This paper introduces an innovative spectrum measurement setup and a new performance metric, airtime utilization, which quantifies the extent of spectrum usage. Our design offers a protocol-independent solution for detailed spectrum analysis across frequency, time, and power dimensions, which is essential for effective spectrum management. The presented experimental Wireless Community Testbed (WCT) is cost-effective for large-scale deployment. Extensive measurements in the 3.1 to 3.7 GHz frequency range are reported to demonstrate the practical application of our setup. The airtime utilization metric is explored through various case studies, showing its impact on understanding spectrum dynamics at different times of day, across weekdays and weekends, as well as long-term statistics over 15 weeks. It is observed that a large portion of the spectrum from 3.17 to 3.4 GHz is underutilized, presenting an opportunity to share the spectrum. The paper emphasizes the importance of dynamic and responsive spectrum allocation strategies to optimize the use of this vital global resource. We also discuss the potential for expanding our network of distributed stand-alone spectrum monitoring systems to enhance real-time, comprehensive oversight of spectrum usage.

In this paper, we explore an indoor downlink cooperative hybrid visible light communication (VLC)/radio frequency (RF) scenario using a relay node to reduce system outage probability. In particular, information can be transmitted to the end user either directly through the VLC link or via the relay node. To re-transmit the decoded information to the end user through the RF link the relay utilizes harvested energy from the source light emitting diode (LED) at the ceiling. We derive the analytical expression for the outage probability of the relayaided hybrid VLC/RF system, considering the randomness of location and receiver orientation for both the relay and the end user. Furthermore, we investigate the effects of the direct current (DC) bias, data rate threshold, and different distributions for the location and orientation of the end user and relay on the outage probability of the system.

A document by Amir Hossein Fahim Raouf . Click on the document to view its contents.

The ever-growing demand for wireless connectivity, coupled with limited spectrum resources, has resulted in spectrum congestion and interference. This research investigates the probability of occupancy in common sub-6 GHz cellular network bands  based on measurements conducted in urban and rural environments. Specifically, we analyze the spectrum occupancy of various long-term evolution (LTE), 5th generation (5G) and Citizens Broadband Radio Service (CBRS) bands used in the United States, considering both uplink and downlink transmissions at altitudes up to 180 meters. Additionally, we explore the influence of altitude on the probability of spectrum occupancy in these bands. Our findings reveal that the probability of occupancy is generally higher in the downlink compared to the uplink. Moreover, we observe that line-of-sight (LoS) signals play a critical role in higher altitudes. These results provide insights spectrum utilization in various cellular bands across different altitudes, with implications on  interference and spectrum coexistence between terrestrial networks and unmanned aerial systems (UASs) in the future.

The growing importance of Underwater Networks (UNs) in mission-critical activities at sea enforces the need for secure Underwater Communications (UCs). Classical encryption techniques can be used to achieve secure data exchange in UNs. However, the advent of Quantum Computing will pose threats to classical cryptography, thus challenging also UCs. Currently, underwater crypto-systems mostly adopt symmetric ciphers, which are considered computationally quantum-robust, but pose the challenge of distributing the secret key upfront. Post-Quantum Public-Key (PQPK) protocols promise to overcome the key distribution problem. The security of PQPK protocols, however, only relies on the assumed computational complexity of some underlying mathematical problems. Moreover, the use of resource hungry PQPK algorithms in resource-constrained environments such as UNs can require non-trivial hardware/software optimization efforts. An alternative approach is underwater Quantum Key Distribution (QKD), which promises unconditional security built upon the physical principles of Quantum Mechanics. This tutorial provides a basic introduction to free-space Underwater QKD (UQKD). At first, the basic concepts of QKD are presented, based on a fully worked out QKD example. A thorough state-of-the-art analysis of UQKD is carried out. The paper subsequently provides a theoretical analysis of the QKD performance through free-space underwater channels, and its dependence on the key optical parameters of the system and seawater. Finally, open challenges, points of strength and perspectives of UQKD are identified and discussed.