Free eBook: Hybrid Positioning
GNSS is a truly amazing technology, but it has its weakness—especially when it comes to locating positions indoors, or in the narrow alleys of a high-rising cityscape.
The dream of universal, millimetre-accurate positioning rests on combining the great strengths of GNSS with the strengths of other technologies—from smartphone sensors to Wi-Fi positioning.
Download this free eBook to learn about the technical challenges and exciting opportunities presented by hybrid technology, and Spirent’s commitment to supporting its development.
Simply enter a few details opposite to receive your free eBook—and happy reading!
Spirent has been the global leader in GNSS testing for near 30 years. Spirent delivers navigation and positioning test equipment and services to governmental agencies, major manufacturers, integrators, test facilities and space agencies worldwide.
As the adoption of location based services becomes more main-
stream, developers are looking for increased accuracy and availability
from positioning solutions. For example services that target
marketing messages need to know which display the user lingered at,
not merely which store they are in, and ideally they would know in
which direction the user is facing!
To provide ubiquitous positioning that reaches indoors and positively
identinulls location and orientation in a multi-story building requires
blending the best of multiple sources of information, in other words,
a hybrid solution.
Page 2SPIRENT eBook
nulldeally such a marriage of technologies allows the strengths of one to
counter the weaknesses of the other in a truly complementary way.
For example the high availability of local low cost inertial sensors
can offset nullnull which may not be available within buildingsnullwhilst
the drift over time inherent in inertial systems can be managed using
regular high accuracy nulles from nullnull, when available.
And the sensors may not be those traditionally associated
with positioning. For example a tourist guide
application describing the scene presented to the
user answering the question nullnullat am nulllooking
at now null may use the users smartphone camera
and cloud computing to overlay captions on the
display with links to appropriate informative
webpages in an augmented reality format.
nully intelligently combining data from multiple sources the designer
aims to retain the best of each and to mitigate their weaknesses.
Truly a case of the whole exceeding the sum of the partsnullf it works!
The peculiar test challenge presented is that development of such a
system cannot be done one sensor at a time. The effective blending
of position information from disparate sources is predicated on an
understanding of their strengths and weaknesses, this will require
careful development and importantly, a test environment which
provides total control over multiple, coherent sources to facilitate
This e-book aims to introduce the technical challenges and
some of the ideas that nullpirent has to provide the
development tools required.
Page 4SPIRENT eBook
nulllobal nullavigation nullatellite nullystems nullnullnull enable you
to locate your position anywhere on the earth nullor around
it nullto within millimetresnull nullow, you have to admit that is
an amanullng statement, and in some cases it is perfectly
true, but there are limits to this incredible technologies
capability. nullavigating, autonomously, using signals from
satellites orbiting some nullnullnullm away is an almost
unbelievable technological achievement and has been the
solution to a myriad of application needs, where knowing
nullwherenull and nullwhennull you are is important. And, the list of
applications for nullnull navigation is growing all the time.
Page 5SPIRENT eBook
nulln the face of it, nullnull would appear to be the panacea for all
navigation and timing requirements. nullelatively low cost, low power,
compact devices enable you to locate yourself and know the current
time with pinpoint precision. nullnull is brilliant but is it sufnullient to
meet all positioning needs on its own.
nullile there is absolutely no doubt that nullnull is a must-have
technology for the nullwherenulland nullwhennullneeds of todaynulls applications,
it is not without its limitations and trade-offs. nulloing back to the
nullwithin millimetresnullstatement, closer inspection reveals that to
achieve this level of accuracy takes some very sophisticated and
relatively expensive nullnull receiver technology. This is out of
the question for many of the applications that
need accurate timing and navigation.
Page 6SPIRENT eBook
nullo what are we left withnullAccuracy of a metrenullA few metresnull
nullundreds of metresnullThe answer is yes to all of these, because the
performance of nullnull is so variable and depends on so many factors
that it is impossible to state exactly how it will perform in a generic
way. nulle can however consolidate performance into nullmeasuresnull
null Availability - The percentage of time a nullosition, nullavigation and
Time nullnullnullsolution is available
null nullntinuity nullnullerformance without non-scheduled interruptions
null nullntegrity nullThe level of trust in the information provided
null Accuracy nullThe degree to which nullT data conforms to the
Page 7SPIRENT eBook
There are many factors that alter how a nullnull receiver performs
against these measures, so letnulls restrict ourselves to the key issues
for consumer applications.
