7,401 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
Joint radar-communication waveform designs using signals from multiplexed users
Joint radar-communication designs are exploited in applications where radar and communications systems share the same frequency band or when both radar sensing and information communication functions are required in the same system. Finding a waveform that is suitable for both radar and communication is challenging due to the difference between radar and communication operations. In this paper, we propose a new method of designing dual-functional waveforms for both radar and communication using signals from multiplexed communications users. Specifically, signals from different communications users multiplexed in the time, code or frequency domains across different data bits are linearly combined to generate an overall radar waveform. Three typical radar waveforms are considered. The coefficients of the linear combination are optimized to minimize the mean squared error with or without a constraint on the signal-to-noise ratio (SNR) for the communications signals. Numerical results show that the optimization without SNR constraint can almost perfectly approximate the radar waveform in all the cases considered, giving good dual-functional waveforms for both radar and communication. Also, among different multiplexing techniques, time division multiple access is the best option to approximate the radar waveform, followed by code division multiple access and orthogonal frequency division multiple access
S-shaped transition trajectory and dynamic development frontier of the financial systemic risk research: a multiple networks analysis
Financial systemic risk has an impact on the real economy and
may trigger a chain reaction in the whole economic system leading
to the financial crisis. Many scholars focus on financial systemic
risk, but few of them are bibliometric analyses. Therefore, this
paper explores the status quo, emerging trends, and transition trajectory through the above analysis method in the research field
from 1990 to 2020. Based on the above analysis, we find the following conclusions: (1) The basic conclusions of the most productive countries, institutions, journals, authors, status quo, and the
change of hotspots in this research field are presented. (2) The
emerging trends in this research field are âcredit riskâ, âcapital shortfallâ, âspill-overâ, âspreadâ, âfinancial marketâ, âinterconnectednessâ,
âtransmissionâ in the last three years. (3) The research field of financial systemic risk presents an S-shaped transition trajectory through
the local forward, the local backward, the global standard, and the
global key-route main path analysis. (4) We find that the most
cited authors are not always at the core of the trajectory of financial systemic risk research. The emerging trend âcredit riskâ is also
recently a core research direction in this research fieldâs transition trajector
Future prospects of mass-degenerate Higgs bosons in the -conserving two-Higgs-doublet model
The scenario of two mass-degenerate Higgs bosons within the general
two-Higgs-doublet model (2HDM) is revisited. We focus on the global picture
when two -even Higgs bosons of and are nearly mass-degenerate. A
global fit to the signal strength of the 125 GeV Higgs measured at the LHC is
performed. Based on the best-fit result of the 2HDM mixing angles
, theoretical constraints, charged and -odd Higgs boson
direct search constraints and the electroweak precision constraints are imposed
to the 2HDM parameter space. We present the signal predictions of the channels for the benchmark models at the LHC 14 TeV runs. We also
study the direct Higgs boson pair productions at the LHC, and the Z-associated
Higgs boson pair production search at the ILC 500 GeV runs, as well as the
indirect probes at the CEPC 250 GeV run. We find that the mass-degenerate Higgs
boson scenario in the Type-II 2HDM can be fully probed by these future
experimental searches.Comment: 31 pages, 9 figures, 5 tables, matches with the PRD published versio
Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges
With the rapid development of marine activities, there has been an increasing
number of maritime mobile terminals, as well as a growing demand for high-speed
and ultra-reliable maritime communications to keep them connected.
Traditionally, the maritime Internet of Things (IoT) is enabled by maritime
satellites. However, satellites are seriously restricted by their high latency
and relatively low data rate. As an alternative, shore & island-based base
stations (BSs) can be built to extend the coverage of terrestrial networks
using fourth-generation (4G), fifth-generation (5G), and beyond 5G services.
Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs.
Despite of all these approaches, there are still open issues for an efficient
maritime communication network (MCN). For example, due to the complicated
electromagnetic propagation environment, the limited geometrically available BS
sites, and rigorous service demands from mission-critical applications,
conventional communication and networking theories and methods should be
tailored for maritime scenarios. Towards this end, we provide a survey on the
demand for maritime communications, the state-of-the-art MCNs, and key
technologies for enhancing transmission efficiency, extending network coverage,
and provisioning maritime-specific services. Future challenges in developing an
environment-aware, service-driven, and integrated satellite-air-ground MCN to
be smart enough to utilize external auxiliary information, e.g., sea state and
atmosphere conditions, are also discussed
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