41 research outputs found
An iterative scheme for feature based positioning using a weighted dissimilarity measure
We propose an iterative scheme for feature-based positioning using a new
weighted dissimilarity measure with the goal of reducing the impact of large
errors among the measured or modeled features. The weights are computed from
the location-dependent standard deviations of the features and stored as part
of the reference fingerprint map (RFM). Spatial filtering and kernel smoothing
of the kinematically collected raw data allow efficiently estimating the
standard deviations during RFM generation. In the positioning stage, the
weights control the contribution of each feature to the dissimilarity measure,
which in turn quantifies the difference between the set of online measured
features and the fingerprints stored in the RFM. Features with little
variability contribute more to the estimated position than features with high
variability. Iterations are necessary because the variability depends on the
location, and the location is initially unknown when estimating the position.
Using real WiFi signal strength data from extended test measurements with
ground truth in an office building, we show that the standard deviations of
these features vary considerably within the region of interest and are neither
simple functions of the signal strength nor of the distances from the
corresponding access points. This is the motivation to include the empirical
standard deviations in the RFM. We then analyze the deviations of the estimated
positions with and without the location-dependent weighting. In the present
example the maximum radial positioning error from ground truth are reduced by
40% comparing to kNN without the weighted dissimilarity measure.Comment: 18 pages, 9 figures, and 1 tabl
Modified Jaccard Index Analysis and Adaptive Feature Selection for Location Fingerprinting with Limited Computational Complexity
We propose an approach for fingerprinting-based positioning which reduces the
data requirements and computational complexity of the online positioning stage.
It is based on a segmentation of the entire region of interest into subregions,
identification of candidate subregions during the online-stage, and position
estimation using a preselected subset of relevant features. The subregion
selection uses a modified Jaccard index which quantifies the similarity between
the features observed by the user and those available within the reference
fingerprint map. The adaptive feature selection is achieved using an adaptive
forward-backward greedy search which determines a subset of features for each
subregion, relevant with respect to a given fingerprinting-based positioning
method. In an empirical study using signals of opportunity for fingerprinting
the proposed subregion and feature selection reduce the processing time during
the online-stage by a factor of about 10 while the positioning accuracy does
not deteriorate significantly. In fact, in one of the two study cases the 90th
percentile of the circular error increased by 7.5% while in the other study
case we even found a reduction of the corresponding circular error by 30%.Comment: 15 pagers, 10 figures, 10 tables, revised version for publishing to
TLBS. arXiv admin note: text overlap with arXiv:1711.0781
Joint Positioning and Radio Map Generation Based on Stochastic Variational Bayesian Inference for FWIPS
Fingerprinting based WLAN indoor positioning system (FWIPS) provides a
promising indoor positioning solution to meet the growing interests for indoor
location-based services (e.g., indoor way finding or geo-fencing). FWIPS is
preferred because it requires no additional infrastructure for deploying an
FWIPS and achieving the position estimation by reusing the available WLAN and
mobile devices, and capable of providing absolute position estimation. For
fingerprinting based positioning (FbP), a model is created to provide reference
values of observable features (e.g., signal strength from access point (AP)) as
a function of location during offline stage. One widely applied method to build
a complete and an accurate reference database (i.e. radio map (RM)) for FWIPS
is carrying out a site survey throughout the region of interest (RoI). Along
the site survey, the readings of received signal strength (RSS) from all
visible APs at each reference point (RP) are collected. This site survey,
however, is time-consuming and labor-intensive, especially in the case that the
RoI is large (e.g., an airport or a big mall). This bottleneck hinders the wide
commercial applications of FWIPS (e.g., proximity promotions in a shopping
center). To diminish the cost of site survey, we propose a probabilistic model,
which combines fingerprinting based positioning (FbP) and RM generation based
on stochastic variational Bayesian inference (SVBI). This SVBI based position
and RSS estimation has three properties: i) being able to predict the
distribution of the estimated position and RSS, ii) treating each observation
of RSS at each RP as an example to learn for FbP and RM generation instead of
using the whole RM as an example, and iii) requiring only one time training of
the SVBI model for both localization and RSS estimation. These benefits make it
outperforms the previous proposed approaches.Comment: 10 pages, 16 figures, and 2 tables. A paper under review of IPIN 201
Feature-wise change detection and robust indoor positioning using RANSAC-like approach
Fingerprinting-based positioning, one of the promising indoor positioning
