Signal Processing - September 2017 - 12

FROM THE GUEST EDITORS
Pau Closas, Marco Luise, José-Ángel Ávila-Rodríguez,
Christopher Hegarty, and Jiyun Lee

Advances in Signal Processing for GNSSs

here am I? What time is it? These
are intimately related questions that
have accompanied humanity for
centuries. From past times when sailors
were excitingly discovering recondite
regions on Earth, to current outer space
exploration, from the fascinating development of calendars by ancient civilizations
all over the world-typically for agricultural purposes-to current developments
of extremely accurate atomic clocks, reliable position and time measures have
played an important role in human progress and will continue to do so.
Today, knowledge about one's own
(or another's) position is used in countless
applications and represents an enabling
piece of information. Mass-market location-based services, whose rise is tightly
related to the advent of smartphones, call
for it. Additionally, most critical infrastructures depend on accurate and secure access
to position and timing references. Such
infrastructures include ubiquitous road/
rail/maritime/air transportation facilities
but also for other applications of importance to everyday life, like the synchronization of distant base stations in cellular
communications, time synchronization in
the power grid, or high-frequency trading
and other banking operations.
In this context, it is fair to claim that
use of global navigation satellite systems
(GNSSs) is the technology of choice
whenever it is available. GNSS is the genDigital Object Identifier 10.1109/MSP.2017.2716318
Date of publication: 6 September 2017

eral term used to identify those systems
and technologies pioneered by the global
positioning system (GPS), which enables
positioning and timing based on a constellation of satellites and other augmentation
systems. GNSS technology today is ubiquitous in many transversal infrastructures
and has become the backbone of all applications where precise position, navigation,
and timing (PNT) of user equipment is
required. Moreover, GNSS is the pervasive PNT technology in outdoor environments, where its performance, coverage,
and reliability exceeds that of other technical solutions.
However, in spite of all its virtues,
challenges and vulnerabilities also exist in
the use of this technology, particularly in
challenging scenarios where signal propagation is either naturally impaired (for
example, due to multipath-rich channels,
ionospheric scintillation, or urban canyons)
or intentionally degraded (for instance,
when jamming devices are in place or in
case of spoofing attacks, where a malicious user tries to deceive the receiver by
forging legitimate-like signals). In those
situations, signal processing techniques
appear extremely useful. In fact, signal
processing has always played a key role in
GNSS design, performance enhancement,
and vulnerabilities mitigation.
This special issue of IEEE Signal Processing Magazine (SPM) is the our attempt
to trigger a discussion and shed some light
on these fundamental topics. With this
said, we will go no further with a written
description of the exciting contributions
IEEE SIGNAL PROCESSING MAGAZINE

September 2017

you will find in this special issue. On the
contrary, we prepared a visual summary
for your perusal that contains the main
topics addressed in this issue.
This special issue starts addressing the
design of special GNSS signals, a topic
of particular interest in the past and still
of great relevance today. It continues with
the discussion of effective techniques for
receiver performance enhancement and
finishes with the analysis of some vulnerabilities. Once you have read the magazine, we hope you will agree with us that
the included material is insightful and
timely. We also hope it will foster further
discussion and application of the diverse
techniques of signal processing to the everchanging field of satellite-based navigation systems.

Acknowledgments
We thank all of the contributors for their
outstanding articles that individually
and as a whole, addressed relevant and
timely aspects in the art of navigation,
highlighting the key role that signal processing takes. We are grateful to SPM's
Editor-in-Chief Prof. Min Wu and IEEE
Signal Processing Society Publications
Administrator Rebecca Wollman for
their continuous support and assistance.
We very much enjoyed putting together
this special issue, and we do believe
that our readers will enjoy it twice as
much-our energetic signal processing
community will contribute to the state
of the art in the field with new and exciting original articles.

Table of Contents for the Digital Edition of Signal Processing - September 2017