Attachment ex parte

This document pretains to SAT-MOD-20031118-00333 for Modification on a Satellite Space Stations filing.

IBFS_SATMOD2003111800333_415563

                                                                                 Repuitoy Cooml
Mobile Satelite Ventures to                                                      mok msier
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                                                                                 SWls tevngnanscon

                                              Jonuary 14, 2005
      Via Hand Delivery
      Ms. Marlene H. Dortch, Secretary
      Federal Communications Commission
      445 12th Street, S.W.
      Washington, D.C. 20554
             Res    Ex Parte Presentation of Mobile Satellite Ventures Subsidiary LLC
                    1B Docket No. 01—185
                    File No. SAT—MOD—20031118—00333 (ATC application)
                    File No. SAT—AMD—20031118—00332 (ATC application)
                    File No. SES—MOD—20031118—01879 (ATC application)
      Dear Ms. Dortch

              Mobile Satellite Ventures Subsidiary LLC ("MSV") hereby submits the attached analysis
      further demonstrating how its L—band AncillaryTerrestrial Component ("ATC") base stations
      will not cause harmfulinterference to Inmarsat aeronautical terminals.
             Please direct any questions regarding this matter to the undersigned.
                                                  Very truly yours,

                                                  Ton C.Levin
     ces     Donald Abelson
             Jim Ball
             Williom Bell
             Richard Engelman
             Chip Fleming
             Howard Gribof®
             Karl Kensinger
             Paul Locke
             Kathym Medey
             Robert Nelson
             Sean O‘More
            Roderick Porter
            Steve Spacth
            David Strickland
            Cassandra Thomas
            Thomas Tyez
            John Janka, Counsel forInmarsat


                   Technical Response to Inmarsat‘s January 5, 2005 Filing
         Downlink Interference Potential. Inmarsat‘s recent filing (January 5, 2005)
continues to show significant errors in the interference analysis ofthe acronautical case,
specificallyin failing to account for shielding by the body ofthe aireraft. When shielding
is accounted for, i is apparent that Inmarsatreceivers will be protected from MSV base
stations operating at the permitted power levels even at very low altitudes.
         MSV has asserted that an AMS(RYSreceiver that is only 35 meters above an ATC
base station (65 meters above ground) can maintain positive margin against overload.
MSV states: "With one ATC base station emitting 32 dBWEIRPper sector and using the
relazed base station antena characteristic, an airborne AMS(RYS receiver can be as low
as 65 meters above ground (only 35 meters above the base station) and still maintain
positive margin against overload. As the horizontal distance between the AMS(RYS
receiver and the base station tower increases, the available margin increases rapidly as
shown in the Table below."". The Table referred to in the above excerpt, illustrates the
aireraft trajectory over the base station and specifiesthe available margin against
overload at different points along the trajectory at horizontaldistance increments of 600
meters. The referenced Table is reproduced below."

 AMS(R)S Receiver Trajectory over one ATC Base Station Emitting 32 dBW EIRP
      per Sector and using the Relaxed Overhead Gain Suppression Pattern
  (AMS(R)S Receiver at 65 Meters Altitude; Base Station Located at X,         = 0, 0 km)
          x          a ar     o|  as    o[    as    as     a o is i i [an] m
          v          2|3          aa    c     as    as     on on [ as [ 3 t
   e mes e          s se       an n     se    an    o      w a n c n w o
  Tez tes 5e um|    es mz     as7 w |   m|    us    se |   s|5 m ms o w | as
     se an          im o|     in m|     wan   in|   «n     n in| w mas| in | mas n

         Inmarsat‘s January 5 filing repeats the assumptions that MSV associates with the
above Table and uses them to extrapolate the overload margin at the zenith ofthe base
station, at which point Inmarsatderives a negative margin.. Then, Inmarsat concludes:
"This shows there is a problem."" However, there‘s no problem. The assumptions stated
by MSV (and used by Inmarsat)are valid only for the points ofthe aireraf‘s trajectory

       ‘ Mobile Satellite Ventures Subsidiary LLC, Opposition, File No. SAT—MOD—
2003111—00333, File No. SAT—AMD—20031118—00332, File No. SES—MOD—20031118—
01879 (December 23, 2004) (*MSF Opposition), Technical Appendix at 2.
       "MSV also stated that t should be emphasized that critical air—to—ground
communications during take—offs and landings rarely, ifever, are based on the use of
Inmarsat‘s system."" See MSV Opposition, Technical Appendix at 3. To which Inmarsat
remains silent.

