Free eBook: The Fundamentals of GNSS Simulation
Global Navigation Satellite System (GNSS) technology underpins many of today’s most exciting technological advances – and GNSS simulation remains the most comprehensive method of testing and perfecting the devices that put it to use in our daily lives.
Download a free eBook to discover:
- The history of GNSS development—from GPS to GLONASS, Galileo, Compass and QZSS
- The general principles of GNSS simulation (and the technical and cost benefits)
- The simulators available for different test applications
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About Spirent
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.
The fundamentals of GNSS Simulation
What is a GNSS Simulator? Why should you use one for testing?
Introduction
The number of applications using Global Navigation Satellite
System (GNSS) technology is continually increasing. So too
is the diversity of these applications. Many applications are
pushing the requirements of GNSS technology further than
ever before. nulln some cases it is necessary to augment GNSS
technology nullth other systems to meet the performance
requirements of a particular application.
Page 2SPIRENT eBook
nullor GNSS to succeed as a statenullfnullhenullrt technologynull
the design of the various parts of the system nullin particular
GNSS receivers nullmust be of a high standard that ensures
reliable performance.
To enable thisnullit is important that the product development
process is based on proper testing from concept to production.
This enullonulldiscusses this testingnulland nully null simulation nullnullich
has been the standard method for over null years nullshould be
the chosen method. nullt also enulllains the concept of simulation
and gives enullmples of different simulators for different test
applications.
Page 3SPIRENT eBook
nulln addition it sets out to provide designersnulldevelopersnull
integrators and testers of GNSS receivers or systems an overvienull
of the technical benenulls offered by GNSS simulation and enulllain
the cost benenulls to procurement managersnullpronullct managers and
nullancial managers nullo need to construct business cases
for pronullcts involving GNSS technologies.
Page 4SPIRENT eBook
What is GNSS?
Global Navigation Satellite System (GNSS) is a general term for
a system that provides navigation and other services to users
nullrldnullde. nullch GNSS employs a constellation of satellitesnullnullich
broadcasts signals that are then processed by GNSS receivers to
determine locationnullspeednulland time for users anynullere nullthin range
of the satellites. This is normally on or nullst above the nullrthnulls surfacenull
but can be in space as nullell.
Page 5SPIRENT eBook
There have been a signinullant number of developments in the
availability of nenullsatellite navigation systems and services (Gnullnull
GalileonullGnullnullnullSnullnullSSnullnulleidounulletc.) correspondingly driving
a need for more testing to connullm the performance
of these systems and associated
enhancements in relation to the designnull
qualinullation and validation of navigation
equipmentnullnullereas in the pastnullGnull nullnull
code nulls the only available service for
the manullrity of commercial applications.
SPIRENT eBook
Global Positioning System (GPS)
and nullher GNSS systems
While the null sponsored Gnull system is the only GNSS nullth a fully
deployed constellation of operational satellitesnullGnullnullnullS is not
far behind and other systems are either in planning or deployment
stages. nullboratory testing here becomes of utmost importance due to
the lacnullof the real livenullnull signals.
Page 7SPIRENT eBook
Global Positioning System (GPS)
The Gnull satellite navigation system nulls originally designed and
funded as a military navigation system. The removal of selective
availability (a deliberate degradation of the satellitenulls clocnullstability)
in nullnull improved the accuracy for nonnullilitary applications using the
null nullarse nullcquisition (nullnull code to much better than nullm in many
operational scenarios. This improved accuracy has enabled Gnull to
be used in many applications and led to the enulllosion of commercial
Gnull applications that nulle are seeing today.
nulln the military spherenullthe null and null nullnull) code encrypted signals
remain the NnullTnullstandard for military nullrecise nullositioning System
(nullS) receivers.
Page 8SPIRENT eBook
The nullnited States continues to invest in the Gnull system.
This investment includes the specinullationnulldesign and launch
of nenullsatellites including the nenullMilitary nullde or Mnullode signal.
The initial Mnullode satellites have already been launchednullnullth
additional launches planned over the nenull decade as the current
satellites reach end of life. nulldditional civil Gnull signals are also
planned at the nullnull and null . The nullst nullnullsatellites have already
been launchednullalthough full operational capability is still
several years anully.
