The ability of a GNSS receiver to handle multiple frequencies from multiple constellations in the calculation of position is essential to optimal error resolution.
Using multi-frequency receivers is the most effective way to remove ionospheric error from the position calculation. Ionospheric error varies with frequency, so it impacts the various GNSS signals differently. By comparing the delays of two GNSS signals, L1 and L2 for example, the receiver can correct for the impact of ionospheric errors.
The modernised wideband signals provide inherent noise and multipath mitigation capabilities. When receivers combine modern wideband signal capabilities with the ability to remove ionospheric error using dual-frequency, significant improvements in both measurement and positioning accuracy can be achieved.
Multi-frequency receivers also provide more immunity to interference. If there is interference in the L2 frequency band around 1227.60 MHz, a multi-frequency receiver will still track L1 and L5 signals to ensure ongoing positioning.
As described previously, a multi-constellation receiver can access signals from several constellations: GPS, GLONASS, BeiDou and Galileo, for example. The use of other constellations in addition to GPS results in a larger number of satellites in the field of view, which has the following benefits:
- Reduced signal acquisition time
- Improved position and time accuracy
- Reduced problems caused by obstructions such as buildings and foliage
- Improved spatial distribution of visible satellites, resulting in improved dilution of precision
When a receiver utilises signals from a variety of constellations, protection from signal blockage is built into the solution. If a signal is blocked due to the surrounding environment, there is a very high likelihood that the receiver can simply pick up a signal from another constellation — ensuring solution continuity. While extremely rare, if a GNSS system fails, there are other systems available.
To determine a position in GNSS-only mode, a receiver must track a minimum of four satellites. In multi-constellation mode, the receiver is more likely to find enough satellites to track, even in challenging GNSS environments.