Spatial Bandwidth Asymptotic Analysis for 3D Large-Scale Antenna Array Communications

In this paper, we study the spatial bandwidth for line-of-sight (LOS) channels with linear large-scale antenna arrays (LSAAs) in 3D space. We provide approximations to the spatial bandwidth at the center of the receiving array, of the form $C R^{-B}$, where $R$ is the radial distance, and $C$ and $B$ are directional-dependent and piecewise constant in $R$. The approximations are valid in the entire radiative region, that is, for $R$ greater than a few wavelengths. When the length of the receiving array is small relative to $R$, the product of the array length and the spatial bandwidth provides an estimate of the available spatial degree-of-freedom (DOF) in the channel. In a case study, we apply these approximations to the evaluation of spatial multiplexing regions under random orientation conditions. The goodness-of-fit of the approximations is demonstrated and some interesting findings about the DOF performance of the channel under 3D and 2D orientation restrictions are obtained, e.g., that, under some conditions, it is better to constrain the receiving array orientation to be uniform over the unit circle in the 2D ground plane rather than uniform over the 3D unit sphere.Comment: 15pages, 11 figures. To be published in IEEE Transactions on Wireless Communications, with additional conten

Low Peak-to-Average Power Ratio FBMC-OQAM System based on Data Mapping and DFT Precoding

Filter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) is an alternative to OFDM for enhanced spectrum flexible usage. To reduce the peak-to-average power ratio (PAPR), DFT spreading is usually adopted in OFDM systems. However, in FBMC-OQAM systems, because the OQAM pre-processing splits the spread data into the real and imaginary parts, the DFT spreading can result in only marginal PAPR reduction. This letter proposes a novel map-DFT-spread FBMC-OQAM scheme. In this scheme, the transmitting data symbols are first mapped with a conjugate symmetry rule and then coded by the DFT. According to this method, the OQAM pre-processing can be avoided. Compared with the simple DFT-spread scheme, the proposed scheme achieves a better PAPR reduction. In addition, the effect of the prototype filter on the PAPR is studied via numerical simulation and a trade-off exists between the PAPR and out-of-band performances

V2V-Assisted V2I MmWave Communication for Cooperative Perception with Information Value-Based Relay

Millimeter-wave (mmWave) vehicular communication is a key technology that enables autonomous vehicles to collaborate in environment perception, thereby improving traffic efficiency and safety to a new level. Many recent works have focused on relay-based solutions to overcome the inherent defects of mmWave, such as the severe path loss and its sensitivity to blockages. However, the selfishness of the vehicles is often ignored. Considering the application-oriented nature of vehicular communication, we propose an information value-based relay strategy for mmWave vehicle-to-infrastructure (V2I) transmission in this paper. Specifically, the vehicles are allowed to make relay decisions based on the evaluation of the value of messages from their own perspectives. To this end, a simple relay probability model based on the required awareness range is introduced. Through the use of stochastic geometry to model the vehicular network, the outage performance is analyzed and the results are validated by simulations. Impacts of both network and application related parameters on the outage performance are investigated. These preliminary results laid the foundation for the further expansion of the information value-based relay strategies to a wider range of network settings

Impact of Channel Aging on Massive MIMO Vehicular Networks in Non-isotropic Scattering Scenarios

Massive multiple-input multiple-output (MIMO) relies on accurate channel estimation for precoding and receiving to achieve its claimed performance advantages. When serving vehicular users, the rapid channel aging effect greatly hinders its advantages, and a careful system design is required to ensure an efficient use of wireless resources. In this paper, we investigate this problem for the first time in a non-isotropic scattering scenario. The von Mises distribution is adopted for the angle of arrival (AoA), resulting in a tunable channel temporal correlation coefficient (TCC) model, which can adapt to different AoA spread conditions through the k parameter and incorporates the isotropic Jakes-Clarke model as a special case. The simulated results in a Manhattan grid-type multi-cell network clearly demonstrate the impact of channel aging on the uplink spectral efficiency (SE) performance and moreover, in order to maximize the area average SE, the size of the transmission block should be optimally selected according to some linear equations of k

