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Haythem Ahmad Bany Salameh 《Mathematical and Computer Modelling》2011,53(11-12):2108-2118
Cognitive radio (CR) is a revolutionary technology in wireless communications that enhances spectrum utilization by allowing opportunistic and dynamic spectrum access. One of the key challenges in this domain is how CR users cooperate to dynamically access the available spectrum opportunities in order to maximize the overall perceived throughput. In this paper, we consider the coordinated spectrum access problem in a multi-user single-transceiver CR network (CRN), where each CR user is equipped with only one half-duplex transceiver. We first formulate the dynamic spectrum access as a rate/power control and channel assignment optimization problem. Our objective is to maximize the sum-rate achieved by all contending CR users over all available spectrum opportunities under interference and hardware constraints. We first show that this problem can be formulated as a mixed integer nonlinear programming (MINLP) problem that is NP-hard, in general. By exploiting the fact that actual communication systems have a finite number of available channels, each with a given maximum transmission power, we transfer this MINLP into a binary linear programming problem (BLP). Due to its integrality nature, this BLP is expected to be NP-hard. However, we show that its constraint matrix satisfies the total unimodularity property, and hence our problem can be optimally solved in polynomial time using linear programming (LP). To execute the optimal assignment in a distributed manner, we then present a distributed CSMA/CA-based random access mechanism for CRNs. We compare the performance of our proposed mechanism with reference CSMA/CA channel access mechanisms designed for CRNs. Simulation results show that our proposed mechanism significantly improves the overall network throughput and preserves fairness. 相似文献
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Nasraoui Haythem Driss Zied Kchaou Hedi 《Journal of Thermal Analysis and Calorimetry》2020,140(6):2721-2732
Journal of Thermal Analysis and Calorimetry - Solar chimney power plant (SCPP) is an interesting project to produce clean and sustainable energy. An efficient SCPP system requires a very high... 相似文献
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A diastereoselective coupling of dimethyl malonate with N‐(tert‐butyl)sulfinyl imines under solvent‐free conditions was developed, using NaHCO3 or NaI as base promoters. The resulting dimethyl 2‐(1‐aminoalkyl)malonates could be easily transformed successively to β‐amino esters and the corresponding β‐lactams with high optical purity. 相似文献
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