**Document IWG-2/011**

**Author: D. Jablonski**

**17 April 2001**

**WRC-2003 ADVISORY COMMITTEE**

**DRAFT PRELIMINARY VIEWS ON WRC-03**

**WRC-2003 Agenda Item: 1.31 -** to consider the additional allocations
to the mobile-satellite service in the 1 -- 3 GHz band, in accordance
with resolutions **226** (**WRC-2000**) and **227** (**WRC-2000**).

**ISSUE** (**Res. 226 only**)**:** Will sharing between aeronautical
mobile telemetry and the Mobile Satellite Service in the band 1518 --
1525 MHz adversely effect flight test operations?

**BACKGROUND** (**Res. 226 only**)**:**

The 1518-1525 MHz band represents a portion of the band 1435-1525 MHz
(known as the "L-band"). The sub-band 1492-1525 MHz is allocated in
Region 2 for MSS. However, the United States has preserved allocation of
the entire band 1435-1525 MHz for flight testing of manned aircraft.
Portions of this band are also in use for flight test telemetry in other
Regions of the world. Res. 226 calls for studies of the potential for
sharing between the Mobile Satellite Service and aeronautical mobile
telemetry (*i.e.*, flight testing).

Because the development of aircraft is increasingly a cooperative
international effort, United States flight test operations may be
affected adversely by possible future changes in the allocation and use
of these bands in other Regions. Concerns include not only
electromagnetic interference issues, but extend to the harmonization of
flight test standards, spectrum, and equipment world-wide. Given the
extraordinary expense of flight test programs, as well as the safety of
life aspects of flight test, these are significant concerns.

The conclusions arrived at during the October 2000 meeting of Working
Party 8D are summarized in the Chairman\'s report, Document 8D/61
Attachment 14. Of interest here are three key points contained in the
Chairman\'s report. First, a consensus has emerged that co-frequency,
co-coverage sharing between flight test and MSS is not practical.
Second, there seem to be no differences in principle with the notion
that flight test operations may routinely be permitted to cause radio
interference to MSS operations. Third, the MSS community has suggested
that the use of highly directed spot beams might allow operation of MSS
systems in close proximity to flight test operations without causing the
latter harmful interference.

As a result of recent studies of the MSS/flight test sharing situation,
the following conclusions and concerns have emerged:

1.  Co-frequency, co-coverage sharing between MSS and Aeronautical
    Flight Test Telemetry is typically not possible.

2.  The definition of what constitutes Co-frequency, co-coverage sharing
    is described by the pfd limits defined in ITU-R Recommendation 1459.

3.  Interference to MSS ground stations by flight test telemetry
    transmitters may occur, and prior coordination to mitigate this may
    not be possible.

4.  Relaxation of the pfd limits specified in Res. 1459 to enable
    sharing is not possible without seriously compromising the flight
    test capabilities of the ground ranges in question.

5.  Interference from and coordination with other interferors may be a
    factor during coordination discussions between flight test operators
    and MSS providers.

6.  The validity of the -138 dBW/m^2^/4kHz pfd level used in earlier
    studies needs to be reaffirmed in light of other data that suggest
    pfd levels 10 - 15 dB higher are more realistic.

7.  The interpretation of idealized antenna ground footprints needs to
    be refined by the addition of satellite orbital data. Specifically,
    proposed orbital positions with respect to flight test sites, and
    maximum lifetime inclination angles of GSO MSS satellites need to be
    considered when analyzing these footprints.

8.  The next generation multi-beam antennas proposed for use at L-band
    will exhibit effects that need to be better understood.

9.  Careful regard must be given to sidelobe, intermodulation, and other
    relevant effects such as out-of-band emissions.

**PRELIMINARY VIEW** (**Res. 226 only**)**:** Based on previous and
ongoing studies, co-frequency, co-coverage sharing between flight test
and MSS is not practical. Second, flight test operations may routinely
need to be permitted to cause radio interference to MSS operations.
Finally, the performance of co-frequency, non-co-coverage MSS satellites
operating at L band remains a topic of concern for flight test
operations. Existing and proposed MSS spot beam antennas exhibit
properties that suggest reallocation of the band 1518 --1525 MHz in
Regions 1 and 3 can have an adverse impact on flight test operations in
the United States. (17 April 2001)