Multi-modality cardiac image computing: a survey

Multi-modality cardiac imaging plays a key role in the management of patients with cardiovascular diseases. It allows a combination of complementary anatomical, morphological and functional information, increases diagnosis accuracy, and improves the efficacy of cardiovascular interventions and clinical outcomes. Fully-automated processing and quantitative analysis of multi-modality cardiac images could have a direct impact on clinical research and evidence-based patient management. However, these require overcoming significant challenges including inter-modality misalignment and finding optimal methods to integrate information from different modalities. This paper aims to provide a comprehensive review of multi-modality imaging in cardiology, the computing methods, the validation strategies, the related clinical workflows and future perspectives. For the computing methodologies, we have a favored focus on the three tasks, i.e., registration, fusion and segmentation, which generally involve multi-modality imaging data, either combining information from different modalities or transferring information across modalities. The review highlights that multi-modality cardiac imaging data has the potential of wide applicability in the clinic, such as trans-aortic valve implantation guidance, myocardial viability assessment, and catheter ablation therapy and its patient selection. Nevertheless, many challenges remain unsolved, such as missing modality, modality selection, combination of imaging and non-imaging data, and uniform analysis and representation of different modalities. There is also work to do in defining how the well-developed techniques fit in clinical workflows and how much additional and relevant information they introduce. These problems are likely to continue to be an active field of research and the questions to be answered in the future

Shannon Capacity of LOS MIMO Channels with Uniform Circular Arrays

The Shannon capacity for the line-of-sight (LOS) multiple-input multiple-output (MIMO) channel between two perfectly aligned uniform circular arrays (UCAs) is derived from the first principles in a tutorial fashion. It is well known that harmonically related complex exponentials (also known in the literature as orbital angular momentum (OAM) modes) are eigenmodes for the spatially continuous channel. We show that the corresponding eigenvalues can be expressed as Bessel functions of the first kind. We also show that the spatially discrete channel between two UCAs with the same finite number of Hertzian dipole antennas on both sides has eigenmodes that are spatially sampled continuous OAM modes, and discrete eigenvalues that are aliased versions of the continuous eigenvalues. Through numerical solution of Maxwell\u27s equations, we verify that the discrete eigenvalues for UCAs with realistic dipole antennas are the same as with the Hertzian dipoles for the studied geometries (1~km hop distance, UCA radius 1 and 2 m, carrier frequency 70 GHz) as long as antenna spacing is not very dense

Shannon Capacity of LOS MIMO Channels with Uniform Circular Arrays

The Shannon capacity for the line-of-sight (LOS) multiple-input multiple-output (MIMO) channel between two perfectly aligned uniform circular arrays (UCAs) is derived from the first principles in a tutorial fashion. It is well known that harmonically related complex exponentials (also known in the literature as orbital angular momentum (OAM) modes) are eigenmodes for the spatially continuous channel. We show that the corresponding eigenvalues can be expressed as Bessel functions of the first kind. We also show that the spatially discrete channel between two UCAs with the same finite number of Hertzian dipole antennas on both sides has eigenmodes that are spatially sampled continuous OAM modes, and discrete eigenvalues that are aliased versions of the continuous eigenvalues. Through numerical solution of Maxwell\u27s equations, we verify that the discrete eigenvalues for UCAs with realistic dipole antennas are the same as with the Hertzian dipoles for the studied geometries (1~km hop distance, UCA radius 1 and 2 m, carrier frequency 70 GHz) as long as antenna spacing is not very dense

Ovariectomy Induces a Shift in Fuel Availability and Metabolism in the Hippocampus of the Female Transgenic Model of Familial Alzheimer's

