Reputation-Based Collaborative Spectrum Sensing Scheme in Cognitive Radio Networks

Collaborative spectrum sensing is proposed to improve the detection performance in cognitive radio (CR) networks. However, most of the current collaborative sensing schemes are vulnerable to the interference of the malicious secondary users (SUs). In this paper we propose a reputation-based collaborative spectrum sensing scheme to improve the security of cooperative sensing by mitigating the impacts of misbehaviors. The fusion center calculates the reputation rating of each SU according to their history reports to weight their sensing results in the proposed scheme. We analyze and evaluate the performance of the proposed scheme and its advantages over previous schemes in expansibility and integrity. Simulation results show that the proposed scheme can minimize the harmful influence from malicious SUs.

高氮低硫型酸雨对桑树幼苗光合性能的影响

为了探明高氮低硫型酸雨对桑树(Morus alba)幼苗叶片结构和光合特性的影响,采用环境可控的温室盆栽法,对一年生秋雨桑实生苗进行模拟酸雨处理。结果发现:用p H为4.5的酸雨处理的桑树叶片结构未发生明显变化,叶绿体基质中无淀粉粒;而p H≤4.0的桑树叶片表层粗糙、叶脉干瘪,叶绿体解离程度随着p H值的下降而加重,叶绿体中有少量的淀粉颗粒。桑树叶片的净光合速率,蒸腾速率、气孔导度随着模拟酸雨pH值下降而显著下降,呼吸速率、光呼吸速率和水分利用效率则显著升高。桑树叶片光化学淬灭系数和电子传递速率随着光强的增大而显著降低,而实际光化学效率和非光化学淬灭值随着光强的增大而显著升高。在光强超过900μmol·m^(-2)·s^(-1)时桑树叶片光系统II吸收光能用于光化学反应的能量减小,而用于热耗散的能量增大。即桑树通过调整叶片呼吸强度、增加热耗散和提高水分利用效率等途径抵抗酸雨,可在适度高氮低硫型酸雨沉降频发地区种植。