452 research outputs found
Fusion of Urban TanDEM-X raw DEMs using variational models
Recently, a new global Digital Elevation Model (DEM) with pixel spacing of
0.4 arcseconds and relative height accuracy finer than 2m for flat areas
(slopes 20%) was created
through the TanDEM-X mission. One important step of the chain of global DEM
generation is to mosaic and fuse multiple raw DEM tiles to reach the target
height accuracy. Currently, Weighted Averaging (WA) is applied as a fast and
simple method for TanDEM-X raw DEM fusion in which the weights are computed
from height error maps delivered from the Interferometric TanDEM-X Processor
(ITP). However, evaluations show that WA is not the perfect DEM fusion method
for urban areas especially in confrontation with edges such as building
outlines. The main focus of this paper is to investigate more advanced
variational approaches such as TV-L1 and Huber models. Furthermore, we also
assess the performance of variational models for fusing raw DEMs produced from
data takes with different baseline configurations and height of ambiguities.
The results illustrate the high efficiency of variational models for TanDEM-X
raw DEM fusion in comparison to WA. Using variational models could improve the
DEM quality by up to 2m particularly in inner-city subsets.Comment: This is the pre-acceptance version, to read the final version, please
go to IEEE Journal of Selected Topics in Applied Earth Observations and
Remote Sensing on IEEE Xplor
The Approximate Capacity Region of the Gaussian Z-Interference Channel with Conferencing Encoders
A two-user Gaussian Z-Interference Channel (GZIC) is considered, in which
encoders are connected through noiseless links with finite capacities. In this
setting, prior to each transmission block the encoders communicate with each
other over the cooperative links. The capacity region and the sum-capacity of
the channel are characterized within 1.71 bits per user and 2 bits in total,
respectively. It is also established that properly sharing the total limited
cooperation capacity between the cooperative links may enhance the achievable
region, even when compared to the case of unidirectional transmitter
cooperation with infinite cooperation capacity. To obtain the results,
genie-aided upper bounds on the sum-capacity and cut-set bounds on the
individual rates are compared with the achievable rate region. In the
interference-limited regime, the achievable scheme enjoys a simple type of
Han-Kobayashi signaling, together with the zero-forcing, and basic relaying
techniques. In the noise-limited regime, it is shown that treating interference
as noise achieves the capacity region up to a single bit per user.Comment: 25 pages, 6 figures, submitted to IEEE Transactions on Information
Theor
A Framework for SAR-Optical Stereogrammetry over Urban Areas
Currently, numerous remote sensing satellites provide a huge volume of
diverse earth observation data. As these data show different features regarding
resolution, accuracy, coverage, and spectral imaging ability, fusion techniques
are required to integrate the different properties of each sensor and produce
useful information. For example, synthetic aperture radar (SAR) data can be
fused with optical imagery to produce 3D information using stereogrammetric
methods. The main focus of this study is to investigate the possibility of
applying a stereogrammetry pipeline to very-high-resolution (VHR) SAR-optical
image pairs. For this purpose, the applicability of semi-global matching is
investigated in this unconventional multi-sensor setting. To support the image
matching by reducing the search space and accelerating the identification of
correct, reliable matches, the possibility of establishing an epipolarity
constraint for VHR SAR-optical image pairs is investigated as well. In
addition, it is shown that the absolute geolocation accuracy of VHR optical
imagery with respect to VHR SAR imagery such as provided by TerraSAR-X can be
improved by a multi-sensor block adjustment formulation based on rational
polynomial coefficients. Finally, the feasibility of generating point clouds
with a median accuracy of about 2m is demonstrated and confirms the potential
of 3D reconstruction from SAR-optical image pairs over urban areas.Comment: This is the pre-acceptance version, to read the final version, please
go to ISPRS Journal of Photogrammetry and Remote Sensing on ScienceDirec
Nighttime Driver Behavior Prediction Using Taillight Signal Recognition via CNN-SVM Classifier
This paper aims to enhance the ability to predict nighttime driving behavior
by identifying taillights of both human-driven and autonomous vehicles. The
proposed model incorporates a customized detector designed to accurately detect
front-vehicle taillights on the road. At the beginning of the detector, a
learnable pre-processing block is implemented, which extracts deep features
from input images and calculates the data rarity for each feature. In the next
step, drawing inspiration from soft attention, a weighted binary mask is
designed that guides the model to focus more on predetermined regions. This
research utilizes Convolutional Neural Networks (CNNs) to extract
distinguishing characteristics from these areas, then reduces dimensions using
