A Tdma Broadcast Satellite-ground Architecture for Atn

7/28/2019 A Tdma Broadcast Satellite-ground Architecture for Atn

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A TDMA BROADCAST SATEL L ITE / GROUNDARCHI TECT URE FOR THE AERONAUTICALTELECOMMUNICATIONS NETWORKMohammed A. Shamma, Rajesh S. RaghavanAnalex Corporation, Cleveland, OH 44142

Contract NAS3-00145, NASA Glenn Research CenterAbstract: An initial evaluation of a TDMAsatellite broadcast architecture with anintegrated ground network is proposed inthis study as one option for the AeronauticalTelecommunications Network (ATN). Thearchitecture proposed consists of a groundbased network that is dedicated to thereception and transmissions of AutomaticDependent Surveillance Broadcast (ADS-B)messages from Mode-S or UAT typesystems, along with tracks from primary andsecondary surveillance radars. Additionally,the ground network could contain VHFDigital Link Mode2, 3 or 4 transceivers forthe reception and transmissions ofController-Pilot Data Link Communications(CPDLC) messages and for voice. Thesecond part of the ATN network consists ofa broadcast satellite based system that ismainly dedicated for the transmission ofsurveillance data as well as En-route FlightInformation Service Broadcast (FIS-B) to allaircraft. The system proposed integratesthose two network to provide a nation widecomprehensive service utilizing near term orexisting technologies and hence keeping theeconomic factor in prospective. The nextfew sections include a backgroundintroduction, the ground subnetwork, thesatellite subnetwork, modeling andsimulations, and conclusion andrecommendations.1. I ntroduction

research stage [11. Several communicationlinks, technologies, and architectures wereconsidered which differ in complexity, cost,and the time frame for its implementation.Herewe are proposing an architecture basedon the following objectives:

- Cost: A system that takes intoaccount the initial cost ofimplementation. Considering thefact that such architectures are notmass produced, the initial costwill likely determine the expectedfinal costs.- New but tested technologies: In thiswe mean a system that relies ontechnologies that are new butalready tested as oppose to beingin the initial research stage. Alsominimum use of what is definedas older technologies is assumed.

- Enough Room for Technologygrowth: while the cost and thetechnologies in existence or nearterm existence determines themain architecture, it is importantto leave room for other not yetmature technologies to beimplemented within thearchitecture at hand withoutsignificant changes, Nonethelesswhere there may significantchanges required, they are noted.

The ATN proposed architecture is illustratedin Figure1. It is divided into three parts.l-The ground sub-Network whichconsists of (but is not limited) twomajor sub components:

The Aeronautical TelecommunicationNetwork (ATN) is comprised of manyentities which are under development or at aThis is a preprint or reprint of a p aper intend ed for presentation at aconference. Because changes may be made before formalpublication, this is mad e available with the u nderstanding hat it willnot be cited or repro duced without the permiss ion of the author.


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a-

b-

2- The

Surveillance System: ADS-B(modeS and UAT) groundtransceivers. Primary andsecondary surveillanceradars (modeS and Air TrafficControl Radar Beacon System(ATCRBS)).CPDLC and voicecommunications network:This consists of VDL 2,3,or4 communication transmittersand receivers (depending onwhich link will be chosen).All VDL links will be in theVHF band and hence will noteffect the surveillancesystems design.

satellite sub-Network whichconsists of two major parts:a-

b-

The next two sections outlines some ofthe details of the ATN parts discussed abovewith the ground links and the airplane nodesmentioned within. While the key element ofthis design comprises the integration ofsatellites with ground based networks, it isalso the architecture which is seen to meetbest all the objectives outlined in thebeginning, cost, new technology, and roomfor improvement.In summary, the architecture works asfollows; aircraft equipped with ADS-B(UAT or ModeS) transceivers transmit theirADS-B message to ground stations that arelocated approximately 150 miles apart(enough distance to receive from anyaltitude). At the same time, aircraft whichare not equipped with ADS-B transceiverswill be detected by the primary or secondarysurveillance radars. The ADS-B groundreceivers, and the radar stations will all beconnected via ground links (such as T1 orfiber, or possibly microwave, or acombination) to the satellite Pround station.

