查看更多>>摘要：To facilitate the integration of terrestrial and satellite mobile communication systems in the future, the new generation of satellite mobile communication system should be Long-term evolution (LTE)-based. In LTE, voice is carried by Internet protocol (IP) packets (voice over IP, VoIP). The feasibility of LTE-based Geosynchronous earth orbit (GEO) satellite mobile communication systems for VoIP is discussed. Detailed link budgets are created for typical handheld terminals. The effectiveness of Physical resource block (PRB) bundling and Transmission time interval (TTI) bundling for the capacity improvement of downlink and uplink are evaluated, and further uplink improvement for low level terminals by Narrowband resource block (NRB) scheme is also studied. The analysis results show that the downlink VoIP transmission is mainly power limited, and optimization of PRB or TTI bundling can maximize the capacity. For uplink, only highlevel terminals can support VoIP under the normal LTE frame structure, and TTI bundling and Resource block (RB) block techniques can help the low-level terminals support VoIP transmission.
查看更多>>摘要：A multi-user detection algorithm for multiple access interference suppression combined with the minimum mean squared error and an artificial fish swarm algorithm is proposed. By taking advantage of the artificial fish swarm algorithm, the proposed algorithm can quickly converge to the optimal solution. The variation in the minimum mean squared error based test results is assigned to the artificial fish swarm algorithm, which is regarded as the initial state of artificial fish. The simulation results show that the proposed algorithm has a better multi-user capacity performance and lower bit-error rate than the minimum mean squared error detector.
查看更多>>摘要：It is critical to design a reliable packet transmission scheme to improve throughput in Energy harvesting Wireless sensor network (EH-WSN) or Battery free Wireless sensor network (BF-WSN). We present the Optimal size and rate (OSR) scheme to improve throughput of communication links in the IEEE 802.15.4 based BF-WSN that harvests radio frequency energy. Based on the defined truncated geometrical distribution, we formulate the optimization problem that maximizes the effective throughput of communication link. The solution of the optimization problem yields the optimal triple, namely the optimal packet size, data rate, and Maximum number of transmission trials (MNTT), which is used in the OSR so that throughput is considerably improved. Simulation results show the OSR scheme can improve throughput.
查看更多>>摘要：An efficient analytical method is proposed to calculate the Shielding effectiveness (SE) of an enclosure with an oblique rectangular aperture. This enclosure was first decomposed into two ones with horizontal rectangular apertures through mirror image and Green function theories. The SE of each decomposed enclosure was calculated by the Robinson's method. The relationship between the SE of the original cavity and those of the decomposed ones was also derived analytically. The SE of the original cavity could be directly obtained from this analytical relationship. The accuracy of the proposed method was validated with measurements and the Transmission line matrix (TLM) solver. The results show that the efficiency was largely improved compared with the TLM solver.
查看更多>>摘要：Micro-motion characteristics play an important role in some applications of radar target classification. In this paper, a classification method of rigid targets in space using radar micro-Doppler signatures is proposed. Based on the attitude kinematics of rigid targets, we analyze feasibility of classification using micro-Doppler signatures by the relationship among inertial properties of typical rigid targets, their micro-motion characteristics, and corresponding modulation to radar echoes. According to the micro-Doppler time-frequency distribution of echoes and the scale of training sample set, Convolutional neural network (CNN) based feature extraction method and softmax Classifier are designed. Simulations are carried out to validate its effectiveness and discuss the impact of observation duration, composition of training data and size of convolutional kernels on its classification robustness and computational cost.
查看更多>>摘要：Constant false-alarm rate Block-sparse Bayesian learning (CFAR-BSBL) algorithm is proposed to reduce the computational complexity and improve Direction of arrival (DOA) estimation accuracy of offgrid signals with coprime array. Firstly, a signal model with normalized noise is built to avoid the learning procedure of noise parameter. Secondly, a block sparse Bayesian framework is built with the introduction of a temporary correlation matrix in order to use t he temporal structure of incident signals. Then the algorithm uses CFAR detection to detect the grids close to the real DOA and relieve the dependence on the number of signals. Finally, an off-grid process based on the closest grids is adopted to deal with the off-grid problem. The proposed CFAR-BSBL algorithm can obtain high accuracy and low complexity DOA estimation of off-grid signals with coprime array.
查看更多>>摘要：Accurate on-wafer large signal charac-terization of RF transistor is crucial for the optimum design of wireless communication circuits. We report a novel and systematic measurement method for the accurate acquisition of input and output power of on-wafer transistors up to 40GHz. This method employs external couplers to extract the travelling waves, combined with a novel large signal calibration algorithm to calculate the power at on-wafer probe tip. The accuracy of this method was bench marked versus conventional approaches in a real measurement bench, and further been verified by characterizing the large signal response of a 0.25μm GaN HEMT device. It is concluded that the measurement uncertainty has been greatly decreased with this new method, especially at mm-wave frequencies.
查看更多>>摘要：A novel structure cavity filter, cross-coupled multi-cavity filter with double-layer structure is proposed. The transmission zero of cross coupling is analyzed qualitatively and quantitatively, while some of the design experience of simulation modeling are summed up and the magnetic coupling and electric coupling of synchronously tuned coupling resonators with double-layer structure are studied. Simulation and experimental results show that the cross-coupled multi-cavity filter with double-layer structure not only can meet the high selectivity requirements, but also save space, which is conducive to miniaturization design. The feasibility, practicability and superior performance of the double-layer multi-cavity filter are fully verified by the experimental samples and the measurement results of the six-pole double-layer base station filter processed by the design model.
查看更多>>摘要：Degradation and self-recovery of poly-crystalline Silicon (poly-Si) Thin film transistor (TFT) by using complementary metal oxide semiconductor (CMOS) inverter were investigated. Under DC stress, degradation mechanisms were clarified by comparing the Voltage transfer characteristics (VTC) of fresh and stressed inverters. It is determined that Negative bias temperature instability (NBTI) of p-TFT dominates the degradation of the inverter under zero bias DC stress. After removing the stress, the VTC continues to be degraded, because the interface trap-states and the grain boundary trap-states increase due to hydrogen species diffusion. It is found out that the VTC is shifted to its right side severely with negative bias stress of VIN. The NBTI of p-TFT is enhanced and the NBTI of n-TFT also plays a role on the degradation. When removing the negative bias stress, the self-recovery of NBTI of n-TFT and the continuing degradation of NBTI of p-TFT become competing mechanisms, together controlling the VTC after-stress behavior. Consequently, the continuing degradation of NBTI of p-TFT is restrained by self-recovery of NBTI of n-TFT.
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