solutions, has been broadly explored owing to the pervasiveness of sensor-rich
mobile devices, the prosperity of opportunistically measurable
location-relevant signals and the progress of data-driven algorithms. One
critical challenge is to controland improve the quality of the reference
fingerprint map (RFM), which is built at the offline stage and applied for
online positioning. The key concept concerningthe quality control of the RFM is
updating the RFM according to the newly measured data. Though varies methods
have been proposed for adapting the RFM, they approach the problem by
introducing extra-positioning schemes (e.g. PDR orUGV) and directly adjust the
RFM without distinguishing whether critical changes have occurred. This paper
aims at proposing an extra-positioning-free solution by making full use of the
redundancy of measurable features. Loosely inspired by random sampling
consensus (RANSAC), arbitrarily sampled subset of features from the online
measurement are used for generating multi-resamples, which areused for
estimating the intermediate locations. In the way of resampling, it can
mitigate the impact of the changed features on positioning and enables to
retrieve accurate location estimation. The users location is robustly computed
by identifying the candidate locations from these intermediate ones using
modified Jaccardindex (MJI) and the feature-wise change belief is calculated
according to the world model of the RFM and the estimated variability of
features. In order to validate our proposed approach, two levels of
experimental analysis have been carried out. On the simulated dataset, the
average change detection accuracy is about 90%. Meanwhile, the improvement of
positioning accuracy within 2 m is about 20% by dropping out the features that
are detected as changed when performing positioning comparing to that of using
all measured features for location estimation. On the long-term collected
dataset, the average change detection accuracy is about 85%.Comment: 36 pages, 20 figures, 2 table
Application of backpropagation neural networks to both stages of fingerprinting based WIPS
We propose a scheme to employ backpropagation neural networks (BPNNs) for
both stages of fingerprinting-based indoor positioning using WLAN/WiFi signal
strengths (FWIPS): radio map construction during the offline stage, and
localization during the online stage. Given a training radio map (TRM), i.e., a
set of coordinate vectors and associated WLAN/WiFi signal strengths of the
available access points, a BPNN can be trained to output the expected signal
strengths for any input position within the region of interest (BPNN-RM). This
can be used to provide a continuous representation of the radio map and to
filter, densify or decimate a discrete radio map. Correspondingly, the TRM can
also be used to train another BPNN to output the expected position within the
region of interest for any input vector of recorded signal strengths and thus
carry out localization (BPNN-LA).Key aspects of the design of such artificial
neural networks for a specific application are the selection of design
parameters like the number of hidden layers and nodes within the network, and
the training procedure. Summarizing extensive numerical simulations, based on
real measurements in a testbed, we analyze the impact of these design choices
on the performance of the BPNN and compare the results in particular to those
obtained using the nearest neighbors (NN) and weighted nearest
neighbors approaches to FWIPS.Comment: 11 pages, 11 figures, published in proceedings UPINLBS 201
WiFi based trajectory alignment, calibration and easy site survey using smart phones and foot-mounted IMUs
Foot-mounted inertial positioning (FMIP) can face problems of inertial drifts
and unknown initial states in real applications, which renders the estimated
trajectories inaccurate and not obtained in a well defined coordinate system
for matching trajectories of different users. In this paper, an approach
adopting received signal strength (RSS) measurements for Wifi access points
(APs) are proposed to align and calibrate the trajectories estimated from foot
mounted inertial measurement units (IMUs). A crowd-sourced radio map (RM) can
be built subsequently and can be used for fingerprinting based Wifi indoor
positioning (FWIP). The foundation of the proposed approach is graph based
simultaneously localization and mapping (SLAM). The nodes in the graph denote
users poses and the edges denote the pairwise constrains between the nodes. The
constrains are derived from: (1) inertial estimated trajectories; (2) vicinity
in the RSS space. With these constrains, an error functions is defined. By
minimizing the error function, the graph is optimized and the
aligned/calibrated trajectories along with the RM are acquired. The
experimental results have corroborated the effectiveness of the approach for
trajectory alignment, calibration as well as RM construction.Comment: 9 figures, 6 pages, paper under review of IPIN 201
Adaptive Neighboring Selection Algorithm Based on Curvature Prediction in Manifold Learning
Recently manifold learning algorithm for dimensionality reduction attracts
more and more interests, and various linear and nonlinear, global and local
algorithms are proposed. The key step of manifold learning algorithm is the
neighboring region selection. However, so far for the references we know, few
of which propose a generally accepted algorithm to well select the neighboring