Availability is perhaps the most signinullant measure to consider given
the kinds of environments consumer devices have to operate in. The
urban scene is undoubtedly a hostile one for a nullnull receiver. Tall
buildings obscure the line of sight navigation signals, and in some
cases - if the obscuration is combined with poor satellite
geometry nullot enough satellites in viewnullnullthere
wonnull be enough signals available to compute a
nullT solution. A minimum of nullsatellites in view
nullo indoors, and things will probably get
much worse. The extremely weak
null.-nullnullnullnullsignals arriving at
the nullrthnulls surface which are not
blocked by a building are further
attenuated by its fabric. nullighly
sensitive receivers are required,
but these have to spend
longer and take more power
to extract the weaker signals
from the noise.
Accuracy is another measure which is signinullantly affected. The
satellite signals, even if they are not obscured, may be renullcted, and
take multiple paths to the receiver antenna, much longer than the
direct path, causing false nullcopiesnull of the signals to arrive, late, at the
receiver corrupting the nullT calculations. nullven worse is the case where
there is no line of sight signal, and the multi-path version is the only
one the receiver sees. nullecause the receiver uses the satellitenulls signals
as nulladio tape-measuresnull any distortion in the signals null.g. time delay,
phase errornullwill degrade the nullT solution accuracy. nulln the case of
weak signals, a high sensitivity receiver may help, but they are more
susceptible to multipath signals.
Page 10SPIRENT eBook
nullo, in practice, the continuously-available millimetric accuracy
heralded at the start is rarely achieved, indeed, accuracy of several
metres can be a challenge. Therefore it is clear that nullnull alone is not
enough. nulle need to consider how to optimise its benenulls and how
to bring the four measures of performance up to acceptable levels
for our application. This can only be achieved by augmenting nullnull.
Adding another system or multiple systems alongside nullnull to help it,
correct it or substitute for it is the practical way forward. nullllectively,
this approach is known as nullybrid nullositioning, the big opportunity
for performance improvement arising from the complementary nature
of the strengths and weaknesses of the various technologies. nulln
combination the technologies can perform better nullore accurate,
higher availability etcnullthan any of the technologies independently.
Team work rather than competition is the way forward it seems!
Page 11SPIRENT eBook
The need for test.
nullith so many potential issues, testing of nullnull navigation systems is
essential. nullpirent has been the leader in this nullld for over null years,
and has solutions for testing receivers on all existing and planned
nullnull systems, as well as new solutions for nullybrid nullositioning.
Page 12SPIRENT eBook
A modern smartphone contains an array of sensors incorporated for a
number of purposes but all potentially available for positioning. nullnull
gyros and accelerometers, barometric sensors and magnetometers all
have a direct application in estimating position.
The inertial sensors can be used in the estimation of position by
sensing the movement of the body from a known initial position.
nulln this way nullnull technology, which provides accurate positions but
not all the time, and inertial technology which allows a position
estimate to be advanced in the absence of any external signals, form
a perfect partnership. The addition of magnetometers to provide
heading and barometric sensors to provide height completes a very
useful set of sensors.
Page 13SPIRENT eBook
As we have seen, the properties of radio wave propagation mean that
they lend themselves to being used for navigation nullafter all, thatnulls
the foundational principle of nullnull.
Page 14SPIRENT eBook
nullo, with that in mind, what is to stop other radio-based techniques
being used for the same purposenullnullell, actually, in some cases
nothing much. nullne such technique is nulli-Fi positioning. nullou have nullin
most urban areas nullmany nullireless Access nulloints transmitting radio
signals with identifying properties. nullou can therefore determine your
position by looking for a nullngerprintnull of Access nulloint visibility in a
large database of such devices. nullmbining this with a measure of
the power level received versus the databasenulls record of the access
pointnulls transmit power to determine range, will enable
you to trilaterate from multiple Access nulloints.
This technique is gaining traction in the marketplace,
with both database technology suppliers and phone
handsetnullhipset manufacturers offering or looking
to offer solutions.
nulli-Fi Access nulloint
Page 15SPIRENT eBook
nullpirent is the only test equipment provider to offer a nulli-Fi test
solution. The nullnullnullnullnulli-Fi Access nulloint nullositioning nullimulator
consists of a nullsmartnull signal generator using a core application
running on an internal nullnullwith touch-screen, remote nullnullcontrol
via nullthernet. Access nulloint nullntrol includes the ability to specifynull
change, nullnulladdress, nullnull, Tnullchannel power levelnullynamic path
loss and simulated nullvisibilitynull nullupporting up to null Access nulloints in
one chassis, and being able to operate with nullpirentnulls nullnullnullnull nullnull
simulators to give coherent nullnullnulli-Fi test signals, makes
the nullnullnullnull nulli-Fi Access nulloint nullositioning nullimulator an
essential test solution for this positioning technology.
