Technology has seamlessly integrated into our lives, transforming how we live, work, and interact. From refrigerators notifying us of missing groceries to smartphones serving as personal assistants, navigation tools, and entertainment hubs, innovation is always at 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.

First, we analyse cooperation within a mobile network in the form of non-orthogonal multiple access (NOMA) and joint transmission coordinated multipoint (JT-CoMP) NOMA. By introducing a new power consumption model, PCM-κ, which accounts for the often-overlooked overhead of successive interference cancellation, we provide a more realistic evaluation of NOMA and JT-CoMP NOMA. 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 this thesis, we also examine cooperation among networks through active infrastructure sharing among mobile network operators (MNOs) on a country scale, referred to as national roaming (NR). Using Dutch network data, our analysis shows that NR can yield significant energy savings.

Finally, we consider a future scenario combining both forms of cooperation, evaluating technologies such as cell-free massive MIMO and neutral hosts. A lamppost-based deployment with wireless fronthaul is studied, highlighting how CPU sharing among operators can consolidate load and enable low-power modes. This analysis offers a forward-looking perspective on how cooperative architectures can enhance energy sustainability in next-generation networks.

Ensuring reliable and ubiquitous mobile network coverage is critical for user experience and competitiveness of mobile network operators (MNOs). To meet varying service demands, MNOs typically over-provision their infrastructure, leading to an increased energy consumption and operational costs. National roaming (NR), a form of cooperation between MNOs, enables infrastructure sharing to reduce redundancy in network infrastructure and improve efficiency by allowing each mobile user to be connected to a base station that provides the best connectivity irrespective of which MNO the user is subscribed to. In this paper, we analyse real-world data from three Dutch municipalities to assess NR’s impact on operational power consumption as well as coverage and throughput relative to the current de-facto operation mode where MNOs operate in an isolated way with no cooperation (NC). We propose an energy-aware user association scheme (EA) with polynomial complexity for the studied NR scenario and compare it to a load-balancing, energy-oblivious alternative. Our results show that NR can reduce power consumption in the radio access network by up to 30%, reduce the fraction of disconnected population (FDP) by 95%, and raise the fraction of satisfied population (FSP) by 50%. Our analysis suggests that energy savings are most significant in dense, overprovisioned networks, while FDP and FSP gains are most notable in sparse deployments. Moreover, we observe that EA outperforms our comparison baseline for both NR and NC scenarios, which implies that current MNOs can decrease their power consumption significantly by following an energy-aware user association scheme that facilitates putting some more BSs in sleep mode without compromising FDP and FSP.

Cell-free massive MIMO (mMIMO) promises to enhance coverage, spectral efficiency, and robustness in dense urban environments by leveraging a distributed approach where multiple access points (APs) cooperate to serve each user. While previous studies have primarily focused on fiber-based fronthaul solutions, wireless fronthaul is gaining traction due to its cost-effectiveness and deployment flexibility. This paper investigates the impact of millimeter-wave wireless fronthaul on the energy efficiency (EE) of cell-free mMIMO, with a specific focus on AP deployment on existing urban infrastructure, such as lampposts. With a case study of three mobile network operators in Amsterdam, we analyze the effects of AP density, AP cluster size, and power allocation strategies on network performance. Our findings reveal that an AP density of approximately 43 APs/km2 optimally balances sum rate and power consumption, while an effective AP clustering and power allocation strategy further enhances EE. Our findings provide data-driven insights for mobile network operators (MNOs) to optimize their network expansion and deployment in urban environments.

Cellular networks have become one of the critical infrastructures, as many services depend increasingly on wireless connectivity. Therefore, it is important to quantify the resilience of existing cellular network infrastructures against potential risks, ranging from natural disasters to security attacks, that might occur with a low probability but can lead to severe disruption of the services. In this paper, we combine models with public data from national bodies on mobile network operator (MNO) infrastructures, population distribution, and urbanity level to assess the coverage and capacity of a cellular network at a country scale. Our analysis offers insights on the potential weak points that need improvement to ensure a low fraction of disconnected population (FDP) and high fraction of satisfied population (FSP). As a resilience improvement approach, we investigate in which regions and to what extent each MNO can benefit from infrastructure sharing or national roaming, i.e., all MNOs act as a single national operator. As our case study, we focus on Dutch cellular infrastructure and model risks as random failures and correlated failures in a geographic region. Our analysis shows that there is a wide performance difference across MNOs and geographic regions in terms of FDP and FSP. However, national roaming consistently offers significant benefits in some regions, e.g., up to 13% improvement in FDP and up to 55% in FSP when the networks function without any failures. We then show that a similar performance improvement can be obtained by partial implementation of national roaming.

