One of the most representative challenges of multi-tier heterogeneous network architectures is the interference management among different Radio Access Technologies. In this sense, in order to achieve the potential increase on network capacity forecasted for 5G, the issue of interference must be addressed. Intelligent energy management, as proposed in the growing area of Green Communications could serve as an appealing solution to the interference issue. However developing an optimal energy management plan requires the understanding of the characteristics of 5G cellular networks that could be exploited to improve energy and resources efficiency. In this work we present a study about challenges in energy-efficient communications and technologies as enablers for green solutions and how this challenges can be extended to meet those of the 5G heterogeneous networks, in order to identify possible solutions to address the energy efficiency and interference mitigation issues.
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Nowadays, there is an interest on technology development in the growing area of green communications for reducing energy consumption in wireless communications. Some works reported in literature claim that there will be an increase of CO2 equivalent emissions by a factor of three until 2020 compared to 2007 (Uriarte-Ramírez & Barboza-Tello, 2014). Societal development will lead to changes in the way mobile and wireless communication systems are used. This has accelerated the implementation of 5G networks that can provide exponentially more capacity, lower latency, ubiquitous connectivity, as well as increased reliability and availability. Those 5G future services such as e-banking, e-learning, and e-health will continue to proliferate. On-demand information and entertainment (e.g. in the form of augmented reality) will progressively be delivered over mobile and wireless communication systems. These developments will lead to an avalanche of mobile and wireless traffic volume predicted to increase a thousand-fold over the next decade (Osseiran, et al., 2014). Thus, those multimedia application services must cope with high data rate demands. However, higher data rates necessitate more energy per bit for a given bit error rate (BER), which in turn increases the overall energy consumption of the system and the production of CO2 emissions that are threat to global warming. Thus, researching energy-efficient designs for high data rate wireless communication systems is a burning issue. Due to escalating expansion of wireless network infrastructures and exponential growth in traffic rate, a considerable amount of worldwide energy is consumed by Information and Communications Technology (ICT) of which more than 70% is being used by radio access part/radio frequency (Mohammad S. & Alagan Anpalagan, 2013) . Climate change and the need to reduce global energy usage are now accepted. Today 4 billion of people on the earth have access to a mobile phone; effective access to information and communications is a proven stimulus to economic development. Recent studies have shown the potential for IT (Information Technology) to reduce energy consumption in other industries. As a key enabler of green solutions on environmental an economic grounds, more energy efficient radio access networks are required. When it is about the power, the consumption of a mobile handset per subscriber is lower than the base station. However manufacturing energy is a larger component in the mobile handset that in the base station. It is mainly due to the fact that lifetime of a base station is longer (typically 10-15 years) compared to a handset (approximately 2 years) (Pollin S., et al., 2008).
Green Communication technologies currently receive a lot of attention. Wireless systems have been optimized in terms of spectrum efficiency and transmission reliability. However, most of the recent efforts have ignored the importance of wireless networks´ environmental responsibility, e.g. energy efficiency and environmental impact. Information and Communications Technology (ICT) already represents around 2% of total of carbon emissions, and this is expected to increase from 0.53 billion tonnes (Gt) carbon dioxide equivalent (CO2e) in 2002 to 1.43 Gt CO2e in 2020. Optimizing the energy efficiency of wireless communication not only reduces environmental impact, but also cuts overall network costs and help make communication more practical and affordable in a pervasive setting. In cellular networking, base station consumes a maximum portion of the total energy used in the system, more than 50% of total energy is consumed by the radio access part, where 50-80% is used for the power amplifier (PA). (Feng, Jiang, Lim, Cimini Jr., & Feng, 2013). There are currently more than 4 millions base stations serving mobile users, each consuming an average of 25 MWh per year. To address this problem, Green Networking has focused bringing architectural changes in base station and network planning. On this last point (network planning) Heterogeneous Networks (HetNets) have emerged as a possible solution for energy efficiency at the base station. In this sense in work we describe 5G Future Network, Green Comm Projects and stand out HetNets as green solutions. The chapter begins with a brief description on 5G Challenges and potential green solutions. Later the Green Comm Projects are described. The following section gives an overview in HetNets and describes how it could be an energy efficient deployment strategy. Next, we introduce challenges in Het Nets and possible solution. Future work and conclusions are given at the end.