Internet of Vehicles (IoV) has drawn great interests recent years. Various IoV applications have emerged for improving the safety, efficiency and comfort on the road. Cloud computing constitutes a popular technique for supporting delay-tolerant entertainment applications. However, for advanced latency-sensitive applications (e.g., auto/assisted driving, emergency failure management), cloud computing may result in excessive delay. Edge computing, which extends computing and storage capabilities to the edge of the network, emerges as an attractive technology. Therefore, to support these computationally intensive and latency-sensitive applications in IoVs, in this paper, we integrate mobile edge computing nodes (i.e., mobile vehicles) and fixed edge computing nodes (i.e., fixed road infrastructures) to provide low-latency computing services cooperatively. For better exploiting these heterogeneous edge computing resources, the concept of software-defined networking (SDN) and edge computing aided IoV (EC-SDIoV) is conceived. Moreover, in a complex and dynamic IoV environment, the outage of both processing nodes and communication links becomes inevitable, which may have life-threatening consequences. In order to ensure the completion with high reliability of latency-sensitive IoV services, we introduce both partial computation offloading and reliable task allocation with reprocessing mechanism to EC-SDIoV. Since the optimization problem is non-convex and NP-hard, a heuristic algorithm, fault-tolerant particle swarm optimization algorithm is designed for maximizing the reliability (FPSO-MR) with latency constraints. Performance evaluation results validate that the proposed scheme is indeed capable of reducing the latency as well as improving the reliability of the EC-SDIoV.

For unforeseen natural disasters, such as earthquakes, hurricanes, and floods, etc., the traditional communication infrastructure is unavailable or seriously disrupted along with persistent secondary disasters. Under such circumstances, it is highly demanded to deploy emergency wireless communication (EWC) networks to restore connectivity in accident/ incident areas. The emerging fifth-generation (5G)/beyond-5G (B5G) wireless communication system, like unmanned aerial vehicle (UAV) assisted networks and intelligent reflecting surface (IRS) based communication systems, are expected to be designed or re-farmed for supporting temporary high quality communications in post-disaster areas. However, the channel characteristics of post-disaster areas quickly change as the secondary disaster resulted topographical changes, imposing new but critical challenges for EWC networks. In this paper, we propose a novel heterogeneous $\mathcal {F}$ composite fading channel model for EWC networks which accurately models and characterizes the composite fading channel with reflectors, path-loss exponent, fading, and shadowing parameters in 5G-UAV based EWC networks. Based on the model, we develop the optimal power allocation scheme with the simple closed-form expression and the numerical results based optimal joint bandwidth-power allocation scheme. We derive the corresponding capacities and compare the energy efficiency between IRS and traditional relay based 5G-UAVs. Numerical results show that the new heterogeneous Fisher-Snedecor $\mathcal {F}$ composite fading channel adapted resource allocation schemes can achieve higher capacity and energy efficiency than those of traditional channel model adapted resource allocation schemes, thus providing better communications service for post-disaster areas.

This letter presents a novel transmission metasurface to achieve orbital angular momentum (OAM) waves at the X-band. The unit cell of the proposed metasurface consists of three dielectric layers and four metallic layers, where the metallic layer is composed of an outer metallic ring and a center quasi-snow patch. A good transmission coefficient of the unit cell is obtained at the operating frequency. Meanwhile, a full 360° phase shift can be achieved by changing the length of the quasi-snow patch. The method of generating OAM waves is studied and analyzed. Based on this method, a metasurface producing a +1-mode OAM wave is designed and simulated. To verify this concept, one prototype is fabricated, assembled, and measured. The measured results agree well with the simulated ones, showing that the +1-mode OAM wave can be generated successfully with a high gain of 14.5 dBi. Moreover, a narrow divergence angle of +/-9° is achieved in the produced OAM wave.

With the ever increasing spectrum demand of broadband multimedia services, cognitive satellite terrestrial networks have emerged as a promising paradigm for future space information networks. To provide services with diverse delay quality-of-service (QoS) requirements in an energy-limited system, in this paper, we investigate energy efficient power allocation for cognitive satellite terrestrial networks. Employing statistical delay-QoS metric, power allocation schemes are formulated as optimization problems to maximize effective energy efficiency of secondary satellite communications while satisfying interference constraints imposed by primary terrestrial communications. Specifically, allowing for the availability of instantaneous channel state information (CSI) of the secondary transmitter-primary receiver link, optimal transmit powers are derived for both cases of statistical and instantaneous interference constraints. Moreover, to provide a theoretical insight on the performance of the considered network, we derive closed-form expressions for the outage probability based on the obtained optimal transmit powers. Simulation results demonstrate the validity of the theoretical results and show the impacts of the delay exponent, interference constraint, and aggregate interference from terrestrial networks on the performance of satellite networks.

Optimal relay selection is investigated for secure cooperative communications against an adaptive eavesdropper that can perform eavesdropping if the eavesdropping link has good channel quality or perform jamming otherwise. A number of decode-and-forward relays are available for legitimate communications, among which one relay can be selected to help. For legitimate communications, three cases for availability of the eavesdropping channel information are considered: full channel knowledge, partial channel knowledge, and statistical channel knowledge. An optimal relay selection scheme is proposed for each case. For the first and third cases, exact secrecy outage probability expressions in closed form are derived, and for the second case, an approximate secrecy outage probability is derived, which is tight in the high main-to-eavesdropper ratio regime. Moreover, secrecy diversity order for the proposed relay selection scheme in each case is also derived, which is shown to be a full secrecy diversity. Finally, numerical results are given to verify the theoretical analysis derived in this paper.

This paper considers a simultaneous wireless information and power transfer (SWIPT) based decode-and-forward relaying network, where the "harvest-then-forward" strategy is employed. We focus on designing optimal static and dynamic transmission schemes of joint time allocation and power splitting to conduct the relay in terms of outage performance and ergodic performance, respectively. In particular, the analytical expressions for the outage probability and ergodic capacity are derived to determine the optimal static power splitting (PS) and time allocation (TA) ratios. Moreover, we study the dynamic transmission scheme and formulate two joint optimization problems to minimize the outage probability and maximize the instantaneous channel capacity. Considering that the two optimization problems are non-convex, a split-step iterative method is proposed to obtain the optimal dynamic PS ratio and TA ratio for minimizing the outage probability, and an alternate convex optimization method is employed to solve the problem of maximizing the instantaneous channel capacity. Simulation results verify the advantages of the proposed schemes over three peer schemes.