Advanced Materials Research Vols. 760-762

Abstract: The technology of OFDM is a multi-carrier technology, and it is a kind of high efficient modulation technique, it has the ability of strong anti multi-path propagation and frequency selective fading, and higher frequency spectrum utilization rate, this technology is applicable to high speed data transmission in the multi-path and fading channel environment. This paper introduces the basic principle of OFDM adaptive system, and the SNR estimation of OFDM adaptive system in Gauss channel through the simulation, this is a theoretical foundation to practical application in the future.

Abstract: The frequency hopping (FH) communication is one of the anti-interference effective means in military wireless communication, the FH number and FH rate of FH radio are the main parameters that determines the performance of the FH radio, these parameters are determined by the structure and the index of the frequency synthesizer, therefore the performance of the FH radio depends very much on the frequency synthesizer, this paper introduces the basic principle of FH radio, the basic methods of frequency synthesizer in the radio, the design scheme frequency synthesizer, and the DDS CMOS chip and the PLL CMOS chip that those used in scheme.

Abstract: A complete set of RFID system is composed of two parts by Reader and Transponder grounds of the action principle Reader launch of unlimited radio waves of a specific frequency energy to Transponder, to drive Transponder circuit ID Code sent internally. Part of the embedded system software is including the operating system software (requires real-time and multi-tasking operation) and application programming. The operating system controls the application programming and hardware interaction, and the application to control the operation and behavior of the system. The paper presents the application of RFID technology in development embedded systems. The experiment shows RFID is superior to ARM in building embedded system.

Abstract: Encryption is the core of security technology. The paper managed to design and implement a kind of reconfigurable cipher unit based on the 3DES/AES and optimized by FPGA technology, which can effectively support diverse cryptographic algorithms and can meet the demand on system performance and flexibility. The unit uses hardware description language VHDL, layout and wire on QuartusII8.0. Finally the system is downloaded to DE2 for testing. The design hardware structure is simple, flexibility, security, which can be widely used in the field of information security.

Abstract: In this paper aiming at maximizing the spectral efficiency, a cross-layer design which combines adaptive modulation and coding (AMC) at the physical layer and truncated automatic repeat request (ARQ) protocol at the data link layer in cooperation system is proposed. In order to analyze the system performance, we first derive a closed form expression of probability density function (PDF) of the received signal-to-noise (SNR) using maximum ratio combing (MRC) at the destination node, the theoretical results and simulation show that the new design outperforms the traditional AMC system especially at low SNR.

Abstract: Anti-jamming of GPS receiver is an important problem in navigation war, and this topic has been well researched recently. However, anti-jamming in the complex receiving environment has not been considered in the most of the researches. To solve this problem a cascade anti-jamming method is proposed in this paper. In this scheme, each channel of the received signal vector is processed by utilizing a method based on STFT, after the signal in each channel passed through the processor, a spatial processing has been employed to, suppress the reserved interferences. The results of simulations show that, it can be seen from the time-frequency spectrum before and after the first step processing that the single-tone and non-stationary interferences have been mitigated, and it demonstrates that the performance of the ideal classic Weiner filter can be achieved in the proposed method.

Abstract: For the reliable operation of the power grid, multi-agent system is applied to multi-level relay protection to improve the fast response of the short-circuit protection. The thesis conducts the simulation concerning the conventional backup protection and the protection mode based on multi-agent system and makes performance comparison. The results prove that multi-agent system can shorten the response time effectively.

Abstract: This paper introduces a design process of a Bi-directional DC-DC converter. The main circuit uses a single-ended forward converter circuit, ARM as controller. The adoption of the synchronous rectify technique and full digital control make the whole system possess the advantages of compact structure, high conversion efficiency, easy control, reliable work and realize the energy conversion in bi-directional freely. We can verify the feasibility of the program through prototype testing.

Abstract: A new kind of gas sensors were prepared via chemical polymerization of polypyrrole (PPy) as sensitive layer on base of Mg₂SiO₄ porous ceramics. Thermal stability of the PPy sensitive layer was characterized with thermogravimetric analysis, including TG and DTA. Chemical structure of the samples was identified with X-ray diffraction (XRD) analysis. Microstructure of the PPy film was observed by a scanning electron microscope (SEM). Chemo-electrical relationship of the gas sensors was investigated with the resistance variation of PPy films at different gas concentrations. Based on series of experimental results, linear behavior of the chemo-electrical relationship was obtained for the gas sensor, y=0.00344x+1.33754, with R²=0.9734.

Abstract: To achieve a certain precision when mapping in accord with a particular proportion or scale with stereo mapping camera, the change of chief ray height of the edge field due to the fluctuation of working temperature is required to be within the range of microns, and at the meantime the size and structure layout of three-linear array stereo mapping camera are determined directly by the configuration of optical system. Based on the requirements of refractive optical system with long focal length, academic calculation and actual optical designs based on two typical configurations for stereoscopic mapping camera are made,the actual working temperature and performance requirements are also taken into consideration, the results including the modulation transfer function, distortion and stability comparison are also given.