文中研究了中继合作协议下具有多面体不确定性系统的鲁棒模型预测控制问题。为了缓解网络化控制系统中远距离传输中的信道严重衰落问题,将放大转发中继合作协议应用到传感器和远程控制器通信链路中,从而提高信号传输质量。由于难以获取...文中研究了中继合作协议下具有多面体不确定性系统的鲁棒模型预测控制问题。为了缓解网络化控制系统中远距离传输中的信道严重衰落问题,将放大转发中继合作协议应用到传感器和远程控制器通信链路中,从而提高信号传输质量。由于难以获取实际系统状态,文中提出了RMPC(Robust Model Predictive Control)框架下的动态输出反馈控制策略。由于传感器和放大转发中继传输功率存在随机性,引入一组具有特定概率分布的随机变量来表征其发射功率。利用奇异值分解技术处理由未知变量耦合引起的非凸问题,提出辅助可解优化问题并得到底层系统的均方稳定性的充分条件。实验结果表明,所提控制框架使系统的控制性能更好,验证了该控制策略的有效性。展开更多
Five samples of LiMgPO_(4):Gd were prepared via five different production processes using a solid-state reaction method.The effects of the preparation process on optically stimulated luminescence(OSL)and thermolumines...Five samples of LiMgPO_(4):Gd were prepared via five different production processes using a solid-state reaction method.The effects of the preparation process on optically stimulated luminescence(OSL)and thermoluminescence(TL)were investigated.Considering its high sensitivity,low fading,and minimum detectable dose(MDD),the LiMgPO_(4):Gd phosphor heated to 900℃for 15 h is concluded to be optimal.The effects of annealing on the OSL sensitivity,relative residual OSL signals measured after 24 h of irradiation,and MDD of LiMgPO_(4):Gd phosphors heated to 900℃for 15 h were also investigated.Considering its high sensitivity,low fading,and MDD,annealing at 350℃for 1 h is concluded to be optimal.The OSL signal of LiMgPO_(4):Gd was derived from the principal TL glow peak.For a maximum integration time of 5 s,the OSL signal was stable,with no fading 30 days after irradiation.LiMgPO_(4):Gd eliminated approximately 2.2%of the OSL signal at each readout for a readout time of 0.1 s,which is sufficient for fast and multiple OSL readout.The sensitivity of LiMgPO_(4):Gd phosphor,annealed for 1 h at 350℃with a reading time of 0.1 s,was found to be approximately 98%of that observed forα-Al_(2)O_(3):C(TLD-500k),which should be sufficient for low-dose measurements in personal,workplace,and environmental dosimetry.展开更多
Stochastic iterative learning control(ILC)is designed for solving the tracking problem of stochastic linear systems through fading channels.Consequently,the signals used in learning control algorithms are faded in the...Stochastic iterative learning control(ILC)is designed for solving the tracking problem of stochastic linear systems through fading channels.Consequently,the signals used in learning control algorithms are faded in the sense that a random variable is multiplied by the original signal.To achieve the tracking objective,a two-dimensional Kalman filtering method is used in this study to derive a learning gain matrix varying along both time and iteration axes.The learning gain matrix minimizes the trace of input error covariance.The asymptotic convergence of the generated input sequence to the desired input value is strictly proved in the mean-square sense.Both output and input fading are accounted for separately in turn,followed by a general formulation that both input and output fading coexists.Illustrative examples are provided to verify the effectiveness of the proposed schemes.展开更多
With the rapid demand for underwater optical communication(UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous s...With the rapid demand for underwater optical communication(UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of "the aperture-averaged scintillation index"(SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time,signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system's performance.Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.展开更多
Zero Crossing Digital Phase Locked Loop with Arc Sine block (AS-ZCDPLL) is used to linearize the phase difference detection, and enhance the loop performance. The loop has faster acquisition, less steady state phase e...Zero Crossing Digital Phase Locked Loop with Arc Sine block (AS-ZCDPLL) is used to linearize the phase difference detection, and enhance the loop performance. The loop has faster acquisition, less steady state phase error, and wider locking range compared to the conventional ZCDPLL. This work presents a Zero Crossing Digital Phase Locked Loop with Arc Sine block (ZCDPLL-AS). The performance of the loop is analyzed under mobile faded channel conditions. The mobile channel is assumed to be two path fading channel corrupted by additive white Gaussian noise (AWGM). It is shown that for a constant filter gain, the frequency spread has no effect on the steady state phase error variance when the loop is subjected to a phase step. For a frequency step and under the same conditions, the effect on phase error is minimal.展开更多
The different realistic propagation channels are faced frequently the multipath fading environments. The main goal of this system design (cognitive radio network) is to improve the efficiency of spectrum access on a n...The different realistic propagation channels are faced frequently the multipath fading environments. The main goal of this system design (cognitive radio network) is to improve the efficiency of spectrum access on a non-interfering basis. This system achieves high utilization for the limited spectrum in order to fulfill needs for all users’ demands which are considered as a problem in wireless communications due to rapidly increasing in wireless applications and service. This system is exposed to attack due to the vulnerabilities existence in this system. So, the main outcome of this paper is to investigate the performance of the cooperative sensing in cognitive radio networks under malicious attacks over different channel impairments, and to illustrate the most suitable individual probability of detection in real faded channel by using Nakagami model. This paper illustrates the effectiveness of the attacks and fading on the performance of spectrum sensing process.展开更多