       > See Inmarsat Ventures Ltd., Reply, File No. SAT—MOD—20031118—00333, File
No. SAT—AMD—20031118—00332, File No. SES—MOD—20031118—01879 (January 5,
2005) ("hmarsat Reply"), Appendix A at 3 & 4.


that MSV addressed in the above Table. Notall of the stated assumptions remain valid,
however, when the elevation angle from the AMS(R}Santenna to the base station
antenna becomes negative and is in the region between —30° and —90°. For that range of
negative elevation angles, the body ofthe aircraft significantly limits the AMS(RJS
anterna gain. The effect ofshielding of aitbome antennas by the aircraft is well
recognized by the RTCA specifications and was first described by MSV in its ATC
Application, Appendix L, at 4 & 5.. The rationale is as follows.
        RTCA Document DO—235A (dssessment ofRadio Frequency Interference
Relevant to the GNSS) provides GNSS antenna pattems at angles below the aireraft
(negative elevation angles). The RTCA assessment is based on results from simulations,
patterm measurements made with GPS antennas mounted on a full—scale fuselage section,
and patten measurements made on a scale—model aircraft. Based on these studies, the
RTCA has concluded that an average back lobe antenna gain below the aircraft of10
dBic is representative ofthe elevation angle range from 30 to —90 degrees below the
horizon. This gain value applies to en—route, non—precision approach, and Category I
precision approach aireraft types. See RTCA/DO—235A, Appendix G.
       With regard to acronautical antennas used for AMS(R)S service, RTCA document
DO—210C (Minimum Operational Performance Standards for Aeronautical Mobile
Sarellite Services (AMSS), defines two types of antennas; a high gain antenna and a low»
gain omni—directional antenna. Performance and coverage specifications for the low—gain
version are similar to those defined by the RTCA for GNSS antennas. The high gain
AMSS antenna is specified to be significantly more directive than the low gain version in
terms of discrimination against adjacent satellite, Tt is reasonable, therefore, to expect
that its average back lobe (below the aircraft) is at least as good as that of the broader—
beam low—gain antenna. Both AMS(R)S and GNSS antennas are installed on top of the
aircraft and use right—hand circular polarization.
        While RTCA/DO—210C does not provide specifications for AMS(R)S antenna
gain below the aircraft, it is reasonable to believe that this gain may be modeled using the
value given by RTCA/DO—235 for GNSS antennas; thatis, 10 dBic for elevation angles
from —30° to —90°. NTIA, in its Ex Parte interference analysis dated November 12, 2002,
used a similar rationale to conclude that an AMS(RJSreceive antenna gain of—10 dBic
below the aircraft may be used to derive a conservative estimate of the received
interference power level.
        Figure 1 below illustrates the geometry between an aireraft and a base station.
As the approaching aireraft reaches point A, representing —30° look—angle toward the base
station, the base station enters the shielded region, below the aireraft, where the


      * See Application of Mobile Satellte Ventures Subsidiary LLC, File No. SAT—
MOD—20031118—00333, File No. SAT—AMD—20031 118—00332, File No. SES—MOD—
20031118—01879 (iled November 18, 2003) (collectively, "MSYATC Application),
Appendix L at 4—5.


 additional 10 dB of isolation is present. ‘The base station remains in the shielded region
 until the aireraft reaches point B.

