Applied Mechanics and Materials Vols. 347-350

Abstract: In cognitive radio networks (CRNs), the secondary users (SUs) need to continuously detect whether the primary users (PUs) occupy the spectrum. In order to improve the spectrum sensing accuracy, a novel reliable cooperative spectrum sensing strategy based on the detection results relayed twice from the secondary relays (SRs) to the secondary source (SS), referred to as CSS-DRT, is proposed in this paper. In this scheme, the spectrum sensing slot is divided into four equal sub-slots. In the first and third sub-slots, the SS and SRs detect the PU by themselves. Then, in the second sub-slot, if the SRs that detect the PU during the first sub-slot are more than or equal to a prespecified quantity, the corresponding SRs will send their flag signals (FSs) to the SS while the others keep quiet, where the FS is narrowband and indicates that the PU is present. Otherwise, if the SRs that detect the PU during the first sub-slot are less than the prespecified quantity, all the SRs will keep quiet in the second sub-slot. Meanwhile, the SS detects the PU based on the received signals from the PU and SRs. And, the SS uses the same method as employed in the second sub-slot to detect the PU in the last sub-slot wherein the SRs send their FSs based on their detections made during the third sub-slot. Finally, an ultimate decision is made by the OR ruler based on the SS detection results obtained during the spectrum sensing slot. Besides, we derive the closed-form expressions of the false alarm and detection probabilities for the proposed CSS-DRT scheme. In the end, simulation and numerical results show that our proposed scheme can achieve better performance than the non-cooperative method and an existing cooperative spectrum sensing method.

Abstract: This paper describes the design and implementation of a mini multi-process micro-kernel embedded Unix-like operating system on ARM platform in technical details, including MMU and memory space mapping, init process, inter-process communication, process management, TTY and tiny shell, multi-level priority-queue schedule, and signaling. The mini OS is developed on Linux platform with GNU tool chain by the author of this paper. The architecture of the mini OS is analogous to that of Minix. Based on it, other operating system components such as file system, network management, and copy-on-write can be appended to form a full-featured embedded operating system. The mini OS can be used for both embedded system application development and related curriculum teaching.

Abstract: This paper proposes a novel stacked tri-band circularly polarized antenna which has three independent ports. To obtain tri-band operation, a stacked three layers of microstrip antenna working at different frequency is presented. Each of them is fed by dual feed probes. The simulated results show that the antenna can cover Compass Navigation Satellite System CNSS B3 1.268 GHz, L band 1.615 GHz and S band 2.49 GHz. The proposed antenna has achieved a bandwidth of 3.1%, 6.8% and 2.3% at each band, respectively. It exhibits small axial ratio under 3dB in three bands for the CNSS applications. Details of the proposed antenna design and results for the obtained tri-band circularly polarized performances are presented and discussed.

Abstract: The GaN HEMT is widely used in high-frequency aspects, use the T-gate to reduce gate resistance is one of the most effective methods to improve the the device maximum oscillation frequency (fmax). But f_max is very sensitive to T-gate size, improper selection may reduce f_max, Therefore, in order to reduce the cost of production, it is necessary to select appropriate simulation T-gate size. We have worked out AlGaN/GaN HEMT with gate length of 0.17μm and f_max values 110GHz. Accuracy of the simulation model is verified by experiment. Then detailed simulates the impact of the T-gate size and we obtain ptimized T-gate size range.

Abstract: This paper introduces the design and implementation of a large points FFT acceleration unit of multi-processor system based on FPGA. It introduces radix-2 DIT-FFT algorithm and the features of hardware platform. It analyzes the FFT acceleration unit overall and divides it into several modules. Then hardware implementations of modules are discussed. The whole FFT acceleration unit is a part of one multi-processor image processing system and the whole system is tested by software and hardware co verification. Results are verified between the software simulation and Virtex6 evaluation board of Xilinx Company. The results are compatible in the range of error. The FFT acceleration unit meets the needs of the whole system and the design is successful.

Abstract: This paper describes the design and implementation of an ARM based embedded operating system micro kernel developed on Linux platform with GNU tool chain in technical details, including the three-layer architecture of the kernel (boot layer, core layer and task layer), multi-task schedule (priority for real-time and round-robin for time-sharing), IRQ handler, SWI handler, system calls, and inter-task communication based on which the micro-kernel architecture is constructed. On the foundation of this micro kernel, more components essential to a practical operating system, such as file system and TCP/IP processing, can be added in order to form a real and practical multi-task micro-kernel embedded operating system.

Abstract: ModBus Protocol is researched and developed by MODICOM company which owns its copyright.The research about Remote Transmit Manage Unit applies the opened ModBus protocol. The text of protocol itself is very simple and can be easily obtained.The protocol is surpported by both domestic manufacturers and international manufacturers.According to the device which we will research,we apply a mini-subsets of Modbus protocol and dont realize all content

Abstract: In order to solve interoperability of the distribution automation devices and Plug and Play issues, propose intelligent power distribution model based on IEC61850, Stratifie according to the method of information: Master level,feeder layer,the terminal layer,device layer, layer monitoring. Use the face of the object model of the distribution automation IED, at the same time, use abstract communication service independent of the specific communication technology model ACSI, Establish distribution network automation system communication system Follow the IEC61850 standard.

Abstract: This paper focus on overvoltage protection and insulation coordination in Modular Multilevel Converter based HVDC system planning. An overvoltage protection scheme, which bases on the topology used inTransbay project by Siemens, is proposed in this paper. Thescheme draws fromthe characteristics of MMC-HVDC systems and the research results in classic HVDC systems, byplacing arresters at some key locations in the MMC-HVDC converter station.With this scheme, the overvoltage at those key pointscan be limitedto an acceptable range and hence protect the key equipment concerned. Since all the DC lines of the project are undersea cables, no lighting overvoltage is considered and 14 faults which could happen are carefully selected to serve as the verification conditions for the insulation design. Based on the PSCAD/EMTDC simulations and the deterministic method, the specified withstand voltage levels of the critical equipment in the converter station is calculated.

Abstract: Around the type of power system of the low frequency oscillation, the mechanism of production, the analysis methods, the analysis tools and suppression method, etc, it summarized the research status of low frequency oscillation of power system. Therefore, based on this research status, the future analysis methods and developmental trend of the low frequency oscillation of power system were discussed.In the power system, the angle of attack among generators, the voltage on the nodal points and the tidal current of junctor and so on had the constant-amplitude or the increased range vibrates, and the oscillation frequency (generally is 0.2~2.5 Hz) is lower than the system frequency. This oscillation form is called the low frequency oscillation[1]. Then the frequency of the low frequency oscillation is low, cycle to be longer,and affected area to be wide, it is also big harm to the power system. Therefore, at present, studying low frequency vibration has the even more important meaning[2].