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A cross-layer design which combines adaptive modulation and coding (AMC) at the physical layer with a hybrid automatic repeat request (HARQ) protocol at the data link layer (LL) is presented, in cooperative relay system over Nakagami-m fading channels with perfect and imperfect channel state information (CSI). In order to maximize spectral efficiency (SE) under delay and packet error rate (PER) performance constraints, a state transition model and an optimization framework with perfect CSI are presented. Then the framework is extended to cooperative relay system with imperfect CSI. The numerical results show that the scheme can achieve maximum SE while satisfying transmitting delay requirements. Compared with the imperfect CSI, the average PER with perfect CSI is much lower and the spectral efficiency is much higher. 相似文献
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阐述网络工程技术的应用型技能教学特点,网络工程实用性教学的策略,包括规划和设计专业建设的网络库、创新培养网络工程人才的教学模式,激发学生的创新思维。 相似文献
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以鳞片石墨(0.300mm)为原料,高锰酸钾为氧化剂,采用化学氧化和分步插层的制备工艺,乙酸辅助插层,高温膨胀制备具有低硫高倍率膨胀石墨(EG),探讨其最佳工艺条件并对其性能进行了表征。结果表明:石墨(g)∶硫酸(ml)∶高锰酸钾(g)=1.0∶6.0∶0.2,反应温度40℃,反应时间为90min;乙酸辅助插层时间为120min,抽滤洗涤至pH值为5~7,60℃干燥烘干可膨胀石墨,900℃下高温膨胀30s,即可得高倍率膨胀石墨;膨胀石墨的性能表征对研究其吸附行为和机理有重要意义。 相似文献