PhD Defence Syllas Rangel Carneiro Magalhaes | Towards More Sustainable Mobile Networks | Is Cooperation the Key?

Towards More Sustainable Mobile Networks | Is Cooperation the Key?

Syllas Rangel Carneiro Magalhaes is a PhD student in the department Design and Analysis of Communication Systems. (Co)Promotors are prof.dr.ir. G.J. Heijenk and dr. S. Bayhan from the faculty of Electrical Engineering, Mathematics and Computer Science, University of Twente.

Technology has seamlessly integrated into our daily lives, transforming how we live, work, and interact with the world. From refrigerators that notify us of missing groceries to smartphones acting as our personal assistants, navigation systems or even entertainment hubs, innovation is always at the reach of our fingertips. To ensure such a seamless integration of the growing number of applications, these technologies rely heavily on advanced cellular infrastructures. However, the rapid expansion of connected applications is generating massive data traffic, raising significant concerns about energy consumption and, ultimately, the environmental sustainability of these networks. In this thesis, we investigate how cooperation within and among mobile networks can enhance sustainability by improving the energy efficiency and reducing overall power consumption. More specifically, this thesis investigates the interplay between cooperation mechanisms and energy performance in mobile communication networks and their impact on different network configurations and optimisation strategies.

One of the techniques identified as promising for supporting the rapid growth of data traffic in mobile networks is non-orthogonal multiple access (NOMA). In Chapter 3, we investigate how realistic the reported energy efficiencies in the literature are and whether joint transmission (JT)-coordinated multipoint (CoMP) can help improve the energy efficiency of such systems. Through a literature review, we find that prior studies on the energy efficiency of NOMA overlook the successive interference cancellation (SIC) overhead and rely on simplistic power consumption models (PCM). To fill this gap, we introduce PCM-k, which accounts for SIC-related power expenditure. Then, to investigate the energy efficiency of NOMA and JT-CoMP NOMA, we formulate a power allocation problem for maximising the energy efficiency and propose a global approach running at a centralised entity and a local algorithm running at a base station. We evaluate the energy efficiency using PCM-k and two PCMs commonly used in the literature. Our numerical investigation shows that simplistic PCMs tend to overestimate the energy efficiency of the network and result in lower throughput and energy efficiency when users have lower rate requirements.

In Chapter 4, we further explore the JT-CoMP NOMA scenario, analysing the impact of the objective function on the system performance. Specifically, we formulate and solve power allocation optimisation problems considering three optimisation objectives: throughput maximisation, energy efficiency maximisation, and power minimisation. Our observations show that one of the main benefits of JT-CoMP NOMA over conventional NOMA is its ability to enhance the channel capacity for cell-edge users under severe channel conditions. However, this improvement in channel capacity for cell-edge users is only marginal, leading to a marginal gain in energy efficiency.

Another promising approach to enhancing the sustainability of mobile networks is exploring a different dimension of cooperation: cooperation among mobile networks. In Chapter 5, we investigate active infrastructure sharing among mobile network operators (MNOs) on a country scale, referred to as national roaming (NR). We perform a case study on Dutch mobile network infrastructure and quantify the power consumption of an NR strategy compared to a no-cooperation setting across three Dutch municipalities of different sizes. Unlike previous studies, we conduct a data-driven analysis to evaluate coverage, throughput, and power consumption of an NR scheme. Our analysis demonstrates that national roaming strategies can significantly reduce energy consumption across diverse urban settings, highlighting their potential for large-scale sustainability gains.

Finally, in Chapter 6, we combine the cooperation within and among mobile networks in a futuristic scenario to understand the full potential of cooperation in mobile networks. We focus on candidate technologies for future mobile generations, such as cell-free massive MIMO and neutral hosts. Using publicly available data from national bodies in the Netherlands, we analyse the energy efficiency of a lamppost-based, cell-free massive MIMO deployment with wireless fronthaul. In particular, we examine the impact of CPU sharing among mobile network operators, where load is consolidated on certain CPUs, allowing others to enter low-power modes. This analysis offers a forward-looking perspective on how cooperative architectures can enhance energy sustainability in next-generation networks.