고영채 교수

We evaluate and optimize the performance of switch and stay diversity systems which have the advantage of offering one of the least complex solutions to mitigating the effect of fading. We study the impact of fading type and severity, unbalanced branches, fading correlation, and imperfect channel estimation on the performance of these systems, and compare this performance with that of more complex diversity schemes such as maximal-ratio combining and selection combining. We also propose, analyze

We investigate the effect of fading correlation and branch gain imbalance on the average output signal-to-noise ratio (SNR) in conjunction with dual selection combining (SC). In particular, starting with the moment generating function of the dual SC output SNR, we derive a closed-form expression for the average output SNR in the general case of correlated unbalanced Nakagami-m fading channels. We then show that the generic result can be further simplified for the special cases of Rayleigh fading

Abstract-Channel state information (CSI) at the transmitter can be used to adapt transmission rate or antenna gains in multi-antenna systems. We propose a rate-adaptive M-QAM scheme equipped with orthogonal space-time block coding with simple outdated, finite-rate feedback over independent flat fading channels. We obtain closed-form expressions for the average BER and throughput for our scheme, and analyze the effects of possibly delayed feedback on the performance gains. We derive optimal switc

An optimum power loading algorithm for transmitter diversity systems over correlated and unbalanced Nakagami (1960) paths and its performance evaluation under perfect channel estimate conditions are derived. In addition, various online estimators of the required Nakagami channel parameters for optimized power loading and the comparison of their mean square error via Monte Carlo simulations are presented. Some of these estimators are used to obtain the performance of optimized transmitter diversi

In this paper, we propose a combined adaptive modulation transmission and output threshold MRC diversity reception scheme for high spectral and power efficiency wireless transceiver design. The modulation constellation size and the number of combined diversity paths are jointly determined to achieve the highest spectral efficiency but with low combining complexity, given the fading channel conditions and the required error rate performance. We derive the statistics of the resulting output signal

We evaluate and optimize the performance of switch and stay diversity systems which have the advantage of offering one of the least complex solutions to mitigating the effect of fading. We study the impact of fading type and severity, unbalanced branches, fading correlation, and imperfect channel estimation on the performance of these systems, and compare this performance with that of more complex diversity schemes such as maximal-ratio combining and selection combining. Because of the simple fo

Low earth orbit satellite (LEOS) communication has emerged as a promising technology to achieve global coverage, while further reducing the end-to-end latency by establishing communication link between LEOSs. In this paper, we analyze the performance of multi-hop LEOS network in terms of bit error rate (BER) and outage probability over mixed radio frequency (RF)/free space optical (FSO) links where RF link is used for the link between ground terminal and LEOS and FSO link is used for establishin

Distributed handover (HO) strategy with low complexity can provide seamless communication in low earth orbit (LEO) satellite networks. However, it is difficult to consider load balancing in distributed HO strategy, which may results in HO failures. In this paper, we propose a graph neural network (GNN) based distributed HO strategy for LEO satellite communication to maximize sum rate by considering load balancing. We first propose target satellite selection method with GNN where each user equipm

We propose a threshold-based multiple optical signal selection scheme (TMOS) for free-space optical wavelength division multiplexing systems. With this scheme, we can obtain higher spectral efficiency while reducing the possible complexity of implementation caused by the beam-selection scheme and without a considerable performance loss. To characterize the performance of our scheme, we statistically analyze the operation characteristics under conventional detection conditions (i.e., heterodyne d

An optimum power loading algorithm for transmitter diversity systems over correlated and unbalanced Nakagami (1960) paths and its performance evaluation under perfect channel estimation conditions are derived. In addition, various on-line estimators of the required Nakagami channel parameters for optimized power loading and the comparison of their mean square error via Monte Carlo simulations are presented. These estimators are used to obtain the performance of optimized transmitter diversity sy

In this paper, we propose a combined adaptive modulation transmission and output threshold MRC diversity reception scheme for high spectral and power efficiency wireless transceiver design. The modulation constellation size and the number of combined diversity paths are jointly determined based on the fading channel conditions and the required error rate performance. We derive the statistics of the resulting output signal-to-noise ratio (SNR) and then use it to analyze the proposed system in ter

This paper considers an uplink multiuser hybrid beamforming system where a base station (BS) communicates with multiple users simultaneously. The performance of the uplink multiuser hybrid beamforming system depends on the effective channel which is given by the product of channel matrix and the analog beams. Therefore, to maximize the performance, we need to acquire information of the channels and select the appropriate analog beams from the set of predefined analog beams. In this paper, we pro

Relying on a simple algorithm for the Laplace transform inversion of cumulative distribution functions, we develop a moment generating function-based numerical technique for the outage probability evaluation of maximal-ratio and equal-gain combining over generalized fading channels.

Accurate and fast algorithms for the local mean level estimation axe very important for the successful implementation of many wireless communication enabling techniques such as handoff, power control, and automatic gain control schemes. In this paper, we present maximum likelihood as well as variance unbiased estimators for the local mean signal decibel power. We consider a generalized Nakagami-m fading environment and show that these estimators are asymptotically efficient in the number of samp