Efficient and reliable neighbor discovery is critical for UAV networks equipped with directional antennas, particularly in dynamic and energy-constrained environments. We present a novel optimization framework that jointly minimizes delay and power consumption using the power-delay product as the optimization metric. The framework is formulated for both synchronous and asynchronous schemes, leveraging upper-bound metrics and a convex-concave procedure to achieve tractable convex formulations. Simulation results validate the theoretical models and show significant improvements over baseline methods. We also conducted real-world experiments, where our method reduced power-delay product by 11% compared to the baseline, though the dual-sector hardware configuration limited the achievable gains. This work provides a comprehensive solution for UAV neighbor discovery, with high potential for scalability in more complex and dynamic environments.

Space-air-ground integration has become paramount in the next generation of wireless communication systems in the era marked by the seamless integration of terrestrial and celestial domains. On the other hand, the age of information (AoI) has recently emerged as a vital metric for evaluating the timeliness and freshness of data in these multi-hop communication systems. This paper focuses on investigating the information freshness of multi-hop satellite IoT systems while considering several automatic repeat request (ARQ) and hybrid ARQ (HARQ) schemes over different hops to promise the reliability of data transmissions. Specifically, a group of remote sensors transmits their data to a terrestrial base station (B) via the code-division multiple access (CDMA) strategy to exploit CDMA’s natural merits, e.g., anti-jamming and simultaneous transmissions. Then, B sends these received data to a data destination (D) via a satellite (R) under the transparent forwarding strategy. We derive the closed form of the outage probability for the CDMA protocol considering multi-user interference (MUI) and the closed form of the end-to-end outage probability for the three kinds of ARQ and HARQ schemes on the dual-hopB-R-Dtransmission, and then finally derive the expression of the corresponding AoI. Finally, numerical results show that simulations match well with the theoretical results, proving the analysis’s correctness and the pros and cons of the different ARQ/HARQ schemes.

Reconfigurable Intelligent Surfaces (RIS) and Un-manned Aerial Vehicles (UAVs) have emerged as promising tech-nologies for the 6th-Generation (6G) network. The integration of RIS with the UAV (RIS-UAV) can enhance ground communication by providing a 360°panoramic reflection. Existing RIS-UAV mainly considers passive elements which suffer from double path loss problems. This motivates the use of the hybrid RIS-UAV equipped with both active and passive RIS elements. This paper investigates the energy efficiency maximisation problem for the hybrid RIS-UAV by optimising the placement of the UAV, subject to the UAV's permitted altitude range. The non-convex optimisation problem is addressed using Particle Swarm Optimisation (PSO) tool and distributed learning algorithm. The numerical results show that the proposed distributed learning algorithm is preferred when optimising the energy efficiency of the hybrid RIS-UAV system. In addition, hybrid RIS-UAV outperforms the fully passive RIS-UAV and the active amplify-and-forward (AF) relay in terms of energy efficiency of the system.

Trust management is a representative research domain to ensure secure communication and cooperation among entities in Vehicular Ad-hoc Networks (VANETs). However, vehicles as entities are not always trustworthy because of the openness characteristics of VANETs, such as various malicious participators, and selfish behaviors. In this paper, we propose a Path-Backtracking-based Trust Management Scheme (PBTMS) for VANETs to evaluate the trustworthiness of entities based on the interaction histories (according to previous interaction counts), message path-backtracking (tracking the origin and route of messages), and multi-path analysis (analyzing the like-lihood of malicious vehicle presence). Specifically, within the PBTMS framework, the trustworthiness of vehicles is meticulously evaluated. By incorporating both entity trust and path trust metrics, PBTMS computes an aggregate trust value for each vehicle. Extensive simulations demonstrate that PBTMS surpasses other baseline algorithms in accuracy, achieving higher precision in evaluating entity trustworthiness.

