Abstract
Colour-shift keying (CSK) is a visible light communication (VLC) modulation scheme used in the existing IEEE 802.15.7 standard. In CSK, information is transmitted by changing the light intensities of the RGB LEDs. In this work, a low-complexity VLC system is proposed using CSK modulation and a novel receiver based on a light-to-frequency (LTF) converter. At the receiver, CSK symbols are interpreted and decoded in terms of frequencies, which are processed by a counter module of a generic microcontroller, thus avoiding the use of analog-to-digital converters (ADCs), which results in a low-cost VLC system. The main contributions of this work are summarized in the following key points: (1) A low-complexity receiver for CSK modulation is introduced; (2) A particle swarm optimization (PSO) algorithm for CSK constellation design is suggested considering the restrictions of the LTF based receiver; (3) Experimental and theoretical validation is perfomed for the proposed multi-colour VLC system. The results show that this system can provide a transmission speed of 100 kbps using a 4-CSK-LTF constellation for a symbol error rate (SER) of 10 − 4 and a signal to noise ratio (SNR) around 35 dB. These results suggest that the analysed system could find applications on those scenarios where low transmission speeds and ease of deployment are the goals.
Highlights
Increasing demand of capacity in communication systems is one the current main concerns in society since the world is in the information age and data requires a communication system capable of transmitting signals around the world with low latency
The measurement of the symbol error rate (SER) as a function of signal to noise ratio (SNR) is plotted for a 4-Colour-shift keying (CSK)-LTF constellation with distances dmin = 5 kHz and dmin = 10 kHz, where the SNR expression is defined as SNR = Eσav2 = 1Eav
The fact that the experimental frequency values do not match with those obtained by the particle swarm optimization (PSO) algorithm, see Figure 10, it yields a mismatch in terms of the minimum distance, and there is a small loss in SER performance, as expected
Summary
Increasing demand of capacity in communication systems is one the current main concerns in society since the world is in the information age and data requires a communication system capable of transmitting signals around the world with low latency. One of the proposed solutions to overcome limitations of RF-based wireless systems is using visible light to transmit data. In order to detect CSK signals, typically, the receiver is equipped with three RGB filters, three systems to transform light intensity to voltage, and three analog-to-digital converters (ADCs). In [18], a receiver capable of transforming light intensity into voltage using only one ADC and photodiode was proposed On this approach, the color emitted by an RGB LED is overlapped over the photodiode and its respective responsivity vector is harnessed, system complexity was simplified. The contribution of this work can be listed as it follows: (1) It proposes the study, analysis, and evaluation of a low-complexity VLC system by using CSK and a Light-To-Frequency (LTF) converter as a receiver [19].
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