Page 9SPIRENT eBook
GnullnullnullSS
nullevelopment of the nullussian GnullnullnullS system began in nullnull and
nulls completed in nullnull. nullecently nullussia hasnullnullth nullndia as a program
partnernullcommitted to restoring the system to full operational
capability (nullnull by nullnull. Spirent has seen a recent upsurge in interest
in combined GnullnullnullnullnullS simulators. This is due to people nullnting
to tanull advantage of additional signals today to improve the
availability of their receiver and system implementations.
Page 10SPIRENT eBook
Galileo
The nulluropean nullnion has committed to the design and validation of
the Galileo system. null prime difference betnulleen this and the other
systems is the proposed civil focus of the Galileo programme.
Galileo is designed to be internullperable nullth Gnull nullth several future
combined Gnullnullalileo receivers already availablenullbringing benenulls
for usersnullof additional satellite availability and improved integrity.
Spirent is an ofnullial supplier of null nullnstellation Simulators (nullnull)
to the Galileo programme. The nullnull are being used for testing the
ground monitoring stations and prototype user receivers.
nulln early nullnull the Galileo pronullct ofnulle announced that it had placed
contracts for the nullst satellitesnulllaunch services and satellite control.
Page 11SPIRENT eBook
nulln March nullnull the Galileo signal specinullation (nullnull interface control
document) nulls issued formally nullth a free licence available to anyone
nullo nullnts to use the information to develop Galileo receivers or
services.
nullasinullenith Satellite System (nullSS)
The nulluasinullenith Satellite System (nullSS) is a regional multi satellite
systemnullpartly designed to provide nullnullnullinullnull signals from satellites in
a nullighly nulllliptical nullrbit (nullnull over nullapan. The constellation and orbits
have been designed to allonulleach satellite to dnullell over the nullapan
land mass for more than null hours a day nullth an elevation above nullnull
providing improved coverage in urban and mountainous areas nullere
the linenullfnullight limitation of classic GNSS systems may be impaired.
The nullst launch of nullSS occured in nullnull.
Page 12SPIRENT eBook
Beidou nullnullmnullss
nullina has indicated it intends to enulland the current geostationary
nulleidou navigation system into a full mediumnullarthnullrbit GNSS
constellationnullaccording to nullina nenull agency nullnhua. nulletails are
currently anullited by the industry on the capability and international
availability of this system. nulln principle the nullmpass open civil signals
should be interoperable nullth the other GNSS systems.
Page 13SPIRENT eBook
nullugmentation systems
Gnull alone does not alnullys provide adequate performancenull
particularly in demanding environments or nullere a high level of
integrity is required. The accuracy and integrity of Gnull nullGNSS can be
greatly enhanced by the use of information derived from observations
from others sensor technologies. The use of augmentation systems
tanulls many forms but all share the same basic obnullctive of improving
Gnull nullGNSS performance andnullr trustnullrthiness.
Page 14SPIRENT eBook
Snullce based nullugmentation Systems (SBnullS)
Space nullased nullugmentation Systems (SnullS) are typically
designed to improve Gnull nullGNSS system integrity and accuracy
for aircraft navigation and particularly landing. SnullS satellites
broadcast correction messages bacnullto nullrthnullnullere suitably
enabled receivers use the SnullS corrections and integrity information
to improve accuracy and integrity. The nullnull nullurope and nullia are
developing their onull SnullS systems. nulln nulluropenullthe nulluropean
Geostationary Navigation nullerlay Service (nullNnull) system enullsts and
is nonulloperational. nulln the nullnull there is the Wide nullea nullugmentation
System (WnullS)nullin nullapan the Multinullunctional Satellite nullugmentation
System (MSnull) and nullndia is focusing on the Gnull nullded Geo
nullugmented Navigation (GnullGnull) system.
Page 15SPIRENT eBook
Snullce based nullugmentation Systems (SBnullS)
Page 16SPIRENT eBook
Ground based nullugmentation Systems (GBnullS)
null alternative approach to spacenullased augmentation is to transmit
correction messages from groundnullased systems. null enullmple
is the nullcal nullea nullugmentation Systems (nullnullS)nullnullich allonull
a suitably equipped receiver to derive enhanced accuracy and
integrity information in a local areanullat an airport for enullmplenull
nullere there are stringent requirements necessary to be met to land
a commercial aircraft. nullnullS can be tested using Spirentnulls unique nullnullS
nullnulldata broadcast signal simulatornullthe GSSnullnull.null
nullnullor more information please contact your local Spirent representative.