region. So in this paper, we propose an adaptive neighboring selection
algorithm, which successfully applies the LLE and ISOMAP algorithms in the
test. It is an algorithm that can find the optimal K nearest neighbors of the
data points on the manifold. And the theoretical basis of the algorithm is the
approximated curvature of the data point on the manifold. Based on Riemann
Geometry, Jacob matrix is a proper mathematical concept to predict the
approximated curvature. By verifying the proposed algorithm on embedding Swiss
roll from R3 to R2 based on LLE and ISOMAP algorithm, the simulation results
show that the proposed adaptive neighboring selection algorithm is feasible and
able to find the optimal value of K, making the residual variance relatively
small and better visualization of the results. By quantitative analysis, the
embedding quality measured by residual variance is increased 45.45% after using
the proposed algorithm in LLE.Comment: 3 figures, from Journal of Harbin Institute of Technolog
Joint Semi-supervised RSS Dimensionality Reduction and Fingerprint Based Algorithm for Indoor Localization
With the recent development in mobile computing devices and as the ubiquitous
deployment of access points(APs) of Wireless Local Area Networks(WLANs), WLAN
based indoor localization systems(WILSs) are of mounting concentration and are
becoming more and more prevalent for they do not require additional
infrastructure. As to the localization methods in WILSs, for the approaches
used to localization in satellite based global position systems are difficult
to achieve in indoor environments, fingerprint based localization
algorithms(FLAs) are predominant in the RSS based schemes. However, the
performance of FLAs has close relationship with the number of APs and the
number of reference points(RPs) in WILSs, especially as the redundant
deployment of APs and RPs in the system. There are two fatal problems, curse of
dimensionality (CoD) and asymmetric matching(AM), caused by increasing number
of APs and breaking down APs during online stage. In this paper, a
semi-supervised RSS dimensionality reduction algorithm is proposed to solve
these two dilemmas at the same time and there are numerous analyses about the
theoretical realization of the proposed method. Another significant innovation
of this paper is jointing the fingerprint based algorithm with CM-SDE algorithm
to improve the localization accuracy of indoor localization.Comment: 14 figures. Institute of Navigation (ION GNSS+ 2014), 27th
International Technical Meeting of The Satellite Division Conference o
Mining geometric constraints from crowd-sourced radio signals and its application to indoor positioning
Crowd-sourcing has become a promising way to build} a feature-based indoor
positioning system that has lower labour and time costs. It can make full use
of the widely deployed infrastructure as well as built-in sensors on mobile
devices. One of the key challenges is to generate the reference feature map
(RFM), a database used for localization, by {aligning crowd-sourced
{trajectories according to associations embodied in the data. In order to
facilitate the data fusion using crowd-sourced inertial sensors and radio
signals, this paper proposes an approach to adaptively mining geometric
information. This is the essential for generating spatial associations between
trajectories when employing graph-based optimization methods. The core idea is
to estimate the functional relationship to map the similarity/dissimilarity
between radio signals to the physical space based on the relative positions
obtained from inertial sensors and their associated radio signals. Namely, it
is adaptable to different modalities of data and can be implemented in a
self-supervised way. We verify the generality of the proposed approach through
comprehensive experimental analysis: i) qualitatively comparing the estimation
of geometric mapping models and the alignment of crowd-sourced trajectories;
ii) quantitatively evaluating the positioning performance. The 68\% of the
positioning error is less than 4.7 using crowd-sourced RFM, which
is on a par with manually collected RFM, in a multi-storey shopping mall, which
covers more than 10, 000 .Comment: 20 pages, 11 figures, accepted to publish on IEEE Acces
The Perfect Match: 3D Point Cloud Matching with Smoothed Densities
We propose 3DSmoothNet, a full workflow to match 3D point clouds with a
siamese deep learning architecture and fully convolutional layers using a
voxelized smoothed density value (SDV) representation. The latter is computed
per interest point and aligned to the local reference frame (LRF) to achieve
rotation invariance. Our compact, learned, rotation invariant 3D point cloud
descriptor achieves 94.9% average recall on the 3DMatch benchmark data set,
outperforming the state-of-the-art by more than 20 percent points with only 32
output dimensions. This very low output dimension allows for near realtime
correspondence search with 0.1 ms per feature point on a standard PC. Our
approach is sensor- and sceneagnostic because of SDV, LRF and learning highly
descriptive features with fully convolutional layers. We show that 3DSmoothNet
trained only on RGB-D indoor scenes of buildings achieves 79.0% average recall
on laser scans of outdoor vegetation, more than double the performance of our
closest, learning-based competitors. Code, data and pre-trained models are
available online at https://github.com/zgojcic/3DSmoothNet.Comment: CVPR 201