365 research outputs found
First-principles study of vibrational and dielectric properties of {\beta}-Si3N4
First-principles calculations have been conducted to study the structural,
vibrational and dielectric properties of {\beta}-Si3N4. Calculations of the
zone-center optical-mode frequencies (including LO-TO splittings), Born
effective charge tensors for each atom, dielectric constants, using density
functional perturbation theory, are reported. The fully relaxed structural
parameters are found to be in good agreement with experimental data. All optic
modes are identified and agreement of theory with experiment is excellent. The
static dielectric tensor is decomposed into contributions arising from
individual infrared-active phonon modes. It is found that high-frequency modes
mainly contribute to the lattice dielectric constant.Comment: 15pages, 1 figure, 5 table
Coherent model for cross-polarization coupling from a single point-like perturbation in optical fibers
The transfer matrix is proposed to describe the coherent cross-polarization coupling (CPC) induced by a single point-like perturbation (PLP) in optical fibers. This matrix remains independent of the fiber length, making it suitable for characterizing the PLP that have a zero-dimensional impact on fiber length. Consequently, the fiber can be fully characterized by a matrix combining the transfer matrix of CPC and the Jones matrix of the fiber birefringence. The polarization performance of fibers exhibiting both CPC and birefringence is analyzed using the developed combined model
Joint Beamforming for RIS-Assisted Integrated Sensing and Communication Systems
Integrated sensing and communications (ISAC) is an emerging critical
technique for the next generation of communication systems. However, due to
multiple performance metrics used for communication and sensing, the limited
degrees-of-freedom (DoF) in optimizing ISAC systems poses a challenge.
Reconfigurable intelligent surfaces (RIS) can introduce new DoF for beamforming
in ISAC systems, thereby enhancing the performance of communication and sensing
simultaneously. In this paper, we propose two optimization techniques for
beamforming in RIS-assisted ISAC systems. The first technique is an alternating
optimization (AO) algorithm based on the semidefinite relaxation (SDR) method
and a one-dimension iterative (ODI) algorithm, which can maximize the radar
mutual information (MI) while imposing constraints on the communication rates.
The second technique is an AO algorithm based on the Riemannian gradient (RG)
method, which can maximize the weighted ISAC performance metrics. Simulation
results verify the effectiveness of the proposed schemes. The AO-SDR-ODI method
is shown to achieve better communication and sensing performance, than the
AO-RG method, at a higher complexity. It is also shown that the
mean-squared-error (MSE) of the estimates of the sensing parameters decreases
as the radar MI increases.Comment: 30 pages, 8 figures. This paper has been submitted to IEEE
Transactions on Communication
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