Page 17SPIRENT eBook
GNSS SimulationnullGeneral Princinulles
Since the early days of GNSSnullthere have essentially been
tnull manullr alternatives available to those nullshing to test a navigation
systemnullnullld test and laboratory simulation. Todaynullbest practice
indicates that most testing is done under controllednullrepeatable
conditions in a secure laboratory. This enables both
nominal and adversarial conditions testingnull
including testing to the limits of both
real and theoretical performance.
nullt also allonull development of receivers
for GNSS systems that are currently
unavailable or lacnullng
a full constellation.
SPIRENT eBook
nullealnullorldnulllivenullnull testing has signinullant dranullacnull nullichnullin
practicenullpreclude controlled testing. null summary of the advantages
of testing nullth GNSS simulatorsnullcompared to live testing nullth actual
GNSS constellationsnullis shonull in the table belonull.
Live Testing nullth nullnullual GNSS nullnstellations LanullnulltonullnullTesting nullth GNSS Simulatonull
No control over constellation signals nullmplete control over constellation signals
nullmited control over environmental conditions nullmplete control over environmental conditions
Not repeatablenullconditions are alnullys changing nullully repeatable
nullnintended interference from nullnullradarnulletc. No unintended interference signals
nullnnullnted signal multipath and obscuration No unnullnted signal effects
No nully to test nullth GNSS constellation errors nullsily test scenarios nullth GNSS constellation errors
nullnullensive nullld testing and vehicle trials nullstnullffective testing in laboratory
nullmited to signals available in GNSS constellations Testing of present and future GNSS signals
nullmpetitors can monitor nullld testing Testing conducted in secure laboratory
Page 19SPIRENT eBook
What is a GNSS Rnullsimulator?
null GNSS simulator provides an effective and efnullient means to test
GNSS receivers and the systems that rely on them. null GNSS simulator
emulates the environment of a GNSS receiver on a dynamic platform
by modelling vehicle and satellite motionnullsignal characteristicsnull
atmospheric and other effectsnullcausing the receiver
to actually navigate according to the parameters
of the test scenario. null GNSS receiver
nullll process the simulated signals
in enullctly the same nully as it nulluld
those from actual GNSS satellites.
Page 20SPIRENT eBook
null GNSS simulator provides a superior alternative for testingnullcompared
to using actual GNSS signals in a live environment. nullnlinull live testingnull
testing nullth simulators provides full control of the simulated satellite
signals and the simulated environmental conditions. With a GNSS
simulatornulltesters can easily generate and run many different test
scenarios for different nullnds of testsnullnullth complete control overnull
null nullatenulltimenulland lonulltionnull Simulators generate
GNSS constellation signals for any location and
time. Scenarios for any location around the
nullrld or in spacenullnullth different times in the
pastnullpresentnullor futurenullcan all be tested
nullthout leaving the laboratory.
SPIRENT eBook
null nullehinulle motionnull Simulators model the motion of the vehicles
containing GNSS receiversnullsuch as aircraftnullshipsnullspacecraft or land
vehicles. Scenarios nullth vehicle dynamicsnullfor different routes and
tranullctories anynullere in the nullrldnullcan all be tested nullthout actually
moving the equipment being tested.
null nullnvinullonmental nullnditionsnull Simulators model effects that impact
GNSS receiver performancenullsuch as atmospheric conditionsnull
obscurationnullmultipath renullctionsnullantenna characteristicsnulland
interference signals. nullarious combinations and levels of these effects
can all be tested in the same controlled laboratory environment.
Page 22SPIRENT eBook
null Signal enullonull and inanullunullnullesnull Simulators provide control over the
content and characteristics of the GNSS constellation signals. Tests
can be run to determine honullequipment nulluld perform if various
GNSS constellation signal errors occurred.
