Lights and Shadows: A Comprehensive Survey on Cooperative and Precoding Schemes to Overcome LOS Blockage and Interference in Indoor VLC

Abstract

Visible light communications (VLC) have received significant attention as a way of moving part of the saturated indoor wireless traffic to the wide and unregulated visible optical spectrum. Nowadays, VLC are considered as a suitable technology, for several applications such as high-rate data transmission, supporting internet of things communications or positioning. The signal processing originally derived from radio-frequency (RF) systems such as cooperative or precoding schemes can be applied to VLC. However, its implementation is not straightforward. Furthermore, unlike RF transmission, VLC present a predominant line-of-sight link, although a weak non-LoS component may appear due to the reflection of the light on walls, floor, ceiling and nearby objects. Blocking effects may compromise the performance of the aforementioned transmission schemes. There exist several surveys in the literature focused on VLC and its applications, but the management of the shadowing and interference in VLC requires a comprehensive study. To fill this gap, this work introduces the implementation of cooperative and precoding schemes to VLC, while remarking their benefits and drawbacks for overcoming the shadowing effects. After that, the combination of both cooperative and precoding schemes is analyzed as a way of providing resilient VLC networks. Finally, we propose several open issues that the cooperative and precoding schemes must face in order to provide satisfactory VLC performance in indoor scenarios.

Performance enhancement for visible light communication based ADO-OFDM

“…It is necessary to study the received power and the path loss in typical environments due to the indoor OWC/VLC channel [13]. There are two link types inside the room: dominant direct link LOS and non-dominant diffuse links arise due to light reflection through the walls, floor, and ceiling [21]. The received power at any point (x,y,z) inside the room and neglecting the diffuse links is given by [13]:…”

“…Where  ½ is half illumination angle and also is called (Radiation semi-angle) [21] Thus, the LOS channel impulse response for indoor OWC/VLC is modeled as [22][21]:…”

BER Comparison and Enhancement of Different Optical OFDM for VLC

“…Optical Wireless Communication (OWC) is a modern communication that uses light as the carrier of information instead of the Radio Frequency (RF); it supports a high data rate communication with extremely secure links [1][2][3][4][5]. Visible Light Communication (VLC) is a type of OWC that uses visible light in data transmission used in many applications [1,3,5,6]. VLC uses Light Emitting Diode (LED) in the transmitter and photo-sensing such as Photodiode (PD) in the receiver [5].…”

“…Visible Light Communication (VLC) is a type of OWC that uses visible light in data transmission used in many applications [1,3,5,6]. VLC uses Light Emitting Diode (LED) in the transmitter and photo-sensing such as Photodiode (PD) in the receiver [5]. Intensity Modulation with Direct Detection (IM/DD) is a helpful technique used with VLC [7].…”

“…Intensity Modulation with Direct Detection (IM/DD) is a helpful technique used with VLC [7]. The Optical Orthogonal frequency-Division Multiplexing (O-OFDM) has widely used in IM/DD systems for the advantages of high data rates transfer, compatible with multicarrier modulation, and symbol interference resistance [5,[7][8][9]. The IM/DD systems require positive real positive signals for data transmission by LED.…”