9,263 research outputs found
UAV Swarm-Enabled Aerial CoMP: A Physical Layer Security Perspective
Unlike aerial base station enabled by a single unmanned aerial vehicle (UAV),
aerial coordinated multiple points (CoMP) can be enabled by a UAV swarm. In
this case, the management of multiple UAVs is important. This paper considers
the power allocation strategy for a UAV swarm-enabled aerial network to enhance
the physical layer security of the downlink transmission, where an eavesdropper
moves following the trajectory of the swarm for better eavesdropping. Unlike
existing works, we use only the large-scale channel state information (CSI) and
maximize the secrecy throughput in a whole-trajectory-oriented manner. The
overall transmission energy constraint on each UAV and the total transmission
duration for all the legitimate users are considered. The non-convexity of the
formulated problem is solved by using max-min optimization with iteration. Both
the transmission power of desired signals and artificial noise (AN) are derived
iteratively. Simulation results are presented to validate the effectiveness of
our proposed power allocation algorithm and to show the advantage of aerial
CoMP by using only the large-scale CSI
Maritime coverage enhancement using UAVs coordinated with hybrid satellite-terrestrial networks
Due to the agile maneuverability, unmanned aerial vehicles (UAVs) have shown great promise for on-demand communications. In practice, UAV-aided aerial base stations are not separate. Instead, they rely on existing satellites/terrestrial systems for spectrum sharing and efficient backhaul. In this case, how to coordinate satellites, UAVs and terrestrial systems is still an open issue. In this paper, we deploy UAVs for coverage enhancement of a hybrid satellite-terrestrial maritime communication network. Using a typical composite channel model including both large-scale and small-scale fading, the UAV trajectory and in-flight transmit power are jointly optimized, subject to constraints on UAV kinematics, tolerable interference, backhaul, and the total energy of the UAV for communications. Different from existing studies, only the location-dependent large-scale channel state information (CSI) is assumed available, because it is difficult to obtain the small-scale CSI before takeoff in practice and the ship positions can be obtained via the dedicated maritime Automatic Identification System. The optimization problem is non-convex. We solve it by using problem decomposition, successive convex optimization and bisection searching tools. Simulation results demonstrate that the UAV fits well with existing satellite and terrestrial systems, using the proposed optimization framework
Optimal Beamforming for Hybrid Satellite Terrestrial Networks with Nonlinear PA and Imperfect CSIT
In hybrid satellite-terrestrial networks (HSTNs), spectrum sharing is crucial
to alleviate the "spectrum scarcity" problem. Therein, the transmit beams
should be carefully designed to mitigate the inter-satellite-terrestrial
interference. Different from previous studies, this work considers the impact
of both nonlinear power amplifier (PA) and large-scale channel state
information at the transmitter (CSIT) on beamforming. These phenomena are
usually inevitable in a practical HSTN. Based on the Saleh model of PA
nonlinearity and the large-scale multi-beam satellite channel parameters, we
formulate a beamforming optimization problem to maximize the achievable rate of
the satellite system while ensuring that the inter-satellite-terrestrial
interference is below a given threshold. The optimal amplitude and phase of
desired beams are derived in a decoupled manner. Simulation results demonstrate
the superiority of the proposed beamforming scheme.Comment: 5 pages, 5 figures, journa
4-Methylanilinium perchlorate 18-crown-6 clathrate
In the title compound, C7H10N+·ClO4
−·C12H24O6, the 4-methylanilinium cation interacts with an 18-crown-6 molecule forming a rotator–stator-like structure through bifurcated N—H⋯(O,O) hydrogen bonds between the ammonium group of the cation and the O atoms of the crown ether molecule. All three components of the structure possess mirror symmetry. The benzene ring is inclined to the mean plane of the crown ether molecule by 86.84 (8)°
- …