While non-orthogonal multiple access (NOMA) improves spectral efficiency, it adds complexity to the receivers due to successive interference cancellation (SIC). Prior studies on the energy efficiency of NOMA overlook the SIC overhead and rely on simplistic power consumption models (PCM). To fill this gap, we first introduce PCM- κ that accounts for SIC-related power expenditure. Then, to investigate the energy efficiency of NOMA and joint transmission (JT)-coordinated multipoint (CoMP) NOMA, we formulate a power allocation problem for maximizing the energy efficiency and propose a global approach running at a centralized entity and a local algorithm running at a base station. We evaluate the energy efficiency using PCM- κ and two PCMs commonly used in the literature. Numerical analysis suggests that using simplistic PCMs leads to a few orders of magnitude overestimation of energy efficiency, especially when the receivers have low rate requirements. Despite the superiority of JT-CoMP NOMA over conventional NOMA in finding a feasible power allocation, the difference in their energy efficiency is only marginal when users have identical rate requirements and more significant in more heterogeneous settings with users having different rate requirements. Moreover, when conventional NOMA is feasible, the optimal solution for JT-CoMP NOMA converges to conventional NOMA.

The pressing need for more energy-efficient networks requires understanding the trade-offs maintained by emerging technologies that are expected to help serve an increasing number of connected devices and meet their rate requirements. While spectral efficiency is typically a key performance indicator, hence used for optimal resource allocation, energy efficiency and power consumption of a wireless network should also be considered while deciding on the potential adoption of a new technology. In this paper, we focus on non-orthogonal multiple access (NOMA) as it is considered as a candidate radio access scheme due to its promise to improve spectral efficiency. With a goal of understanding whether joint transmission offers benefits over conventional NOMA, we investigate the performance of joint-transmission NOMA and NOMA considering three objectives: throughput maximization (SumRate), energy efficiency maximization (EE), and power minimization (minP). Different from the literature, we incorporate a power consumption model that accounts for the overhead introduced by successive interference cancellation that is necessary to distinguish the intended signal of a NOMA receiver from the interfering signals aimed for other users in the same cluster. After formulating the optimal power allocation problems, we present our solution steps to make the original problems convex for solving them optimally. Our numerical analysis shows that, for the studied two-cell scenario, joint-transmission offers a benefit only in terms of finding a feasible power allocation while NOMA fails in more cases irrespective of the considered objective. Additionally, our investigation of trade-offs between the investigated problems shows orders of magnitude difference in energy efficiency and throughput for small variations in power consumption.

Mobile network operators (MNOs) in a country operate independent of each other, although inter-operator collaboration such as national roaming (NR) can offer benefits in terms of resilience, coverage, throughput, and energy efficiency. In some countries, regulations impose realization of national roaming as a fallback strategy, e.g., when an operator cannot offer sufficient coverage while the other can. However, tighter inter-operator collaboration can unlock even more opportunities. In this work, we quantify the benefits in terms of coverage, capacity, and power consumption that can be gained by national roaming as a fallback strategy and as a default strategy wherein all MNOs are operated as a single network. We use public data from national bodies in the Netherlands to study the gains for the Dutch MNOs and investigate the resilience gain also under random failures of base stations, e.g., due to hardware or software errors. Our analysis shows that all MNOs can benefit from a tight cooperation reflected in lower fraction of disconnected population, higher fraction of satisfied population, and lower power consumption for transmission. Despite not offering the same level of benefits, NR as a fallback strategy can also offer gains, in particular for MNOs with less ubiquitous network deployment. Moreover, in comparison to no cooperation, both cooperation approaches provide resilience to isolated failures and result in less severe performance degradation.

In this work, a resource allocation problem is investigated for a relay-based multiuser cooperative orthogonal frequency division multiple access (OFDMA) uplink system, considering a very large antenna array at the base station and nonlinear power amplifiers (PAs) in both user and relay nodes. Firstly, a theoretical characterization of the considered scenario is performed. Then, some analytical expressions for the nonlinear distortion (NLD) variance and the PA constant of a third-order polynomial PA are derived, as well as the instantaneous signal-to-noise ratio (SNR) of the considered system is calculated. Then, a low-complexity suboptimal relay selection and subcarrier allocation technique is proposed for the considered scenario based on the developed expressions. Numerical simulation results are presented to validate the derived expressions and to evaluate the performance of the proposed technique.

This paper presents two new per-subcarrier relay selection techniques for cooperative orthogonal frequency division multiplexing (OFDM) communication systems with nonlinear power amplifiers (PAs) and considering the amplify-and-forward (AF) protocol. The proposed techniques are based on a developed theoretical expression for the instantaneous signal-to-noise ratio (SNR) of an AF cooperative OFDM system taking into account the nonlinear distortions introduced by the relays' PAs. Our results show that both the proposed techniques can significantly improve the system capacity when compared to a classical relay selection method. Numerical simulation results are presented to validate the performance of the proposed techniques.

This work proposes the formulation of a data rate maximization problem in an orthogonal frequency division multiplexing (OFDM) system taking into account the distortions inserted by a third-order (3rd) polynomial nonlinear power amplifier (PA). Based on this formulation, two suboptimal heuristic algorithms are proposed for power allocation in the considered scenario. The two heuristics, named HH-MI (Hughes-Hartogs - Modified 1) and HH-M2 (Hughes-Hartogs - Modified 2), are based on the HH algorithm. These methods try to maximize the system capacity, but taking into account the distortions inserted by a nonlinear PA. One of the advantages of such techniques is that energy gains can be obtained, as the power is only allocated if the distortions do not affect system. Finally, we present a performance analysis in which the gains of the proposed heuristics are demonstrated with respect to the conventional HH.