spectrum access. In this paper, we identify the PUs' traffic patterns and then maximize SU transmission accordingly. First a theoretical framework is developed to cluster PU traffic patterns based on a Bayesian nonparametric inference model, in which the number of traffic types is unknown. Second, in order to exploit the spectrum holes, we study a sensing-transmission structure to optimize the SU transmission strategy. Specifically, we exploit the short and long transmission opportunities based on the PU traffic pattern and channel idle time distribution. Finally, we propose a threshold-based sensing-transmission method that optimizes the SU utility, while protecting PU transmissions. Both sensing and transmission errors are considered for perfect sensing with/without acknowledgement-based transmission and imperfect sensing, respectively. From the simulation results, we show that the proposed technique outperforms the nonparametric mean shift clustering algorithm. Furthermore, we utilize these clustering results to optimize the SU's transmission strategy with perfect and imperfect sensing. We compare our proposed technique with the probabilistic sensing-transmission structure and show the performance gain in terms of throughput.</P>
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Distributed Channel Allocation Using Kernel Density Estimation in Cognitive Radio Networks
M. Ejaz Ahmed,김주석,Runkun Mao,송주빈,Husheng Li 한국전자통신연구원 2012 ETRI Journal Vol.34 No.5
Typical channel allocation algorithms for secondary users do not include processes to reduce the frequency of switching from one channel to another caused by random interruptions by primary users, which results in high packet drops and delays. In this letter, with the purpose of decreasing the number of switches made between channels, we propose a nonparametric channel allocation algorithm that uses robust kernel density estimation to effectively schedule idle channel resources. Experiment and simulation results demonstrate that the proposed algorithm outperforms both random and parametric channel allocation algorithms in terms of throughput and packet drops.
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Coconut shell waste as an alternative lightweight aggregate in concrete- A review
Muhammad ,Aslam,Waqas, Aziz,M. Jahanzaib, Khalil,M. Jahanzaib, Ali,Muhammad, Raheel,Aayzaz, Ahmed,Muhammad Fahad, Ejaz Techno-Press 2022 Advances in materials research Vol.11 No.4
This review article highlights the physical, mechanical, and chemical properties of coconut shells, and the fresh and hardened properties of the coconut shell concrete are summarized and were compared with other types of aggregates. Furthermore, the structural behavior in terms of flexural, shear, and torsion was also highlighted, with other properties including shrinkage, elastic modulus, and permeability of the coconut shell concrete. Based on the reviewed literature, concrete containing coconut shell as coarse aggregate with normal sand as fine showed the 28-day compressive strength between 2 and 36 MPa with the dried density range of 1865 to 2300 kg/m<sup>3</sup>. Coconut shell concretes showed a 28-day modulus of rupture and splitting tensile strength values in the ranges of 2.59 to 8.45 MPa and 0.8 to 3.70 MPa, respectively, and these values were in the range of 5-20% of the compressive strength. The flexural behavior of CSC was found similar to other types of lightweight concrete. There were no horizontal cracks on beams which indicate no bond failure. Whereas, the diagonal shear failure was prominent in beams with no shear reinforcements while flexural failure mode was seen in beams having shear reinforcement. Under torsion, CSC beams behave like conventional concrete. Finally, future recommendations are also suggested in this study to investigate the innovative lightweight aggregate concrete based on the environmental and financial design factors.
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