Specifications

Operation 21
Operation
Multipath Mitigation
Overview
Multipath occurs when GPS signals arrive at the receiver after being reflected off
some object. The reflected signals always travel a longer path length than the direct
signal. This leads to measurement errors in the receiver which is trying to measure the
direct path length to the satellite. The techniques for rejecting the reflected signals are
known as multipath mitigation.
The receiver implements the latest advances in Ashtech Multipath Rejection
Technology: the Enhanced Strobe Correlator™.
This correlator drastically improves multipath mitigation over the traditional
correlator schemes such as standard (1-chip) correlator spacing or narrow (1/10 chip)
correlator spacing.
The Enhanced Strobe Correlator™ works well in any kind of multipath environment,
specular as well as diffuse, regardless of the number of multipath signals present, its
ability to track is not significantly impacted in low SNR environment and it does not
give away other receiver performance, such as noise performance.
A detailed description of Enhanced Strobe Correlation performance is given in
“Enhanced Strobe Correlator Multipath Rejection for Code & Carrier”, Lionel
Garin, Jean-Michel Rousseau, Proceedings of ION-GPS'97 Sept. 16-19 1997, Kansas
City, Missouri.
Evaluating Correlator Performance
Theoretical analysis of the different multipath mitigation techniques is a
straightforward analysis of how much error hypothetical multipath signals would
cause. A plot of multipath mitigation performance is made by assuming a reflected
signal with a certain power (usually half the power of the direct signal) and a certain
delay. The induced error on the range measurement is then calculated and plotted.
Figure 2.5 shows the error envelopes induced by a multipath signal half the strength
ANT offset Distance from Antenna Phase Center to
Antenna Edge
00.0000
ANT horizontal
azimuth
Azimuth measured from Reference Point to
Antenna Phase Center
00000.00
ANT horizontal
distance
Distance from Reference Point to Antenna
Phase Center
00.0000
Table 2.4: Default Values (continued)
Parameter Description Default