Hybrid RF/VLC Systems: A Comprehensive Survey on Network Topologies, Performance Analyses, Applications, and Future Directions

Abstract

Wireless communications refer to data transmissions in unguided propagation media through the use of wireless carriers such as radio frequency (RF) and visible light (VL) waves. The rising demand for high data rates, especially, in indoor scenarios, overloads conventional RF technologies. Therefore, technologies such as millimeter waves (mmWave) and cognitive radios have been adopted as possible solutions to overcome the spectrum scarcity and capacity limitations of the conventional RF systems. In parallel, visible light communication (VLC) has been proposed as an alternative solution, where a light source is used for both illumination and data transmission. In comparison to RF links, VLC links present a very high bandwidth that allows much higher data rates. VLC exhibits also immunity to interference from electromagnetic sources, has unlicensed channels, is a very low power consumption system, and has no health hazard. VLC is appealing for a wide range of applications including reliable communications with low latency such as vehicle safety communication. Despite the major advantages of VLC technology and a variety of its applications, its use has been hampered by its cons such as its dependence on a line of sight connectivity. Recently, hybrid RF/VLC systems were proposed to take advantage of the high capacity of VLC links and better connectivity of RF links. Thus, hybrid RF/VLC systems are envisioned as a key enabler to improve the user rates and mobility on the one hand and to optimize the capacity, interference and power consumption of the overall network on the other hand. This paper seeks to provide a detailed survey of hybrid RF/VLC systems. This paper represents an overview of the current developments in the hybrid RF/VLC systems, their benefits and limitations for both newcomers and expert researchers.

Vertical Handover-based Hybrid RF/VLC Scheme for e-Health Applications (VHO-HeA)

“…The SDN controller manages the network, assigns network resources to body sensors, and executes the PSA algorithm to efficiently select RF link or VLC link for the body sensors. The VLC transmitters utilize the same light wave bandwidth; hence, there is high co-channel interference in the overlapped area of VLC hotspots [4]. Therefore, the VLC link is assumed to be blocked in these areas.…”

“…When the controller detects there is a need for handover, it execute the link selection algorithm and calculates the handover delay. The decision for selecting the communication band is triggered by a time interval, which is called dwell time [4], [24] or handover time threshold in order to prevent unnecessary handovers which degrade the quality of communication needed for achieving the WBAN's QoS. Since choosing the optimal VLC channel among the presented channels is an NP-hard problem, the controller executes the Pareto simulated annealing (PSA) [25].…”

“…The main advantages of VLC technology are the large and unregulated available bandwidth [4], the inherent security and privacy of optical systems [5], and its safety due to the zero-radio emission. Hence, as an alternative to communication systems that operates in the RF band (3 kHz to 300 GHz), the use of visible light band (400 THz to 800 THz) for wireless communications has been proposed [4]. Bell and Tainter in 1880 were the first to present the idea of using light to transmit a signal (photo-phone) as discussed in [6].…”

“…Various networks have been studied using VLC technology especially in indoor, outdoor, vehicular and underwater scenarios. The main advantages of VLC technology are the large and unregulated available bandwidth [4], the inherent security and privacy of optical systems [5], and its safety due to the zero-radio emission. Hence, as an alternative to communication systems that operates in the RF band (3 kHz to 300 GHz), the use of visible light band (400 THz to 800 THz) for wireless communications has been proposed [4].…”

“…Following this achievement, various studies focused on the use of white-LEDs in communication systems. In 2011, the first IEEE standard related to VLC is IEEE 802.15.7 was published by IEEE 802.15 working group for Wireless Personal Area Networks [4]. Fig.…”