This paper presents a multi-user Visible Light Communication (VLC)-based Internet of Things (IoT) system using multi band-Carrierless Amplitude and Phase (m-CAP) modulation for IoT applications. The proposed system uses a digital m-CAP modulator embedded in a ceiling LED light fixture and analog receivers, aiming at low-cost, low-power, and small-sized IoT devices. The performance was evaluated in terms of the filtering stage design and the usage of guard bands. Different pairs of emitter and receiver filters were considered. While Bessel and Butterworth analog filters were tested in the analog receiver, the digital m-CAP modulator pulse shaping filter considered raised cosine filters, as well as digital matched filters for the analog Bessel and Butterworth filters. Regarding the guard bands, two approaches were considered: either by using the raised cosine roll-off factor (bandwidth compression) or by suppressing the even bands. The Bit Error Rate (BER) performance was obtained by simulation. The usage of the Bessel filter in the receiver, along with a digital matched filter, proved to be the best solution, achieving a BER lower than ${10}^{-3}$ for an Eb/No of 6 dB, using a third-order filter. Furthermore, guard bands should be used in order to mitigate inter-band interference in order to have improved performance when multiple users intend to simultaneously communicate.

Future IoT systems will require progressively smaller sizes, cost, complexity and power consumption. This paper proposes a new architecture using a hybrid m-CAP/QAM system with the goal to provide such features to future VLC based IoT devices. The proposed system architecture uses a ceiling LED light fixture implementing an m-CAP digital modulator, connected to several IoT devices, implemented by analog demodulators. The simulated performance presents an increase on BER when compared to a digital m-CAP receiver, between 1 and 2 dB. Nevertheless, considering IoT scenarios, having low cost/size/power devices can surpass the performance penalty.

The technical feasibility of developing an Internet of Things multi‐user communication system is evaluated based on a central digital multiband carrierless amplitude and phase transmitter, which broadcasts data on multiple channels for a number of low‐cost/low‐power devices. It addresses the issue of carrier synchronisation, which is critical in real‐world implementations because of imperfections of devices and the delays of the system. A simulation model for the traditional Costas Loop is presented, along with performance results, which demonstrate the system's ability to synchronise with pull‐in and lock ranges of ±800 and ±900 Hz, respectively. The loop requires 1.194 ms to be in the locked state, allowing the system to lock within 6 symbols period. In addition, the authors measured the performance of the system in the presence of noise and interference from other modulated bands. The results showed that noise and interference did not degrade the system's performance. Although the system was unable to lock when energy was present in adjacent bands, alternative options such as a high order phase‐locked loop and hybrid frequency‐division multiple access and time‐division multiple access, can improve system performance without significantly increasing the cost and complexity of the devices.

Visible Light Communication is an emerging technology in Optical Wireless Communication where the Light Emitting Diodes (LEDs) are utilized for transmission of data. The luminance of the LEDs increases with the forward current; however, for high current levels the heat generated by non-radiative recombination of carriers increases the LED junction temperature, decreasing the efficiency and the lifetime of the devices. Therefore, the design of high power LED driver circuits needs to take into account the unavoidable local heating produced by high power components. In this paper, we performed thermal analysis of an LED driver mounted on Printed Circuit Boards (PCBs) using Thermal Risk Management (TRM) software and studied the heat dissipated by various components on PCBs composed of different dielectric materials such as FR4 and Diamond. Based on TRM simulations, the replacement of FR4 with diamond caused the junction temperature to decrease from 64°C to 45.2°C for a forward current level of 350 mA. The replacement of FR4 with diamond thus effectively improves the thermal management of LEDs and corresponding driver circuits.

This paper discusses the feasibility and implementation of a complete Optical Wireless Communications (OWC) system emulator. The emulating platform comprises the ability to model all the key aspects of an OWC system, such as the emitter, the channel and the receiver. In order to implement the proposed architecture, Field-Programmable Gate Arrays (FPGAs) were chosen due to their flexibility and processing power. The proposed architecture operates in real time with a sampling frequency of 250MHz. The achieved results demonstrate the channel effects on signal transmission, allowing designers to improve system design from the early stages of the project. For illustration purposes, the results demonstrate the transmission of a 4-Quadrature Amplitude Modulation (QAM) Orthogonal Frequency Division Multiplexing (OFDM) modulated signal through the channel. As it is demonstrated, several important metrics, such as channel frequency response, bit error rates or signal constellations, are readily available, through a dedicated interface with Matlab.