Bu Xiangyuan

Image reconstruction algorithms for radio tomographic imaging

Radio tomgographic imaging (RTI) is a method of imaging the attenuation caused by objects obstruction within the area surrounded by wireless sensor nodes. The image reconstruction of RTI is an ill-posed problem because the pixels are more than the RSS measurements. Therefore, conventional methods such as least square method are not applicable because the solutions amplify the noise by dividing small singular values. In this paper, we discuss three algorithms i.e. LBP, Tikhonov regularization and projected Landweber iteration to obtain the imaging results. LBP is very simple and needs little hardware resources. Tikhonov regularization method makes a good balance between image quality and regularization error and we use L-curve method to choose regularization parameter. Projected Landweber iteration method can further improve the imaging results while it needs lots of computation. All the three algorithms can be used to meet different requirement of applications. The experiment results are also presented to validate the effectiveness of algorithms.

A Novel Method of Channel Estimation in Broadband MIMO-OFDM Systems

Channel estimation is critical in designing broadband multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, a parametric channel estimation method based on least square (LS) criteria is proposed in this paper, and the MSE performance using optimal training pilots is also given here, which proves this estimation method can improve the estimation precision greatly in sparse channel. Since such method needs the multi-path time delays information of the channel, the probabilistic data association (PDA) method was employed to estimate the multi-path time delays. Simulation results show that both the bit error rate (BER) and the mean square error (MSE) performance of the proposed method are better than the traditional LS channel estimation method.

Design a MIL-STD-188-220c Compatible Radio Digital Message Transfer Device Adapter

The MIL-STD-188-220 protocol is the interconnection standard between DMTDs in battlefield of America DOD. Its the only standardized protocol in tactical mobile networks by now. The protocol models and performance simulations are widely discussed, but mostly based on software simulations and rarely in the implementation issues. This paper is mainly focused on the protocol implementations and system performance analysis. The implementation is a MIL-STD-220C compatible device, which completing the entire data link layer operation and a part of network layer operation in a single FPGA(field programmable gate array) chip to achieve minimum response time and stable performance. The communication adapter function diagram, working flowchart and performance figures are listed.

Iterative Detection of OFDM Signals in Sparse Channels

An iterative detection method of OFDM signals for sparse channels is proposed in this paper. Pilot based channel estimation is used as the initialization of the detection, expectation maximization algorithm is then used to detect OFDM signals iteratively. The path delay information, noise power and the covariance matrix of the channel response are needed in this method, so the methods of estimating all these channel parameters are also given. The simulation results prove the efficiency of the iterative algorithm, and also prove that by using the estimation parameters of the channel, the performance can nearly approximate the performance of a system with perfect channel state information.

Subspace-Based Semi-Blind Channel Estimation for STC-OFDM Systems

A subspace based semi-blind channel estimation method is proposed for space time coding orthogonal frequency division multiplexing (STC-OFDM) systems with two transmit antennas and two receive antennas, which have no cyclic prefix. The algorithm of blind estimation is first given, and a few pilots are used to solve the disadvantage of high computation and slow convergence. By theoretical analysis, it is established that multi-channel identifiability is guaranteed up to two scalars. The method does not need preceding or constant-modulus modulating and is not limited by the real inputs or symmetric inputs, simulation results demonstrate the performance of the semi-blind algorithm.

A study of signal-processing about wind and temperature profiler radars in the troposphere

The accurate acquisition of atmospheric parameters is important in practice. There are a lot of disadvantages in the old detecting methods. A new method of remotely measuring wind and atmospheric temperature is given in the paper by combining the acoustic and radar techniques. The theory of this method is discussed in detail. An advanced PMC interface and DSP technologies is used in developing the whole digit measurement platform. In the end, the signal processing technique is set forth correspondingly.