Optical Asymmetric Modulation for VLC Systems

The explosive growth of connected devices and the increasing number of broadband users have led to an unprecedented growth in traffic demand. To this effect, the next generation wireless systems are envisioned to meet this growth and offer a potential data rate of 10 Gbps or more. In this context, an attractive solution to the current spectrum crunch issue is to exploit the visible light spectrum for the realization of high-speed commutation systems. However, this requires solutions to certain challenges relating to visible light communications (VLC), such as the stringent requirements of VLC-based intensity modulation and direct detection (IM/DD), which require signals to be real and unipolar. The present work proposes a novel power-domain multiplexing based optical asymmetric modulation (OAM) scheme for indoor VLC systems, which is particularly adapted to transmit high-order modulation signals using linear real and unipolar constellations that fit into the restrictions of IM/DD systems. It is shown that the proposed scheme provides improved system performance that outperforms alternative modulation schemes, at no extra complexity

New challenges in wireless and free space optical communications

AbstractThis manuscript presents a survey on new challenges in wireless communication systems and discusses recent approaches to address some recently raised problems by the wireless community. At first a historical background is briefly introduced. Challenges based on modern and real life applications are then described. Up to date research fields to solve limitations of existing systems and emerging new technologies are discussed. Theoretical and experimental results based on several research projects or studies are briefly provided. Essential, basic and many self references are cited. Future researcher axes are briefly introduced

Indoor Visible Light Communication:A Tutorial and Survey

Abstract With the advancement of solid-state devices for lighting, illumination is on the verge of being completely restructured. This revolution comes with numerous advantages and viable opportunities that can transform the world of wireless communications for the better. Solid-state LEDs are rapidly replacing the contemporary incandescent and fluorescent lamps. In addition to their high energy efficiency, LEDs are desirable for their low heat generation, long lifespan, and their capability to switch on and off at an extremely high rate. The ability of switching between different levels of luminous intensity at such a rate has enabled the inception of a new communication technology referred to as visible light communication (VLC). With this technology, the LED lamps are additionally being used for data transmission. This paper provides a tutorial and a survey of VLC in terms of the design, development, and evaluation techniques as well as current challenges and their envisioned solutions. The focus of this paper is mainly directed towards an indoor setup. An overview of VLC, theory of illumination, system receivers, system architecture, and ongoing developments are provided. We further provide some baseline simulation results to give a technical background on the performance of VLC systems. Moreover, we provide the potential of incorporating VLC techniques in the current and upcoming technologies such as fifth-generation (5G), beyond fifth-generation (B5G) wireless communication trends including sixth-generation (6G), and intelligent reflective surfaces (IRSs) among others

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC

Study, analysis and application of Optical OFDM, Single Carrier (SC) and MIMO in Intensity Modulation Direct Detection (IM/DD)

With the rapid growth of wireless data demands and saturation of radio frequency (RF) capacity, visible light communication (VLC) has become a promising candidate to complement conventional RF communication, especially for indoor short range applications. However the performance of the system depends on the propagation and type of system used. An optical Orthogonal Frequency Division Multiplexing (O-OFDM) together with multiple input multiple output (MIMO) in different scenario and modulation techniques are studied in the thesis. A novel optical wireless communication (OWC) multi-cell system with narrow field of view (FOV) is studied. In this system the intensity modulated beam from four light sources are used for communication. The system allows beams to be concentrated in specific areas of the room to serve multiple mobile devices with low interference and hence increase system capacity. The performance of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM), direct current biased optical OFDM (DCO-OFDM) and single carrier (SC) modulation are then compared in this system considering single user and multiusers scenarios. The performance of the multi-cell is compared with single cell with wide FOV. It is shown that the capacity for multi-cell system increases with the number of users to 4 times the single user capacity. Also the findings show that multi-cell system with narrow beams can outperform a single wide beam system in terms of coverage area and hence average throughput of about 2.7 times the single wide beam system capacity. One of the impairments in line of sight (LOS) OWC systems is coverage which degrades the performance. A mobile receiver with angular diversity detectors in MIMO channels is studied. The objective is to improve the rank of the channel matrix and hence system throughput. Repetition coding (RC), spatial multiplexing (SMP) and spatial modulation (SM) concepts are used to evaluate throughput across multiple locations in a small room scenario. A novel adaptive spatial modulation (ASM) which is capable of combating channel rank deficiency is devised. Since the receiver is mobile, the channel gains are low in some locations of the room due to the lack of LOS paths between transmitters and receivers. To combat the situation adaptive modulation and per antenna rate control (PARC) is employed to maximise spectral efficiency. The throughputs for fixed transmitters and receivers are compared with the oriented/inclined detectors for different cases. Angular diversity detectors offer a better throughput improvement than the state of the art vertical detectors, for example in ASM angular diversity receiver gives throughput of about 1.6 times that of vertical detectors. Also in SMP the angular detectors offer throughput about 1.4 times that of vertical detectors. SMP gives the best performance compared to RC, SM and ASM, for example SMP gives throughput about 2.5 times that of RC in both vertical detectors and angular diversity receivers. Again SMP gives throughput about 6 times that of SM in both vertical detectors and angular diversity receivers. Also SMP provides throughput about 2 times that of ASM in both vertical detectors and angular diversity receivers. ASM exhibit improvement in throughput about average factor of 3.5 times SM performance in both vertical detectors and angular diversity detectors. As the performance of the system may be jeopardized by obstructions, specular and diffuse reflection models for indoor OWC systems using a mobile receiver with angular diversity detectors in MIMO channels are considered. The target is to improve the MIMO throughput compared to vertically oriented detectors by exploiting reflections from different reflecting surfaces in the room. The throughput across multiple locations in the small room by using RC, SMP and SM approaches is again evaluated. The results for LOS only channels against LOS with specular or diffuse reflection conditions, for both vertical and angular oriented receivers are then compared. The results show that exploiting specular and diffuse reflections provide significant improvements in link performance. For example the reflection coefficient (α) of 0.9 and the antenna separation of 0.6 m, RC diffuse model shows throughput improvement of about 1.8 times that of LOS for both vertical detectors and angular diversity receivers. SM diffuse model shows throughput improvement of about 3 times that of LOS for both vertical detectors and angular diversity receivers. ASM diffuse model shows throughput improvement of about 2 times that of LOS for both vertical detectors and angular diversity receivers. SMP diffuse model shows throughput improvement of about 1.5 times that of LOS for both vertical detectors and angular diversity receiver