Satellite ground stations usedto transmit TIS-B and FIS-Bmessages collected from allthe ADS-B and radar groundtransceivers.The satellite itself used torelay the satellite groundstations TIS-B and FIS-Bmessages to all the aircraft.

3- Ground links used to connect allthe surveillance, VDL, andground satellite stations to eachother or to main stations.consistsof VDL, ADS-B, andSatellite equipment.

4- Theairplanetransceivers, which

Figure 1: ATN major components

"Satellite ground stations are presumed to belocated in strategic locations such as at theground control centers of each of the majorairspace sectors. Data collected will befiltered to remove any redundant messagesreceived by more than one system (i.e. oneaircraft message seen by more than oneADS-B receiver as well as with radar) and aTIS-B message will be constructed per eachto transmit to the satellite. The satelliteground stations will access the satellite viaaTDMA accessing scheme hence at eachsatellite ground station the filtered data willbe queued and a burst will be transmittedwithin the corresponding time slots. Thesatellite will receive those messages andsimply broadcast it down to the aircraftwhich will listen to the slots of interestbased on the region of interest. At the sametime while this is happening, CPDLC dataand voice will be transmitted and receivedvia ground VDL links with no satelliteusage. Also, FIS-B messages will becreated and sent along with TIS-B messagesfrom each of the ground stations to bebroadcast to all the aircraft. The systems


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can have redundancies in the form ofredundant satellite transponders, redundantground stations or reliance on radar vs.ADS-B, redundant ground links via othermeans if necessary. The details of thoseredundancies were not investigated for thisstudy

2. The Ground NetworkThe ground network, shown in Figure2,consists of a network of ground-basedradar sites, as well as stations listening toADS-B transmissions from nearby aircraft.

..........~ '. . . . \ ......'G'G"--'- d \-Figure2: Surveillance GroundSubnetwork

The ground-based radars are of threetypes: primary surveillance radars, locatedat major airports, higher power en-routeradars,and secondary surveillance radars co-located with the first two types, whichinterrogate transponders on board aircraft inthe vicinity. The secondary surveillanceradars are of two types: Air Traffic ControlRadar Beacon System (ATCRBS) and ModeSelect (Mode S.) The ATCRBS radars, inturn, are divided into two further types:older radars interrogating aircraft at a higherrate using a sliding window, and newermonopulse radars which interrogate aircraft

at a slower rate. Secondary surveillanceradars are described further in [2].

Supplementing the radar systems areADS-B ground stations which listen toADS-B transmissions from aircraft sent viathe Mode S and Universal AccessTransceiver (UAT) data links. Commercialaircraft, and other high-performance jetaircraft optionally broadcast their position,velocity, and intent information using ModeS, while most general aviation aircraftoptionally use UAT. The minimum aviationsystem performance standards for ADS-Bare described in [3],and descriptions of theMode S and UAT data links as used inADS-B can be found in [4]and [ 5 ] .

The ground-based ADS-B listeningstations, and the primary, enroute, andsecondary surveillance radar sites feed theirinformation to TIS-B ground stations, whichprocess the incoming data to removeredundant information. The TIS-B groundstations then uplink filtered data to aircraftvia a satellite network to provide a completesituational awareness picture to aircraftequipped to receive TIS-B information.

Redundant data needs to be removedfor the following reasons:1) ADS-B transmissions from thesame aircraft may be heard bymore than one listening station

in the ground-based network.However, that informationshould be relayed via satelliteonly once.Even when an aircraftbroadcasts ADS data, it isprobably being tracked byground-based radars as well(except in remote areas.) Thesatellite ground stations shouldonly uplink whichever data iscollected that is of a higherquality.

