Energy Efficiency of Wireless Access - Impact of Power Amplifiers and Load Variations

In order to ensure seamless coverage and sustainable exponential growth of capacity, there is a keen interest in the development and deployment of highly energy efficient wireless systems and solutions. To design an energy efficient network, it is important to consider the facts that the variations in traffic demand in both temporal and spatial domains are significant, and the power consumption of cellular networks is mostly dominated by macro base stations where the power amplifiers (PAs) consume around 55-70 percent of total energy. One of the main challenges lies in coping with this load variations considering that the PAs attain high efficiency only at around the maximum output power level. In this thesis, we propose energy efficient system level solutions for wireless access network that consider the non-ideal efficiency characteristics of the PA and the load variations.  We model and incorporate the PA efficiency in the energy-delay trade-off present in Shannon's channel capacity model in order to investigate the energy saving potential in a wireless access network at the cost of additional flow-level delay. We propose a best response iteration based distributed power control algorithm where the cells identify the power levels for different user locations to minimize energy consumption under delay constraints. We observe that energy saving potential strongly depends on the network load and PA efficiency characteristics. We also investigate the impact of additional delay in the downlink on the energy consumption of the mobile terminal.  Heterogeneous network is the leading technology for the next-generation cellular networks. We investigate the energy-efficient densification and load sharing between the layers of a heterogeneous network while taking into consideration the PA efficiency and temporal load variations (TLV). We also study the impact of PA efficiency and energy-delay trade-off on the energy efficient network densification.  Massive MIMO (MM) is another leading candidate technology to cater for very high capacity demand. We consider a multi-cell MM system and provide the guidelines to dimension the PA for the antennas. We also develop energy efficient antenna adaptation schemes that allow the cells to dynamically adapt the number of antennas to the TLV in order to maintain high energy efficiency (EE) throughout the day. Our results indicate that these proposed antenna adaptation schemes can improve the EE significantly

Green Backhauling for Rural Areas

Providing wireless broadband access to rural and remote areas is becoming a big challenge for wireless operators, mostly because of the need for a cost-effective and low energyconsuming mobile backhaul. However, to the best of our knowledge, energy consumption of different options for backhauling of future rural wireless broadband networks has not been studied yet. Therefore, in this paper we assess the energy consumption of future rural wireless broadband network deployments and backhaul technologies. In the wireless segment, two deployment strategies are considered, one with macro base station only, and one with small base stations. In the backhaul segment, two wireless, i.e., microwave and satellite, and one optical fiber based (i.e., long reach passive optical networks) solutions are considered. These options are compared in terms of their ability to satisfy coverage, capacity and QoS requirements of a number of rural users in the time span that goes from 2010 until 2021. From the presented results it is possible to conclude that wireless backhaul solutions can significantly increase the energy consumption of the access network. In contrast, the long reach PON based backhaul has much higher energy efficiency and in the long term might be a better choice for wireless operators