Encl. (1) to COMDTINST 16577.2
USCG DGPS CONOP
1. INTRODUCTION
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1.1 Purpose
This Document is to ensure that all members of the Coast Guard's radionavigation and logistic
support community share a common vision on how the DGPS Navigation Service will be
implemented. The three specific objectives of this Concept of Operations (CONOP) are: (1) to
provide a framework to include operations, logistics, and maintenance of the DGPS service, (2) to
identify changes that must be made to the existing radiobeacon support infrastructure, and (3) to be
the U.S. Coast Guard organizational document that identifies internal support responsibility
assignments. This document, coupled with electronic equipment support plans will begin the
recurring budget process to provide future funds for the DGPS service life-cycle maintenance costs.
The key element which must be understood is that the level of effort devoted to the marine
radiobeacon must be increased. DGPS radiobeacons will be a top priority on the National level as
the critical segment in the newest public navigation service. Current radiobeacon policy, from
equipment failure response to preventive maintenance, must be revised as the majority of beacons
will be much more than individual navigation aids. The DGPS service availability and reliability
requirements are achievable ONLY with long-term organizational support commitment.
1.2 Background
DGPS is an enhancement of the U.S. Department of Defense's Global Positioning System (GPS). A
network of ground based reference stations provides corrections to the GPS satellite ranging
measurements. Each reference station monitors all satellites in view, comparing the measured
ranges with expected measurements based on the reference stations surveyed location. Separate
corrections are calculated for each satellite, allowing the user maximum flexibility in the choice of
satellites for navigation. These differential corrections are then transmitted from the reference
station to GPS users who apply the corrections to their received GPS signals.
Marine radiobeacons located at each reference station broadcast corrections to users. The
corrections are modulated on the radiobeacon carrier. (285-325 kHz band) in the form of Minimum
Shift Keying (MSK) modulation. The modulation data rate for any beacon can be 50, 100, or 200
bits per second (bps).
The accuracy of the Coast Guard's DGPS Navigation Service is expected to be better than 10
meters (2 drms) in all approaches to major U.S. harbors. The system will also be capable of
warning the user when it is not performing within specified tolerances, and can prevent the DGPS
user from using unhealthy satellites. Warning times for the DGPS system are less than ten seconds.
Additional subject background on the Service architecture, definitions, and DGPS development
history is provided in the appendices.
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