Each listening station in the groundnetwork generates ADS-B packets at aspecified rate for the purposes of thesimulation, as opposed to actually listening


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to many aircraft. This is done in order tospeed up the simulation. The ADS-B trafficis generated at the intervals specified forindividual aircraft in RTCA DO-260A, the1090 MHz Extended Squitter MOPS,divided by a mean number of aircraft perground station, defined at simulation time.

The packets transmitted are 112 bitMode S packets, again chosen forconvenience. ADS-B and TIS-Binformation relayed to the satellite groundstations in a real system are likely to beMode S Extended Squitters. Althoughdifferent packet formats may be used withinthe SATCOM network, in the currentexperiment the ModeS format was retainedbecause in a SATCOM system, each groundstation will still need to relay the 56 bitADS-B payload, as well as the24bit ICAOaddress. Using a 112 bit packet allows forfour bytes of header information, at leastsome of which will definitely be present inany SATCOM link.

The primary reasons for the existenceof the TIS-B satellite network can bedescribed as follows:

1) Not all aircraft are equippedwith ADS-B, and even aircraftthat are equipped may be usingeither ModeS, or UAT, but notboth. Aircraft sending ADS-Binformation, will receive ADSinformation broadcast over thesame data link (Mode S orUAT) that the aircraft use totransmit their own ADS-B data.An external source (the satellitenetwork) is needed to providedata about aircraft using theother data link, or about aircraftwhich are not transmittingADS-B information at all. Thelast group of aircraft are onlyseen by ground-based radar.The range of ADS-B is limitedby the transmitter power of thesending aircraft, and by theinterference environmentpresent between sending and

2)

receiving aircraft. Theinterference environment forMode S ADS-B consists ofreplies to ModeSand ATCRBSground radars which are sent onthe same frequency (1090MHz) The interferenceenvironment for the UAT datalink consists of military JTIDStransmissions and interferencefrom TACANDMEnavigational aids.

The ground network is structured in ahierarchical fashion. ADS-B listeningstations and primary, enroute, andsecondary surveillance radar sites, feedtheir information to regional processingcenters via either T1 or optical links.The regional centers in turn, forward thecollected information to one or moresatellite uplink ground stations. Multiplesatellite uplinks may be used to combatthe effects of local weather disturbanceson the uplink transmissions. Thedownlink to aircraft will not be asaffected by weather since most aircraftusing the service will beflying above thecloud layer.

3. The Satellite NetworkFigure3 shows an OPNET [6] network

layout which also serves to illustrate thearchitecture of the satellite sub-Network.The figure is shown for the continentalUnited States (CONUS) but can be easilygeneralized to other areas of the globe. Thesatellite ground stations are assumedcollocated (not required but preferably foreconomical reasons) with the regionalcontrol centers hence there are 20 within theCONUS. In addition to the 20 stations weshow a central processing center that isconnected to all stations which can be usefor multi purposes including redundancymanagement in case of weather, malfunctionor upgrade reasons, global data


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manipulations, and other. The Geostationarysatellite is located at (W101 degrees) toserve those stations. Again the satellitelocation is chosen to serve theCONUS andsurrounding area but can be used for most ofthe North and South American continentswith more satellites needed to fill the globeif necessary.

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Figure 3: CONUS Satellite sub-Network(note that each node above corresponds to asector withasatellite earth station andADS-Bground stations as shown by Figure 2. Thesatellite node is not shown).

As described in the last section and in theintroduction, each of the ground stations willbe transmitting a burst of messages at aTDMA rateof 0.01second time slots with a0.005guard band. Hence for 20stations weare able to receive a TIS-B or a FIS-B fasterthan the minimum required rate of 1 persecond. Note the time slots can be increasedfive fold and still meet that requirement.Again if more ground stations are added tofill other regions then correspondinglysmaller time slots will have to be used.Other types of accessing schemes can beconsidered, none the less TDMA is widelyused and hence from a implementation pointit is an acceptable choice. Also, since forthis architecture, we are not requiringuplinks from the airplanes to ground (or noReturn channels), as well as the broadcastfeature, the need for more capacity via otheraccessing schemes is not the main issue. In

