75
1 INTRODUCTION
In Korea, technologies on WA‐DGNSS (Wide area
differential GNSS) are being jointly developed by a
consortium of universities and research organization
[1, 2, 3, 4, 5, 6] for the construction of system in the
nearfuture.
Figure1.KoreanWA‐DGNSSArchitecture
WA‐DGNSS system comprises WRS (Wide area
Reference Station), WMS (Wide area Master
Station)/GES,GEOsatelliteandUsersegment(Fig.1).
WRS performs the quality monitoring of navigation
message decoded from the received GNSS (GPS,
Galileoetc)satellite,andtransmitsthemonitoredand
processeddate tothe WMS viaterrestrial
communicationnetwork.
WMS generates the correction messages by
processingthedatereceivedfromWRSs,anduplinks
them to the GEO sat
ellite via GES (Ground Earth
Station). GEO satellite transmits the correction
messageanditsown navigationmessageto theuser
withthesamefrequencyastheGNSSsatellite.
WA‐DGNSS compensates for the weakness of
GNSS in terms of accuracy, int
egrity, continuity and
availability. SBAS (Satellite Based Augmentation
System) broadcasts GPS correction message and its
integrity in real time via GEO satellite in wide area.
WAAS, EGNOS and MSAS provide services in the
U.S., EU and Japan respectively. Also GAGAN,
Flexible Software Design for Korean WA-DGNSS
Reference Station
W.S.Choi,S.S.Chhattan,J.E.Kye&W.Y.Han
ICTConvergenceAutonomousResearchTeam,ElectronicsandTelecommunicationsResearchInstitute,Korea
H.Yun&C.Kee
M
echanical and Aerospace Engineering and Institute of Advanced Aerospace Technology, Seoul National University,
Korea
ABSTRACT:Inthispaper,wedescribethesoftwaredesignresultsofWA‐DGNSS referencestationthatwillbe
constructedinKoreainthenearfuture.SoftwaredesignoftheWRS(WideareaReferenceStation)iscarriedout
by a
pplying object oriented software methodology in order to provide flexibilities: easy of model change
(namely ionospheric delay model etc) and system addition (Galileo, GLONASS in addition to GPS etc).
Softwaredesignresultsincludetheusecasediagramsforthefunctionstobeexecuted,thearchitecturediagram
showingcomponentsandtheirrelat
ionships,theactivitydiagramsofbehaviorsandmodelsamongthem,and
classdiagramsdescribingtheattributeandoperation.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 7
Number 1
March 2013
DOI:10.12716/1001.07.01.09
76
SDCM etc are being planned operational in India,
Russiaetc.
Thispaperdescribesthedetaileddesignresultsof
theWRSsoftware.UsecasesoftheWRS aredefined
and designed in order to fulfill the WRS functions.
Architecturedesign,activitydiagramdesignandclass
diagramdesignarefollowedinordertocompletethe
WRSsoftwaredesignbya
pplyingtheobjectoriented
softwaremethodology.
2 WRSFUNCTIONS
WRS (Wide area Reference Station) collects and
processes the GPS navigation data, and calculates
errorssuchas ionosphericdelay, tropospheric delay,
pseudorange residuals etc. And WRS sends the
calculated errors to WMS(Wide area Master Station)
togeneratethewideareadifferent
ialdata.
ThefollowingisasummaryofWRSFunctions:
CollectRawGPSData
DetermineSatelliteOrbits
DetermineSatelliteCorrections
DetermineSatelliteIntegrity
CalculateIonosphericDelay
CalculateTroposphericDelay
CalculatePseudorange
EstimatePseudorangeResiduals
MonitorDataQualit
y
DetermineWRSIntegrity
PerformDataVerification
TransmitRawandPre‐processedDatatoWMS
Logdata
InordertoimplementtheWRSfunctions,wetake
a software approach that provides flexibilities in
softwarearchitectureofeasymodelchangesandeasy
system addition or deletion, namely adding
GLONASS in addition to GPS. Thiscan be regarded
asanadv
antageoftheWRSsoftwaredesign.
3 DIRECTIONSINWRSSOFTWAREDESIGN
WRSDesigniscarriedoutbyapplyingaUMLbased
softwaremethodology,andthedesignresultsinclude
Use case diagram, Architecture diagram, Activity
diagram and Class diagram. It is also designed to
provide TCP/IP communication with WMS to send
thegenerateddatainWRS.
Inorder to providetheflexibilit
yofthe software,
theWRSsoftwareisdesignedinmodularconceptfor
easy maintenance: minimizing the effect to other
componentsduetoacomponentchangesandsystem
addition.
Throughpreliminary designof WRSsoftware [6],
UML (Unified Modeling Language) ba
sed use case
diagramisdesigned,andsoftwarearchitecturedesign
is followed. Input, Processing and output are also
definedforeachcomponent.
In detailed design, activity diagram required for
carrying out WRS functions is designed, and class
diagrams are designed as the final step for WRS
softwaredesign.
4 WRSSOFTWAREDESIGN
4.1 UseCaseDiagram
Use case diagram comprises with Actors and Use
Cases. Actors int
eracting within the WRS software
consist of four components such as Time, WRS
Operator, WRS Administrator and WMS. Time
triggers an event when time int
erval expires or new
data arrives within the system. WRS Operator
performs various tasks related to raw and pre‐
processed GNSS and WRS data. WRS Administrator
is responsible for configuration and maintenance of
the WRS software. WMS actor requests the raw or
pre‐processeddataorWRSdatafromWRSsoftware.
