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Canadian Marine Differential Global Positioning System (DGPS) Broadcast Standard

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Figure 1: Image of how the DGPS Navigation Service works

Figure 1 - System Concept of the DGPS Navigation Service

The Canadian DGPS Navigation Service augments the Navstar Global Positioning System (GPS) by providing localized pseudo range correction factors and ancillary information that are broadcast over a network of strategically located MF marine radio beacons. This service will provide the mariner with a horizontal accuracy of 10 meters or better, 95 % of the time in all coverage areas.

The user equipment receives system status and data updates on a continuous basis. The DGPS Reference Station utilizes a NAD 83 datum for its antenna surveyed position. Therefore, the user equipment suite will compute the NAD 83 Datum when operating in the differential mode. The DGPS Navigation Service not only enhances the accuracy of the Standard Positioning Service (SPS), but also provides real time integrity, monitoring and reporting (for further information on the SPS, see the Global Positioning System Standard Positioning Service Signal Specification dated November 5, 1993, published by the US Department of Defense).

DGPS transmissions will be broadcast in the 285 KHz to 325 KHz band that is allocated for maritime radio navigation (radio beacons). Marine radio beacons will be exclusively used to broadcast DGPS signals on the main carrier using Minimum Shift Keying (MSK) Modulation. There will be no radiobeacon identity tone. The modulated signal will contain DGPS information and the identification of the transmitting DGPS station.

Figure 1 contains a system concept of the DGPS Navigation Service. A typical DGPS station comprises control stations (CSs), reference stations (RSs), their associated integrity monitors (IMs) to ascertain the status and the integrity of the broadcast, and the MF radio beacon transmitter to broadcast DGPS information to users. A control monitor (CM) located at a 24 hour staffed Coast Guard operational site maintains two-way communications via dial up lines with the DGPS stations. The CM monitors the status of the system.

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