• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.8-13
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• 2017

Compare with other communication system based RF technology, Optical Camera Communication (OCC) has limitation on data rate due to the low frame rate of camera. The limitation on data rate can be solved with multiple-input and multiple-output (MIMO) technology; and it is the final target of all researches on OCC. The MIMO topology can be implemented easily without breaking out the architecture of image sensor. For image sensor classification, there are two architectures have been developed: rolling shutter and global shutter. The operation of two techniques is different so the performance is also different. In this paper we analyze and evaluate the performance of the MIMO architecture for OCC.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.10
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• pp.4738-4758
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• 2017

Resource allocation plays a crucial role in multiuser multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems to improve overall system performance. While previously proposed resource allocation algorithms are mainly designed from the point of view of the information-theoretic, we formulate the resource allocation problem as an average bit error rate (BER) minimization problem subject to a total power constraint when considering employing realistic MIMO detection techniques. Subsequently, we derive the optimal subcarrier and power allocation algorithms for three types of well-known MIMO detectors, including the maximum likelihood (ML) detector, linear detectors, and successive interference cancellation (SIC) detectors. To reduce the complexity, we also propose a two-step suboptimal algorithm that separates subcarrier and power allocation for each detector. We also analyze the diversity gain of the proposed suboptimal algorithms for various MIMO detectors. Simulation results confirm that the proposed suboptimal algorithm for each detector can achieve a comparable performance with the optimal allocation with a much lower complexity. Moreover, it is shown that the suboptimal algorithms perform better than the conventional algorithms that are known in the literature.

• Journal of the Optical Society of Korea
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• v.19 no.1
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• pp.74-79
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• 2015

A novel color clustered optical RGB multiple-input multiple-output (MIMO) system is presented. As visible light can be divided into three primary regions of red, green and blue, data can be modulated and transmitted separately using these three color clusters. Each color cluster comprised of 30 RGB LEDs is modulated using on-off-keying (OOK), and selection combining is performed at the receiver, producing a diversity effect within that color cluster. The simulations demonstrate that the proposed RGB MIMO VLC system provides high performance via a relatively simple design of MIMO. Moreover, the proposed system ensures sufficient illumination from LEDs and offers extended distance if more LEDs are applied.

• Journal of the Optical Society of Korea
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• v.20 no.2
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• pp.276-282
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• 2016

A 2 Gbit/s visible-light communication (VLC) scheme using time-frequency color-clustered (TFCC) multiple-input multiple-output (MIMO) based on blue, cyan, yellow, and red (BCYR) light-emitting diodes (LEDs) is presented. In the proposed scheme, BCYR LEDs are employed to form four different color clusters. Data transmission using the four color clusters is performed in MIMO, so that the scheme achieves a very high speed of data transmission. Moreover, the scheme employs the TFCC strategy to yield high performance in terms of bit error rate (BER). TFCC operates in such a way that the original data and the two delayed versions of the data are multiplied by orthogonal frequencies and then transmitted using a specific color of the BCYR LED. In the receiver, color filters are employed to detect the data transmitted from the desired cluster. Selection combining (SC) is also performed to yield a diversity effect within each color cluster, to further improve the performance. Performance evaluation demonstrates that the proposed TFCC MIMO VLC offers a data rate of 2 Gbit/s and a bit error rate of 4×10^-5, at an E_b/N_o value of merely 3 dB.

• Journal of Communications and Networks
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• v.17 no.6
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• pp.634-646
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• 2015

Assuming perfect channel state information (CSI) at the transmitter and receiver, the optimization problem of maximizing the minimum Euclidean distance between two received signals by a linear precoder is considered for multiple-input multiple-output (MIMO) systems with arbitrary dimensions and arbitraryary quadrature amplitude modulation (QAM) input. A general precoding framework is first presented based on the Gram matrix, which is shown for 2-dimensional (2-D) and 3-dimensional (3-D) MIMO systems when employing the ellipse expanding method (EEM). An extended precoder for high-dimensional MIMO system is proposed following the precoding framework, where the Gram matrix for high-dimensional precoding matrix can be generated through those chosen from 2-D and 3-D results in association with a permutation matrix. A complexity-reduced maximum likelihood detector is also obtained according to the special structure of the proposed precoder. The analytical and numerical results indicate that the proposed precoder outperforms the other precoding schemes in terms of both minimum distance and bit error rate (BER).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1A
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• pp.8-18
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• 2011

