• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10C
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• pp.981-990
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• 2006

In this paper, we introduce the concept of a subcarrier-based virtual multiple antennas (SV-MIMO) for OFDM cellular systems, where the multiple antenna techniques are performed on a set of subcarriers, not on the actual multiple antennas. The virtual multiple antenna system can support multiple users simultaneously as well as reduce inter-cell interference (ICI) form adjacent cells with a single antenna. Also, this technique is easily extended to multiple antenna environments. The virtual multiple antenna techniques can be divided into a virtual smart antenna technique and a virtual MIMO technique. Especially, this method effectively reduces ICI at cell boundary with frequency reuse factor equal to 1, and can support flexible resource allocation depending on the amount of interference. It is shown by simulation that the proposed method is superior to conventional method under the same condition of data transmission.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3C
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• pp.127-132
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• 2011

In this paper, we propose a cooperative communication scheme for high transmission efficiency and coverage extension under multipath fading environment of moving networks. The proposed scheme uses a Space-Time Block Code (STBC) for improvement of receiving performance by using virtual Multiple-Input Multiple-Output(MIMO) transmit diversity. It can also achieve faster transmission time than a conventional scheme by using virtual MIMO configurations. Simulation results have shown that the proposed scheme provides SNR improvement and has faster transmission time compared to the conventional scheme, since it can utilize the good properties of spatial diversity and coding gain by using virtual MIMO configuration. In this paper, we propose simulations of UWB communication system to show validity by using the MATLAB.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.4
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• pp.17-22
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• 2015

In this paper, we propose a cooperative vehicle communication scheme for high transmission efficiency and coverage extension under multipath fading environment of moving vehicle networks. The proposed scheme uses a Network coding scheme for improvement of receiving performance by using virtual Multiple-Input Multiple-Output(MIMO) transmit diversity. Simulation results have shown that the proposed scheme also provides alleviated Inter Symbol Interference(ISI) and Inter Channel Interference(ICI) as well as Signal-to-Noise Ratio(SNR) improvement and improve 3dB compared to the conventional scheme, since it can utilize the good properties of spatial diversity and coding gain by using virtual MIMO configuration. In this paper, we propose simulations of Ultra-Wideband(UWB) communication system to show validity by using the MATLAB.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.51-58
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• 2008

We propose a new duplex which does not require guard resources in MIMO environments. In the proposed duplex, two virtual channels in spatial domain are generated by preceding and postcoding MIMO channels, not to use guard resources in either the time or frequency domain. The capacity can be improved by properly selecting precoder and postcoder. We show the improved capacity of the proposed duplex outperforms conventional duplexes even without guard resources.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.3 s.345
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• pp.32-38
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• 2006

In this paper, an intercell interference (ICI) reduction technique is proposed for OFDM-based cellular systems using the concept of virtual multiple antenna where multiple antenna techniques are performed on a set of subcarriers, not on the actual antenna array. The proposed technique is especially effective for user terminals with a single antenna at cell boundary in fully-loaded OFDM cellular systems with a frequency reuse factor equal to 1. Proposed ICI reduction techniques developed for SISO and MISO environments are shown to be robust to symbol timing offsets and efficient for various cell environments by adjusting group size depending on the number of adjacent cells. Also, the concept of a virtual signature randomizer (VSR) is introduced to improve channel separability in the virtual MIMO approach. It is shown by simulation that the proposed techniques are effective in reducing ICI and inter-sector interference compared with the conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12A
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• pp.1161-1167
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• 2005

In this Paper, a concept of virtual smart antenna (SA) is introduced for orthogonal Sequency division multiplexing (OFDM)-based cellular systems with a frequency reuse factor equal to 1. The OFDM-based cellular system is robust to multipath channels but has a disadvantage that the intercell interference (ICI) caused by adjacent base stations is large at the edge of a cell. In this paper, after deriving the symbol timing offset estimation scheme for the OFDM signal received from multiple base stations in a quasi-static fading channel, the ICI cancellation method based on virtual smart antenna is proposed using the steering vector formed by the symbol timing offset of the desired signal and interference signals.

• Journal of Advanced Navigation Technology
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• v.12 no.5
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• pp.437-443
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• 2008

In this paper, we derive the optimum number of users which can maximize the information theoretic sum capacity in multiuser OFDM virtual MIMO uplink system. In which, there are multiple antennas at the base station and a number of users with single transmit antenna. Pilot-assisted channel state estimation is assumed for a block fading channel and time-varying fading channel. We analyze the tradeoff between the multiplexing gain and pilot overhead especially in low SNR regime and conclude that the optimum number of users is min ($N_r$,LT/2 ) in frequency nonselective block fading channel and approximately equal to min ($N_r$, ${\lfloor}{\sqrt{LT+1}}-1{\rfloor}$) in time varying fading channel. assuming the same pilot and signal pwoer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.6
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• pp.535-544
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• 2013

This paper considers an uplink power control scheme for a virtual multi-input multi-output (MIMO) multi-cell system where multiple mobile stations with single transmit antenna form a virtual MIMO link. Unlike the conventional approach of the game theoretic formulation to add a power penalty term to improve the performance, a constraint on the total effective interference power is introduced to the maximization of the utility function of the transmission rate with linear receive beamforming. Introducing inertia, we show that the proposed power control is guaranteed to converge. The simulation results verify that the proposed power allocation can significantly improve the performance in an interference limited multi-cell system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.1
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• pp.27-32
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• 2016

In this paper, we proposed a soft decision-directed channel estimation based on MMSE estimation for MIMO-OFDM system. While the conventional method employs only pilot signals for channel estimation, the proposed algorithm performs channel estimation using pilot and reliable data signals. We also proposed selection criterion among reliable data signal for channel estimation. From numerical simulations, we show that the proposed channel estimator achieves 1 dB performance gain over conventional channel estimators.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.7
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• pp.805-810
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• 2014

Cooperative communication, which transmit signal via arbitrary number of relays, enhances the overall communication performance by providing virtual Multi-Input Multi-Output (MIMO) gain without imposing multiple antennal limitation in physical system. There are two representative relaying protocols, i.e., Amplify-and-Forward (AF) and Decode-and-Forward (DF), where we analyze the performance of cooperative communication by adopting DF relaying protocol applying partially differential modulation. The performance is based on symbol error rate (SER), and the effect of relay location on the performance is analyzed. We also compare the performance of the proposed scheme with the system which uses differential modulation scheme.