# A Brief Overview of Energy Efficiency Resources in Emerging Wireless Communication Systems
## 1 Introduction  
The COVID-19 pandemic is one of many factors that proves the tremendous rise in the use of wireless communication systems in recent times. By having to work or study from home, numerous organizations/schools were forced to increase their utilization of the internet for their operation, thereby making wireless communication more essential in today's world. One current primary concern in wireless communication is energy consumption. Therefore, an increase in the use of wireless communication implies that more energy is consumed. The question that then arises is, what technologies can be combined to produce an excellent energy framework in wireless communication? The deployment of enabling technologies has therefore become necessary [1]. Different technologies like Digital Subscriber Line (DSL), infrared communication, satellite communication, microwave transmission, Wireless Fidelity (Wi-Fi), Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE), etc., have been employed in the provisioning of wireless communication [2]. There has been difficulty in efficiently combining these different technologies to provide a faster and more reliable communication system in the form of a heterogeneous network [3]. The adoption of smallheterogeneous cells in future wireless communication is increasing because of its energy-saving features such as better handling of traffic in smaller areas, increased capacity and speed, etc. One crucial factor that brings about the need for heterogeneous networks is the limitation of sites for the commissioning of base stations [4]. Generally, telecommunication base stations consume so much energy, causing very high operational expenditure and a rise in the carbon emitted by the stations, which causes environmental hazards [5]. In 2015, research revealed that a tower that houses a single base station in Nigeria utilizing a 15-20 kVA diesel generator consumes an average of 50 L of diesel daily. Using this as an estimate for base stations in the country and assuming the generators run on average 17 h per day: for an estimate of 3000 generators working daily in the country, 1.5 million litres of diesel are consumed. At 140 naira per litre, a minimum of 210 million naira is spent daily on the energy consumption of telecommunication in Nigeria. Furthermore, it can be deduced that a telecommunication provider running five base stations would be spending a minimum of 0.98 million monthly on just energy consumption [6]. The grid power supply in Nigeria is still being improved for a constant supply. Therefore, telecommunication providers who require a continuous power supply have no other option but to depend hugely on diesel generators. Another identified disadvantage other than the very high operational cost is the harmful environmental influence caused by the increased CO2 emission per kWh consumed [5]. The need for more utilization of renewable energy in Nigeria is becoming imminent. The mass integration of photovoltaic cells can be adopted to get an overall energy-efficient wireless communication framework [7]. An optimized optical wireless communication (OWC) system can be deployed to produce an energy-efficient framework for a wireless system. An optimized OWC system is a communication system that is both energy and spectrally efficient [8]. Energy efficiency implies that lesser power is consumed during the networking of signals. In contrast, spectrum efficiency indicates that maximum information is obtained from a given signal bandwidth at a particular period. With optical wireless communication, a world connected by light is realizable. Visible light communication (VLC) is an OWC network that operates from 380 nm to 750 nm [2]. Visible light frequency ranges from 430 THz to 790 THz, having a bandwidth of about 360 THz, being a significant advantage of the optical wireless communication system [9, 10]. Another advantage of the larger bandwidth is the increased number of users connected to the network per time.