Visible light communication (VLC) using optical sources which can be simultaneously utilized for illumination and communication is currently an attractive option for wireless personal area network. Improving the data rate in optical wireless communication system is challenging due to the limited bandwidth of the optical sources. In this paper, we design the singular value decomposition (SVD)-based multiplexing multi-input multi-output (MIMO) system to support two data streams in optical wireless channels. In order to improve the spectral efficiency, the rate adaptation using multi-level pulse amplitude modulation (PAM) is applied according to the channel condition and we propose the method to allocate the optical power, the offset and the size of modulation scheme theoretically under the constraints of the nonnegativity of the modulated signals, the aggregate optical power and the bit error rate (BER) requirement. The simulation results show that the proposed allocation method gives the better performance than the method to allocate the optical power equally for each data stream.

• ETRI Journal
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• v.35 no.3
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• pp.371-377
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• 2013

An effective signal detection algorithm with low complexity is presented for multiple-input multiple-output orthogonal frequency division multiplexing systems. The proposed technique, QR-MLD, combines the conventional maximum likelihood detection (MLD) algorithm and the QR algorithm, resulting in much lower complexity compared to MLD. The proposed technique is compared with a similar algorithm, showing that the complexity of the proposed technique with T=1 is a 95% improvement over that of MLD, at the expense of about a 2-dB signal-to-noise-ratio (SNR) degradation for a bit error rate (BER) of $10^{-3}$. Additionally, with T=2, the proposed technique reduces the complexity by 73% for multiplications and 80% for additions and enhances the SNR performance about 1 dB for a BER of $10^{-3}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.706-711
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• 2012

The current visible light communication (VLC) systems have a short transmission distance and a low data rate. To overcome this, we studied on the method of appling MIMO technology to VLC. However, it is difficult to apply the original MIMO technology used in RF frequency to wireless VLC. In VLC system, a lens can be used to separate the transmitted signals. And, if we use an image sensor as the receiver, MIMO technology can be applied to LED wireless visible light communication. In this paper, we report an experiment of $2{\times}2$ LED wireless visible light communication using a commercial image sensor receiver. We show the experimental demonstration with a transmission length of 10.5 m and a data rate of 200 bit/s.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.9
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• pp.797-801
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• 2013

Visible light communication (VLC) is a rapidly growing area of research and applications, due to the potential and predicted high efficiency of bandwidth. One of the key challenges in VLC technology is the choice of devices which are going to be deployed VLC features. Smartphone rationally uses the most widely deployed visible light sensor i.e. image sensor in camera, which could be used to receive the intensity modulated data. Image sensor based VLC system would be the most deployable scenario but initially the capacity was not much attractive compared with photodetector based VLC system. Here, the spatial multiplexing is proposed in MIMO based VLC system to increase the system capacity by utilizing the property of spatial separation of optical light sources in smartphone's camera module. The active pixels of imaging plane act as the multiple receivers which could be able to use on MIMO spatial multiplexing to enhance the system performance.

• Journal of information and communication convergence engineering
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• v.10 no.3
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• pp.220-224
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• 2012

We report an experimental demonstration of $4{\times}4$ multiple-input multiple-output (MIMO) wireless visible light communications (VLC) using a charge-coupled device image sensor receiver instead of a photodiode receiver. An image sensor is a kind of digital camera, which is used in most mobile devices such as smart phones or laptop computers and a promising commercial candidate for a VLC receiver. The transmission distance of the experimental result is over 10 m, enough for most indoor communication applications. We expect that the MIMO VLC technique based on image sensor receivers can be widely used with the development of high-speed image sensors.