J plink Frequency(GHz) 29.750%miink Frequency(GHz) 19.95LGSO SatelliteTansponder ParametersJ plink qmder saturation luxdensity (dBW/mh2) -96Xponder saturatcmElRP (dBW) 54

Uplink receive noise temp (K)Uplink receiveCYT (dWK) 13.9

575.44Uplink receive gain (dBi) 41.50000047

telliie Aiiitude (km) 35786TCHubStation Parameterstenna diameter( mmit gain (dBi)

.. ~Wpower(dBW)mit ElRP (dBW)ewgain (d8i)ystem Noise Temp (d6-K)EwCYT ( d m 2.455.2620589217(50.12watts)72.2620589251.7911775226.67 (464.52K)25.12117752

Elevation angletosatellite (deg) 40Aircratt Terminal Parametersewgain (dB)ystem Noise Temp (dEK)EWW(dB/K) 3725 (316.23K)12

1OOOOOOO

4013.3086495743.3456752237780.30419-213.4628304-0.461666838-14.56591541-185.2728554

37780.30419-209.991949-0.447838163-1316.23K79.41685937

76.414335587.414335582

EWNo (dB) lb6;QPSK; r=1/2 convcode 4.5

Table1: Satellite System Parameters perTransponder (Final resultsof link marginshown obtained from more detailed modelsr71)


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[7] more results are shown for trade offbetween TDMA and CDMA accessing. Insummary the choice of TDMA for thisarchitecture is appropriate because we havefixed ground links that can be synchronizedwith less effort, as well as the fact that wecan use the full power settings. The linksproposed are not rigid at this stage but arerecommended to be in the Ka band mainlyto reduce the antenna sizes to be mounted onthe aircraft [SI. Other advantages of Kaband such as higher bandwidth availabilityare not applicable or critical since mobileand broadcast FCC requirements limits theavailable bandwidth to500Mhz regardless.The C band, Ku band, and Ka band all havethe same allocations, hence the main thrustwill be antenna size and available spectrumat time of implementation. None the less, ifthe antenna sizes and cost of mountingissues are not taken into account, then inreality the lower bands (Le. C band) will bebetter with respect to rain, and weatherattenuation. Table 1 below shows some ofthe parameters assumed for the satellitesystem per an assumed 27 Mhz transponder.

4.Modeling and SimulationsThe previous two sections summarized

the ground and satellite networksrespectively and Figures 2 and 3 wereobtained from the architecture built usingthe simulation package OPNET [6]. Theaircrafts were simulated by transmittingADS-B message sets directly from the ADS-B ground stations (shown in Figure 2) at themean rate of 10 ADS-B sets (correspondingto 10 aircraft per ground station perARTCC) with a standard deviation of(0.4*mean rate) using a uniformdistribution. The reason for not includingthe aircraft as separate mobile nodes wasmainly to speed up simulation time and notdue to inability to do so as per thedescription in Section 2. The one mobilenode in Figure 3 was included for testingpurposes to check reception quality at higheraircraft speeds.

The data traffic modeled in thissimulation was only ADS-B messagespurely for matter of convenience. The datatraffic could conceivably include TIS-Bmessages generated from radar, as well asFIS-B information as well, provided thatadditional resources are allocated (i.e. higherbandwidth transponders, or additionaltransponders on the satellite and groundends).

Figure 4 is a plot of two of the groundstations. The top plot shows the TDMAburst transmission rate for one groundstation from Figure 3 (and Figure 2).Similarly, the bottom plot shows the TDMAtransmission rate for another ground station.The other stations are not shown, but theprofiles will look similar taking differenttime slots per station. The time betweeneach burst of TDMA transmissions is seenas equal to the total number of stationsminus 1 (or 20-1=19) multiplied by eachstation time slot (in this case 0.01 sec).

