235
1 INTRODUCTION
Thepaperisdedicatedtopresenttheconceptofthe
integrated communication system for UAV
(Unmanned Aerial Vehicle) data and telemetry
transmission. UAV is one of the elements of the
Proteusproject,whichisdedicatedfordevelopingan
integratedsystemmobilesystemforcounterterrorism
and rescue operations. In
the project Institute of
Radioelectronicsismainlyresponsiblefordeveloping
the entire communication system for all system
components. The aim of this paper is to present
generalviewattheconceptofthesystem,whichisthe
communication system for controlling the UAV and
collectingthe information from it.In
the paper both
the concept of the system and elements of its
realizationarepresented.
2 PROTEUSPROJECT
The project “Integrated Mobile System for
Counterterrorism and Rescue Operations”
PROTEUS is realized by consortium of leading
science centers in Poland headed by Industrial
ResearchInstituteforAutomationandMeasurement
PIAP
[1].TheProteusProjectisaimedatdevelopment
ofamodernsystem,whichinthefuturewillbeable
to support operations of police, fire service and the
otherservicesresponsibleforsecurityofoursociety.
The designed system will include i.a.: three multi
functional robots, unmanned aircraft and mobile
command
centre.TheProteusisgoingtomakeuseof
a range of innovative technologies integration of
whichintooneefficientlyfunctioningsystemposesa
seriouschallengetoengineersworkingontheproject.
Intensification of violent weather phenomena, of
terrorism and ever increasing dependency of a man
on technology are the
circumstances in which fire
service and police have to reach for newer
Integrated Communications System for the Remote
Operation of Unmanned Aerial Vehicle
K.Kurek,T.Keller,J.Modelski,Y.Yashchyshyn,M.Piasecki,G.Pastuszak,
M.Darmetko&P.Bajurko
InstituteofRadioelectronics,WarsawUniversityofTechnology,Warsaw,Poland
ABSTRACT: The aim of the paper is to present the concept of the integrated system dedicated for
communication and remote operation of the unmanned aerial vehicle (UAV). In the paper the concept and
realizationofthiskindofwirelesscommunicationssystemis
presented.Thesystemconsistsoftwointegrated
solutionsunidirectionalbroadcasttransmissionofvideo,audioanddatafromUAV totheoperatorswithin
the mobile command centre and twoway communication with the telemetry and control subsystem. The
systemsareintegratedwithinthesinglechassisandplacedontheUAV
toensureproperoperationoftheflying
robot.Thespecificelementsofthesystemarepresentedaswellasmainrequirementsandconnectedwiththem
developmentmethodsarealsodiscussedinthepaper.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 7
Number 2
June 2013
DOI:10.12716/1001.07.02.11
236
technological solutions, which can improve their
operations. One of solutions like that will be the
Proteussystem.
2.1 TheaimsoftheProteusProject
The Proteus is a stateoftheart integrated system
intended for counterterrorism and crisis
managementoperations.Operationsoftheemergency
servicesaretobe
supportedbythreemultifunctional
robots, unmanned aircraft and mobile command
centre. The system is to be completely integrated,
whichisaninnovationonaglobalscaleandposesa
seriouschallengetoengineersinvolvedintheproject.
Every device being a component of the Proteus
performs a strictly defined
function, and
simultaneously is an integral part of the system.
Elements of the Proteus are already used in rescue
services and military structures, but bringing them
together to create one operational unit is innovative
evenonaglobalscale. Itisonlythebeginningforthis
kind of solutionsto be
developed in the world, and
additionallytheyarecreatedvirtuallyexclusivelyfor
the military purposes. The IT system of the Proteus
willallowforthepresentation ofthegathereddatain
aclearway,theircomparisonwithreferencedata,and
with aid of GIS systems (Geographic Information
System is a
system for acquisition, processing and
presentation of data with reference to geographic
location)itwillenable,forinstance,determinationof
directioninwhichspreadschemicalcontaminationor
fire. It will significantly enhance and speed up
decision making processes, enabling the supervision
and insight into the region under threat.
Interconnection of existing
elements and solutions
into an integrated system capable of performing
varioustasksdependingontheneeds,istheessence
oforiginalityoftheProteusProject.
