[Show abstract][Hide abstract] ABSTRACT: In order to provide the basic theory and reference for the vertical actuator, a precision piezoelectric actuator is designed in the paper. Firstly, working principle and mechanical design are presented. Then motion principles of this actuator are investigated. Finally output characteristics, load characteristics and frequency characteristics are tested and analyzed. The research results reveal that the step distance is adjustable, and when the drive voltage is 120V, the step distance is 1.4μm stably. Under the same conditions, due to gravity, the step distance of crawling up is less than crawling down. With the increasing of the driving voltage, the actuator load capacity is on linear growth. The displacement of actuator has a non-linear relationship with the frequency of drive signals. To sum up, the vertical actuator is a stable but multivariable system, the performance of their campaigns is affected by a variety of factors.
[Show abstract][Hide abstract] ABSTRACT: Cognitive radio is a promising technology for more efficient utilization of radio spectrum. It can sense the available spectrum and use temporarily-unused licensed spectrum without interfering with primary users. Spectrum sensing performance of an individual unlicensed secondary user will be seriously degraded due to the effect of channel fading. In order to alleviate this problem, we propose an effective cooperation spectrum sensing scheme based on energy detection, which is achieved by using a selective-weighted combination of local decision statistics from cooperative secondary users. The weight allocated to each cooperative secondary user is determined through evaluating the contribution of local sensing to the final decision making. Simulation results show that the proposed cooperation scheme can provide significant performance improvements in spectrum sensing of cognitive radio networks.
[Show abstract][Hide abstract] ABSTRACT: Cognitive radio is an advanced technology for more efficient spectrum utilization systems based on opportunistic spectrum sharing. The security-related issue is very important. This paper proposes that frequency hopping technology is introduced into the cognitive radio system in order to guarantee security. The design of frequency hopping pattern, which is the key issue for the cognitive radio system with frequency hopping technology, is illustrated. And the interference suppression performance of cognitive radio systems with frequency hopping technology is investigated. Performance analysis and simulation results verify the validity of the proposed method.