Maritime communication demands have surged due to diverse applications such as transoceanic shipping, offshore resource exploration, and emergency rescue. However, current communication systems are unable to meet the diverse data rate demands of maritime applications. In this paper, we propose a space-air-ground-sea integrated network (SAGSIN) that combines onshore base stations, uncrewed aerial vehicles, high-altitude platform stations, and low Earth orbit satellites to provide seamless and reliable communication across vast oceanic regions. Based on stochastic geometry, we model the spatial distribution of network devices on spherical surfaces. The Matérn hard-core point process (MHCPP) is used to model the deployment of both ground and aerial devices, considering the minimum spacing to avoid overdense and collisions. Aerial relays are used to extend the coverage of coastal base stations, with relay selection aimed at maximizing the end-to-end channel capacity. Analytical expressions for the uplink coverage probability are derived by considering the receiver’s decoding threshold. Furthermore, the analysis is extended to the communication probability by incorporating quality of service (QoS) with data rate as the metric. Numerical results validate the accuracy of the proposed model and demonstrate that SAGSIN can effectively extend reliable communication from coastal regions to the deep ocean. Furthermore, dynamic QoS scheduling across heterogeneous links, each with different transmission capabilities, can enhance overall system efficiency to meet diverse QoS demands.

Nonterrestrial networks (NTN) are pivotal, enabling technologies for achieving global and ubiquitous connectivity in the sixth generation (6G) of wireless systems. On the other hand, nonorthogonal multiple access (NOMA) emerges as a promising candidate for the next-generation multiple access (NGMA), designed to enable massive connectivity and improve spectral efficiency. In this article, we investigate the synergy between NTN and NOMA [power-domain NOMA (PD-NOMA)], which are integral in addressing the connectivity challenges of 6G. First, we present an overview of NTN, detailing their types, unique characteristics, and the challenges they face. Then, we explain the foundational principles of NOMA, such as power allocation and access strategies. We, then, argue the suitability of NOMA as an NGMA technology for 6G and how it addresses the specific challenges associated with NTN. Furthermore, we explore the integration and the interplay of NTN and NOMA with emerging technologies such as millimeter-wave (mmWave), terahertz (THz) frequencies, reconfigurable intelligent surfaces (RISs), and integrated sensing and communication (ISAC) systems. These advancements are critical in meeting the 6G requirements for extremely high data rates and improved spectral efficiency, enhancing the overall functionality of NTN and NOMA. We, then, examine how NTN using NOMA can use different architectural frameworks, including cellular, cell-free (CF), ad hoc, and integrated access and backhaul (IAB) systems, and detailed several use cases where the integration of NTN and NOMA could have a significant impact, such as in vehicular communications, the Internet of Things (IoT), urban air mobility (UAM), and achieving global connectivity. To optimize NTN using NOMA, we present a comprehensive overview of the mathematical optimization algorithms and machine learning tools. Finally, we elaborate on the primary challenges associated with merging NTN with NOMA and propose relevant future research avenues.

In this paper, we study vehicular communications (VCs) at intersections, in the presence of interference over Nakagami-m fading channels. The interference are originated from vehicles located on two perpendicular roads. We derive the outage probability, and closed forms are obtained. The outage probability is derived when the destination is on the road (vehicle, cyclist, pedestrian) or outside the road (base station, road side unit). We compare the performance of line of sight (LOS) scenarios and non-line of sight (NLOS) scenarios, and show that NLOS scenarios offer better performance than LOS scenarios. We also compare intersection scenarios with highway scenarios, and show that the performance of intersection scenarios are worst than highway scenarios as the destination moves toward the intersection. Finally, we investigate the performance of VCs in a realistic scenario involving several lanes. All the analytical results are validated by Monte-Carlo simulations.

