107 research outputs found
Modulated Unit-Norm Tight Frames for Compressed Sensing
In this paper, we propose a compressed sensing (CS) framework that consists
of three parts: a unit-norm tight frame (UTF), a random diagonal matrix and a
column-wise orthonormal matrix. We prove that this structure satisfies the
restricted isometry property (RIP) with high probability if the number of
measurements for -sparse signals of length
and if the column-wise orthonormal matrix is bounded. Some existing structured
sensing models can be studied under this framework, which then gives tighter
bounds on the required number of measurements to satisfy the RIP. More
importantly, we propose several structured sensing models by appealing to this
unified framework, such as a general sensing model with arbitrary/determinisic
subsamplers, a fast and efficient block compressed sensing scheme, and
structured sensing matrices with deterministic phase modulations, all of which
can lead to improvements on practical applications. In particular, one of the
constructions is applied to simplify the transceiver design of CS-based channel
estimation for orthogonal frequency division multiplexing (OFDM) systems.Comment: submitted to IEEE Transactions on Signal Processin
Securing Large-Scale D2D Networks Using Covert Communication and Friendly Jamming
We exploit both covert communication and friendly jamming to propose a
friendly jamming-assisted covert communication and use it to doubly secure a
large-scale device-to-device (D2D) network against eavesdroppers (i.e.,
wardens). The D2D transmitters defend against the wardens by: 1) hiding their
transmissions with enhanced covert communication, and 2) leveraging friendly
jamming to ensure information secrecy even if the D2D transmissions are
detected. We model the combat between the wardens and the D2D network (the
transmitters and the friendly jammers) as a two-stage Stackelberg game.
Therein, the wardens are the followers at the lower stage aiming to minimize
their detection errors, and the D2D network is the leader at the upper stage
aiming to maximize its utility (in terms of link reliability and communication
security) subject to the constraint on communication covertness. We apply
stochastic geometry to model the network spatial configuration so as to conduct
a system-level study. We develop a bi-level optimization algorithm to search
for the equilibrium of the proposed Stackelberg game based on the successive
convex approximation (SCA) method and Rosenbrock method. Numerical results
reveal interesting insights. We observe that without the assistance from the
jammers, it is difficult to achieve covert communication on D2D transmission.
Moreover, we illustrate the advantages of the proposed friendly
jamming-assisted covert communication by comparing it with the
information-theoretical secrecy approach in terms of the secure communication
probability and network utility
Achieving Covert Communication in Large-Scale SWIPT-Enabled D2D Networks
We aim to secure a large-scale device-to-device (D2D) network against
adversaries. The D2D network underlays a downlink cellular network to reuse the
cellular spectrum and is enabled for simultaneous wireless information and
power transfer (SWIPT). In the D2D network, the transmitters communicate with
the receivers, and the receivers extract information and energy from their
received radio-frequency (RF) signals. In the meantime, the adversaries aim to
detect the D2D transmission. The D2D network applies power control and
leverages the cellular signal to achieve covert communication (i.e., hide the
presence of transmissions) so as to defend against the adversaries. We model
the interaction between the D2D network and adversaries by using a two-stage
Stackelberg game. Therein, the adversaries are the followers minimizing their
detection errors at the lower stage and the D2D network is the leader
maximizing its network utility constrained by the communication covertness and
power outage at the upper stage. Both power splitting (PS)-based and time
switch (TS)-based SWIPT schemes are explored. We characterize the spatial
configuration of the large-scale D2D network, adversaries, and cellular network
by stochastic geometry. We analyze the adversary's detection error minimization
problem and adopt the Rosenbrock method to solve it, where the obtained
solution is the best response from the lower stage. Taking into account the
best response from the lower stage, we develop a bi-level algorithm to solve
the D2D network's constrained network utility maximization problem and obtain
the Stackelberg equilibrium. We present numerical results to reveal interesting
insights
Defect solitons supported by nonlocal PT symmetric superlattices
The existence and stability of defect solitons supported by parity-time (PT)
symmetric superlattices with nonlocal nonlinearity are investigated. In the
semi-infinite gap, in-phase solitons are found to exist stably for positive or
zero defects, but can not exist in the presence of negative defects with strong