Page 23SPIRENT eBook
Why simulate?
nullf nulle consider a fullynullperational GNSSnullsuch as Gnullnullit is very easy
to assume that to test a receiver you nulluld simply connect it to a
suitable antennanullput the antenna out of the nearest nullndonullnullor
on the roof of a vehicle or building and checnullthat the receiver can
locatenulltracnulland navigate on the GNSS signals received.
To some enullentnullthis assumption nulluld be acceptable.
This method nullnullich nullll herein be referred to as
nullive Snullnull nullnulluld indeed verify that
the receivernulls fundamental null and
processing circuits are basically nullrnullng.
Page 24SPIRENT eBook
nullonullevernullnulle are interested in testingnullnot simply checnullng for
operation. Thereforenullnullve Snull should never be relied upon for
anything more than a simple operational checnullto connullm successful
operation in the presence of real nullrld impairmentsnulland should
certainly not be relied upon for any testing during a productnulls
conception nulldesign nulldevelopment nullproduction and integration
life cycle. There are honullever times nullen testing real nullrld signals
is the easiest nully to connullm performance in the presence of real
nullrld impairments or real nullrld operational challenges. null nullecord null
nulllaybacnullsystem complements the capability of a GNSS simulatornull
enabling the full nullichnessnull of the real nullrld environment to be
captured and played bacnullin the lab.
We nullll nonullloonullin some detail at the reasons behind these facts.
Page 25SPIRENT eBook
nullonulledge
nullt the time of a nullve Snull testnullthere are several unnullonulls.
The unnullonulls includenull
Satellite nullonull enullonull nullover timenullthese errors should be
accounted for in the navigation message and corrections
broadcastnullbut because this message is updated
infrequentlynullit is possible for a clocnullerror to enullstnull
nullich is not being corrected for. This nullll result
in an incorrect pseudorange measurementnulland
hence an error in the receivernulls computed
position. nullepeat tests nullll see a different
clocnullbehaviour and nullll therefore
differ in their results.
SPIRENT eBook
nullsing a satellite simulatornullthere are no errors on the satellite clocnullnull
unless you nullsh there to benulland then they are precisely nullonull and
can be applied at nullonull times. nullsonullnullen the test is repeatednullany
clocnullerrors denulled nullll be identical to the previous test.
Satellite onullit enullonull nullThe position of each
satellite as declared in the navigation message
is different to its enullct physical position in
orbit. This is due to several orbital errors that
are caused in part by the gravitational effects
of the SunnullMoon and nullrthnullnullich serve to
add perturbations to the satellites position.
Page 27SPIRENT eBook
nullven though the nature of the perturbations is relatively steady
and predictable (as are the satellite orbits) the orbital corrections
broadcast in the navigation message nullll not be completely accuratenull
againnulldue to the inherent error in the prediction and estimation
techniquesnullplus infrequent updating of the information.
With a simulatornullit is possible to either remove all orbital errors and
use a nullperfectnull constellationnullor allonullfully quantinullble errors to enullst
in a controlled manner.
Page 28SPIRENT eBook
Navigation data enullonull nullnull nullth any data transmission systemnullerrors
occur in the data as a result of the modulationnulldemodulation and
transmission processes. There is robustness built in asnullfor enullmple
nullth the Gnull systemnullthe last nullbits of each nullrd of the navigation
message are parity bitsnulland are used for bit error detection. nullonullevernull
errors can still occurnulland these nullll not be accounted for.
With a simulatornullit is not possible for navigation data errors to occurnull
unless they are deliberately applied. null
Page 29SPIRENT eBook
nulltmosnullenullinullenullonull nullThe GNSS signals have to pass through the
layers of the atmospherenullnullich in its tnull main parts comprises the
nullonosphere and the Troposphere. nullree electrons in the ionosphere
(null to nullnullnull above the earthnulls surface) cause the modulation of a
GNSS signal to be delayed in proportion to the electron density (its
speed of propagation through the ionosphere is referred to as the
group velocity). The same condition causes the null carrier phase to be
advanced by the same amount. (nullts speed of propagation through the
ionosphere is referred to as the phase velocity)
This dispersive effect of the ionosphere varies according to latitude.
nullt is relatively stable in the temperate regionsnullbut can nullctuate
signinullantly in the equatorial or polar regions.
