277 research outputs found
Downlink Channel Covariance Matrix Reconstruction for FDD Massive MIMO Systems with Limited Feedback
The downlink channel covariance matrix (CCM) acquisition is the key step for
the practical performance of massive multiple-input and multiple-output (MIMO)
systems, including beamforming, channel tracking, and user scheduling. However,
this task is challenging in the popular frequency division duplex massive MIMO
systems with Type I codebook due to the limited channel information feedback.
In this paper, we propose a novel formulation that leverages the structure of
the codebook and feedback values for an accurate estimation of the downlink
CCM. Then, we design a cutting plane algorithm to consecutively shrink the
feasible set containing the downlink CCM, enabled by the careful design of
pilot weighting matrices. Theoretical analysis shows that as the number of
communication rounds increases, the proposed cutting plane algorithm can
recover the ground-truth CCM. Numerical results are presented to demonstrate
the superior performance of the proposed algorithm over the existing benchmark
in CCM reconstruction
6G Non-Terrestrial Networks Enabled Low-Altitude Economy: Opportunities and Challenges
The unprecedented development of non-terrestrial networks (NTN) utilizes the
low-altitude airspace for commercial and social flying activities. The
integration of NTN and terres- trial networks leads to the emergence of
low-altitude economy (LAE). A series of LAE application scenarios are enabled
by the sensing, communication, and transportation functionalities of the
aircrafts. The prerequisite technologies supporting LAE are introduced in this
paper, including the network coverage and aircrafts detection. The LAE
functionalities assisted by aircrafts with respect to sensing and communication
are then summarized, including the terrestrial and non-terrestrial targets
sensing, ubiquitous coverage, relaying, and traffic offloading. Finally,
several future directions are identified, including aircrafts collaboration,
energy efficiency, and artificial intelligence enabled LAE.Comment: This paper has been submitted to IEEE for possible publicatio
Stochastic switching of TiO2 based memristive devices with identical initial memory states
In this work, we show that identical TiO2-based memristive devices that possess the same initial resistive states are only phenomenologically similar as their internal structures may vary significantly, which could render quite dissimilar switching dynamics. We experimentally demonstrated that the resistive switching of practical devices with similar initial states could occur at different programming stimuli cycles. We argue that similar memory states can be transcribed via numerous distinct active core states through the dissimilar reduced TiO2-x filamentary distributions. Our hypothesis was finally verified via simulated results of the memory state evolution, by taking into account dissimilar initial filamentary distribution
Joint Beamforming Design and Stream Allocation for Non-Coherent Joint Transmission in Cell-Free MIMO Networks
We consider joint beamforming and stream allocation to maximize the weighted
sum rate (WSR) for non-coherent joint transmission (NCJT) in user-centric
cell-free MIMO networks, where distributed access points (APs) are organized in
clusters to transmit different signals to serve each user equipment (UE). We
for the first time consider the common limits of maximum number of receive
streams at UEs in practical networks, and formulate a joint beamforming and
transmit stream allocation problem for WSR maximization under per-AP transmit
power constraints. Since the integer number of transmit streams determines the
dimension of the beamformer, the joint optimization problem is mixed-integer
and nonconvex with coupled decision variables that is inherently NP-hard. In
this paper, we first propose a distributed low-interaction reduced weighted
minimum mean square error (RWMMSE) beamforming algorithm for WSR maximization
with fixed streams. Our proposed RWMMSE algorithm requires significantly less
interaction across the network and has the current lowest computational
complexity that scales linearly with the number of transmit antennas, without
any compromise on WSR. We draw insights on the joint beamforming and stream
allocation problem to decouple the decision variables and relax the
mixed-integer constraints. We then propose a joint beamforming and linear
stream allocation algorithm, termed as RWMMSE-LSA, which yields closed-form
updates with linear stream allocation complexity and is guaranteed to converge
to the stationary points of the original joint optimization problem. Simulation
results demonstrate substantial performance gain of our proposed algorithms
over the current best alternatives in both WSR performance and convergence
time
Glymphatic transport is reduced in rats with spontaneous pituitary tumor
BACKGROUND AND OBJECTIVE: Pituitary tumor in patients induces adverse alterations in the brain, accompanied by cognitive deficits. Dysfunction of glymphatic waste clearance results in accumulation of neurotoxic products within the brain, leading to cognitive impairment. However, the status of glymphatic function in the brain with pituitary tumor is unknown. Using magnetic resonance imaging (MRI) and an advanced mathematical modeling, we investigated the changes of glymphatic transport in the rats carrying spontaneous pituitary tumor.
