Ayoung Heo

Joint Optimization of Source and Relay for MIMO Two-Way Relay Networks Using MSE Duality

In this letter, the joint optimization of a source-relay pair is proposed for multiple-input multiple-output (MIMO) two-way relay networks. In these networks, since the joint beamformer design problem based on the minimum mean square error (MMSE) is known to be non-convex, it cannot be solved analytically. In order to solve the problem, a novel iterative algorithm is proposed that uses duality relationships. First, the MSE duality for MIMO two-way relay networks is presented; then, this duality is applied to the proposed optimization method, which provides closed-form solutions for all subproblems. Because the proposed algorithm does not involve convex optimization software packages, it efficiently reduces the computational complexity. The numerical results demonstrate that the proposed method improves the MSE performance compared with the conventional method.

Improvement of range precision in laser detection and ranging system by using two Geiger mode avalanche photodiodes

In this paper, the improvement of range precision in a laser detection and ranging (LADAR) system by using two Geiger mode avalanche photodiodes (GmAPDs) is described. The LADAR system is implemented by using two GmAPDs with a beam splitter and applying comparative process to their ends. Then, the timing circuit receives the electrical signals only if each GmAPDs generates electrical signals simultaneously. Though this system decreases the energy of a laser-return pulse scattered from the target, it is effective in reducing the range precision. The experimental results showed that the average value of standard deviation of time of flights was improved from 61 mm to 37 mm when the pulse energy is 0.6 μJ. When the time bin width is 0.5 ns, the single-shot precision error of the LADAR system was also improved from 280 mm to 67 mm.

Adaptive relay selection for hybrid relay systems

Hybrid relay systems using Amplify-and-Forward protocol (AF) and Decode-and-Forward protocol (DF) together are introduced in cooperative networks. For hybrid systems, we propose adaptive relay selection scheme to maximize the overall received Signal to Noise Ratio (SNR) at the destination. At first two relays are selected among many according to the instantaneous channel conditions. One is a relay to operate as the Amplify-and-Forward protocol and the other is a relay to operate as the Decode-and-Forward protocol. Next the total transmission power is allocated to the source and two selected relays. Simulation results show that the proposed scheme achieves better performance than that of conventional cooperative schemes.

Sum Rate Maximization of an MIMO Two-Way Relay System Using MSE Duality

In this letter, we propose a novel joint beamforming scheme using mean-square error (MSE) duality to maximize the sum rate of a multiple-input multiple-output (MIMO) two-way relay system. It is difficult to solve the sum rate maximization problem directly due to its non-convexity. To manage this difficulty, the optimization problem is reformulated as a problem that minimizes the product of the minimum mean-square errors. Then, we show that the per stream MSE duality holds in a two-way relay system under cross power constraints. Based on the per stream MSE duality, an alternate algorithm is proposed to jointly optimize the linear transceivers. The simulation results demonstrate that the proposed scheme outperforms the existing linear schemes in view of the sum rate maximization.

Smart sensing strategy for SPRT considering fast changing sample statistics in cognitive radio systems

This paper proposes an efficient design strategy for sequential detectors to reliably detect primary users signals, especially in a fast fading scenario. We study computation of the log-likelihood ratio for coping with fast changing sample variances of received signal and noise, which are considered random variables. First, we analyze the detectability of the conventional generalized log-likelihood ratio (GLLR) scheme considering fast changing sample statistics caused by fast fading effects. Second, we propose a methodology for performing the sequential probability ratio test in a robust and efficient manner with known probability density functions of the received signal and noise variances. Finally, our simulation result shows that in this fast fading environments the proposed sensing method is robust and reduces sensing time compared with the detection using purely the conventional GLLR scheme.

Noise reduction of hyperspectral images using a joint bilateral filter with fused images

In this paper, we propose a denoising method for hyperspectral images using a joint bilateral filter. The joint bilateral filter with the fused image of hyperspectral image bands is applied on the noisy image bands. This fused image is a single grayscale image that is obtained by the weighted summation of hyperspectral image bands. It retains the features and details of each hyperspectral image band. Therefore the joint bilateral filter with the fused image is powerful in reducing noise while preserving the characteristics of the individual spectral bands. We evaluated the performance of the proposed noise reduction method on hyperspectral imaging systems, which we developed for visible and near-infrared spectral regions. Experimental results show that the proposed method outperforms the conventional approaches, such as the basic bilateral filter.

Adaptive relay selection and power allocation for hybrid relay systems

In this paper, we propose an adaptive power allocation method for hybrid relay systems that employ the amplify-and-forward and decode-and-forward protocols simultaneously. The total transmission power is analytically allocated to a source and two selected relays by the proposed power allocation criterion to maximize the overall received signal-to-noise ratio at the destination. Simulation results show that the proposed scheme achieves better performance than that of conventional cooperative schemes or hybrid systems with equal power allocation.

Visualization of Hyperspectral Images Using Bilateral Filtering with Spectral Angles

This paper presents an extended bilateral filter with spectral angles and a visualization scheme for hyperspectral image data. The conventional bilateral filter used to be implemented using a position vector and a luminance value at each pixel in the scene. Since hyperspectral image data can provide a spectrum vector that has hundreds of bands at each pixel, we propose an extended bilateral filter using spectral angles. The proposed bilateral filter can be used for extracting and preserving the spectrum edges of the hyperspectral image. A visualization scheme for hyperspectral images exploiting the proposed bilateral filter has been also proposed. When objects that have the similar tristimulus intensity but different spectrums are mixed, they can be separated through the proposed visualization scheme. The resulting images show that the proposed scheme facilitates anomaly detection in the hyperspectral scenes.

Design of multiple demeaning filters for small target detection in infrared imageries

In this paper, we propose multiple demeaning filters for small target detection in infrared (IR) images. The use of a demeaning filter is a promising method which detects a small object by removing the background components with a mean filter. The main factors in the design of a demeaning filter are two types of demeaning methods and the size of its window. We compare two demeaning methods, the sliding window method and the grid method, and we analyze the trade-off between the window size and the performance of the demeaning filters and present limitations related to their use. To overcome the drawbacks of a conventional demeaning filter, the use of multiple demeaning filters with filters of various sizes is considered. The proposed method not only has the advantage of being able to detect a small object in a densely cluttered environment, but it also can be used with low complexity with an integral image. Experimental results demonstrate the robustness and stability of the proposed multiple demeaning filters with low computational complexity compared with conventional methods.

Adaptive relay selection on individual power constraint for hybrid relay systems

Hybrid relay systems using an amplify and forward (AF) protocol and a decode and forward (DF) protocol together are introduced in cooperative networks. For this hybrid system with a power constraint, we propose an adaptive relay selection algorithm to extend the network lifetime while avoiding the degradation of the received signal to noise ratio (SNR) at the destination. In the adaptive relay selection algorithm, two relays are selected among many as the channel state information (CSI) and the residual power of each relay are considered. One is chosen to operate in the AF protocol, and the other is in the DF protocol. Simulation results show that the proposed algorithm achieves better performance than those of conventional methods.