Papers by Keyword: Doppler

Abstract: This paper discusses the techniques of attitude, velocity ad position estimation from GNSS carrier phase measurements, and investigates the performance of the lower precision MEMS based INS/GNSS system based on carrier phase measurements. Generally, a GPS receiver estimates the position and velocity from code phase and Doppler measurements. Double differenced carrier phase measurements provide more accurate velocity and position estimation compared to code and Doppler measurements. However, for position measurement, the integer ambiguity is required to be removed. Multiples antennae approach is used to derive the attitude information from carrier phase measurements in order to control the large initial misalignment angles for initialization of the integration process or to utilize during benign dynamics. Lever arm effect is considered to compensate for the separation of GNSS antenna and IMU location. The derived three GNSS observables are used to correct the INS through optimal Kalman filtering in a closed loop. Simulation results indicates the effectiveness of the integrated system for airborne as well as for land navigation vehicles.

Abstract: Study a suitable algorithm for implementation of spread spectrum tt&c signals capture software.Analyzes in detail the serial capture pseudo-code algorithm based on FFT, according to the measurement and control conditions, in consideration of pseudo-code doppler and deal with the impact of bandwidth on the basis of, put forward the suitable for software implement methods of capture, primarily through the establishment of a distributed system simulation model and implements a spread spectrum tt&c signals of quasi real-time processing, prove the validity of the method.

Abstract: A new method based on fractional correlation theory for estimating the Doppler and multipath time delay of the wideband echoes for LFM pulse radar by only one pulse signal is presented. First, the Doppler is estimated by energy cumulation of multipath component based on fractional correlation transform. Then, an order-reduced signal is reconstructed combining the Doppler with the prior knowledge of the transmitted signal, and the echoes signal is converted to many single-frequency signals. Finally, the multipath time delay is obtained by the dechirping method. The method is adapted for low SNR noise, can restrain the affection of the cross-items, and has a high time-delay estimation resolution. Some computer simulations are given in this paper and the results show that the new method is valid.

Abstract: With the difficulty to detect and locate the hidden insects, microwave Doppler theory has been used to solve this problem. In this paper, we establish a microwave reflection model using the insects body as the reflector. According to the three different movement patterns of the experimental insects, we implement the MATALAB simulation.By analyzing the reflected signal using the time-frequency analysis, we can easily distinguish the movement patterns of the insects with high sensitivity. The hidden insects can be efficiently detected without any harm. It has great significance to the further development of the hidden insect detection technology.

Abstract: Inertial navigation systems exhibit position errors that tend to grow with time in an unbounded mode. This degradation is due, in part, to errors in the initialization of the inertial measurement unit and inertial sensor imperfections such as accelerometer biases and gyroscope drifts. Mitigation to this growth and bounding the errors is to update the inertial navigation system periodically with external position (and/or velocity, attitude) fixes. The synergistic effect is obtained through external measurements updating the inertial navigation system using Kalman filter algorithm. It is a natural requirement that the inertial data and data from the external aids be combined in an optimal and efficient manner. In this paper an efficient method for integration of Strapdown Inertia Navigation System (SINS), Global Positioning System (GPS) and Doppler radar is presented using a centralized linear Kalman filter by treating vector measurements with uncorrelated errors as scalars. Two main advantages have been obtained with this improved scheme. First is the reduced computation time as the number of arithmetic computation required for processing a vector as successive scalar measurements is significantly less than the corresponding number of operations for vector measurement processing. Second advantage is the improved numerical accuracy as avoiding matrix inversion in the implementation of covariance equations improves the robustness of the covariance computations against round off errors.

Abstract: Mounting accuracy is of great importance to the performance of the Doppler-based navigation techniques. In this paper, a novel method for alignment calibration of IMU and Doppler sensors is presented. The presented scheme is based on the information from INS/GPS integration and Doppler. Different from previously reported techniques, not only the misalignments but also the scale factor error is considered in this study. By using a Kalman filter, the alignment matrix which is consisted of a misalignment matrix multiplying with a scale factor is estimated. The performance of the alignment estimates is evaluated with field experimental data over Yangzi River. Experimental results shown the estimates obtained by the proposed method perform much better than the existing solution. By using the proposed method, the accuracies of the transformed velocity and positioning are both increased.

Abstract: Radiometric interferometry is one of the main tools in support of spacecraft navigation. Because it does not lose sensitivity to spacecraft declination when the spacecraft is near earth's equatorial plane, as is the case for Doppler tracking. As a working mode, DOD measurement can acquire differential doppler information which is an important observation value used for orbit determination. To perform DOD tracking, the spacecraft needs to transmit high frequency sinewave tone which is usually specially designed. In this paper, we discussed algorithm of DOD measurement using traditional ranging tones. And experiment was performed with ranging tone of China CE'2, data was recorded with baseline which is combined with Shanghai station and Beijing station. Theoretical analysis testifies high accuracy of our algorithm.

Abstract: The technologies of image block, pyramid and multi-threading were used in this program to design the high-speed image generation display module and the processes of image data scheduling and mapping and solve the problems of large-capacity image data modeling and high-speed displaying. The technology of direct digital frequency synthesis (DDS) was used to design the Doppler shifting signal generation module and the multi-processor parallel system architecture, which can analog the Doppler frequency shifting of the data communication signals and solve the problem of the authenticity of communication signals during the simulated flight.

Abstract: A Doppler diversity receiver for OFDM is proposed by Kim B C[1], which requires channel estimation at the receiver, so its structure is complicated, what’s more, the receiver needs a large amount of calculation. Different from it, we use the differential phase modulation technology in the OFDM Doppler receiver, so the receiver can recover the original data without channel estimation, and the implement is simple, the computational complexity is low. However, experiment results show that the BER of the new receiver is higher than the conventional, and it can not get performance gains by diversity either.