2.2 Systemcomponents
Afterdetailedresearchthepotentialrequirementsof
futureusersofProteus(thedepartmentsresponsible
for rescue operations and counterterrorism), Proteus
system architecture
and its components have been
defined.Asaresultofmanyweeksofinterviewswith
Fire Department personnel, police and counter
terrorism services, the main system concept was
developed,consistingofthefollowingmainelements:
Mobile Command Center MCC‐the Proteus
“brain”, the large truck eq uipped with complex
communications and operation systems. This is
where, owing to data acquisition and
interpretation, decisions affecting the action will
bemade.Apartfromprocessingandintegrationof
data coming from the system components taking
part in action (robots,
unmanned aircraft), the
MCCwillbeincontinuouscommunications with
command posts of police, fire service and crisis
managementcenters
MobileRobotOperatorCentreMROC‐tothesite
of operation all robots will be carried by Mobile
RobotOperatorCentre mounted (similarlyas the
MCC)onachassisofatruck.Itiseq uippedwith
devicesforrapidloadingandunloadingofrobots,
portable robot operator stands (PROS) and a
systemofcommunicationswithcommandcentre.
Mobilerobots‐directlytotheoperationsitethree
types of mobile robots are sent, every one of
different functionalities and purpose. The Small
MobileRobot(SMR)isarobotofsmalldimensions
andveryhighmobility,intendedforoperationsin
places of hard accessibility. In turn, main task of
the
Mobile Intervention Robot (MIR) is
intervention. Larger and heavier, it will be
equipped with manipulator and set of sensors
intended for determination of threat levels. The
largestofthreerobotswillbetheMobileEnhanced
FunctionalityRobot(MEFR).Massofabout300kg,
capabilityofcarryingweightsofmassupto
40kg
withamanipulatorofrangeof2meters,structure
enabling the installation of additional devices:
sensors,negotiationpackageorpyrotechnicguns;
UnmannedAerialVehicleUAVitisdesignedto
provide online data from the operation site.
Owingtocamerasandothersensorsinstalledon
boardthepersonincommandofactionwillhave
attheir disposal a wide picture of situation from
theplaceofintervention.
All components of
the Proteus will be mobile,
whichwillenabletheirtransportationtotheplaceof
intervention, and modula r structure of the whole
allows for rapid adaptation to the specifics of the
particular action. All system components will be
equipped with a coherent communication system,
whichenablesthemtointeractintheaction,
evenin
cases when they are deployed in different units.
Thanks to the statement of the needs of the specific
operationofdifferentcomponents,eachtimeitwillbe
abletobeadaptedtothenatureofthethreatandthe
scaleandtypeofactivities.
2.3 Proteuscommunicationsystem
architecture
The main objective implemented by the project
PROTEUS communication system is to provide
efficient and effective methods of communication
between all elements of the integrated system to
support counterterrorism and anticrisis activities.
Based on “Tactical and Technical Assumptions”
documents for the specific operations and on
reference scenarios for
different actions, the
integrated architecture of the PROTEUS
communicationsystemhasbeendeveloped[2].
Ensuringeffectivecommunicationbetweensystem
componentsrequirestheuseofdifferentsystemsfor
differentapplications.Oneoftheprimarytasksisto
create a system that allows efficient transmission of
image data, voice and telemetry from
mobile robots
andunmannedshipflyingrobotsforbothoperators
and the mobile position management the action. An
equallyimportantelementistoproposeasolutionfor
the transmission of signals control the operation of
robot.
Inbothofthesesystemsimportantissuesareboth
ranges,whichareassumedtobe
achievable,aswell
asdelaysintransmissionofsignalsinbothdirections
(small enough to be able to smoothly control the
operation of robots by means of video signals
received from them). Due to the fact that there has
beenseparationofthemobilecontrolstationfromthe
237
position of the mobile robot operators, it is also
necessary to design a dedicated radio link just to
transfer between these system components, with the
useofthetransmissionlinkwhichcouldbecapableto
transmitfullinformationgatheredfromalltherobots
( transfer stream of high bitrate),
also with strict
restrictions on the ranges and delays. An important
element of the system is also providing voice
communicationbetweentheparticipantsoftheaction
and the communication system with the outside
world.
