• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권11호
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• pp.5410-5426
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• 2019

With the advent of the fifth-generation (5G) era, Massive multiple-input multiple-output (MIMO) relay systems have experienced the rapid development. Recently, the performance analysis models of Massive MIMO relay systems have been proposed, which are mostly based on Rayleigh fading channels. In order to create a more suitable model for 5G Internet of Things scenarios, our study is based on the Rician fading channels, where line-of-sight (LOS) path exists in the channels. In this paper, we assume the channel state information (CSI) is perfect. In this case, we use statistical information to derive the analytical exact closed-form expression for the achievable sum rate of the uplink for the Massive MIMO two-hop relay system over Rician fading channels. Moreover, considering the different communication scenarios, we derive the analytical exact closed-form expression for the achievable sum rates of the uplink for other three scenarios. Finally, based on these expressions, we make simulations and analyze the performance under different transmit powers and Rician-factors, which provides a theoretical basis and reference for further research.

• International journal of advanced smart convergence
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• 제9권4호
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• pp.42-51
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• 2020

In this paper, the authors propose the pseudo complex correlation coefficient (PCCC) of the two complex random variables (RV), because the four real correlation coefficients (RCC) of the corresponding four real RVs cannot be obtained only from the complex correlation coefficient (CCC) of given two complex RV. Such observation is motivated by the general statement; "The complex jointly-Gaussian random M-vector cannot be completely described by the complex covariance matrix, even though the real Gaussian random 2M-vector can be completely descried by the real covariance matrix. Therefore, in order to describe completely the complex jointly-Gaussian random M-vector, we need an additional matrix, namely the complex pseudo-covariance matrix, along with the complex covariance matrix." Then, we apply PCCC to correlated information sources (CIS) for non-orthogonal multiple access (NOMA) in 5G system, and investigate impact of the proposed PCCC on the achievable data rate of the stronger channel user in the conventional successive interference cancellation (SIC) NOMA with CIS. It is shown that for the given same CCC, the achievable data rates with the different PCCC are different, because the corresponding RCC are different. We also show that as the absolute value of the same CCC increases, the impact of the different PCCC becomes more significant.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권1호
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• pp.108-125
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• 2015

We propose a new time-division half-duplex estimate-and-forward (EF) relaying strategy suitable for a relay with mobility. We reconfigure EF relaying to guarantee a strong relay-destination link which is required to achieve a high rate using EF relaying. Based on the reconfigured model, we optimize the relaying strategy to attain a high rate irrespective of the relay position with preserving the total transmit bandwidth and energy. The proposed relaying strategy achieves high communication reliability for any relay position, which differs from conventional EF and decode-and-forward (DF) relaying schemes.

• Journal of the Optical Society of Korea
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• 제16권2호
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• pp.107-114
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• 2012

In this paper, we propose a new modulation scheme called multi-coded variable pulse position modulation (MC-VPPM) for visible light communication systems. Two groups of signals (Pulse Width Modulation (PWM) and Pulse Position Modulation (PPM) groups) are multi-coded by orthogonal codes for transmitting data simultaneously. Then, each multi-level value of the multi-coded signal is converted to pulse width and position which results in not only an improved data rate, but also a processing gain in reception. In addition, we introduce average duty ratio and cyclic shift concepts in PWM through which dimming control for light illumination can be supported without any degradation in communication performance. Through simulation, we confirm that the proposed MC-VPPM shows a comparable BER curve and much greater achievable data rate than the conventional VPPM scheme using a visible light optical channel environment.

• 전기학회논문지
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• 제65권12호
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• pp.2177-2182
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• 2016

Using the existing exact but quite complicated symbol error rate (SER) expressions for M-ary phase shift keying (M-PSK) and M-ary differential phase shift keying (M-DPSK), we derive effective and concise closed-form asymptotic SER formulas especially in Rician-Nakagami fading channels. The derived formulas can be utilized to efficiently verify the achievable error rate performances of M-PSK and M-DPSK systems for the Rician-Nakagami fading environments. In addition, by exploiting the modulation gains directly obtained from the asymptotic SER formulas, we also theoretically demonstrate that M-DPSK suffers an asymptotic SER performance loss of 3.01dB with respect to M-PSK for a given M in Rician-Nakagami fading channels at high signal-to-noise ratio (SNR).

