The rapid advancement of drone technology has revolutionized both the civilian and military sectors, enabling a wide range of applications, from commercial deliveries to battlefield reconnaissance. However, the misuse of drones has introduced significant security threats, necessitating the development of robust anti-drone systems. This paper provides a comprehensive review of anti-drone technologies and defense strategies. It explores the rise of drones, their dual-use potential, and the growing need for countermeasures. The study examines the evolution of anti-drone technologies, classifies existing systems, and analyzes case studies of drone-related incidents. It also highlights the correlation between drone threats and the use of anti-drone solutions. Furthermore, this review differentiates between military and civilian defense frameworks, emphasizing the impact of drone misuse on national security and public safety. This study discusses current defense strategies, technological challenges, and complex regulatory landscapes. Finally, it outlines future directions for developing and deploying anti-drone technologies, aiming to raise awareness among policymakers and technologists about the critical role that these systems play in national defense.

Wireless communication has revolutionized the evolution of humankind. The rapid growth and development of mobile communication has created an ecosystem better than what has been before. However, issues such as ample energy consumption and resulting carbon emissions, a lack of proper disposal mechanisms for large amounts of electronic waste, and the recycling of electronic materials interrupt growth. When the world is waiting for the implementation of 6G mobile communication technology, it is mandatory to resolve these issues for the sustainability of 6G technology. In this review, we present the superiority of 6G over previous generations accompanied by issues that cause extensive damage to the environment. To mitigate this adverse effect, we present a lifecycle analysis of 6G wireless communication technology from production to disposal, focusing on issues surrounding electronic waste, energy consumption, and environmental impact. This study explains the intricacies of electronic parts, toxic compounds, and the dangers of incorrect disposal techniques. It also investigates energy consumption issues specific to 6G technology, such as manufacturing processes and network infrastructures that require considerable energy. We also present a quantitative evaluation of the 6G lifecycle in detail. In addition, we present a comprehensive strategy and insights to make 6G sustainable. Furthermore, we suggest an ecological policy for all stakeholders for the sustainability of 6G. We also present political and commercial implications for 6G. As the process of 6G development continues, we show the impact of network fragmentation on standardization, which helps improve sustainability. Finally, we conclude that while the existing research has made significant advances in 6G, there is a need for correct disposal techniques to refine the key government policies for managing e-waste. New cooling technologies and renewable energy sources must be adopted to reduce the current greenhouse emission of 200 g of CO₂ and energy consumption of 2.5 kWh per GB for 6G networks.

In contrast with the traditional cryptography, physical layer security has attracted the attention of many researchers having aim at reinforcing the security of communication systems. As far as vehicular communication is concerned, it is challenging to maintain secure and reliable communication between the connected vehicles due to the density, mobility, and dynamic network topology. This paper considers a vehicle to infrastructure communication in which a legitimately fixed transmitter equipped with a single antenna transmits a confidential message to a legitimate mobile receiver equipped with multiple antennas in the presence of a passive mobile eavesdropper. In such a single input multiple output wireless system, the receiver performs the maximal ratio combining technique assuming constant vehicle speed. We assume that the antennas are closely spaced and depending upon the imperfect channel state information (CSI), we derive the closed-form expressions for the average outage probability, secrecy outage probability, and average secrecy outage rate over the uniform, exponential, and arbitrary correlated Nakagami-m channels for dual antenna branches. In order to gain insight we also perform the high SNR asymptotic analysis of the outage probability and secrecy outage probability. Simulations are conducted to validate the accuracy of our derived analytic expressions. The computation error analysis is carried out to provide the suitability of the correlation type at the legitimate receiver side. Our findings suggest that the performance of the case with exponential channel correlation is better than those for the uniform and arbitrary. Numerical results show the joint effect of vehicle mobility and the antenna correlation on secrecy performance. Moreover, we also observed that the imperfect knowledge of the CSI degrades the security of the confidential messages severely under the effect of mobility.

The fifth-generation networks, designed to provide a better quality of service and spectrum utilization, are rapidly being deployed across the world. 3GPP has proposed a fairness criterion, referred to as “3GPP fairness”, for the coexistence of 5G New Radio in unlicensed spectrum (NR-U) and WiFi in Release 16. In this correspondence, we derive an analytical expression to determine if the 3GPP fairness is achieved in a given network configuration. We model achieving the 3GPP fairness as an optimization problem and show how to use Sequential Quadratic Programming to find the optimal 5G NR-U parameters from a pre-decided range. We test the optimizer in various conditions and inspect the effect of various parameters. Our results reveal that the optimizer is able to predict the best possible parameters for 3GPP fairness and therefore the proposed method proves useful for tuning 5G NR-U parameters during their coexistence with WiFi.

Due to the scarcity of channel availability in IEEE 802.11p standard, applications related to infotainment and multimedia services are vulnerable to suffer from delays and connectivity. Cognitive radio (CR) has the potential to overcome the issue of spectrum scarcity. By making use of the CR technology, secondary users (SU) can access a radio frequency spectrum other than 802.11p through spectrum sensing. Majority of low complex existing algorithms are based on energy detection that are considering the static environment of SUs. In practice, the algorithms, which considers mobility are mainly focused on low vehicle speed. However, the combined effect of primary user (PU) activity statistics and SU mobility has not been tackled while evaluating the performance of opportunistic spectrum access. In particular, this work considers the joint impact of PU activity and vehicle mobility on spectrum sensing performance by considering single lane and double lane vehicular scenarios. We also evaluate the impact of traffic densities on sensing performance. The main contribution of this work is to show the impact of PU activity statistics on sensing performance by deriving analytical expressions for miss-detection probability. These expressions are used for analysis and simulation of cognitive radio enabled vehicular communications. From our observations, it is noted that the probability of vehicle connectivity is improved approximately by 50 $\%$ for initial distance of SU when spectrum sensing is employed under PU activity.