MmWave FANETs play an increasingly important role in the development of UAVs technology. Fast neighbor discovery is a key bottleneck in mmWave FANETs. In this paper, we propose a two-way neighbor discovery algorithm based on a spatial multi-channel through cross-layer optimization. Firstly, we give two boundary conditions of the physical (PHY) layer and media access control (MAC) layer for successful link establishment of mmWave neighbor discovery and give the optimal pairing of antenna beamwidth in different stages and scenarios using cross-layer optimization. Then, a mmWave neighbor discovery algorithm based on a spatial multi-channel is proposed, which greatly reduces the convergence time by increasing the discovery probability of nodes in the network. Finally, a random reply algorithm is proposed based on dynamic reserved time slots. By adjusting the probability of reply and the number of reserved time slots, the neighbor discovery time can be further reduced when the number of nodes is larger. Simulations show that as the network scale is 100 to 500 nodes, the convergence time is 10 times higher than that of the single channel algorithm.

Blockage in millimeter wave (mmWave) channels can severely degrade the efficiency of air-to-ground (A2G) communications between unmanned aerial vehicles (UAVs) and base stations (BSs). Although relay-aided transmission has proved to be effective in mitigating the negative impact of blockage on mmWave communications, how to efficiently select the optimal relaying UAV for A2G communications remains an open problem. To enable optimal relay selection, the UAV under blockage should probe neighboring UAVs for the quality of their A2G links, which incurs non-negligible beam training overheads. Moreover, most existing studies ignore the impacts of UAV orientations as well as the finite sizes of beam codebooks on the performance of relay selection. In view of these challenges, we study the design of relay probing strategies for UAV mmWave A2G communications to maximize the expected achievable throughput between the UAV under blockage and the BS. Different from existing work, we jointly consider beam training overhead, the limited number of neighboring UAVs, the finite sizes of UAV codebooks, and the orientation of neighboring UAVs in our schematic design. Besides, we derive the closed-form expression for the distribution of achievable throughput when a specific neighboring UAV is adopted as the relay, in order to facilitate the development of the optimal relay probing strategy. Extensive simulation results demonstrate the accuracy of our analysis and the superiority of the obtained relay probing strategy.

Industrial Internet of Things (IIoT) brings opportunities for innovation and upgrading to industrial production, but meanwhile, it poses unprecedented challenges on the physical layer of wireless communications. In this paper, we propose a novel frequency hopping transmission scheme for IIoT, which owns much high efficiency and strong anti-jamming ability. This new scheme is built based on the combination of Coherent Fast Frequency Hopping (CFFH) and Cyclic Code Shift Key (CCSK), named Phase Cyclic Shift Keying Based Coherent Fast Frequency Hopping (PCSK-CFFH). For the proposed PCSK-CFFH system, the shift of orthogonal base sequence is adopted to modulate the phases among inter-hop, instead of transmitting each hop with the same phase as conventional CFFH. This scheme is able to further exploit the extra dimensions of CFFH signals and enables the CFFH system to transmit additional information at no extra cost on either bandwidth or power. Moreover, the BER performance of the proposed PCSK-CFFH system is analyzed theoretically. To improve its ability against severe narrow-band jamming, the selection combing is introduced in our scheme. Furthermore, the anti-jamming performance of the proposed PCSK-CFFH system is also demonstrated. Finally, the simulation results are shown to demonstrate that: By introducing the inter-hop dimension to CFFH, PCSK-CFFH improves the power efficiency and spectrum efficiency by multiple times and simultaneously inherits the excellent anti-jamming performance of conventional CFFH system. It can be concluded that the proposed PCSK-CFFH scheme has a great potential to be applied to low-power and highly reliable IIoT communications.