With the emergence of various applications in Intelligent Transportation Systems (ITS), the cooperative communication among vehicles has become increasingly important to provide transportation data services. However, vehicles with selfish behaviors rarely provide high-performance communication services to others, resulting in a low packet delivery ratio and a high end-to-end delay. It is extremely challenging to substantially alleviate the influence of selfish vehicles in vehicular networks, because of the network topology and unstable communication qualities. To address the above problems, the Social similarity and Reputation Based Routing (SRBR) is proposed, considering social relationships, vehicle behaviors, and transmission capacity. The social similarity can improve network performance by leveraging the social relationships of vehicles, while reputation mechanisms can effectively defend against selfish vehicles’ attacks. Additionally, to integrate the above two-dimensional metrics, fuzzy logic is employed. Furthermore, extensive results show SRBR outperforms other baseline schemes in terms of delivery ratio, average latency, and overhead ratio.

Due to its low latency and high data rates support, mmWave communication has been an important player for vehicular communication. However, this carries some disadvantages such as lower transmission distances and inability to transmit through obstacles. This work presents a Contextual Multi-Armed Bandit Algorithm based beam selection to improve connection stability in next generation communications for vehicular networks. The algorithm, through machine learning (ML), learns about the mobility contexts of the vehicles (location and route) and helps the base station make decisions on which of its beam sectors will provide connection to a vehicle. In addition, the proposed algorithm also smartly extends, via relay vehicles, beam coverage to outage vehicles which are either in NLOS condition due to blockages or not served any available beam. Through a set of experiments on the city map, the effectiveness of the algorithm is demonstrated, and the best possible solution is presented.

Unmanned aerial vehicle (UAV) is increasingly becoming a promising tool in communication system. On one hand, UAV has been used as an aerial communication platform to provide wireless communications. On the other hand, UAV has been employed as an aerial user equipment to perform arbitrary missions. Both of these applications are promising in terms of cost, flexibility, and automation. Nevertheless, existing works usually consider these applications separately. This limits the role of UAV in future communication system. Thus, in this paper, we relax this limitation and further visualize what UAV might provide us in the future. Specifically, we present a vision of UAV in future communication system along with new applications and capabilities. This vision provides a blueprint on how engineers can design the future communication system with UAVs playing prominent roles. We then review the current advances of UAV communications to understand the gap between vision and reality. Lastly, we outline the critical issues, challenges, and future directions toward this vision.

Abstract Unmanned aerial vehicles (UAVs) have gained considerable interests in numerous civil applications. To push forward its potentials, cellular-connected UAVs have been introduced. Nevertheless, cellular networks face several bottlenecks such as spectrum scarcity and limited concurrent connectivity. To address these issues, non-orthogonal multiple access (NOMA) can be adopted. NOMA provides several opportunities for cellular-connected UAVs such as larger rate region, balanced performance between system throughput and fairness, and reduced delay. In this paper, we review important findings of the related studies, and outline new opportunities and challenges in NOMA for cellular-connected UAVs. Monte-Carlo simulations are then performed to analyze the new aerial user’s (AU)’s signal characteristics and evaluate the NOMA performance for co-existence of AU and terrestrial user (TU). Our preliminary results show that NOMA is a promising strategy for cellular-connected UAVs.

Efficiency of cellular-connected UAVs is challenged by spectrum inefficiency, limited number of concurrent connectivity, and strong interference. To overcome these issues, in this paper, we study the performance of downlink non-orthogonal multiple access for cellular-connected UAVs. We develop a novel framework based on stochastic geometry for the co-existence of aerial users (AUs) and terrestrial users (TUs), where the spatial distribution of the base stations (BSs) follows a Poisson Point Process. In our analysis, two user association policies and two types of receive antennas are considered while an inter-cell interference coordination (ICIC) technique is also in place. As the main performance measures, we then analytically derive the coverage probability and average rate of AUs and TUs. These derivations are then used to provide quantitative insights on the impact of different system parameters and settings including AU's altitude, TU's distance from the BS, power allocation, successive interference cancellation (SIC) constraints, user association policy, antenna beamwidth, and the number of coordinated BSs. Based on our analysis we then propose an interference-aware scheme based on maximum-SINR user association, directional antenna, and ICIC. A benchmark scheme based on minimum-distance user association, omni-directional antenna, and without ICIC is considered. Compared to the benchmark scheme, our proposed scheme improves the AU's coverage probability by threefold and TU's average rate by six-fold. Compared to the orthogonal multiple access, our proposed scheme trades off a slight reduction in the AU's coverage probability (~1%) with a significant increase in the achieved rate of the TUs (603Kbps/resource block).