Duetothecomplexstructureofthesystemitwas
not possible to propose a single,
integrated system
thatcancombinedifferentrequirements.Therefore,to
ensuretheparticularfunctionalities,thestructurehas
been proposed composed from several
complementarycommunicationssystems.Duetothe
demands of the need to ensure low latency data
transmission and constant transmission of images
fromdifferentrobotsitseems reasonabletodividethe
communication system for dedicated to each task
subsystems:
Thesystemfortransmissionvideodata,voiceand
telemetryfromUAVandmobilerobots,basedon
broadcasting transmission, allowing to receive
informationfromtherobotsbothbyoperatorsand
mobilerobotoperationcentre;
Lowrate communications system to transmit
control data to the robot, also used for the
transmission of telemetry data between system
components;
The above two systems are integrated in one
chassisandlocatedattheUAVandmobilerobotsand
are the main element of this paper. However, there
are
alsothreeadditionalcommunicationsystemsused
fordifferentapplications:
Mobilecommunicationsystemforcommunication
betweenmobilecommandcenterandmobilerobot
operatorcentre,dedicatedtotransferinformation
collected from all the robots to the command
center,inordertoillustratethetacticalsituation;
Thesystemforvoicecommunication,allowingfor
voice communication between the participants of
the action and to transfer small data from the
sensors (implemented as a system that resembles
thefunctionalityofradiocommunicationtrunking
system;
The system for external communication which
offers highspeed access to external network and
capableofusingbothavarietyofexternalsources
(meteorological services,databases, external
expertise, ...) as well as access to external
departmentalandtelecommunicationsnetworks;
The main challenges facing the designers of
communication systems within
the project , are
related primarily with the need to ensure wireless
transmission over long distances while providing
verylowlatencyandworkinginvarious,sometimes
extreme environmental conditions. Established
communication systems have to be flexible and
modularsolutionswhichmeetthestrictrequirements
forimmunity,compatibilityandoveralldimensions.
Carried
out work related to the latest
developments in multimedia techniques (efficient
hardware implementations of source encoders and
multiplexing mechanisms of data) as well as with
issues of radio communication (channel encoding,
antenna systems, propagation). The project uses the
advantages of various elements of the different
networktypes(broadcastsystemsbased
onDVBT/
H radio networks, data transmission systems,
telecommunication systems) for specific tasks and
functionalities.
3 INTEGRATEDSYSTEMFORCOMMUNICATION
WITHUAV
Thesystemforremotecontrollingandcollectingthe
multimedia data from UAV is aimed to enable
transmission of audio, video and data with a
relativelyhighdata
rates.Itisasystemofvideo,voice
and telemetry data transmission from mobile robots
and UAV, based on broadcasting transmission. The
information is transmitted to both operators and
mobile robot operator centre. Based on Tactical and
Technical Guidelines and reference scenarios of the
potential actions (documents prepared by the
emergency and security services), there have been
basicparameters and requirements tobe met bythe
specifiedcommunicationsystem.
Basic requirements for the system indicate which
particularly important parameters must meet the
system to enable the application for receiving
information from the UAV. The system should
providedataratesofseveral
Mbit/satrangesindirect
communication UAV‐operator of up to 10km.
Anothervery importantrequirement is the
transmissiondelay‐includingtheprocessingtimein
transmitterandreceivermodulesitshouldn’texceed
100ms. The transmission should be encrypted using
theAES128protocol,andthemodulesshouldensure
properoperationat
ambienttemperaturesfrom‐30to
+50 ° C and relative humidity of up to 95%. An
important limitation is the maximum size of the
modules(limitedduetotheavailablefreespaceinthe
UAV) and the weight. Below main elements of the
systemwillbedescribed.
3.1 Sourceencoder
To
meetthehighdataraterequirementforthesystem
some manner of source encoding was needed. The
proposed encoder is compatible with H.264/AVC
standard with Main or High Profile. However, the
encoder does not have all the compression options
consistentwiththeseprofiles,asitdoesnot support
MBAFF mode,
the mode frame field at the
macroblock level, and only sequences consisting
exclusively of the frames, or only from the fields.
Furthermore, no Bframes are generated, which
would result in the formation of a significant and
unacceptabledelaysinthecircuitvideotransmission.
In the project there was assumed
also, that the
sequencesareencodedinstandarddefinition720x576
(576p), using only the frames of type I and P. This
allows to obtain the lowest delay between the time
youcollectvideodataanddisplayingthem.
238
Figure1.BlockdiagramoftheH.264/AVCencoder
TheencodertreatedasanindependentIPmodule
should be scalable to 1080p HDTV resolution with
increasing the clock frequency. It is assumed that a
proposedresolutionforPALtheclockof100MHzis
sufficient. Control of the degree of compression
ensuresthatthesizeofthestreamdoesnot
exceedthe
capacity of the radio transmission path and
thepossibleelementsofanetwork.