Figure 4: Plots a and b, TDMAtransmissions from satellite groundstations(only two station shownof the20)Also, it is worth noting that during oneTDMA time slot, the burst rate is atmaximum setting until all the packets in theground station queue are transmitted. If thequeue is emptied before the end of one timeslot then the transmitter will stay idle unless


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it receives any packets within that time inwhich case it will transmit those directly (atleast based on the present design).The satellite on the other hand is receivingfrom all of the ground stations and hence itsdata rate profile has no gaps (assuming allstations are active) and that is shown by thetop plot of Figure5. Since the satellite is abent pipe, it simply re-transmits all the datait receives at the downlink frequency whereit will be intercepted by the receiving mobile(or fixed) nodes. The second plot of Figure5 shows the received S/N at the satellitenode. It is worth noting that this value islarge compared to that shown in Table 1ofthe link budget analyses due mainly to notincluding rain attenuation (14.56 db) (Le.clear sky condition) along with polarizationand atmospheric attenuation effects (1 dband 0.5 db respectively) in the channelmodel of the simulation used. Note that ifwe subtract those values from the S/N valueseen in plot, we arrive at the values showninTable 1 for the Uplink taking into accountthe 20 Mhz of bandwidth assumed toconvert to S/No in db-hz. In numericalterms (30-14.4-1 0.5)+1OLOG(20e6)=87.1which is very close to the values found inTable 1for the S/No of 85.3. The reasonfor the 1.8 db difference comes from avariation in the antenna gains (amounting toalmost 0.7 db) and small path distancedifferences due to the locations of thestations and the satellite. Hence, we hadkept that in mind as we arrived at the verysmall BER using the standard BER tablesfor QPSK in OPNET (not shown). Even ifwe included those additional terms wewould still have negligible BER thatmatches with the link budget results ofTable 1.The data rate from each TDMA satelliteground station is set at 10e6 bits/sec pertransponder on board the satellite using YzFEC and QPSK. Note in Table 1, it isassumed that the Bandwidth occupied by achannel with data rate Rb is 2*Rb (which isa worse case formula) and hence thebandwidth occupied for 10e6 bits/sec is 20Mhz. This bandwidth fits well within one

typical satellite transponder with enoughadditional room for higher data rates that areneeded for transmission of other than TIS-Bmessages such as FIS-B, control and pagingchannels, and others. Needless to say ifhigher data rate are needed then the use ofhigher bandwidth satellite transponders is anoption, or the use of more than one isanother more costly option. Otherperformance parameters were observed fromthe simulation that are not shown hereincluded queue sizes and number of packetsreceived, power levels, and several more.

Figure5: Plots a and b, TDMA receptionsat satellite (first Plot shows bits/secthroughput, second plot show S/N in db)On the downlink side, the signal wasobserved from a moving mobile node(airplane in flight), and at the fixed earth

stations. With clear sky conditions thereception between the aircraft and the earthfixed nodes differs due to the different gainsof antennas, and the path distance (hencepath loss) all stated in Table 1. The plots ofFigure 6 shows the received signal data rateat the mobile node (or aircraft) as per the topplot. This is the same profile as thatreceived by the satellite becauseof the bentpipe operation of the satellite alreadydescribed. Also the second plot shows theS/N received at the aircraft node. Again justas in the Uplink verification, we see herethat the values are very similar to Table 1


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taking out the polarization effects of 1 dband the atmospheric attenuation of 0.5 db.Note the rain attenuation is not included dueto the aircraft being at higher altitudes in theEn Route phase. With that the numerical0.5)+101og(20e6)=79.3 which is practicallythe same as the number shown in Table 1.Again the BER are very negligible at theS/N from the QPSK BER vs. S/N standardcurves.