Connecting aerial users (AU)s to cellular networks expands the potential of many applications. Nevertheless, existing cellular networks are not designed to efficiently serve AUs and terrestrial users (TU)s. Limited spectrum and high interference make the task even more challenging. Thus, in this paper, we examine the feasibility of fixed-power non-orthogonal multiple access (NOMA) scheme in meeting the demands of AUs and TUs by leveraging stochastic geometry. To this end, we propose a tractable framework for evaluating the coverage of AU and TU in cellular networks, where BSs are distributed using Poisson Point Process (PPP). We then derive the coverage probability of AU and TU. Using these analytical expressions, we further analyze the impact of different network parameters such as AU's altitude, TU's distance, and power allocation, and obtain key insights for designing an efficient NOMA scheme. Our results show that i) increasing AU's altitude does not always degrade the signal-to-interference ratio (SIR), ii) fixed-power NOMA scheme cannot be employed solely to serve AU's control and command (C& C) link, iii) pairing a near TU with a typical AU may prevent significant performance degradation, and iv) mitigating the interference of TU could improve the performance of AU.

Scarcity of the radio spectrum and high inter-cell interference (ICI) are major impediments to efficient connectivity in cellular-connected unmanned aerial vehicles (UAV)s. To address these issues, we propose aerial-terrestrial network non-orthogonal multiple access (ATN-NOMA). In the proposed scheme, we pair the aerial user (AU) and terrestrial user (TU) in a NOMA setting to leverage their asymmetric channel gains and rate demands in downlink communication. The high ICI issue at the AU receiver is further managed by equipping the AU with an adjustable beamwidth directional antenna and forming a distributed beamforming among the coordinated terrestrial base stations (BSs). The proposed ATN-NOMA scheme obtains the optimal beamwidth and power allocation to maximize the TUs' sum-rate subject to the AU's Quality-of-Service (QoS) requirement. The corresponding optimization is a non-convex optimization problem for which we exploit the structure of the problem to obtain a local optimal solution. We further compare TUs' sum-rate and AU's outage probability of the proposed scheme with multiple schemes. Simulation results show that our proposed scheme significantly outperforms the existing schemes and further demonstrate a robust performance against UAV altitude variations.

In this paper, we consider a downlink wireless communication system with the co-existence of ground user (GU) and mobile aerial user (AU). Existing solutions rely on orthogonal multiple access (OMA) to support these users, however, OMA is unable to provide the best rate and outage performance because its spectral efficiency is limited by the users' channel conditions and rate requirements. Thus, we propose an aerial-ground non-orthogonal multiple access (AG-NOMA) scheme that pairs the GU and AU for data and control links, respectively. Unlike terrestrial non-orthgonal multiple access (NOMA), the key idea of AG-NOMA is to exploit the asymmetric features of the channels and rate demands of the GU and AU in the downlink communication. Based on these opportunities, we investigate the maximum achievable GU rate over a time-varying wireless channel while satisfying the AU Quality-of-Service (QoS) requirement with perfect and partial channel state information (CSI). For perfect CSI, we derive the optimal successive interference cancellation (SIC) policy, power allocation, GU rate, and feasibility conditions in closed-form expressions. For partial CSI, we also derive the suboptimal SIC policy and power allocation in closed-form expressions, and further discussed a tradeoff between the achievable rate and reliability. This tradeoff depends on the system parameters, and thus we have suggested some appropriate parameters based on theoretical support and standard requirements to strike a balance between rate and reliability. Our simulation results show that AG-NOMA scheme with perfect and partial CSI can achieve up to +99% GU rate-improvement as compared to OMA and provide a more sustainable rate-improvement and/or lower outage probability than terrestrial NOMA scheme.

