2,474 research outputs found
Joint Device Positioning and Clock Synchronization in 5G Ultra-Dense Networks
In this article, we address the prospects and key enabling technologies for
highly efficient and accurate device positioning and tracking in 5G radio
access networks. Building on the premises of ultra-dense networks as well as on
the adoption of multicarrier waveforms and antenna arrays in the access nodes
(ANs), we first formulate extended Kalman filter (EKF)-based solutions for
computationally efficient joint estimation and tracking of the time of arrival
(ToA) and direction of arrival (DoA) of the user nodes (UNs) using uplink
reference signals. Then, a second EKF stage is proposed in order to fuse the
individual DoA/ToA estimates from one or several ANs into a UN position
estimate. Since all the processing takes place at the network side, the
computing complexity and energy consumption at the UN side are kept to a
minimum. The cascaded EKFs proposed in this article also take into account the
unavoidable relative clock offsets between UNs and ANs, such that reliable
clock synchronization of the access-link is obtained as a valuable by-product.
The proposed cascaded EKF scheme is then revised and extended to more general
and challenging scenarios where not only the UNs have clock offsets against the
network time, but also the ANs themselves are not mutually synchronized in
time. Finally, comprehensive performance evaluations of the proposed solutions
on a realistic 5G network setup, building on the METIS project based outdoor
Madrid map model together with complete ray tracing based propagation modeling,
are provided. The obtained results clearly demonstrate that by using the
developed methods, sub-meter scale positioning and tracking accuracy of moving
devices is indeed technically feasible in future 5G radio access networks
operating at sub-6GHz frequencies, despite the realistic assumptions related to
clock offsets and potentially even under unsynchronized network elements.Comment: Submitted to IEEE Transactions on Wireless Communications in March
2016. This is the revised version of the original article, and it is under
review at the moment. 15 pages, 9 figure
Inter-Vehicle Range Estimation from Periodic Broadcasts
Dedicated short-range communication (DSRC) enables vehicular communication
using periodic broadcast messages. We propose to use these periodic broadcasts
to perform inter-vehicle ranging. Motivated by this scenario, we study the
general problem of precise range estimation between pairs of moving vehicles
using periodic broadcasts. Each vehicle has its own independent and
unsynchronized clock, which can exhibit significant drift between consecutive
periodic broadcast transmissions. As a consequence, both the clock offsets and
drifts need to be taken into account in addition to the vehicle motion to
accurately estimate the vehicle ranges. We develop a range estimation algorithm
using local polynomial smoothing of the vehicle motion. The proposed algorithm
can be applied to networks with arbitrary number of vehicles and requires no
additional message exchanges apart from the periodic broadcasts. We validate
our algorithm on experimental data and show that the performance of the
proposed approach is close to that obtained using unicast round-trip time
ranging. In particular, we are able to achieve sub-meter ranging accuracies in
vehicular scenarios. Our scheme requires additional timestamp information to be
transmitted as part of the broadcast messages, and we develop a novel timestamp
compression algorithm to minimize the resulting overhead.Comment: 16 page
Joint Ranging and Clock Parameter Estimation by Wireless Round Trip Time Measurements
In this paper we develop a new technique for estimating fine clock errors and
range between two nodes simultaneously by two-way time-of-arrival measurements
us- ing impulse-radio ultra-wideband signals. Estimators for clock parameters
and the range are proposed that are robust with respect to outliers. They are
analyzed numerically and by means of experimental measurement campaigns. The
technique and derived estimators achieve accuracies below 1Hz for frequency
estimation, below 1 ns for phase estimation and 20 cm for range estimation, at
4m distance using 100MHz clocks at both nodes. Therefore, we show that the
proposed joint approach is practical and can simultaneously provide clock
synchronization and positioning in an experimental system.Comment: IEEE Journal on Selected Areas in Communications (Accepted
Joint Ranging and Clock Synchronization for Dense Heterogeneous IoT Networks
Synchronization and ranging in internet of things (IoT) networks are
challenging due to the narrowband nature of signals used for communication
between IoT nodes. Recently, several estimators for range estimation using
phase difference of arrival (PDoA) measurements of narrowband signals have been
proposed. However, these estimators are based on data models which do not
consider the impact of clock-skew on the range estimation. In this paper,
clock-skew and range estimation are studied under a unified framework. We
derive a novel and precise data model for PDoA measurements which incorporates
the unknown clock-skew effects. We then formulate joint estimation of the
clock-skew and range as a two-dimensional (2-D) frequency estimation problem of
a single complex sinusoid. Furthermore, we propose: (i) a two-way communication
protocol for collecting PDoA measurements and (ii) a weighted least squares
(WLS) algorithm for joint estimation of clock-skew and range leveraging the
shift invariance property of the measurement data. Finally, through numerical
experiments, the performance of the proposed protocol and estimator is compared
against the Cramer Rao lower bound demonstrating that the proposed estimator is
asymptotically efficient.Comment: 52nd Annual Asilomar Conference on Signals, Systems, and Computer
Fundamental Limits of Wideband Localization - Part I: A General Framework
The availability of positional information is of great importance in many
commercial, public safety, and military applications. The coming years will see
the emergence of location-aware networks with sub-meter accuracy, relying on
accurate range measurements provided by wide bandwidth transmissions. In this
two-part paper, we determine the fundamental limits of localization accuracy of
wideband wireless networks in harsh multipath environments. We first develop a
general framework to characterize the localization accuracy of a given node
here and then extend our analysis to cooperative location-aware networks in
Part II.
