Specifications

22 Z-Family Techncial Reference Manual
of the direct signal, for the Standard Correlator, the very well known Narrow
Correlator and the new Ashtech Enhanced Strobe Correlator. The x-axis shows the
multipath delay, which is the extra distance that the reflected signal travels compared
to the direct signal. The y-axis shows the induced range error caused by a multipath
signal with the indicated delay. As the multipath delay increases, the error oscillates
between the positive and negative error envelope.
In a real situation, multipath is usually a combination of many reflections, all with
different delays and different power. Real-life multipath is often described as either
close-in multipath or far multipath. Close-in multipath occurs when the reflecting
surface is close to the satellite antenna direct line, and the delay is small; usually,
these reflections come from a surface near the antenna, for example, an antenna on a
tripod on the ground would pick up close-in multipath from reflections off the ground
below and around the tripod.
Figure 2.6 is a blow up of Figure 2.5 and shows that Enhanced Strobe Correlation
techniques prove much better than usual techniques, especially for close-in multipath
that is attenuated by a factor of 3. Very close-in multipath causes only a small change
Figure 2.5: Relative Performance of Multipath Mitigation Techniques
0 100 200 300 400 500
-100
-80
-60
-40
-20
0
20
40
60
80
100
Multipath Delay (meters)
Tracking Error (meters)
Multipath Code Error Envelopes
Generic Standard
Correlator
Narrow Standard
Correlator
Ashtech
Enhanced Strobe
Correlator
Multipath:
Amplitude -3 dBs
Phase 0,180 deg.
BW = 10.5 MHz