Page 16SPIRENT eBook
What is Cellular Positioning?
nullllular positioning utilinulles the cellular network
infrastructure to compute position and obtain a fast
and coarse location estimate. nullmpared to A-nullnullA-
nullnullAnull, cellular network positioning is generally
faster nullnullsecondsnull but it is less accurate nullnullmeters
to several kilometresnull nullt is quite often used as
nullfallbacknulltechnology when nullnull nullnullAnull and nulli-Fi
signals are unavailable.
Page 17SPIRENT eBook
nullll nulldentinullation nullell-nullnull the simplest location technology, locates
a user based on the cell they are using, though the accuracy of
this technique varies widely. nullll-null positioning establishes the cell
to which a user equipment nullnull is currently connected and uses
that cell location as a rough estimate of the nullnull s current position.
nullcell-null positioning extends the nullll-null positioning technique with
supplementary information that narrows down the location within the
cell where the null is located. This supplementary information includes
Timing advance and nulleighbour cell measurements.
nullllular network triangulation, either signal strength-based or time-
based, can be used to improve accuracy and time-based methods
such as Time nullifference of Arrival are common.
Page 1nullSPIRENT eBook
nullllular positioning methods currently in use comprisenullnullll identity
nullell-nullnullpositioningnullnullnhanced cell identity nullcell-nullnullpositioningnull
Assisted nulllobal nullositioning nullystem null-nullnull positioningnullAdvanced
Forward nullnk Trilateration nullFnullTnullin nullnull networks, nullnhanced
nullbserved Time nullifference null-nullTnull in nullnullnull networks and nullplink
time difference of arrival nullTnullAnullpositioning. nullbserved downlink
time difference of arrival nullTnullAnullpositioning technique is currently
under discussion for nullTnullnetworks.
Page 1nullSPIRENT eBook
Why Cellular Network Positioning?
nullnullllular nulletworks cover manullrity of populated areas
null nullllular technology is built into all mobile phones and increasing
number of other mobile devices nullike connected nullnullnull
null orks indoors and in urban environments
null ery fast response time
null nullmplementary to nullnull and
other nullcation Technologies
nullnull nullelatively poor accuracy
Page 20SPIRENT eBook
nullven though all these techniques have some limitations, it is possible
to use some as stand-alone or in connullnction with nullnull and other
technologies to overcome the individual limitations. nullnsidering the
global scale and spread of cellular networks, cellular positioning
would form an integral part of any hybrid strategy.
Page 21SPIRENT eBook
The complications faced by engineers aiming to meet the ever
increasing requirements of emerging location based services nullnullnull
on accuracy and availability of positioning solutions mean looking
for different and sometimes novel sources of positioning information.
nullse of cell-id techniques, nulli-Fi and other sensors such as low cost
nullnull inertial are becoming more common and present unique
test challenges. The nullnullnullnull rises to the challenge by enabling
the user to record two channels of serial digital data alongside the
digitinulled nullnull spectra. nullignals direct from sensors or via a bus such
as nullnullus are captured and buried within the nullnull data ensuring
coherent playback. An alternative use of this facility is to record a
timing signal such as a nullnullderived nullps which allows subsequent
synchroninulltion of external systems such as rate tables etc.
Page 22SPIRENT eBook
Comprehensive, End-to-End Location Technology Testing
nullpirentnulls nullnull nullcation Technology is the evolution of the solution
known for years as the nullpirent nullTnull. nullt offers the most advanced,
comprehensive environment available for testing A-nullnullnullnullAnull-
enabled nullnull nullTnulland nullTnulldevices.
nullcation testing can be performed for standalone or hybrid location
technology using A-nullnulland A-nullnullAnull with nulli-Fi, nullll null and nullnull.
This fully automated, nullxible and connullurable solution offers nullntrol
and nullser nulllane implementations, including complete nullnull support.
nullpirent plays a manullr role in the development of test requirements
and specinullations for location technologies within leading standards
Page 23SPIRENT eBook
– a conclusion onullsorts
An unfortunate but inescapable conclusion is that
whilst each technology has its strengths none are on
their own sufnullient to satisfy the accuracy, availability,
integrity and cost requirements of the burgeoning
location based services market. A combination of
complementary technologies would appear to hold the
answer but blending the approaches to get the best
of each is a challenging technical task. nullpirent aims
to support this endeavour by drawing on its extensive
experience and wide range of tools to provide bespoke
test solutions for hybrid positioning developers.
Page 24SPIRENT eBook
nulle hope you found this Hybrid Positioning nullnullok of interest.
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