Yeonsoo Jang

Improved QRD-M algorithm based on adaptive threshold for MIMO systems

Multiple-input multiple-output (MIMO) has been considered as a promising technique due to the fact that it dramatically increases the system throughput. In MIMO systems, signal detection at the receiver is regarded as one of the challenging tasks. Maximum likelihood (ML) detection provides minimum bit error rate (BER) by searching all possible candidates, however, its computational complexity grows exponentially as the number of antennas or modulation level increases. In order to reduce the complexity, QR decomposition (QRD)-M algorithm was proposed. The QRD-M algorithm achieves near ML performance by selecting M candidates in each layer, however, its complexity is still high when the number of M is large. In this paper, we propose an adaptive M selection scheme in QRD-M algorithm which provides comparable performance to the conventional QRD-M algorithm with significantly low complexity. In the proposed detection algorithm, the number of survival candidate symbols is determined by using an adaptive threshold to exclude unreliable candidate symbols. In order to verify the proposed algorithm, we present the BER of the proposed algorithm compared with that of the conventional QRD-M algorithm and analyze the computational complexities of the proposed and conventional algorithms.

Generalized BER Expression of MPSK in the Presence of Phase Error

In this letter, we derive an exact and general closed-form expression for the bit error rate (BER) of Gray coded M-ary phase shift keying (MPSK) in the presence of a fixed phase error. We also propose a very simple and tight approximate expression from the derived exact expression. To validate the exactness of the proposed exact and general expression and the tightness of the proposed approximation, we compare the results obtained from the proposed expressions with those from computer simulations. We also present the average BER results of MPSK for random phase errors caused by phase-locked loop or imperfect channel estimation by using the derived expressions.

Bounds for Eigenvalues of Spatial Correlation Matrices With the Exponential Model in MIMO Systems

It is important to understand the properties of spatial correlation matrices in multiple-input multiple-output (MIMO) systems. In this paper, we derive new bounds for the maximum and minimum eigenvalues of spatial correlation matrices characterized by the exponential model. The new upper bounds for the maximum and minimum eigenvalues are tighter than the previously known bounds. Moreover, the new lower bound for the minimum eigenvalue, which has not yet been derived in the literature as a function of the number of antennas, is also tight. In order to predict the behavior of these bounds, we investigate the gap between the lower and upper bounds. These bounds are directly applicable to the analysis of wireless communication scenarios, such as uniform planar arrays and ill-conditioned channels, which are expected to be widely used for massive MIMO systems.

Bit Error Floor of MPSK in the Presence of Phase Error

In mobile communication systems, one of the most significant factors of the bit-error-rate (BER) performance degradation of M-ary phase-shift keying (MPSK) is random phase error caused by phase-locked loop (PLL) or imperfect channel estimation. For high-signal-to-noise-power-ratio (SNR) regions, the effect of random phase error on BER performance becomes dominant and results in an irreducible BER called the bit error floor. In this paper, we derive a bit error floor expression of Gray-coded MPSK when random phase error exists and show that the bit error floor in fading channels converges to the bit error floor in additive white Gaussian noise (AWGN) channels. The derived expression is simple and accurate in the error floor region; hence, it can offer a convenient way to calculate the irreducible BER of MPSK in the presence of phase error.

Multipath effect on radar detection of nonfluctuating targets

We derive the probability density function (PDF) of a received radar signal in the presence of multipath when a reflecting surface with an arbitrary reflection coefficient exists. Using the PDF, we present the detection probabilities of nonfluctuating targets for various reflection coefficients and analyze the multipath effect on radar detection.

Partial Retransmission Turbo HARQ Using the Sign Transitions of A Posteriori Values

대용량 데이터 전송을 위한 무선 통신 시스템에서는 높은 신뢰도를 보장하는 오류 보상 기법이 요구되며, 그러한 기법 중 하나로 재전송 방식과 터보 부호를 결합한 터보 HARQ(Hybrid Automatic Repeat Request) 기법이 여러 문헌에서 연구되어 오고 있다. 기존 터보 HARQ 기법의 경우, 수신 데이터의 일부분이 오류 정정 가능함에도 불구하고 NAK 신호 발생 시에 송신단에서는 정해진 정보 패킷 전체를 반복 전송하게 된다. 이와 같은 과정에서 재전송이 요구되는 정보 패킷 중 필요한 일부만을 송신할 경우 시스템의 전송 효율을 높일 수 있다. 본 논문에서는 전송 효율을 높이기 위한 방법으로 사후 정보 값의 부호 변화를 이용한 오류 데이터 판단 기준 및 부분 재전송 방식을 이용한 터보 HARQ 기법을 제안한다. 제안된 기법에 대한 모의 실험을 통해 전송 효율을 도출하고 성능을 분석한다.

Blind Classification of Line-Coding Schemes Based on Characteristic Features

In modern defense technology, signal intelligence plays an important role in military operations as an intelligence source. Among its target signals, telemetry and telecommand signals can use line-coding schemes for their advantageous properties in the presentation of binary data of transmission systems. Therefore, in a non-cooperative context, blind classification of the line-coding scheme is the final crucial step in recovering target information from an unknown received signal. In this paper, we examine the characteristic features of line-coding schemes and then propose a simple blind classification algorithm for the schemes. We also analyze correct classification probabilities of the proposed algorithm in a noiseless and noisy environment through computer simulations. The proposed method can discern line-coding schemes, allowing reconstruction of the original information data.

Required Performance Analysis of Wavefront Distortion System against Monopulse Radar

One of the effective jamming methods to disturb monopulse radars is a wavefront distortion. Most well-known wavefront distortion is the cross eye technique which uses two transmitters. The cross eye can make angle error regardless of monopulse radar structure but high accuracies of phase and amplitude between two transmitters should be needed to make large angle error. Thus, the accuracies of phase and amplitude are essentially required performance parameters for implementation of wavefront distortion systems and the required values of accuracy is dependant on amount of angle error. In this paper, we derive expressions for minimum required values of phase difference and amplitude ratio according to amount of angle error and analyze the results.

Clutter mapping and performance analysis for vehicular radar systems

Modern vehicular radar operates in various ground environments and its performance is affected by topography. In this paper, we propose clutter maps of existent areas for vehicular radars using the Weibull distribution, and present the performance of the radar system based on the clutter maps. Then, we analyze the radar signal processing performance for the various clutter maps when moving target indicator and constant false alarm detector are employed.

Design and Performance Analysis of DSP Prototype for High Data Rate Transmission of Lunar Orbiter

Many countries all over the world have been doing lunar exploration projects. Korea has also been doing basic research on lunar exploration. The development of communication systems for lunar exploration projects is one of the most important aspects of performing a successful lunar mission. In this paper, we design a DSP (Digital Signal Processor) prototype based on the requirement analysis of a communication link for lunar exploration and implement its core module considering the international standards for deep space communications to perform a basic research on baseband processor development. It is verified by comparing the bit error rate of the DSP prototype with that of a computer simulation.