DoD Uplinks Status ReportDane E. Ericksen, P.E., CSRTE, 8-VSB, CBNT

Chairman, SBE FCC Liaison CommitteeChairman, ATSC TSG S3 Specialist Group on Digital ENG

Senior Engineer, Hammett & Edison, Inc., Consulting EngineersSan Francisco, California

Abstract

In the ET Docket 00-258 Fourth MO&O, theFCC affirmed that DoD uplinks could useboth the 1.8 GHz federal government SGLSband and the refarmed 2 GHz TV BASband, albeit subject to successful frequencycoordination with incumbent BAS, CARSand LTTS licensees. As a result of thatdecision, SBE has been in contact with DoDregarding how those uplinks will protect2 GHz TV BAS operations. This paperreports the results of the first two SBEmeetings with DoD representatives.

Background

In the July 7, 2003, ET Docket FourthNotice of Proposed Rulemaking (NPRM)the FCC proposed authorizing up to elevenDepartment of Defense (DoD) tracking,telemetry and commanding (TT&C) satelliteuplink stations that now use 1,761–1,842MHz federal government Space GroundLink Subsystem (SGLS) band to be able toalso use the refarmed 2,025–2,110 MHz TVBroadcast Auxiliary Services (BAS) band.This move was triggered by the reallocationof the 1,710–1,755 MHz federal governmentband to the commercial sector, for still moreAdvanced Wireless Services (AWS)spectrum.

This, in turn, supposedly meant findingadditional capacity for DoD uplinks nowoperating in that band due to the relocationof other Federal users from 1710-1755 MHzinto the SGLS band. DoD, IRAC(Interdepartmental Radio AdvisoryC o m m i t t e e ) , N T I A ( N a t i o n a lTelecommunications and Information

Administration (NTIA), and, of course, theFCC, decided that the 2 GHz electronicnews gathering (ENG) band would be agood place for these relocated DoD uplinks.The DoD uplinks are located in Camp Parks(CA, near San Francisco), New Boston(NH), Denver, Albuquerque, CapeCanaveral (FL), Colorado Springs, Lompoc(CA), Kaena Point, Oahu (HI), ProspectHarbor (ME) and Guam. The uplinks willhave maximum equivalent isotropic radiatedpowers (EIRPs) of up to 104 dBm operatinginto a 13-meter uplink dish. The side lobesuppression of the uplink dish is only about60 dB or so, meaning that the leakagetoward the horizontal, and therefore towardENG receive only (ENG-RO) sites, could beas high as 44 dBm EIRP. Since a typicalENG truck has an EIRP of around 65 dBm,this means that the DoD uplinks would haveco-channel "leakage" at low elevation anglesthat could be only 20 dB less power than themain beam power of an ENG truck.

Despite the opposition comments of theSociety of Broadcast Engineers, Inc. (SBE),the National Association of Broadcasters(NAB), the Association for MaximumService Television (MSTV), and others, inthe October 21, 2004, ET Docket 00-258Seventh Report and Order (R&O) the FCCdecided that DoD uplinks in the 2 GHz TVBAS band could be made to work.

SBE, NAB and MSTV then filed Petitionsfor Reconsideration of the Seventh R&O,but in an April 11, 2006, MemorandumOpinion and Order (MO&O) theCommission affirmed its Seventh R&Odecision. Thus, the issue of the wisdom ofcreating a co-channel allotment with 2 GHz

TV BAS stations, and also CommunityAntenna Relay Service (CARS) TV Pickupstations and Local Television TransmissionService (LTTS) stations, is moot. The taskfacing broadcasters is now to make thesharing work. Perhaps the brightest spot ofthe Seventh R&O was the unequivocaldecision that the newcomer DoD uplinksmust protect incumbent TV BAS, CARSand LTTS operations. Further, in the FourthMO&O, the Commission clarified thatprotection of 2 GHz TV BAS operationsincludes the protection of existing ENG-ROsites.

