GPS Overview Appendix B
MPC User Manual Rev 0D 91
B.5.2 Dual Station Differential Positioning
It is the objective of operating in differential mode to either eliminate or greatly reduce most of the
errors introduced by the above types of system biases. Pseudorange differential positioning is quite
effective in removing most of the biases caused by satellite clock error, ionospheric and tropospheric
delays (for baselines less than 50 km), ephemeris prediction errors, and SA. However, the biases
caused by multipath reception and receiver clock offset are uncorrelated between receivers and thus
cannot be cancelled by "between receiver single differencing" operation.
Differential operation requires that stations operate in pairs. Each pair consists of a reference station
and a remote station
. A differential network could also be established when there is more than one
remote station linked to a single reference station.
In order for the differential pair to be effective, differential positioning requires that both reference
and remote station receivers track and collect satellite data simultaneously from common satellites.
When the two stations are in relatively close proximity (< 50 km), the pseudorange bias errors are
considered to be nearly the same and can be effectively cancelled by the differential corrections.
However, if the baseline becomes excessively long, the bias errors begin to decorrelate, thus reducing
the accuracy or effectiveness of the differential corrections.
Figure 84: Typical Differential Configuration
Remote Station
Reference Station
Modem
Radio Data Link
Differential
Corrections
Output
Differential
Corrections
Input
GPS Receiver
GPSAntenna
With Chokering
