Sung-Yoon Jung

Novel FEC Coding Scheme for Dimmable Visible Light Communication Based on the Modified Reed–Muller Codes

In this letter, we propose a novel forward error correction (FEC) coding method using a modified Reed-Muller (RM) code for providing accurate dimming control in on-off keying (OOK) based visible light communication (VLC) systems. The proposed FEC scheme has a property that produces exactly same occurrence probability of 1s and 0s. Therefore, it can contain minimal compensation symbols in supporting multiple dimming target values. Moreover, VLC with our proposed scheme provides more coding gain than VLC scheme with the conventional FEC codes [the first-order RM and Reed-Solomon (RS) codes]. Simulation results for various dimming target values show that the proposed scheme leads to at least 2 dB or more signal-to-noise ratio (SNR) gain in 1% bit error rate (BER) than two FEC codes.

Modified Reed–Muller Coding Scheme Made From the Bent Function for Dimmable Visible Light Communications

In this letter, we propose a new forward error correction (FEC) coding method using a coset constructed from a bent function and a Reed-Muller (RM) code for providing accurate dimming control in on-off keying-based visible light communication (VLC) systems. By partitioning the coset made from bent function and the first-order RM codes, the new FEC scheme can be made to be suitable for dimming close to 0% or 100%. Therefore, it can contain minimal compensation symbols in supporting multiple dimming target values, which causes improved coding gain when the total amount of frame data is fixed. Simulation results for various dimming target values show that the proposed scheme leads to about 1-dB signal-to-noise ratio gain in 10-2 bit error rate compared with other three FEC codes.

Modulation and coding for dimmable visible light communication

The recent interest in short-range optical wireless communication technology driven by the widespread deployment of solid state lighting has led to significant efforts on the standardization of visible light communication. In such efforts, the consideration of dimming support poses fundamental challenges on the VLC system design that have not been addressed elsewhere. This article overviews the technical considerations for enhancing the VLC physical layer by summarizing the state-of-the-art advancements in modulation and coding technologies dedicated to VLC systems. In addition, the technical challenges for system enhancement under lighting restrictions are described.

Modeling and analysis of variable PPM for visible light communications

Variable pulse position modulation (VPPM) is a new modulation scheme that supports simultaneously illumination with dimming control and communication. In this paper, the transmitter, optical wireless channel, and receiver structure of VPPM were modeled mathematically, and their error performance for examining the communication performance according to dimming level and data rate was analyzed. The results highlight the need for careful consideration of the tradeoff between the dimming flexibility and communication performance according to the channel condition in VPPM.

Location awareness using Angle-of-arrival based circular-PD-array for visible light communication

LEDs (Light Emitting Diodes) are considered by many researcher to represent the next-generation lighting technology. Furthermore indoor LED lighting has a potential to converge with IT technology such as Visible Light Communication (VLC) based Location Awareness. In this paper, we suggest Angle of Arrival (AOA) estimation algorithm under VLC environment in order to find out the location of a light source (LED) using circular-PD-array. We propose truncated-weighting method in order to enhance the accuracy of estimated AOA. Through simulations, we confirm that the number of PDs in circular-PD-array affects the AOA estimation error performance of a light source. In addition, our proposed truncated-weighting scheme shows better AOA estimation performance than those of simple average and Max schemes. Based on AOA algorithms, we also investigate the performance indoor location estimation. As a consequence, we can final that our truncated scheme also shows better location awareness performance than other conventional ones.

Evaluation of visible light communication channel delay profiles for automotive applications

In this article, we present channel delay profiles based on simulated data regarding the practical conditions for the use of visible light communication (VLC) in automotive applications such as Intelligent Transportation Systems (ITS). Practical vehicular LED headlamp and street lamp that consider the lighting regulation for transportation are used to design the ITS scenarios based on VLC. We modeled two usage scenarios, crossroad and metropolitan street, using the CATIA V5 tool. Measurements for the VLC channel delay profile evaluation were then gathered by using a ray-tracing scheme employing commercial LightTools software under the vehicle-to-vehicle and vehicle-to-infrastructure (V2I) communication links. From the obtained channel impulse responses from both scenarios, we derived the VLC channel delay profiles. From them, we found that the common property of the delay profile was composed of dominant multiple line of sight (LOS) links and a less number of non-LOS delay taps. However, the channel delay profile for the V2I link and metropolitan scenario show more dispersive channel characteristics due to the reflection and diffusion of the visible light.

Multi-coded Variable PPM for High Data Rate Visible Light Communications

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.

A SNR analysis of the visible light channel environment for visible light communication

In this paper, we provide Signal-to-Noise Ratio (SNR) analysis of visible light channel environment reflecting practical conditions for the usage of Visible Light Communication (VLC) in Intelligent Transportation System (ITS). Considering practical LED lights (Headlamp and Streetlamp), we perform 3D computer simulations in two ITS scenario. Through simulation, we can notice that VLC can be used even in day time in Vehicle-to-Infra (V2I) scenario cases. However, more study about how to mitigate day time ambient noise is still required to support VLC in day time Vehicle-to-Vehicle (V2V) scenario.

Simplified Maximum-Likelihood Precoder Selection for Spatial Multiplexing Systems

In this paper, we consider a precoder selection criterion for the maximum-likelihood (ML) detector in limited-feedback spatial multiplexing systems. The exhaustive search for the optimal ML precoder selection requires very high computational complexity. As a good compromise, we propose a simple precoder selection scheme for the ML detector. Numerical results show that the proposed scheme achieves both the diversity order of the ML detector and the performance enhancement of the limited-feedback spatial multiplexing.

Cognitive vision communication based on LED array and image sensor

In this paper, we propose a brand new communication concept, called as “vision communication” based on LED array and image sensor. This system consists of LED array as a transmitter and digital device which include image sensor such as CCD and CMOS as receiver. In order to transmit data, the proposed communication scheme simultaneously uses the digital image processing and optical wireless communication scheme. Therefore, the cognitive communication scheme is possible with the help of recognition techniques used in vision system. By using LED array as transmitter, the increase of data rate is possible similar to MIMO skills used in traditional wireless communications. In addition, image sensor makes it possible to spatially separate the optical noises such as sun light and ambient lights in communication environment. Through experiment based on practical test bed system, we confirm the validity of the proposed vision communications based on LED array and image sensor.