                             Figure 1: Aircraft Shiclded Region



  30°             c90°                                                          P               30°
              Shielded                                                       Shielded
               region          o                                              region
                                   a


                                       downtilt




        Based on the above, the Table below presents the overload profile associated with
the aircraft‘s rajectory, in increments ofapproximately 45 meters ofhorizontaldistance,
as the aircraft ravels from (X, Y) = (—0.3, —0.3) km to (%, Y) = (0.3, 0.3) km (the base
station is at (X, ¥) = (0,0) km). It is seen that over a horizontal distance of
approximately 200 meters centered aboutthe base station zenith the overload margin is
approximately zero dB; not —6 dB as Inmarsatasserts." For a horizontal distance that is
greater than approximately 100 meters from the base station zenith, the overload margin
increases to over 4 dB.°




        * See Inmarsat Reply, Appendix A at4.
         * When the elevation angle from the AMS(R}S antenna to the base station antenna
is in the region between —30° and —90°, the antenna gain ofthe AMS(R} receiver is
assumed to be —10 dBic. Over this (near—zenith) region all three sectors ofthe ATC base
station are assumed to impact the AMS(R)R receiver equally.       Outside of the stated near—
zenith region the antenna gain ofthe AMS(R)S receiver is assumed to be 0 dBic and only
one sector of the ATC base station (the one radiating in the direction of the AMS(R)$
receiver) is assumed to impact the AMS(RJSreceiver.


 AMS(R)S Receiver Trajectory over one ATC Base Station Emitting 32 dBW EIRP
      per Sector and using the Relaxed Overhead Gain Suppression Pattern
 (AMS(R)S Receiver at 65 Meters Altitude; Base Station Located at X, Y = 0, 0 km)
         x          as   as      as   as     ar    a1    on a or on ar TT To
         v          as   o     s      aa    an     w     on e ai"| [ a| as on on
  dremm|            4o   on     on    n      on    w     n w w n e s se [
  Te nee 5e ame)]   se   ns    snn    17    ses   |s     ce n |s is e | s| wne se
     wegs n         en   vaa   is     ras   c      ons   ae ar ons css 100| ie se on

        Finally, as the aireraft travels from (X, Y) = (0.3, 0.3) km to (X, Y) = (1, 1) km
significant positive margin is maintained, contrary to Inmarsat‘s assertion, as seen from
the Table below. Over this region, thaireraf‘s body shielding is 0 dB, and only one
sector of the base station (the one facing towards the aireraf) is assumed to influence the
AMS(R)S receiver.
AMS(R)S Receiver Trajectory over one ATC Base Station Emitting 32 dBW EIRP
     per Sector and using the Relaxed Overhead Gain Suppression Pattern
(AMS(R)S Receiver at 65 Meters Altitude; Base Station Located at X, Y = 0, 0 km)
        x           a     a    a o a o                   s a o        o           & w as
        y           7|    ar   oi o as"| o               o as"| o7    o     o     as" on in
  Gre max ie|       @     on   o ce an c                 c o o        ce   on     n e e
  s hes 5e ue       s|   sea   s | es se| s |            ma one o |   uo   cma   on|s sns
    wegan           en   es    an ass on an              rir m| on    i    im    i| is n


Jan 14 2008 2iiirh           morite snTELLITE VENTURES                7092902770                     p.e




                                          CERTIFICATION

           1, Dr, Peter D. Kurabinis, Vice President & Chief Technical Officer of Mobile Satellite
    Ventures Subsidiary LLC (‘MSV")cextify under penlty of perjury that:

           1 am the technically qualified person with overall responsibility for preperation ofthe
    information contained in the foregoing. T am familiar with the requirements ofthe
    Commission‘s rules, and the information contained in the foregoing is rue end correct.
                                                                  on January 14, 2005



                                                        Dr. Peicr D. Kerabinfs
                                                        Vice President & ChiefTechnical Officer



Document Created: 2005-01-27 16:18:45
Document Modified: 2005-01-27 16:18:45

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