First DoD/SBE Meeting- El Segundo

The first DoD/SBE meeting occurred onNovember 8, 2006, in El Segundo,California, at The Aerospace Corporation.The Aerospace Corporation is a majorgovernment non-profit consulting firm thatsupports DoD in all of its space programs.Present for SBE were President ChrissScherer, Immediate Past President RayBenedict, Director Ralph Beaver (Chairmanof the SBE Frequency CoordinationCommittee), Director Dane Ericksen(Chairman of the SBE FCC LiaisonCommittee), SBE General Council ChrisImlay, and SBE Executive Director JohnPoray. There were nine DoDrepresentatives, three of which were activeduty USAF officers, plus four civilian DoDand two Aerospace Corporation persons.

Decisions from the first meeting included:

1. While no agreements have been reachedformally, DoD considers that the protectioncriteria for ENG-RO sites would be a noisethreshold degradation of no greater than 0.5dB has merit (this was the protection criteriacited in the Seventh R&O).

2. DoD indicated that they will make everyeffort to avoid operation in the 2,025-2,025.5 MHz lower Data Return Link (DRL)band, and in the 2,109.5-2,110 MHz upperDRL band. This is in recognition of theimportant role that the forty 25-kHz wide

DRL channels are likely to play in futureENG operations.

3. While the DoD/SBE meetings areintended to provide guidance to both DoDand broadcasters regarding protection ofENG operations, the actual frequencycoordination for each DoD uplink operatingin the 2 GHz TV BAS band will have toinclude all local TV BAS, CARS and LTTSlicensees. Meetings with these locallicensees will be held in a venue near the to-be-converted uplink, and will include thelocal above-1 GHz BAS frequencycoordinator.

It should be noted that a 0.5 dB noisethreshold degradation criteria constitutes afrequency re-use criteria, which is animportant element of an overarchingfrequency-sharing criteria. Under frequencyre-use, the two operations are engineered sothat both co-channel transmissions can occurin the same area and at the same time,without interference being caused to eitherparty. This is commonly done for fixed,point-to-point terrestrial microwave links.However, those links have the considerablebenefit of using highly directive, large-diameter parabolic dish transmitting andreceiving antennas, and typically beingcross-polarized with a nearby co-channellink. Additionally, the path geometriesbetween fixed links in known in advance,and does not change. Unfortunately, theseconditions do not apply for ENG operations,which, by their very nature, are itinerant ormobile in nature, and are often notscheduled in advance (although some ENGuses, such as the coverage of nationalpolitical conventions or sports coverage, canbenefit from advance frequencycoordination).

Other technical details learned during thefirst meeting were than the uplink disheswould be 13-meter antennas rather than the10-meter antennas estimated by SBE in itsFourth NPRM comments. Also that themaximum Unified S-Band (USB) EIRPwould be 104 dBm, as opposed to the 115

dBm maximum EIRP for SGLS operations(USB is the term the NASA and DoD usesfor the 2 GHz TV BAS band). Further, itwas learned that the 104 dBm EIRP anemergency, spacecraft-in-trouble, powerlevel. The EIRP typically used for normal,99% of the time communications would be a14 dB lower 90 dBm EIRP. Finally, it waslearned that the occupied bandwidth of atypical USB uplink signal would be about 2MHz.

Second DoD/SBE Meeting- Las Vegas

The second SBE/DoD meeting was held onJanuary 11, 2007, in Las Vegas, Nevada

(this coincided with the ConsumerElectronics Show and the winter SBEExecutive Committee meeting). Preliminaryinterference calculations for the first DoDuplink scheduled to operate in the 2 GHz TVBAS band, at Vandenberg AFB nearLompoc, California, were reviewed at thismeeting.

The validity of the SBE-proposed 161 km(100 mile) inclusion radius around a DoDuplink was tested. As shown by Figures 1, 2and 3 below, a total of twenty-six SouthernCalifornia known or possible ENG-ROreceive sites were tested.

Figure 1. Possible and actual Southern California ENG-RO sites tested for main-beamillumination by the Vandenberg USB uplink dish.

Figure 2 (top):Vandenberg uplink areasites.

Figure 3 (bottom):Los Angeles area sites.

Shadowgraph studieswere then made. Thesestudies indicated that allof the possible/actualENG-RO sites more than161 km from theVandenberg upl inklacked line-of-sight to apresumed 9.1-meter (30-feet) AGL receivingantenna at the studiedsites. While greater AGLheights for mountain-topENG receiving antennasare certainly possible,these shadowgraph mapsindicate that at least forthe Vandenberg uplinkthat ENG-RO sites morethan 161 km distant areunlikely to be affected.

