Assignment help on Challenges of visible light communications in indoor environments

Abstract

Visible light communications (VLC) is an emerging technology in today’s world which has achieved significant popularity as an alternative to radio frequency (RF) technology. VLS has several advantages over traditional systems, such as providing sufficient security and remarkably consistent transmission rate. Using Light-emitting diodes (LEDs) in VLC adds to these advantages, in particular for indoor environment or short range communications. However, there are also many challenges involved in fully implementing VLC in indoor environments. The main aim of this body of work is to review further some of these challenges such as: limited modulation bandwidth of LEDs, Inter symbol interference (ISI) with reference to precision of indoor positioning systems. Reviewing the current solutions, with emphasis placed on the recent research in this domain, has led to the identification of research gaps and revealed opportunities for future work in the successful implementation of VLC in indoor environments. In particular this body of work highlights that research in SNR(Signal-to-noise ratio) level handling and modulation techniques on SDVLC systems with respect to throughput as those needing attention and yielding the most interim value to the existing body of knowledge.

Introduction

Visible light communications VLC is an evolving technology that uses the visible range (370-780nm) for both lighting and transmitting data. It is becoming a popular technology for its several advantages, the VLC spectrum is unlicensed and therefore it can be used as a substitute of radio frequency (RF) spectrum and thereby reduce the clogging of the 2.4 GHz ISM (industrial medical, scientific) band. It also provides a higher level of security and high transmission rates than is obtained with radio frequencies because the different VLC signals of neighbouring rooms will not interfere with each other (Jovicic, Junyi & Richardson 2013). Today white Light-emitting diodes (LEDs) can be seen almost everywhere starting from the displays of electronic devices to the advertisements on billboards. For having increasing luminous efficacy (lm/W) high power and lifetime LEDs have started to work as an alternative to other illumination sources. Moreover, high rate modulation can be applied to them over other illumination sources and therefore LEDs are widely used for the implementation of VLC with lighting (Borogovac et al. 2011).  By modulating the amplitude of the LEDs increasing data rate is obtained in VLC and this technique is known as intensity modulation/direct detection (IM/DD). In IM/DD systems the two main components are VLC transmitter and VLC receiver wherein the transmitter a DC bias is applied to manage the lighting and a silicon photodiode is used as a receiver for transforming the received optical signal into an electric signal. The electrical signal is further amplified using a transimpedance amplifier whose output signal is finally fed into a digital baseband processor (Jovieic, Junyi & Richardson 2013). VLC has eminent benefits in wide bandwidth, high transmission rate, adjustable coverage as well as it is environmentally friendly, cost effective and energy efficient. LEDs are also used for VLC implementation in an indoor environment, as a result, it is becoming a popular means of high speed communication in an indoor environment or for short range communications (Hua et al. 2014). Although implementation of VLC in indoor environments have numerous advantages there are some significant problems associated with this VLC implementation that need to be addressed (Elgal, Mesleh & Haas 2011). Among these problems the following are identified as imposing several constraints on the systems: low modulation bandwidth, multipath fading via Inter Symbol Interference (ISI), co-channel interference for multiple transmitters, uplink bandwidth and high precision in indoor positioning systems (Hussein & Elmirghani 2015). In addition, there are also minor challenges such as maintaining communications when the lights arc off (Borogovac et al. 2011). Finally, the effect of shot noise on VLC receivers when they are revealed to the sunlight  therefore reducing transmission rate (Jovicic, Junyi & Richardson 2013). This literature review mainly focuses on elaborating and juxtaposing the proposed solutions by researchers for a number of major challenges associated with the implementation in indoor environment and thereby enabling to find future research scope that is not appropriately addressed by those solutions.