Message Passing Based Target Localization under Range Deception Jamming in Distributed MIMO Radar

Recent research shows that distributed radar has great potential in recognizing and countering deception jamming. In this letter, we investigate how to use deception bistatic range measurements to estimate the target location and deception ranges, and propose a message passing based method for target localization under range deception jamming in distributed MIMO radar. Firstly, the a posteriori distribution of the target location is derived, but its maximization is intractable. Then we represent the joint distribution of the relevant variables as a factor graph model and a highly efficient message passing algorithm is developed, where the target location and deception ranges are estimated iteratively. The Cramer-Rao bound is also derived and numerical simulations are provided to demonstrate the superiority of the proposed method

Unsupervised Image Registration for Video SAR

Existing approaches for SAR image registration focus on the global transformation correction between SAR images. However, there are often local deformations between images. Due to the time-changing viewpoint of video SAR, the images suffer a lot from local deformations, which can result in false alarms in moving target detection. This article presents an unsupervised image registration approach for the use of video SAR moving target detection, which has good registration performance and acceptable processing efficiency. The designed unsupervised learning-based framework is a cascade of two convolutional neural networks. The first network directly predicts the parameters of the rigid transformation between the reference and unregistered images, and recovers the global transformation between them. Then, the second network uses the reference image and the registered image from the first network as input and then predicts a displacement field. After that, we put a limitation on the predicted displacement field to prevent moving target shadows from being aligned. Finally, the displacement field with limitation is used to compensate local deformations between the two images. Processing results of real video SAR images have shown good performance of the proposed approach with convincing generation ability

Approximate Message Passing with Unitary Transformation for Robust Bilinear Recovery

Recently, several promising approximate message passing (AMP) based algorithms have been developed for bilinear recovery with model {C}$are jointly recovered with known$\boldsymbol{A}-k$from the noisy measurements$\boldsymbol{Y}$. The bilinear recovery problem has many applications such as dictionary learning, self-calibration, compressive sensing with matrix uncertainty, etc. In this work, we propose a new approximate Bayesian inference algorithm for bilinear recovery, where AMP with unitary transformation (UTAMP) is integrated with belief propagation (BP), variational inference (VI) and expectation propagation (EP) to achieve efficient approximate inference. It is shown that, compared to state-of-The-Art bilinear recovery algorithms, the proposed algorithm is much more robust and faster, leading to remarkably better performance

Fine-resolution forest tree height estimation across the Sierra Nevada through the integration of spaceborne LiDAR, airborne LiDAR, and optical imagery

<p>Forests of the Sierra Nevada (SN) mountain range are valuable natural heritages for the region and the country, and tree height is an important forest structure parameter for understanding the SN forest ecosystem. There is still a need in the accurate estimation of wall-to-wall SN tree height distribution at fine spatial resolution. In this study, we presented a method to map wall-to-wall forest tree height (defined as Lorey’s height) across the SN at 70-m resolution by fusing multi-source datasets, including over 1600 <i>in situ</i> tree height measurements and over 1600 km² airborne light detection and ranging (LiDAR) data. Accurate tree height estimates within these airborne LiDAR boundaries were first computed based on <i>in situ</i> measurements, and then these airborne LiDAR-derived tree heights were used as reference data to estimate tree heights at Geoscience Laser Altimeter System (GLAS) footprints. Finally, the random forest algorithm was used to model the SN tree height from these GLAS tree heights, optical imagery, topographic data, and climate data. The results show that our fine-resolution SN tree height product has a good correspondence with field measurements. The coefficient of determination between them is 0.60, and the root-mean-squared error is 5.45 m.</p

Target Detection in Passive MIMO Radar Networks Based on Moments Space

This work deals with the issue of target detection in passive multiple-input and multiple-output (MIMO) radar networks. Compared to distributed detection, centralized detection offers better performance but at the cost of high communication and computational costs. To address this issue, we propose a novel moments space based centralized detection method, where the moments of received signal amplitudes are computed as their features, and a low complexity moments space log-likelihood ratio test is proposed. As only the moments need to be sent to the fusion center, the proposed method enjoys low communication and computational costs. Numerical results demonstrate that the proposed method significantly outperforms existing methods in various scenarios

