Hyeongyong Lim

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.

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.

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.

Asymptotic BER Comparison of MPSK and MDPSK in Lognormal Fading Channels

The bit error rate (BER) performance loss of M-ary differential phase-shift keying (MDPSK) with respect to M-ary phase-shift keying (MPSK) in wireless fading channels has been extensively studied, but the understanding of this problem in lognormal fading channels has been limited. The most recent work has shown the asymptotic BER performance losses of BDPSK and QDPSK with respect to BPSK and QPSK, respectively, in the lognormal fading channels. However, it is not known how the modulation order increases. In this paper, we derive the general expression of the relative BER performance loss of MDPSK with respect to MPSK for arbitrary M over the lognormal fading channels in high signal-to-noise ratio regimes. We start our analysis by investigating the asymptotic BER performance losses of MDPSK with respect to MPSK for M = 4, 8, and 16. Using the regularity of these results, we obtain the general closed-form expression of the relative BER performance loss in the lognormal fading channels.

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.