nonlocality. In the first gap, out-of-phase solitons are stable for positive or
zero defects, whereas in-phase solitons are stable for negative defects. The
dependence of soliton stabilities on modulation depth of the PT potentials is
studied. It is interesting that solitons can exist stably for positive and zero
defects when the PT potentials are above the phase transition points.Comment: 12 figures, 6 pages, Accepted by EP
A High-Quality Mach-Zehnder Interferometer Fiber Sensor by Femtosecond Laser One-Step Processing
During new fiber sensor development experiments, an easy-to-fabricate simple sensing structure with a trench and partially ablated fiber core is fabricated by using an 800 nm 35 fs 1 kHz laser. It is demonstrated that the structure forms a Mach-Zehnder interferometer (MZI) with the interference between the laser light passing through the air in the trench cavity and that in the remained fiber core. The fringe visibilities are all more than 25 dB. The transmission spectra vary with the femtosecond (fs) laser ablation scanning cycle. The free spectral range (FSR) decreases as the trench length increases. The MZI structure is of very high fabrication and sensing repeatability. The sensing mechanism is theoretically discussed, which is in agreement with experiments. The test sensitivity for acetone vapor is about 104 nm/RIU, and the temperature sensitivity is 51.5 pm/°C at 200 ~ 875 °C with a step of 25 °C
A High-Quality Mach-Zehnder Interferometer Fiber Sensor by Femtosecond Laser One-Step Processing
During new fiber sensor development experiments, an easy-to-fabricate simple sensing structure with a trench and partially ablated fiber core is fabricated by using an 800 nm 35 fs 1 kHz laser. It is demonstrated that the structure forms a Mach-Zehnder interferometer (MZI) with the interference between the laser light passing through the air in the trench cavity and that in the remained fiber core. The fringe visibilities are all more than 25 dB. The transmission spectra vary with the femtosecond (fs) laser ablation scanning cycle. The free spectral range (FSR) decreases as the trench length increases. The MZI structure is of very high fabrication and sensing repeatability. The sensing mechanism is theoretically discussed, which is in agreement with experiments. The test sensitivity for acetone vapor is about 104 nm/RIU, and the temperature sensitivity is 51.5 pm/°C at 200 ~ 875 °C with a step of 25 °C
A High-Quality Mach-Zehnder Interferometer Fiber Sensor by Femtosecond Laser One-Step Processing
During new fiber sensor development experiments, an easy-to-fabricate simple sensing structure with a trench and partially ablated fiber core is fabricated by using an 800 nm 35 fs 1 kHz laser. It is demonstrated that the structure forms a Mach-Zehnder interferometer (MZI) with the interference between the laser light passing through the air in the trench cavity and that in the remained fiber core. The fringe visibilities are all more than 25 dB. The transmission spectra vary with the femtosecond (fs) laser ablation scanning cycle. The free spectral range (FSR) decreases as the trench length increases. The MZI structure is of very high fabrication and sensing repeatability. The sensing mechanism is theoretically discussed, which is in agreement with experiments. The test sensitivity for acetone vapor is about 104 nm/RIU, and the temperature sensitivity is 51.5 pm/°C at 200 ~ 875 °C with a step of 25 °C
SenseFi: A library and benchmark on deep-learning-empowered WiFi human sensing
Over the recent years, WiFi sensing has been rapidly developed for privacy-preserving, ubiquitous human-sensing applications, enabled by signal processing and deep-learning methods. However, a comprehensive public benchmark for deep learning in WiFi sensing, similar to that available for visual recognition, does not yet exist. In this article, we review recent progress in topics ranging from WiFi hardware platforms to sensing algorithms and propose a new library with a comprehensive benchmark, SenseFi. On this basis, we evaluate various deep-learning models in terms of distinct sensing tasks, WiFi platforms, recognition accuracy, model size, computational complexity, and feature transferability. Extensive experiments are performed whose results provide valuable insights into model design, learning strategy, and training techniques for real-world applications. In summary, SenseFi is a comprehensive benchmark with an open-source library for deep learning in WiFi sensing research that offers researchers a convenient tool to validate learning-based WiFi-sensing methods on multiple datasets and platforms.Nanyang Technological UniversityPublished versionThis research is supported by NTU Presidential Postdoctoral Fellowship, ‘‘Adaptive Multi-modal Learning for Robust Sensing and Recognition in Smart Cities’’ project fund (020977-00001), at the Nanyang Technological University, Singapore
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