Audio encoding is done in parallel to video
encodingusingMPEG4/AACcoding.Anotherdevice
based on ARM microprocessor is used as a bridge
betweenEthernetandFPGAdevice.Ethernetisused
both for sending control
commands to encoder and
for sending encoded stream to transmitter.
Communication between FPGA and ARM is
performedwith use of EPI and I2Cinterfaces. ARM
microprocessor translates commands sent to the
encoderinATstandardtoI2Csignalscontrollingthe
device.PoweroverEthernet (PoE) is usedto deliver
powerto
thedevice.
Functional diagram of the proposed encoder is
showninFigure1.Thebasicprocessingunitadopted
in the encoder is a macroblock, however individual
modules can also operate on smaller blocks. The
processingofmacroblockwasdividedintofivesteps:
roughestimationoftraffic
accuratetrafficestimationandINTRAprediction
theDSPloop
modeselection
binaryencoder(entropy)
Alltheseelementshavebeenimplemented,tested
and verified in the laboratory environmentand
currently they are tested in the typical operation’s
conditions.
The target runtime platform of the source
encoding/decoding subsystem is a set of printed
circuitboardsstackedoneachotherintheformof
a
ʺsandwichʺ. Functional model was based on the
combined kits FGPA Stratix 3 (DKDEV3SL150N)
and ARM (DKLM3S9B96). The encoding unit uses
algorithms of high complexity, because of that
achievement of the assumed parameters of the
encoder is only possible with use of higherend of
FPGA
devices. Final version of encoder is based on
AlteraAriamodelFPGAdevices.
3.2 DSPBlock
Based on required parameters of transmission and
knowing typical operating conditions, DVBT [3]
system was picked for video transmission between
robots/UAV and operator or command center.
Broadcast transmission was set as one of the
requirements, and OFDM modulation used in the
systemhelpstopreventharmfuleffectsofmultipath
propagation,commoninurbanenvironments.DVBT
transmitter can be divided into two distinct parts:
digitalsignalprocessing(DSP)block,andanalogpart
ofthetransmitter.
Figure2.BlockdiagramofthePROTEUStransmitter’sDSP
block[4]
Digital part of the transmitter was based on the
FPGA device, allowing for parallel execution of the
algorithms [4]. The functional diagram of the DSP
blockispresentedinFigure2.EPIinterfaceisusedfor
incomingMPEG2transportstream,whileI2Cisused
to receive commands form ARM microprocessor
(implementing Ethernet controller as in encoder
module).AES cipher is used to prevent receiving of
the signal by offtheshelf devices capable of DVBT
and MPEG4 decoding. AES algorithmis uses ECB
mode, and 128 byte key. Channel coding and
modulationisdoneaccordingtoDVBTstandard.
All
thecoderatesand modulationschemesareallowed,
but transmission is limited to 2k mode (using 1512
active OFDM carriers). Hierarchical transmission
options were also omitted, as not needed by the
projectrequirements.
To ensure compliance with DVBT standard and
help validate DSP part of the transmitter gbDVB
Simulator
wasused.Testplatformforthesystemwas
basedonthesamedevicesasinencoder.TheStratix
structuresbelongtothehighestAlteraseriesoffering
the greatest potential, but with high power
consumption and price. Further evaluation of
hardware resources occupied by the transmitter,
allowedtopickmuchsmaller
andcheaperdeviceasa
target for final model. Altera Cyclone IV
(EP4CE75F23I7)was chosen.Finalmodelwasdonein
thesame“sandwich”technologyastheencoder.
3.3 RFradiotransmitter
One of the elements of the transmission system for
video, audio and data signal is a radio transmitter,
which enables
the oneway wireless link between
mobile robot and the operator and the command
center. This link is a transmission channel for video
239
signalsfromcamerasinstalledontheRM,makingit
possible to use them to conduct followsite or
remotely control a robot, it is therefore of
fundamental importance for the realization of the
mostsignificantfunctionalityofthesystem.
