Narrow Results

In this paper, we focus on preamble-based time of arrival (TOA) estimation for orthogonal frequency division multiplexing (OFDM) systems in non-line-of-sight (NLOS) environments. Recent development in wireless communication-based positioning systems exploiting TOA methods faces a major challenge for the TOA estimation in NLOS condition. Because of the possible obstruction of the direct path, the signal component from direct propagation can be very weak and therefore, the performance of TOA estimation will be dramatically degraded. An accurate TOA estimation utilizing channel estimation is presented. The proposed approach consists of three stages. First, we obtain coarse integer TOA estimation by correlation detection. Second, Maximum-likelihood criterion is employed in channel impulse response estimation to get the fine integer TOA estimate. We exploit the multipath interference cancellation with channel equalization in frequency domain. Finally, to break the limitation by sampling interval, fractional TOA estimate by linear fit is obtained. Compared with the off-the-shelf method, the simulation results show that our method achieves more precise TOA estimation.

We propose an innovate program in order to improve the distribution of magnetic particles aggregated in magnetic field by changing the radius of the pole(R) and the spacing between two poles(D). The finite element software ANSYS is used to research the changes in magnetic flux density and magnetic gradient in the experiment. The analysis by Origin indicates that the force along radius reduced to less than half of the original, improving the aggregation at the center greatly.