Drone networks offer rapid network deployment to areas that can pose access difficulty. This paper investigates the deployment of multi-hop drone-based unmanned aerial vehicles networks with a focus on the self-organization aspect. When rescue drones carry out their rescue operations which may fly faraway from the gateway, relay drones are autonomously deployed to maintain connectivity. We study the multiple dedicated connections where each rescue drone is connected to the gateway via dedicated relay drones. We show that this approach lacks sharing of relay drones and thus requires more relay drones. We then propose a centralized greedy algorithm and a distributed solution to significantly reduce the number of relay drones. We show that while the distributed self-organized drones (DSOD) solution requires a slightly higher number of relay drones than the greedy algorithm, it eliminates the need for global message exchange which makes it attractive for practical use.

Non-orthogonal multiple access (NOMA) with power-domain user multiplexing has been considered as one of the potential candidates of the fifth-Generation (5G) systems. In this paper, a two-stage user selection algorithm is proposed based on proportional fairness for downlink NOMA with zero-forcing beamforming (PF-NOMA-ZFBF) in order to improve the throughput-fairness trade-off for NOMA system. We focus on short term fairness, where short term refers to the minimum time window in which a specified fairness is guaranteed and evaluated using Jain's index. A transmit power allocation then applied to enhance the throughput of NOMA system. Simulation results show that the proposed PF-NOMA-ZFBF significantly improves user fairness index with at least 38.96% over conventional NOMA-ZFBF while maintaining the total system sum-rate (near maximum).

The surge in global population is compelling a shift toward smart agriculture practices. This coupled with the diminishing natural resources, limited availability of arable land, increase in unpredictable weather conditions makes food security a major concern for most countries. As a result, the use of Internet of Things (IoT) and data analytics (DA) are employed to enhance the operational efficiency and productivity in the agriculture sector. There is a paradigm shift from use of wireless sensor network (WSN) as a major driver of smart agriculture to the use of IoT and DA. The IoT integrates several existing technologies, such as WSN, radio frequency identification, cloud computing, middleware systems, and end-user applications. In this paper, several benefits and challenges of IoT have been identified. We present the IoT ecosystem and how the combination of IoT and DA is enabling smart agriculture. Furthermore, we provide future trends and opportunities which are categorized into technological innovations, application scenarios, business, and marketability.

Two‐path successive relaying (TPSR) improves spectral efficiency of relay under half‐duplex constraint. However, when the relay pair is operating in non‐orthogonal channels, the capacity of TPSR can be severely degraded by inter‐relay interference (IRI). Relay selection has been proposed in the existing literature to mitigate the IRI. However, existing opportunistic TPSR (OSR) schemes limit the pool of potential relay pair choices. Eventually, the performance of existing OSR schemes is underestimated. This study proposes four OSR schemes to improve the achievable performance of OSR schemes in terms of ergodic capacity and outage probability. The proposed schemes select a pair of relays jointly from the N potential relays. This increases the pool of potential relay pairs quadratically. Acknowledging the fact that OSR is only good for certain operating conditions, adaptive schemes that dynamically switches between OSR and opportunistic half‐duplex relaying (OHR) are proposed. The simulation results show that the proposed schemes outperform the existing OSR, OHR and full‐duplex relaying schemes significantly. The asymptotic ergodic capacity analysis of the proposed schemes increases logarithmically with the quadratic of N . The diversity and multiplexing tradeoff analysis reveals that the proposed schemes achieve the full diversity and multiplexing gain given a large number of potential relays.