G
90
O
C/A
LPF
BPF2
C/A
LPF
DSP
I
Q
BPF1
μ
C
SPI
ADF4350
ADL5370
ATMega168
DAC904
DAC904
AVD
driver
Power
amplifier
Figure3.BlockdiagramoftheRFtransmitter
AVDtransmitterwascarriedoutaccordingtothe
flowchartshowninFigure3.Theinputofthedevice
arethetwopathsIandQintheformof14bitparallel
bus. These buses are used for sending samples of I
andQcomponentsoftheOFDMsignalgeneratedby
theDSPblock.Thedigitalsignalsareconvertedinto
analog signals using digital to analog converters
(DAC). These converters, Analog Devices AD9772A
[5] are characterized by the achievable processing
speed of not less than150 MSPS (million samples
per second), which is the value which gives the
analog signal with
bandwidth wider than expected
widthofthechannel (8MHz).Importantqualityof
those converters is built in 2x interpolation filter,
allowingforoversamplingintimedomain.
Oversampling is essential for generating OFDM
signal with good spectral characteristics. Most
importantly,itallows forfiltersoflesserordertobe
used.
Analog signals generated at the output of the
transducersaresubjectedtolowpassfilterwithtwo
identical lowpass filters (LPF) with a bandwidth
correspondingtothewidthofthechannel.Obtained
in this way signals are given to the input I and Q
quadrature mixer (ADL5370 module [6]).
The mixer
outputsignalissubjectedtofiltration(BPF1)deleting
the outofband mixing products, and passed to the
amplifierblock.
As a carrier wave generator (G), a module
ADF4350 [7] has been used. This generator
characterizes with a compact design, in which is
integratedcontrollerPLLloopandVCO
generatorin
order to significantly simplifying the design of the
transmitter.Choosingthecarrierfrequencyispossible
byappropriateprogrammingofthegenerator,which
isdoneviaSPIcompatibleinterface.Producedsignal
ischaracterizedbyalowphasenoiseandasignificant
level of harmonics. In order to remove harmonic
products, there was used the bandpass filter at the
outputofgenerator(BPF2).
For described above transmission path there is a
microprocessor controller (μC) assigned, developed
onATmega168microcontroller[8]ontheboardLO
TVASP. Its task is programming of the ADF4350
generator according to the instructions coming
from
thecontroller.Thissolutionincreasestheflexibilityof
thestructureofthetransmitter.Itallowsformoving
the issue of track configuration the programmable
electroniccomponentstoahigherlevelofabstraction,
allowing the driver software does not need to take
into account the structural details, and only care
about the fulfillment of functional requirements. An
additionaladvantageofthisapproachisthattheAVD
controller software will not require any changes to
modify the transmission track construction are not
due to expansion of functionality, but made for
example, to upgrade the transmitter or the
optimizationofitsparameters.
3.4
TCTMsubsystem
The aim of the TCTM subsystem is to enable the
transmission of the control signals to robots and
telemetry data from robots to the operators and
commandcentre.Thetransmitted data are relatively
low bit rates. The main task of this subsystem is to
ensurethecontrol of
mobilerobots byoperators via
the operator console, or directly from MROC. This
system is also responsible for the transmission of
telemetrydatafromsensorsplacedontherobots.
Asforbasicparameters oftheplannedsystem,it
was decided to use Ethernet 100Mb / s (RJ45). The
system should be
able to provide telemetry data
transmission and control with bit rate 20kbit/s
obtaining ranges analogous to the ranges of video
transmissionsystem.Transmissionsystemoperatesin
the ISM band (use of radio equipment in the band
freeddoesnotrequire a radio license). The required
standard 128bit AES encryption, the
keys are
providedbythecontrolunit.
For the purpose of the control and telemetry
systemtherehasbeenselectedrangeof863870MHz
Inthisrangeradioequipmentcanoperatewithpower
25mWerp,theonlyexceptionisthesubrange869.40
‐ 869.65 MHz where the equipment
is authorized to
work with the power of up to 500mW. It should be
noted that these frequency ranges are also intended
for ISM equipment. Devices operating in this band
must accept harmful interference which may be
causedbyISMequipmentandotherradiodevices.
In view of the determined requirements
for the
subsystem TCTM there were analyzed available on
the market and currently developed technical
solutionsfortheirfulfillment.
Controllingofthemoduleandusingtheinterfaces
isbasedontheARMmicroprocessor.Duetousethe
Ethernet,USBandpossibleCANinterfacestherehas
beenchosenmicroprocessorwithbuilt
insupportfor
these peripheral interfaces. In addition, due to the
large amount of software needed to support AES
encryption,amodulewithhardwareimplementation
of the encryption has been used. The required
transmissionspeedisslow,sothereispossibletouse
an ARM7 processor architecture with reduced to
48MHz.TheprocessorsintheARM7architectureare
now widely available from many manufacturers,
including minimization of dimensions of the