Figure 4. Shadowgraphshowing line-of-sightconditions for theVandenberg uplinkantenna in the San LuisObispo/SantaMaria/Santa Barbara area.

Figure 5. Shadowgraphshowing line-of-sightconditions for theVandenberg uplinkantenna in the LosAngeles area.

The radiation pattern envelope (RPE) ofthe 13 meter USB uplink antenna thatDoD will use was also discussed. Figure 6shows the RPE from zero to 10° off axis,and Figure 7 shows the RPE from zero to180° off axis (these are calculated, ratherthan measured, RPEs). Note that Figure 7shows the additional side lobe suppressionthat might be possible by applying a 1.5-meter (5-foot) metal shroud around thecircumference of the uplink antenna.These tentative shroud calculations weredone by The Aerospace Corporationengineers; they do not include furthersuppression of side lobes that might be

possible if the interior of the shroud islined with microwave absorbing material.although whether this will prove to be apractical retrofit is still being studied. Forexample, and as shown by Figures 8 and 9,when a terrestrial point-to-pointmicrowave dish is shrouded and lined withmicrowave absorbing mater ia l ,improvements in the off-axis suppressionof almost 30 dB are possible. It should benoted that any DoD antenna modificationmust be studied in detail and may not besupportable when all system factors areconsidered.

Figure 6 (below). Calculated RPE of 13-meter DoD USB uplink dish, zero to ±10° off axis.Courtesy of The Aerospace Corporation (Preliminary).

Theta (Degrees)

0 1 2 3 4 5 6 7 8 9 10

Gain (dB)

-10

-5

0

5

10

15

20

25

30

35

40

45

50Computed Pattern for 13 M Antenna at 2.0675 GHz

Raytrack - LH SacksParabolas:Pb13m1.fPb113m0701058a1.pgwWLAMBDA=0.7Jan 08 2007

Diameter = 13.0 MetersComputed Peak Gain = 48.6 dB(feed and line losses not included)

Figure 7 (above). Calculated RPE of 13-m USB uplink dish, zero to ±180° off axis.Courtesy of The Aerospace Corporation (Preliminary).

Figures 8 (left) and 9 (right). RPEs for Andrew Corporation standard performance, highperformance and ultra high performance parabolic antennas at 2 GHz and at 6 GHz. Thesefigures are courtesy of Andrew Corporation.

Theta (Degrees)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Gain (dB)

-50

-40

-30

-20

-10

0

10

20

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40

50

Computed Pattern for 13 M Antenna at 2.0675 GHz Effect of 5 Ft. Shroud

Raytrack - LH SacksParabolas:Pb13m1.fPb113m0701058a.pgwWLAMBDA=0.7Jan 08 2007

Diameter = 13.0 MetersComputed Peak Gain = 48.6 dB(feed and line losses not included)

Without Shroud

Wth 5-ft Shroud

Next Tasks

Look Angle Histograms

DoD personnel indicated that the azimuthsand elevation angles for a particular uplinkas it tracks various military satellites(many in non-geosynchronous orbits)could be made, to see if these operationalarcs include the azimuth(s) and elevationangle(s) to nearby ENG-RO sites thatmight not be terrain-shielded to the uplinklocation. For example, Figure 10 showsthe terrain profile from the Vandenberguplink to the ENG-RO site at BroadcastPeak, and Figure 11 shows the terrainprofile to the ENG-RO site at Cuesta Peak.These are clearly unobstructed paths,where free space path loss (FSPL)conditions would apply.

Figure 10. Vandenberg uplink toBroadcast Peak terrain profile. Path is59.7 km at 123°T. Profile extends 5 kmpast the ENG-RO site.

Figure 11. Vandenberg uplink to CuestaPeak terrain profile. Path is 61.3 kmbearing 347°T. Profile extends 5 km pastthe ENG-RO site.

If the Vandenberg uplink elevation angleis at least 10°, then for the Broadcast PeakENG-RO site the predicted receive carrierlevel (RCL) at the ENG receiver input portcan be estimated as +104 dBm EIRP worstcase "emergency" power, -14 dB forroutine, low power operation, -7.8 dBbandwidth factor (i.e., 10log(2 MHz/12MHz = -7.8 dB), -50 dB side lobesuppression, -134.3 dB FSPL, + 20 dBiassumed receive antenna gain = -82.1dBm RCL. This misses the 0.5 dB noisethreshold criteria RCL limit of -104.1 dBmby some 22 dB (i.e., a co-channelundesired signal of -104.1 dBm added to a-95 dBm at-threshold coded orthogonalfrequency division multiplex (COFDM)desired ENG signal would degrade thenoise threshold to -94.5 dBm, or a 0.5-dBdegradation).

