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Now showing items 17 - 22 of 22

  • Novel Preamble-Based Channel Estimation for OFDM/OQAM Systems

    Jinfeng Du   Svante Signell  

    OFDM/OQAM has been considered as an attractive alternative to classic OFDM with cyclic prefix (CP) over doubly dispersive channels. By utilising well designed pulse shapes and removing CP; OFDM/OQAM has the advantage of reduced outof-band energy and a theoretically higher spectral efficiency. However; channel estimation over doubly dispersive channels has been a big problem for OFDM/OQAM due to the nonorthogonality between the real and imaginary parts of its modulated signals. Therefore conventional channel estimation (CE) methods used for OFDM cannot be directly applied to OFDM/OQAM. Recently a preamble-based CE method interference approximation method (IAM) has been proposed to ease this task. By treating the intrinsic interference from neighbour symbols as known information; two heuristic preamble sequences have been constructed based on tentative observations; which turn out to be suboptimal. In this paper; we present a general theoretical framework for IAM preamble design and apply it to identify the optimal IAM preamble sequence which results in a higher gain. Numerical results have verified the effectiveness of the theoretical framework and a gain of 2.4 dB against CPOFDM has been demonstrated with the new preamble in various doubly dispersive channels with a QPSK modulation.
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  • Gbps User Rates Using mmWave Relayed Backhaul with High Gain Antennas

    Jinfeng Du   Efe Onaran   Dmitry Chizhik   Sivarama Venkatesan   Reinaldo A. Valenzuela  

    Delivering Gbps high user rate over long distances (∼1 km) is challenging, and the abundant spectrum available in millimeter wave band cannot solve the challenge by its own due to the severe path loss and other limitations. Since it is economically challenging to deploy wired backhaul every few hundred meters, relays (e.g., wireless access points) have been proposed to extend the coverage of a base station which has wired connection to the core network. These relays, deployed every few hundred meters, serve the users in their vicinity and are backhauled to the base station through wireless connections. In this work, the wireless relayed backhaul design has been formulated as a topology-bandwidth-power joint optimization problem, and the influence of path loss, angular spread, array size, and RF power limitation on the user rate has been evaluated. It has been shown that for a linear network deployed along the street at 28 GHz, when high joint directional gain (50 dBi) is available, 1 Gbps user rate within cell range of 1 km can be delivered using 1.5 GHz of bandwidth (using single polarization antennas). The user rates drop precipitously when joint directional gain is reduced, or when the path loss is much more severe. When the number of RF chains is limited, the benefit of larger arrays will eventually be surpassed by the increased channel estimation penalty as the effective beamforming gain saturates owing to the channel angular spread.
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  • Research on the failure of the induced draft fan's shaft in a power boiler

    Jinfeng Du   Jun Liang   Lei Zhang  

    Highlights • In this paper, the failure investigation had been paid attention to the analysis of failure cases which ranged from material performance, equipment's design to service condition of equipment, and thus the preventive measures were developed in order to avoid the recurrence of the similar failure. Abstract The failure of the induced draft fan's shaft in a power boiler was been analyzed. The performances of material applied satisfied the design requirement. The order torsional vibration showed anomaly at the shaft's smallest diameter for the design condition and the actual radius of that chamfer less than the design radius caused more significant stress concentration. The additive effect of the abnormal torsional vibration and the higher stress concentration induced the microcrack's initiation along the network pearlite's interface. The vibration and the alternating torsional loading in the induced draft fan's service led to crack growing along the different direction and fracture presenting the typical ratchet-like characteristic.
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  • PAX3 inhibits β-Tubulin-III expression and neuronal differentiation of neural stem cell

    Sixian Cao   Jinfeng Du   Yan Lv   Hengrong Lin   Zuming Mao   Man Xu   Mei Liu   Yan Liu  

    Abstract PAX3 functions at the nodal point in neural stem cell maintenance and differentiation. Using bioinformatics methods, we identified PAX3 as a potential regulator of β-Tubulin-III (TUBB3) gene transcription, and the results indicated that PAX3 might be involved in neural stem cell (NSC) differentiation by orchestrating the expression of cytoskeletal proteins. In the present study, we reported that PAX3 could inhibit the differentiation of NSCs and the expression of TUBB3. Further, using luciferase and electrophoretic mobility shift assays, we demonstrated that PAX3 could bind to the promoter region of TUBB3 and inhibit TUBB3 transcription. Finally, we confirmed that PAX3 could bind to the promoter region of endogenous TUBB3 in the native chromatin of NSCs. These findings indicated that PAX3 is a pivotal factor targeting various molecules during differentiation of NSCs in vitro . Highlights • PAX3 expression is negatively correlated with the TUBB3 expression. • PAX3 inhibits the neuronal differentiation characterized with TUBB3 expression. • PAX3 binds the promoter region of TUBB3 gene and inhibit the TUBB3 transcription.
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  • Design of isotropic orthogonal transform algorithm-based multicarrier systems with blind channel estimation

    Jinfeng Du   Pei Xiao   Jinsong Wu   Qingchun Chen  

    Orthogonal frequency division multiplexing (OFDM) technique has gained increasing popularity in both wired and wireless communication systems. However, in the conventional OFDM systems the insertion of a cyclic prefix (CP) and the transmission of periodic training sequences for purpose of channel estimation decrease the system’s spectral efficiency. As an alternative to OFDM, isotropic orthogonal transform algorithm (IOTA)-based multicarrier system adopts a proper pulse shaping with good time and frequency localisation properties to avoid interference and maintain orthogonality in real field among sub-carriers without the use of CP. In this study, the authors propose linearly precoded IOTA-based multicarrier systems to achieve blind channel estimation by utilising the structure of auto-correlation and cross-correlation matrices introduced by precoding. The results show that the proposed IOTA-based multicarrier systems achieve better power and spectral efficiency compared with the conventional OFDM systems.
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  • Numerical simulation on the effect of welding parameters on welding residual stresses in T92/S30432 dissimilar welded pipe

    Lei Zhao   Jun Liang   Qunpeng Zhong   Chao Yang   Biao Sun   Jinfeng Du  

    Highlights • The peak residual stress is located at HAZ of T92 steel side. • By changing welding parameter to reduce residual stress on dissimilar welds. • Small groove angle greatly reduces peak residual stress in HAZ of T92 steel side. • More layer number reduces peak tensile residual stress on welds and S30432 steel. • Small heat input reduces peak tensile residual stress on welds and S30432 steel. Abstract Dissimilar welded joints are commonly used in fossil power plants to connect martensitic steel components and austenitic stainless steel piping systems. The integrity for such welded structures is depended on residual stresses induced by manufacturing process. In this paper, the characteristics of residual stresses on the dissimilar welded pipe between T92 steel and S30432 steel were investigated using finite element method. Moreover, the effects of heat input, groove shape and layer number on the residual stress distribution were studied to find the approach to reduce the residual stress. The numerical results revealed that the hoop and axial stress in heat affected zone (HAZ) of T92 steel side of the dissimilar welded joint had sharp gradients. By decreasing the groove angle, the peak values of the hoop and axial stress on T92 steel side were reduced greatly while the peak values in welded metal and HAZ of S30432 steel side differed little. Furthermore, more layer number and less heat input decreased the peak value of the tensile residual stress on welded metal and S30432 steel side, but had little effect on the residual stress in T92 steel side.
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