Page 30SPIRENT eBook
The troposphere (nullto nullnull) also affects GNSS
signals. nullariations in pressurenulltemperature and
humidity combine to delay the signal. nullnlinull
the ionospherenullthe troposphere is a nonnull
dispersive mediumnullso it delays both the
carrier and code equally. The troposphere
is divided into tnull componentsnull
nullet and dry. The dry component
contributes to nullnullof the delaynullbut
can be predicted very accurately.
The nullet component is more
difnullult to predict due to
large variation in atmospheric
distribution (or more simplynull
the nulleathernull
SPIRENT eBook
The changes to the signal caused by the atmosphere directly
contribute to range measurement errorsnullnullich cause the receiver to
compute an incorrect position.
The effects of the atmosphere on GNSS signals are modellednulland
these models are used by the receivernulltogether nullth correction
parameters in the navigation data to partially correct atmospheric
errors. nullual frequency receivers can go a long nully to eliminating
the errorsnullbut single frequency receivers (nullich most commercial
ones are) can only use the models available. These models are only
partly successful in removing atmospheric errorsnullso there is alnullys a
residual error due to the atmosphere.
Page 32SPIRENT eBook
With a simulatornullit is possible to completely disable the atmospherenull
thereby removing the errors. nullternativelynullerrors can be applied to a
nullonull modelnulland are therefore fully accounted for.
Page 33SPIRENT eBook
nullultinullth nullGNSS signals are linenullfnullightnulland can be regarded in the
same nully as rays of light. nullf a signal ray falls upon an nullnullenullctive
surface at an angle less than the critical angle of internal renullctionnullit
nullll be renullctednullnullth some attenuation. Thereforenullit is possible for
a receiver to not only receive the direct linenullfnullight raynullbut also the
renullcted version. The receiver has no nully of nullonullng nullich one of
the tnull is the true nullnull signalnullso it uses bothnulland inherits the delay
error present on the renullcted signal.
Page 34SPIRENT eBook
This is an illustration of a simple
single renullcted ray. nulln realitynull
multipath is much more complenull
but the net effect is still an error
in the receivernulls position estimate.
Page 35SPIRENT eBook
With a simulatornullit is possible to eliminate multipath completelynullor
to apply multipath to signals using various multipath models. nulln this
nullynullmultipath can be applied in a nullonullnullcontrolled manner enabling
its effects on receiver performance to be accurately analynullednulland
the appropriate design alterations or mitigations to be applied. With
nullve Snullnullit is impossible to quantify the multipath conditions present
at any one timenulland therefore impossible to analynulle and improve a
receivernulls performance in its presence.
null More information on testing multipath performance of GNSS receivers can be found
in this Spirent enullonull
Page 36SPIRENT eBook
nullntenullfenullennull nullGNSS signals are very nulleanull
nullen they reach the receivers antennanulldue
to the fact that they have travelled a long
nully from the satellites. This manulls them
vulnerable to interference from enullernal
sources. nullnterference can be deliberate
(nullonull as nullmming or spoonullg) or
unintentional. The vulnerability of GNSS to
interference has been nullell documented
and the discussion is beyond the scope
of this document.
Page 37SPIRENT eBook
nullnterference not only introduces errors in a receivernulls position
computationnullbut can stop it navigating altogether. The problem this
causes if interference is present (and cannot be stopped) during a
nullve Snull test is obvious.
With a simulatornullthannullullynullno such interference enullsts by defaultnull
but if requirednullit is possible to simulate it in a controlled and
repeatable manner. nullnterference nullich changes as a function of
the pronullmity of its source to the receiver can be applied using an
interference simulation system such as Spirentnulls GSSnullnull .
Page 38SPIRENT eBook
Renullatability
When you perform testing on a GNSS receivernulland it highlights
nulleanullesses in the designnullthe normal process is to manull changes to
the design nullth a vienullto improving it. To connullm if improvements
have been madenullyou need to repeat the same tests enullctly. nullf nullve
Snull is being usednullit nullll be impossible to ensure subsequent tests
are subnullcting the receiver to the same conditions as the original test.
The most obvious difference is the fact that time has progressednulland
the constellation visible to the receiver nullll be completely different.
