Xiaotao Huang

TOA Estimation in IR UWB Ranging with Energy Detection Receiver Using Received Signal Characteristics

The energy detection (ED) receiver is a feasible solution for time of arrival (TOA) estimation in ultra wideband (UWB) ranging. The task of TOA estimation under UWB multipath channel is to determine the first path (FP). In the ED receiver, threshold-crossing (TC) is used a lot. However, the threshold should be elaborately chosen, or else the false detection probability will be high. But it is difficult to acquire the optimal threshold. In the study, we propose a novel method to estimate the TOA based on the received signal characteristics, which are that the TOA of the noise sample that exceeds the threshold is random while the TOA of the FP is definite. The method detects the FP by calculating the frequencies of different samples crossing the thresholds over a sequence of received pulses. Simulation results verify its effectiveness in the IEEE 802.15.4a channels. Comparison results with other methods are also presented to prove the superiority of our method.

First Path Detection Using Rank Test in IR UWB Ranging with Energy Detection Receiver under Harsh Environments

To estimate time of arrival (TOA) in impulse radio (IR) ultra wideband (UWB) ranging under harsh environments, the rank test is adopted in the study to detect the first path (FP) in dense multipath with energy detection (ED) receiver. Most TOA estimation methods work well in the additive white Gaussian noise (AWGN). Actually, the background noise could be non-Gaussian. Moreover, the received signal could be polluted by outliers. In these cases, traditional threshold based methods perform badly, as there may be extraordinary large samples in the output of the receiver. These samples will interfere with the detection of the sample containing the FP. A novel and practical method based on the rank test is proposed to deal with these problems. The FP detection is based on the ranks of the received data samples instead of the samples. Simulations are carried out to demonstrate its effectiveness in the IEEE 802.15.4a channels.

Sparse Time-Frequency Representation Based Feature Extraction Method for Landmine Discrimination

Low-frequency ultra-wideband synthetic aperture radar is a promising technology for landmine detection. According to the scattering characteristics of body-of-revolution (BOR) along with azimuth angles, a discriminator based on Bayesian decision rule is proposed, which uses sequential features, i.e., double-hump distance. First, the algorithm estimates the target scatterings in all azimuth angles based on regions of interest. Second, sequential aspect features are extracted by sparse time-frequency representation. Third, the distributions of features are obtained by training samples, and then the posterior probability of landmine class is computed as an input to the classifler adopting Mahalanobis distance. The experimental results indicate that the proposed algorithm is efiective in BOR target discrimination.

Preliminary study on noncooperative positioning using UWB impulse radio

Impulse radio ultra wideband (IR UWB) is a promising technology for positioning. Many papers about UWB positioning focus on cooperative target. The study considers UWB positioning for noncooperative target, which means that the target is passive and does not transmit signal. There are few papers in the literature on the field. Existing papers place great emphasis on positioning algorithms instead of time based ranging techniques. In addition, they do not pay much attention on the propagation characteristics of the IR UWB signal in the special usage scenario, which is different from that in cooperative positioning. In the study, we present our understanding on the field. First, we point the importance of TOA estimation in noncooperative positioning. Then, we propose a novel UWB channel to explore the signal propagation characteristics. It is a two-stage cascade multipath channel. In the simulation, energy detection receiver is used to estimate the TOA of the special direct path.

Entropy based TOA estimation in IR UWB ranging with energy detection receiver under dense multipath environment

To estimate the time of arrival (TOA) of the first path (FP) in ultra wideband (UWB) ranging, we propose an entropy based method. In the energy detection (ED) receiver, thresholding crossing (TC) is used a lot to detect the FP. The threshold should be carefully chosen, or else the false alarm rate will be high. Our method detects the FP from a different angle based on the arrival characteristics of the dense multipath, which is that the FP is always followed by many other strong paths. During a short interval, the TOAs of these paths are definite and the samples which contain these multipath signals can exceed the suboptimal threshold in most cases, while the TOAs of the few TC noise samples before the FP are random. We use the entropy to measure the randomness of the distribution of the last TC sample before the current one. Then the FP is determined by choosing the sample which has very large entropy and is followed by a sample with very low entropy. Simulation results verify its effectiveness with IEEE 802.15.4a Standard.