calculation shows (7.8-1-

Figure 6: Reception at aircraft (first Plotshows bitslsec throughput, second plotshowsS/N in db)Finally, the plot of Figure 7 shows atypical queue size in packets at a satelliteground station. As predicted, the queuebuilds up until its time for the beginning ofthe stations time slot at which case is dropsdown rapidly based on the given TDMAburst rate. Although the packets arrivingfrom all the ADS-B transmission are randomin quantity due to the uniform distributionimposed, they average in the mean to values

that are predictable. If more packets were tobe sent (via increasing the mean of the ADS-B sets transmission, or the number ofaircrafts) to values larger than 10, the queuewould have kept building up due to inabilityof the TDMA processor to catch up. Theway to compensate for higher rates or largernumber of aircrafts is by utilizing higherbandwidth transponders, or by using

multiple transponders for the satellite andthe ground ends. In the next section, morecomments are made with respect to theoptions available to increase overall systemcapacity in terms of data rates or aircrafts.

Figure 7 Queue build up and emptyoperation at a typical ground TDMAtransmitter.

5. Conclusions andRecomrnenda ionsA simulation was built and a proposedarchitecture was presented for the use ofAMSS for the ATN. Specifically, the use ofsatellite links for the transmission andbroadcastingof TIS-B and FIS-B messages

was proposed as an alternative to groundbased proposals. The architecture considersuse of ground ADS-B mode S, and UATtransceivers as well asVDL, and secondaryand primary surveillance radars, all fortransmission of ADS-B, CPDLC, andpresent radar operations. In addition, asingle (and if necessary more) satellitetransponder is used in a bent pipe methodalong with satellite ground stations, one foreach of the sectors. The satellite earthstations would collect ADS-B and radarinformation from all the aircraft within itssector, filter the data to removeredundancies and to create TIS-B messages.The TIS-B messages are then queued along


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with other data such as FIS-B andtransmitted at the TDMA time slotsdesignated for each earth station. Thesatellite receiver takes all the messages fromall satellite ground stations and simply downlinks the data which will then be received byreceivers on board the aircraft. The presentarchitecture does not require a satellitetransmission capability on board the aircraft(only reception) and hence simplifies thesatellite as well as the aircraft transceiverdesign. The aircraft receiver will be able toget the data from any location in theCONUS (or satellite coverage area) and it isenvisioned that on board displays can feedthat information into a CONUS, or localmaps which will show the aircraft in a givenarea. This capability will be useful for freeflight planning, for initial flight plans, andfor predicting future traffic patterns at anylocation based on the intent messages of theADS-B. Also, last but not least the FIS-Binformation will be more readily availablefor not only the local areas but for any areawithin the satellite earth stations and satellitebroadcast coverage area. The availability ofinformation that is not simply localized tothe aircraft position will be useful not onlyto the pilots for flight planning, but also forthe airlines, and the FAA center.In summary the advantages of using thesatellite links and the architecture proposedhere are among many:

broadcast capability to wide areas andareas that are outside the range ofground stations signals such as overoceanic regions.

- The reception only (or broadcastoption) requirement for the aircraftsimplifies and reduces the cost of theaircraft equipment as well as thesatellite system itself. The broadcastcapability of satellites is ideal forsuch an application.Having TIS-B, and FIS-B datareadily available about any area (orwithin CONUS for a non-globaldesign) is beneficial for the airlines,

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FAA, and pilots in making flightplans, free flight, and scheduling.The satellite links are reliable for EnRoute.

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- Each transponder on the satellite,with a data rate of 10 Mbps, iscapable of supporting twenty ARTCCuplink sites, each being fed from 33TIS-B ground stations, each relayingADS-B information from a mean of10 aircraft +/- 40%. With twotransponders on the satellite each at adifferent frequency, it would bepossible to support 660 aircraft perARTCC, with TDMA slots of 0.02seconds, with one transponderhandling eastern traffic, and the otherhandling western traffic.Using two transponders each with a27 (or higher bandwidths such as 36Mhz), it is possible to realize theproposed design. Hence for a shortterm application it is a cost effectivemethod that can utilize satellites thatare already in operation by simplyleasing one (or if needed more)transponders. Additionallyredundancy can be achieved by usingother satellite transponders for backUP.While other accessing schemes couldhave been considered, TDMA is anacceptable option that is not difficultto achieve especially since the groundstations are fixed nodes (as oppose tomobile) hence the synchronization isnot as difficult. TDMA is used inmany existing satellite architecturesand hence the capability, andequipment is readily available. Atthis point it is also worth noting that adynamic TDMA slot assignment canalso be considered as an option toaccommodating the differences in thedensity of the airspace over differentsectors.

