The flickering is functioning the led for data

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The flickering is functioning the LED for data transmission, if LED is ON then it transmits digital ‘1’ and if OFF, it transmits digital ‘0’[4][5].
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3 1234567890 ‘’“” ICITDA 2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 325 (2018) 012013 doi:10.1088/1757-899X/325/1/012013 2.2. Modulation The modulation signals is used to switch LED at desired frequencies that contains information to be transmitted. According to [6] there are several technique of modulation in LiFi. Modulation techniques is needed in order the communication is still available even the illumination is not required. Because of that, a modulation technique may support a dimmable illumination. The variation in intensity of light corresponding to the information in the message signal. There are many typical of modulation in LiFi i.e. Single Carrier Modulation (SCM), Multiple Carrier Modulation (MCM), and Colour Modulation. 2.2.1. Single Carrier Modulation (SCM) SCM is a modulation multiplexed any number of signal, then modulated individually with different frequency[7]. SCM using a microwave as a subcarrier and an optical carrier. Modulation technique in SCM are on-off keying (OOK), pulse-position modulation (PPM), and pulse-amplitude modulation (PAM). SCM is suitable for low-to- moderate data rates applications. 2.2.2. Multiple Carrier Modulation (MCM) Because of the performance of SCM degrades as their spectral efficiency increase. SCM also require complex equalization process when employed at high data rates. MCM is developed to replace the disadvantage of SCM. There are several kinds of MCM i.e. OFDM. The difference between SCM and MCM summarised in table 1. Table 1. Difference technique of LiFi Modulation Modulation Characteristic SCM OOK Transmit data by sequentially turning on and off the LED, the reliable communication range would decrease at low dimming levels, and increasing and decreasing the brighteness of the LED would cause the data rate to decrease PPM Provide efficient and dimming support in variable pulse position modulation (VPPM) PAM Sensitive to signal distortion[8], combination with other modulation technique to get a better performance MCM OFDM Excellent for situations where multiple transmitters are used simultaneously, avoid shadowing effects, the interference can be mitigated by shifting the system bandwidth to higher frequency[9] DCO-OFDM The substantial energy dissipation due to the biasing [10] ACO-OFDM Efficient in term of optical power for lower SNR value for IM/DD channel [11] PAM-DMT Better optical power efficiency compared to DCO- OFDM [12] AHO-OFDM Support various dimming targets to achieve system performance [12] Flip-OFDM Equivalent with the ACO-OFDM in term of spectral efficiency and error performance[13] U-OFDM Equivalent with the ACO-OFDM in term of spectral efficiency and error performance[13]
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4 1234567890 ‘’“” ICITDA 2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 325 (2018) 012013 doi:10.1088/1757-899X/325/1/012013 3. The Architecture of LiFi According to [14] the paper categorized the architecture based on layered. Figure 3 is the layered architecture of LiFi. In layered architecture, LiFi consist of 3 stages i.e. application layer, MAC layer,
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