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Oxford Technical Solutions
The heading software in the RT enables significantly better performance and coverage
compared to GNSS-only solutions.
GLONASS
GLONASS capability adds the ability to utilise the Russian satellite constellation
GLONASS as well as the American constellation GPS. This means an extra 24 satellites
are available for the RT to lock on to and obtain position and velocity updates from.
In open sky conditions, the addition of GLONASS capability is of little benefit as the
GPS signals are unlikely to be interrupted and full accuracy can be achieved almost 100%
of the time. However, in open-road testing situations there are likely to be bridges, trees,
and tall buildings that can block the view of satellites or cause multipath effect errors. In
these situations, GPS and GLONASS receivers are able to maintain 1 cm accurate RTK
positioning mode at times when GPS-only receivers are not. They are also able to re-
establish RTK lock and resolve its ambiguities after an obstruction faster.
Note: at this time, gx/ix processing does not support GLONASS. To take full advantage
of GLONASS capability, standard processing must be used.
250 Hz
1. All product divisions have the option of coming with a 250 Hz version of the inertial
measurement unit (IMU). The IMUs used in 100 Hz and 250 Hz products are
essentially the same, both with a fundamental sampling frequency of 1000 Hz. The
difference is the 3D filter used to integrate the accelerations and angular rates has a
smaller time step in the 250 Hz models, allowing a higher update rate.
2. However, because of the smaller time step, measurements that depend on angular
acceleration are typically noisier on the 250 Hz products. The noise can be managed
by filtering the data to limit the bandwidth.
Satellite differential corrections
To improve the positioning accuracy of standard GNSS, two satellite-based differential
correction services are available. These are SBAS and TerraStar.
Services such as WAAS and EGNOS, are wide-area differential corrections provided for
free. They can provide an accuracy of better than 1 m CEP. WAAS is available in North
America; EGNOS is available in Europe; MSAS is available in Japan; GAGAN is
available in India; SDCM is available in Russia. Other parts of the world are not covered
and cannot use this service.
TerraStar is a subscription service. RT systems that have TerraStar capability include the
necessary hardware to receive corrections. It is necessary to pay a license fee to activate
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