The use of infrared radiation as a medium for high-speed short-range wireless digital communication is discussed. Available infrared links and local-area networks are described. Advantages and drawbacks of the infrared medium are compared to those of radio and microwave media. The physical characteristics of infrared channels using intensity modulation with direct detection (IM/DD) are presented including path losses and multipath responses. Natural and artificial ambient infrared noise sources are characterized. Strategies for designs of transmitter and receivers that maximize link signal-to-noise ratio (SNR) are described. Several modification formats are discussed in detail, including on-off keying (OOK) pulse-position modulation (PPM), and subcarrier modulation. The performance of these techniques in the presence of multipath distortion is quantified. Techniques for multiplexing the transmissions of different users are reviewed. The performance of an experimental 50-Mb/s on-off-keyed diffuse infrared link is described.

Wireless Infrared Communications

A multiplicity of autonomous terminals simultaneously transmits data streams to a compact array of antennas. The array uses imperfect channel-state information derived from transmitted pilots to extract the individual data streams. The power radiated by the terminals can be made inversely proportional to the square-root of the number of base station antennas with no reduction in performance. In contrast if perfect channel-state information were available the power could be made inversely proportional to the number of antennas. Lower capacity bounds for maximum-ratio combining (MRC), zero-forcing (ZF) and minimum mean-square error (MMSE) detection are derived. An MRC receiver normally performs worse than ZF and MMSE. However as power levels are reduced, the cross-talk introduced by the inferior maximum-ratio receiver eventually falls below the noise level and this simple receiver becomes a viable option. The tradeoff between the energy efficiency (as measured in bits/J) and spectral efficiency (as measured in bits/channel use/terminal) is quantified for a channel model that includes small-scale fading but not large-scale fading. It is shown that the use of moderately large antenna arrays can improve the spectral and energy efficiency with orders of magnitude compared to a single-antenna system.

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Energy and Spectral Efficiency of Very Large Multiuser MIMO Systems

A multiplicity of autonomous terminals simultaneously transmits data streams to a compact array of antennas. The array uses imperfect channel-state information derived from transmitted pilots to extract the individual data streams. The power radiated by the terminals can be made inversely proportional to the square-root of the number of base station antennas with no reduction in performance. In contrast if perfect channel-state information were available the power could be made inversely proportional to the number of antennas. Lower capacity bounds for maximum-ratio combining (MRC), zero-forcing (ZF) and minimum mean-square error (MMSE) detection are derived. A MRC receiver normally performs worse than ZF and MMSE. However as power levels are reduced, the cross-talk introduced by the inferior maximum-ratio receiver eventually falls below the noise level and this simple receiver becomes a viable option. The tradeoff between the energy efficiency (as measured in bits/J) and spectral efficiency (as measured in bits/channel use/terminal) is quantified. It is shown that the use of moderately large antenna arrays can improve the spectral and energy efficiency with orders of magnitude compared to a single-antenna system.

Newness and distinctiveness is claimed in the features of ornamentation as shown inside the broken line circle in the accompanying representation.

Display screen or portion thereof with graphical user interface

A mobile terminal including a body; a touchscreen provided to a front and extending to side of the body and configured to display content; and a controller configured to detect one side of the body comes into contact with one side of an external terminal, display a first area on the touchscreen corresponding to a contact area of the body and the external terminal and a second area including the content, receive an input of moving the content displayed in the second area to the first area, display the content in the first area, and share the content in the first area with the external terminal.

Mobile terminal and method for controlling the same

In this letter, we present indoor multipath dispersion characteristics for visible light communications (VLC). Since the VLC uses a wide spectrum between 380 nm and 780 nm, the conventional narrowband model for infrared may not apply. We generalize the Barry's model by including wavelength-dependent white LED characteristics and spectral reflectance of indoor reflectors. We perform a computer simulation to compare the power delay profile of the VLC with that of infrared communications. From our studies, we show that the VLC provides a larger transmission bandwidth than infrared communications.

Indoor Channel Characteristics for Visible Light Communications

Visible light communication (VLC) uses solid-state lightings to transmit information; therefore, it is necessary that modulation schemes for VLC provide dimming control. In this letter, we propose a multiple pulse position modulation (MPPM) to offer both functions of modulating data-stream and controlling the brightness at the same time. According to the dimming level, we control the number of pulses of MPPM in one symbol duration. We analyze communication performance in terms of the normalized power requirement and spectral efficiency. From our studies, we show that MPPM is superior to variable on-off keying (VOOK) and variable pulse position modulation (VPPM) proposed in the IEEE 802.15 VLC task group.

Modulations for Visible Light Communications With Dimming Control

This paper considers the uncoded multiple-input multiple-output (MIMO) system with linear minimum mean square error (MMSE) detection under ideal fast fading. The distribution of SINR at the output of the MMSE detection is derived for a small number of transmit and receive antennas. We present new approximation for the Gaussian Q-function driven by numerical simulation. Based on the SINR distribution and new approximation for Q-function, we analyze the performance of linear MMSE detection under ideal fast fading environment. By comparing the analytical results and Monte Carlo simulated results, we validate the analytical results.

Performance Analysis of MIMO System with Linear MMSE Receiver

An improved discrete Fourier transform (DFT)-based channel estimation for orthogonal frequency division multiplexing systems is proposed. Conventional DFT-based channel estimations improve the performance by suppressing time domain noise. However, they potentially require information on channel impulse responses and may also result in mean-square error (MSE) floor due to incorrect channel information such as channel delay spread. In contrast, our purposed channel estimation can improve the performance by deciding significant channel taps adaptively without requiring any channel statistical information. Significant channel taps are detected on the basis of a predetermined threshold. The optimal threshold to reduce the MSE of the estimation is also derived, and it is confirmed by computer simulation. Simulation results demonstrate that the proposed algorithm can improve the MSE performance ~6.5 dB compared with the conventional DFT-based estimation, and the MSE floor is not observed in any channels.

Efficient DFT-based channel estimation for OFDM systems on multipath channels

The channel model for indoor wireless optical communication links is unusual in that it combines the intensity-modulation constraints of the Poisson photon-counting channel with the multipath dispersion, bandwidth constraints, and additive white Gaussian noise of the conventional radio channel. In this paper we examine the performance of several modulation schemes on the indoor wireless optical channel. Modulation schemes having low duty cycle, such as pulse-position modulation (PPM), offer improved power efficiency at the expense of decreased bandwidth efficiency. We compare the power and bandwidth efficiency of several forms of PPM, including multiple PPM, overlapping PPM, convolutional coded PPM, and trellis coded OPPM. We also examine the differences between the wireless infrared communications channel and the quantum-limited photon-counting channel.

Hyuncheol Park

Papers

Indoor Channel Characteristics for Visible Light Communications

Modulations for Visible Light Communications With Dimming Control

Performance Analysis of MIMO System with Linear MMSE Receiver

Efficient DFT-based channel estimation for OFDM systems on multipath channels

Modulation analysis for wireless infrared communications