Principal Component Analysis (PCA). Finally, the Support Vector Machine (SVM)
is used to predict the behavior of the vehicles. To train and evaluate the
model, a large-scale dataset is collected from two types of dash-cams and
Insta360 cameras from the rear view of Ford Motor Company vehicles. This
dataset includes over 12k frames captured during both daytime and nighttime
hours. To address the limited nighttime data, a unique pixel-wise image
processing technique is implemented to convert daytime images into realistic
night images. The findings from the experiments demonstrate that the proposed
methodology can accurately categorize vehicle behavior with 92.14% accuracy,
97.38% specificity, 92.09% sensitivity, 92.10% F1-measure, and 0.895 Cohen's
Kappa Statistic. Further details are available at
https://github.com/DeepCar/Taillight_Recognition.Comment: 12 pages, 10 figure
Cooperative Protocols for Relay and Interference Channels with Half-Duplex Constraint
Enabling cooperation among nodes of a wireless network can significantly reduce the required
transmit power as well as the induced intra-network interference. Due to the practical
half-duplexity constraint of the cooperating nodes, they are prohibited to simultaneously
transmit and receive data at the same time-frequency resource. The purpose of this
dissertation is to illustrate the value of cooperation in such an environment. To understand
how to cooperate efficiently, information theory is employed as a useful tool, which not only
determines the fundamental limits of communication (i.e., capacity) over the considered
network, but also provides insights into the design of a proper transmission scheme for that
network.
In this thesis, two simple but yet important types of wireless networks, namely Relay
Channel, and Interference Channel are studied. In fact, these models constitute building
blocks for larger networks. The first considered channel is a diamond-shaped relay channel
consisting of a source, a destination, and two parallel relays. The second analyzed channel
is an interference channel composed of two transmitter-receiver pairs with out-of-band
transmitter cooperation, also referred to as conferencing encoders. While characterizing
the capacity of these channels are difficult, a simpler and a more common approach is to
find an achievable scheme for each channel that ensures a small gap from the capacity for
all channel parameters.
In chapter 2, the diamond relay channel is investigated in detail. Because of the half-duplex
nature of the relays, each relay is either in transmit or receive mode, making
four modes possible for the two-relay combination, specifically, 1) broadcast mode (both
relays receive) 2,3) routing modes (one relay transmits, another receives) 4) multiple-access
mode (both relays transmit). An appropriate scheduling ( i.e., timing over the modes) and
transmission scheme based on the decode-and-forward strategy are proposed and shown
to be able to achieve either the capacity for certain channel conditions or at most 3.6 bits below the capacity for general channel conditions. Particularly, by assuming each
transmitter has a constant power constraint over all modes, a parameter Δ is defined,
which captures some important features of the channel. It is proven that for Δ=0 the
capacity of the channel can be attained by successive relaying, i.e., using modes 2 and 3
defined above in a successive manner. This strategy may have an infinite gap from the
capacity of the channel when Δ≠0. To achieve rates as close as 0.71 bits to the capacity,
it is shown that the cases of Δ>0 and Δ<0 should be treated differently. Using new
upper bounds based on the dual problem of the linear program associated with the cut-set
bounds, it is proven that the successive relaying strategy needs to be enhanced by an
additional broadcast mode (mode 1), or multiple access mode (mode 4), for the cases of Δ0, respectively. Furthermore, it is established that under average power
constraints the aforementioned strategies achieve rates as close as 3.6 bits to the capacity
of the channel.
In chapter 3, a two-user Gaussian Interference Channel (GIC) is considered, in which
encoders are connected through noiseless links with finite capacities. The setup can be
motivated by downlink cellular systems, where base stations are connected via infrastructure
backhaul networks. In this setting, prior to each transmission block the encoders
communicate with each other over the cooperative links. The capacity region and the
sum-capacity of the channel are characterized within some constant number of bits for
some special classes of symmetric and Z interference channels. It is also established that
properly sharing the total limited cooperation capacity between the cooperative links may
enhance the achievable region, even when compared to the case of unidirectional transmitter
cooperation with infinite cooperation capacity. To obtain the results, genie-aided upper
bounds on the sum-capacity and cut-set bounds on the individual rates are compared with
the achievable rate region. The achievable scheme enjoys a simple type of Han-Kobayashi
signaling, together with the zero-forcing, and basic relaying techniques
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