Direct-to-Device (D2D) satellite communications—where standard mobile devices connect directly with satellites—offer a promising solution to extend coverage and improve network resilience. This paper examines the spectrum allocation and regulatory challenges of enabling D2D satellite services in the European Union (EU), situating the analysis within the broader evolution of International Telecommunication Union (ITU) regulatory processes. While anchored in the preparations for the World Radiocommunication Conference 2027 (WRC-27), the study emphasizes that regulatory developments are dynamic and extend beyond a single conference cycle, ensuring long-term relevance for spectrum governance. The paper provides an overview of satellite communication fundamentals and defines key D2D concepts, including Internet of Things (IoT) use cases and differences between terrestrial mobile bands and Mobile-Satellite Service (MSS) bands. The analysis highlights the current EU landscape for MSS spectrum, particularly the 2 GHz S-band, and its upcoming licensing challenges. It contrasts the EU approach with international developments—notably the United States’ new “Supplemental Coverage from Space” framework and the United Kingdom’s satellite-to-mobile integration plans—to draw lessons for spectrum-sharing models. Technical and regulatory challenges for integrating D2D are identified, and potential alternative frequency bands and spectrum-sharing techniques are explored. A policy roadmap is proposed, outlining short-, medium-, and long-term actions for EU policymakers and stakeholders to enable D2D services. The study ultimately supports the formulation of a forward-looking regulatory framework that secures Europe’s role in shaping the future of hybrid satellite-terrestrial connectivity.

Free-space optical (FSO) communications have emerged as a promising complement to conventional radio-frequency (RF) systems due to their high bandwidth, low interference, and license-free spectrum. Visible-light FSO communication, using laser diodes or LEDs, offers potential for short-range data links, but performance is highly wavelength-dependent under varying atmospheric conditions. This study presents an experimental evaluation of three visible laser diodes at 650 nm (red), 532 nm (green), and 405 nm (violet), focusing on their optical output power, quantum efficiency, and modulation behavior across a range of driving currents and frequencies. A custom laboratory testbed was developed using an Atmega328p microcontroller and a Visual Basic control interface, allowing precise control of current and modulation frequency. A silicon photovoltaic cell was employed as the optical receiver and energy harvester. The results demonstrate that the 650 nm red laser consistently delivers the highest quantum efficiency and optical output, with stable performance across electrical and modulation parameters. These findings support the selection of 650 nm as the most energy-efficient and versatile wavelength for short-range, cost-effective visible-light FSO communication. This work provides experimentally grounded insights to guide wavelength selection in the development of energy-efficient optical wireless systems.

This paper delves into the imperative need for coexistence and compatibility in the 470–694 MHz frequency band, as mandated by the World Radiocommunication Conference 2015 (WRC-15) and the WRC-23. It focuses on challenges in the coexistence of Digital Terrestrial Television Broadcasting (DTTB) and International Mobile Telecommunications-2020 (IMT-2020) services in downlink-only mode, particularly in adjacent-channel scenarios. Using Monte Carlo simulations, the study evaluates the probability of interference from IMT base stations with DTTB reception. The analysis thoroughly investigates the impact of the IMT transmitter’s Adjacent Channel Leakage Ratio (ACLR) and the DTTB receiver’s Adjacent-Channel Selectivity (ACS) on the probability of interference. The results demonstrate a significant degradation in the DTTB reception probability at the edge of coverage based on standard assumptions. To address these challenges, this paper provides recommendations for mitigating interference. These include defining enhanced ACLR regulations for IMT base stations, implementing antenna discriminations, providing specialized filters, and establishing national coordination procedures. The research provides valuable insights for informed decision making in spectrum management within the 470–694 MHz band, aiming to facilitate the coexistence of DTTB and IMT-2020 services, in line with international regulations and best practices.

According to Resolution 235 adopted during the World Radiocommunication Conference 2015 (WRC-15) and the preliminary agenda item 1.5 of WRC-2023, the International Telecommunication Union Radiocommunication Sector (ITU-R) has been entrusted to carry out sharing and compatibility studies between broadcasting and mobile services in the frequency range 470–694 MHz in Region 1. This study specifically focuses on evaluating electromagnetic compatibility in potential co-channel sharing scenarios between Digital Terrestrial Television Broadcasting (DTTB) and International Mobile Telecommunications (IMT) systems within the 470–694 MHz frequency band that may arise in the foreseeable future. To assess the conditions for coexistence, a Monte Carlo simulation method implemented through the SEAMCAT software version 5.4.2 is employed, examining six potential interference scenarios. The simulation results yield the minimum coordination distance required between IMT and DTTB services in the 470–694 MHz band based on the protection criteria to ensure harmonious coexistence while maintaining satisfactory performance. Furthermore, the study investigates the impact of various factors such as transmitter power, antenna heights, coverage radius, antenna discrimination, and antenna tilt angle on the separation distances. The focus lies primarily on critical interference scenarios across neighboring countries’ borders. The simulation outcomes confirm that sharing the same frequency band between IMT and DTTB networks would result in significant mutual interference. Nevertheless, carefully analyzing diverse parameters and assumptions helped provide recommendations to reduce the required separation distances. These findings are valuable for broadcasters, mobile operators, and regulators in establishing the technical coexistence conditions for DTTB and IMT in the new band.

Recently, the issue of monitoring and repairing leakage from cable television networks have re-emerged, particularly after the International Telecommunication Union released a part of the ultra-high frequency spectrum to mobile broadband services. The newly allocated spectrum, known as the digital dividend bands, was traditionally used throughout Europe for digital TV broadcasting. The emerging problem is the mutual interference between the new frequency spectrum utilized by the Mobile/Fixed Communication Networks and the band used by cable TV providers to offer their services. This article is a brief overview and a starting point for extensive research in this area. We started with a simple description of the cable television system and mobile/fixed communication networks focusing on the aspects associated with ingress and egress interference issues. We also discussed the approaches for detecting and measuring mutual interference and reviewed the relevant literature. This article is concluded with some proposed measures for reducing or mitigating mutual interference.