# Adaptive Polling Medium Access Control Protocol for Optic Wireless Networks
## 1 Introduction  
The high reliance on the internet is the major cause of sudden increase in new Internet subscribers. In fact, the number of Internet subscribers increases every year at unpredictable rate. For example, Cisco forecasts that the global mobile data traffic will grow from an annual rate of 86.9 Exabytes of the year 2016 to 587.4 Exabytes in 2021 [1]. Statistics show that between 2016 and 2021, mobile traffic is expected to increase two times faster than fixed network traffic [1]. Furthermore, the high reliance on social networks and other web-based applications available on the Internet are the major cause of high traffic from mobile devices such as smartphones, tablets, and other handheld devices [2]. The radio waves of the electromagnetic spectrum have been exploited for wireless networks signal transmission over the past decades. However, excessive Internet subscribers have stretched the radio spectrum to its limit. There is no more spectrum for new subscribers while the number of new users is increasing every year. Several solutions have been proposed to address the problem of new capacity demand such as the use of unlicensed radio spectrum. However, the proposed new solutions cause other problems such as high energy consumption, signal interference, capital and operating expenditure [3; 4]. Exploiting the visible light spectrum for signal transmission is the promising solution to the increasing internetcapacity demand. There are many reasons that support this argument such as significant bandwidth available in the visible light spectrum i.e., from 430 nm to 790 nm, inherent physical security, no impact on human health, low capital expenditure, and energy efficiency. Different groups such as [5; 6; 7; 8; 9; 10; 11; 12] have demonstrated that visible light spectrum can be used for communication purpose. Unlike visible light communication (VLC) that focuses on point to point communication, light fidelity (LiFi) is an extension of VLC that uses light emitting diodes (LEDs) to provide fully networked visible light wireless access network [13; 14]. Although at its infancy stage, LiFi has demonstrated potential advantages of using visible light spectrum in communication. Applications of VLC include vehicular networks, indoor mobile network, indoor localization, visible light sensing, gesture recognition, under water communication systems, security systems and health sector [15]. The existence of LEDs in automobiles promotes the use of VLC in transportation systems [16; 17; 18; 19]. In [20], the authors suggest the VLC-based vehicular network for urban mobile crowd sensing that aims at supporting driving automation. The performance of VLC with respect to full duplex communication is investigated in [21] where numerical results show that there is an increase of 10% in data delivery rate. Localization of user equipment is another interesting application of VLC technology, in particular where radio frequency and GPS may not work or give inaccurate information [22]. The VLC-based beaconing infrastructure for indoor localization applications is designed in [23]. This study demonstrates that unknown camera location can be determined accurately by using four fixed beacons. Moreover, VLC can play a significant role in cooperative communication by exploiting light sources available in indoor environments as relay nodes [24]. Furthermore, VLC can be used in real time applications such as command control systems, and air traffic control systems. The authors in [25] suggest a VLC-based real time vital signal transmission system. Results from this study demonstrate that exploiting VLC for real time systems improves communication speed. Unlike other spectrums, visible light spectrum is not harmful to human health; thus, it can be used in medical care for communication purpose. A hybrid VLC-request frame (RF) system for health communication system is presented in [26]. The proposed system can be used to transmit laboratory test to patients.