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GIAC memo 1999/04/30

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<TITLE>GIAC Memo: Implementation of the Third Civil GPS Signal</TITLE>


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	<td><img src="fgcsicon.gif" width=110 height=115 align="left" border=0></td>

	<td align="right" valign="center"><FONT SIZE="+3"><STRONG>GIAC </STRONG></font>

	<FONT SIZE="+2"><STRONG>GPS Interagency Advisory Council</STRONG></font>



<tr><td colspan="2" align="right">April 30, 1999</td></tr>

<tr><td colspan="2"><p>&nbsp;</p></td></tr>


	<td valign="TOP">MEMORANDUM FOR:  </td>

	<td valign="TOP">Colonel Richard Skinner, USAF

<br>Principal Deputy Assistant Secretary of Defense

<br>(C3ISR and Space Systems)

<p>Joseph F. Canny

<br>Deputy Assistant Secretary for Transportation Policy

<br>Department of Transportation




	<td valign="TOP">FROM:      </td>

	<td valign="TOP">          Charles W. Challstrom

<br>               Chair, GPS Interagency Advisory Council</td>



	<td valign="TOP">SUBJECT:</td>

	<td valign="TOP">Implementation of the Third Civil GPS Signal</td>



<p>This memorandum provides input to the Interagency GPS Executive

Board (IGEB) Senior Steering Group (SSG) for Third Civil GPS

Signal Implementation and its working groups on behalf of the GPS

Interagency Advisory Council (GIAC).</p>

<p>With regard to the study of potential interference of various

systems and the third signal at 1176.45 megahertz (MHz), GIAC

members note that the aviation requirements are so stringent that

almost all Federal civilian non-transportation use of the third

signal will be adequately protected if aviation requirements are

met. This is based, in part, on information contained in the

U.S. Radiocommunications Sector Fact Sheet, Document No: US

WP8D/12, 6 March 1999. This document identifies an integrity

requirement for vertical navigation sensor error of one event per

500,000,000 Category-III approaches. Given the spatial extent of

an airport approach, and the number and distribution of airports

within the United States, this aviation risk criterion should

serve for the operation of geodetic and timing GPS receivers.</p>

<p>I must caution, however, that current and future civil

applications cannot always be measured by aviation requirements.

This was illustrated in the recent Chief Executive Officer

Roundtable, held at the Department of Commerce in December 1998,

GPS has major impact on the agriculture, automotive, aviation,

banking, communications, construction, lumber, shipping, space

systems, surveying, and transportation sectors. In this meeting

it was pointed out that "accuracy is addictive." In many cases,

this accuracy will be obtained by use of various widelane

combinations of the carrier phase on all three GPS frequencies,

and will be at the level of just a few centimeters.</p>

<p>For example, the National Oceanic and Atmospheric Administration

has been engaged in a demonstration project where the keel of a

ship has been positioned to within a few centimeters relative to

the underwater hydrography. This technology will enable

increased throughput, higher profits, and greater safety of

shipping operations in our Nation's ports and harbors. One can

conceive of a future scenario where an interference source could

be controlled for aviation through operational or procedural

protocols such as scheduling or routing. Such a solution may

work for aviation, but may not mitigate the problem for precision

shipping and land transport.</p>

<p>Further, GIAC understands that IGEB SSG Working Group 1

(Feasibility of Coexistence) prepared to recommend to the

National Telecommunications and Information Agency that no

frequency allocation exceptions be granted for systems

incorporating Ultra WideBand radar (UWB) at this time. We

endorse this recommendation, since low power UWB systems may be

situated in close proximity to both transportation and non

transportation applications of GPS. Resolution of this potential

interference issue will likely require studies and field tests

prior to any licensing activity for this system.</p>

<p>Based on reports by GIAC representatives to the Working Groups,

GIAC endorses the proposed hybrid signal structure. It has

superior characteristics due, in part, to placing data messages

on one channel, and the carrier on a different channel. This

will allow carrier phase tracking under adverse levels of

interference that would prevent receipt of the data message. The

proposed hybrid signal structure appears to be a very robust

choice for precision positioning applications.</p>


<font face="Arial" size="-1">

for information write:



<br>NOAA, National Geodetic Survey, N/NGS

<br>1315 East-West Highway, Room 8657

<br>Silver Spring, Maryland  20910-3282</font>


Last Updated: Feb 01, 2007 04:09 PM
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