User's Manual Part 1

74 OEMV Family Installation and Operation User Manual Rev 5B
Chapter 5 Positioning Modes of Operation
NovAtel's dual frequency GNSS receivers have several important performance advantages depending
on your positioning requirements. Dual frequency allows direct measurement of the signal delay
through the ionosphere and is critical to fast and reliable integer ambiguity resolution when
positioning using carrier measurements.
Dual frequency can improve the performance of DGPS, SBAS, and RTK positioning. Using RTCM
type 15 messages allows the DGPS user to apply a local ionospheric correction to their dual frequency
receiver to improve code positioning performance on larger baselines (hundreds of km). SBAS
positioning is improved by applying a local correction instead of using the SBAS ionospheric grid,
and RTK solutions are improved on long baselines by using an ionosphere free solution.
By default the OEMV-1, OEMV-1G, OEMV-3, DL-V3 and ProPak-V3 models with L-Band software
support the standard Canada-Wide Differential Global Positioning System (CDGPS) sub-meter L1/L2
service and the OmniSTAR Virtual Base Station (VBS) sub-meter L1 service. The OmniSTAR VBS
service is upgradeable on the OEMV-3, DL-V3 and ProPak-V3 to the Extra Performance (XP)
decimeter L1/L2 service or High Performance (HP) sub-decimeter L1/L2 service. Refer also to the
AUTH command in the OEMV Firmware Reference Manual.
The OEMV family of receivers operate in the most accurate positioning mode possible with the
signals available, and immediately drop to the next positioning mode if the current signal times out.
The following single and dual frequency modes of operation are described further in this chapter:
• Single Point
• Satellite-Based Augmentation System (SBAS)
• Pseudorange Differential
• L-Band
• Carrier-Phase Differential
Refer to the GPS Overview section of the GPS+ Reference Manual for an overview of GPS
positioning.
5.1 Single-Point
The NovAtel OEMV family receivers are capable of absolute 3-D single-point positioning accuracies
of 1.8 meters Root Mean Square (RMS
1
) (GDOP < 2; no multipath).
The general level of accuracy available from single-point operation may be suitable for many types of
positioning such as ocean going vessels, general aviation, and recreational vessels that do not require
position accuracies of better than 1.8 meters RMS. However, increasingly more and more applications
desire and require a much higher degree of accuracy and position confidence than is possible with
single-point pseudorange positioning. This is where differential GPS (DGPS) plays a dominant role in
higher accuracy real-time positioning systems (see the following sections of this chapter).
1. RMS: Root Mean Square (a probability level of 68%)