Global Positioning System Reference
In-Depth Information
Fig. 3. The MAC positioning concept
These single differences are numerically small and have not a relevant transmission size,
considering for example that the tropospheric corrections can be transmitted with a lower
rate than the ionospheric ones (e.g. 2 - 5 seconds).
This new strategy implies that the network software should not perform any interpolation
of the estimated biases. This interpolation, however, is only shifted to the rover, which has
the possibility to choose different interpolative models or to apply a multi-base positioning.
Therefore, the rover receiver must have more computing power, so this positioning mode
does not fit well to older receivers.
For very large networks, it is possible to transmit data from a subset of the network stations
(sub-network or cell). Even in this case the positioning performed by the rover is accurate
and fast. Even in this case, the result of the rover positioning is independent of the used cell.
5. NRTK developments and problems
It wonders if, due to the GPS and GLONASS modernization and the development of the
Compass and Galileo constellations, the NRTK positioning will become obsolete. Over the
last ten years, several authors (e.g. Chen et al., 2004) ask this question. In summary:
•
After a large number of simulations, it is possible to conclude that, in the master-rover
differential real-time positioning, the phase ambiguity solution will be almost
instantaneous, making it unnecessary the use of a network of GNSS reference stations.
However, in high ionospheric activity scenarios, the ambiguity fixing probability in the
master-rover positioning will be very low. With a reference station network the
ionosphere bias will be reduced (Stankov & Jakowskia, 2007).
•
In differential positioning, the maximum distance between the master and the rover
will be increased from 10 kms to 20 kms with the same reliability. Even the network
Search WWH ::
Custom Search