In this paper, we characterize localization accuracy in terms of a
performance measure called the squared position error bound (SPEB), and
introduce the notion of equivalent Fisher information to derive the SPEB in a
succinct expression. This methodology provides insights into the essence of the
localization problem by unifying localization information from individual
anchors and information from a priori knowledge of the agent's position in a
canonical form. Our analysis begins with the received waveforms themselves
rather than utilizing only the signal metrics extracted from these waveforms,
such as time-of-arrival and received signal strength. Hence, our framework
exploits all the information inherent in the received waveforms, and the
resulting SPEB serves as a fundamental limit of localization accuracy.Comment: To appear in IEEE Transactions on Information Theor
Cooperative Joint Localization and Clock Synchronization Based on Gaussian Message Passing in Asynchronous Wireless Networks
Localization and synchronization are very important in many wireless
applications such as monitoring and vehicle tracking. Utilizing the same time
of arrival (TOA) measurements for simultaneous localization and synchronization
is challenging. In this paper, we present a factor graph (FG) representation of
the joint localization and time synchronization problem based on TOA
measurements, in which the non-line-of-sight measurements are also taken into
consideration. On this FG, belief propagation (BP) message passing and
variational message passing (VMP) are applied to derive two fully distributed
cooperative algorithms with low computational requirements. Due to the
nonlinearity in the observation function, it is intractable to compute the
messages in closed form and most existing solutions rely on Monte Carlo
methods, e.g., particle filtering. We linearize a specific nonlinear term in
the expressions of messages, which enables us to use a Gaussian representation
for all messages. Accordingly, only the mean and variance have to be updated
and transmitted between neighboring nodes, which significantly reduces the
communication overhead and computational complexity. A message passing schedule
scheme is proposed to trade off between estimation performance and
communication overhead. Simulation results show that the proposed algorithms
perform very close to particle-based methods with much lower complexity
especially in densely connected networks.Comment: 38 pages one column, To appear in IEEE Transactions on Vehicular
Technolog
Joint ranging and synchronization for an anchorless network of mobile nodes
Synchronization and localization are critical challenges for the coherent
functioning of a wireless network, which are conventionally solved
independently. Recently, various estimators have been proposed for pairwise
synchronization between immobile nodes, based on time stamp exchanges via
two-way communication. In this paper, we consider a \textit{network of mobile
nodes} for which a novel joint time-range model is presented, treating both
unsynchronized clocks and the pairwise distances as a polynomial function of
\textit{true} time. For a set of nodes, a pairwise least squares solution is
proposed for estimating the pairwise range parameters between the nodes, in
addition to estimating the clock offsets and clock skews. Extending these
pairwise solutions to network-wide ranging and clock synchronization, we
present a central data fusion based global least squares algorithm. A unique
solution is non-existent without a constraint on the cost function (\eg clock
reference node). Ergo, a constrained framework is proposed and a new
Constrained \Cramer\ Rao Bound (CCRB) is derived for the joint time-range
model. In addition, various constraints are proposed and their effects on the
proposed algorithms are studied. Simulations are conducted and the proposed
algorithm is shown to approach the theoretical limits.Comment: In submissio
Modified CRB for Location and Velocity Estimation using Signals of Opportunity
We consider the problem of localizing two sensors using signals of
opportunity from beacons with known positions. Beacons and sensors have
asynchronous local clocks or oscillators with unknown clock skews and offsets.
We model clock skews as random, and analyze the biases introduced by clock
asynchronism in the received signals. By deriving the equivalent Fisher
information matrix for the modified Bayesian Cram\'er-Rao lower bound (CRLB) of
sensor position and velocity estimation, we quantify the errors caused by clock
asynchronism
Scalable and Passive Wireless Network Clock Synchronization
Clock synchronization is ubiquitous in wireless systems for communication,
sensing and control. In this paper we design a scalable system in which an
indefinite number of passively receiving wireless units can synchronize to a
single master clock at the level of discrete clock ticks. Accurate
synchronization requires an estimate of the node positions. If such information
is available the framework developed here takes position uncertainties into
account. In the absence of such information we propose a mechanism which
enables simultaneous synchronization and positioning. Furthermore we derive the
Cramer-Rao bounds for the system which show that it enables synchronization
accuracy at sub-nanosecond levels. Finally, we develop and evaluate an online
estimation method which is statistically efficient
TW-TOA Based Positioning in the Presence of Clock Imperfections
This paper studies the positioning problem based on two-way time-of-arrival
(TW-TOA) measurements in asynchronous wireless sensor networks. Since the
optimal estimator for this problem involves difficult nonconvex optimization,
we propose two suboptimal estimators based on squared-range least squares and
least absolute mean of residual errors. The former approach is formulated as a
general trust region subproblem which can be solved exactly under mild
conditions. The latter approach is formulated as a difference of convex
functions programming (DCP), which can be solved using a concave-convex
procedure. Simulation results illustrate the high performance of the proposed
techniques, especially for the DCP approach
- …