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. INDEX TERMS Radio frequency (RF), visible light communication (VLC), hybrid RF/VLC, wireless fidelity (Wi-Fi), hybrid networks, hybrid RF/VLC environments.

In this paper, we present a wireless system for monitoring human vital signs like breathing and heartbeat via visible light sensing (VLS). Typical techniques for tracking heathcondition require body contact and most of these techniques are intrusive in nature. Body contact might irritate the patient's skin and he/she might feel uncomfortable while sensors are touching their body. However, in this method, we can estimate the breathing and heartbeat rates without any body contact using a photo-detector. Vitals monitoring using VLS make use of the idea that reflected light signal off the human body received at the photo-detector will be affected by the chest motion during heartbeats and breathing. We implemented the system using off-the-shelf photo-detector and a signal acquisition system and obtained the results for different people and in different scenarios. We found out that the accuracy of our system compared to FDA approved equipment to measure heartbeats and breathing rate is 94%. This system can be used in various domains and applications in medical facilities and in residential homes.A provisional patent (US#62/639,524) has been obtained for this work.

The introduction of light emitting diodes (LED) in automotive exterior lighting systems provides opportunities to develop viable alternatives to conventional communication and sensing technologies. Most of the advanced driver-assist and autonomous vehicle technologies are based on Radio Detection and Ranging (RADAR) or Light Detection and Ranging (LiDAR) systems that use radio frequency or laser signals, respectively. While reliable and real-time information on vehicle speeds is critical for traffic operations management and autonomous vehicles safety, RADAR or LiDAR systems have some deficiencies especially in curved road scenarios where the incidence angle is rapidly varying. In this paper, we propose a novel speed estimation system so-called the Visible Light Detection and Ranging (ViLDAR) that builds upon sensing visible light variation of the vehicle's headlamp. We determine the accuracy of the proposed speed estimator in straight and curved road scenarios. We further present how the algorithm design parameters and the channel noise level affect the speed estimation accuracy. For wide incidence angles, the simulation results show that the ViLDAR outperforms RADAR/LiDAR systems in both straight and curved road scenarios.A provisional patent (US#62/541,913) has been obtained for this work.

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