Gong Wenbin

Channel Calibration of Amplitude-Phase Errors of DBF Transmitter Based on Maximum Likelihood Estimation

Smart antenna technology can significantly improve the coverage radius, increase channel capacity, reduce transmitting power as well as overcome multipath effects by adaptive beamforming. The performance of digital beamforming is greatly affected by the amplitude-phase inconsistency among the channels. We propose a method of calibrating amplitude-phase errors of RF channels of DBF transmitting antenna together with its realization architecture. A maximum likelihood estimation method is used to calculate the amplitude-phase calibration coefficients of the channels and a compensation matrix is constructed in the FPGA so as to accomplish the calibration procedure. In order to get rid of the nonlinear operation in the estimation algorithm, adjustment is made and thus improves the dynamic range of the algorithm. Prototype of a 61-channel digital beamforming transmitting antenna system with a calibration loop is developed and experiment is carried out under different error conditions. The result of the experiment demonstrates that the proposed algorithm and its realization architecture is of high performance and very economic.

Molecular Dynamics Simulation of Damage to Coiled Carbon Nanotubes under C Ion Irradiation

The stability of coiled carbon nanotubes under C ion irradiation is investigated by molecular dynamics simulations. The defect statistics shows that small curvature coiled carbon nanotubes have better radiation tolerance than normal straight carbon nanotubes. To understand the effect of the curvature on defect production, the threshold displacement energies for the upper and lower walls, as well as those for the side parts, are calculated. The results show that the lower wall has better radiation tolerance than the upper wall. For the upper wall, a small increase in the curvature of nanotube axis gives rise to an increase in the radiation tolerance and then a decrease with the curvature becomes larger. However, for the lower wall, as the curvature of the nanotube axis increases, the radiation tolerance increases as the bonds compressed slightly in our simulation.

QPSK/OQPSK Signal Detection with IF AGC on LEO Satellite

The effect of IF (intermediate frequency) analog AGC on QPSK/OQPSK signal detection is evaluated for LEO satellite system where Doppler drift, large dynamic range of signal power and low Eb/No condition are difficult to deal with. The way of setting reference value of logarithmic power based AGC is discussed. Coherent accumulation and non-coherent accumulation are used for detecting, while signals PDF and performance vs. accumulation times are derived mathematically. Experiment shows that with 60 KHz Doppler offset, Eb/No=0dB under QPSK/OQPSK, only 16 bits was consumed to detect the signal with 99.9% detection probability and 0.1% false alarm probability.