Jai-Hoon Lee

A multi-user beamforming scheme in MIMO downlink channels for multi-cell networks

In this paper, a multi-user beamforming scheme is presented in multi-user multi-input multi-output (MIMO) downlink channels with other cell interference (OCI). The proposed scheme consists of maximizing signal-to-leakage-and-noise ratio (SLNR) and whitening the OCI for power allocation. The conventional scheme which eliminates perfectly intra-cell interference has several problems such as antenna constraints and noise enhancement. The proposed scheme has resolved these problems and could obtain an additional channel gain by the number of antennas. We confirm the increasing of the performance via numerical results.

Characterization of Hazardous Gases Using an Infrared Hyperspectral Imaging System

A rapid algorithm for passive remote sensing of gases with an infrared hyperspectral imaging system is reported that includes approximate and precise measurements. In the former, the spectral region of interest for the analytes is identified. In the latter, fitting calculations in the selected range and for spectral similarity measurements are employed to remove erroneous pixels from the approximate measurement to better characterize the gas sample. The results verify that the algorithm reduced the time for qualitative and quantitative determination of gases compared with conventional approaches.

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.

Closed-form interpolations for MISO-OFDM beamforming codewords

We derive a spherical linear interpolation (SLI) with a closed-form phase term. The derived SLI is compared with the geodesic interpolation. Simulation results show that both schemes are efficient and similar when the channels are highly correlated, since their objectives are equivalent in a sense of minimizing the distance between two adjacent codewords.

New framework for inter-cell interference coordination

This paper proposes a new indicator for inter-cell interference coordination (ICIC) in downlink communications. Inter-cell interference may degrade the bit rate at cell boundaries, which prevents sufficient data rate. ICIC is an important technology for alleviating this degradation and improving the data rate at cell boundaries. We propose a new framework for downlink ICIC using an Intended Energy Distribution (IED) index, which is exchanged between adjacent base stations, to improve the ICIC performance over an interbase-station interface.

A CSI feedback scheme for beamforming at AF relays

In cooperative wireless communications, beamforming at relays can be employed to increase the signal-to-noise ratio (SNR). Since beamforming at relays requires that channel state information (CSI) be exchanged, an efficient CSI feedback scheme is proposed to reduce the feedback overhead incorporating an optimization of the combining and beamforming weights. With 802.16e OFDMA time-division duplexing (TDD) systems, the proposed scheme feeds common information back to relays for beamforming, which should be acquired by a destination for combining. The simulation results verify that the proposed scheme reduces the feedback overhead and improves computational efficiency.

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.

MIMO precoding in the ad hoc networks

In this paper, multi-user multi-input multi-output (MIMO) precoding in the ad hoc networks is presented. The ad hoc channel model is considered and the leakage based concept extended centralized systems to distributed networks. The conventional scheme simply use own inverse channel matrices and can be suffered a noise enhancement problem. This paper presents that the leakage based precoding provides also strong performance in the ad hoc networks. It is proven using the achievable sum rate simulations.