These are factors that by themselves nullll ensure the test conditions
cannot repeat. The other characteristics that nullll not remain nulled are
atmospheric innullences and satellite performance.
Page 39SPIRENT eBook
Thereforenullnullve Snull is unsuitable as a method for testing nullth a vienull
to manullng design improvements.
With a constellation simulatornullevery time a test scenario is runnullthe
signals produced are identical. The scenario nullll start at the same
time on the same datenulland the satellite positions nullll be identical null
even donull to the relative phase offsets betnulleen the different signals.
nulln this nully you can guarantee that the receiver is being stimulated
nullth the enullct same signals every time the test is run. nullnly this nully
can you fully determine any improvement (or othernullse) the design
alterations have made.
Page 40SPIRENT eBook
nullroper measurement of physical design changes is not the only
reason for performing completely repeatable testing. nullf the results
of testing are required as input to a verinullation or certinullation
processnullthey must be reliable and unnullmbiguous. nullor enullmplenullif
tnull companies are building receivers for a certain critical or safety
of life applicationnulland they have to be certinulld to an international
test standardnullthen the test conditions must be identical to avoid
one company having an advantage over the other. The test methods
used in test standards should alnullys be designed to reduce the
measurement uncertainty as far as possible to preserve the integrity
of the tests.
Page 41SPIRENT eBook
nullntrollability
With any comprehensive testingnull
nullite and accurate control of the
test conditions is essential.
nullinenulluning of a design or system
parameter can often demand
very smallnullcloselynullontrolled
manipulation of the test
conditions.
Page 42SPIRENT eBook
With a nullve Snull test methodnullthere is little that you have control of.
With the enullception of the physical location of the test antennanullthere
is in fact nothing else that you have any control over. nullou cannot
nullnd bacnulltimenulldisable the atmospherenulladnullst the satellite signalsnull
errorsnulldatanullorbits nullall of nullich are parameters you need to have
complete control over.
Page 43SPIRENT eBook
nullcuracy
null GNSS null nullnstellation Simulator is a
precision piece of test equipment and if properly
maintainednullits performance is accurately
specinulld and controlled. The nullelity of a
simulatornulls signals is much better than the
signals from a real GNSS systemnullnullich not
only allonull advanced testing of a receivernulls
true nullaboratorynull performancenullbut means
that signal noise contributions due to
the simulator are nullell belonullthe level
of thermal noisenulland therefore nullll
not contribute any noise errors
to the test.
Page 44SPIRENT eBook
Tnull parameters closely related to accuracy are quality and reliability.
The precision engineering employed in the simulatornulls design and
constructionnulland the quality control processes governing these
disciplines ensure that the equipment gives reliable service for
many years.
Page 45SPIRENT eBook
Record nullPlayback Systems do hanull a role to nullay
Thorough evaluation of receiver performance requires that the impact
of these various sources of previously described impairments is
assessed. null emerging technique for performing this testing is by
recording the null signal for subsequent playbacnullin the lab
null previously mentioned simulation allonull absolute control of the test
environment nullere individual sources of impairment can be added
or removed at nullll. Simulation also allonull the evaluation of signals
not yet available from space or enullremes of vehicle motion nullich may
be enullensive or difnullult to trial. nullndeed the generation of synthetic
signals derived from mathematical models represents the ultimate
in control.
Page 46SPIRENT eBook
nullonullevernullthe generation of an environment that can be said to be
truly representative requires enullertise and could require verinullation
to connullm that the combination of impairments is valid. The nullecord
and nulllaybacnullapproach allonull an actual environment to be captured
and replayed at nullllnullcomplete nullth realnullife propagationnullfades and
interference. nullt is by its nature representative of the real nullrld and so
complements simulation as a source of GNSS signals for test.
nullsing a nullecord nullnulllaybacnullSystem avoids the need to continually
return to the nullld by providing representative GNSS signals in the lab
and being able to repeatably reproduce the recorded null nullerever and
nullenever required.
null More information on nullecord nullnulllaybacnullSystems can be found in the GSSnullnull nullS Webinar
or by donullloading the enulloonull .
