Current Issue : October - December Volume : 2015 Issue Number : 4 Articles : 6 Articles
A joint communication and ranging system would constitute a unique platform for future weapon platform or intelligent\ntransportation system to affect the essential tasks of Identification Friend or Foe (IFF) system and location sharing services, in\nterms of both spectrum efficiency and cost effectiveness. In this paper, the design of efficient modulation system which is suitable\nfor simultaneously performing both data transmission and range measurement is proposed. The approach is based on extended\nbinary phase shift keying (EBPSK) or M-ary Position Phase Shift Keying (MPPSK) modulated waveforms utilized in digital\ncommunication. In particular, requirements that allow for employing such signals for range measurements are investigated. Also,\nConstant False Alarm Rate (CFAR) target detection performances of the new proposed system are discussed when target velocity\nand time delay take different values.Moreover, Doppler tolerance range of impacting filter for demodulating EBPSK/MPPSK pulse\nsignal at 10GHz is considered. In addition to theoretical considerations, the paper presents simulations and measurement results\nof the new systems, demonstrating the high spectral utilization of integrated communication and ranging applications....
For low earth orbit (LEO) satellite GPS receivers, space-based augmentation system (SBAS) ephemeris/clock corrections can be\napplied to improve positioning accuracy in real time.The SBAS correction is only available within its service area, and the prediction\nof the SBAS corrections during the outage period can extend the coverage area. Two time series forecasting models, autoregressive\nmoving average (ARMA) and autoregressive (AR), are proposed to predict the corrections outside the service area. A simulated\nGPS satellite visibility condition is applied to the WAAS correction data, and the prediction accuracy degradation, along with the\ntime, is investigated. Prediction results using the SBAS rate of change information are compared, and the ARMA method yields a\nbetter accuracy than the rate method. The error reductions of the ephemeris and clock by the ARMA method over the rate method\nare 37.8% and 38.5%, respectively.The AR method shows a slightly better orbit accuracy than the rate method, but its clock accuracy\nis even worse than the rate method. If the SBAS correction is sufficiently accurate comparing with the required ephemeris accuracy\nof a real-time navigation filter, then the predicted SBAS correction may improve orbit determination accuracy....
To reduce the impact of uncertainties caused by unknown motion parameters on searching plan ofmoving targets and improve the\nefficiency of UAV�s searching, a novel distributedMulti-UAVs cooperative search control method for moving target is proposed in\nthis paper. Based on detection results of onboard sensors, target probability map is updated using Bayesian theory. A Gaussian\ndistribution of target transition probability density function is introduced to calculate prediction probability of moving target\nexistence, and then target probability map can be further updated in real-time. A performance index function combining with\ntarget cost, environment cost, and cooperative cost is constructed, and the cooperative searching problem can be transformed into\na central optimization problem. To improve computational efficiency, the distributed model predictive control method is presented,\nand thus the control command of each UAV can be obtained.The simulation results have verified that the proposed method can\navoid the blindness of UAV searching better and improve overall efficiency of the team effectively....
This paper presents an optimum control scheme of firing time and firing phase angle by taking impact point deviation as optimum\nobjective function which takes account of the difference of longitudinal and horizontal correction efficiency, firing delay, roll rate,\nflight stability, and so forth. Simulations indicate that this control scheme can assure lateral impulse thrusters are activated at time\nand phase angle when the correction efficiency is higher. Further simulations show that the impact point dispersion is mainly\ninfluenced by the total impulse deployed, and the impulse, number, and firing interval need to be optimized to reduce the impact\npoint dispersion of rockets. Live firing experiments with two trajectory correction rockets indicate that the firing control scheme\nworks effectively....
Theaimof this paper is the assessment of the capability of controllers based on the combined actuation of flaps and variable-stiffness\ndevices to alleviate helicopter main rotor vibratory hub loads. Trailing-edge flaps are positioned at the rotor blade tip region,whereas\nvariable-stiffness devices are located at the pitch link and at the blade root. Control laws are derived by an optimal control procedure\nbased on the best trade-off between control effectiveness and control effort, under the constraint of satisfaction of the equations\ngoverning rotor blade aeroelastic response.The numerical investigation concerns the analysis of performance and robustness of the\ncontrol techniques developed, through application to a four-bladed helicopter rotor in level flight. The identification of the most\nefficient control configuration is also attempted...
In order to implement the uniformload distribution of the power-split transmission system, a pseudostatic model is built. Based on\nthe loaded tooth contact analysis (LTCA) technique, the actual meshing process of each gear pair is simulated and the fitting curve of\ntime-varying mesh stiffness is obtained. And then, the torsional angle deformation compatibility conditions are proposed according\nto the closed-loop characteristic of power flow, which will be combined with the torque equilibrium conditions and elastic support\nconditions to calculate the transfer torque of each gear pair. Finally, the load-sharing coefficient of the power-split transmission\nsystem is obtained, and the influences of the installation errors are analyzed.The results show that the above-mentioned installation\nerrors comprehensively influence the load-sharing characteristics, and the reduction of only one error could not effectively achieve\nperfect load-sharing characteristics. Allowing for the spline clearance floating and constrained by the radial spacing ring, the\ninfluence of the floating pinion is analyzed. It shows that the floating pinion can improve the load-sharing characteristics. Through\nthe comparison between the theoretical and related experimental data, the reasonability and feasibility of the above-proposed\nmethod and model are verified....
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