The loss of communication system during natural disaster is known to hamper the efficiency of disaster response. In most cases, the paralyzed communication system often appears as one of the factors which delays the disaster response and complicates the rescue operation. However, if the communication systems including the mobile network are in working conditions, they are usually congested. Hence there is a need for an improved emergency communication system (ECS) to provide reliability and improve system performance during emergency. Furthermore, most of the works on ECS are based on theoretical simulations which can not capture the real world scenario. Taking into account the structure of the internet of things, which includes sensing, computing and communicating, this paper presents an ECS which consists of a wireless relay node, a disaster sensing and detection system. The relay node serves as a temporary communication station to help victims equipped with mobile phones to maintain a reliable communication link with the next available base station in the vicinity. Meanwhile, the sensors are used to detect abnormal changes in environmental parameters such as temperature and water level. The design is implemented on software defined radios. The simulated and measured results shows significant improvement in terms of data and bit error rate over the direct communication scheme.

Relaying is a promising technique to improve wireless physical-layer security. Existing literature shows that a full-duplex relay can further improve the secrecy capacity and secrecy outage probability compared to conventional half-duplex relay, but this comes at a price of sophisticated implementation. For sake of easy implementation, two-path successive relaying has been proposed to emulate the full-duplex relay by scheduling a pair of half-duplex relays to assist the source transmission alternately. However, the performance of two-path successive relaying in secrecy communication remains unexplored. This paper proposes a secrecy two-path successive relaying protocol for a scenario with one source, one destination and two half-duplex relays. The relays operate alternately in a time division mode to forward messages continuously from source to destination in the presence of an eavesdropper. To further confuse the eavesdropper, the source and relay are scheduled to transmit jamming signals at appropriate intervals. Analytical results on the secrecy outage probability reveals that the proposed protocol is able to deliver the target secrecy rate when the SNR of the eavesdropping channels are high. In addition, the secrecy outage probability of the proposed protocol is the joint secrecy outage probability of the relay pair. Numerical simulations show that the proposed protocol achieves the highest ergodic secrecy capacity and lowest secrecy outage probability compared to the existing half duplex relaying, full duplex relaying and full duplex jamming schemes.

This paper proposes solution to optimize the peak side lobes level (PSLL) in a distributed random antenna array (RAA) when locations of the nodes in the array cannot be manipulated. Using the conventional beam forming method, RAA produces a poor beam pattern with high side lobe level, which greatly reduces the performance and the efficiency of the antenna. Existing literature focuses on finding the best position of antenna placement in RAA to lower the side lobes. This is not feasible when the user has no autonomy over the position of the antenna elements. Our proposed solution achieves beam pattern with much lower PSLL regardless of the array size and number of nodes in the array. The proposed method also enables up to 40% of energy savings when the size of array is small and 20% of savings when bigger array size is considered.

We consider a scenario where multiple pairs of users exchange information within pair, with the help of a dedicated multi-antenna relay. The protocol integrates the idea of analogue network coding in mixing two data streams originating from the same user pair, together with the spatial multiplexing of the data streams originating from different user pairs. The key feature of the protocol is that it enables both the relay and the users to participate in interference cancellation. We propose several beamforming schemes for the multi-antenna relay and evaluate the performance using information theoretical metrics such as ergodic capacity, outage probability and diversity and multiplexing tradeoff. Analytical and simulation results justify that the ergodic capacity, outage probability and diversity and multiplexing tradeoff of the proposed beamforming schemes outperform comparable schemes.

One of the main challenges in the wireless broadcast channels is the co-channel interference among multiple destinations. Practical linear precoding techniques such as zero-forcing beamforming (ZFBF) is used to avoid the co-channel interference. However, the achievable diversity order of the ZFBF is bounded by the number of transmitter antennas. In this paper, we introduce a spectral efficient cooperative broadcast channels transmission protocol in the MISO channels using linear precoding. We evaluate the performance of the proposed protocol using the diversity and multiplexing tradeoff. The proposed protocol can achieve the maximum diversity order expressed as a sum of the transmitter antennas and the number of participating relays. For a large number of relay candidates, the diversity and multiplexing tradeoff of the proposed protocol completely surpasses the performance of the comparable scheme. Simulations have also shown the outage probability of the proposed protocol outperforms the existing scheme.