Page 47SPIRENT eBook
nullnullbility
nulln practically all nullonull applications nullere vehicle motion is presentnull
a simulator nullll far enullceed the dynamics required to simulate that
motion. nullt is therefore possible to test a receiver nullell beyond the
boundaries of its intended operational environment nullsomething
not possible by any other means. This allonull the true manullmum
performance of the receiver to be characterinulled and accurately
denullated for the intended application.
Page 48SPIRENT eBook
nullmmercial nullability
No pronullct survives nullthout a sound business case. Those responsible
for managing pronullcts and setting budgets nullll have to tanull this
into account. nullt is often nullongly assumed that simulation only saves
money over real nullld trials for applications involving highnullynamics
on sophisticated platforms. nullor enullmplenullit is very obvious that there
is no nully a spacenullrade receiver can be nullnull in orbit purely in order
to test honullnullell it nullrnullnullbut nullat is often not so obvious is the
fact that simulation can prove to be more cost effective for much less
sophisticated applications. null fenullmonths of drive testing nullll pay for
a simulator and in many cases manulls its choice over real nullld trials
academic.
Page 49SPIRENT eBook
null leading nulluropean automotive manufacturer calculated that the
total cost of performing a real drive test is in the order of nullnullper
day. Notnullthstanding the technical issues nullth realnullorld tests
already discussednullthe nullancial costnullenenulls alone are enough to
demonstrate the viability of simulation.
Page 50SPIRENT eBook
The methodology onullsimulation
So farnullnulle have discussed the reasons for selecting simulation as
the preferred GNSS test method. nulln this section nulle nullll loonullat the
methodology of simulationnullenullmples of different simulators and
honullthey may be used for testing in different applications.
Page 51SPIRENT eBook
To renullap nulle remember that an null nullnstellation Simulator reproduces
the environment of a GNSS receiver on a dynamic platform by
modelling vehicle and satellite motionnullsignal characteristicsnull
atmospheric and other effectsnullcausing the receiver to navigate on
the simulatornulls null signalnullaccording to the parameters of the test
scenario. What a simulator is not is a magic bonullnullich reproduces
the real nullrld in its entirety. nullonullevernullfar from being a limitationnull
this is an important benenull. nulln the same nully that an null design
engineer nulluld not use a random noise generator nullen he really
needs a controlled and quantinulld test signalnulla GNSS
receiver tester nulluld not use a random realnull
nullrld signalnulleproducing device nullen
he really needs a controllable and
repeatable simulated GNSS
test signal.
Page 52SPIRENT eBook
null receivernulls performance nullll vary depending on the severity of
the errors and effects applied to the null signal. nulligure nullshonull a
representation of the signal nullnullthrough a typical simulatornullnullth
the various effects being addednulluntil the nullal null outputnullfrom nullich
the complenullresultant null signal is output to the receiver under test.
This principle applies to all simulatorsnullnullth the number of effects
depending on the capability of the simulatornulland its intended
application.
nulligure null Simulation signal nullnull
Page 53SPIRENT eBook
nulligure null shonull a typical setnullp in more detail. null Spirent GSSnullnull
simulator is pictured. nullosition nullelocity and Time data (typically in
NMEA nullnull format) from the receiver can be fed bacnullto the simulator
control softnullre and compared nullth the simulated nulltruthnull data. This
nullll give a very accurate measure of the receivernulls performance against
the nullonull characteristics of the simulatornulls signal.
nulligure null Simulation test setnullp
Page 54SPIRENT eBook
Pernullrming a simulator test
Setting up and running a receiver test using a simulator is relatively
straight fornullrd. nullt can be summarised in tnull stagesnull
null nullenullition null nullunnullime
The nullenullition stage is nullere the required test parameters are setnullp
using the simulator control softnullre. nullt this stage you need tonull
• Understand the application for the receiver to be tested, and the
operating environment
• Determine the tests you need to perform
• Define the test scenario with the appropriate effects
• Understand how to connect the receiver to the simulator in order
to maintain the appropriate Rnull conditionsnull
nullore information on this subnullct can be found by donullloading the Spirent nullpplication Note null nullnnecting an null Simulator to a GNSS nulleceiver null
Page 55SPIRENT eBook
The nullunnullime stage is nullere the scenario is running and the simulator
hardnullre is producing the requisite null signal.
nullt this stage you need tonull
null nullbserve the receiver under test and manipulate the simulator
as appropriate.
null nullalyse the receiver performance. This can be undertanulln either in
realnullime or by postnullest analysis of recorded data. nullccess to the
simulation data (the data used to create the test signal) can be
gained in various nullys from datanulltreaming to logging to a nulle.
