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Lim, Wansu,Yun, Changho,Kim, Kiseon Optical Society of America 2009 Optics express Vol.17 No.6
<P>This paper analytically investigates a bit error rate (BER) performance of radio over free space optical (FSO) systems considering laser phase noise under Gamma-Gamma turbulence channels. An external modulation using a dual drive Mach-Zehnder modulator (DD-MZM) and a phase shifter is employed because a DD-MZM is robust against a laser chirp and provides high spectral efficiency. We derive a closed form average BER as a function of different turbulence strengths and laser diode (LD) linewidth, and investigate its analytical behavior under practical scenario. As a result, for a given average SNR with normalized perturbation, it is shown that the difference of average BER corresponding to two LDs (with linewidth of 624 MHz and 10 MHz) under weak turbulence is almost 3 times larger than that under strong turbulence.</P>
Lim, Wansu,Yun, Changho,Yang, Yeon-Mo,Lee, Hyunju,Kim, Kiseon IEEE 2009 Journal of optical communications and networking Vol.1 No.7
<P>The enhanced burst-polling dynamic bandwidth allocation (EBDBA) method is proposed to support broadband access networks based on quality of service for Ethernet passive optical networks (EPONs). EBDBA adaptively increases or decreases the minimum guaranteed bandwidth of the three traffic clasess¿expedited forwarding (EF), assured forwarding (AF), and best effort (BE) traffic¿according to the requested bandwidth of an optical network unit. Therefore, network resources are efficiently utilized and adaptively allocated to the three traffic classes for unbalanced traffic conditions. Simulation results using OPNET show that EBDBA outperforms conventional bandwidth allocation schemes in terms of the average packet delay (it decreases the maximum performance range to 68%) and the network throughput (it increases the maximum performance range to 20%) at a given offered load of 1.2.</P>
Wansu Lim,Tae-Sik Cho,Changho Yun,Kourtessis, Pandelis,Kiseon Kim,Yeon-Mo Yang IEEE 2012 IEEE transactions on aerospace and electronic syst Vol.48 No.2
<P>An analytical time-domain model is presented to analyze a radio over free space optical (RoFSO) system considering the scintillation effect with a log-normal distribution. This analytical model uses a dual-drive Mach-Zehnder modulator (DD-MZM) and photodetector (PD) for typical optical double sideband (ODSB) and single sideband (OSSB) signals. We show the output current of PD as a function of the summation of each frequency component in time domain. Finally, we calculate the received signal power with respect to the power spectral density (PSD) and derive a closed-form average bit error rate (BER) performance.</P>
Lim, Wansu,Cho, Tae-Sik,Yun, Changho,Kim, Kiseon The Optical Society 2009 Optics express Vol.17 No.23
<P>In this paper, we derive the average bit error rate (BER) of subcarrier multiplexing (SCM)-based free space optics (FSO) systems using a dual-drive Mach-Zehnder modulator (DD-MZM) for optical single-sideband (OSSB) signals under atmospheric turbulence channels. In particular, we consider the third-order intermodulation (IM3), a significant performance degradation factor, in the case of high input signal power systems. The derived average BER, as a function of the input signal power and the scintillation index, is employed to determine the optimum number of SCM users upon the designing FSO systems. For instance, when the user number doubles, the input signal power decreases by almost 2 dBm under the log-normal and exponential turbulence channels at a given average BER.</P>
이더넷 수동 광통신망을 위한 가변형 최소 보증 대역폭을 이용한 동적 대역폭 할당 기법의 제안
임완수(Lim Wansu),윤창호(Yun Changho),이현주(Lee Hyunju),양연모(Yang Yeonmo),김기선(Kim Kiseon) 대한전자공학회 2007 대한전자공학회 학술대회 Vol.2007 No.7
Ethernet passive optical network (EPON) is a technology to solve the access network bottleneck and to realize fiber to the home (FTTH). In EPON, the dynamic bandwidth allocation (DBA) is important because all users share common line in upstream. In this paper, we propose new DBA named as modified EPON dynamic scheduling algorithm (MEDSA) and simulate new DBA using Matlab.
An optimal location strategy for multiple drone base stations in massive MIMO
유제니오,Wansu Lim,Martin Maier 한국통신학회 2022 ICT Express Vol.8 No.2
The concept of drone base stations (DBSs) has been applied to reduce the distance of the wireless link between a macro base station and its active users under diverse scenarios in military communications, smart industries, and high-density networks, and to provide service in topologies with damaged infrastructure. In this paper, we address the optimal positioning of multiple DBSs in a multiple-input multiple-output wireless network setting. We present a low-complexity machine learning-based algorithm to optimize the location of the DBSs by minimizing the collective wireless received signal strength experienced by the active terminals. The proposed algorithm reduces the propagation loss in the system and provides a lower bit error rate when compared with the Euclidean cost benchmark.