This is the published version. Copyright 2013 Public Library of Science.Previously, we demonstrated that reproductive senescence in female triple transgenic Alzheimer's (3×TgAD) mice was paralleled by a shift towards a ketogenic profile with a concomitant decline in mitochondrial activity in brain, suggesting a potential association between ovarian hormone loss and alteration in the bioenergetic profile of the brain. In the present study, we investigated the impact of ovariectomy and 17β-estradiol replacement on brain energy substrate availability and metabolism in a mouse model of familial Alzheimer's (3×TgAD). Results of these analyses indicated that ovarian hormones deprivation by ovariectomy (OVX) induced a significant decrease in brain glucose uptake indicated by decline in 2-[18F]fluoro-2-deoxy-D-glucose uptake measured by microPET-imaging. Mechanistically, OVX induced a significant decline in blood-brain-barrier specific glucose transporter expression, hexokinase expression and activity. The decline in glucose availability was accompanied by a significant rise in glial LDH5 expression and LDH5/LDH1 ratio indicative of lactate generation and utilization. In parallel, a significant rise in ketone body concentration in serum occurred which was coupled to an increase in neuronal MCT2 expression and 3-oxoacid-CoA transferase (SCOT) required for conversion of ketone bodies to acetyl-CoA. In addition, OVX-induced decline in glucose metabolism was paralleled by a significant increase in Aβ oligomer levels. 17β-estradiol preserved brain glucose-driven metabolic capacity and partially prevented the OVX-induced shift in bioenergetic substrate as evidenced by glucose uptake, glucose transporter expression and gene expression associated with aerobic glycolysis. 17β-estradiol also partially prevented the OVX-induced increase in Aβ oligomer levels. Collectively, these data indicate that ovarian hormone loss in a preclinical model of Alzheimer's was paralleled by a shift towards the metabolic pathway required for metabolism of alternative fuels in brain with a concomitant decline in brain glucose transport and metabolism. These findings also indicate that estrogen plays a critical role in sustaining brain bioenergetic capacity through preservation of glucose metabolism

Spaceborne miniaturized UHF dual band helix antenna with a small frequency ratio

This study proposes a novel miniaturized circularly polarized (CP) ultrahigh frequency (UHF) quadrifilar helix antenna for spaceborne applications. The dual-band operation is realized using four inverted-U shaped helical strips (IUSHSs) that are rotated and alternately arranged on the four faces of a hollow polyimide cuboid in a sequential rotation manner, which effectively reduces the size of the antenna. Furthermore, the four IUSHSs are connected by a cross-shape strip at the top of the antenna to control the dual resonant frequencies, resulting in a small dual-band frequency ratio. The proposed antenna is both lightweight and robust when compared with the conventional miniaturized CP antennas operating at similar bands with similar performance. In particular, its compact radiator provides effective miniaturized spaceborne solution without the need of high-dielectric coefficient materials. A device for spaceborne application that operates at 402/505 MHz is designed, fabricated, measured, and in-orbit tested with a weight of 651 g and an effective size of 0.161 7 0.161 7 0.228 λ3402MHz (λ402MHz is the wavelength at 402 MHz). The measured gain and axial ratio of the proposed antenna are better than 5.32 dBi and 2.18 dB, respectively, within 2 and 12 MHz bandwidth for the two bands. The test results proved that the methods used to design the proposed antenna are effective

Random Style Transfer based Domain Generalization Networks Integrating Shape and Spatial Information

Deep learning (DL)-based models have demonstrated good performance in medical image segmentation. However, the models trained on a known dataset often fail when performed on an unseen dataset collected from different centers, vendors and disease populations. In this work, we present a random style transfer network to tackle the domain generalization problem for multi-vendor and center cardiac image segmentation. Style transfer is used to generate training data with a wider distribution/ heterogeneity, namely domain augmentation. As the target domain could be unknown, we randomly generate a modality vector for the target modality in the style transfer stage, to simulate the domain shift for unknown domains. The model can be trained in a semi-supervised manner by simultaneously optimizing a supervised segmentation and an unsupervised style translation objective. Besides, the framework incorporates the spatial information and shape prior of the target by introducing two regularization terms. We evaluated the proposed framework on 40 subjects from the M\&Ms challenge2020, and obtained promising performance in the segmentation for data from unknown vendors and centers.Comment: 11 page