• International journal of advanced smart convergence
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• 제12권4호
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• pp.20-25
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• 2023

Increasing demand for increasing higher data rate in order to solve computationally tasks timely and connecting many user equipment simultaneously have requested researchers to develop novel technology in the area of mobile communications. Intelligent reflecting surface (IRS) have been enabling technologies for commercialization of the fifth generation (5G) networks and the sixth generation (6G) systems. In this paper, we investigate a bit-error rate (BER) analysis on IRS technologies for non-orthogonal multiple access (NOMA) systems. First, we derive a BER expression for IRS-NOMA systems with Rician fading channels. Then, we validate the BER expression by Monte Carlo simulations, and show numerically that BER expressions are in good agreement with simulations. Moreover, we investigate the BER of IRS-NOMA systems with Rician fading channels for various numbers of IRS elements, and show that the BERs improve as the number of IRS elements increases.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권1호
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• pp.152-167
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• 2016

This paper investigates the simultaneous wireless information and power transfer (SWIPT) for two-hop orthogonal frequency division multiplexing (OFDM) decode-and-forward (DF) relay network, where a relay harvests energy from radio frequency signals transmitted by a source and then uses the harvested energy to assist information transmission from the source to its destination. The power splitting receiver is considered at the relay. To explore the performance limit of such a SWIPT-enabled system, a resource allocation (RA) optimization problem is formulated to maximize the achievable information rate of the system, where the power allocation, the subcarrier pairing and the power splitting factor are jointly optimized. As the problem is non-convex and there is no known solution method, we first decompose it into two separate subproblems and then design an efficient RA algorithm. Simulation results demonstrate that our proposed algorithm can achieve the maximum achievable rate of the system and also show that to achieve a better system performance, the relay node should be deployed near the source in the SWIPT-enabled two-hop OFDM DF relay system, which is very different from that in conventional non-SWIPT system where the relay should be deployed at the midpoint of the line between the source and the destination.

• 한국정보통신학회논문지
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• 제21권3호
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• pp.509-515
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• 2017

본 논문에서는 다수의 릴레이가 존재하는 협력 통신 환경에서 릴레이 노드들의 신뢰도 정보를 이용한 릴레이 선택 기법을 고려한다. 먼저, 신뢰도에 따라 릴레이 노드들이 송신단의 정보 전송을 도와주는 경우와 전송을 도와주지 않는 경우 모두를 고려한 정보 전송률의 기댓값을 유도한다. 다음으로 주어진 신뢰도 정보를 이용하여 수신단에서 달성 가능한 정보 전송률의 기댓값을 최대화하는 릴레이 선택 기법을 제안한다. 마지막으로 시뮬레이션을 통하여 제안하는 릴레이 선택 기법이 릴레이 노드의 신뢰도 정보를 이용하지 않는 기존의 릴레이 선택 기법과 비교하여 더 우수한 성능을 나타냄을 보인다.

• 한국통신학회논문지
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• 제41권5호
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• pp.512-519
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• 2016

이 논문은 다중안테나를 이용한 무선전력전송에 기반한 인지무선(Cognitive Radio,CR) 네트워크에서 스펙트럼 활용방안을 다룬다. 무선 전력전송 기반의 CR 통신 시스템은 스펙트럼 사용효율을 높이기 위해 허가되지 않은 이차사용자(Secondary User,SU)가 기존의 일차 사용자(Primary User,PU)에 의해 사용되지 않는 스펙트럼을 활용하여 전력을 채집하고 정보를 보낼 수 있는 시스템이다. 본 논문에서는 스펙트럼 사용효율을 높이기 위해 이차 기지국이 다중 안테나(Multi-antenna)를 사용하여, PU에 대한 간섭 제거 및 에너지 빔포밍을 할 수 있는 전송기법을 제안하고, 이에 따른 정보전송량을 최대로 얻기 위한 프레임 스케쥴링 기법을 제시한다.

• 한국통신학회논문지
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• 제41권12호
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• pp.1903-1913
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• 2016

본 논문은 광역 셀 기지국이 sub-array 구조의 거대 배열 안테나를 가지고 있는 무선 백홀 하향 링크 시스템에서 두 단계 빔 형성 및 수신 빔 형성 기법을 제안하였다. 또한, 시스템 성능 비교를 위해, 제로 포싱 프리코더(zero-forcing precoder)를 이용한 세 단계 빔 형성 기법을 적용하여 수신 소형 셀 기지국들의 전송률 성능을 계산하였다. 무선 백홀 채널의 채널 산란 및 거리감쇄 특성 등을 고려할 때 공간 다중화를 위한 프리코딩 기술뿐만 아니라 거리감쇄를 극복하기 위한 지향성 빔 형성 기술이 접목되어야 한다. 따라서 첫 번째 단계에서는 DFT(discrete-Fourier transform) 기반의 고정 빔 패턴을 설계하였다. 결과적으로, 피드백 량을 줄이면서 동시에 전송률 성능을 높이기 위해서는 제안한 두 단계 빔 형성 및 수신 빔 형성 기법을 선택하는 것이 공간 다중화를 고려할 때 유리하다는 것을 확인하였다.