文摘文中研究了中继合作协议下具有多面体不确定性系统的鲁棒模型预测控制问题。为了缓解网络化控制系统中远距离传输中的信道严重衰落问题,将放大转发中继合作协议应用到传感器和远程控制器通信链路中,从而提高信号传输质量。由于难以获取实际系统状态,文中提出了RMPC(Robust Model Predictive Control)框架下的动态输出反馈控制策略。由于传感器和放大转发中继传输功率存在随机性,引入一组具有特定概率分布的随机变量来表征其发射功率。利用奇异值分解技术处理由未知变量耦合引起的非凸问题,提出辅助可解优化问题并得到底层系统的均方稳定性的充分条件。实验结果表明,所提控制框架使系统的控制性能更好,验证了该控制策略的有效性。
文摘Five samples of LiMgPO_(4):Gd were prepared via five different production processes using a solid-state reaction method.The effects of the preparation process on optically stimulated luminescence(OSL)and thermoluminescence(TL)were investigated.Considering its high sensitivity,low fading,and minimum detectable dose(MDD),the LiMgPO_(4):Gd phosphor heated to 900℃for 15 h is concluded to be optimal.The effects of annealing on the OSL sensitivity,relative residual OSL signals measured after 24 h of irradiation,and MDD of LiMgPO_(4):Gd phosphors heated to 900℃for 15 h were also investigated.Considering its high sensitivity,low fading,and MDD,annealing at 350℃for 1 h is concluded to be optimal.The OSL signal of LiMgPO_(4):Gd was derived from the principal TL glow peak.For a maximum integration time of 5 s,the OSL signal was stable,with no fading 30 days after irradiation.LiMgPO_(4):Gd eliminated approximately 2.2%of the OSL signal at each readout for a readout time of 0.1 s,which is sufficient for fast and multiple OSL readout.The sensitivity of LiMgPO_(4):Gd phosphor,annealed for 1 h at 350℃with a reading time of 0.1 s,was found to be approximately 98%of that observed forα-Al_(2)O_(3):C(TLD-500k),which should be sufficient for low-dose measurements in personal,workplace,and environmental dosimetry.
基金supported by the National Natural Science Foundation of China(61673045)the Fundamental Research Funds for the Central Universities(XK1802-4)
文摘Stochastic iterative learning control(ILC)is designed for solving the tracking problem of stochastic linear systems through fading channels.Consequently,the signals used in learning control algorithms are faded in the sense that a random variable is multiplied by the original signal.To achieve the tracking objective,a two-dimensional Kalman filtering method is used in this study to derive a learning gain matrix varying along both time and iteration axes.The learning gain matrix minimizes the trace of input error covariance.The asymptotic convergence of the generated input sequence to the desired input value is strictly proved in the mean-square sense.Both output and input fading are accounted for separately in turn,followed by a general formulation that both input and output fading coexists.Illustrative examples are provided to verify the effectiveness of the proposed schemes.
基金supported by the fund from Xi’an Institute of Optics and Precision Mechanics。
文摘With the rapid demand for underwater optical communication(UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of "the aperture-averaged scintillation index"(SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time,signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system's performance.Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.
文摘Zero Crossing Digital Phase Locked Loop with Arc Sine block (AS-ZCDPLL) is used to linearize the phase difference detection, and enhance the loop performance. The loop has faster acquisition, less steady state phase error, and wider locking range compared to the conventional ZCDPLL. This work presents a Zero Crossing Digital Phase Locked Loop with Arc Sine block (ZCDPLL-AS). The performance of the loop is analyzed under mobile faded channel conditions. The mobile channel is assumed to be two path fading channel corrupted by additive white Gaussian noise (AWGM). It is shown that for a constant filter gain, the frequency spread has no effect on the steady state phase error variance when the loop is subjected to a phase step. For a frequency step and under the same conditions, the effect on phase error is minimal.
文摘The different realistic propagation channels are faced frequently the multipath fading environments. The main goal of this system design (cognitive radio network) is to improve the efficiency of spectrum access on a non-interfering basis. This system achieves high utilization for the limited spectrum in order to fulfill needs for all users’ demands which are considered as a problem in wireless communications due to rapidly increasing in wireless applications and service. This system is exposed to attack due to the vulnerabilities existence in this system. So, the main outcome of this paper is to investigate the performance of the cooperative sensing in cognitive radio networks under malicious attacks over different channel impairments, and to illustrate the most suitable individual probability of detection in real faded channel by using Nakagami model. This paper illustrates the effectiveness of the attacks and fading on the performance of spectrum sensing process.