Total18usecasesaredefinedinordertofulfillthe
WRS funct
ions as UC1 Collect Data, UC2 Determine
SatelliteOrbitsetc.
One of the WRS use cases, the UC8‐Calculate
Pseudorange is shown in Fig.2. This use case
calculates the pseudorange, and the actors are Time,
WRSOperatorandWMS.
Figure2.UseCase‐CalculatePseudorange(UC8)
4.2 WRSSoftwareArchitecture
Based on the Use cases designed, WRS software
architecture (Fig. 3) is configured to perform the
defined use cases, and some components have sub‐
components respectively. Input, Processing and
Outputfor eachsub‐component aredefinedinorder
to carry out the use cases designed. In component
level,subcomponentcanbeaddedordeletedinorder
to reflect the changes in model or system. The WRS
software is configured so tha
t other GNSS such as
Galileo can be easily added to the current system
architecture. This property provides the flexibility in
WRS software system, and it can be regarded as
adv
antagesforthissoftwaredesignapproach.
The WRS software architecture comprises 19
components such as Navigation Message Receiver,
Navigation Message Decoder, Data Handler, Data
QualityMonitor,SVIntegrityMonitor,WRSIntegrity
77
Monitor, WRS‐WMS Network Monitor, Data
Processor, Meteorological Station, SV Azimuth and
Elevation Calculator, Pseudorange Calculator, WRS
Position Calculator, Independent Data Verifier, Raw
and Pre‐processed Data Buffer, WRS Information
Manager, WRS Operation and Maintenance, Data
Logger,DataDisplayUnit,WRS‐WMSInterfaceUnit.
Figure3.WRSSoftwareArchitecture
78
5 WRSSOFTWAREACTIVITYDIAGRAM
Activity diagram is designed to represent the
workflows of stepwise activities and actions of WRS
software.
Elements of activity diagram include Start Node,
FinishNode,Activity,Action,ControlFlow,Decision
NodeandFork/JoinNodes.
Major processing actions include calculations of
ionospheric delay, tropospheric delay, SV clock
correction,pseudorange,pseudorangeresiduals,data
transmissiontoWMSetc.
5.1 WRSSoftwareClassDiagram
Cla
ss diagrams are designed to describe the static
structure of the WRS software, and each class in the
diagram has attribute, operation and relationship
withotherclasses.
Class Diagrams of the WRS software comprise
with four categories: Raw and Pre‐processed Data
Holder Classes, Data Processing Classes, Data
Logging and Transmission Task Classes, Parsing
RINEXFilesClasses.
The following is an example of det
ails for one of
the classes, i.e. AlmanacDataProcessor Class (Fig. 4)
designedasrelationshipsandoperations.
Relationships:
_______________________________________________
RelationshipType SourceTarget
_______________________________________________
Association
Source‐>PublicPublic
DestinationAlmanacDataProcessor AlmanacData
Association
Source‐>PublicPublic
DestinationAlmanacDataProcessorSatellitePosition
_______________________________________________
Operations:
_______________________________________________
MethodParameters Description
_______________________________________________
Almanac‐ AlmanacData Constructs
DataProcessor() [in] AlmanacDataProcessor
Void almanacData objectandinitializesthe
Public membervariableswith
providedalmanacdata.
correctAlmanacdouble[in]
ReferenceTime()gpsTransmission‐ Correctsalmanac
doubleTimereferencetime.
Publicdouble[in]
satelliteClockError
AlmanacData[in]
almanacData
_______________________________________________
AlmanacDataProcessor
+ correctAlmanacReferenceTime(gpsTransmissionTime :double, satelliteClockError :double,
almanacData :AlmanacData) :double
+ determineSatellitePosition(almanacData :AlmanacData) :SatellitePosition
+ determineSatellitePosition() :SatellitePosition
+ isAlmanacDataValid(almanacData :AlmanacData) :bool
+ isAlmanacDataValid() :bool
«constructor»
+
A
lmanacDataProcessor(almanacData :AlmanacData) :void
+
A
lmanacDataProcessor() :void
Figure4.AlmanacDataProcessorClass
6 CONCLUSIONS
In this paper, we described the software design
results of the Korean WRS. Software design results
include use case diagram, architecture diagram,
activity diagram and class diagram. The WRS
softwaredesignalsotakesaflexiblearchitecturethat
facilitates software maintenance, namely ease of
model change and system addition such as addition
of G
alileo by applying the object oriented software
methodology.Thisflexiblesoftwaredesignapproach
canberegardedasanadvantageoftheWRSsoftware
desgn.
Implementation of the WRS software will be
followedbyvalidatingeachcomponent,anditwillbe
integrated with the WMS for AIT (Assembly and
Integration Testing). System level comprehensive
validat
ionwillbeperformedforcompletenessofWRS
softwaredevelopment.
ACKNOWLEDGEMENT
This research was a part of the project titled “WA‐
DGNSS Development” funded by the Ministry of
Land,TransportandMaritimeAffairs,Korea.
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