This data can then be used to compare the receivernulls performance
nullth the nulltruthnull simulation data.
Page 56SPIRENT eBook
Snullrentnull nullultinullNSS simulation nullatnullrms
Spirent offers a nullde range of test systems and capabilities to meet
your MultinullNSS test needs. nullur MultinullNSS systems are designed
nullth future development in mind and are enullandable to address
tomorronullnulls test requirements as nullell as todays. Whether you are
undertanullng nullnullperformance testingnullintegrating devices into your
product linenullverifying performance or assessing manufacture of
MultinullNSS devicesnullSpirent has a MultinullNSS test system available
today to match your needs.
Page 57SPIRENT eBook
The GSS8000 MultinullNSS nullnstellation Simulatornullnullp to three
null carriersnullselected from a range of constellations and signals
(GnullnullGalileonullGnullnullnullS and nulluanull nullenith Satellite System)nullcan be
accommodated in a single signal generator chassis. This enables
multiple signals from a single constellation or hybrid systems nullth
signals from multiple constellations to be tested. The architecture
supports future nullmpass signals.
Page 58SPIRENT eBook
The GSS6700 MultinullNSS Simulation System offers up to null channels
of combined GnullnullnullSnullGnullnullnullS and Galileo null signals from a
single chassisnullnull channels for each constellation. The GSSnullnull is
available nullth onenulltnull or three constellations enabled. nullifferent
softnullre capabilities and nullnullbility are available to suit different test
needs. nullor enullsting Spirent STnullnullnull
or GSSnullnull customers nullo today test
GnullnullnullS null onlynullthe GSSnullnull offers
the ability to simulate not only Gnullnull
SnullS but also GnullnullnullS and Galileo.
Page 59SPIRENT eBook
The GSS6300 MultinullNSS Signal Generator is designed specinullally
for production test applications nullere a single channel is required
for controlled GNSS testing. The GSSnullnull can generate a singlenull
combined GnullnullnullSnullGnullnullnullS and Galileo signal to enable testing
of Gnull only or MultinullNSS devices in a production environment.
nullor enullsting Spirent GSSnullnull customersnull
the GSSnullnull has an identical capabilitynull
form factor and interfaces nullen specinulld
in GnullnullnullS connulluration. nulln additionnull
the GSSnullnull offers the benenull of onnull
site (even innullacnull upgradability to add
GnullnullnullS and Galileo generation capability
concurrently nullth GnullnullnullS.
Page 60SPIRENT eBook
nullor more information on GNSS
applicationsnullGNSS receiver testing
and the benenulls that GNSS
simulation can offer younull
visit nullnull.spirent.comnullositioning
Snullnullent GSS8000
MultinullNSS nullnstellation Simulator
Snullnullent GSS6700
MultinullNSS nullnstellation system
Snullnullent GSS6300
MultinullNSS Signal generator
Page 61SPIRENT eBook
Spirentnulls GSSnullnull GnullnullnullnullnullS nullecord and
nulllaybacnullSystem is a completenullstandalone
systemnullpurpose designed for gathering data
in the nullld and replaying it nullth optimal
nullelity and performance bacnullin the lab.
The GSSnullnull simulates Winulli netnullrnullelements
to enable labnullased testing of the latest Winulli
positioning technology. The GSSnullnull can nullrnullas
a standnulllone test instrument or in connullnction
nullth Spirentnulls GnullnullNSS and automated location
test products.
The GSSnullnull can also be combined nullth Spirentnulls
range of Gnull and multinullNSS Simulation Systems
to test true hybrid location performance
Snullnullent GSS6400 Snullnullent GSS5700
Page 62SPIRENT eBook
nullf you found this The fundamentals of GNSS simulation nullnullonull
enullonullof interestnullnulle thinnullyounullll denullitely linull the Spirent
nullpplication Notenull nullundamental GNSS nullenullivenullnullanullnullenullisation .
nullonullload it here.
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on a regular basis. nullonullarnullthis linnull
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