• Journal of the Optical Society of Korea
• /
• v.16 no.2
• /
• pp.107-114
• /
• 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.

• ETRI Journal
• /
• v.35 no.5
• /
• pp.927-930
• /
• 2013

We propose a visible light communication system in which the color and brightness are controllable. Pulse width modulation and variable pulse position modulation (VPPM) schemes are used to control the color and brightness, respectively. A digital algorithm to decode VPPM signals is suggested and implemented. A seamless transmission is observed in a testbed experiment under various environmental conditions. The proposed scheme can be applied to emotional-lighting-based wireless optical communication.

• Journal of Sensor Science and Technology
• /
• v.27 no.1
• /
• pp.6-12
• /
• 2018

In this paper, a 32-variable pulse position modulation (32-VPPM) scheme is proposed to support a red-green-blue light-emitting-diode (RGB-LED)-based optical camera communication (OCC) system. Our proposed modulation scheme is designed to enhance the OCC data transmission rate, which is targeted for the wearable biomedical data monitoring system. The OCC technology has been utilized as an alternative solution to the radio frequency (RF) wireless system for long-term self-healthcare monitoring. Different biomedical signals, such as electrocardiograms, photoplethysmograms, and respiration signals are being monitored and transmitted wirelessly from the wearable biomedical device to the smartphone receiver. A common 30 frames per second (fps) smartphone camera with a CMOS image sensor is used to record a transmitted optical signal. Moreover, the overall proposed system architecture, modulation scheme, and data demodulation are discussed in this paper. The experimental result shows that the proposed system is able to achieve > 9 kbps using only a common smartphone camera receiver.

• Journal of Institute of Control, Robotics and Systems
• /
• v.21 no.1
• /
• pp.76-79
• /
• 2015

Visible light communication (VLC) is a short range optical communication technology using light emitting diodes. In this paper, we implement variable pulse position modulation (VPPM) defined in the IEEE 802.15.7 standard with a Cortex-M processor, which is a new modulation scheme for VLC providing a dimming control mechanism for flicker-free optical communication. The synchronization procedure between the transmitter and receiver is not defined clearly in the VPPM standard. In order to synchronize the transmitter and receiver easily, two overhead bits are used including one start bit and one stop bit modulated by on-off keying (OOK). Experimental results under various environmental conditions show that the proposed VPPM can support a seamless 100 Kbps data rate with 10 levels in the dimming control.

• Journal of Satellite, Information and Communications
• /
• v.7 no.3
• /
• pp.41-46
• /
• 2012

Visible light communication(VLC) system based on LED devices has some specific advantages compared with RF system. First, visible light is harmless to human and there is no limit to using frequency band. Also, VLC system has good security performance, and it can use the very wide frequency band for data transmission. However, for simultaneously using the illumination and data transmission in VLC systems, degradation of code rate is occurred. So, in this paper, we proposed the novel line coding scheme for flicker free and efficient dimming control in VLC systems. From the simulation results, it is confirmed that proposed scheme has good flicker, dimming, and transmission performance compared to conventional variable pulse position modulation(VPPM) scheme.

• Journal of the Optical Society of Korea
• /
• v.16 no.3
• /
• pp.203-209
• /
• 2012

Visible light communications (VLC) use modern solid-state light-emitting diodes (LEDs) to broadcast information. Emerging white-light LEDs allow the combination of lighting and optical wireless communication in one optical source. In this paper, a new LED lighting design using one-chip-type white LEDs is proposed for efficient illumination and optical wireless communications under the existence of several obstacles. Lighting and communication performance are analyzed to show the effectiveness of the proposed LED lighting. Specifically, the signal-to-noise ratio considering intersymbol interference and the bit-error rate of variable pulse position modulation (VPPM) with dimming control are considered.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.4
• /
• pp.1276-1291
• /
• 2014

In the field of visible light communication (VLC), light-emitting diodes (LEDs) are used for transmitting data via visible light. In this study, we analyze pulse dual slope modulation (PDSM) as a means of delivering information in VLC. PDSM involves the modulation of symmetrical slope pulses to encode binary 0s and 1s, and owing to the moderately increasing and decreasing pulse shapes that are created, this method enables more spectral efficiency than the variable pulse position modulation (VPPM) technique currently adopted in IEEE 802.15.7. In particular, PDSM allows for the avoidance of intra-frame flicker by providing idle pulses in a spectrum-efficient way. A simple detection scheme is proposed for PDSMsignals, and its bit error rate (BER) is analyzed mathematically at varying slopes to validate the process through simulation. The BER performance of PDSM detection using dual sampling is compared to the performances of PDSM and VPPM using correlation detection. It is found that, when the probability of idle pulse transmission is less than 0.08 and higher than 0, the BER of dual sampling PDSM is lower than that of PDSM using correlation detection over the entire light intensity range.

• Journal of Institute of Control, Robotics and Systems
• /
• v.22 no.2
• /
• pp.75-82
• /
• 2016

Visible light communication (VLC) using LED lamps is suitable for implementing an indoor positioning system in an indoor environment where the global positioning system (GPS) signal does not reach. In this paper, we present an indoor positioning system for mobile robots using a VLC beacon and fuzzy rules. This system consists of an autonomous mobile robot, VLC modules, and device application software. Fuzzy rules are applied to plan the global and local paths along which the mobile robot navigates indoors. The VLC transmitter modules are attached to the wall or the ceiling as beacons to transmit their own location information. The variable pulse position modulation (VPPM) algorithm is used to transmit data, which is a new modulation scheme for VLC providing a dimming control mechanism for flicker-free optical communication. The mobile robot has a receiver module to receive the location information while performing its mission in the environment where VLC transmitters are deployed.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.26 no.12B
• /
• pp.1695-1702
• /
• 2001

This paper describes a design of CMOS infrared (IR) wireless data link IC which can be used in IrDA(Infrared Data Association) application from 4 Mb/s to 100 Mb/s The implemented chip consists of variable gain transimpedance amplifier which has a gain range from 60 dB to 100 dB, AGC (automatic gain control) circuits, AOC(automatic offset control) loop, 4 PPM (pulse position modulation) modulator/demodulator and DLL(delay locked loops). This infrared optical link If was implemented using commercial 0.25 um 1-poly 5-metal CMOS process. The chip consumes 25 mW at 100 Mb/s with 2.5 V supply voltage excluding buffer amplifier. The die area of prototype IC is 1.5 mm $\times$ 1 mm.

• KIPS Transactions on Computer and Communication Systems
• /
• v.11 no.1
• /
• pp.35-42
• /
• 2022

Visible light communication (VLC) is a method of transmitting data through LED blinking and is vulnerable to eavesdropping because the illumination affects the wide range of area. IEEE standard 802.15.7 defines On-Off Keying (OOK), Variable Pulse Position Modulation (VPPM), and Color Shift Keying (CSK) as modulation. In this paper, we propose an encryption method in VPPM for secure communication. The VPPM uses an encoding method called 4B6B where 16 different outputs are represented with 6-bit. This paper extends the number of outputs to 20, to add complexity while not violating the 4B6B generation conditions. Then each entry in the extended 4B6B table is scrambled using vigenère cipher. The probability of decrypting each 6-bit data is $\frac{1}{20}$. Eavesdropper should perform $\sum\limits_{k=1}^{n}20^k$ number of different trials to decrypt the message if the number of keys is n. The proposed method can be applied to OOK of PHY II and CSK of PHY III. We further discuss the secure encoding that can be used in OOK and CSK without performance degradation.