An Investigation of Energy Efficiency in Heterogeneous Wireless Networks

Energy efficiency is an important issue as the amount of high rate multimedia wireless communication grows substantially in order to accommodate more users. Over the past 10 years, there has been an unprecedented growth in the wireless information transfer volume and the associated wireless node density. This is especially true in urban areas in which over 50% of the world's population reside. Currently, there are over 7 billion active handsets and 4 million cell-sites globally. Additional infrastructure, in particular Wi-Fi hotspots in urban areas, has reached over 350 nodes per square kilometre. On the other hand, telecommunications operators and vendors are also facing a serious challenge as the total energy consumed by network infrastructure as well as the CO2 emissions resulting from their manufacturing and operation increase significantly. Recently, it has been reported that energy costs can account for as much as half of a mobile carrier's annual operating expenses. Moreover, the environmental and financial consequences would also be disastrous if the aggregate energy consumption of Information and Communication Technologies (ICT) were to follow the predicted growth trajectory. The current combination of the energy consumption of service centres and wireless communication networks accounts for 2–4% of global CO2 emissions and is expected to reach up to 10% in less than 10 years. Therefore it is essential for the research community to investigate state-of-the-art technologies, such as energy-efficient network architecture and protocols, energy-efficient wireless transmission techniques, energy-efficient home networking, and opportunistic spectrum sharing without causing tremendous harmful interference pollution to meet the challenges to improve energy efficiency in communications. As there are many ways to improve energy efficiency in wireless communications illustrated above, this thesis mainly focuses on improving the energy efficiency through the enhancement of network capacity. It starts to examine the relative merits of Long Term Evolution (LTE) femtocell access points (FAP) and 802.11n Wi-Fi radio access technologies (RATs) so as to establish a baseline system-level performance. The results from Monte-Carlo simulations reveal that LTE-femtocells best suit small home networks, providing a high level of spectral- and energy-efficiency. With this result in mind, attention is paid to the next generation of heterogeneous cellular networks, in more detail, in the DownLink (DL) of Orthogonal Frequency Division Multiple Access (OFDMA) based LTE networks. The thesis furthers the study of interference avoidance for a heterogeneous network and applies a novel Radio Resource Management (RRM) algorithm for indoor femtocells. After this, the thesis examines how to create an algorithm that optimises the location of home FAP(s) with respect to the dominant interference. This investigation covers the scenarios of single room single FAP, single room multiple FAPs and multi-room multi-floor multi-FAPs. Finally, special attention is paid to evaluate the system-level performance using a stochastic-geometry theoretical framework which acts as a fundamental basis in the analysis of heterogeneous networks and paves the way for the study of mitigating interference using a frequency-selective-surface (FSS) and the work of the trade-off between interference mitigation via FSS for indoor home network and outdoor-indoor resource sharing by turning on and off the FSS.