Applied Mechanics and Materials Vols. 719-720

Abstract: To solve the space dispersion (SD) problem which makes the beam formed deviate from its expected direction in wideband digital array beamforming, a new wideband digital array beamformer (WDBF) is designed by introducing an identical variable fractional delay (VFD) filter on each sensor. The VFD filter is an all-pass filter with an infinite impulse response, thus it requires less filter order compared with finite impulse response filter. Since the VFD designed is suitable within the whole fractional delay range of-0.5 to 0.5 in sampling interval, the new beamformer designed is suitable for any direction without redesigning the fractional delay filter. In this way, the real-time property of the new beamformer is guaranteed. Simulation results show that the VFD deigned in this paper is high in precision. Applying it in the new WDBF, the SD problem is solved and the beam formed approximates the ideal beam very well.

Abstract: In this paper, we propose a content-based routing algorithm for WInternet Pipe Communication Protocol. A filter model based on a multilevel index structure is established to judge the covering relation between two subscription criteria. Furthermore, our routing algorithm takes advantage of covering relations and link status among nodes to build a virtual message distribution tree for each OutGate. Meanwhile, it supports nodes join and leave dynamically without impacting the routing accuracy. Analysis result shows it can reduce the message matching costs, keep the load balance among nodes and improve the transmission performance of WInternet to some extent.

Abstract: In the paper, we investigate LDPC-coded differential amplitude/phase modulation (APM) schemes for correlated Rayleigh fading channels. Through the observation for the mutual information of the extrinsic log-likelihood ratio (LLR) values of the variable nodes in the LDPC decoder, it is found that the code design methods investigated in the previous literature loses their accuracy. Consequently, a modified code design method for the outer LDPC code is proposed in this paper. It is shown that the searched LDPC code effectively improves the error performance, when compared to the convolutional-coded scheme investigated in the previous literature.

Abstract: A comprehensive theoretical model of direct detection (DD) optical orthogonal frequency division multiplexing (OOFDM) system is described in general. The principle of OOFDM is introduced in detail. Several key technologies in DD-OOFDM system have been discussed. The advantages and methods for optical single sideband (OSSB) and channel estimation are analyzed completely. Other key technologies are introduced briefly.

Abstract: With the popularity of the network and mobile Internet, numerous social network platforms appeared in the world. Also, there have been a large number of users using a plurality of social network platforms at the same time. When these users use multiple social network platforms, they need to overcome many difficulties such as switching social network client applications frequently and so on. This article takes consideration of the needs of the multiple social networks’ users, proposing a solution to solve multi-barrier problem, and demonstrating the feasibility and effectiveness of the method by actual cases.

Abstract: —when the noise cancellation system ( NC ) is used in the down link of the power line carrier terminal, it can cancel the background noise and narrowband interference, but the downlink signal tone distorts at the same time. This is because the VAD algorithm of the NC system is sensitive to dramatic changes in the power of signal tone. Through detailed researches on time frequency characteristics of signal tone and error factors of network transmission, a new signal tone detection algorithm that applicable to downlink NC system was put forward, The algorithm detects signal tones through changes of frequency-domain power and time-domain signal period of every frame. After theoretical evaluation and practice tests, it is observed that the above-mentioned algorithm can correctly detect signal tones without influence on functions of the NC system, so as to avoid the occurrence of distortion.

Abstract: The noise coefficient and the power gain of a low noise amplifier affect the whole performance of the receiver. This paper presents the design and simulation of 2-stage low noise amplifier using the MGA633P8 and TQP3M9028’s S parameters to set S2P files. Not only analyze how to insert elements to match a broadband circuit, but also make some optimization by using the Agilent ADS in the case of small signal. Simulation results show that the proposed work implements a high performance of 2-stage low noise amplifier which works at 824 MHZ to 1980 MHZ, the gain is greater than 25 db, the noise coefficient is less than 0.6, input and output standing wave ratio (SWR) are both less than 1.3.

Abstract: In this paper, the effect of device flicker noise on the characteristics of both opto-electronic oscillator and Photonic-delay homodyne phase noise measurement system is analyzed. An analytic theory model of opto-electronic oscillator (OEO) is derived and verified by experiments in this paper, where the flicker and white noise are both considered. The sensitivity of Photonic-delay homodyne phase noise measurement system is improved by using high-linear photodetector and low-phase noise amplifier resulting from decreasing systematic phase noise.

Abstract: Two 81-96 GHz frequency triplers, one balanced and one single device, are implemented using a 0.10 μm GaAs pHEMT process. The EM simulation results show that the triplers perform a best conversion gain of -6.8 and -4.7 dB for the balanced and the single device, respectively. The conversion gain of the balanced tripler operating from 81 to 96 GHz is above -9.6 dB at 3dBm input power. The conversion gain of the single device operating from 81 to 96 GHz is above -8 dB at -0.5dBm input power. The fundamental and second harmonic suppression are as high as 30 dB over the whole operating frequency (81-96 GHz) for both circuits.

Abstract: A novel efficient hybrid accelerated method is proposed for the fast analysis of the monostatic electromagnetic scattering problems arising from volume-surface integral equations (VSIE) formulation. In the first step, by utilizing the low rank property, several largest eigenvalues and corresponding eigenvectors of the multiple right hand sides can be computed and saved efficiently by adaptive cross approximation (ACA) algorithm. The iterative solution of linear equations is required at these principle eigenvectors. Compared with solving linear equations at each angle repeatedly, the proposed method is able to greatly reduce the number of equations. In the second step, a disturbed symmetric successive over-relaxation (D-SSOR) preconditioner is constructed to speed up the convergence rate of iterative methods. Numerical results demonstrate that the present method can reduce the computational time significantly for monostatic VSIE calculation with high accuracy.