Abstract
This work explores the performance of a distinct power saving and relatively simple design visible light communication system based on pulse position modulation (PPM) modulation scheme in a real life (i.e. diffuse) scenario. The mathematical background for both communication and illumination performance is developed for the Sub-Carrier Pulse Position Modulation (SC-LPPM) Scheme in non-line-of-sight (NLOS) environment. An evaluative study is then carried out to provide an integrated picture for the SC-LPPM performance under several system/environmental parameters. Adding the NLOS components increases the total received power, but still, the LOS component dominates. At the corners of a typical room, the received optical power enhances by 120% when including NLOS components, while at room center the optical power enhances only by 12%. For illumination, the NLOS components improve the system’s lighting performance and ensure meeting illumination standards. It provides an extra illumination of about 260 lux at room corner and 175 lux at room center over LOS scenario. Wall reflectivity ( $\rho $ ), subcarrier modulation factor (SCMF), and the number of time slots (L) are environmental/system parameters that can significantly optimize the overall performance. For diffuse scenario, a BER of $10^{-5}$ to $10^{-7}$ with $L=4$ , normal wall reflectivity (plaster walls $\rho =0.8$ ) and 100% SCMF (i.e. 20 mW/LED) can be achieved easily at bit rates of 1 to 2 Mbps. These BER performance levels can be enhanced by selecting wall painting/ materials with high reflectivity. As a power saving scheme, increasing SCMF with low power/LED level can greatly enhance the BER performance in the diffuse scenario. A remarkable BER performance of $10^{-9}$ can be reached when increasing SCMF by 25% (i.e. to reach 25 mW/LED) under the same conditions ( $L=4$ , $\rho =0.8$ and 1–2 Mbps). At higher data rates the performance is getting worse but still can be optimized, controlled, and enhanced through using a careful choice of environmental and system parameters that can be selected from this work.
Highlights
Visible light communication (VLC) gained a growing interest in research and development at a global level as a supplement to radio frequency (RF) technology [1], [2]
Sub-carrier pulse position modulation (SC-LPPM) scheme is introduced in [5] and it has the distinct advantage of reducing the total LED power consumption while maintaining both efficient communication and illumination performance [26]
It is noteworthy to mention that this work is based on the mathematical model that is presented in section II, previous literatures investigated the performance of other types of PPM schemes practically [31], [32]
Summary
The receiving surface is divided into 20 × 20 segments that form a grid that helps in calculating the power rating and illumination within the room As it can be observed from Fig. (a), the strongest LOS components are directly under the lighting sources and it decreases as the Rx moves towards the room corners to vary from 0.62 mW to 0.13 mW respectively. From Fig. it can be shown that increasing the SCMF (from 25 % to 125%) results in enhancing the system BER performance for both LOS and NLOS scenarios due to the effect of the diffuse power. Such improvement comes with a small price paid in system total power consumption which is the main advantage of such scheme. The increase of 25% in SCMF corresponds to a 5 mW increase per LED lamp, such increase can be assumed as a low cost for increasing the system performance
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