Advanced Materials Research Vols. 989-994

Abstract: According to the characteristics of PCM / FM signals, we propose a new method based on STFT resolve tune software. Firstly, the spectral characteristics of PCM / FM signal is given use of the spectrum PCM / FM signal is demodulated theoretical basis. This paper discusses in detail the basic principles of this demodulation method and implementation process, analyze the demodulation performance and complexity of the method.

Abstract: In this paper, an adaptive filter method for Chirp signal in additional white Gaussian noise (AWGN) is studied. First, we analyze conception and character of FRFT (Fractional Fourier Transform), and the results shows that Chirp signal has energy concentration character in FRFT domain. Then, an adaptive filtering method is introduced in FRFT domain, and a test is done for separating Chirp signal from AWGN by the filtering method. Last, performance of this filtering method is studied, and the SNR improvement expression is concluded to verifying its advantages, it depends on the performance of adaptive filter basically. At last, the results show that this filtering algorithm is simple in computation and easy in implementation.

Abstract: Aimed at the problem that the demodulation threshold of non-coherent demodulation technology of PCM/FM telemetry system using frequency modulation in the present situation of aerospace measurement and control is higher, research a kind of multiple symbol detection based on maximum likelihood thought (Multi-Symbol Detection, MSD) demodulation method. This paper introduces the principle of multiple symbol detection and aiming at the shortcomings of the previous synchronization method, studies a kind of symbol decision process and synchronization of the combination of synchronization method.

Abstract: Chirp signal has been used widely in radar signals, and the Fractional Fourier transform is one of the most effective tools to analyze Chirp signal. In this paper, the concept of FRFT and the estimation theory of Chirp signal are introduced firstly. Then, we study three Chirp signal detection algorithms based on character of Chirp signal energy concentrated in a certain FRFT domain. Finally, in order to test the estimation abilities of the frequency modulation rate and the central frequency of FRFT to Chirp signal, and compare the operation time of parameters estimation under different SNR of the three algorithms, we simulate performance of the Three methods, and the final simulation results show that the three method have remarkable capabilities of detecting Chirp signal with low SNR. In contrast, the two-searching method doesn’t need planar search, consumedly reducing the computation cost at the same precision.

Abstract: Exploiting the sparsity of MR signals, Compressed Sensing MR imaging (CS-MRI) is one of the most promising approaches to reconstruct a MR image with good quality from highly under-sampled k-space data. The group sparse method, which exploits additional sparse representation of the spatial group structure, can promote the overall sparsity degree, thereby leading to better reconstruction performance. In this work, an efficient superpixel/group assignment method, simple linear iterative clustering (SLIC), is incorporated to CS-MRI studies. A variable splitting strategy and classic alternating direct method is employed to solve the group sparse problem. The results indicate that the proposed method is capable of achieving significant improvements in reconstruction accuracy when compared with the state-of-the-art reconstruction methods.

Abstract: The traditional method of demodulation for PCM/FM telemetry demodulation threshold is higher and the computation of the larger problem, research an orthogonal baseband after rotation, Symbol Detection (Multi - Symbol Detection, MSD) technology: the first frequency under the intermediate frequency digital telemetry signals processing, single sign on orthogonal baseband signal correlation matching, and then apply compound spinning technology to meet at the same time for multiple element symbols at the same time Detection, the purpose of the final design step length synchronization method with demodulation smoothly.

Abstract: in view of the incomplete signal and other issues brought by the threshold trigger in the conventional blast wave signal test, this paper designed a post-trigger data high-speed collection method, adopted the ARM7 kernel MCU to complete the design of the hardware scheme and preparation of the corresponding test software, then developed the post-trigger data high-speed collector prototype, and completed the explosive shock wave signal collection through the test. Experiments show that the post-trigger high-speed data collector developed in this paper has the characteristics of simple interface circuit, high precision collection, good reliability, simple operation, which can meet the test requirements of blast wave.

Abstract: In underground channel environment, features of wireless mobile channel and channel modeling are discussed, and methods of calculating wireless channel model parameters by adopting even-interval tapped delay wire model are proposed. On this basis, Matlab simulation are carred out, whose results serve as theoretical foundation and criterion for further study of underground wireless communication system.

Abstract: For the issue of MIMO airborne radar clutter modeling in different environment conditions, a clutter modeling method based on composite model is proposed. It builds different types of clutter model through the changes of model parameters. The clutter model consists of clutter amplitude distribution model, and clutter cell scattering model. After considering the error factors such as element error, channel error, clutter fluctuation, a clutter modeling method based on composite model under error conditions is proposed. Finally, the computer simulation is made about the amplitude, the back-scatter coefficient, error factors, the space-time MV spectrum and the characteristic spectrum of different types of clutter through changing the model parameters. The simulation results show that: In ideal conditions, the Clutter Spectrum has good space-time characteristic, but in error conditions, the clutter fluctuates tempestuously, and in different environment conditions the fluctuation degree is different.

Abstract: The genetic algorithm is a randomized search method for a class of reference biological evolution of the law evolved, with global implicit parallelism inherent and better optimization. This paper presents an adaptive genetic algorithm to optimize the use of BP neural network method, namely the structure of weights and thresholds to optimize BP neural network to achieve the recognition of banknotes oriented. Experimental results show that after using genetic algorithms to optimize BP neural network controller can accurately and quickly achieved recognition effect on banknote recognition accuracy compared to traditional BP neural network has been greatly improved, improved network adaptive capacity and generalization ability.