Massive MIMO as an Extreme Learning Machine

This work shows that a massive multiple-input multiple-output (MIMO) system with low-resolution analog-to-digital converters (ADCs) forms a natural extreme learning machine (ELM). The receive antennas at the base station serve as the hidden nodes of the ELM, and the low-resolution ADCs act as the ELM activation function. By adding random biases to the received signals and optimizing the ELM output weights, the system can effectively tackle hardware impairments, such as the nonlinearity of power amplifiers and the low-resolution ADCs. Moreover, the fast adaptive capability of ELM allows the design of an adaptive receiver to address time-varying effects of MIMO channels. Simulations demonstrate the promising performance of the ELM-based receiver compared to conventional receivers in dealing with hardware impairments

A Unitary Transform Based Generalized Approximate Message Passing

We consider the problem of recovering an unknown signal from general nonlinear measurements obtained through a generalized linear model (GLM). Based on the unitary transform approximate message passing (UAMP) and expectation propagation, a unitary transform based generalized AMP (GUAMP) algorithm is proposed for general measurement matrices, in particular highly correlated matrices. Experimental results on quantized compressed sensing demonstrate that the proposed GUAMP significantly outperforms state-of-the-art Generalized AMP (AMP) and generalized vector AMP (GVAMP) under correlated matrices

Modeling of Correlated Complex Sea Clutter Using Unsupervised Phase Retrieval

The spatially and temporally correlated sea clutter with phase information is valuable for marine radar applications. The major difficulty of coherent sea clutter modeling is the generation of the continuous phases. This article presents a new phase retrieval approach for modeling the correlated complex sea clutter based on unsupervised neural networks. The unsupervised short-term and long-term neural networks have been developed for the phase retrieval on different term scales. Both these networks have the same input layer and feature extraction module, and however, the number of output neurons is different. The amplitude sea clutter series and the desired Doppler spectrum are fed into the network in parallel, and their features are extracted by two parallel bidirectional long short-term memory (Bi-LSTM) networks which sufficiently utilize the correlations of sea clutter data. These features are concatenated and fused by a residual network (ResNet). The phases can be successfully obtained by constraining to the desired Doppler spectrum and the given amplitudes of sea clutter series. This proposed approach has been verified by the measured Ice Multiparameter Imaging X-Band (IPIX) radar data, and it can precisely model the complex sea clutter with specified statistic characteristics and Doppler properties. The amplitude root mean square error (RMSE) between the obtained and measured Doppler spectra is only 1.5065 with the interval between adjacent frames equals to 32. The RMSE of Doppler central frequency and spectrum width is 6.9306 and 1.2293 Hz, respectively. It shows robustness with the change of range resolution and interval

Message Passing Based Block Sparse Signal Recovery for DOA Estimation Using Large Arrays

This work deals with directional of arrival (DOA) estimation with a large antenna array. We first develop a novel signal model with a sparse system transfer matrix using an inverse discrete Fourier transform (DFT) operation, which leads to the formulation of a structured block sparse signal recovery problem with a sparse sensing matrix. This enables the development of a low complexity message passing based Bayesian algorithm with a factor graph representation. Simulation results demonstrate the superior performance of the proposed method

Efficient Direct Target Localization for Distributed MIMO Radar with Expectation Propagation and Belief Propagation

It has been shown that direct target localization in distributed multiple input multiple output (MIMO) radar can outperform indirect localization significantly, but conventional direct localization methods suffer from both high computational complexity and high communication cost. In this work, we address the issues by designing an efficient factor graph based message passing approach to direct localization, which greatly reduces the computational complexity and communication cost. First, a factor graph representation for the problem of direct localization is developed, which, however, involves difficult local functions. Inspired by expectation propagation (EP), we design an iterative method to solve the problem, where both EP and belief propagation (BP) are used to make message passing in the factor graph tractable, leading to a low complexity message passing iterative method. We show that the message passing based method are very suitable for decentralized processing and can be employed in distributed radars with different configurations. Extensive comparisons with state-of-the-art indirect and direct methods are provided, which show that the proposed method can achieve similar performance to the exhaustive search-based direct localization methods while with much lower computational complexity and communication cost, and it outperforms significantly indirect localization methods at low signal to noise ratios