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RTCM RECOMMENDED STANDARDS FOR
DIFFERENTIAL NAVSTAR GPS SERVICE


RTCM Paper 194-93/SC 104-STD

AUTHOR

Radio Technical Commission for Maritime Services

PREFACE (quoted by permission)

This recommended standards document has been developed by
RTCM SC-104 to replace the document entitled "RTCM Recommended
Standards for Differential Navstar GPS Service, Version 2.0" issued on
January 1, 1990. Experience has shown that the recommended data format
and message structure were generally sound, and that the 25% overhead required
for the parity coding guarantees a highly robust channel for the differential
GPS corrections.
The results of usage of the RTCM SC-104 standard have been have been
highly successful. While 8-10 meters (95%) was originally targeted for
shipboard applications, results have generally been better than 5 meters,
often achieving 1-3 meters.
These results have been obtained using the C/A code pseudorange
measurements, with varying amounts of integrated Doppler smoothing. Real-time
kinematic techniques will enable decimeter accuracy for those applications
amenable to them.
Governments have taken advantage of the SC-104 standard by prescribing it
as the format for publicly supported radiobeacon broadcasts of differential
GPS corrections. Scandinavian and North American countries have announced
plans to equip their coastal waters with these services. This medium is
highly attractive because of its inexpensiveness and accessibility.

The major revisions in Version 2.1 have been the following:

1. Update chapters 1-3, and add a section on GLONASS.
2. To allow service providers to define the meaning of the station health
field.
3. To fix some message types previously designated as tentative, and to add
new messages which support real-time kinematic applications.
4. Provide additional guidance material in Chapter 5 and Appendices I-IV.

There is additional work currently in progress to address messages to
support differential GLONASS, provide guidance for interfacing between
radiobeacon-based data links and GPS receivers, and to provide standards
for ground-based radiobeacons differential GPS stations. Documentation
on these topics will be released as the work is completed.

EDITIONS

DOCUMENT: RTCM RECOMMENDED STANDARDS FOR DIFFERENTIAL
NAVSTAR GPS SERVICE, VERSION 2.1, RTCM PAPER 194-93/SC 104-STD

Version 2.1, dated January 25, 1994, is the current edition.

HOW TO ORDER (from RTCM memo dated January 25, 1994)

Price: The publication may be ordered at a prepaid price of $50.00
(U.S. Dollars). Prepaid order price includes handling and shipping charges
for shipment via book-rate mail to U.S./Canada destinations and via
surface mail to destinations other than U.S./Canada.

Expedited Delivery: If expedited delivery is desired please add $4.00
(U.S. Dollars) per copy for shipment via first class mail to U.S./Canada
destinations and $10.00 (U.S. Dollars) per copy for shipment via air-mail to
destinations other than U.S./Canada.

ALSO STILL AVAILABLE

DOCUMENT: RTCM RECOMMENDED STANDARDS FOR DIFFERENTIAL
NAVSTAR GPS SERVICE, VERSION 2.0, RTCM PAPER 134-89/SC 104-68

Price/Delivery: The publication may be ordered at a prepaid price of $40.00
(U.S. Dollars), for shipment via book-rate mail to U.S./Canada destinations
other than U.S./ Canada. For expedited delivery please add $3.00
(U.S. Dollars) per copy for shipment via first class mail to U.S./Canada
air-mail to destinations other than U.S./Canada.

FOR ALL ORDERS

Payment Methods: RTCM documents are only shipped on a prepaid basis. We do not
accept purchase orders, COD or credit cards. Payment is required in U.S.
dollars by check or by money order. Bank transfers are not acceptable forms of
payment due to excessive bank charges.

Ordering Procedure: All orders must identify specific document being ordered
and number of copies. Orders, with payment as specified above, should be sent
to:
RTCM
1800 Diagonal Rd
SUITE 600
Alexandria, VA. 22314, U.S.A

For additional information, contact the RTCM Office at the above address, or
telephone (703) 684-4481.

TABLE OF CONTENTS

INTRODUCTION 1-1 thru 1-10
THE NEED FOR DIFFERENTIAL GPS SERVICE 2-1 thru 2-10
EQUIPMENT CONFIGURATION AND DESIGN REQUIREMENTS 3-1 thru 3-14
RECOMMENDED DATA MESSAGE FORMAT 4-1 thru 4-48
USER EQUIPMENT INTERFACE 5-1 thru 5-4

Date Last Updated: 2002-05-08