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/km2optimally 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.

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.