Red, green, and blue (RGB) light-emitting diodes (LEDs) are widely used in everyday illumination, particularly where color-changing lighting is required. On the other hand, digital cameras with color filter arrays over image sensors have been also extensively integrated in smart devices. Therefore, optical camera communications (OCC) using RGB LEDs and color cameras is a promising candidate for cost-effective parallel visible light communications (VLC). In this paper, a single RGB LED-based OCC system utilizing a combination of undersampled phase-shift on-off keying (UPSOOK), wavelength-division multiplexing (WDM), and multiple-input-multiple-output (MIMO) techniques is designed, which offers higher space efficiency (3 bits/Hz/LED), long-distance, and nonflickering VLC data transmission. A proof-of-concept test bed is developed to assess the bit-error-rate performance of the proposed OCC system. The experimental results show that the proposed system using a single commercially available RGB LED and a standard 50-frame/s camera is able to achieve a data rate of 150 bits/s over a range of up to 60 m.Index Terms: Optical camera communication (OCC), visible light communications (VLC), non-flickering communication, red, green, and blue (RGB) light-emitting diode (LED), undersampled phase shift on-off keying (UPSOOK), wavelength division multiplexing (WDM), multiple-input-multiple-output (MIMO).
Abstract-Widespread use of white light-emitting diodes and ubiquitous smart devices offer the opportunity to establish visible light communications (VLC) which has become a hot research topic based on the growing number of publications over the last decade. Camera-based VLC, namely optical camera communications (OCC), provide many unique features when compared with a single photodiode-based system, such as the ability to separate incident light in spatial and color domains. OCC technology represents a promising approach to utilize the benefits of VLC in beyond-5G scenarios and is one of the key technologies of the Internet of Things. Establishing a long communication channel in OCC, as well as non-flickering illumination in using low-frame-rate camera detectors, requires special modulation schemes. This article provides an overview of the principles of three categories of modulation schemes for OCC systems using a low-frame-rate camera detector. In addition, a series of undersampled modulation schemes are proposed and discussed to achieve flicker-free OCC with higher spectral efficiency. In addition, framing structures are designed to solve problems occurring in OCC systems using particular modulation schemes. To evaluate the performance of these modulation schemes, measured bit error rate values are shown. Finally, challenges in the implementation of OCC systems are also outlined.Index Terms -optical camera communications, non-flickering illumination, undersampled phase shift ON-OFF keying, undersampled quadrature-amplitude-modulation, visible light communications, optical wireless communications
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