-

-

increase throughput by


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- The use of the ground part of thisarchitecture conforms with theaccepted standards that are proposingVDL, Mode S and radar for thevarious communications andnavigations services for the ATN.Although in the present architecturethe satellite earth stations werelocated at each sector control center,it is possible to reduce the number ofthem assuming the sectors data canbe shared. Nonetheless, the use ofone satellite station per air sector isbeneficial from many aspects:a- It can provide redundancy in caseof weather, service outage, or any

other reasons that may requireone of the station to stopoperating.

b- For a future outlook where theremay be a possibility of utilizingspot beams, for uplink capabilityin which case gateways will benecessary and hence theavailability of such stationswithin each spot beam is useful.

Possible disadvantages of theFor other than En Route, the satellitelinks can fail with a small percentagewhen receiving during rain. That isfor altitudes below the clouds (orbelow 5 Km) it is possible that thesignals will fade causing a loss ofreception. This disadvantage can beovercome at airport locations for theaircraft that are landing or taking offby providing back up ground basedbroadcasts via an alternate link. Theinformation in that link could belocalized to reduce data rates until thesatellite signal becomes available.Note the rain fade will also effect thetransmissions of the satellite earthstations, and in that case it isnecessary to re-route the data usingthe central ground station to transmitfrom else where. Hence in that case

-

architecture proposed are:-

it is more feasible and not as difficult(in addition to being a necessity) totransmit the information.

- While the satellite broadcast cancover remote areas, oceanic or other,the lack of ground stations in thoseremote areas makes the availability ofthe messages to be transmitted toground (which include ADS-B, UAT,CPDLC) an issue. Unless HFfrequency is assumed, or a morecostly satellite uplink design isavailable, that disadvantage is thereregardless of the useof satellite linksfor broadcasting.

6. AcknowledgementsThe work in this paper was performed

as part of the research into Communications,Navigation, and Surveillance (CNS) systemsfor the Distributed AirlGround TrafficManagement (DAG-TM) concept [9]. TheDAG-TM Concept is funded by theAdvanced Air Transportation Technologies(AATT) project office at NASA AmesResearch Center at Moffett Field, CA. CNSstudies for DAG-TM are being performedby contractor personnel of AnalexCorporation at NASA Glenn ResearchCenter in Cleveland, OH.References[1lNational A irspace System Architecture-FAA,http:l/www. aa.govlnasarchitecture[2] Stevens, Michael C., SecondarySurveillance Radar, Artech House,Norwood, MA, 1988.[3] RTCA DO-242A, Minimum AviationSystem Performance Standards for ADS-B,2002.[4] RTCA, DO-260A, MinimumOperational Performance Standards for 1090[5] RTCA, DO-282, Minimum OperationalPerformance Standards for UAT ADS-B,2002

MHz ADS-B, 2002


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[6] Opnet Modeler, Opnet TechnologiesInC., Bethesda, Maryland,http://www.opnet.com.[7] R. Kerczewski, M. Shamma, R. Spence,R. Apaza, Emerging AeronauticalCommunications Architecture Condept forFuture Air Traffic ManagementRequirements, 8* Ka Band UtilizationConference, Italy, September, 2002.[SI M. Shamma, An Evaluation of CDMAand TDMA Communications Architecturesfor the Aeronautical Mobile SatelliteService, 21st Digital Avionics SystemsConference in Irvine. California.[9] AATT Project, ASC Program, NASA,1999, Concept Definition for DAG-TM,Ver. 1O, Moffett Field, CA.

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A Tdma Broadcast Satellite-ground Architecture for Atn