Vehicular communications (VCs) protocols offer useful contributions in the context of accident prevention thanks to the transmission of alert messages. This is even truer at road intersections since these areas exhibit higher collision risks and accidents rate. On the other hand, non-orthogonal multiple access (NOMA) has been show to be a suitable candidate for five generation (5G) of wireless systems. In this paper, we propose and evaluate the performance of VCs protocol at road intersections, named adaptive cooperative NOMA (ACN) protocol. The transmission occurs between a source and two destinations. The transmission is subject to interference originated from vehicles located on the roads. The positions of the interfering vehicles follow a Poison point process (PPP). First, we calculate the outage probability related to ACN protocol, and closed form expressions are obtained. Then we compare it with other existing protocols in the literature. We show that ACN protocol offers a significant improvement over the existing protocols in terms of outage probability, especially at the intersection. We show that the performance of ACN protocol increases compared to other existing protocols for high data rates. The theoretical results are verified with Monte-Carlo simulations.

In this paper, we study cooperative non-orthogonal multiple access scheme (NOMA) for millimeter wave (mmWave) vehicular networks at intersection roads. The intersection consists of two perpendicular roads. Transmissions occur between a source, and two destinations nodes with a help of a relay. We assume that the interference come from a set of vehicles that are distributed as a one dimensional homogeneous Poisson point process (PPP). Our analysis includes the effects of blockage from buildings at intersections. We derive closed form outage probability expressions for cooperative NOMA, and compare them with cooperative orthogonal multiple access (OMA). We show that cooperative NOMA offers a significant improvement over cooperative OMA, especially for high data rates. We also show that as the nodes reach the intersection, the outage probability increases. Counter-intuitively, we show that the non line of sigh (NLOS) scenario has a better performance than the line of sigh (LOS) scenario. The analysis is verified with MonteCarlo simulations.

In this paper, we study cooperative vehicular communications (VC) transmission schemes using non-orthogonal multiple access scheme (NOMA) at intersections, in the presence of interference, when two destination nodes are involved. First, we derive the outage probability expressions for the two destination nodes. We also derive the outage probability expressions whether the destination nodes are on the roads (vehicle, cyclist, pedestrian) or outside the roads (base station, road side unit).We compare the performance of cooperative NOMA with cooperative orthogonal multiple access (OMA), and we show that NOMA has a better performance than OMA. We also show that the cooperative NOMA outperforms NOMA using direct transmission. Finally, we compare cooperative NOMA in intersection scenarios with highway scenarios, and show that the performance of intersection scenario are worst than highway in terms of outage probability.

Vehicular communications (VC) have been proved to provide useful contributions in the context of accident prevention thanks to the transmission of alert messages. This is even truer at road intersections since these areas exhibit higher collision risks. In this paper, we study VC at road intersections, considering non-orthogonal multiple access (NOMA) in the presence of interference, when two destination nodes are involved. First, we calculate the outage probability for each destination node. Then we calculate the outage probability when the destination nodes are either on the road (vehicle, cyclist, pedestrian) or outside the road (base station, road side unit). Closed forms are obtained for specific values of the path loss exponent. We compare the performance of NOMA with orthogonal multiple access (OMA) and we show that NOMA has a better performance than OMA. We also compare NOMA performance in two different scenarios, road intersections and highways, and show that the outage probability is higher in the first scenario.

The paper investigates the improvement of using maximum ratio combining (MRC) in cooperative vehicular communications (VCs) transmission schemes considering non-orthogonal multiple access scheme (NOMA) at intersections. The transmission occurs between a source and two destination nodes with a help of a relay. The transmission is subject to interference originated from vehicles that are located on the roads. Closed form outage probability expressions are obtained. We compare the performance of MRC cooperative NOMA with a classical cooperative NOMA, and show that implementing MRC in cooperative NOMA transmission offers a significant improvement over the classical cooperative NOMA in terms of outage probability. We also compare the performance of MRC cooperative NOMA with MRC cooperative orthogonal multiple access (OMA), and we show that NOMA has a better performance than OMA. Finally, we show that the outage probability increases when the nodes come closer to the intersection, and that using MRC considering NOMA improves the performance in this context. The analysis is verified with Monte Carlo simulations.