A NOVEL MINEFIELD DETECTION APPROACH BASED ON MORPHOLOGICAL DIVERSITY

Battlefleld surveillance is a common application of synthetic aperture radar (SAR), in which minefleld detection is a challenging task. In this paper, a novel minefleld detection approach is proposed via the morphological diversities between targets and background. Firstly, SAR image speckle is suppressed efiectively by total variation, and targets edges are preserved well. Secondly, a nonlinear transform is introduced to map the special distributed targets, e.g., landmines, into spot targets. Lastly, the modiflcation of morphological component analysis is adopted to improve the signal- to-clutter ratio and separate the spot targets from image. The performance of the proposed approach is validated by using the data acquired over an airship mounted SAR system.

Analysis of TOA estimation using the received signal characteristics in IR UWB ranging with energy detection receiver

The energy detection (ED) receiver is a practical solution for time of arrival (TOA) estimation in ultra wideband (UWB) ranging. The task of TOA estimation under UWB dense multipath channel is to determine the direct path (DP). In the ED receiver, threshold-crossing (TC) is used a lot. However, the threshold should be elaborately chosen, or else the false detection probability will be high. It is difficult to acquire the optimal threshold. In our previous study, we have proposed a novel method to estimate the TOA based on the received signal characteristics, which is effective and robust. However, there is not enough in-depth analysis of the method in the original paper in which the novel method is proposed. In this study, we make a further analysis of the method in several aspects, especially some key parameters which can affect the TOA estimation performance of our method. Some important and interesting conclusions are drawn in this paper. Simulations are carried out to verify these conclusions in the IEEE 802.15.4a channels.

Moving target detection and velocity estimation using multiple subband DPCA and ATI method for triple-channel UWB SAR

With long coherent processing time, the ATI method is suitable to detect moving targets with multi-channel UWB SAR system. However, the traditional ATI method will induce the blind velocity and the velocity ambiguity. Moreover, its detection performance will drop rapidly when the moving target signal is contaminated by the foliaged clutter. To overcome these shortcomings of traditional ATI method, this paper proposes a new multiple subband DPCA and ATI method for triple-channel UWB SAR. By applying a DPCA step before ATI, the introduced method can ldquosift outrdquo the interfering clutter from moving targetpsilas signal and alleviate the influence of clutter on the interfering phase. Moreover, the introduced method can detect moving targets without blind velocity and estimate their range velocities without ambiguity by combining the interferograms at different subband central frequencies. The validity of the proposed method is proved based on the experiments on UWB SAR real data.

Application of time reversal for TOA estimation in UWB ranging under dense multipath channel

In most time-based ultra-wide bandwidth (UWB) localization systems, ranging is usually accomplished by the time-of-arrival (TOA) estimation of the first path, which is more challenging in dense multipath channels. This paper proposes a novel time reversal (TR) based method for TOA estimation in UWB ranging. It uses a time reversed version of channel impulse response (CIR) to compensate for the highly cluttered environments. After the time reversed waveform is retransmitted into the same channel, the performance of TOA estimation will be significantly improved by simply search the maximum peak in the output of the receiver. The advantages of TR based method are verified by simulations using the classical IEEE 802.15.4a channel models. Results show that the bias and root mean square error (RMSE) of TR based method are greatly reduced compared to the usually used maximum likelihood method.

TOA estimation in IR UWB ranging using rank statistics with energy detection receiver under harsh conditions

To improve time of arrival (TOA) estimation in impulse radio ultra wideband (IR UWB) ranging under harsh conditions, a novel method based on the rank statistics of the received signals is proposed to detect the first path (FP) in dense multipath, in which the FP is not always the strongest. Under the energy detection (ED) receiver, many threshold based methods are proposed for TOA estimation in the AWGN. However, many of them do not work well under harsh conditions, for example, when the noise is non-Gaussian or when there are outliers in the received signal. In these situations, there will be more random large samples in the output of the ED receiver, which will affect the FP detection, as it will be hard to model the received signal. The proposed method can solve the problem and it does not require prior information. Simulation results demonstrate its effectiveness.