However, if the uplink azimuth never gotwithin ±100° of the 123°T direction fromthe Vandenberg uplink to Broadcast Peak,the off-axis suppression would improve byanother 24 dB, reducing the RCL of theundesired DoD signal from -82.1 dBm to-106.1 dBm. This would then not onlymeet, but surpass, the 0.5 dB noisethreshold degradation criteria. So astatistical look-arc analysis maydemonstrate that a DoD uplink dish is sounlikely to be aimed in the direction of anENG-RO site that protection of that ENG-RO can be effectively provided, evenwhen line-of-sight conditions exist. Ofcourse, if the look arc statistical analysisshows that the uplink antenna frequentlysweeps through an arc that places lesssuppressed side lobes towards the ENG-RO site, then other mitigation measureswill be required.

Possible D/U Interference Criteria inLieu of Noise Threshold ProtectionCriteria in Certain Cases

Another area for planned future work is toderive the desired-to-undesired (D/U)signal ratio that a 12 or 6 MHz widedigital ENG signal needs in order to not bedegraded by a 2 MHz wide USB signal.This could be accomplished in alaboratory using variable attenuators anddirectional couplers to introduce anundesired USB uplink signal into a digitalENG signal. The necessary D/U ratios forvarious levels of the "desired" ENG signal,and for various digital modulationschemes and combinations of forwarderror correction, could then be derived.Let's assume, for discussion purposes, thatthe most susceptible ENG signal is foundto require a D/U ratio of 25 dB or better inorder to not be affected. Let us alsoassume that an analysis of RCLs for aparticular ENG-RO site show that 99% ofthe time the weakest incoming signal is -60 dBm (as opposed to the assumedreceiver threshold value of -95 dBm).Then applying a D/U interference criteriainstead of a noise threshold protectioncriteria may be reasonable. Doing sowould then allow a RCL of -85 dBm forthe undesired DoD uplink signal, asopposed to a limit of less than or equal to -104.1 dBm. Of course, it would be up toeach TV Pickup, CARS, and LTTSlicensee near a newcomer DoD uplinkwhether to accept a D/U ratio interferencecriteria rather than a noise thresholdprotection criteria. But in some situationsthat might be a reasonable approach.

Summary

Encouraging progress continues to bemade. Especially if adding microwaveabsorbing material to an uplink dishshroud can reduce the side lobe leakage byanother 20 dB or so (and this must beexamined further and approached

cautiously), then at least for theVandenberg uplink the goal of frequencyre-use has utility as a critical element ofachieving an equitable frequency sharingstrategy, at least to established ENG-ROsites.

For 2 GHz TV BAS receivers used byENG relay trucks or satellite ENG (S-ENG) trucks that are themselves equippedwith ENG receivers, frequency sharing,and real-time frequency coordination, willstill be necessary. This is because, unlikefixed ENG-RO sites, the location of anENG relay truck or an S-ENG truck willoften not be known in advance. However,this should prove to be a much moretolerable burden than having to frequencycoordinate regularly used ENG-RO sites.

Acknowledgements

The author wishes to acknowledge thecooperation of Mr. Fred Moorefield of theUSAF Frequency Management Agency.Also the cooperation and assistance of Dr.Albert "Buzz" Merrill of The AerospaceCorporation, as well as all of the otherDoD representatives.

The work of SBE President ChrissScherer, SBE Immediate Past PresidentRay Benedict , SBE FrequencyCoordination Director Ralph Beaver, SBEGeneral Counsel Chris Imlay, and SBEExecutive Director John Poray, has alsobeen instrumental in this effort. It shouldbe noted that SBE officers and directorsvolunteer their time, and are generally notreimbursed for travel expenses.

Finally, I wish to thank Mr. Howard Fineof the Southern California FrequencyCoordinating Committee (SCFCC) for hisongoing and immeasurably helpfulassistance.