METHODS: Rats (22-24 months, female, Wistar) with and without pituitary tumor (n = 7/per group) underwent the identical experimental protocol. MRI measurements, including T2-weighted imaging and dynamic 3D T1-weighted imaging with intracisternal administration of contrast agent, were performed on each animal. The contrast-induced enhancement in the circle of Willis and in the glymphatic influx nodes were observed on the dynamic images and verified with time-signal-curves (TSCs). Model-derived parameters of infusion rate and clearance rate that characterize the kinetics of glymphatic tracer transport were evaluated in multiple representative brain regions.
RESULTS: Our imaging data demonstrated a higher incidence of partially enhanced circle of Willis (86 vs. 14%; p \u3c 0.033) and a lower incidence of enhancement in glymphatic influx nodes of pituitary (71 vs. 100%) and pineal (57 vs. 86%) recesses in the rats with pituitary tumor than in the rats with normal appearance of pituitary gland, indicating an intensification of impaired peri-vascular pathway and impeded glymphatic transport due to the presence of pituitary tumor. Consistently, our kinetic modeling and regional cerebral tissue quantification revealed significantly lower infusion and clearance rates in all examined regions in rats with spontaneous pituitary tumor than in non-tumor rats, representing a suppressed glymphatic transport in the brain with pituitary tumor.
CONCLUSION: Our study demonstrates the compromised glymphatic transport in the rat brain with spontaneous pituitary tumor. The reduced efficiency in cerebral waste clearance increases the risk for neurodegeneration in the brain that may underlie the cognitive impairment commonly seen in patients with pituitary tumors
Cell Treatment for Stroke in Type Two Diabetic Rats Improves Vascular Permeability Measured by MRI
Treatment of stroke with bone marrow stromal cells (BMSC) significantly enhances brain remodeling and improves neurological function in non-diabetic stroke rats. Diabetes is a major risk factor for stroke and induces neurovascular changes which may impact stroke therapy. Thus, it is necessary to test our hypothesis that the treatment of stroke with BMSC has therapeutic efficacy in the most common form of diabetes, type 2 diabetes mellitus (T2DM). T2DM was induced in adult male Wistar rats by administration of a high fat diet in combination with a single intraperitoneal injection (35mg/kg) of streptozotocin. These rats were then subjected to 2h of middle cerebral artery occlusion (MCAo). T2DM rats received BMSC (5x106, n = 8) or an equal volume of phosphate-buffered saline (PBS) (n = 8) via tail-vein injection at 3 days after MCAo. MRI was performed one day and then weekly for 5 weeks post MCAo for all rats. Compared with vehicle treated control T2DM rats, BMSC treatment of stroke in T2DM rats significantly (
Non-intrusive load monitoring for multi-objects in smart building
The rapidly expansion of Internet of Things (IoT) has ignited renewed interest in energy disaggregation via nonintrusive load monitoring (NILM). Compared to the more frequent NILM approach of training one model for each appliance, this paper proposes a multi-label learning approach based on the widely cited sequence2point convolutional neural network (CNN). Using the smart meter readings collected in an office building, we demonstrate the accuracy and practicality of the proposed network compared to start-of-the-art one-to-one NILM models
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